0 - π Quantum transition in a carbon nanotube Josephson junction: Universal phase dependence and orbital degeneracy

NASA Astrophysics Data System (ADS)

Delagrange, R.; Weil, R.; Kasumov, A.; Ferrier, M.; Bouchiat, H.; Deblock, R.

2018-05-01

In a quantum dot hybrid superconducting junction, the behavior of the supercurrent is dominated by Coulomb blockade physics, which determines the magnetic state of the dot. In particular, in a single level quantum dot singly occupied, the sign of the supercurrent can be reversed, giving rise to a π-junction. This 0 - π transition, corresponding to a singlet-doublet transition, is then driven by the gate voltage or by the superconducting phase in the case of strong competition between the superconducting proximity effect and Kondo correlations. In a two-level quantum dot, such as a clean carbon nanotube, 0- π transitions exist as well but, because more cotunneling processes are allowed, are not necessarily associated to a magnetic state transition of the dot. In this proceeding, after a review of 0- π transitions in Josephson junctions, we present measurements of current-phase relation in a clean carbon nanotube quantum dot, in the single and two-level regimes. In the single level regime, close to orbital degeneracy and in a regime of strong competition between local electronic correlations and superconducting proximity effect, we find that the phase diagram of the phase-dependent transition is a universal characteristic of a discontinuous level-crossing quantum transition at zero temperature. In the case where the two levels are involved, the nanotube Josephson current exhibits a continuous 0 - π transition, independent of the superconducting phase, revealing a different physical mechanism of the transition.

Te vacancy-driven superconductivity in orthorhombic molybdenum ditelluride

NASA Astrophysics Data System (ADS)

Cho, Suyeon; Kang, Se Hwang; Yu, Ho Sung; Kim, Hyo Won; Ko, Wonhee; Hwang, Sung Woo; Han, Woo Hyun; Choe, Duk-Hyun; Jung, Young Hwa; Chang, Kee Joo; Lee, Young Hee; Yang, Heejun; Wng Kim, Sung

2017-06-01

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have received great attentions because of diverse quantum electronic states such as topological insulating (TI), Weyl semimetallic (WSM) and superconducting states. Recently, the superconducting states emerged in pressurized semimetallic TMDs such as MoTe2 and WTe2 have become one of the central issues due to their predicted WSM states. However, the difficulty in synthetic control of chalcogen vacancies and the ambiguous magneto transport properties have hindered the rigorous study on superconducting and WSM states. Here, we report the emergence of superconductivity at 2.1 K in Te-deficient orthorhombic T d-MoTe2-x with an intrinsic electron-doping, while stoichiometric monoclinic 1T‧-MoTe2 shows no superconducting state down to 10 mK, but exhibits a large magnetoresistance of 32 000% at 2 K in a magnetic field of 14 T originating from nearly perfect compensation of electron and hole carriers. Scanning tunnelling spectroscopy and synchrotron x-ray diffraction combined with theoretical calculations clarify that Te vacancies trigger superconductivity via intrinsic electron doping and the evolution of the T d phase from the 1T‧ phase below 200 K. Unlike the pressure-induced superconducting state of monoclinic MoTe2, this Te vacancy-induced superconductivity is emerged in orthorhombic MoTe2, which is predicted as Weyl semimetal, via electron-doping. This chalcogen vacancy induced-superconductivity provides a new route for cultivating superconducting state together with WSM state in 2D van der Waals materials.

Theory of parametrically amplified electron-phonon superconductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babadi, Mehrtash; Knap, Michael; Martin, Ivar

2017-07-01

Ultrafast optical manipulation of ordered phases in strongly correlated materials is a topic of significant theoretical, experimental, and technological interest. Inspired by a recent experiment on light-induced superconductivity in fullerenes [M. Mitrano et al., Nature (London) 530, 461 (2016)], we develop a comprehensive theory of light-induced superconductivity in driven electron-phonon systemswith lattice nonlinearities. In analogy with the operation of parametric amplifiers, we show how the interplay between the external drive and lattice nonlinearities lead to significantly enhanced effective electron-phonon couplings. We provide a detailed and unbiased study of the nonequilibrium dynamics of the driven system using the real-time Green's functionmore » technique. To this end, we develop a Floquet generalization of the Migdal-Eliashberg theory and derive a numerically tractable set of quantum Floquet-Boltzmann kinetic equations for the coupled electron-phonon system. We study the role of parametric phonon generation and electronic heating in destroying the transient superconducting state. Finally, we predict the transient formation of electronic Floquet bands in time-and angle-resolved photoemission spectroscopy experiments as a consequence of the proposed mechanism.« less

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Opačić, M.; Lazarević, N.; Šćepanović, M.

2015-11-16

Polarized Raman scattering spectra of superconducting K x Fe2-y Se2 and non-superconducting K0.8Fe1.8Co0.2Se2 single crystals were measured in the temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in the frequency range from 150 to 325 cm-1 in both compounds, suggesting that the K0.8Fe1.8Co0.2Se2 single crystal also has a two-phase nature. The temperature dependence of the Raman mode energy is analyzed in terms of lattice thermal expansion and phonon–phonon interaction. The temperature dependence of the Raman mode linewidth is dominated by temperature-induced anharmonic effects. It is shown that the change in Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. An abrupt change of the A1g mode energy nearmore » $${{T}_{\\text{C}}}$$ was observed in K x Fe2-y Se2, whereas it is absent in non-superconducting K0.8Fe1.8Co0.2Se2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below the critical temperature.« less

Quantum metallicity on the high-field side of the superconductor-insulator transition.

PubMed

Baturina, T I; Strunk, C; Baklanov, M R; Satta, A

2007-03-23

We investigate ultrathin superconducting TiN films, which are very close to the localization threshold. Perpendicular magnetic field drives the films from the superconducting to an insulating state, with very high resistance. Further increase of the magnetic field leads to an exponential decay of the resistance towards a finite value. In the limit of low temperatures, the saturation value can be very accurately extrapolated to the universal quantum resistance h/e2. Our analysis suggests that at high magnetic fields a new ground state, distinct from the normal metallic state occurring above the superconducting transition temperature, is formed. A comparison with other studies on different materials indicates that the quantum metallic phase following the magnetic-field-induced insulating phase is a generic property of systems close to the disorder-driven superconductor-insulator transition.

Nonequilibrium optical control of dynamical states in superconducting nanowire circuits.

PubMed

Madan, Ivan; Buh, Jože; Baranov, Vladimir V; Kabanov, Viktor V; Mrzel, Aleš; Mihailovic, Dragan

2018-03-01

Optical control of states exhibiting macroscopic phase coherence in condensed matter systems opens intriguing possibilities for materials and device engineering, including optically controlled qubits and photoinduced superconductivity. Metastable states, which in bulk materials are often associated with the formation of topological defects, are of more practical interest. Scaling to nanosize leads to reduced dimensionality, fundamentally changing the system's properties. In one-dimensional superconducting nanowires, vortices that are present in three-dimensional systems are replaced by fluctuating topological defects of the phase. These drastically change the dynamical behavior of the superconductor and introduce dynamical periodic long-range ordered states when the current is driven through the wire. We report the control and manipulation of transitions between different dynamically stable states in superconducting δ 3 -MoN nanowire circuits by ultrashort laser pulses. Not only can the transitions between different dynamically stable states be precisely controlled by light, but we also discovered new photoinduced hidden states that cannot be reached under near-equilibrium conditions, created while laser photoexcited quasi-particles are outside the equilibrium condition. The observed switching behavior can be understood in terms of dynamical stabilization of various spatiotemporal periodic trajectories of the order parameter in the superconductor nanowire, providing means for the optical control of the superconducting phase with subpicosecond control of timing.

Nonequilibrium optical control of dynamical states in superconducting nanowire circuits

PubMed Central

Madan, Ivan; Baranov, Vladimir V.

2018-01-01

Optical control of states exhibiting macroscopic phase coherence in condensed matter systems opens intriguing possibilities for materials and device engineering, including optically controlled qubits and photoinduced superconductivity. Metastable states, which in bulk materials are often associated with the formation of topological defects, are of more practical interest. Scaling to nanosize leads to reduced dimensionality, fundamentally changing the system’s properties. In one-dimensional superconducting nanowires, vortices that are present in three-dimensional systems are replaced by fluctuating topological defects of the phase. These drastically change the dynamical behavior of the superconductor and introduce dynamical periodic long-range ordered states when the current is driven through the wire. We report the control and manipulation of transitions between different dynamically stable states in superconducting δ3-MoN nanowire circuits by ultrashort laser pulses. Not only can the transitions between different dynamically stable states be precisely controlled by light, but we also discovered new photoinduced hidden states that cannot be reached under near-equilibrium conditions, created while laser photoexcited quasi-particles are outside the equilibrium condition. The observed switching behavior can be understood in terms of dynamical stabilization of various spatiotemporal periodic trajectories of the order parameter in the superconductor nanowire, providing means for the optical control of the superconducting phase with subpicosecond control of timing. PMID:29670935

Critical behavior at a dynamic vortex insulator-to-metal transition

DOE PAGES

Poccia, Nicola; Baturina, Tatyana I.; Coneri, Francesco; ...

2015-09-10

An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables elucidating open questions concerning the nature of competing vortex states and phase transitions between them. A square array creates the egg crate potential in which magnetic field-induced vortices are frozen into a vortex insulator. We observe a vortex insulator-to-vortex metal transition driven by the applied electric current and determine critical exponents strikingly coinciding with those for thermodynamic liquid-gas transition. Lastly, our findings offer a comprehensive description of dynamic critical behavior and establish a deep connection between equilibrium and nonequilibriummore » phase transitions.« less

Critical behavior at a dynamic vortex insulator-to-metal transition.

PubMed

Poccia, Nicola; Baturina, Tatyana I; Coneri, Francesco; Molenaar, Cor G; Wang, X Renshaw; Bianconi, Ginestra; Brinkman, Alexander; Hilgenkamp, Hans; Golubov, Alexander A; Vinokur, Valerii M

2015-09-11

An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables investigation of the nature of competing vortex states and phase transitions between them. A square array creates the eggcrate potential in which magnetic field-induced vortices are frozen into a vortex insulator. We observed a vortex insulator-vortex metal transition driven by the applied electric current and determined critical exponents that coincided with those for thermodynamic liquid-gas transition. Our findings offer a comprehensive description of dynamic critical behavior and establish a deep connection between equilibrium and nonequilibrium phase transitions. Copyright © 2015, American Association for the Advancement of Science.

Magnetic field induced transition in superconducting LaTiO3/SrTiO3 interfaces

NASA Astrophysics Data System (ADS)

Biscaras, J.; Bergeal, N.; Hurand, S.; Feuillet-Palma, C.; Rastogi, A.; Budhani, R. C.; Grilli, M.; Caprara, S.; Lesueur, J.

2013-07-01

Superconductivity at the LaTiO3/SrTiO3 interface is studied by low temperature and high magnetic field measurements as a function of a back-gate voltage. We show that it is intimately related to the appearance of a low density (a few 1012 cm-2) of high mobility carriers, in addition to low mobility ones always present in the system. These carriers form superconducting puddles coupled by a metallic two-dimensional electron gas, as revealed by the analysis of the phase transition driven by a perpendicular magnetic field. Two critical fields are evidenced, and a quantitative comparison with a recent theoretical model is made.

Perspectives of disproportionation driven superconductivity in strongly correlated 3d compounds.

PubMed

Moskvin, A S

2013-02-27

Disproportionation in 3d compounds can give rise to an unconventional electron-hole Bose liquid with a very rich phase diagram, from a Bose metal, to a charge ordering insulator and an inhomogeneous Bose-superfluid. Optimal conditions for disproportionation driven high-T(c) superconductivity are shown to be realized only for several Jahn-Teller d(n) configurations that permit the formation of well defined local composite bosons. These are the high-spin d(4), low-spin d(7), and d(9) configurations given the octahedral crystal field, and the d(1), high-spin d(6) configurations given the tetrahedral crystal field. The disproportionation reaction has a peculiar 'anti-Jahn-Teller' character lifting the bare orbital degeneracy. Superconductivity in the d(4) and d(6) systems at variance with d(1), d(7), and d(9) systems implies unavoidable coexistence of the spin-triplet composite bosons and the magnetic lattice. We argue that unconventional high-T(c) superconductivity, observed in quasi-2d cuprates with tetragonally distorted CuO(6) octahedra and iron-based layered pnictides/chalcogenides with tetrahedrally coordinated Fe(2+) ions presents a key argument to support the fact that the disproportionation scenario is at work in these compounds.

Quantum memristor in a superconducting circuit

NASA Astrophysics Data System (ADS)

Salmilehto, Juha; Sanz, Mikel; di Ventra, Massimiliano; Solano, Enrique

Memristors, resistive elements that retain information of their past, have garnered interest due to their paradigm-changing potential in information processing and electronics. The emergent hysteretic behaviour allows for novel architectural applications and has recently been classically demonstrated in a simplified superconducting setup using the phase-dependent conductance in the tunnel-junction-microscopic model. In this contribution, we present a truly quantum model for a memristor constructed using established elements and techniques in superconducting nanoelectronics, and explore the parameters for feasible operation as well as refine the methods for quantifying the memory retention. In particular, the memristive behaviour is shown to arise from quasiparticle-induced tunneling in the full dissipative model and can be observed in the phase-driven tunneling current. The relevant hysteretic behaviour should be observable using current state-of-the-art measurements for detecting quasiparticle excitations. Our theoretical findings constitute the first quantum memristor in a superconducting circuit and act as the starting point for designing further circuit elements that have non-Markovian characteristics The authors acknowledge support from the CCQED EU project and the Finnish Cultural Foundation.

Dimensionality Driven Enhancement of Ferromagnetic Superconductivity in URhGe.

PubMed

Braithwaite, Daniel; Aoki, Dai; Brison, Jean-Pascal; Flouquet, Jacques; Knebel, Georg; Nakamura, Ai; Pourret, Alexandre

2018-01-19

In most unconventional superconductors, like the high-T_{c} cuprates, iron pnictides, or heavy-fermion systems, superconductivity emerges in the proximity of an electronic instability. Identifying unambiguously the pairing mechanism remains nevertheless an enormous challenge. Among these systems, the orthorhombic uranium ferromagnetic superconductors have a unique position, notably because magnetic fields couple directly to ferromagnetic order, leading to the fascinating discovery of the reemergence of superconductivity in URhGe at a high field. Here we show that uniaxial stress is a remarkable tool allowing the fine-tuning of the pairing strength. With a relatively small stress, the superconducting phase diagram is spectacularly modified, with a merging of the low- and high-field superconducting states and a significant enhancement of the superconductivity. The superconducting critical temperature increases both at zero field and under a field, reaching 1 K, more than twice higher than at ambient pressure. This enhancement of superconductivity is shown to be directly related to a change of the magnetic dimensionality detected from an increase of the transverse magnetic susceptibility: In addition to the Ising-type longitudinal ferromagnetic fluctuations, transverse magnetic fluctuations also play an important role in the superconducting pairing.

Weak phase stiffness and nature of the quantum critical point in underdoped cuprates

DOE PAGES

Yildirim, Yucel; Ku, Wei

2015-11-02

We demonstrate that the zero-temperature superconducting phase diagram of underdoped cuprates can be quantitatively understood in the strong binding limit, using only the experimental spectral function of the “normal” pseudogap phase without any free parameter. In the prototypical (La 1–xSr x) 2CuO 4, a kinetics-driven d-wave superconductivity is obtained above the critical doping δ c ~ 5.2%, below which complete loss of superfluidity results from local quantum fluctuation involving local p-wave pairs. Near the critical doping, an enormous mass enhancement of the local pairs is found responsible for the observed rapid decrease of phase stiffness. Lastly, a striking mass divergencemore » is predicted at δ c that dictates the occurrence of the observed quantum critical point and the abrupt suppression of the Nernst effects in the nearby region.« less

Thermodynamic signature of a magnetic-field-driven phase transition within the superconducting state of an underdoped cuprate

NASA Astrophysics Data System (ADS)

Kemper, J. B.; Vafek, O.; Betts, J. B.; Balakirev, F. F.; Hardy, W. N.; Liang, Ruixing; Bonn, D. A.; Boebinger, G. S.

2016-01-01

More than a quarter century after the discovery of the high-temperature superconductor (HTS) YBa2Cu3O6+δ (YBCO; ref. ), studies continue to uncover complexity in its phase diagram. In addition to HTS and the pseudogap, there is growing evidence for multiple phases with boundaries which are functions of temperature (T), doping (p) and magnetic field. Here we report the low-temperature electronic specific heat (Celec) of YBa2Cu3O6.43 and YBa2Cu3O6.47 (p = 0.076 and 0.084) up to a magnetic field (H) of 34.5 T, a poorly understood region of the underdoped H-T-p phase space. We observe two regimes in the low-temperature limit: below a characteristic magnetic field H' ~ 12-15 T, Celec/T obeys an expected H1/2 behaviour; however, near H' there is a sharp inflection followed by a linear-in-H behaviour. H' rests deep within the superconducting phase and, thus, the linear-in-H behaviour is observed in the zero-resistance regime. In the limit of zero temperature, Celec/T is proportional to the zero-energy electronic density of states. At one of our dopings, the inflection is sharp only at lowest temperatures, and we thus conclude that this inflection is evidence of a magnetic-field-driven quantum phase transition.

Exotic s-wave superconductivity in alkali-doped fullerides.

PubMed

Nomura, Yusuke; Sakai, Shiro; Capone, Massimo; Arita, Ryotaro

2016-04-20

Alkali-doped fullerides (A3C60 with A = K, Rb, Cs) show a surprising phase diagram, in which a high transition-temperature (Tc) s-wave superconducting state emerges next to a Mott insulating phase as a function of the lattice spacing. This is in contrast with the common belief that Mott physics and phonon-driven s-wave superconductivity are incompatible, raising a fundamental question on the mechanism of the high-Tc superconductivity. This article reviews recent ab initio calculations, which have succeeded in reproducing comprehensively the experimental phase diagram with high accuracy and elucidated an unusual cooperation between the electron-phonon coupling and the electron-electron interactions leading to Mott localization to realize an unconventional s-wave superconductivity in the alkali-doped fullerides. A driving force behind the exotic physics is unusual intramolecular interactions, characterized by the coexistence of a strongly repulsive Coulomb interaction and a small effectively negative exchange interaction. This is realized by a subtle energy balance between the coupling with the Jahn-Teller phonons and Hund's coupling within the C60 molecule. The unusual form of the interaction leads to a formation of pairs of up- and down-spin electrons on the molecules, which enables the s-wave pairing. The emergent superconductivity crucially relies on the presence of the Jahn-Teller phonons, but surprisingly benefits from the strong correlations because the correlations suppress the kinetic energy of the electrons and help the formation of the electron pairs, in agreement with previous model calculations. This confirms that the alkali-doped fullerides are a new type of unconventional superconductors, where the unusual synergy between the phonons and Coulomb interactions drives the high-Tc superconductivity.

Evidence of superconductivity-induced phonon spectra renormalization in alkali-doped iron selenides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Opačić, M.; Lazarević, N.; Šćepanović, M.

2015-11-16

Polarized Raman scattering spectra of superconducting K xFe 2-ySe 2 and nonsuperconducting K 0.8Fe 1.8Co 0.2Se 2 single crystals were measured in a temperature range from 10 K up to 300 K. Two Raman active modes from the I4/mmm phase and seven from the I4/m phase are observed in frequency range from 150 to 325 cm -1 in both compounds, suggesting that K 0.8Fe 1.8Co 0.2Se 2 single crystal also has two-phase nature. Temperature dependence of Raman mode energy is analyzed in terms of lattice thermal expansion and phonon-phonon interaction. Temperature dependence of Raman mode linewidth is considered as temperature-inducedmore » anharmonic effects. It is shown that change of Raman mode energy with temperature is dominantly driven by thermal expansion of the crystal lattice. Abrupt change of the A 1g mode energy near T C was observed in K xFe 2-ySe 2 , whereas it is absent in K 0.8Fe 1.8Co 0.2Se 2. Phonon energy hardening at low temperatures in the superconducting sample is a consequence of superconductivity-induced redistribution of the electronic states below critical temperature.« less

Multiple quantum criticality in a two-dimensional superconductor

NASA Astrophysics Data System (ADS)

Biscaras, J.; Bergeal, N.; Hurand, S.; Feuillet-Palma, C.; Rastogi, A.; Budhani, R. C.; Grilli, M.; Caprara, S.; Lesueur, J.

2013-06-01

The diverse phenomena associated with the two-dimensional electron gas (2DEG) that occurs at oxide interfaces include, among others, exceptional carrier mobilities, magnetism and superconductivity. Although these have mostly been the focus of interest for potential future applications, they also offer an opportunity for studying more fundamental quantum many-body effects. Here, we examine the magnetic-field-driven quantum phase transition that occurs in electrostatically gated superconducting LaTiO3/SrTiO3 interfaces. Through a finite-size scaling analysis, we show that it belongs to the (2+1)D XY model universality class. The system can be described as a disordered array of superconducting puddles coupled by a 2DEG and, depending on its conductance, the observed critical behaviour is single (corresponding to the long-range phase coherence in the whole array) or double (one related to local phase coherence, the other one to the array). A phase diagram illustrating the dependence of the critical field on the 2DEG conductance is constructed, and shown to agree with theoretical proposals. Moreover, by retrieving the coherence-length critical exponent ν, we show that the quantum critical behaviour can be clean or dirty according to the Harris criterion, depending on whether the phase-coherence length is smaller or larger than the size of the puddles.

Multiple quantum criticality in a two-dimensional superconductor.

PubMed

Biscaras, J; Bergeal, N; Hurand, S; Feuillet-Palma, C; Rastogi, A; Budhani, R C; Grilli, M; Caprara, S; Lesueur, J

2013-06-01

The diverse phenomena associated with the two-dimensional electron gas (2DEG) that occurs at oxide interfaces include, among others, exceptional carrier mobilities, magnetism and superconductivity. Although these have mostly been the focus of interest for potential future applications, they also offer an opportunity for studying more fundamental quantum many-body effects. Here, we examine the magnetic-field-driven quantum phase transition that occurs in electrostatically gated superconducting LaTiO3/SrTiO3 interfaces. Through a finite-size scaling analysis, we show that it belongs to the (2+1)D XY model universality class. The system can be described as a disordered array of superconducting puddles coupled by a 2DEG and, depending on its conductance, the observed critical behaviour is single (corresponding to the long-range phase coherence in the whole array) or double (one related to local phase coherence, the other one to the array). A phase diagram illustrating the dependence of the critical field on the 2DEG conductance is constructed, and shown to agree with theoretical proposals. Moreover, by retrieving the coherence-length critical exponent ν, we show that the quantum critical behaviour can be clean or dirty according to the Harris criterion, depending on whether the phase-coherence length is smaller or larger than the size of the puddles.

Superconductivity in Weyl semimetal candidate MoTe2.

PubMed

Qi, Yanpeng; Naumov, Pavel G; Ali, Mazhar N; Rajamathi, Catherine R; Schnelle, Walter; Barkalov, Oleg; Hanfland, Michael; Wu, Shu-Chun; Shekhar, Chandra; Sun, Yan; Süß, Vicky; Schmidt, Marcus; Schwarz, Ulrich; Pippel, Eckhard; Werner, Peter; Hillebrand, Reinald; Förster, Tobias; Kampert, Erik; Parkin, Stuart; Cava, R J; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A

2016-03-14

Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS2), recently discovered unexpected properties of WTe2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that bulk MoTe2 exhibits superconductivity with a transition temperature of 0.10 K. Application of external pressure dramatically enhances the transition temperature up to maximum value of 8.2 K at 11.7 GPa. The observed dome-shaped superconductivity phase diagram provides insights into the interplay between superconductivity and topological physics.

Superconductivity in Weyl semimetal candidate MoTe2

PubMed Central

Qi, Yanpeng; Naumov, Pavel G.; Ali, Mazhar N.; Rajamathi, Catherine R.; Schnelle, Walter; Barkalov, Oleg; Hanfland, Michael; Wu, Shu-Chun; Shekhar, Chandra; Sun, Yan; Süß, Vicky; Schmidt, Marcus; Schwarz, Ulrich; Pippel, Eckhard; Werner, Peter; Hillebrand, Reinald; Förster, Tobias; Kampert, Erik; Parkin, Stuart; Cava, R. J.; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A.

2016-01-01

Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS2), recently discovered unexpected properties of WTe2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that bulk MoTe2 exhibits superconductivity with a transition temperature of 0.10 K. Application of external pressure dramatically enhances the transition temperature up to maximum value of 8.2 K at 11.7 GPa. The observed dome-shaped superconductivity phase diagram provides insights into the interplay between superconductivity and topological physics. PMID:26972450

Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe 1.9Ni 0.1As 2

DOE PAGES

Song, Yu; Lu, Xingye; Abernathy, Douglas L.; ...

2015-11-06

In this study, we use inelastic neutron scattering to study the temperature and energy dependence of the spin excitation anisotropy in uniaxial-strained electron-doped iron pnictide BaFe 1.9Ni 0.1As 2 near optimal superconductivity (T c = 20K). Our work has been motivated by the observation of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of electron-underdoped iron pnictides under uniaxial pressure, which has been attributed to a spin-driven Ising-nematic state or orbital ordering. Here we show that the spin excitation anisotropy, a signature of the spin-driven Ising-nematic phase, exists for energies below 60 meV in uniaxial-strained BaFe 1.9Ni 0.1As 2. Sincemore » this energy scale is considerably larger than the energy splitting of the d xz and d yz bands of uniaxial-strained Ba(Fe 1–xCox) 2As 2 near optimal superconductivity, spin Ising-nematic correlations are likely the driving force for the resistivity anisotropy and associated electronic nematic correlations.« less

Critical current enhancement driven by suppression of superconducting fluctuation in ion-gated ultrathin FeSe

NASA Astrophysics Data System (ADS)

Harada, T.; Shiogai, J.; Miyakawa, T.; Nojima, T.; Tsukazaki, A.

2018-05-01

The framework of phase transition, such as superconducting transition, occasionally depends on the dimensionality of materials. Superconductivity is often weakened in the experimental conditions of two-dimensional thin films due to the fragile superconducting state against defects and interfacial effects. In contrast to this general trend, superconductivity in the thin limit of FeSe exhibits an opposite trend, such as an increase in critical temperature (T c) and the superconducting gap exceeding the bulk values; however, the dominant mechanism is still under debate. Here, we measured thickness-dependent electrical transport properties of the ion-gated FeSe thin films to evaluate the superconducting critical current (I c) in the ultrathin FeSe. Upon systematically decreasing the FeSe thickness by the electrochemical etching technique in the Hall bar-shaped electric double-layer transistors, we observed a dramatic enhancement of I c reaching about 10 mA and corresponding to about 107 A cm‑2 in the thinnest condition. By analyzing the transition behavior, we clarify that the suppressed superconducting fluctuation is one of the origins of the large I c in the ion-gated ultrathin FeSe films. These results indicate the existence of a robust superconducting state possibly with dense Cooper pairs at the thin limit of FeSe.

Principle and experimental investigation of current-driven negative-inductance superconducting quantum interference device

NASA Astrophysics Data System (ADS)

Li, Hao; Liu, Jianshe; Zhang, Yingshan; Cai, Han; Li, Gang; Liu, Qichun; Han, Siyuan; Chen, Wei

2017-03-01

A negative-inductance superconducting quantum interference device (nSQUID) is an adiabatic superconducting logic device with high energy efficiency, and therefore a promising building block for large-scale low-power superconducting computing. However, the principle of the nSQUID is not that straightforward and an nSQUID driven by voltage is vulnerable to common mode noise. We investigate a single nSQUID driven by current instead of voltage, and clarify the principle of the adiabatic transition of the current-driven nSQUID between different states. The basic logic operations of the current-driven nSQUID with proper parameters are simulated by WRspice. The corresponding circuit is fabricated with a 100 A cm-2 Nb-based lift-off process, and the experimental results at low temperature confirm the basic logic operations as a gated buffer.

NOVEL TECHNIQUE OF POWER CONTROL IN MAGNETRON TRANSMITTERS FOR INTENSE ACCELERATORS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kazakevich, G.; Johnson, R.; Neubauer, M.

A novel concept of a high-power magnetron transmitter allowing dynamic phase and power control at the frequency of locking signal is proposed. The transmitter compensating parasitic phase and amplitude modulations inherent in Superconducting RF (SRF) cavities within closed feedback loops is intended for powering of the intensity-frontier superconducting accelerators. The con- cept uses magnetrons driven by a sufficient resonant (in- jection-locking) signal and fed by the voltage which can be below the threshold of self-excitation. This provides an extended range of power control in a single magnetron at highest efficiency minimizing the cost of RF power unit and the operationmore » cost. Proof-of-principle of the proposed concept demonstrated in pulsed and CW regimes with 2.45 GHz, 1kW magnetrons is discussed here. A conceptual scheme of the high-power transmitter allowing the dynamic wide-band phase and y power controls is presented and discussed.« less

Rf system for the NSLS coherent infrared radiation source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Broome, W.; Biscardi, R.; Keane, J.

1995-05-01

The existing NSLS X-ray Lithography Source (XLS Phase I) is being considered for a coherent synchrotron radiation source. The existing 211 MHz warm cavity will be replaced with a 5-cell 2856 MHz superconducting RF cavity, driven by a series of 2 kW klystrons. The RF system will provide a total V{sub RF} of 1.5 MV to produce {sigma}{sub L} = 0.3 mm electron bunches at an energy of 150 MeV. Superconducting technology significantly reduces the required space and power needed to achieve the higher voltage. It is the purpose of this paper to describe the superconducting RF system and cavity,more » power requirements, and cavity design parameters such as input coupling, Quality Factor, and Higher Order Modes.« less

A fully superconducting bearing system for flywheel applications

NASA Astrophysics Data System (ADS)

Xu, Ke-xi; Wu, Dong-jie; Jiao, Y. L.; Zheng, M. H.

2016-06-01

A fully superconducting magnetic suspension structure has been designed and constructed for the purpose of superconducting bearing applications in flywheel energy storage systems. A thrust type bearing and two journal type bearings, those that are composed of melt textured high-Tc superconductor YBCO bulks and Nd-Fe-B permanent magnets, are used in the bearing system. The rotor dynamical behaviors, including critical speeds and rotational loss, are studied. Driven by a variable-frequency three-phase induction motor, the rotor shaft attached with a 25 kg flywheel disc can be speeded up to 15 000 rpm without serious resonance occurring. Although the flywheel system runs stably in the supercritical speeds region, very obvious rotational loss is unavoidable. The loss mechanism has been discussed in terms of eddy current loss and hysteresis loss.

Impurity Induced Phase Competition and Supersolidity

NASA Astrophysics Data System (ADS)

Karmakar, Madhuparna; Ganesh, R.

2017-12-01

Several material families show competition between superconductivity and other orders. When such competition is driven by doping, it invariably involves spatial inhomogeneities which can seed competing orders. We study impurity-induced charge order in the attractive Hubbard model, a prototypical model for competition between superconductivity and charge density wave order. We show that a single impurity induces a charge-ordered texture over a length scale set by the energy cost of the competing phase. Our results are consistent with a strong-coupling field theory proposed earlier in which superconducting and charge order parameters form components of an SO(3) vector field. To discuss the effects of multiple impurities, we focus on two cases: correlated and random distributions. In the correlated case, the CDW puddles around each impurity overlap coherently leading to a "supersolid" phase with coexisting pairing and charge order. In contrast, a random distribution of impurities does not lead to coherent CDW formation. We argue that the energy lowering from coherent ordering can have a feedback effect, driving correlations between impurities. This can be understood as arising from an RKKY-like interaction, mediated by impurity textures. We discuss implications for charge order in the cuprates and doped CDW materials such as NbSe2.

Quantum Memristors with Superconducting Circuits

PubMed Central

Salmilehto, J.; Deppe, F.; Di Ventra, M.; Sanz, M.; Solano, E.

2017-01-01

Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. For realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methods to quantify memory retention in the system. PMID:28195193

Vortices and quasiparticles near the superconductor-insulator transition in thin films.

PubMed

Galitski, Victor M; Refael, G; Fisher, Matthew P A; Senthil, T

2005-08-12

We study the low temperature behavior of an amorphous superconducting film driven normal by a perpendicular magnetic-field (B). For this purpose we introduce a new two-fluid formulation consisting of fermionized field-induced vortices and electrically neutralized Bogoliubov quasiparticles (spinons) interacting via a long-ranged statistical interaction. This approach allows us to access a novel non-Fermi-liquid phase, which naturally interpolates between the low B superconductor and the high B normal metal. We discuss the properties of the resulting "vortex metal" phase.

Possible exotic superconductivity in the monolayer and bilayer silicene

NASA Astrophysics Data System (ADS)

Yang, Fan; Yao, Yugui; Zhang, Li-Da; Liu, Cheng-Cheng; Liu, Feng

2014-03-01

Silicene, the silicon-based counterpart of graphene, has attracted a lot of research interest since synthesized recently. Similar honeycomb lattice structures of the two systems let them share most of their marvelous physical properties. The most important structural difference between the two systems lie in the noncoplanar lowbuckled geometry in silicene, which brings up a lot of interesting physical consequence to the system. Here we focus on possible exotic superconductivity (SC) in the family, via random phase approximation (RPA) study on the relevant Hubbard-models. Two systems of this family are studied, including the monolayer and bilayer silicene. For the former system, we found an electric-field driven quantum phase transition (QPT) from chiral d+id to f-wave SC when the field is perpendicular to the silicene plane. For the latter system, we found that even the undoped system is intrinsically metallic and superconducting with chiral d+id symmetry and tunable Tc which can be high . Our study not only provides a new playground for the study of the exotic SC, but also brings a new epoch to the familiar Si industry.

Strong interplay between stripe spin fluctuations, nematicity and superconductivity in FeSe

DOE PAGES

Wang, Qisi; Shen, Yao; Pan, Bingying; ...

2015-12-07

In iron-based superconductors the interactions driving the nematic order (that breaks four-fold rotational symmetry in the iron plane) may also mediate the Cooper pairing. The experimental determination of these interactions, which are believed to depend on the orbital or the spin degrees of freedom, is challenging because nematic order occurs at, or slightly above, the ordering temperature of a stripe magnetic phase. In this paper, we study FeSe—which exhibits a nematic (orthorhombic) phase transition at T s = 90 K without antiferromagnetic ordering—by neutron scattering, finding substantial stripe spin fluctuations coupled with the nematicity that are enhanced abruptly on coolingmore » through T s. A sharp spin resonance develops in the superconducting state, whose energy (~4 meV) is consistent with an electron–boson coupling mode revealed by scanning tunnelling spectroscopy. The magnetic spectral weight in FeSe is found to be comparable to that of the iron arsenides. Finally, our results support recent theoretical proposals that both nematicity and superconductivity are driven by spin fluctuations.« less

Strong interplay between stripe spin fluctuations, nematicity and superconductivity in FeSe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Qisi; Shen, Yao; Pan, Bingying

In iron-based superconductors the interactions driving the nematic order (that breaks four-fold rotational symmetry in the iron plane) may also mediate the Cooper pairing. The experimental determination of these interactions, which are believed to depend on the orbital or the spin degrees of freedom, is challenging because nematic order occurs at, or slightly above, the ordering temperature of a stripe magnetic phase. In this paper, we study FeSe—which exhibits a nematic (orthorhombic) phase transition at T s = 90 K without antiferromagnetic ordering—by neutron scattering, finding substantial stripe spin fluctuations coupled with the nematicity that are enhanced abruptly on coolingmore » through T s. A sharp spin resonance develops in the superconducting state, whose energy (~4 meV) is consistent with an electron–boson coupling mode revealed by scanning tunnelling spectroscopy. The magnetic spectral weight in FeSe is found to be comparable to that of the iron arsenides. Finally, our results support recent theoretical proposals that both nematicity and superconductivity are driven by spin fluctuations.« less

The strength of electron electron correlation in Cs3C60

NASA Astrophysics Data System (ADS)

Baldassarre, L.; Perucchi, A.; Mitrano, M.; Nicoletti, D.; Marini, C.; Pontiroli, D.; Mazzani, M.; Aramini, M.; Riccó, M.; Giovannetti, G.; Capone, M.; Lupi, S.

2015-10-01

Cs3C60 is an antiferromagnetic insulator that under pressure (P) becomes metallic and superconducting below Tc = 38 K. The superconducting dome present in the T - P phase diagram close to a magnetic state reminds what found in superconducting cuprates and pnictides, strongly suggesting that superconductivity is not of the conventional Bardeen-Cooper-Schrieffer (BCS) type We investigate the insulator to metal transition induced by pressure in Cs3C60 by means of infrared spectroscopy supplemented by Dynamical Mean-Field Theory calculations. The insulating compound is driven towards a metallic-like behaviour, while strong correlations survive in the investigated pressure range. The metallization process is accompanied by an enhancement of the Jahn-Teller effect. This shows that electronic correlations are crucial in determining the insulating behaviour at ambient pressure and the bad metallic nature for increasing pressure. On the other hand, the relevance of the Jahn-Teller coupling in the metallic state confirms that phonon coupling survives in the presence of strong correlations.

Electron correlations and magnetism in iron-based superconductors

NASA Astrophysics Data System (ADS)

Birgeneau, Robert

We have carried out a comprehensive study of the phase diagram, structures and phase transitions in the system RbxFeySe2-zSz. We find that the iron content is crucial in stabilizing the stripe antiferromagnetic (AF) phase (y 1.5), the block AF phase (y 1,6) and the iron vacancy-free metallic phase (y 2). These phases are separated by first order transitions. In going from superconducting Rb0.8Fe2Se2 to non-superconducting Rb0.8Fe2S2 we observe in our ARPES experiments little change in the Fermi surface topology but an increase in the overall bandwidth by a factor of 2, hence demonstrating that moderate correlation is essential in achieving high Tc. We show also using neutron scattering that for z =0 there is a sharp magnetic resonance mode well below the superconducting gap which is replaced by a broad hump structure above the gap for z 1. This is accompanied by an insignificant change in Tc. This implies a concomitant change from sign-reversed to sign preserved Cooper-Pairing symmetry driven by the change in electron band width. In this talk we will discuss the overall significance of this rich behavior observed in this alkali Fe-chalcogenide system. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division of the U.S. Department of Energy under Contract No. DE-AC02-05-CH11231 within the Quantum Materials Program (KC2202).

Superconductivity driven by pairing of the coherent parts of the physical electrons

NASA Astrophysics Data System (ADS)

Su, Yuehua; Zhang, Chao

2018-03-01

How the superconductivity in unconventional superconductors emerges from the diverse mother normal states is still a big puzzle. Whatever the mother normal states are the superconductivity is normal with BCS-like behaviours of the paired quasiparticles in condensation. To reconcile the diverse mother normal states and the normal superconductivity in unconventional superconductors, we revisit a proposal that the emergence of the low-energy coherent parts of the physical electrons, which survive from the interaction correlations, is an essential prerequisite for superconductivity. The superconductivity is driven by the pair condensation of these coherent parts of the physical electrons. Moreover the incoherent parts of the physical electrons can enhance the superconducting transition temperature Tc although they are not in driving role in the emergence of the superconductivity. Some experimental responses of the coherent parts of the physical electrons are predicted.

Bi-2212/1T-TaS 2 Van der Waals junctions: Interplay of proximity induced high-T c superconductivity and CDW order

DOE PAGES

Li, Ang J.; Zhu, Xiaochen; Stewart, G. R.; ...

2017-07-05

Understanding the coexistence, competition and/or cooperation between superconductivity and charge density waves (CDWs) in the transition metal dichalcogenides (TMDs) is an elusive goal which, when realized, promises to reveal fundamental information on this important class of materials. Here in this paper, we use four-terminal current-voltage measurements to study the Van der Waals interface between freshly exfoliated flakes of the high-T c superconductor, Bi-2212, and the CDW-dominated TMD layered material, 1T-TaS 2. For highly transparent barriers, there is a pronounced Andreev reflection feature providing evidence for proximity-induced high-Tc superconductivity in 1T-TaS 2 with a surprisingly large energy gap (~20 meV) equalmore » to half that of intrinsic Bi-2212 (~40 meV). Our systematic study using conductance spectroscopy of junctions with different transparencies also reveals the presence of two separate boson modes, each associated with a “dip-hump” structure. Finally, we infer that the proximityinduced high-T c superconductivity in the 1T-TaS 2 is driven by coupling to the metastable metallic phase coexisting within the Mott commensurate CDW (CCDW) phase and associated with a concomitant change of the CCDW order parameter in the interfacial region.« less

Bi-2212/1T-TaS2 Van der Waals junctions: Interplay of proximity induced high-T c superconductivity and CDW order.

PubMed

Li, Ang J; Zhu, Xiaochen; Stewart, G R; Hebard, Arthur F

2017-07-05

Understanding the coexistence, competition and/or cooperation between superconductivity and charge density waves (CDWs) in the transition metal dichalcogenides (TMDs) is an elusive goal which, when realized, promises to reveal fundamental information on this important class of materials. Here, we use four-terminal current-voltage measurements to study the Van der Waals interface between freshly exfoliated flakes of the high-T c superconductor, Bi-2212, and the CDW-dominated TMD layered material, 1T-TaS 2 . For highly transparent barriers, there is a pronounced Andreev reflection feature providing evidence for proximity-induced high-T c superconductivity in 1T-TaS 2 with a surprisingly large energy gap (~20 meV) equal to half that of intrinsic Bi-2212 (~40 meV). Our systematic study using conductance spectroscopy of junctions with different transparencies also reveals the presence of two separate boson modes, each associated with a "dip-hump" structure. We infer that the proximity-induced high-T c superconductivity in the 1T-TaS 2 is driven by coupling to the metastable metallic phase coexisting within the Mott commensurate CDW (CCDW) phase and associated with a concomitant change of the CCDW order parameter in the interfacial region.

Bi-2212/1T-TaS 2 Van der Waals junctions: Interplay of proximity induced high-T c superconductivity and CDW order

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Ang J.; Zhu, Xiaochen; Stewart, G. R.

Understanding the coexistence, competition and/or cooperation between superconductivity and charge density waves (CDWs) in the transition metal dichalcogenides (TMDs) is an elusive goal which, when realized, promises to reveal fundamental information on this important class of materials. Here in this paper, we use four-terminal current-voltage measurements to study the Van der Waals interface between freshly exfoliated flakes of the high-T c superconductor, Bi-2212, and the CDW-dominated TMD layered material, 1T-TaS 2. For highly transparent barriers, there is a pronounced Andreev reflection feature providing evidence for proximity-induced high-Tc superconductivity in 1T-TaS 2 with a surprisingly large energy gap (~20 meV) equalmore » to half that of intrinsic Bi-2212 (~40 meV). Our systematic study using conductance spectroscopy of junctions with different transparencies also reveals the presence of two separate boson modes, each associated with a “dip-hump” structure. Finally, we infer that the proximityinduced high-T c superconductivity in the 1T-TaS 2 is driven by coupling to the metastable metallic phase coexisting within the Mott commensurate CDW (CCDW) phase and associated with a concomitant change of the CCDW order parameter in the interfacial region.« less

Current driven transition from Abrikosov-Josephson to Josephson-like vortex in mesoscopic lateral S/S’/S superconducting weak links

PubMed Central

Carapella, G.; Sabatino, P.; Barone, C.; Pagano, S.; Gombos, M.

2016-01-01

Vortices are topological defects accounting for many important effects in superconductivity, superfluidity, and magnetism. Here we address the stability of a small number of such excitations driven by strong external forces. We focus on Abrikosov-Josephson vortex that appears in lateral superconducting S/S’/S weak links with suppressed superconductivity in S’. In such a system the vortex is nucleated and confined in the narrow S’ region by means of a small magnetic field and moves under the effect of a force proportional to an applied electrical current with a velocity proportional to the measured voltage. Our numerical simulations show that when a slow moving Abrikosov-Josephson vortex is driven by a strong constant current it becomes unstable with respect to a faster moving excitation: the Josephon-like vortex. Such a current-driven transition explains the structured dissipative branches that we observe in the voltage-current curve of the weak link. When vortex matter is strongly confined phenomena as magnetoresistance oscillations and reentrance of superconductivity can possibly occur. We experimentally observe these phenomena in our weak links. PMID:27752137

Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors

NASA Astrophysics Data System (ADS)

Garaud, Julien; Corticelli, Alberto; Silaev, Mihail; Babaev, Egor

2018-02-01

In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. For example, a dirty two-band system with interband impurity scattering undergoes a sharp crossover between the s± state (which favors phase antilocking) and the s++ state (which favors phase locking). We discuss here that the situation can be much more complex in the presence of an external field or superconducting currents. In an external applied magnetic field, dirty two-band superconductors do not feature a sharp s±→s++ crossover but rather a washed-out crossover to a finite region in the parameter space where both s± and s++ states can coexist for example as a lattice or a microemulsion of inclusions of different states. The current-carrying regions such as the regions near vortex cores can exhibit an s± state while it is the s++ state that is favored in the bulk. This coexistence of both states can even be realized in the Meissner state at the domain's boundaries featuring Meissner currents. We demonstrate that there is a magnetic-field-driven crossover between the pure s± and the s++ states.

Quantum Memristors with Superconducting Circuits

DOE PAGES

Salmilehto, J.; Deppe, F.; Di Ventra, M.; ...

2017-02-14

Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. Here in this paper, for realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methodsmore » to quantify memory retention in the system.« less

A Josephson radiation comb generator.

PubMed

Solinas, P; Gasparinetti, S; Golubev, D; Giazotto, F

2015-07-20

We propose the implementation of a Josephson Radiation Comb Generator (JRCG) based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. When the magnetic flux crosses a diffraction node of the critical current interference pattern, the superconducting phase undergoes a jump of π and a voltage pulse is generated at the extremes of the SQUID. Under periodic drive this allows one to generate a sequence of sharp, evenly spaced voltage pulses. In the frequency domain, this corresponds to a comb-like structure similar to the one exploited in optics and metrology. With this device it is possible to generate up to several hundreds of harmonics of the driving frequency. For example, a chain of 50 identical high-critical-temperature SQUIDs driven at 1 GHz can deliver up to a 0.5 nW at 200 GHz. The availability of a fully solid-state radiation comb generator such as the JRCG, easily integrable on chip, may pave the way to a number of technological applications, from metrology to sub-millimeter wave generation.

Coherence-enhanced phase-dependent dissipation in long SNS Josephson junctions: Revealing Andreev bound state dynamics

NASA Astrophysics Data System (ADS)

Dassonneville, B.; Murani, A.; Ferrier, M.; Guéron, S.; Bouchiat, H.

2018-05-01

One of the best known causes of dissipation in ac-driven quantum systems stems from photon absorption causing transitions between levels. Dissipation can also be caused by the retarded response to the time-dependent excitation, and in general gives insight into the system's relaxation times and mechanisms. Here we address the dissipation in a mesoscopic normal wire with superconducting contacts, that sustains a dissipationless supercurrent at zero frequency and that may therefore naively be expected to remain dissipationless at a frequency lower than the superconducting gap. We probe the high-frequency linear response of such a normal metal/superconductor (NS) ring to a time-dependent flux by coupling it to a highly sensitive multimode microwave resonator. Far from being the simple, dissipationless derivative of the supercurrent-versus-phase relation, the ring's ac susceptibility also displays a dissipative component whose phase dependence is a signature of the dynamical processes occurring within the Andreev spectrum. We show how dissipation is driven by the competition between two mechanisms. The first is the relaxation of the Andreev level distribution function, while the second corresponds to microwave-induced transitions within the spectrum. Depending on the relative strength of those contributions, dissipation can be maximal at π , a phase at which the proximity-induced minigap closes, or can be maximal near π /2 , a phase at which the dc supercurrent is maximal. We also find that the dissipative response paradoxically increases at low temperature and can even exceed the normal-state conductance. The results are successfully confronted with theoretical predictions of the Kubo linear response and time-dependent Usadel equations, derived from the Bogoliubov-de Gennes Hamiltonian describing the SNS junction. These experiments thus demonstrate the power of the ac susceptibility measurement of individual hybrid mesoscopic systems in probing in a controlled way the quantum dynamics of Andreev bound states. By spanning different physical regimes, our experiments provide unique access to inelastic scattering and spectroscopy of an isolated quantum coherent system, and reveal the associated relaxation times. This technique should be a tool of choice to investigate topological superconductivity and detect the topological protection of edge states.

Phase slips in superconducting weak links

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kimmel, Gregory; Glatz, Andreas; Aranson, Igor S.

2017-01-01

Superconducting vortices and phase slips are primary mechanisms of dissipation in superconducting, superfluid, and cold-atom systems. While the dynamics of vortices is fairly well described, phase slips occurring in quasi-one- dimensional superconducting wires still elude understanding. The main reason is that phase slips are strongly nonlinear time-dependent phenomena that cannot be cast in terms of small perturbations of the superconducting state. Here we study phase slips occurring in superconducting weak links. Thanks to partial suppression of superconductivity in weak links, we employ a weakly nonlinear approximation for dynamic phase slips. This approximation is not valid for homogeneous superconducting wires andmore » slabs. Using the numerical solution of the time-dependent Ginzburg-Landau equation and bifurcation analysis of stationary solutions, we show that the onset of phase slips occurs via an infinite period bifurcation, which is manifested in a specific voltage-current dependence. Our analytical results are in good agreement with simulations.« less

Method for forming bismuth-based superconducting ceramics

DOEpatents

Maroni, Victor A.; Merchant, Nazarali N.; Parrella, Ronald D.

2005-05-17

A method for reducing the concentration of non-superconducting phases during the heat treatment of Pb doped Ag/Bi-2223 composites having Bi-2223 and Bi-2212 superconducting phases is disclosed. A Pb doped Ag/Bi-2223 composite having Bi-2223 and Bi-2212 superconducting phases is heated in an atmosphere having an oxygen partial pressure not less than about 0.04 atmospheres and the temperature is maintained at the lower of a non-superconducting phase take-off temperature and the Bi-2223 superconducting phase grain growth take-off temperature. The oxygen partial pressure is varied and the temperature is varied between about 815.degree. C. and about 835.degree. C. to produce not less than 80 percent conversion to Pb doped Bi-2223 superconducting phase and not greater than about 20 volume percent non-superconducting phases. The oxygen partial pressure is preferably varied between about 0.04 and about 0.21 atmospheres. A product by the method is disclosed.

Effects of Co and Mn doping in K0.8Fe2-ySe2 revisited.

PubMed

Zhou, Tingting; Chen, Xiaolong; Guo, Jiangang; Jin, Shifeng; Wang, Gang; Lai, Xiaofang; Ying, Tianping; Zhang, Han; Shen, Shijie; Wang, Shunchong; Zhu, Kaixing

2013-07-10

Accumulated evidence indicates that phase separation occurs in potassium intercalated iron selenides, a superconducting phase coexisting with the antiferromagnetic phase K2Fe4Se5, the so-called '245 phase'. Here, we report a comparative study of substitution effects by Co and Mn for Fe sites in K0.8Fe2-ySe2 within the phase separation scenario. Our results demonstrate that Co and Mn dopants have distinct differences in occupancy and hence in the suppression mechanism of superconductivity upon doping of Fe sites. In K0.8Fe2-xCoxSe2, Co prefers to occupy the lattice of the superconducting phase and suppresses superconductivity very quickly, obeying the magnetic pair-breaking mechanism or the collapse of the Fermi surface nesting mechanism. In contrast, in K0.8Fe1.7-xMnxSe2, Mn shows no preferential occupancy in the superconducting phase or the 245 phase. The suppression of superconductivity can be attributed to restraining of the superconducting phase and meanwhile inducing another non-superconducting phase by Mn doping.

BCS superconductors: The out-of-equilibrium response to a laser pulse

NASA Astrophysics Data System (ADS)

Avella, Adolfo

2018-05-01

The dynamics of a 2D d-wave BCS superconductor driven out-of-equilibrium by a perpendicularly-impinging polarized laser pulse is analyzed on varying the laser pulse characteristics. The observed effects include: oscillations both in the amplitude and in the phase of the superconducting order parameter, suppression of the superconductivity, but also its enhancement with a strong dependence on all varying parameters and, in particular, on the polarization in plane of the applied vector potential and on the value of its frequency. This study opens up the possibility to distinguish very clearly the behavior of the nodal and anti-nodal non-thermal excitations and to tackle some of the puzzling results of the current experimental scenario in the field.

Fast ferroelectric phase shifters for energy recovery linacs

DOE PAGES

Kazakov, S. Yu; Shchelkunov, S. V.; Yakovlev, V. P.; ...

2010-11-24

Fast phase shifters are described that use a novel barium strontium titanate ceramic that can rapidly change its dielectric constant as an external bias voltage is changed. These phase shifters promise to reduce by ~10 times the power requirements for the rf source needed to drive an energy recovery linac (ERL). Such phase shifters will be coupled with superconducting radiofrequency cavities so as to tune them to compensate for phase instabilities, whether beam-driven or those caused by microphonics. The most promising design is presented, which was successfully cold tested and demonstrated a switching speed of ~30 ns for 77 deg, correspondingmore » to < 0.5 ns per deg of rf phase. As a result, other crucial issues (losses, phase shift values, etc.) are discussed.« less

Survival probability of an edge Majorana in a one-dimensional p-wave superconducting chain under sudden quenching of parameters

NASA Astrophysics Data System (ADS)

Rajak, Atanu; Dutta, Amit

2014-04-01

We consider the temporal evolution of a zero-energy edge Majorana of a spinless p-wave superconducting chain following a sudden change of a parameter of the Hamiltonian. Starting from one of the topological phases that has an edge Majorana, the system is suddenly driven to the other topological phase or to the (topologically) trivial phases and to the quantum critical points (QCPs) separating these phases. The survival probability of the initial edge Majorana as a function of time is studied following the quench. Interestingly when the chain is quenched to the QCP, we find a nearly perfect oscillation of the survival probability, indicating that the Majorana travels back and forth between two ends, with a time period that scales with the system size. We also generalize to the situation when there is a next-nearest-neighbor hopping in a superconducting chain and there results in a pair of edge Majorana at each end of the chain in the topological phase. We show that the frequency of oscillation of the survival probability gets doubled in this case. We also perform an instantaneous quenching of the Hamiltonian (with two Majorana modes at each end of the chain) to an another Hamiltonian which has only one Majorana mode in equilibrium; the MSP shows oscillations as a function of time with a noticeable decay in the amplitude. On the other hand for a quenching which is reverse to the previous one, the MSP decays rapidly and stays close to zero with fluctuations in amplitude.

Decompression-Driven Superconductivity Enhancement in In2 Se3.

PubMed

Ke, Feng; Dong, Haini; Chen, Yabin; Zhang, Jianbo; Liu, Cailong; Zhang, Junkai; Gan, Yuan; Han, Yonghao; Chen, Zhiqiang; Gao, Chunxiao; Wen, Jinsheng; Yang, Wenge; Chen, Xiao-Jia; Struzhkin, Viktor V; Mao, Ho-Kwang; Chen, Bin

2017-09-01

An unexpected superconductivity enhancement is reported in decompressed In 2 Se 3 . The onset of superconductivity in In 2 Se 3 occurs at 41.3 GPa with a critical temperature (T c ) of 3.7 K, peaking at 47.1 GPa. The striking observation shows that this layered chalcogenide remains superconducting in decompression down to 10.7 GPa. More surprisingly, the highest T c that occurs at lower decompression pressures is 8.2 K, a twofold increase in the same crystal structure as in compression. It is found that the evolution of T c is driven by the pressure-induced R-3m to I-43d structural transition and significant softening of phonons and gentle variation of carrier concentration combined in the pressure quench. The novel decompression-induced superconductivity enhancement implies that it is possible to maintain pressure-induced superconductivity at lower or even ambient pressures with better superconducting performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Josephson Photodetectors via Temperature-to-Phase Conversion

NASA Astrophysics Data System (ADS)

Virtanen, P.; Ronzani, A.; Giazotto, F.

2018-05-01

We theoretically investigate the temperature-to-phase conversion (TPC) process occurring in dc superconducting quantum interferometers based on superconductor-normal-metal-superconductor (S -N -S ) mesoscopic Josephson junctions. In particular, we predict the temperature-driven rearrangement of the phase gradients in the interferometer under the fixed constraints of fluxoid quantization and supercurrent conservation. This mechanism allows sizeable phase variations across the junctions for suitable structure parameters and temperatures. We show that the TPC can be a basis for sensitive single-photon sensors or bolometers. We propose a radiation detector realizable with conventional materials and state-of-the-art nanofabrication techniques. Integrated with a superconducting quantum-interference proximity transistor as a readout setup, an aluminum-based TPC calorimeter can provide a large signal-to-noise ratio >100 in the 10-GHz-10-THz frequency range and a resolving power larger than 1 02 below 50 mK for terahertz photons. In the bolometric operation, electrical noise equivalent power of approximately 10-22 W /√{Hz } is predicted at 50 mK. This device can be attractive as a cryogenic single-photon sensor operating in the giga- and terahertz regime with applications in dark-matter searches.

Emergent superconductivity in an iron-based honeycomb lattice initiated by pressure-driven spin-crossover.

PubMed

Wang, Yonggang; Ying, Jianjun; Zhou, Zhengyang; Sun, Junliang; Wen, Ting; Zhou, Yannan; Li, Nana; Zhang, Qian; Han, Fei; Xiao, Yuming; Chow, Paul; Yang, Wenge; Struzhkin, Viktor V; Zhao, Yusheng; Mao, Ho-Kwang

2018-05-15

The discovery of iron-based superconductors (FeSCs), with the highest transition temperature (T c ) up to 55 K, has attracted worldwide research efforts over the past ten years. So far, all these FeSCs structurally adopt FeSe-type layers with a square iron lattice and superconductivity can be generated by either chemical doping or external pressure. Herein, we report the observation of superconductivity in an iron-based honeycomb lattice via pressure-driven spin-crossover. Under compression, the layered FePX 3 (X = S, Se) simultaneously undergo large in-plane lattice collapses, abrupt spin-crossovers, and insulator-metal transitions. Superconductivity emerges in FePSe 3 along with the structural transition and vanishing of magnetic moment with a starting T c  ~ 2.5 K at 9.0 GPa and the maximum T c  ~ 5.5 K around 30 GPa. The discovery of superconductivity in iron-based honeycomb lattice provides a demonstration for the pursuit of transition-metal-based superconductors via pressure-driven spin-crossover.

Observing single quantum trajectories of a superconducting qubit: ensemble properties and driven dynamics

NASA Astrophysics Data System (ADS)

Weber, Steven; Murch, K. W.; Chantasri, A.; Dressel, J.; Jordan, A. N.; Siddiqi, I.

2014-03-01

We use weak measurements to track individual quantum trajectories of a superconducting qubit embedded in a microwave cavity. Using a near-quantum-limited parametric amplifier, we selectively measure either the phase or amplitude of the cavity field, and thereby confine trajectories to either the equator or a meridian of the Bloch sphere. We analyze ensembles of trajectories to determine statistical properties such as the most likely path and most likely time connecting pre and post-selected quantum states. We compare our results with theoretical predictions derived from an action principle for continuous quantum measurement. Furthermore, by introducing a qubit drive, we investigate the interplay between unitary state evolution and non-unitary measurement dynamics. This work was supported by the IARPA CSQ program and the ONR.

Disorder-induced inhomogeneities of the superconducting state close to the superconductor-insulator transition.

PubMed

Sacépé, B; Chapelier, C; Baturina, T I; Vinokur, V M; Baklanov, M R; Sanquer, M

2008-10-10

Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap Delta in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in Delta, and growth of the Delta/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.

Hidden magnetism and quantum criticality in the heavy fermion superconductor CeRhIn5.

PubMed

Park, Tuson; Ronning, F; Yuan, H Q; Salamon, M B; Movshovich, R; Sarrao, J L; Thompson, J D

2006-03-02

With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.

Second order phase transition in thermodynamic geometry and holographic superconductivity in low-energy stringy black holes

NASA Astrophysics Data System (ADS)

Rizwan, C. L. Ahmed; Vaid, Deepak

2018-05-01

We study holographic superconductivity in low-energy stringy Garfinkle-Horowitz-Strominger (GHS) dilaton black hole background. We finds that superconducting properties are much similar to s-wave superconductors. We show that the second-order phase transition indicated from thermodynamic geometry is not different from superconducting phase transition.

Nonequilibrium dynamic phases in driven vortex lattices with periodic pinning

NASA Astrophysics Data System (ADS)

Reichhardt, Charles Michael

1998-12-01

We present the results of an extensive series of simulations of flux-gradient and current driven vortices interacting with either random or periodically arranged pinning sites. First, we consider flux-gradient-driven simulations of superconducting vortices interacting with strong randomly-distributed columnar pinning defects, as an external field H(t) is quasi-statically swept from zero through a matching field Bsb{phi}. Here, we find significant changes in the behavior of the local flux density B(x, y, H(t)), magnetization M(H(t)), critical current Jsb{c}(B(t)), and the individual vortex flow paths, as the local flux density crosses Bsb{phi}. Further, we find that for a given pin density, Jsb{c}(B) can be enhanced by maximizing the distance between the pins for B < Bsb{phi}. For the case of periodic pinning sites as a function of applied field, we find a rich variety of ordered and partially-ordered vortex lattice configurations. We present formulas that predict the matching fields at which commensurate vortex configurations occur and the vortex lattice orientation with respect to the pinning lattice. Our results are in excellent agreement with recent imaging experiments on square pinning arrays (K. Harada et al., Science 274, 1167 (1996)). For current driven simulations with periodic pinning we find a remarkable number of dynamical plastic flow phases. Signatures of the transitions between these different dynamical phases include sudden jumps in the current-voltage curves, hysteresis, as well as marked changes in the vortex trajectories and vortex lattice order. These phases are outlined in a series of dynamic phase diagrams. We show that several of these phases and their phase-boundaries can be understood in terms of analytical arguments. Finally, when the vortex lattice is driven at varying angles with respect to the underlying periodic pinning array, the transverse voltage-current V(I) curves show a series of mode-locked plateaus with the overall V(I) forming a devil's staircase structure.

Phase-locking transition in a chirped superconducting Josephson resonator.

PubMed

Naaman, O; Aumentado, J; Friedland, L; Wurtele, J S; Siddiqi, I

2008-09-12

We observe a sharp threshold for dynamic phase locking in a high-Q transmission line resonator embedded with a Josephson tunnel junction, and driven with a purely ac, chirped microwave signal. When the drive amplitude is below a critical value, which depends on the chirp rate and is sensitive to the junction critical current I0, the resonator is only excited near its linear resonance frequency. For a larger amplitude, the resonator phase locks to the chirped drive and its amplitude grows until a deterministic maximum is reached. Near threshold, the oscillator evolves smoothly in one of two diverging trajectories, providing a way to discriminate small changes in I0 with a nonswitching detector, with potential applications in quantum state measurement.

Pressure-induced Td to 1T' structural phase transition in WTe 2

DOE PAGES

Zhou, Yonghui; Chen, Xuliang; Li, Nana; ...

2016-07-01

WTe 2 is provoking immense interest owing to its extraordinary properties, such as large positive magnetoresistance, pressure-driven superconductivity and possible type-II Weyl semimetal state. Here we report results of high-pressure synchrotron X-ray diffraction (XRD), Raman and electrical transport measurements on WTe 2. Both the XRD and Raman results reveal a structural transition upon compression, starting at 6.0 GPa and completing above 15.5 GPa. We have determined that the high-pressure lattice symmetry is monoclinic 1T' with space group of P21/m. This transition is related to a lateral sliding of adjacent Te-W-Te layers and results in a collapse of the unit cellmore » volume by ~20.5%. The structural transition also casts a pressure range with the broadened superconducting transition, where the zero resistance disappears.« less

Suppression of the antiferromagnetic order when approaching the superconducting state in a phase-separated crystal of K x Fe 2 - y Se 2

DOE PAGES

Li, Shichao; Gan, Yuan; Wang, Jinghui; ...

2017-09-06

Here, we combined elastic and inelastic neutron scattering techniques, magnetic susceptibility, and resistivity measurements to study single-crystal samples of K xFe 2-ySe 2, which contain the superconducting phase that has a transition temperature of ~31 K. In the inelastic neutron scattering measurements, we also observe both the spin-wave excitations resulting from the block antiferromagnetic ordered phase and the resonance that is associated with the superconductivity in the superconducting phase, demonstrating the coexistence of these two orders. From the temperature dependence of the intensity of the magnetic Bragg peaks, we find that well before entering the superconducting state, the development ofmore » the magnetic order is interrupted, at ~42 K. We consider this result to be evidence for the physical separation of the antiferromagnetic and superconducting phases; the suppression is possibly due to the proximity effect of the superconducting fluctuations on the antiferromagnetic order.« less

Suppression of the antiferromagnetic order when approaching the superconducting state in a phase-separated crystal of K x Fe 2 - y Se 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Shichao; Gan, Yuan; Wang, Jinghui

Here, we combined elastic and inelastic neutron scattering techniques, magnetic susceptibility, and resistivity measurements to study single-crystal samples of K xFe 2-ySe 2, which contain the superconducting phase that has a transition temperature of ~31 K. In the inelastic neutron scattering measurements, we also observe both the spin-wave excitations resulting from the block antiferromagnetic ordered phase and the resonance that is associated with the superconductivity in the superconducting phase, demonstrating the coexistence of these two orders. From the temperature dependence of the intensity of the magnetic Bragg peaks, we find that well before entering the superconducting state, the development ofmore » the magnetic order is interrupted, at ~42 K. We consider this result to be evidence for the physical separation of the antiferromagnetic and superconducting phases; the suppression is possibly due to the proximity effect of the superconducting fluctuations on the antiferromagnetic order.« less

Superconductivity in highly disordered dense carbon disulfide.

PubMed

Dias, Ranga P; Yoo, Choong-Shik; Struzhkin, Viktor V; Kim, Minseob; Muramatsu, Takaki; Matsuoka, Takahiro; Ohishi, Yasuo; Sinogeikin, Stanislav

2013-07-16

High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ~6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity.

Superconductivity mediated by quantum critical antiferromagnetic fluctuations: the rise and fall of hot spots

NASA Astrophysics Data System (ADS)

Wang, Xiaoyu; Schattner, Yoni; Berg, Erez; Fernandes, Rafael

The maximum transition temperature Tc observed in the phase diagrams of several unconventional superconductors takes place in the vicinity of a putative antiferromagnetic quantum critical point. This observation motivated the theoretical proposal that superconductivity in these systems may be driven by quantum critical fluctuations, which in turn can also promote non-Fermi liquid behavior. In this talk, we present a combined analytical and sign-problem-free Quantum Monte Carlo investigation of the spin-fermion model - a widely studied low-energy model for the interplay between superconductivity and magnetic fluctuations. By engineering a series of band dispersions that interpolate between near-nested and open Fermi surfaces, and by also varying the strength of the spin-fermion interaction, we find that the hot spots of the Fermi surface provide the dominant contribution to the pairing instability in this model. We show that the analytical expressions for Tc and for the pairing susceptibility, obtained within a large-N Eliashberg approximation to the spin-fermion model, agree well with the Quantum Monte Carlo data, even in the regime of interactions comparable to the electronic bandwidth. DE-SC0012336.

Magnetism in Na-filled Fe-based skutterudites

DOE PAGES

Xing, Guangzong; Fan, Xiaofeng; Zheng, Weitao; ...

2015-06-01

The interplay of superconductivity and magnetism is a subject of ongoing interest, stimulated most recently by the discovery of Fe-based superconductivity and the recognition that spin-fluctuations near a magnetic quantum critical point may provide an explanation for the superconductivity and the order parameter. We investigate magnetism in the Na filled Fe-based skutterudites using first principles calculations. NaFe 4Sb 12 is a known ferromagnet near a quantum critical point. We find a ferromagnetic metallic state for this compound driven by a Stoner type instability, consistent with prior work. In accord with prior work, the magnetization is overestimated, as expected for amore » material near an itinerant ferromagnetic quantum critical point. NaFe 4P 12 also shows a ferromagnetic instability at the density functional level, but this instability is much weaker than that of NaFe 4Sb 12, possibly placing it on the paramagnetic side of the quantum critical point. NaFe 4As 12 shows intermediate behavior. We also present results for skutterudite FeSb 3, which is a metastable phase that has been reported in thin film form.« less

Instability of Insulators near Quantum Phase Transitions

NASA Astrophysics Data System (ADS)

Doron, A.; Tamir, I.; Levinson, T.; Ovadia, M.; Sacépé, B.; Shahar, D.

2017-12-01

Thin films of amorphous indium oxide undergo a magnetic field driven superconducting to insulator quantum phase transition. In the insulating phase, the current-voltage characteristics show large current discontinuities due to overheating of electrons. We show that the onset voltage for the discontinuities vanishes as we approach the quantum critical point. As a result, the insulating phase becomes unstable with respect to any applied voltage making it, at least experimentally, immeasurable. We emphasize that unlike previous reports of the absence of linear response near quantum phase transitions, in our system, the departure from equilibrium is discontinuous. Because the conditions for these discontinuities are satisfied in most insulators at low temperatures, and due to the decay of all characteristic energy scales near quantum phase transitions, we believe that this instability is general and should occur in various systems while approaching their quantum critical point. Accounting for this instability is crucial for determining the critical behavior of systems near the transition.

Dissipative preparation of antiferromagnetic order in the Fermi-Hubbard model

NASA Astrophysics Data System (ADS)

Kaczmarczyk, J.; Weimer, H.; Lemeshko, M.

2016-09-01

The Fermi-Hubbard model is one of the key models of condensed matter physics, which holds a potential for explaining the mystery of high-temperature superconductivity. Recent progress in ultracold atoms in optical lattices has paved the way to studying the model’s phase diagram using the tools of quantum simulation, which emerged as a promising alternative to the numerical calculations plagued by the infamous sign problem. However, the temperatures achieved using elaborate laser cooling protocols so far have been too high to show the appearance of antiferromagnetic (AF) and superconducting quantum phases directly. In this work, we demonstrate that using the machinery of dissipative quantum state engineering, one can observe the emergence of the AF order in the Fermi-Hubbard model with fermions in optical lattices. The core of the approach is to add incoherent laser scattering in such a way that the AF state emerges as the dark state of the driven-dissipative dynamics. The proposed controlled dissipation channels described in this work are straightforward to add to already existing experimental setups.

Conventional superconductivity in the type-II Dirac semimetal PdTe2

NASA Astrophysics Data System (ADS)

Das, Shekhar; Amit, Sirohi, Anshu; Yadav, Lalit; Gayen, Sirshendu; Singh, Yogesh; Sheet, Goutam

2018-01-01

The transition metal dichalcogenide PdTe2 was recently shown to be a unique system where a type-II Dirac semimetallic phase and a superconducting phase coexist. This observation has led to wide speculation on the possibility of the emergence of an unconventional topological superconducting phase in PdTe2. Here, through direct measurement of the superconducting energy gap by scanning tunneling spectroscopy, and temperature and magnetic-field evolution of same, we show that the superconducting phase in PdTe2 is conventional in nature. The superconducting energy gap is measured to be 326 μ eV at 0.38 K, and it follows a temperature dependence that is well described within the framework of Bardeen-Cooper-Schrieffer's theory of conventional superconductivity. This is surprising because our quantum oscillation measurements confirm that at least one of the bands participating in transport has topologically nontrivial character.

Bulk superconductivity in bismuth oxysulfide Bi4O4S3.

PubMed

Singh, Shiva Kumar; Kumar, Anuj; Gahtori, Bhasker; Shruti; Sharma, Gyaneshwar; Patnaik, Satyabrata; Awana, Veer P S

2012-10-10

A very recent report on the observation of superconductivity in Bi(4)O(4)S(3) [Mizuguchi, Y.; http://arxiv.org/abs/1207.3145] could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here the synthesis of Bi(4)O(4)S(3) at 500 °C by a vacuum encapsulation technique and its basic characterizations. The as-synthesized Bi(4)O(4)S(3) was contaminated with small amounts of Bi(2)S(3) and Bi impurities. The majority phase was found to be tetragonal (space group I4/mmm) with lattice parameters a = 3.9697(2) Å and c = 41.3520(1) Å. Both AC and DC magnetization measurements confirmed that Bi(4)O(4)S(3) is a bulk superconductor with a superconducting transition temperature (T(c)) of 4.4 K. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H(c1)) at 2 K for the new superconductor was found to be ~15 Oe. Magnetotransport measurements showed a broadening of the resistivity (ρ) and a decrease in T(c) (ρ = 0) with increasing magnetic field. The extrapolated upper critical field H(c2)(0) was ~31 kOe with a corresponding Ginzburg-Landau coherence length of ~100 Å . In the normal state, the ρ ~ T(2) dependence was not indicated. Hall resistivity data showed a nonlinear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as-synthesized Bi(4)O(4)S(3). On the other hand, Bi heat-treated at the same temperature is not superconducting, thus excluding the possibility of impurity-driven superconductivity in the newly discovered superconductor Bi(4)O(4)S(3).

Hybrid simulation of fishbone instabilities in the EAST tokamak

DOE PAGES

Shen, Wei; Wang, Feng; Fu, G. Y.; ...

2017-08-11

Hybrid simulations with the global kinetic-magnetohydrodynamic (MHD) code M3D-K have been carried out to investigate the linear stability and nonlinear dynamics of beam-driven fishbone in the experimental advanced superconducting tokamak (EAST) experiment. Linear simulations show that a low frequency fishbone instability is excited at experimental value of beam ion pressure. The mode is mainly driven by low energy beam ions via precessional resonance. Our results are consistent with the experimental measurement with respect to mode frequency and mode structure. When the beam ion pressure is increased to exceed a critical value, the low frequency mode transits to a beta-induced Alfvenmore » eigenmode (BAE) with much higher frequency. This BAE is driven by higher energy beam ions. Nonlinear simulations show that the frequency of the low frequency fishbone chirps up and down with corresponding hole-clump structures in phase space, consistent with the Berk-Breizman theory. In addition to the low frequency mode, the high frequency BAE is excited during the nonlinear evolution. Furthermore, for the transient case of beam pressure fraction where the low and high frequency modes are simultaneously excited in the linear phase, only one dominant mode appears in the nonlinear phase with frequency jumps up and down during nonlinear evolution.« less

Superconducting properties and vortex dynamics of bismuth strontium calcium copper oxide nanoribbons with and without periodic array of nanoscale holes

NASA Astrophysics Data System (ADS)

Avci, Sevda

The distinguishing features of high-temperature superconducting materials are the dynamics of vortex matter in the mixed state which are greatly affected by the high anisotropy and the Josephson coupling between layers. Experiments have focused on investigating melting and dynamic phases of vortex matter with random pinning. However, the advancements in sample preparation techniques have made it possible to investigate the vortex matter with periodic pinnings, since it can serve as a model system to study periodic elastic media such as electron crystals driven on substrates with arrays of defects. It also offers the possibility to increase the critical current of a superconductor through a matching effect which represents itself as peaks (dips) in the field dependences of the critical current (magnetoresisance). This effect is due to the enhanced pinning strength at matching fields where the density of the flux quanta is equal to or multiple times that of the pins. This dissertation reports investigation on the dynamics of vortex matter with periodic pinning array by utilizing BSCCO-2212 crystalline nanoribbons containing periodic arrays of nanoscale holes. Systematic transport measurements reveal the existence of possible intermediate phases of a soft solid and/or a mixture of solid and liquid during melting for the melting transition from solid to a pure liquid. The results of this research demonstrate that the matching effect can be an effective tool in revealing the nature of various vortex phases during melting transition. In addition, anomalous resistive peaks below Tc and the effect of magnetic field orientation on superconductivity of BSCCO-2212 nanoribbons with array of nanoscale holes are also investigated. Angle-dependent magnetoresistances are scaled as H=Hthetacostheta. Therefore, only the perpendicular component of the magnetic field affects the superconductivity. Moreover, layers in BSCCO nanoribbons are lying in the a-b plane parallel to each other. Moreover, at large currents and fields, the resistance shows a non-monotonic dependence on temperature, even showing values that are higher than the normal state resistance for certain ranges of parameters. Observed behavior is attributed to the brick-wall morphology of the nanoribbons leading to a competition between normal and superconductive tunneling that is known to take place in granular superconductive systems.

Superconductivity in highly disordered dense carbon disulfide

PubMed Central

Dias, Ranga P.; Yoo, Choong-Shik; Struzhkin, Viktor V.; Kim, Minseob; Muramatsu, Takaki; Matsuoka, Takahiro; Ohishi, Yasuo; Sinogeikin, Stanislav

2013-01-01

High pressure plays an increasingly important role in both understanding superconductivity and the development of new superconducting materials. New superconductors were found in metallic and metal oxide systems at high pressure. However, because of the filled close-shell configuration, the superconductivity in molecular systems has been limited to charge-transferred salts and metal-doped carbon species with relatively low superconducting transition temperatures. Here, we report the low-temperature superconducting phase observed in diamagnetic carbon disulfide under high pressure. The superconductivity arises from a highly disordered extended state (CS4 phase or phase III[CS4]) at ∼6.2 K over a broad pressure range from 50 to 172 GPa. Based on the X-ray scattering data, we suggest that the local structural change from a tetrahedral to an octahedral configuration is responsible for the observed superconductivity. PMID:23818624

Phase diagram and electronic indication of high-temperature superconductivity at 65 K in single-layer FeSe films.

PubMed

He, Shaolong; He, Junfeng; Zhang, Wenhao; Zhao, Lin; Liu, Defa; Liu, Xu; Mou, Daixiang; Ou, Yun-Bo; Wang, Qing-Yan; Li, Zhi; Wang, Lili; Peng, Yingying; Liu, Yan; Chen, Chaoyu; Yu, Li; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Chen, Xi; Ma, Xucun; Xue, Qikun; Zhou, X J

2013-07-01

The recent discovery of possible high-temperature superconductivity in single-layer FeSe films has generated significant experimental and theoretical interest. In both the cuprate and the iron-based high-temperature superconductors, superconductivity is induced by doping charge carriers into the parent compound to suppress the antiferromagnetic state. It is therefore important to establish whether the superconductivity observed in the single-layer sheets of FeSe--the essential building blocks of the Fe-based superconductors--is realized by undergoing a similar transition. Here we report the phase diagram for an FeSe monolayer grown on a SrTiO3 substrate, by tuning the charge carrier concentration over a wide range through an extensive annealing procedure. We identify two distinct phases that compete during the annealing process: the electronic structure of the phase at low doping (N phase) bears a clear resemblance to the antiferromagnetic parent compound of the Fe-based superconductors, whereas the superconducting phase (S phase) emerges with the increase in doping and the suppression of the N phase. By optimizing the carrier concentration, we observe strong indications of superconductivity with a transition temperature of 65±5 K. The wide tunability of the system across different phases makes the FeSe monolayer ideal for investigating not only the physics of superconductivity, but also for studying novel quantum phenomena more generally.

Implementation of adiabatic geometric gates with superconducting phase qubits.

PubMed

Peng, Z H; Chu, H F; Wang, Z D; Zheng, D N

2009-01-28

We present an adiabatic geometric quantum computation strategy based on the non-degenerate energy eigenstates in (but not limited to) superconducting phase qubit systems. The fidelity of the designed quantum gate was evaluated in the presence of simulated thermal fluctuations in a superconducting phase qubits circuit and was found to be quite robust against random errors. In addition, it was elucidated that the Berry phase in the designed adiabatic evolution may be detected directly via the quantum state tomography developed for superconducting qubits. We also analyze the effects of control parameter fluctuations on the experimental detection of the Berry phase.

Metal-insulator-superconductor transition of spin-3/2 atoms on optical lattices

NASA Astrophysics Data System (ADS)

De Silva, Theja N.

2018-01-01

We use a slave-rotor approach within a mean-field theory to study the competition of metallic, Mott-insulating, and superconducting phases of spin-3/2 fermions subjected to a periodic optical lattice potential. In addition to the metallic, the Mott-insulating, and the superconducting phases that are associated with the gauge symmetry breaking of the spinon field, we identify an emerging superconducting phase that breaks both roton and spinon field gauge symmetries. This superconducting phase emerges as a result of the competition between spin-0 singlet and spin-2 quintet interaction channels naturally available for spin-3/2 systems. The two superconducting phases can be distinguished from each other by quasiparticle weight. We further discuss the properties of these phases for both two-dimensional square and three-dimensional cubic lattices at zero and finite temperatures.

Unexpected superconductivity at nanoscale junctions made on the topological crystalline insulator Pb0.6Sn0.4Te

NASA Astrophysics Data System (ADS)

Das, Shekhar; Aggarwal, Leena; Roychowdhury, Subhajit; Aslam, Mohammad; Gayen, Sirshendu; Biswas, Kanishka; Sheet, Goutam

2016-09-01

Discovery of exotic phases of matter from the topologically non-trivial systems not only makes the research on topological materials more interesting but also enriches our understanding of the fascinating physics of such materials. Pb0.6Sn0.4Te was recently shown to be a topological crystalline insulator. Here, we show that by forming a mesoscopic point-contact using a normal non-superconducting elemental metal on the surface of Pb0.6Sn0.4Te, a superconducting phase is created locally in a confined region under the point-contact. This happens when the bulk of the sample remains to be non-superconducting, and the superconducting phase emerges as a nano-droplet under the point-contact. The superconducting phase shows a high transition temperature Tc that varies for different point-contacts and falls in a range between 3.7 K and 6.5 K. Therefore, this Letter presents the discovery of a superconducting phase on the surface of a topological crystalline insulator, and the discovery is expected to shed light on the mechanism of induced superconductivity in topologically non-trivial systems in general.

Multicomponent order parameter superconductivity of Sr2RuO4 revealed by topological junctions

NASA Astrophysics Data System (ADS)

Anwar, M. S.; Ishiguro, R.; Nakamura, T.; Yakabe, M.; Yonezawa, S.; Takayanagi, H.; Maeno, Y.

2017-06-01

Single crystals of the Sr2RuO4 -Ru eutectic system are known to exhibit enhanced superconductivity at 3 K in addition to the bulk superconductivity of Sr2RuO4 at 1.5 K. The 1.5 K phase is believed to be a spin-triplet, chiral p -wave state with a multicomponent order parameter, giving rise to chiral domain structure. In contrast, the 3 K phase is attributable to enhanced superconductivity of Sr2RuO4 in the strained interface region between Ru inclusion of a few to tens of micrometers in size and the surrounding Sr2RuO4 . We investigate the dynamic behavior of a topological junction, where a superconductor is surrounded by another superconductor. Specifically, we fabricated Nb/Ru/Sr2RuO4 topological superconducting junctions, in which the difference in phase winding between the s -wave superconductivity in Ru microislands induced from Nb and the superconductivity of Sr2RuO4 mainly governs the junction behavior. Comparative results of the asymmetry, hysteresis, and noise in junctions with different sizes, shapes, and configurations of Ru inclusions are explained by the chiral domain-wall motion in these topological junctions. Furthermore, a striking difference between the 1.5 and 3 K phases is clearly revealed: the large noise in the 1.5 K phase sharply disappears in the 3 K phase. These results confirm the multicomponent order-parameter superconductivity of the bulk Sr2RuO4 , consistent with the chiral p -wave state, and the proposed nonchiral single-component superconductivity of the 3 K phase.

Single qubit operations using microwave hyperbolic secant pulses

NASA Astrophysics Data System (ADS)

Ku, H. S.; Long, J. L.; Wu, X.; Bal, M.; Lake, R. E.; Barnes, Edwin; Economou, Sophia E.; Pappas, D. P.

2017-10-01

It has been known since the early days of quantum mechanics that hyperbolic secant pulses possess the unique property that they can perform full-cycle Rabi oscillations on two-level quantum systems independently of the pulse detuning. More recently, it was realized that they induce detuning-controlled phases without changing state populations. Here, we experimentally demonstrate the properties of hyperbolic secant pulses on superconducting transmon qubits and contrast them with the more commonly used Gaussian and square waves. We further show that these properties can be exploited to implement phase gates, nominally without exiting the computational subspace. This enables us to demonstrate a microwave-driven Z rotation with a single control parameter, the detuning.

Summary of development of 70 MW class model superconducting generator--research and development of superconducting for electric power application

NASA Astrophysics Data System (ADS)

Oishi, Ikuo; Nishijima, Kenichi

2002-03-01

A 70 MW class superconducting model generator was designed, manufactured, and tested from 1988 to 1999 as Phase I, which was Japan's national project on applications of superconducting technologies to electric power apparatuses that was commissioned by NEDO as part of New Sunshine Program of AIST and MITI. Phase II then is now being carried out by almost same organization as Phase I. With the development of the 70 MW class superconducting model generator, technologies for a 200 MW class pilot generator were established. The world's largest output (79 MW), world's longest continuous operation (1500 h), and other sufficient characteristics were achieved on the 70 MW class superconducting model generator, and key technologies of design and manufacture required for the 200 MW class pilot generator were established. This project contributed to progress of R&D of power apparatuses. Super-GM has started the next project (Phase II), which shall develop the key technologies for larger-capacity and more-compact machine and is scheduled from 2000 to 2003. Phase II shall be the first step for commercialization of superconducting generator.

Two distinct superconducting phases in LiFeAs

PubMed Central

Nag, P. K.; Schlegel, R.; Baumann, D.; Grafe, H.-J.; Beck, R.; Wurmehl, S.; Büchner, B.; Hess, C.

2016-01-01

A non-trivial temperature evolution of superconductivity including a temperature-induced phase transition between two superconducting phases or even a time-reversal symmetry breaking order parameter is in principle expected in multiband superconductors such as iron-pnictides. Here we present scanning tunnelling spectroscopy data of LiFeAs which reveal two distinct superconducting phases: at = 18 K a partial superconducting gap opens, evidenced by subtle, yet clear features in the tunnelling spectra, i.e. particle-hole symmetric coherence peak and dip-hump structures. At Tc = 16 K, these features substantiate dramatically and become characteristic of full superconductivity. Remarkably, the distance between the dip-hump structures and the coherence peaks remains practically constant in the whole temperature regimeT ≤ . This rules out the connection of the dip-hump structures to an antiferromagnetic spin resonance. PMID:27297474

Method and composition for improving flux pinning and critical current in superconductors

DOEpatents

Morris, Donald E.

1995-01-01

Superconducting materials and methods of forming superconducting materials are disclosed. Highly oxidized superconductors are heated at a relatively high temperature so as to release oxygen, which migrates out of the material, and form a non-superconducting phase which does not diffuse out of grains of the material. The material is then reoxidized at a lower temperature, leaving the non-superconducting inclusions inside a superconducting phase. The non-superconducting inclusions act as pinning centers in the superconductor, increasing the critical current thereof.

Method and composition for improving flux pinning and critical current in superconductors

DOEpatents

Morris, D.E.

1995-07-04

Superconducting materials and methods of forming superconducting materials are disclosed. Highly oxidized superconductors are heated at a relatively high temperature so as to release oxygen, which migrates out of the material, and form a non-superconducting phase which does not diffuse out of grains of the material. The material is then reoxidized at a lower temperature, leaving the non-superconducting inclusions inside a superconducting phase. The non-superconducting inclusions act as pinning centers in the superconductor, increasing the critical current thereof. 14 figs.

Monolithic mm-wave phase shifter using optically activated superconducting switches

NASA Technical Reports Server (NTRS)

Romanofsky, Robert R. (Inventor); Bhasin, Kul B. (Inventor)

1992-01-01

A phase shifter is disclosed having a reference path and a delay path, light sources, and superconductive switches. Each of the superconductive switches is terminated in a virtual short circuit, which may be a radial stub. Switching between the reference path and delayed path is accomplished by illuminating the superconductive switches connected to the desired path, while not illuminating the superconductive switches connected to the other path.

Resonance fluorescence trajectories in superconducting qubit

NASA Astrophysics Data System (ADS)

Naghiloo, Mahdi; Tan, Dian; Harrington, Patrick; Lewalle, Philippe; Jordan, Andrew; Murch, Kater

We employ phase-sensitive amplification to perform homodyne detection of the resonance fluorescence from a driven superconducting artificial atom. Entanglement between the emitter and its fluorescence allows us to track the individual quantum state trajectories of the emitter. We analyze the ensemble properties of these trajectories by considering paths that connect specific initial and final states. By applying a stochastic path integral formalism, we calculate equations of motion for the most likely path between two quantum states and compare these predicted paths to experimental data. Drawing on the mathematical similarity between the action formalism of the most likely quantum paths and ray optics, we study the emergence of caustics in quantum trajectories-situations where multiple extrema in the stochastic action occur. We observe such multiple most likely paths in experimental data and find these paths to be in reasonable quantitative agreement with theoretical calculations. Supported by the John Templeton Foundation.

Impact of Disorder on the Superconducting Phase Diagram in BaFe2(As1-xPx)2

NASA Astrophysics Data System (ADS)

Mizukami, Yuta; Konczykowski, Marcin; Matsuura, Kohei; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada

2017-08-01

In many classes of unconventional superconductors, the question of whether the superconductivity is enhanced by the quantum-critical fluctuations on the verge of an ordered phase remains elusive. One of the most direct ways of addressing this issue is to investigate how the superconducting dome traces a shift of the ordered phase. Here, we study how the phase diagram of the iron-based superconductor BaFe2(As1-xPx)2 changes with disorder via electron irradiation, which keeps the carrier concentrations intact. With increasing disorder, we find that the magneto-structural transition is suppressed, indicating that the critical concentration is shifted to the lower side. Although the superconducting transition temperature Tc is depressed at high concentrations (x ≳ 0.28), it shows an initial increase at lower x. This implies that the superconducting dome tracks the shift of the antiferromagnetic phase, supporting the view of the crucial role played by quantum-critical fluctuations in enhancing superconductivity in this iron-based high-Tc family.

Hidden phase in a two-dimensional Sn layer stabilized by modulation hole doping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ming, Fangfei; Mulugeta Amare, Daniel; Tu, Weisong

Semiconductor surfaces and ultrathin interfaces exhibit an interesting variety of two-dimensional quantum matter phases, such as charge density waves, spin density waves and superconducting condensates. Yet, the electronic properties of these broken symmetry phases are extremely difficult to control due to the inherent difficulty of doping a strictly two-dimensional material without introducing chemical disorder. Here we successfully exploit a modulation doping scheme to uncover, in conjunction with a scanning tunnelling microscope tip-assist, a hidden equilibrium phase in a hole-doped bilayer of Sn on Si(111). This new phase is intrinsically phase separated into insulating domains with polar and nonpolar symmetries. Itsmore » formation involves a spontaneous symmetry breaking process that appears to be electronically driven, notwithstanding the lack of metallicity in this system. This modulation doping approach allows access to novel phases of matter, promising new avenues for exploring competing quantum matter phases on a silicon platform.« less

Hidden phase in a two-dimensional Sn layer stabilized by modulation hole doping

DOE PAGES

Ming, Fangfei; Mulugeta Amare, Daniel; Tu, Weisong; ...

2017-03-07

Semiconductor surfaces and ultrathin interfaces exhibit an interesting variety of two-dimensional quantum matter phases, such as charge density waves, spin density waves and superconducting condensates. Yet, the electronic properties of these broken symmetry phases are extremely difficult to control due to the inherent difficulty of doping a strictly two-dimensional material without introducing chemical disorder. Here we successfully exploit a modulation doping scheme to uncover, in conjunction with a scanning tunnelling microscope tip-assist, a hidden equilibrium phase in a hole-doped bilayer of Sn on Si(111). This new phase is intrinsically phase separated into insulating domains with polar and nonpolar symmetries. Itsmore » formation involves a spontaneous symmetry breaking process that appears to be electronically driven, notwithstanding the lack of metallicity in this system. This modulation doping approach allows access to novel phases of matter, promising new avenues for exploring competing quantum matter phases on a silicon platform.« less

Stripe-like nanoscale structural phase separation in superconducting BaPb 1-xBi xO 3

DOE PAGES

Giraldo-Gallo, P.; Zhang, Y.; Parra, C.; ...

2015-09-16

The phase diagram of BaPb 1-xBi xO 3 exhibits a superconducting “dome” in the proximity of a charge density wave phase. For the superconducting compositions, the material coexists as two structural polymorphs. Here we show, via high resolution transmission electron microscopy, that the structural dimorphism is accommodated in the form of partially disordered nanoscale stripes. Identification of the morphology of the nanoscale structural phase separation enables determination of the associated length scales, which we compare to the Ginzburg-Landau coherence length. Thus, we find that the maximum T c occurs when the superconducting coherence length matches the width of the partiallymore » disordered stripes, implying a connection between the structural phase separation and the shape of the superconducting dome.« less

Superconductivity. Observation of broken time-reversal symmetry in the heavy-fermion superconductor UPt₃.

PubMed

Schemm, E R; Gannon, W J; Wishne, C M; Halperin, W P; Kapitulnik, A

2014-07-11

Models of superconductivity in unconventional materials can be experimentally differentiated by the predictions they make for the symmetries of the superconducting order parameter. In the case of the heavy-fermion superconductor UPt3, a key question is whether its multiple superconducting phases preserve or break time-reversal symmetry (TRS). We tested for asymmetry in the phase shift between left and right circularly polarized light reflected from a single crystal of UPt3 at normal incidence and found that this so-called polar Kerr effect appears only below the lower of the two zero-field superconducting transition temperatures. Our results provide evidence for broken TRS in the low-temperature superconducting phase of UPt3, implying a complex two-component order parameter for superconductivity in this system. Copyright © 2014, American Association for the Advancement of Science.

Superconductivity and Competing Ordered Phase in RuPn (Pn = As, P)

NASA Astrophysics Data System (ADS)

Hirai, Daigorou; Takayama, Tomohiro; Hashizume, Daisuke; Yamamoto, Ayako; Takagi, Hidenori

2011-03-01

Unconventional superconductivity likely manifests itself when some competing electronic phases are suppressed down to zero temperature such as cuprates and iron-pnictide superconductors. Therefore, the correlated metallic state neighboring a competing electronic ordering can be a promising playground for unconventional superconductivity. Here we report superconductivity emerging adjacent to electronically ordered phases of RuPn (Pn = As, P). We found that RuAs(P) exhibits phase transitions at 240 (265) K, which is discerned as a drop of magnetic susceptibility or a resistivity upturn. Such anomalies can be suppressed by substituting Rh to the Ru site. Accompanied by the disappearance of the electronic order, superconductivity was found to emerge below 1.8 K and 3.8 K for RuAs and RuP, respectively. The superconductivity in Rh substituted RuPn, which neighbors a competing electronic order, might exhibit an exotic pairing state as seen in the unconventional superconductors known to date.

Multiple topological electronic phases in superconductor MoC

NASA Astrophysics Data System (ADS)

Huang, Angus; Smith, Adam D.; Schwinn, Madison; Lu, Qiangsheng; Chang, Tay-Rong; Xie, Weiwei; Jeng, Horng-Tay; Bian, Guang

2018-05-01

The search for a superconductor with non-s -wave pairing is important not only for understanding unconventional mechanisms of superconductivity but also for finding new types of quasiparticles such as Majorana bound states. Materials with both topological band structure and superconductivity are promising candidates as p +i p superconducting states can be generated through pairing the spin-polarized topological surface states. In this work, the electronic and phonon properties of the superconductor molybdenum carbide (MoC) are studied with first-principles methods. Our calculations show that nontrivial band topology and s -wave Bardeen-Cooper-Schrieffer superconductivity coexist in two structural phases of MoC, namely the cubic α and hexagonal γ phases. The α phase is a strong topological insulator and the γ phase is a topological nodal-line semimetal with drumhead surface states. In addition, hole doping can stabilize the crystal structure of the α phase and elevate the transition temperature in the γ phase. Therefore, MoC in different structural forms can be a practical material platform for studying topological superconductivity.

Calorimetric Measurements of Magnetic-Field-Induced Inhomogeneous Superconductivity Above the Paramagnetic Limit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agosta, Charles C.; Fortune, Nathanael A.; Hannahs, Scott T.

We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor. kappa-(BEDT-TTF)(2) Cu(NCS)(2) as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit Hp is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field superconducting state displays themore » bulk paramagnetic ordering of spin domains required of the FFLO state. These results rule out the alternate possibility of spin-density wave ordering in the high-field superconducting phase. The phase diagram determined from our measurements-including the observation of a phase transition into the FFLO phase at Hp-is in good agreement with recent NMR results and our own earlier tunnel-diode magnetic penetration depth experiments but is in disagreement with the only previous calorimetric report.« less

Calorimetric Measurements of Magnetic-Field-Induced Inhomogeneous Superconductivity Above the Paramagnetic Limit

NASA Astrophysics Data System (ADS)

Agosta, Charles C.; Fortune, Nathanael A.; Hannahs, Scott T.; Gu, Shuyao; Liang, Lucy; Park, Ju-Hyun; Schleuter, John A.

2017-06-01

We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor κ -(BEDT -TTF )2Cu (NCS )2 as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit Hp is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field superconducting state displays the bulk paramagnetic ordering of spin domains required of the FFLO state. These results rule out the alternate possibility of spin-density wave ordering in the high-field superconducting phase. The phase diagram determined from our measurements—including the observation of a phase transition into the FFLO phase at Hp—is in good agreement with recent NMR results and our own earlier tunnel-diode magnetic penetration depth experiments but is in disagreement with the only previous calorimetric report.

Theory of disordered unconventional superconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keles, A.; Andreev, A. V.; Spivak, B. Z., E-mail: spivak@uw.edu

In contrast to conventional s-wave superconductivity, unconventional (e.g., p- or d-wave) superconductivity is strongly suppressed even by relatively weak disorder. Upon approaching the superconductormetal transition, the order parameter amplitude becomes increasingly inhomogeneous, leading to effective granularity and a phase ordering transition described by the Mattis model of spin glasses. One consequence of this is that at sufficiently low temperatures, between the clean unconventional superconducting and the diffusive metallic phases, there is necessarily an intermediate superconducting phase that exhibits s-wave symmetry on macroscopic scales.

Phase Separation of Superconducting Phases in the Penson-Kolb-Hubbard Model

NASA Astrophysics Data System (ADS)

Jerzy Kapcia, Konrad; Czart, Wojciech Robert; Ptok, Andrzej

2016-04-01

In this paper, we determine the phase diagrams (for T = 0 as well as T > 0) of the Penson-Kolb-Hubbard model for two dimensional square lattice within Hartree-Fock mean-field theory focusing on an investigation of superconducting phases and on a possibility of the occurrence of the phase separation. We obtain that the phase separation, which is a state of coexistence of two different superconducting phases (with s- and η-wave symmetries), occurs in definite ranges of the electron concentration. In addition, increasing temperature can change the symmetry of the superconducting order parameter (from η-wave into s-wave). The system considered exhibits also an interesting multicritical behaviour including bicritical points. The relevance of the results to experiments for real materials is also discussed.

The physics of inhomogeneous striped superconductors

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Eroles, J.; Balatsky, A. V.; Bishop, A. R.

2001-05-01

We present a minimal model of a doped Mott insulator that simultaneously supports antiferromagnetic stripes and d-wave superconductivity. At the unrestricted mean-field level, the various phases of the cuprates, including weak and strong pseudogap phases, and two different types of superconductivity in the underdoped and the overdoped regimes, find a natural interpretation. We argue that on the underdoped side, the superconductor is intrinsically inhomogeneous — striped nanoscale coexistence of superconductivity and magnetism — and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. On the overdoped side, the state is overall homogeneous and the superconductivity is of the classical BCS type.

Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first-order phase transition

NASA Astrophysics Data System (ADS)

Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.; Kreyssig, Andreas; Ran, S.; Bud'ko, Sergey L.; Canfield, Paul C.; Mompean, Federico J.; García-Hernández, Mar; Munuera, Carmen; Guillamón, Isabel; Suderow, Hermann

2018-01-01

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co-substituted CaFe2As2 . We use atomic force, magnetic force, and scanning tunneling microscopy to identify the domains and characterize their properties, finding in particular that tetragonal superconducting domains are very elongated, more than several tens of micrometers long and about 30 nm wide; have the same Tc as unstrained samples; and hold vortices in a magnetic field. Thus, biaxial strain produces a phase-separated state, where each phase is equivalent to what is found on either side of the first-order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of the order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first-order quantum phase transitions lead to nanometric-size phase separation under the influence of strain.

Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe 2 As 2 close to a first-order phase transition

DOE PAGES

Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.; ...

2018-01-09

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co substituted CaFe 2As 2. We use Atomic Force, Magnetic Force and Scanning Tunneling Microscopy (AFM, MFM and STM) to identify the domains and characterize their properties, nding in particular that tetragonal superconducting domains are very elongated, more than several tens of μm long and about 30 nm wide, have the same Tc than unstrained samples and hold vortices in a magnetic eld. Thus, biaxial strain produces a phase separated state, where each phase is equivalent to what is found at either side of the rstmore » order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first order quantum phase transitions lead to nanometric size phase separation under the influence of strain.« less

Optimization of the superconducting phase of hydrogen sulfide

NASA Astrophysics Data System (ADS)

Degtyarenko, N. N.; Masur, E. A.

2015-12-01

The electron and phonon spectra, as well as the densities of electron and phonon states of the SH3 phase and the stable orthorhombic structure of hydrogen sulfide SH2, are calculated for the pressure interval 100-225 GPa. It is found that the I4/ mmm phase can be responsible for the superconducting properties of metallic hydrogen sulfide along with the SH3 phase. Sequential stages for obtaining and conservation of the SH2 phase are proposed. The properties of two (SH2 and SH3) superconducting phases of hydrogen sulfide are compared.

Phase relations in KxFe2-ySe2 and the structure of superconducting KxFe2Se2 via high-resolution synchrotron diffraction

NASA Astrophysics Data System (ADS)

Shoemaker, Daniel P.; Chung, Duck Young; Claus, Helmut; Francisco, Melanie C.; Avci, Sevda; Llobet, Anna; Kanatzidis, Mercouri G.

2012-11-01

Superconductivity in iron selenides has experienced a rapid growth, but not without major inconsistencies in the reported properties. For alkali-intercalated iron selenides, even the structure of the superconducting phase is a subject of debate, in part because the onset of superconductivity is affected much more delicately by stoichiometry and preparation than in cuprate or pnictide superconductors. If high-quality, pure, superconducting intercalated iron selenides are ever to be made, the intertwined physics and chemistry must be explained by systematic studies of how these materials form and by and identifying the many coexisting phases. To that end, we prepared pure K2Fe4Se5 powder and superconductors in the KxFe2-ySe2 system, and examined differences in their structures by high-resolution synchrotron and single-crystal x-ray diffraction. We found four distinct phases: semiconducting K2Fe4Se5, a metallic superconducting phase KxFe2Se2 with x ranging from 0.38 to 0.58, the phase KFe1.6Se2 with full K occupancy and no Fe vacancy ordering, and a oxidized phase K0.51(5)Fe0.70(2)Se that forms the PbClF structure upon exposure to moisture. We find that the vacancy-ordered phase K2Fe4Se5 does not become superconducting by doping, but the distinct iron-rich minority phase KxFe2Se2 precipitates from single crystals upon cooling from above the vacancy ordering temperature. This coexistence of separate metallic and semiconducting phases explains a broad maximum in resistivity around 100 K. Further studies to understand the solubility of excess Fe in the KxFe2-ySe2 structure will shed light on the maximum fraction of superconducting KxFe2Se2 that can be obtained by solid state synthesis.

Dynamics of correlation-frozen antinodal quasiparticles in superconducting cuprates

PubMed Central

Cilento, Federico; Manzoni, Giulia; Sterzi, Andrea; Peli, Simone; Ronchi, Andrea; Crepaldi, Alberto; Boschini, Fabio; Cacho, Cephise; Chapman, Richard; Springate, Emma; Eisaki, Hiroshi; Greven, Martin; Berciu, Mona; Kemper, Alexander F.; Damascelli, Andrea; Capone, Massimo; Giannetti, Claudio; Parmigiani, Fulvio

2018-01-01

Many puzzling properties of high–critical temperature (Tc) superconducting (HTSC) copper oxides have deep roots in the nature of the antinodal quasiparticles, the elementary excitations with wave vector parallel to the Cu–O bonds. These electronic states are most affected by the onset of antiferromagnetic correlations and charge instabilities, and they host the maximum of the anisotropic superconducting gap and pseudogap. We use time-resolved extreme-ultraviolet photoemission with proper photon energy (18 eV) and time resolution (50 fs) to disclose the ultrafast dynamics of the antinodal states in a prototypical HTSC cuprate. After photoinducing a nonthermal charge redistribution within the Cu and O orbitals, we reveal a dramatic momentum-space differentiation of the transient electron dynamics. Whereas the nodal quasiparticle distribution is heated up as in a conventional metal, new quasiparticle states transiently emerge at the antinodes, similarly to what is expected for a photoexcited Mott insulator, where the frozen charges can be released by an impulsive excitation. This transient antinodal metallicity is mapped into the dynamics of the O-2p bands, thus directly demonstrating the intertwining between the low- and high-energy scales that is typical of correlated materials. Our results suggest that the correlation-driven freezing of the electrons moving along the Cu–O bonds, analogous to the Mott localization mechanism, constitutes the starting point for any model of high-Tc superconductivity and other exotic phases of HTSC cuprates. PMID:29507885

Influence of microstructure on superconductivity in KxFe2−ySe2 and evidence for a new parent phase K2Fe7Se8

PubMed Central

Ding, Xiaxin; Fang, Delong; Wang, Zhenyu; Yang, Huan; Liu, Jianzhong; Deng, Qiang; Ma, Guobin; Meng, Chong; Hu, Yuhui; Wen, Hai-Hu

2013-01-01

The search for new superconducting materials has been spurred on by the discovery of iron-based superconductors whose structure and composition is qualitatively different from the cuprates. The study of one such material, KxFe2−ySe2 with a critical temperature of 32 K, is made more difficult by the fact that it separates into two phases—a dominant antiferromagnetic insulating phase K2Fe4Se5, and a minority superconducting phase whose precise structure is as yet unclear. Here we perform electrical and magnetization measurements, scanning electron microscopy and microanalysis, X-ray diffraction and scanning tunnelling microscopy on KxFe2−ySe2 crystals prepared under different quenching processes to better understand the relationship between its microstructure and its superconducting phase. We identify a three-dimensional network of superconducting filaments within this material and present evidence to suggest that the superconducting phase consists of a single Fe vacancy for every eight Fe-sites arranged in a √8 x √10 parallelogram structure. PMID:23695691

Formation mechanism of superconducting phase and its three-dimensional architecture in pseudo-single-crystal K xFe 2-ySe 2

DOE PAGES

Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.; ...

2016-02-11

Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition.more » It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

A minimal model of striped superconductors

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Balatsky, A. V.; Bishop, A. R.

2001-12-01

We present a minimal model of high-temperature superconductors that simultaneously supports antiferromagnetic stripes and d-wave superconductivity. At the unrestricted mean-field level, the various phases of the cuprates, including weak and strong pseudogap phases, and two different types of superconductivity in the underdoped and the overdoped regimes, find a natural interpretation. We argue that on the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. On the overdoped side, the state is overall homogeneous and the superconductivity is of a classical BCS type.

Driven superconducting quantum circuits

NASA Astrophysics Data System (ADS)

Nakamura, Yasunobu

2014-03-01

Driven nonlinear quantum systems show rich phenomena in various fields of physics. Among them, superconducting quantum circuits have very attractive features such as well-controlled quantum states with design flexibility, strong nonlinearity of Josephson junctions, strong coupling to electromagnetic driving fields, little internal dissipation, and tailored coupling to the electromagnetic environment. We have investigated properties and functionalities of driven superconducting quantum circuits. A transmon qubit coupled to a transmission line shows nearly perfect spatial mode matching between the incident and scattered microwave field in the 1D mode. Dressed states under a driving field are studied there and also in a semi-infinite 1D mode terminated by a resonator containing a flux qubit. An effective Λ-type three-level system is realized under an appropriate driving condition. It allows ``impedance-matched'' perfect absorption of incident probe photons and down conversion into another frequency mode. Finally, the weak signal from the qubit is read out using a Josephson parametric amplifier/oscillator which is another nonlinear circuit driven by a strong pump field. This work was partly supported by the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST), Project for Developing Innovation Systems of MEXT, MEXT KAKENHI ``Quantum Cybernetics,'' and the NICT Commissioned Research.

Boundaries for martensitic transition of 7Li under pressure

DOE PAGES

Schaeffer, Anne Marie; Cai, Weizhao; Olejnik, Ella; ...

2015-08-14

We report that physical properties of lithium under extreme pressures continuously reveal unexpected features. These include a sequence of structural transitions to lower symmetry phases, metal-insulator-metal transition, superconductivity with one of the highest elemental transition temperatures, and a maximum followed by a minimum in its melting line. The instability of the bcc structure of lithium is well established by the presence of a temperature-driven martensitic phase transition. The boundaries of this phase, however, have not been previously explored above 3 GPa. All higher pressure phase boundaries are either extrapolations or inferred based on indirect evidence. Here we explore the pressuremore » dependence of the martensitic transition of lithium up to 7 GPa using a combination of neutron and X-ray scattering. We find a rather unexpected deviation from the extrapolated boundaries of the hR3 phase of lithium. Furthermore, there is evidence that, above ~3 GPa, once in fcc phase, lithium does not undergo a martensitic transition.« less

Superconducting quantum circuits theory and application

NASA Astrophysics Data System (ADS)

Deng, Xiuhao

Superconducting quantum circuit models are widely used to understand superconducting devices. This thesis consists of four studies wherein the superconducting quantum circuit is used to illustrate challenges related to quantum information encoding and processing, quantum simulation, quantum signal detection and amplification. The existence of scalar Aharanov-Bohm phase has been a controversial topic for decades. Scalar AB phase, defined as time integral of electric potential, gives rises to an extra phase factor in wavefunction. We proposed a superconducting quantum Faraday cage to detect temporal interference effect as a consequence of scalar AB phase. Using the superconducting quantum circuit model, the physical system is solved and resulting AB effect is predicted. Further discussion in this chapter shows that treating the experimental apparatus quantum mechanically, spatial scalar AB effect, proposed by Aharanov-Bohm, can't be observed. Either a decoherent interference apparatus is used to observe spatial scalar AB effect, or a quantum Faraday cage is used to observe temporal scalar AB effect. The second study involves protecting a quantum system from losing coherence, which is crucial to any practical quantum computation scheme. We present a theory to encode any qubit, especially superconducting qubits, into a universal quantum degeneracy point (UQDP) where low frequency noise is suppressed significantly. Numerical simulations for superconducting charge qubit using experimental parameters show that its coherence time is prolong by two orders of magnitude using our universal degeneracy point approach. With this improvement, a set of universal quantum gates can be performed at high fidelity without losing too much quantum coherence. Starting in 2004, the use of circuit QED has enabled the manipulation of superconducting qubits with photons. We applied quantum optical approach to model coupled resonators and obtained a four-wave mixing toolbox to operate photons states. The model and toolbox are engineered with a superconducting quantum circuit where two superconducting resonators are coupled via the UQDP circuit. Using fourth order perturbation theory one can realize a complete set of quantum operations between these two photon modes. This helps open a new field to treat photon modes as qubits. Additional, a three-wave mixing scheme using phase qubits permits one to engineer the coupling Hamiltonian using a phase qubit as a tunable coupler. Along with Feynman's idea using quantum to simulate quantum, superconducting quantum simulators have been studied intensively recently. Taking the advantage of mesoscopic size of superconducting circuit and local tunability, we came out the idea to simulate quantum phase transition due to disorder. Our first paper was to propose a superconducting quantum simulator of Bose-Hubbard model to do site-wise manipulation and observe Mott-insulator to superfluid phase transition. The side-band cooling of an array of superconducting resonators is solved after the paper was published. In light of the developed technology in manipulating quantum information with superconducting circuit, one can couple other quantum oscillator system to superconducting resonators in order manipulation of its quantum states or parametric amplification of weak quantum signal. A theory that works for different coupling schemes has been studied in chapter 5. This will be a platform for further research.

Dynamical Cooper pairing in nonequilibrium electron-phonon systems

DOE PAGES

Knap, Michael; Babadi, Mehrtash; Refael, Gil; ...

2016-12-08

In this paper, we analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced nonequilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Finally, our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.

Superconducting phase transitions in mK temperature range in splat-cooled U0.85Pt0.15 alloys

NASA Astrophysics Data System (ADS)

Kim-Ngan, N.-T. H.; Tarnawski, Z.; Chrobak, M.; Sowa, S.; Duda, A.; Paukov, M.; Buturlim, V.; Havela, L.

2018-05-01

We present the temperature and magnetic-field dependence of the electrical resistivity (ρ(T,B)) in the mK temperature range used as a diagnostic tool for the superconductivity of U-Pt alloys prepared by splat-cooling technique. In most of the investigated alloys, a single resistivity drop was observed at the superconducting transition. For splat-cooled U0.85Pt0.15 (U-15 at% Pt) alloys, two drops were revealed around 0.6 K and 1 K tentatively attributed to the superconducting phase transitions of the γ-U phase and α-U phase. The ρ(T,B) characteristics were found to depend on the cooling rate. The superconductivity is characterized by very high upper critical fields, reaching 4.5 T in the 0 K limit.

Interface-induced superconductivity at ∼25 K at ambient pressure in undoped CaFe2As2 single crystals

PubMed Central

Zhao, Kui; Lv, Bing; Deng, Liangzi; Huyan, Shu-Yuan; Xue, Yu-Yi; Chu, Ching-Wu

2016-01-01

Superconductivity has been reversibly induced/suppressed in undoped CaFe2As2 (Ca122) single crystals through proper thermal treatments, with Tc at ∼25 K at ambient pressure and up to 30 K at 1.7 GPa. We found that Ca122 can be stabilized in two distinct tetragonal (T) phases at room temperature and ambient pressure: PI with a nonmagnetic collapsed tetragonal (cT) phase at low temperature and PII with an antiferromagnetic orthorhombic (O) phase at low temperature, depending on the low-temperature annealing condition. Neither phase at ambient pressure is superconducting down to 2 K. However, systematic annealing for different time periods at 350 °C on the as-synthesized crystals, which were obtained by quenching the crystal ingot from 850 °C, reveals the emergence of superconductivity over a narrow time window. Whereas the onset Tc is insensitive to the anneal time, the superconductive volume fraction evolves with the time in a dome-shaped fashion. Detailed X-ray diffraction profile analyses further reveal mesoscopically stacked layers of the PI and the PII phases. The deduced interface density correlates well with the superconducting volume measured. The transport anomalies of the T–cT transition, which is sensitive to lattice strain, and the T–O transition, which is associated with the spin-density-wave (SDW) transition, are gradually suppressed over the superconductive region, presumably due to the interface interactions between the nonmagnetic metallic cT phase and the antiferromagnetic O phase. The results provide the most direct evidence to date for interface-enhanced superconductivity in undoped Ca122, consistent with the recent theoretical prediction. PMID:27799564

Superconducting dome in doped quasi-two-dimensional organic Mott insulators: A paradigm for strongly correlated superconductivity

NASA Astrophysics Data System (ADS)

Hébert, Charles-David; Sémon, Patrick; Tremblay, A.-M. S.

2015-11-01

Layered organic superconductors of the BEDT family are model systems for understanding the interplay of the Mott transition with superconductivity, magnetic order, and frustration, ingredients that are essential to understand superconductivity also in the cuprate high-temperature superconductors. Recent experimental studies on a hole-doped version of the organic compounds reveals an enhancement of superconductivity and a rapid crossover between two different conducting phases above the superconducting dome. One of these phases is a Fermi liquid, the other not. Using plaquette cellular dynamical mean field theory with state-of-the-art continuous-time quantum Monte Carlo calculations, we study this problem with the two-dimensional Hubbard model on the anisotropic triangular lattice. Phase diagrams as a function of temperature T and interaction strength U /t are obtained for anisotropy parameters t'=0.4 t ,t'=0.8 t and for various fillings. As in the case of the cuprates, we find, at finite doping, a first-order transition between two normal-state phases. One of theses phases has a pseudogap while the other does not. At temperatures above the critical point of the first-order transition, there is a Widom line where crossovers occur. The maximum (optimal) superconducting critical temperature Tcm at finite doping is enhanced by about 25% compared with its maximum at half filling and the range of U /t where superconductivity appears is greatly extended. These results are in broad agreement with experiment. Also, increasing frustration (larger t'/t ) significantly reduces magnetic ordering, as expected. This suggests that for compounds with intermediate to high frustration, very light doping should reveal the influence of the first-order transition and associated crossovers. These crossovers could possibly be even visible in the superconducting phase through subtle signatures. We also predict that destroying the superconducting phase by a magnetic field should reveal the first-order transition between metal and pseudogap. Finally, we predict that electron doping should also lead to an increased range of U /t for superconductivity but with a reduced maximum Tc. This work also clearly shows that the superconducting dome in organic superconductors is tied to the Mott transition and its continuation as a transition separating pseudogap phase from correlated metal in doped compounds, as in the cuprates. Contrary to heavy fermions for example, the maximum Tc is definitely not attached to an antiferromagnetic quantum critical point. That can also be verified experimentally.

The reaction process of the Bi-Sr-Ca-Cu-O system and the forming mechanism of the 2212 superconducting phase

NASA Astrophysics Data System (ADS)

Xiong, Guohong; Wang, Minquan; Fan, Xianping; Tang, Xiaoming

1993-02-01

The reaction process and the reaction behavior of each component in the Bi-Sr-Ca-Cu-O system are presented in this paper. It reveals that the reaction is carried out in three different stages: forming of an insulating interphase at 680°C 790°C, forming of the 2212 superconducting phase at 790°C 860°C and forming often semiconducting phases in the presence of the liquid phase at 860°C 970°C. It is also confirmed that the 2212 superconducting phase ( T c=85 K) is formed by the reaction of a trinary interphase together with CuO, SrO and CaO. A new two-step method is presented to prepare the 2212 superconducting phase by a presynthesized interphase.

Detection of geometric phases in superconducting nanocircuits

PubMed

Falci; Fazio; Palma; Siewert; Vedral

2000-09-21

When a quantum-mechanical system undergoes an adiabatic cyclic evolution, it acquires a geometrical phase factor' in addition to the dynamical one; this effect has been demonstrated in a variety of microscopic systems. Advances in nanotechnology should enable the laws of quantum dynamics to be tested at the macroscopic level, by providing controllable artificial two-level systems (for example, in quantum dots and superconducting devices). Here we propose an experimental method to detect geometric phases in a superconducting device. The setup is a Josephson junction nanocircuit consisting of a superconducting electron box. We discuss how interferometry based on geometrical phases may be realized, and show how the effect may be applied to the design of gates for quantum computation.

Topological quantum phase transitions and edge states in spin-orbital coupled Fermi gases.

PubMed

Zhou, Tao; Gao, Yi; Wang, Z D

2014-06-11

We study superconducting states in the presence of spin-orbital coupling and Zeeman field. It is found that a phase transition from a Fulde-Ferrell-Larkin-Ovchinnikov state to the topological superconducting state occurs upon increasing the spin-orbital coupling. The nature of this topological phase transition and its critical property are investigated numerically. Physical properties of the topological superconducting phase are also explored. Moreover, the local density of states is calculated, through which the topological feature may be tested experimentally.

Superfluid phase stiffness in electron doped superconducting Gd-123

NASA Astrophysics Data System (ADS)

Das, P.; Ghosh, Ajay Kumar

2018-05-01

Current-voltage characteristics of Ce substituted Gd-123 superconductor exhibits nonlinearity below a certain temperature below the critical temperature. An exponent is extracted using the nonlinearity of current-voltage relation. Superfluid phase stiffness has been studied as a function of temperature following the Ambegaokar-Halperin-Nelson-Siggia (AHNS) theory. Phase stiffness of the superfluid below the superconducting transition is found to be sensitive to the change in the carrier concentration in superconducting system. There may be a crucial electron density which affects superfluid stiffness strongly. Electron doping is found to be effective even if the coupling of the superconducting planes is changed.

Particle-hole symmetry reveals failed superconductivity in the metallic phase of two-dimensional superconducting films

DOE PAGES

Breznay, Nicholas P.; Kapitulnik, Aharon

2017-09-15

Electrons confined to two dimensions display an unexpected diversity of behaviors as they are cooled to absolute zero. Noninteracting electrons are predicted to eventually “localize” into an insulating ground state, and it has long been supposed that electron correlations stabilize only one other phase: superconductivity. However, many two-dimensional (2D) superconducting materials have shown surprising evidence for metallic behavior, where the electrical resistivity saturates in the zero-temperature limit; the nature of this unexpected metallic state remains under intense scrutiny. We report electrical transport properties for two disordered 2D superconductors, indium oxide and tantalum nitride, and observe a magnetic field–tuned transition frommore » a true superconductor to a metallic phase with saturated resistivity. Lastly, this metallic phase is characterized by a vanishing Hall resistivity, suggesting that it retains particle-hole symmetry from the disrupted superconducting state.« less

Particle-hole symmetry reveals failed superconductivity in the metallic phase of two-dimensional superconducting films

PubMed Central

Breznay, Nicholas P.; Kapitulnik, Aharon

2017-01-01

Electrons confined to two dimensions display an unexpected diversity of behaviors as they are cooled to absolute zero. Noninteracting electrons are predicted to eventually “localize” into an insulating ground state, and it has long been supposed that electron correlations stabilize only one other phase: superconductivity. However, many two-dimensional (2D) superconducting materials have shown surprising evidence for metallic behavior, where the electrical resistivity saturates in the zero-temperature limit; the nature of this unexpected metallic state remains under intense scrutiny. We report electrical transport properties for two disordered 2D superconductors, indium oxide and tantalum nitride, and observe a magnetic field–tuned transition from a true superconductor to a metallic phase with saturated resistivity. This metallic phase is characterized by a vanishing Hall resistivity, suggesting that it retains particle-hole symmetry from the disrupted superconducting state. PMID:28929135

Particle-hole symmetry reveals failed superconductivity in the metallic phase of two-dimensional superconducting films.

PubMed

Breznay, Nicholas P; Kapitulnik, Aharon

2017-09-01

Electrons confined to two dimensions display an unexpected diversity of behaviors as they are cooled to absolute zero. Noninteracting electrons are predicted to eventually "localize" into an insulating ground state, and it has long been supposed that electron correlations stabilize only one other phase: superconductivity. However, many two-dimensional (2D) superconducting materials have shown surprising evidence for metallic behavior, where the electrical resistivity saturates in the zero-temperature limit; the nature of this unexpected metallic state remains under intense scrutiny. We report electrical transport properties for two disordered 2D superconductors, indium oxide and tantalum nitride, and observe a magnetic field-tuned transition from a true superconductor to a metallic phase with saturated resistivity. This metallic phase is characterized by a vanishing Hall resistivity, suggesting that it retains particle-hole symmetry from the disrupted superconducting state.

Three superconducting phases with different categories of pairing in hole- and electron-doped LaFeAs1 -xPxO

NASA Astrophysics Data System (ADS)

Miyasaka, S.; Uekubo, M.; Tsuji, H.; Nakajima, M.; Tajima, S.; Shiota, T.; Mukuda, H.; Sagayama, H.; Nakao, H.; Kumai, R.; Murakami, Y.

2017-06-01

The phase diagram of the LaFeAs1 -xPxO system has been extensively studied through hole and electron doping as well as As/P substitution. It has been revealed that there are three different superconducting phases with different Fermi surface (FS) topologies and thus with possibly different pairing glues. One of them is well understood as spin fluctuation-mediated superconductivity within a FS nesting scenario. Another one with the FSs in a bad nesting condition must be explained in a different context such as orbital or spin fluctuation in a strongly correlated electronic system. In both phases, T -linear resistivity was commonly observed when the superconducting transition temperature Tc becomes the highest value, indicating that the strength of bosonic fluctuation determines Tc. In the last superconducting phase, the nesting condition of FSs and the related bosonic fluctuation are moderate. Variety of phase diagram characterizes the multiple orbital nature of the iron-based superconductors which are just near the boundary between weak and strong correlation regimes.

Synthesis of superconducting phases in Tl-Ba-Ca-Cu-O system

NASA Astrophysics Data System (ADS)

Bayya, S. S.; Stangle, G. C.; Snyder, R. L.

1992-04-01

This paper describes various novel processing techniques for the synthesis of superconducting phases in the Ti-Ba-Ca-Cu-O system. A Self propagating high temperature synthesis technique has been used to synthesize phase pure 2212 and 2223. Various engineering parameters are identified for this process. A glass-ceramic (melt quench) technique with subsequent post heat-treatment produced pure 2201 and 2212 phases. Tl2O3 itself is not a very good glass former and the addition of other glass formers is necessary to form stable glasses. Only the gallate glass system has been found to stabilize the 2201 and 2212 superconducting phases. Molten salt synthesis studies showed that the superconducting phases in the thallium system are stable in the NaCl-KCl eutectic salt system. Highly textured 2201 grains (about 60 μm×60 ¯ platelets) were grown by this technique. Various potential applications of these techniques are also discussed.

Rashba sandwiches with topological superconducting phases

NASA Astrophysics Data System (ADS)

Volpez, Yanick; Loss, Daniel; Klinovaja, Jelena

2018-05-01

We introduce a versatile heterostructure harboring various topological superconducting phases characterized by the presence of helical, chiral, or unidirectional edge states. Changing parameters, such as an effective Zeeman field or chemical potential, one can tune between these three topological phases in the same setup. Our model relies only on conventional nontopological ingredients. The bilayer setup consists of an s -wave superconductor sandwiched between two two-dimensional electron gas layers with strong Rashba spin-orbit interaction. The interplay between two different pairing mechanisms, proximity induced direct and crossed Andreev superconducting pairings, gives rise to multiple topological phases. In particular, helical edge states occur if crossed Andreev superconducting pairing is dominant. In addition, an in-plane Zeeman field leads to a two-dimensional gapless topological phase with unidirectional edge states, which were previously predicted to exist only in noncentrosymmetric superconductors. If the Zeeman field is tilted out of the plane, the system is in a topological phase hosting chiral edge states.

Superconductivity in multiple phases of compressed GeS b2T e4

NASA Astrophysics Data System (ADS)

Greenberg, E.; Hen, B.; Layek, Samar; Pozin, I.; Friedman, R.; Shelukhin, V.; Rosenberg, Y.; Karpovski, M.; Pasternak, M. P.; Sterer, E.; Dagan, Y.; Rozenberg, G. Kh.; Palevski, A.

2017-02-01

Here we report the discovery of superconductivity in multiple phases of the compressed GeS b2T e4 (GST) phase change memory alloy, which has attracted considerable attention for the last decade due to its unusual physical properties with many potential applications. Superconductivity is observed through electrical transport measurements, both for the amorphous (a -GST) and for the crystalline (c -GST) phases. The superconducting critical temperature Tc continuously increases with applied pressure, reaching a maximum Tc=6 K at P =20 GPa for a -GST, whereas the critical temperature of the cubic phase reaches a maximum Tc=8 K at 30 GPa. This material system, exhibiting a superconductor-insulator quantum phase transition, has an advantage over disordered metals since it has a continuous control of the crystal structure and the electronic properties using pressure as an external stimulus.

Process for preparing superconducting film having substantially uniform phase development

DOEpatents

Bharacharya, Raghuthan; Parilla, Philip A.; Blaugher, Richard D.

1995-01-01

A process for preparing a superconducting film, such as a thallium-barium-calcium-copper oxide superconducting film, having substantially uniform phase development. The process comprises providing an electrodeposition bath having one or more soluble salts of one or more respective potentially superconducting metals in respective amounts adequate to yield a superconducting film upon subsequent appropriate treatment. Should all of the metals required for producing a superconducting film not be made available in the bath, such metals can be a part of the ambient during a subsequent annealing process. A soluble silver salt in an amount between about 0.1% and about 4.0% by weight of the provided other salts is also provided to the bath, and the bath is electrically energized to thereby form a plated film. The film is annealed in ambient conditions suitable to cause formation of a superconductor film. Doping with silver reduces the temperature at which the liquid phase appears during the annealing step, initiates a liquid phase throughout the entire volume of deposited material, and influences the nucleation and growth of the deposited material.

Process for preparing superconducting film having substantially uniform phase development

DOEpatents

Bharacharya, R.; Parilla, P.A.; Blaugher, R.D.

1995-12-19

A process is disclosed for preparing a superconducting film, such as a thallium-barium-calcium-copper oxide superconducting film, having substantially uniform phase development. The process comprises providing an electrodeposition bath having one or more soluble salts of one or more respective potentially superconducting metals in respective amounts adequate to yield a superconducting film upon subsequent appropriate treatment. Should all of the metals required for producing a superconducting film not be made available in the bath, such metals can be a part of the ambient during a subsequent annealing process. A soluble silver salt in an amount between about 0.1% and about 4.0% by weight of the provided other salts is also provided to the bath, and the bath is electrically energized to thereby form a plated film. The film is annealed in ambient conditions suitable to cause formation of a superconductor film. Doping with silver reduces the temperature at which the liquid phase appears during the annealing step, initiates a liquid phase throughout the entire volume of deposited material, and influences the nucleation and growth of the deposited material. 3 figs.

Electron—phonon Coupling and the Superconducting Phase Diagram of the LaAlO3—SrTiO3 Interface

PubMed Central

Boschker, Hans; Richter, Christoph; Fillis-Tsirakis, Evangelos; Schneider, Christof W.; Mannhart, Jochen

2015-01-01

The superconductor at the LaAlO3—SrTiO3 interface provides a model system for the study of two-dimensional superconductivity in the dilute carrier density limit. Here we experimentally address the pairing mechanism in this superconductor. We extract the electron—phonon spectral function from tunneling spectra and conclude, without ruling out contributions of further pairing channels, that electron—phonon mediated pairing is strong enough to account for the superconducting critical temperatures. Furthermore, we discuss the electron—phonon coupling in relation to the superconducting phase diagram. The electron—phonon spectral function is independent of the carrier density, except for a small part of the phase diagram in the underdoped region. The tunneling measurements reveal that the increase of the chemical potential with increasing carrier density levels off and is zero in the overdoped region of the phase diagram. This indicates that the additionally induced carriers do not populate the band that hosts the superconducting state and that the superconducting order parameter therefore is weakened by the presence of charge carriers in another band. PMID:26169351

Superconductivity bordering Rashba type topological transition

DOE PAGES

Jin, M. L.; Sun, F.; Xing, L. Y.; ...

2017-01-04

Strong spin orbital interaction (SOI) can induce unique quantum phenomena such as topological insulators, the Rashba effect, or p-wave superconductivity. Combining these three quantum phenomena into a single compound has important scientific implications. Here we report experimental observations of consecutive quantum phase transitions from a Rashba type topological trivial phase to topological insulator state then further proceeding to superconductivity in a SOI compound BiTeI tuned via pressures. The electrical resistivity measurement with V shape change signals the transition from a Rashba type topological trivial to a topological insulator phase at 2 GPa, which is caused by an energy gap closemore » then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature T C of 5.3 K. Structure refinements indicate that the consecutive phase transitions are correlated to the changes in the Bi–Te bond and bond angle as function of pressures. As a result, the Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.« less

d +i d chiral superconductivity in a triangular lattice from trigonal bipyramidal complexes

NASA Astrophysics Data System (ADS)

Lu, Chen; Zhang, Li-Da; Wu, Xianxin; Yang, Fan; Hu, Jiangping

2018-04-01

We model the newly predicted high-Tc superconducting candidates constructed by corner-shared trigonal bipyramidal complexes with an effective three-orbital tight-binding Hamiltonian and investigate the pairing symmetry of their superconducting states driven by electron-electron interactions. Our combined weak- and strong-coupling-based calculations consistently identify the chiral d +i d superconductivity as the leading pairing symmetry in a wide doping range with realistic interaction parameters. This pairing state has a nontrivial topological Chern number and can host gapless chiral edge modes, and the vortex cores under magnetic field can carry Majorana zero modes.

Phase-incoherent superconducting pairs in the normal state of Ba(Fe(1-x)Co(x))₂As₂.

PubMed

Sheet, Goutam; Mehta, Manan; Dikin, D A; Lee, S; Bark, C W; Jiang, J; Weiss, J D; Hellstrom, E E; Rzchowski, M S; Eom, C B; Chandrasekhar, V

2010-10-15

The normal state properties of the recently discovered ferropnictide superconductors might hold the key to understanding their exotic superconductivity. Using point-contact spectroscopy we show that Andreev reflection between an epitaxial thin film of Ba(Fe(0.92)Co(0.08))₂As₂ and a silver tip can be seen in the normal state of the film up to temperature T∼1.3T(c), where T(c) is the critical temperature of the superconductor. Andreev reflection far above T(c) can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the ferropnictide superconductors.

Sustained phase separation and spin glass in Co-doped K x Fe 2 - y Se 2 single crystals

DOE PAGES

Ryu, Hyejin; Wang, Kefeng; Opacic, M.; ...

2015-11-19

We describe Co substitution effects in K xFe 2-y-zCo zSe 2 (0.06 ≤ z ≤ 1.73) single crystal alloys. By 3.5% of Co doping superconductivity is suppressed whereas phase separation of semiconducting K 2Fe 4Se 5 and superconducting/metallic K xFe 2Se 2 is still present. We show that the arrangement and distribution of superconducting phase (stripe phase) is connected with the arrangement of K, Fe and Co atoms. Semiconducting spin glass is found in proximity to superconducting state, persisting for large Co concentrations. At high Co concentrations ferromagnetic metallic state emerges above the spin glass. This is coincident withmore » changes of the unit cell, arrangement and connectivity of stripe conducting phase.« less

Quantum heat engine with coupled superconducting resonators

NASA Astrophysics Data System (ADS)

Hardal, Ali Ü. C.; Aslan, Nur; Wilson, C. M.; Müstecaplıoǧlu, Özgür E.

2017-12-01

We propose a quantum heat engine composed of two superconducting transmission line resonators interacting with each other via an optomechanical-like coupling. One resonator is periodically excited by a thermal pump. The incoherently driven resonator induces coherent oscillations in the other one due to the coupling. A limit cycle, indicating finite power output, emerges in the thermodynamical phase space. The system implements an all-electrical analog of a photonic piston. Instead of mechanical motion, the power output is obtained as a coherent electrical charging in our case. We explore the differences between the quantum and classical descriptions of our system by solving the quantum master equation and classical Langevin equations. Specifically, we calculate the mean number of excitations, second-order coherence, as well as the entropy, temperature, power, and mean energy to reveal the signatures of quantum behavior in the statistical and thermodynamic properties of the system. We find evidence of a quantum enhancement in the power output of the engine at low temperatures.

Quantum heat engine with coupled superconducting resonators.

PubMed

Hardal, Ali Ü C; Aslan, Nur; Wilson, C M; Müstecaplıoğlu, Özgür E

2017-12-01

We propose a quantum heat engine composed of two superconducting transmission line resonators interacting with each other via an optomechanical-like coupling. One resonator is periodically excited by a thermal pump. The incoherently driven resonator induces coherent oscillations in the other one due to the coupling. A limit cycle, indicating finite power output, emerges in the thermodynamical phase space. The system implements an all-electrical analog of a photonic piston. Instead of mechanical motion, the power output is obtained as a coherent electrical charging in our case. We explore the differences between the quantum and classical descriptions of our system by solving the quantum master equation and classical Langevin equations. Specifically, we calculate the mean number of excitations, second-order coherence, as well as the entropy, temperature, power, and mean energy to reveal the signatures of quantum behavior in the statistical and thermodynamic properties of the system. We find evidence of a quantum enhancement in the power output of the engine at low temperatures.

Lone pair effect, structural distortions, and potential for superconductivity in Tl perovskites.

PubMed

Schoop, Leslie M; Müchler, Lukas; Felser, Claudia; Cava, R J

2013-05-06

Drawing the analogy to BaBiO3, we investigate via ab initio electronic structure calculations potential new superconductors of the type ATlX3 with A = Rb and Cs and X = F, Cl, and Br, with a particular emphasis on RbTlCl3. On the basis of chemical reasoning, supported by the calculations, we show that Tl-based perovskites have structural and charge instabilities driven by the lone pair effect, similar to the case of BaBiO3, effectively becoming A2Tl(+)Tl(3+)X6. We find that upon hole doping of RbTlCl3, structures without Tl(+) and Tl(3+) charge disproportionation become more stable, although the ideal cubic perovskite, often viewed as the best host for superconductivity, should not be the most stable phase in the system. The known superconductor (Sr,K)BiO3 and hole doped RbTlCl3, predicted to be most stable in the same tetragonal structure, display highly analogous calculated electronic band structures.

Two-Dimensional Superconductivity in the Cuprates Revealed by Atomic-Layer-by- Layer Molecular Beam Epitaxy

DOE PAGES

A. T. Bollinger; Bozovic, I.

2016-08-12

Various electronic phases displayed by cuprates that exhibit high temperature superconductivity continue to attract much interest. We provide a short review of several experiments that we have performed aimed at investigating the superconducting state in these compounds. Measurements on single-phase films, bilayers, and superlattices all point to the conclusion that the high-temperature superconductivity in these materials is an essentially quasi-two dimensional phenomenon. With proper control over the film growth, high-temperature superconductivity can exist in a single copper oxide plane with the critical temperatures as high as that achieved in the bulk samples.

Possibility of high temperature superconducting phases in PdH

NASA Astrophysics Data System (ADS)

Tripodi, Paolo; Di Gioacchino, Daniele; Borelli, Rodolfo; Vinko, Jenny Darja

2003-05-01

Possible new superconducting phases with a high critical transition temperature (Tc) have been found in stable palladium-hydrogen (PdHx) samples for stoichiometric ratio x=H/Pd⩾1, in addition to the well-known low critical transition temperature (0⩽Tc⩽9) when x is in the range (0.75⩽x⩽1.00). Possible new measured superconducting phases with critical temperature in the range 51⩽Tc⩽295 K occur. This Tc varies considerably with every milli part of x when x exceeds unit. A superconducting critical current density Jc⩾6.1×104 A cm-2 has been measured at 77 K with HDC=0 T.

Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductors

PubMed Central

Qin, Wei; Xiao, Di; Chang, Kai; Shen, Shun-Qing; Zhang, Zhenyu

2016-01-01

Normal superconductors with Rashba spin-orbit coupling have been explored as candidate systems of topological superconductors. Here we present a comparative theoretical study of the effects of different types of disorder on the topological phases of two-dimensional Rashba spin-orbit coupled superconductors. First, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorder, which close and reopen the quasiparticle gap of the paired electrons in a nontrivial manner. Secondly, the superconducting nature of a topological superconductor is found to be robust against Anderson disorder, but the topological nature is not, converting the system into a topologically trivial state even in the weak scattering limit. These topological phase transitions are distinctly characterized by variations in the topological invariant. We discuss the central findings in connection with existing experiments, and provide new schemes towards eventual realization of topological superconductors. PMID:27991541

Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductors

NASA Astrophysics Data System (ADS)

Qin, Wei; Xiao, Di; Chang, Kai; Shen, Shun-Qing; Zhang, Zhenyu

2016-12-01

Normal superconductors with Rashba spin-orbit coupling have been explored as candidate systems of topological superconductors. Here we present a comparative theoretical study of the effects of different types of disorder on the topological phases of two-dimensional Rashba spin-orbit coupled superconductors. First, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorder, which close and reopen the quasiparticle gap of the paired electrons in a nontrivial manner. Secondly, the superconducting nature of a topological superconductor is found to be robust against Anderson disorder, but the topological nature is not, converting the system into a topologically trivial state even in the weak scattering limit. These topological phase transitions are distinctly characterized by variations in the topological invariant. We discuss the central findings in connection with existing experiments, and provide new schemes towards eventual realization of topological superconductors.

Controllable 0–π Josephson junctions containing a ferromagnetic spin valve

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.

Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such ‘π-junctions’ were first realized experimentally in 2001, and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and pi by changing the relativemore » orientation of the two magnetizations. These controllable 0–π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Here, phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting ‘programmable logic’, where they could function in superconducting analogues to field-programmable gate arrays.« less

Controllable 0–π Josephson junctions containing a ferromagnetic spin valve

DOE PAGES

Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.; ...

2016-03-14

Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such ‘π-junctions’ were first realized experimentally in 2001, and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and pi by changing the relativemore » orientation of the two magnetizations. These controllable 0–π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Here, phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting ‘programmable logic’, where they could function in superconducting analogues to field-programmable gate arrays.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yong; Xing, Qingfeng; Straszheim, Warren E.

Here, we report how the superconducting phase forms in pseudo-single-crystal K xFe 2-ySe 2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition.more » It should be emphasized that the phase separation in pseudo-single-crystal K xFe 2-ySe 2 is caused by the iron-vacancy order-disorder transition. The shrinkage of the high-temperature phase and the expansion of the newly created iron-vacancy-ordered phase during the phase separation rule out the mechanism of spinodal decomposition proposed in an early report [Wang et al, Phys. Rev. B 91, 064513 (2015)]. Since the formation of the superconducting phase relies on the occurrence of the iron-vacancy order-disorder transition, it is impossible to synthesize a pure superconducting phase by a conventional solid state reaction or melt growth. By focused ion beam-scanning electron microscopy, we further demonstrate that the superconducting phase forms a contiguous three-dimensional architecture composed of parallelepipeds that have a coherent orientation relationship with the iron-vacancy-ordered phase.« less

Impact of cool-down conditions at Tc on the superconducting rf cavity quality factor

NASA Astrophysics Data System (ADS)

Vogt, J.-M.; Kugeler, O.; Knobloch, J.

2013-10-01

Many next-generation, high-gradient accelerator applications, from energy-recovery linacs to accelerator-driven systems (ADS) rely on continuous wave (CW) operation for which superconducting radio-frequency (SRF) systems are the enabling technology. However, while SRF cavities dissipate little power, they must be cooled by liquid helium and for many CW accelerators the complexity as well as the investment and operating costs of the cryoplant can prove to be prohibitive. We investigated ways to reduce the dynamic losses by improving the residual resistance (Rres) of niobium cavities. Both the material treatment and the magnetic shielding are known to have an impact. In addition, we found that Rres can be reduced significantly when the cool-down conditions during the superconducting phase transition of the niobium are optimized. We believe that not only do the cool-down conditions impact the level to which external magnetic flux is trapped in the cavity but also that thermoelectric currents are generated which in turn create additional flux that can be trapped. Therefore, we investigated the generation of flux and the dynamics of flux trapping and release in a simple model niobium-titanium system that mimics an SRF cavity in its helium tank. We indeed found that thermal gradients along the system during the superconducting transition can generate a thermoelectric current and magnetic flux, which subsequently can be trapped. These effects may explain the observed variation of the cavity’s Rres with cool-down conditions.

Phase diagram of the underdoped cuprates at high magnetic field

NASA Astrophysics Data System (ADS)

Chakraborty, Debmalya; Morice, Corentin; Pépin, Catherine

2018-06-01

The experimentally measured phase diagram of cuprate superconductors in the temperature-applied magnetic field plane illuminates key issues in understanding the physics of these materials. At low temperature, the superconducting state gives way to a long-range charge order with increasing magnetic field; both the orders coexist in a small intermediate region. The charge order transition is strikingly insensitive to temperature and quickly reaches a transition temperature close to the zero-field superconducting Tc. We argue that such a transition along with the presence of the coexisting phase is difficult to obtain in a weak coupling competing orders formalism. We demonstrate that for some range of parameters there is an enlarged symmetry of the strongly coupled charge and superconducting orders in the system depending on their relative masses and the coupling strength of the two orders. We establish that this sharp switch from the superconducting phase to the charge order phase can be understood in the framework of a composite SU(2) order parameter comprising the charge and superconducting orders. Finally, we illustrate that there is a possibility of the coexisting phase of the competing charge and superconducting orders only when the SU(2) symmetry between them is weakly broken due to biquadratic terms in the free energy. The relation of this sharp transition to the proximity to the pseudogap quantum critical doping is also discussed.

Cesium vacancy ordering in phase-separated C s x F e 2 - y S e 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taddei, K. M.; Sturza, M.; Chung, D. Y.

2015-09-01

By simultaneously displaying magnetism and superconductivity in a single phase, the iron based superconductors provide a model system for the study of magnetism’s role in superconductivity. The class of intercalated iron selenide superconductors is unique amongst these in having the additional property of phase separation and coexistence of two distinct phases - one majority phase with iron vacancy ordering and strong antiferromagnetism and the other a poorly understood minority microscopic phase with a contested structure. Adding to the intrigue, the majority phase has never been found to show superconductivity on its own while the minority phase has never been successfullymore » synthesized separate from the majority phase. In order to better understand this minority phase, a series of high quality CsxFe2-ySe2 single crystals with (0.8 ≤ x ≤ 1; 0 ≤ y ≤ 0.3) were grown and studied. Neutron and x-ray powder diffraction performed on ground crystals show the average structure of the minority phase to be I4/mmm, however, the temperature evolution of its lattice parameters shows it to be distinct from the high temperature I4/mmm parent structure. Neutron and x-ray diffraction experiments performed on single crystal samples reveal the presence of previously unobserved discrete superlattice reflections that remove the degeneracy of the Cs sites in both the majority and minority phases and reduce their structural symmetries from body-centered to primitive. Group theoretical analysis in conjunction with structural modeling shows that the observed superlattice reflections originate from a three-dimensional Cs vacancy ordering in the minority phase. This model predicts a 25% vacancy of the Cs site which is consistent with the site’s refined occupancy. Magnetization measurements performed in tandem with neutron single crystal diffraction provide evidence that the minority phase is the host of superconductivity. Our results also reveal a superconducting dome in which the superconducting transition temperature varies as a function of the valence of iron.« less

Evolution of High-Temperature Superconductivity from a Low-T_{c} Phase Tuned by Carrier Concentration in FeSe Thin Flakes.

PubMed

Lei, B; Cui, J H; Xiang, Z J; Shang, C; Wang, N Z; Ye, G J; Luo, X G; Wu, T; Sun, Z; Chen, X H

2016-02-19

We report the evolution of superconductivity in an FeSe thin flake with systematically regulated carrier concentrations by the liquid-gating technique. With electron doping tuned by the gate voltage, high-temperature superconductivity with an onset at 48 K can be achieved in an FeSe thin flake with T_{c} less than 10 K. This is the first time such high temperature superconductivity in FeSe is achieved without either an epitaxial interface or external pressure, and it definitely proves that the simple electron-doping process is able to induce high-temperature superconductivity with T_{c}^{onset} as high as 48 K in bulk FeSe. Intriguingly, our data also indicate that the superconductivity is suddenly changed from a low-T_{c} phase to a high-T_{c} phase with a Lifshitz transition at a certain carrier concentration. These results help to build a unified picture to understand the high-temperature superconductivity among all FeSe-derived superconductors and shed light on the further pursuit of a higher T_{c} in these materials.

Exotic magnetic states in Pauli-limited superconductors.

PubMed

Kenzelmann, M

2017-03-01

Magnetism and superconductivity compete or interact in complex and intricate ways. Here we review the special case where novel magnetic phenomena appear due to superconductivity, but do not exist without it. Such states have recently been identified in unconventional superconductors. They are different from the mere coexistence of magnetic order and superconductivity in conventional superconductors, or from competing magnetic and superconducting phases in many materials. We describe the recent progress in the study of such exotic magnetic phases, and articulate the many open questions in this field.

Growth and structural characterization of large superconducting crystals of La 2 - x Ca 1 + x Cu 2 O 6

DOE PAGES

Schneeloch, J. A.; Guguchia, Z.; Stone, M. B.; ...

2017-12-01

Lmore » arge crystals of a 2 - x Ca 1 + x Cu 2 O 6 (a-Ca-2126) with x = 0:10 and 0.15 have been grown and converted to bulk superconductors by high-pressure oxygen annealing. The superconducting transition temperature, T c, is as high as 55 K; this can be raised to 60 K by post-annealing in air. Here we present structural and magnetic characterizations of these crystals using neutron scattering and muon spin rotation techniques. While the as-grown, non-superconducting crystals are single phase, we nd that the superconducting crystals contain 3 phases forming coherent domains stacked along the c axis: the dominant a-Ca-2126 phase, very thin (1.5 unit-cell) intergrowths of a 2CuO 4, and an antiferromagnetic a 8Cu 8O 20 phase. We propose that the formation and segregation of the latter phases increases the Ca concentration of the a-Ca-2126, thus providing the hole-doping that supports superconductivity.« less

Growth and structural characterization of large superconducting crystals of La 2 - x Ca 1 + x Cu 2 O 6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneeloch, J. A.; Guguchia, Z.; Stone, M. B.

Lmore » arge crystals of a 2 - x Ca 1 + x Cu 2 O 6 (a-Ca-2126) with x = 0:10 and 0.15 have been grown and converted to bulk superconductors by high-pressure oxygen annealing. The superconducting transition temperature, T c, is as high as 55 K; this can be raised to 60 K by post-annealing in air. Here we present structural and magnetic characterizations of these crystals using neutron scattering and muon spin rotation techniques. While the as-grown, non-superconducting crystals are single phase, we nd that the superconducting crystals contain 3 phases forming coherent domains stacked along the c axis: the dominant a-Ca-2126 phase, very thin (1.5 unit-cell) intergrowths of a 2CuO 4, and an antiferromagnetic a 8Cu 8O 20 phase. We propose that the formation and segregation of the latter phases increases the Ca concentration of the a-Ca-2126, thus providing the hole-doping that supports superconductivity.« less

Proximity coupling in superconductor-graphene heterostructures.

PubMed

Lee, Gil-Ho; Lee, Hu-Jong

2018-05-01

This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable 2D platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given.

Proximity coupling in superconductor-graphene heterostructures

NASA Astrophysics Data System (ADS)

Lee, Gil-Ho; Lee, Hu-Jong

2018-05-01

This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable 2D platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given.

Role of Co3O4 Nanoparticles in Dielectric Properties of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ Superconducting Phase

NASA Astrophysics Data System (ADS)

Imran, M.; Mumtaz, M.; Naveed, M.; Khan, M. Nasir

2018-04-01

Cobalt oxide (Co3O4) nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconducting phase were prepared by sol-gel and solid-state reaction methods, respectively. Co3O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (Co3O4)x/CuTl-1223, x = 0-2.0 wt.%, nanoparticles-superconductor composites. The unchanged crystal structure of the host CuTl-1223 superconducting phase (i.e. tetragonal) revealed that Co3O4 nanoparticles were settled at the grain boundaries. Superconducting properties of the CuTl-1223 phase were overall suppressed due to hole-charge carriers interaction at the grain boundaries. The dielectric properties of (Co3O4)x/CuTl-1223 composites were investigated by varying the test frequencies from 40 Hz to 100 MHz and operating temperatures from 77 to 298 K. The values of dielectric properties were found maximal at lower frequencies and started to decrease at higher frequencies. So, the dielectric properties of the CuTl-1223 superconducting phase can be tuned by varying the contents of (Co3O4) nanoparticles, test frequencies as well as operating temperatures.

Holographic entanglement entropy in imbalanced superconductors

NASA Astrophysics Data System (ADS)

Dutta, Arghya; Modak, Sujoy Kumar

2014-01-01

We study the behavior of holographic entanglement entropy (HEE) for imbalanced holographic superconductors. We employ a numerical approach to consider the robust case of fully back-reacted gravity system. The hairy black hole solution is found by using our numerical scheme. Then it is used to compute the HEE for the superconducting case. The cases we study show that in presence of a mismatch between two chemical potentials, below the critical temperature, superconducting phase has a lower HEE in comparison to the AdS-Reissner-Nordström black hole phase. Interestingly, the effects of chemical imbalance are different in the contexts of black hole and superconducting phases. For black hole, HEE increases with increasing imbalance parameter while it behaves oppositely for the superconducting phase. The implications of these results are discussed.

Pressure-induced structural phase transformation and superconducting properties of titanium mononitride

NASA Astrophysics Data System (ADS)

Li, Qian; Guo, Yanan; Zhang, Miao; Ge, Xinlei

2018-03-01

In this work, we have systematically performed the first-principles structure search on titanium mononitride (TiN) within Crystal Structure AnaLYsis by Particle Swarm Optimization (CALYPSO) methodology at high pressures. Here, we have confirmed a phase transition from cubic rock-salt (fcc) phase to CsCl (bcc) phase of TiN at ∼348 GPa. Further simulations reveal that the bcc phase is dynamically stable, and could be synthesized experimentally in principle. The calculated elastic anisotropy decreases with the phase transformation from fcc to bcc structure under high pressures, and the material changes from ductile to brittle simultaneously. Moreover, we found that both structures are superconductive with the superconducting critical temperature of 2-12 K.

Anomalous expansion of the copper-apical-oxygen distance in superconducting cuprate bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Hua; Yacoby, Yizhak; Butko, Vladimir Y.

2010-08-27

We have introduced an improved x-ray phase-retrieval method with unprecedented speed of convergence and precision, and used it to determine with sub-Angstrom resolution the complete atomic structure of epitaxial La{sub 2-x}Sr{sub x}CuO{sub 4} ultrathin films. We focus on superconducting heterostructures built from constituent materials that are not superconducting in bulk samples. Single-phase metallic or superconducting films are also studied for comparison. The results show that this phase-retrieval diffraction method enables accurate measurement of structural modifications in near-surface layers, which may be critically important for elucidation of surface-sensitive experiments. Specifically we find that, while the copper-apical-oxygen distance remains approximately constant inmore » single-phase films, it shows a dramatic increase from the metallic-insulating interface of the bilayer towards the surface by as much as 0.45 {angstrom}. The apical-oxygen displacement is known to have a profound effect on the superconducting transition temperature.« less

Deterministic phase slips in mesoscopic superconducting rings

PubMed Central

Petković, I.; Lollo, A.; Glazman, L. I.; Harris, J. G. E.

2016-01-01

The properties of one-dimensional superconductors are strongly influenced by topological fluctuations of the order parameter, known as phase slips, which cause the decay of persistent current in superconducting rings and the appearance of resistance in superconducting wires. Despite extensive work, quantitative studies of phase slips have been limited by uncertainty regarding the order parameter's free-energy landscape. Here we show detailed agreement between measurements of the persistent current in isolated flux-biased rings and Ginzburg–Landau theory over a wide range of temperature, magnetic field and ring size; this agreement provides a quantitative picture of the free-energy landscape. We also demonstrate that phase slips occur deterministically as the barrier separating two competing order parameter configurations vanishes. These results will enable studies of quantum and thermal phase slips in a well-characterized system and will provide access to outstanding questions regarding the nature of one-dimensional superconductivity. PMID:27882924

Deterministic phase slips in mesoscopic superconducting rings.

PubMed

Petković, I; Lollo, A; Glazman, L I; Harris, J G E

2016-11-24

The properties of one-dimensional superconductors are strongly influenced by topological fluctuations of the order parameter, known as phase slips, which cause the decay of persistent current in superconducting rings and the appearance of resistance in superconducting wires. Despite extensive work, quantitative studies of phase slips have been limited by uncertainty regarding the order parameter's free-energy landscape. Here we show detailed agreement between measurements of the persistent current in isolated flux-biased rings and Ginzburg-Landau theory over a wide range of temperature, magnetic field and ring size; this agreement provides a quantitative picture of the free-energy landscape. We also demonstrate that phase slips occur deterministically as the barrier separating two competing order parameter configurations vanishes. These results will enable studies of quantum and thermal phase slips in a well-characterized system and will provide access to outstanding questions regarding the nature of one-dimensional superconductivity.

Deterministic phase slips in mesoscopic superconducting rings

DOE PAGES

Petković, Ivana; Lollo, A.; Glazman, L. I.; ...

2016-11-24

The properties of one-dimensional superconductors are strongly influenced by topological fluctuations of the order parameter, known as phase slips, which cause the decay of persistent current in superconducting rings and the appearance of resistance in superconducting wires. Despite extensive work, quantitative studies of phase slips have been limited by uncertainty regarding the order parameter’s free-energy landscape. Here we show detailed agreement between measurements of the persistent current in isolated flux-biased rings and Ginzburg–Landau theory over a wide range of temperature, magnetic field and ring size; this agreement provides a quantitative picture of the free-energy landscape. Furthermore, we also demonstrate thatmore » phase slips occur deterministically as the barrier separating two competing order parameter configurations vanishes. These results will enable studies of quantum and thermal phase slips in a well-characterized system and will provide access to outstanding questions regarding the nature of one-dimensional superconductivity.« less

Detection of surface impurity phases in high T.sub.C superconductors using thermally stimulated luminescence

DOEpatents

Cooke, D. Wayne; Jahan, Muhammad S.

1989-01-01

Detection of surface impurity phases in high-temperature superconducting materials. Thermally stimulated luminescence has been found to occur in insulating impurity phases which commonly exist in high-temperature superconducting materials. The present invention is sensitive to impurity phases occurring at a level of less than 1% with a probe depth of about 1 .mu.m which is the region of interest for many superconductivity applications. Spectroscopic and spatial resolution of the emitted light from a sample permits identification and location of the impurity species. Absence of luminescence, and thus of insulating phases, can be correlated with low values of rf surface resistance.

Topological superconductor to Anderson localization transition in one-dimensional incommensurate lattices.

PubMed

Cai, Xiaoming; Lang, Li-Jun; Chen, Shu; Wang, Yupeng

2013-04-26

We study the competition of disorder and superconductivity for a one-dimensional p-wave superconductor in incommensurate potentials. With the increase in the strength of the incommensurate potential, the system undergoes a transition from a topological superconducting phase to a topologically trivial localized phase. The phase boundary is determined both numerically and analytically from various aspects and the topological superconducting phase is characterized by the presence of Majorana edge fermions in the system with open boundary conditions. We also calculate the topological Z2 invariant of the bulk system and find it can be used to distinguish the different topological phases even for a disordered system.

Cesium vacancy ordering in phase-separated C s x F e 2 - y S e 2

DOE PAGES

Taddei, Keith M.; Sturza, M.; Chung, Duck -Yung; ...

2015-09-14

By simultaneously displaying magnetism and superconductivity in a single phase, the iron-based superconductors provide a model system for the study of magnetism's role in superconductivity. The class of intercalated iron selenide superconductors is unique among these in having the additional property of phase separation and coexistence of two distinct phases—one majority phase with iron vacancy ordering and strong antiferromagnetism, and the other a poorly understood minority microscopic phase with a contested structure. Adding to the intrigue, the majority phase has never been found to show superconductivity on its own while the minority phase has never been successfully synthesized separate frommore » the majority phase. In order to better understand this minority phase, a series of high-quality Cs xFe 2–ySe 2 single crystals with (0.8 ≤ x ≤ 1;0 ≤ y ≤ 0.3) were grown and studied. Neutron and x-ray powder diffraction performed on ground crystals show that the average I4/mmm structure of the minority phase is distinctly different from the high-temperature I4/mmm parent structure. Moreover, single-crystal diffraction reveals the presence of discrete superlattice reflections that remove the degeneracy of the Cs sites in both the majority and minority phases and reduce their structural symmetries from body centered to primitive. Group theoretical analysis in conjunction with structural modeling shows that the observed superlattice reflections originate from three-dimensional Cs vacancy ordering. This model predicts a 25% vacancy of the Cs site in the minority phase which is consistent with the site's refined occupancy. Magnetization measurements performed in tandem with neutron single-crystal diffraction provide evidence that the minority phase is the host of superconductivity. Lastly, our results also reveal a superconducting dome in which the superconducting transition temperature varies as a function of the nominal valence of iron.« less

Continuous and reversible tuning of the disorder-driven superconductor–insulator transition in bilayer graphene

PubMed Central

Lee, Gil-Ho; Jeong, Dongchan; Park, Kee-Su; Meir, Yigal; Cha, Min-Chul; Lee, Hu-Jong

2015-01-01

The influence of static disorder on a quantum phase transition (QPT) is a fundamental issue in condensed matter physics. As a prototypical example of a disorder-tuned QPT, the superconductor–insulator transition (SIT) has been investigated intensively over the past three decades, but as yet without a general consensus on its nature. A key element is good control of disorder. Here, we present an experimental study of the SIT based on precise in-situ tuning of disorder in dual-gated bilayer graphene proximity-coupled to two superconducting electrodes through electrical and reversible control of the band gap and the charge carrier density. In the presence of a static disorder potential, Andreev-paired carriers formed close to the Fermi level in bilayer graphene constitute a randomly distributed network of proximity-induced superconducting puddles. The landscape of the network was easily tuned by electrical gating to induce percolative clusters at the onset of superconductivity. This is evidenced by scaling behavior consistent with the classical percolation in transport measurements. At lower temperatures, the solely electrical tuning of the disorder-induced landscape enables us to observe, for the first time, a crossover from classical to quantum percolation in a single device, which elucidates how thermal dephasing engages in separating the two regimes. PMID:26310774

Continuous and reversible tuning of the disorder-driven superconductor-insulator transition in bilayer graphene.

PubMed

Lee, Gil-Ho; Jeong, Dongchan; Park, Kee-Su; Meir, Yigal; Cha, Min-Chul; Lee, Hu-Jong

2015-08-27

The influence of static disorder on a quantum phase transition (QPT) is a fundamental issue in condensed matter physics. As a prototypical example of a disorder-tuned QPT, the superconductor-insulator transition (SIT) has been investigated intensively over the past three decades, but as yet without a general consensus on its nature. A key element is good control of disorder. Here, we present an experimental study of the SIT based on precise in-situ tuning of disorder in dual-gated bilayer graphene proximity-coupled to two superconducting electrodes through electrical and reversible control of the band gap and the charge carrier density. In the presence of a static disorder potential, Andreev-paired carriers formed close to the Fermi level in bilayer graphene constitute a randomly distributed network of proximity-induced superconducting puddles. The landscape of the network was easily tuned by electrical gating to induce percolative clusters at the onset of superconductivity. This is evidenced by scaling behavior consistent with the classical percolation in transport measurements. At lower temperatures, the solely electrical tuning of the disorder-induced landscape enables us to observe, for the first time, a crossover from classical to quantum percolation in a single device, which elucidates how thermal dephasing engages in separating the two regimes.

High speed superconducting flywheel system for energy storage

NASA Astrophysics Data System (ADS)

Bornemann, H. J.; Urban, C.; Boegler, P.; Ritter, T.; Zaitsev, O.; Weber, K.; Rietschel, H.

1994-12-01

A prototype of a flywheel system with auto stable high temperature superconducting bearings was built and tested. The bearings offered good vertical and lateral stability. A metallic flywheel disk, ø 190 mm x 30 mm, was safely rotated at speeds up to 15000 rpm. The disk was driven by a 3 phase synchronous homopolar motor/generator. Maximum energy capacity was 3.8 Wh, maximum power was 1.5 KW. The dynamic behavior of the prototype was tested, characterized and evaluated with respect to axial and lateral stiffness, decay torques (bearing drag), vibrational modes and critical speeds. The bearings supports a maximum weight of 65 N at zero gap, axial and lateral stiffness at 1 mm gap were 440 N/cm and 130 N/cm, respectively. Spin down experiments were performed to investigate the energy efficiency of the system. The decay rate was found to depend upon background pressure in the vacuum chamber and upon the gap width in the bearing. At a background pressure of 5x10 -4 Torr, the coefficient of friction (drag-to-lift ratio) was measured to be 0.000009 at low speeds for 6 mm gap width in the bearing. Our results indicate that further refinement of this technology will allow operation of higly efficient superconducting flywheels in the kWh range.

Effect of doping in the Bi-Sr-Ca-Cu-O superconductor

NASA Technical Reports Server (NTRS)

Akbar, S. A.; Wong, M. S.; Botelho, M. J.; Sung, Y. M.; Alauddin, M.; Drummer, C. E.; Fair, M. J.

1991-01-01

The results of the effect of doping on the superconducting transition in the Bi-Sr-Ca-Cu-O system are reported. Samples were prepared under identical conditions with varying types (Pb, Sb, Sn, Nb) and amounts of dopants. All samples consisted of multiple phases, and showed stable and reproducible superconducting transitions. Stabilization of the well known 110 K phase depends on both the type and amount of dopant. No trace of superconducting phase of 150 K and above was observed.

Superconductivity in Bi/Ni bilayer system: Clear role of superconducting phases found at Bi/Ni interface

NASA Astrophysics Data System (ADS)

Liu, L. Y.; Xing, Y. T.; Merino, I. L. C.; Micklitz, H.; Franceschini, D. F.; Baggio-Saitovitch, E.; Bell, D. C.; Solórzano, I. G.

2018-01-01

Bi/Ni bilayers with varying Bi and Ni layer thicknesses have been prepared by (a) pulsed-laser deposition (PLD) at 300 K and (b) thermal evaporation at 4.2 K. A two-step superconducting transition appears on the electrical transport measurements in the samples prepared by PLD. High-resolution transmission and scanning transmission electron microscopy, supported by energy-dispersive x-ray spectroscopy (EDXS) analysis, reveal that two superconducting intermetallic alloys, namely NiBi and NiBi3, are formed by interdiffusion, if the bilayers are prepared at 300 K. The Tc of the two phases behaves very differently in an external magnetic field and the upper critical magnetic fields at zero temperature [Bc 2(0 ) ] were estimated as 1.1 and 7.4 T, respectively. The lower value corresponds to the Bc 2(0) of NiBi3 phase and the higher one is supposed to be of NiBi. These alloys are responsible for the superconductivity and the two-step transition appearing in the Bi/Ni bilayer system. Surprisingly, the Bi-rich phase (NiBi3) is formed near the Ni layer, while the Ni-rich phase (NiBi) is formed far from the Ni layer. The EDXS analysis at nanometer scale clearly shows an unusual increase of Ni concentration near the interface of Bi/substrate. The limited thickness of Bi layer in the interdiffusion process results in an unexpected distribution of Ni concentration. Samples prepared at 4.2 K after annealing at 300 K do not show any superconductivity, which indicates that a nonepitaxial Bi/Ni interface does not induce superconductivity in the case interdiffusion does not occur. These results offer a deeper understanding of the superconductivity in the Bi/Ni bilayer system.

New superconducting cyclotron driven scanning proton therapy systems

NASA Astrophysics Data System (ADS)

Klein, Hans-Udo; Baumgarten, Christian; Geisler, Andreas; Heese, Jürgen; Hobl, Achim; Krischel, Detlef; Schillo, Michael; Schmidt, Stefan; Timmer, Jan

2005-12-01

Since one and a half decades ACCEL is investing in development and engineering of state of the art particle-therapy systems. A new medical superconducting 250 MeV proton cyclotron with special focus on the present and future beam requirements of fast scanning treatment systems has been designed. The first new ACCEL medical proton cyclotron is under commissioning at PSI for their PROSCAN proton therapy facility having undergone successful factory tests especially of the closed loop cryomagnetic system. The second cyclotron is part of ACCEL's integrated proton therapy system for Europe's first clinical center, RPTC in Munich. The cyclotron, the energy selection system, the beamline as well as the four gantries and patient positioners have been installed. The scanning system and major parts of the control software have already been tested. We will report on the concept of ACCEL's superconducting cyclotron driven scanning proton therapy systems and the current status of the commissioning work at PSI and RPTC.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co substituted CaFe 2As 2. We use Atomic Force, Magnetic Force and Scanning Tunneling Microscopy (AFM, MFM and STM) to identify the domains and characterize their properties, nding in particular that tetragonal superconducting domains are very elongated, more than several tens of μm long and about 30 nm wide, have the same Tc than unstrained samples and hold vortices in a magnetic eld. Thus, biaxial strain produces a phase separated state, where each phase is equivalent to what is found at either side of the rstmore » order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first order quantum phase transitions lead to nanometric size phase separation under the influence of strain.« less

Topological superconductivity in the extended Kitaev-Heisenberg model

NASA Astrophysics Data System (ADS)

Schmidt, Johann; Scherer, Daniel D.; Black-Schaffer, Annica M.

2018-01-01

We study superconducting pairing in the doped Kitaev-Heisenberg model by taking into account the recently proposed symmetric off-diagonal exchange Γ . By performing a mean-field analysis, we classify all possible superconducting phases in terms of symmetry, explicitly taking into account effects of spin-orbit coupling. Solving the resulting gap equations self-consistently, we map out a phase diagram that involves several topologically nontrivial states. For Γ <0 , we find a competition between a time-reversal symmetry-breaking chiral phase with Chern number ±1 and a time-reversal symmetric nematic phase that breaks the rotational symmetry of the lattice. On the other hand, for Γ ≥0 we find a time-reversal symmetric phase that preserves all the lattice symmetries, thus yielding clearly distinguishable experimental signatures for all superconducting phases. Both of the time-reversal symmetric phases display a transition to a Z2 nontrivial phase at high doping levels. Finally, we also include a symmetry-allowed spin-orbit coupling kinetic energy and show that it destroys a tentative symmetry-protected topological order at lower doping levels. However, it can be used to tune the time-reversal symmetric phases into a Z2 nontrivial phase even at lower doping.

Magnetic imaging of antiferromagnetic and superconducting phases in R bxF e2 -yS e2 crystals

NASA Astrophysics Data System (ADS)

Hazi, J.; Mousavi, T.; Dudin, P.; van der Laan, G.; Maccherozzi, F.; Krzton-Maziopa, A.; Pomjakushina, E.; Conder, K.; Speller, S. C.

2018-02-01

High-temperature superconducting (HTS) cuprate materials, with the ability to carry large electrical currents with no resistance at easily reachable temperatures, have stimulated enormous scientific and industrial interest since their discovery in the 1980's. However, technological applications of these promising compounds have been limited by their chemical and microstructural complexity and the challenging processing strategies required for the exploitation of their extraordinary properties. The lack of theoretical understanding of the mechanism for superconductivity in these HTS materials has also hindered the search for new superconducting systems with enhanced performance. The unexpected discovery in 2008 of HTS iron-based compounds has provided an entirely new family of materials for studying the crucial interplay between superconductivity and magnetism in unconventional superconductors. Alkali-metal-doped iron selenide (AxF e2 -yS e2 , A =alkali metal ) compounds are of particular interest owing to the coexistence of superconductivity at relatively high temperatures with antiferromagnetism. Intrinsic phase separation on the mesoscopic scale is also known to occur in what were intended to be single crystals of these compounds, making it difficult to interpret bulk property measurements. Here, we use a combination of two advanced microscopy techniques to provide direct evidence of the magnetic properties of the individual phases. First, x-ray linear dichroism studies in a photoelectron emission microscope, and supporting multiplet calculations, indicate that the matrix (majority) phase is antiferromagnetic whereas the minority phase is nonmagnetic at room temperature. Second, cryogenic magnetic force microscopy demonstrates unambiguously that superconductivity occurs only in the minority phase. The correlation of these findings with previous microstructural studies and bulk measurements paves the way for understanding the intriguing electronic and magnetic properties of these compounds.

Dielectric properties of (SWCNTs)x GdBa2CuO7-δ superconductor nanocomposites

NASA Astrophysics Data System (ADS)

Anas, M.; Ebrahim, S.; Eldeen, I. G.; Awad, R.; Abou-Aly, A. I.

2017-11-01

Gd-123 superconducting phase was prepared by solid-state reaction technique. Single-walled carbon nanotubes (SWCNTs) were added in Gd-123 superconducting matrix with different concentrations during the final sintering process to obtain (SWCNTs)x GdBa2Cu3O7-δ (x = 0.0-0.1 wt.%) nanoparticles-superconductor composite. The influence of SWCNTs addition on the phase formation, structural, morphological, superconducting and dielectric properties of Gd-123 phase was investigated. It was found that SWCNTs addition enhance the phase formation and does not change the crystal structure of the host Gd-123 superconducting phase. The superconducting properties of Gd-123 samples were improved after the addition of SWCNTs up to x = 0.06 wt.% due to the enhancement in intergrain connectivity by healing up of micro-cracks and reduction of defects, while these properties were retarded with further increase in x. The dielectric response of (SWCNTs)x Gd-123 superconducting phase with x = 0.0, 0.01, 0.04, 0.05, 0.06 and 0.1 wt.% was measured from 100 KHz to 5 MHz at 77 K. The results reveal that for both real (𝜀‧) and imaginary (𝜀″) parts of dielectric constant, the frequency of dispersion increased by increasing SWCNTs amount up to 0.06 wt.%, then this frequency shifted to lower values for x > 0.06 wt.%. The results were discussed according to the presence and interference of both interfacial and dipolar polarizations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salmilehto, J.; Deppe, F.; Di Ventra, M.

Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. Here in this paper, for realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methodsmore » to quantify memory retention in the system.« less

Possible mechanism to enhance spin-fluctuation-mediated superconductivity in two-dimensional organic conductor

NASA Astrophysics Data System (ADS)

Nonoyama, Yoshito; Maekawa, Yukiko; Kobayashi, Akito; Suzumura, Yoshikazu; Yamada, Jun-ichi

2008-10-01

Mechanisms of superconductivity in quasi-two-dimensional organic conductors have been investigated using an extended Hubbard model by using the transfer energies between BDA-TTP molecules for β-(BDA-TTP)2I3 based on the X-ray experiment data and the extended Hückel calculation. We obtain several mean-field solutions with charge orderings which may represent short-range orderings or low-energy fluctuations in the low-dimensional electronic system. In the pressure-temperature phase diagram, a charge ordered metal state almost degenerates with a normal metal state between an insulating phase with charge ordering and the normal metal phase. Using the random phase approximation (RPA) and the linearized gap equation, the transition temperature of the superconducting state is estimated for the charge-ordered metal state and the normal metal state. It is found that transition temperature of the superconductivity induced by spin fluctuations in the charge-ordered metal state is much higher than that of the normal metal state and that the superconductivity in the charge-ordered metal state is the gapless d-wave. This suggests that the short range charge ordering may also contribute to an enhancement of spin-fluctuation-mediated superconductivity. The difference in the superconducting states between β-(BDA-TTP)2I3 and β-(BDA-TTP)2SbF6 are briefly discussed.

Low Temperature X-Ray Diffraction Study on CaFe2As2

NASA Astrophysics Data System (ADS)

Huyan, Shuyuan; Deng, Liangzi; Wu, Zheng; Zhao, Kui; Lv, Bing; Xue, Yiyu; Chu, Ching-Wu; B. Lv Collaboration; HPLT (Paul C. W. Chu) Team

For undoped CaFe2As2 single crystals, we observed that utilizing thermal treatments could stabilize two pure tetragonal phases PI and PII. Both phases are non-superconducting, while the superconductivity with a Tc up to 25 K can be induced through proper thermal treatment. Room temperature X-ray studies suggest that the origin of superconductivity arises from the interface of the mesoscopically stacked layers of PI and PII. To further investigate, a systematic low temperature X-ray study was conducted over a series of thermal treated CaFe2As2 single crystals. From which, we observed the phase aggregation of PI and PII upon cooling, more importantly, an ordered stacking structure exists at low temperature, which closely related to superconducting volume fraction and the ratio of PI and PII. These results further support the proposal of interface-enhanced superconductivity in undoped CaFe2As2. UT Dallas

Spiral magnetic order and pressure-induced superconductivity in transition metal compounds.

PubMed

Wang, Yishu; Feng, Yejun; Cheng, J-G; Wu, W; Luo, J L; Rosenbaum, T F

2016-10-06

Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. Using a synchrotron-based non-resonant X-ray magnetic diffraction technique, we reveal a spiral spin order in MnP and trace its pressure evolution towards superconducting order via measurements in a diamond anvil cell. Judging from the magnetostriction, ordered moments vanish at the quantum phase transition as pressure increases the electron kinetic energy. Spins remain local in the disordered phase, and the promotion of superconductivity is likely to emerge from an enhanced coupling to residual spiral spin fluctuations and their concomitant suppression of phonon-mediated superconductivity. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity.

Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure

NASA Astrophysics Data System (ADS)

Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

2016-03-01

Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30-70 K in pressure range of 100-170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50-70 K in pressure range of 100-150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.

Superconducting compounds and alloys research

NASA Technical Reports Server (NTRS)

Otto, G.

1975-01-01

Resistivity measurements as a function of temperature were performed on alloys of the binary material system In sub(1-x) Bi sub x for x varying between 0 and 1. It was found that for all single-phase alloys (the pure elements, alpha-In, and the three intermetallic compounds) at temperatures sufficiently above the Debye-temperature, the resistivity p can be expressed as p = a sub o T(n), where a sub o and n are composition-dependent constants. The same exponential relationship can also be applied for the sub-system In-In2Bi, when the two phases are in compositional equilibrium. Superconductivity measurements on single and two-phase alloys can be explained with respect to the phase diagram. There occur three superconducting phases (alpha-In, In2Bi, and In5Bi3) with different transition temperatures in the alloying system. The magnitude of the transition temperatures for the various intermetallic phases of In-Bi is such that the disappearance or occurrence of a phase in two component alloys can be demonstrated easily by means of superconductivity measurements.

Disordered Kitaev chains with long-range pairing.

PubMed

Cai, Xiaoming

2017-03-22

We study the competition of disorder and superconductivity for a generalized Kitaev model in incommensurate potentials. The generalized Kitaev model describes one dimensional spinless fermions with long-range p-wave superconducting pairing, which decays with distance l as a power law  ∼[Formula: see text]. We focus on the transition from the topological superconducting phase to the topologically trivial Anderson localized phase, and effects of the exponent α on this phase transition. In the topological superconducting phase, for a system under open boundary condition the amplitude of zero-mode Majorana fermion has a hybrid exponential-algebraic decay as the distance increases from the edge. In the Anderson localized phase, some single-particle states remain critical for very strong disorders and the number of critical states increases as α decreases. In addition, except for critical disorders, the correlation function always has an exponential decay at the short range and an algebraic decay at the long range. Phase transition points are also numerically determined and the topological phase transition happens earlier at a smaller disorder strength for a system with smaller α.

Current limiting behavior in three-phase transformer-type SFCLs using an iron core according to variety of fault

NASA Astrophysics Data System (ADS)

Cho, Yong-Sun; Jung, Byung-Ik; Ha, Kyoung-Hun; Choi, Soo-Geun; Park, Hyoung-Min; Choi, Hyo-Sang

To apply the superconducting fault current limiter (SFCL) to the power system, the reliability of the fault-current-limiting operation must be ensured in diverse fault conditions. The SFCL must also be linked to the operation of the high-speed recloser in the power system. In this study, a three-phase transformer-type SFCL, which has a neutral line to improve the simultaneous quench characteristics of superconducting elements, was manufactured to analyze the fault-current-limiting characteristic according to the single, double, and triple line-to-ground faults. The transformer-type SFCL, wherein three-phase windings are connected to one iron core, reduced the burden on the superconducting element as the superconducting element on the sound phase was also quenched in the case of the single line-to-ground fault. In the case of double or triple line-to-ground faults, the flux from the faulted phase winding was interlinked with other faulted or sound phase windings, and the fault-current-limiting rate decreased because the windings of three phases were inductively connected by one iron core.

Conventional magnetic superconductors

DOE PAGES

Wolowiec, C. T.; White, B. D.; Maple, M. B.

2015-07-01

We discuss several classes of conventional magnetic superconductors including the ternary rhodium borides and molybdenum chalcogenides (or Chevrel phases), and the quaternary nickel-borocarbides. These materials exhibit some exotic phenomena related to the interplay between superconductivity and long-range magnetic order including: the coexistence of superconductivity and antiferromagnetic order; reentrant and double reentrant superconductivity, magnetic field induced superconductivity, and the formation of a sinusoidally-modulated magnetic state that coexists with superconductivity. We introduce the article with a discussion of the binary and pseudobinary superconducting materials containing magnetic impurities which at best exhibit short-range “glassy” magnetic order. Early experiments on these materials led tomore » the idea of a magnetic exchange interaction between the localized spins of magnetic impurity ions and the spins of the conduction electrons which plays an important role in understanding conventional magnetic superconductors. Furthermore, these advances provide a natural foundation for investigating unconventional superconductivity in heavy-fermion compounds, cuprates, and other classes of materials in which superconductivity coexists with, or is in proximity to, a magnetically-ordered phase.« less

Phase diagram and neutron spin resonance of superconducting NaFe 1 - x Cu x As

DOE PAGES

Tan, Guotai; Song, Yu; Zhang, Rui; ...

2017-02-03

In this paper, we use transport and neutron scattering to study the electronic phase diagram and spin excitations of NaFe 1-xCu xAs single crystals. Similar to Co- and Ni-doped NaFeAs, a bulk superconducting phase appears near x≈2% with the suppression of stripe-type magnetic order in NaFeAs. Upon further increasing Cu concentration the system becomes insulating, culminating in an antiferromagnetically ordered insulating phase near x≈50%. Using transport measurements, we demonstrate that the resistivity in NaFe 1-xCu xAs exhibits non-Fermi-liquid behavior near x≈1.8%. Our inelastic neutron scattering experiments reveal a single neutron spin resonance mode exhibiting weak dispersion along c axis inmore » NaFe 0.98Cu 0.02As. The resonance is high in energy relative to the superconducting transition temperature T c but weak in intensity, likely resulting from impurity effects. These results are similar to other iron pnictides superconductors despite that the superconducting phase in NaFe 1-xCu xAs is continuously connected to an antiferromagnetically ordered insulating phase near x≈50% with significant electronic correlations. Finally, therefore, electron correlations is an important ingredient of superconductivity in NaFe 1-xCu xAs and other iron pnictides.« less

Inhomogeneous Phase Effect of Smart Meta-Superconducting MgB2

NASA Astrophysics Data System (ADS)

Li, Yongbo; Chen, Honggang; Qi, Weichang; Chen, Guowei; Zhao, Xiaopeng

2018-05-01

The inhomogeneous phase of a smart meta-superconductor has a great effect on its superconductivity. In this paper, the effect of concentration, dimensions, electroluminescence (EL) intensity, and distribution of the inhomogeneous phase on the superconducting critical temperature (TC) has been systematically investigated. An ex situ solid sintering was utilized to prepare smart meta-superconducting MgB2 doped with six kinds of electroluminescent materials, such as YVO4{:}Eu^{3+} and Y2O3{:}Eu^{3+} flakes. Elemental mappings through energy dispersive spectroscopy (EDS) show that the inhomogeneous phase is comparatively uniformly dispersed around the MgB2 particles; thus V, Y, and Eu were accumulated at a small area. The measurement results show that the optimum doping concentration of the meta-superconducting MgB2 is 2.0 wt%. The offset temperature (TC^{{ off}}) of the sample doped with 2.0 wt% dopant A is 1.6 K higher than that of pure MgB2. The improvement in TC^{{ off}} is likely related to the sizes, thickness, and EL intensity of the inhomogeneous phase of MgB2 smart meta-superconductor. This experiment provides a novel approach to enhance TC.

Crystal structure and superconducting properties of KSr2Nb3O10

NASA Astrophysics Data System (ADS)

Kawaguchi, T.; Horigane, K.; Itoh, Y.; Kobayashi, K.; Horie, R.; Kambe, T.; Akimitsu, J.

2018-05-01

We performed X-ray diffraction (XRD) and DC magnetic susceptibility measurements to elucidate the crystal structure and superconducting properties of KSr2Nb3O10. From the diffraction pattern indexing, it was found that KSr2Nb3O10 crystallizes with monoclinic symmetry, space group P21/m(11). We succeeded in preparing high temperature (HT) and low temperature (LT) phases of KSr2Nb3O10 powder samples synthesized by a conventional solid state reaction and an ion-exchange reaction, respectively. Superconductivity was observed at 4 K by Li intercalation and it was found that the superconducting volume fraction of the LT phase ( 1.4%) is clearly larger than that of the HT phase (0.07%).

Emergence of Quantum Phase-Slip Behaviour in Superconducting NbN Nanowires: DC Electrical Transport and Fabrication Technologies.

PubMed

Constantino, Nicolas G N; Anwar, Muhammad Shahbaz; Kennedy, Oscar W; Dang, Manyu; Warburton, Paul A; Fenton, Jonathan C

2018-06-16

Superconducting nanowires undergoing quantum phase-slips have potential for impact in electronic devices, with a high-accuracy quantum current standard among a possible toolbox of novel components. A key element of developing such technologies is to understand the requirements for, and control the production of, superconducting nanowires that undergo coherent quantum phase-slips. We present three fabrication technologies, based on using electron-beam lithography or neon focussed ion-beam lithography, for defining narrow superconducting nanowires, and have used these to create nanowires in niobium nitride with widths in the range of 20⁻250 nm. We present characterisation of the nanowires using DC electrical transport at temperatures down to 300 mK. We demonstrate that a range of different behaviours may be obtained in different nanowires, including bulk-like superconducting properties with critical-current features, the observation of phase-slip centres and the observation of zero conductance below a critical voltage, characteristic of coherent quantum phase-slips. We observe critical voltages up to 5 mV, an order of magnitude larger than other reports to date. The different prominence of quantum phase-slip effects in the various nanowires may be understood as arising from the differing importance of quantum fluctuations. Control of the nanowire properties will pave the way for routine fabrication of coherent quantum phase-slip nanowire devices for technology applications.

Pressure-driven phase transition from antiferromagnetic semiconductor to nonmagnetic metal in the two-leg ladders A Fe 2 X 3 ( A = Ba , K ; X = S , Se )

DOE PAGES

Zhang, Yang; Lin, Lingfang; Zhang, Jun -Jie; ...

2017-03-15

The recent discovery of superconductivity in BaFe 2S 3 has stimulated considerable interest in 123-type iron chalcogenides. This material is the first reported iron-based two-leg ladder superconductor, as opposed to the prevailing two-dimensional layered structures of the iron superconductor family. Once the hydrostatic pressure exceeds 11 GPa, BaFe 2S 3 changes from a semiconductor to a superconductor below 24 K. Although previous calculations correctly explained its ground-state magnetic state and electronic structure, the pressure-induced phase transition was not successfully reproduced. In this work, our first-principles calculations show that with increasing pressure the lattice constants as well as local magnetic momentsmore » are gradually suppressed, followed by a first-order magnetic transition at a critical pressure, with local magnetic moments dropping to zero suddenly. Our calculations suggest that the self-doping caused by electrons transferred from S to Fe may play a key role in this transition. The development of a nonmagnetic metallic phase at high pressure may pave the way to superconductivity. As extensions of this effort, two other 123-type iron chalcogenides, KFe 2S 3 and KFe 2Se 3, have also been investigated. KFe 2S 3 also displays a first-order transition with increasing pressure, but KFe 2Se 3 shows instead a second-order or weakly first-order transition. Here, the required pressures for KFe 2S 3 and KFe 2Se 3 to quench the magnetism are higher than for BaFe 2S 3. Further experiments could confirm the predicted first-order nature of the transition in BaFe 2S 3 and KFe 2S 3, as well as the possible metallic/superconductivity state in other 123-type iron chalcogenides under high pressure.« less

Resonance fluorescence and quantum interference of a single NV center

NASA Astrophysics Data System (ADS)

Ma, Yong-Hong; Zhang, Xue-Feng; Wu, E.

2017-11-01

The detection of a single nitrogen-vacancy center in diamond has attracted much interest, since it is expected to lead to innovative applications in various domains of quantum information, including quantum metrology, information processing and communications, as well as in various nanotechnologies, such as biological and subdiffraction limit imaging, and tests of entanglement in quantum mechanics. We propose a novel scheme of a single NV center coupled with a multi-mode superconducting microwave cavity driven by coherent fields in squeezed vacuum. We numerically investigate the spectra in-phase quadrature and out-of-phase quadrature for different driving regimes with or without detunings. It shows that the maximum squeezing can be obtained for optimal Rabi fields. Moreover, with the same parameters, the maximum squeezing is greatly increased when the detunings are nonzero compared to the resonance case.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yufeng; Zhou, Yonghui; Guo, Zhaopeng

Weyl semimetal defines a material with three-dimensional Dirac cones, which appear in pair due to the breaking of spatial inversion or time reversal symmetry. Superconductivity is the state of quantum condensation of paired electrons. Turning a Weyl semimetal into superconducting state is very important in having some unprecedented discoveries. In this work, by doing resistive measurements on a recently recognized Weyl semimetal TaP under pressures up to about 100 GPa, we show the concurrence of superconductivity and a structure transition at about 70 GPa. It is found that the superconductivity becomes more pronounced when decreasing pressure and retains when themore » pressure is completely released. High-pressure x-ray diffraction measurements also confirm the structure phase transition from I41md to P-6m2 at about 70 GPa. More importantly, ab-initial calculations reveal that the P-6m2 phase is a new Weyl semimetal phase and has only one set of Weyl points at the same energy level. Our discovery of superconductivity in TaP by high pressure will stimulate investigations on superconductivity and Majorana fermions in Weyl semimetals.« less

Identifying the chiral d-wave superconductivity by Josephson φ0-states.

PubMed

Liu, Jun-Feng; Xu, Yong; Wang, Jun

2017-03-07

We propose the Josephson junctions linked by a normal metal between a d + id superconductor and another d + id superconductor, a d-wave superconductor, or a s-wave superconductor for identifying the chiral d + id superconductivity. The time-reversal breaking in the chiral d-wave superconducting state is shown to result in a Josephson φ 0 -junction state where the current-phase relation is shifted by a phase φ 0 from the sinusoidal relation, other than 0 and π. The ground-state phase difference φ 0 and the critical current can be used to definitely confirm and read the information about the d + id superconductivity. A smooth evolution from conventional 0-π transitions to tunable φ 0 -states can be observed by changing the relative magnitude of two types of d-wave components in the d + id pairing. On the other hand, the Josephson junction involving the d + id superconductor is also the simplest model to realize a φ 0 - junction, which is useful in superconducting electronics and superconducting quantum computation.

Identifying the chiral d-wave superconductivity by Josephson φ0-states

PubMed Central

Liu, Jun-Feng; Xu, Yong; Wang, Jun

2017-01-01

We propose the Josephson junctions linked by a normal metal between a d + id superconductor and another d + id superconductor, a d-wave superconductor, or a s-wave superconductor for identifying the chiral d + id superconductivity. The time-reversal breaking in the chiral d-wave superconducting state is shown to result in a Josephson φ0-junction state where the current-phase relation is shifted by a phase φ0 from the sinusoidal relation, other than 0 and π. The ground-state phase difference φ0 and the critical current can be used to definitely confirm and read the information about the d + id superconductivity. A smooth evolution from conventional 0-π transitions to tunable φ0-states can be observed by changing the relative magnitude of two types of d-wave components in the d + id pairing. On the other hand, the Josephson junction involving the d + id superconductor is also the simplest model to realize a φ0- junction, which is useful in superconducting electronics and superconducting quantum computation. PMID:28266582

Superconducting matrix fault current limiter with current-driven trigger mechanism

DOEpatents

Yuan; Xing

2008-04-15

A modular and scalable Matrix-type Fault Current Limiter (MFCL) that functions as a "variable impedance" device in an electric power network, using components made of superconducting and non-superconducting electrically conductive materials. An inductor is connected in series with the trigger superconductor in the trigger matrix and physically surrounds the superconductor. The current surge during a fault will generate a trigger magnetic field in the series inductor to cause fast and uniform quenching of the trigger superconductor to significantly reduce burnout risk due to superconductor material non-uniformity.

Superconductivity in Hydrides Doped with Main Group Elements Under Pressure

NASA Astrophysics Data System (ADS)

Shamp, Andrew; Zurek, Eva

2017-01-01

A priori crystal structure prediction techniques have been used to explore the phase diagrams of hydrides of main group elements under pressure. A number of novel phases with the chemical formulas MHn, n > 1 and M = Li, Na, K, Rb, Cs; MHn, n > 2 and M= Mg, Ca, Sr, Ba; HnI with n > 1 and PH, PH2, PH3 have been predicted to be stable at pressures achievable in diamond anvil cells. The hydrogenic lattices within these phases display a number of structural motifs including H2δ- , H-, H-3 , as well as one-dimensional and three-dimensional extended structures. A wide range of superconducting critical temperatures, Tcs, are predicted for these hydrides. The mechanism of metallization and the propensity for superconductivity are dependent upon the structural motifs present in these phases, and in particular on their hydrogenic sublattices. Phases that are thermodynamically unstable, but dynamically stable, are accessible experimentally. The observed trends provide insight on how to design hydrides that are superconducting at high temperatures.

Pressure-enhanced superconductivity in Eu 3 Bi 2 S 4 F 4

DOE PAGES

Luo, Yongkang; Zhai, Hui -Fei; Zhang, Pan; ...

2014-12-17

The pressure effect on the newly discovered charge-transferred BiS 2-based superconductor, Eu 3Bi 2S 4F 4, with a T c of 1.5 K at ambient pressure, is investigated by transport and magnetic measurements. Accompanied with the enhancement of metallicity under pressures, the onset superconducting transition temperature increases abruptly around 1.0 GPa, reaching ~10.0 K at 2.26 GPa. Alternating current magnetic susceptibility measurements indicate that a new superconducting phase with a higher T c emerges and dominates at high pressures. In the broad pressure window of 0.68GPa≤p≤2.00 GPa, the high-T c phase coexists with the low-T c phase. Hall effect measurementsmore » reveal a significant difference in electronic structures between the two superconducting phases. As a result, our work devotes the effort to establish the commonality of pressure effect on the BiS 2-based superconductors, and also uncovers the importance of electron carrier density in the high-T c phase.« less

Visualizing heavy fermion confinement and Pauli-limited superconductivity in layered CeCoIn 5

DOE PAGES

Gyenis, András; Feldman, Benjamin E.; Randeria, Mallika T.; ...

2018-02-07

Layered material structures play a key role in enhancing electron–electron interactions to create correlated metallic phases that can transform into unconventional superconducting states. The quasi-two-dimensional electronic properties of such compounds are often inferred indirectly through examination of bulk properties. Here we use scanning tunneling microscopy to directly probe in cross-section the quasi-two-dimensional electronic states of the heavy fermion superconductor CeCoIn 5. Our measurements reveal the strong confined nature of quasiparticles, anisotropy of tunneling characteristics, and layer-by-layer modulated behavior of the precursor pseudogap gap phase. In the interlayer coupled superconducting state, the orientation of line defects relative to the d-wave ordermore » parameter determines whether in-gap states form due to scattering. Spectroscopic imaging of the anisotropic magnetic vortex cores directly characterizes the short interlayer superconducting coherence length and shows an electronic phase separation near the upper critical in-plane magnetic field, consistent with a Pauli-limited first-order phase transition into a pseudogap phase.« less

Superconducting scanning tunneling microscopy tips in a magnetic field: Geometry-controlled order of the phase transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eltschka, Matthias, E-mail: m.eltschka@fkf.mpg.de; Jäck, Berthold; Assig, Maximilian

The properties of geometrically confined superconductors significantly differ from their bulk counterparts. Here, we demonstrate the geometrical impact for superconducting scanning tunneling microscopy (STM) tips, where the confinement ranges from the atomic to the mesoscopic scale. To this end, we compare the experimentally determined magnetic field dependence for several vanadium tips to microscopic calculations based on the Usadel equation. For our theoretical model of a superconducting cone, we find a direct correlation between the geometry and the order of the superconducting phase transition. Increasing the opening angle of the cone changes the phase transition from first to second order. Comparingmore » our experimental findings to the theory reveals first and second order quantum phase transitions in the vanadium STM tips. In addition, the theory also explains experimentally observed broadening effects by the specific tip geometry.« less

Unified Phase Diagram for Iron-Based Superconductors.

PubMed

Gu, Yanhong; Liu, Zhaoyu; Xie, Tao; Zhang, Wenliang; Gong, Dongliang; Hu, Ding; Ma, Xiaoyan; Li, Chunhong; Zhao, Lingxiao; Lin, Lifang; Xu, Zhuang; Tan, Guotai; Chen, Genfu; Meng, Zi Yang; Yang, Yi-Feng; Luo, Huiqian; Li, Shiliang

2017-10-13

High-temperature superconductivity is closely adjacent to a long-range antiferromagnet, which is called a parent compound. In cuprates, all parent compounds are alike and carrier doping leads to superconductivity, so a unified phase diagram can be drawn. However, the properties of parent compounds for iron-based superconductors show significant diversity and both carrier and isovalent dopings can cause superconductivity, which casts doubt on the idea that there exists a unified phase diagram for them. Here we show that the ordered moments in a variety of iron pnictides are inversely proportional to the effective Curie constants of their nematic susceptibility. This unexpected scaling behavior suggests that the magnetic ground states of iron pnictides can be achieved by tuning the strength of nematic fluctuations. Therefore, a unified phase diagram can be established where superconductivity emerges from a hypothetical parent compound with a large ordered moment but weak nematic fluctuations, which suggests that iron-based superconductors are strongly correlated electron systems.

Methods of Phase and Power Control in Magnetron Transmitters for Superconducting Accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kazadevich, G.; Johnson, R.; Neubauer, M.

Various methods of phase and power control in magnetron RF sources of superconducting accelerators intended for ADS-class projects were recently developed and studied with conventional 2.45 GHz, 1 kW, CW magnetrons operating in pulsed and CW regimes. Magnetron transmitters excited by a resonant (injection-locking) phasemodulated signal can provide phase and power control with the rates required for precise stabilization of phase and amplitude of the accelerating field in Superconducting RF (SRF) cavities of the intensity-frontier accelerators. An innovative technique that can significantly increase the magnetron transmitter efficiency at the widerange power control required for superconducting accelerators was developed and verifiedmore » with the 2.45 GHz magnetrons operating in CW and pulsed regimes. High efficiency magnetron transmitters of this type can significantly reduce the capital and operation costs of the ADSclass accelerator projects.« less

Competing Quantum Orderings in Cuprate Superconductors:

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Balatsky, A. V.; Bishop, A. R.

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.

Implementing quantum optics with parametrically driven superconducting circuits

NASA Astrophysics Data System (ADS)

Aumentado, Jose

Parametric coupling has received much attention, in part because it forms the core of many low-noise amplifiers in superconducting quantum information experiments. However, parametric coupling in superconducting circuits is, as a general rule, simple to generate and forms the basis of a methodology for interacting microwave fields at different frequencies. In the quantum regime, this has important consequences, allowing relative novices to do experiments in superconducting circuits today that were previously heroic efforts in quantum optics and cavity-QED. In this talk, I'll give an overview of some of our work demonstrating parametric coupling within the context of circuit-QED as well as some of the possibilities this concept creates in our field.

Superconductivity in the Nb-Ru-Ge σ phase

DOE PAGES

Carnicom, Elizabeth M.; Xie, Weiwei; Sobczak, Zuzanna; ...

2017-12-07

Here, we show that the previously unreported ternary σ-phase material Nb 20.4Ru 5.7Ge 3.9 (Nb 0.68Ru 0.19Ge 0.13) is a superconductor with a critical temperature of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and specific heat measurements were used to characterize the superconducting transition. The Sommerfeld constant γ for Nb 20.4Ru 5.7Ge 3.9 is 91 mJ mol-f.u. -1K -2 (~3 mJ mol-atom -1K -2) and the specific heat anomaly at the superconducting transition, ΔC/γT c, is approximately 1.38. The zero-temperature upper critical field (µ 0Hc 2(0)) was estimated to be 2 T by resistance data. Field-dependent magnetization data analysis estimated µmore » 0Hc 1(0) to be 5.5 mT. Thus, the characterization shows Nb 20.4Ru 5.7Ge 3.9 to be a type II BCS superconductor. This material appears to be the first reported ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously reported binary Nb-Ru, Nb-Ge, or Ru-Ge σ-phases shows that all three elements are necessary to stabilize the material. An analogous σ-phase in the Ta-Ru-Ge system did not display superconductivity above 1.7 K, which suggests that electron count cannot govern the superconductivity observed. Preliminary characterization of a possible superconducting σ-phase in the Nb-Ru-Ga system is also reported.« less

Appearance of superconductivity at the vacancy order-disorder boundary in KxFe2 -ySe2

NASA Astrophysics Data System (ADS)

Duan, Chunruo; Yang, Junjie; Ren, Yang; Thomas, Sean M.; Louca, Despina

2018-05-01

The role of phase separation and the effect of Fe-vacancy ordering in the emergence of superconductivity in alkali metal doped iron selenides AxFe2 -ySe2 (A = K, Rb, Cs) is explored. High energy x-ray diffraction and Monte Carlo simulation were used to investigate the crystal structure of quenched superconducting (SC) and as-grown nonsuperconducting (NSC) KxFe2 -ySe2 single crystals. The coexistence of superlattice structures with the in-plane √{2 }×√{2 } K-vacancy ordering and the √{5 }×√{5 } Fe-vacancy ordering were observed in both the SC and NSC crystals alongside the I4/mmm Fe-vacancy-free phase. Moreover, in the SC crystals, an Fe-vacancy-disordered phase is additionally proposed to be present. Monte Carlo simulations suggest that it appears at the boundary between the I4/mmm vacancy-free phase and the I4/m vacancy-ordered phases (√{5 }×√{5 } ). The vacancy-disordered phase is nonmagnetic and is most likely the host of superconductivity.

Emergence of superconductivity and magnetic ordering tuned by Fe-vacancy in alkali-metal Fe chalcogenides RbxFe2-ySe2

NASA Astrophysics Data System (ADS)

Kobayashi, Yoshiaki; Kototani, Shouhei; Itoh, Masayuki; Sato, Masatoshi

2014-12-01

Samples of RbxFe2-ySe2 exhibiting superconductivity [superconducting (SC) samples] undergo a phase-separation into two phases, a Fe-vacancy ordered phase with antiferromagnetic (AFM) transition at TN1~500 K (AFM1 phase) and a phase with little Fe- vacancy and SC transition at Tc~30 K (SC phase). The samples of RbxFe2-ySe2 exhibiting no SC behaviour (non-SC samples) are phase-separated into three phases, the AFM1 phase, another AFM phase with TN2 ~150 K (AFM2 phase), and a paramagnetic phase with no SC transitions (paramagnetic non-SC phase). In this paper, we present the experimental results of magnetic susceptibility, electrical resistivity, and NMR measurements on single crystals of RbxFe2-ySe2 to reveal physical properties of these co-existing phases in the SC and non-SC samples. The 87Rb and 77Se NMR spectra show that the Fe vacancy concentration is very small in the Fe planes of the SC phase, whereas the AFM2 and paramagnetic non-SC phases in non-SC samples have larger amount of Fe vacancies. The randomness induced by the Fe vacancy in the non-SC samples makes the AFM2 and paramagnetic non-SC phases insulating/semiconducting and magnetically active, resulting in the absence of the superconductivity in RbxFe2-ySe2.

Electrons, phonons and superconductivity in rocksalt and tungsten-carbide phases of CrC.

PubMed

Tütüncü, H M; Baǧcı, S; Srivastava, G P; Akbulut, A

2012-11-14

We present results of ab initio theoretical investigations of the electronic structure, phonon dispersion relations, electron-phonon interaction and superconductivity in the rocksalt and tungsten-carbide phases of CrC. It is found that, compared to the stable tungsten-carbide phase, the metastable rocksalt phase is characterized by a much larger electronic density of states at the Fermi level. The phonon spectra of the rocksalt phase exhibit anomalies in the dispersion curves of both the transverse and longitudinal acoustic branches along the main symmetry directions. A combination of these characteristic electronic and phonon properties leads to an order of magnitude larger value of the electron-phonon coupling constant (λ = 2.66) for the rocksalt phase compared to that for the tungsten-carbide phase (λ = 0.24). Our calculations suggest that superconducting transition temperature values of 0.01 K and 25-35 K may be expected for the tungsten-carbide and rocksalt phases, respectively.

Light-Enhanced Spin Fluctuations and d -Wave Superconductivity at a Phase Boundary

NASA Astrophysics Data System (ADS)

Wang, Yao; Chen, Cheng-Chien; Moritz, B.; Devereaux, T. P.

2018-06-01

Time-domain techniques have shown the potential of photomanipulating existing orders and inducing new states of matter in strongly correlated materials. Using time-resolved exact diagonalization, we perform numerical studies of pump dynamics in a Mott-Peierls system with competing charge and spin density waves. A light-enhanced d -wave superconductivity is observed when the system resides near a quantum phase boundary. By examining the evolution of spin, charge, and superconducting susceptibilities, we show that a subdominant state in equilibrium can be stabilized by photomanipulating the charge order to allow superconductivity to appear and dominate. This work provides an interpretation of light-induced superconductivity from the perspective of order competition and offers a promising approach for designing novel emergent states out of equilibrium.

Phonon properties of iron-based superconductors

NASA Astrophysics Data System (ADS)

Gupta, Yuhit; Goyal, Megha; Sinha, M. M.

2018-05-01

Earlier, it was thought there is antagonist relationship between superconductivity and ferromagnetic materials, But, a discovery of iron-based superconductors have removed this misconception. It gives an idea to make a review on the superconductivity properties of different materials. The new iron-based superconductors' present symmetry breaking competing phases in the form of tetragonal to orthorhombic transition. It consists of mainly four families [1111], [111], [122], and [11] type. Superconductivity of iron-based superconductors mainly related with the phonons and there is an excellent relation between phonons and superconductivity. Phonons properties are helpful in predicting the superconducting properties of materials. Phonon properties of iron-based superconductors in various phases are summarized in this study. We are presenting the review of phonon properties of iron-based superconductors.

Competing quantum orderings in cuprate superconductors: A minimal model

NASA Astrophysics Data System (ADS)

Martin, I.; Ortiz, G.; Balatsky, A. V.; Bishop, A. R.

2001-02-01

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.

Superconducting H5S2 phase in sulfur-hydrogen system under high-pressure

PubMed Central

Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Katayama-Yoshida, Hiroshi; Oda, Tatsuki; Suzuki, Naoshi

2016-01-01

Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system. PMID:26983593

Full-switching FSF-type superconducting spin-triplet magnetic random access memory element

NASA Astrophysics Data System (ADS)

Lenk, D.; Morari, R.; Zdravkov, V. I.; Ullrich, A.; Khaydukov, Yu.; Obermeier, G.; Müller, C.; Sidorenko, A. S.; von Nidda, H.-A. Krug; Horn, S.; Tagirov, L. R.; Tidecks, R.

2017-11-01

In the present work a superconducting Co/CoOx/Cu41Ni59 /Nb/Cu41Ni59 nanoscale thin film heterostructure is investigated, which exhibits a superconducting transition temperature, Tc, depending on the history of magnetic field applied parallel to the film plane. In more detail, around zero applied field, Tc is lower when the field is changed from negative to positive polarity (with respect to the cooling field), compared to the opposite case. We interpret this finding as the result of the generation of the odd-in-frequency triplet component of superconductivity arising at noncollinear orientation of the magnetizations in the Cu41Ni59 layer adjacent to the CoOx layer. This interpretation is supported by superconducting quantum interference device magnetometry, which revealed a correlation between details of the magnetic structure and the observed superconducting spin-valve effects. Readout of information is possible at zero applied field and, thus, no permanent field is required to stabilize both states. Consequently, this system represents a superconducting magnetic random access memory element for superconducting electronics. By applying increased transport currents, the system can be driven to the full switching mode between the completely superconducting and the normal state.

TRILEX and G W +EDMFT approach to d -wave superconductivity in the Hubbard model

NASA Astrophysics Data System (ADS)

Vučičević, J.; Ayral, T.; Parcollet, O.

2017-09-01

We generalize the recently introduced TRILEX approach (TRiply irreducible local EXpansion) to superconducting phases. The method treats simultaneously Mott and spin-fluctuation physics using an Eliashberg theory supplemented by local vertex corrections determined by a self-consistent quantum impurity model. We show that, in the two-dimensional Hubbard model, at strong coupling, TRILEX yields a d -wave superconducting dome as a function of doping. Contrary to the standard cluster dynamical mean field theory (DMFT) approaches, TRILEX can capture d -wave pairing using only a single-site effective impurity model. We also systematically explore the dependence of the superconducting temperature on the bare dispersion at weak coupling, which shows a clear link between strong antiferromagnetic (AF) correlations and the onset of superconductivity. We identify a combination of hopping amplitudes particularly favorable to superconductivity at intermediate doping. Finally, we study within G W +EDMFT the low-temperature d -wave superconducting phase at strong coupling in a region of parameter space with reduced AF fluctuations.

Electronic disorder and magnetic-field-induced superconductivity enhancement in Fe1+y(Te1-xSex)

NASA Astrophysics Data System (ADS)

Hu, Jin; Liu, Tijiang; Qian, Bin; Mao, Zhiqiang

2012-02-01

The iron chalcogenide Fe1+y(Te1-xSex) superconductor system exhibits a unique electronic and magnetic phase diagram distinct from those seen in iron pnictides: bulk superconductivity does not appear immediately following the suppression of long-range (π,0) AFM order. Instead, an intermediate phase with weak charge carrier localization appears between AFM order and bulk superconductivity (Liu et al., Nat. Mater. 9, 719 (2010)). In this talk, we report our recent studies on the relationship between the normal state and superconducting properties in Fe1+y(Te1-xSex). We show that the superconducting volume fraction VSC and normal state metallicity significantly increase while the normal state Sommerfeld coefficient γ and Hall coefficient RH drop drastically with increasing Se content in the underdoped superconducting region. Additionally, VSC is surprisingly enhanced by magnetic field in heavily underdoped superconducting samples. The implications of these results will be discussed. Our analyses suggest that the suppression of superconductivity in the underdoped region is associated with electronic disorder caused by incoherent magnetic scattering arising from (π,0) magnetic fluctuations.

Superconductivity in doped Dirac semimetals

NASA Astrophysics Data System (ADS)

Hashimoto, Tatsuki; Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

2016-07-01

We theoretically study intrinsic superconductivity in doped Dirac semimetals. Dirac semimetals host bulk Dirac points, which are formed by doubly degenerate bands, so the Hamiltonian is described by a 4 ×4 matrix and six types of k -independent pair potentials are allowed by the Fermi-Dirac statistics. We show that the unique spin-orbit coupling leads to characteristic superconducting gap structures and d vectors on the Fermi surface and the electron-electron interaction between intra and interorbitals gives a novel phase diagram of superconductivity. It is found that when the interorbital attraction is dominant, an unconventional superconducting state with point nodes appears. To verify the experimental signature of possible superconducting states, we calculate the temperature dependence of bulk physical properties such as electronic specific heat and spin susceptibility and surface state. In the unconventional superconducting phase, either dispersive or flat Andreev bound states appear between point nodes, which leads to double peaks or a single peak in the surface density of states, respectively. As a result, possible superconducting states can be distinguished by combining bulk and surface measurements.

Neutron scattering study on the magnetic and superconducting phases of MnP

NASA Astrophysics Data System (ADS)

Yano, Shinichiro; Lancon, Diane; Ronnow, Henrik; Hansen, Thomas; Gardner, Jason

We have performed series of neutron scattering experiments on MnP. MnP has been investigated for decades because of its rich magnetic phase diagram. The magnetic structure of MnP is ferromagnetic (FM) below TC = 291 K. It transforms into a helimagnetic structure at TS = 47 K with a propagation vector q = 0 . 117a* . Superconductivity was found in MnP under pressures of 8 GPa with a TSC around 1 K by J.-G. Cheng. Since Mn-based superconductors are rare, and the superconducting phase occurs in the vicinity of FM, new magnetic and helimagnetic phases, there is a need to understand how the magnetism evolves as one approach the superconducting state. MnP is believed to be a double helix magnetic structure at TS = 47 K. We observed new 2 δ and 3 δ satellite peaks whose intensity are 200 ~ 1000 times smaller than these of 1 δ satellite peaks on the cold triple axis spectrometer SIKA under zero magnetic fields. We also found the periods of helimagnetic structure changes as a function of temperature. If time permits, we will discuss recent experiments under pressure. However, we have complete picture of magnetic structure of this system with and without applied pressure, revealing the interplay between the magnetic and superconducting phases.

Pressure-induced superconductivity in a three-dimensional topological material ZrTe5

PubMed Central

Zhou, Yonghui; Wu, Juefei; Ning, Wei; Li, Nana; Du, Yongping; Chen, Xuliang; Zhang, Ranran; Chi, Zhenhua; Wang, Xuefei; Zhu, Xiangde; Lu, Pengchao; Ji, Cheng; Wan, Xiangang; Yang, Zhaorong; Sun, Jian; Yang, Wenge; Tian, Mingliang; Zhang, Yuheng; Mao, Ho-kwang

2016-01-01

As a new type of topological materials, ZrTe5 shows many exotic properties under extreme conditions. Using resistance and ac magnetic susceptibility measurements under high pressure, while the resistance anomaly near 128 K is completely suppressed at 6.2 GPa, a fully superconducting transition emerges. The superconducting transition temperature Tc increases with applied pressure, and reaches a maximum of 4.0 K at 14.6 GPa, followed by a slight drop but remaining almost constant value up to 68.5 GPa. At pressures above 21.2 GPa, a second superconducting phase with the maximum Tc of about 6.0 K appears and coexists with the original one to the maximum pressure studied in this work. In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopy combined with theoretical calculations indicate the observed two-stage superconducting behavior is correlated to the structural phase transition from ambient Cmcm phase to high-pressure C2/m phase around 6 GPa, and to a mixture of two high-pressure phases of C2/m and P-1 above 20 GPa. The combination of structure, transport measurement, and theoretical calculations enable a complete understanding of the emerging exotic properties in 3D topological materials under extreme environments. PMID:26929327

Two-dimensional lattice gauge theories with superconducting quantum circuits

PubMed Central

Marcos, D.; Widmer, P.; Rico, E.; Hafezi, M.; Rabl, P.; Wiese, U.-J.; Zoller, P.

2014-01-01

A quantum simulator of U(1) lattice gauge theories can be implemented with superconducting circuits. This allows the investigation of confined and deconfined phases in quantum link models, and of valence bond solid and spin liquid phases in quantum dimer models. Fractionalized confining strings and the real-time dynamics of quantum phase transitions are accessible as well. Here we show how state-of-the-art superconducting technology allows us to simulate these phenomena in relatively small circuit lattices. By exploiting the strong non-linear couplings between quantized excitations emerging when superconducting qubits are coupled, we show how to engineer gauge invariant Hamiltonians, including ring-exchange and four-body Ising interactions. We demonstrate that, despite decoherence and disorder effects, minimal circuit instances allow us to investigate properties such as the dynamics of electric flux strings, signaling confinement in gauge invariant field theories. The experimental realization of these models in larger superconducting circuits could address open questions beyond current computational capability. PMID:25512676

Direct observation of ballistic Andreev reflection

NASA Astrophysics Data System (ADS)

Klapwijk, T. M.; Ryabchun, S. A.

2014-12-01

An overview is presented of experiments on ballistic electrical transport in inhomogeneous superconducting systems which are controlled by the process of Andreev reflection. The initial experiments based on the coexistence of a normal phase and a superconducting phase in the intermediate state led to the concept itself. It was followed by a focus on geometrically inhomogeneous systems like point contacts, which provided a very clear manifestation of the energy and direction dependence of the Andreev reflection process. The point contacts have recently evolved towards the atomic scale owing to the use of mechanical break-junctions, revealing a very detailed dependence of Andreev reflection on the macroscopic phase of the superconducting state. In present-day research, the superconducting in homogeneity is constructed by clean room technology and combines superconducting materials, for example, with low-dimensional materials and topological insulators. Alternatively, the superconductor is combined with nano-objects, such as graphene, carbon nanotubes, or semiconducting nanowires. Each of these "inhomogeneous systems" provides a very interesting range of properties, all rooted in some manifestation of Andreev reflection.

Coherent quantum phase slip.

PubMed

Astafiev, O V; Ioffe, L B; Kafanov, S; Pashkin, Yu A; Arutyunov, K Yu; Shahar, D; Cohen, O; Tsai, J S

2012-04-18

A hundred years after the discovery of superconductivity, one fundamental prediction of the theory, coherent quantum phase slip (CQPS), has not been observed. CQPS is a phenomenon exactly dual to the Josephson effect; whereas the latter is a coherent transfer of charges between superconducting leads, the former is a coherent transfer of vortices or fluxes across a superconducting wire. In contrast to previously reported observations of incoherent phase slip, CQPS has been only a subject of theoretical study. Its experimental demonstration is made difficult by quasiparticle dissipation due to gapless excitations in nanowires or in vortex cores. This difficulty might be overcome by using certain strongly disordered superconductors near the superconductor-insulator transition. Here we report direct observation of CQPS in a narrow segment of a superconducting loop made of strongly disordered indium oxide; the effect is made manifest through the superposition of quantum states with different numbers of flux quanta. As with the Josephson effect, our observation should lead to new applications in superconducting electronics and quantum metrology.

Superconductivity in Potassium-Doped Metallic Polymorphs of MoS2.

PubMed

Zhang, Renyan; Tsai, I-Ling; Chapman, James; Khestanova, Ekaterina; Waters, John; Grigorieva, Irina V

2016-01-13

Superconducting layered transition metal dichalcogenides (TMDs) stand out among other superconductors due to the tunable nature of the superconducting transition, coexistence with other collective electronic excitations (charge density waves), and strong intrinsic spin-orbit coupling. Molybdenum disulfide (MoS2) is the most studied representative of this family of materials, especially since the recent demonstration of the possibility to tune its critical temperature, Tc, by electric-field doping. However, just one of its polymorphs, band-insulator 2H-MoS2, has so far been explored for its potential to host superconductivity. We have investigated the possibility to induce superconductivity in metallic polytypes, 1T- and 1T'-MoS2, by potassium (K) intercalation. We demonstrate that at doping levels significantly higher than that required to induce superconductivity in 2H-MoS2, both 1T and 1T' phases become superconducting with Tc = 2.8 and 4.6 K, respectively. Unusually, K intercalation in this case is responsible both for the structural and superconducting phase transitions. By adding new members to the family of superconducting TMDs, our findings open the way to further manipulate and enhance the electronic properties of these technologically important materials.

Type-I and type-II topological nodal superconductors with s -wave interaction

NASA Astrophysics Data System (ADS)

Huang, Beibing; Yang, Xiaosen; Xu, Ning; Gong, Ming

2018-01-01

Topological nodal superconductors with protected gapless points in momentum space are generally realized based on unconventional pairings. In this work we propose a minimal model to realize these topological nodal phases with only s -wave interaction. In our model the linear and quadratic spin-orbit couplings along the two orthogonal directions introduce anisotropic effective unconventional pairings in momentum space. This model may support different nodal superconducting phases characterized by either an integer winding number in BDI class or a Z2 index in D class at the particle-hole invariant axes. In the vicinity of the nodal points the effective Hamiltonian can be described by either type-I or type-II Dirac equations, and the Lifshitz transition from type-I nodal phases to type-II nodal phases can be driven by external in-plane magnetic fields. We show that these nodal phases are robust against weak impurities, which only slightly renormalizes the momentum-independent parameters in the impurity-averaged Hamiltonian, thus these phases are possible to be realized in experiments with real semi-Dirac materials. The smoking-gun evidences to verify these phases based on scanning tunneling spectroscopy method are also briefly discussed.

Quantum phase slip phenomenon in ultra-narrow superconducting nanorings

NASA Astrophysics Data System (ADS)

Arutyunov, Konstantin Yu.; Hongisto, Terhi T.; Lehtinen, Janne S.; Leino, Leena I.; Vasiliev, Alexander L.

2012-02-01

The smaller the system, typically - the higher is the impact of fluctuations. In narrow superconducting wires sufficiently close to the critical temperature Tc thermal fluctuations are responsible for the experimentally observable finite resistance. Quite recently it became possible to fabricate sub-10 nm superconducting structures, where the finite resistivity was reported within the whole range of experimentally obtainable temperatures. The observation has been associated with quantum fluctuations capable to quench zero resistivity in superconducting nanowires even at temperatures T-->0. Here we demonstrate that in tiny superconducting nanorings the same phenomenon is responsible for suppression of another basic attribute of superconductivity - persistent currents - dramatically affecting their magnitude, the period and the shape of the current-phase relation. The effect is of fundamental importance demonstrating the impact of quantum fluctuations on the ground state of a macroscopically coherent system, and should be taken into consideration in various nanoelectronic applications.

Coexistence of multiphase superconductivity and ferromagnetism in lithiated iron selenide hydroxide [(L i1 -xF ex) OH ]FeSe

NASA Astrophysics Data System (ADS)

Urban, Christian; Valmianski, Ilya; Pachmayr, Ursula; Basaran, Ali C.; Johrendt, Dirk; Schuller, Ivan K.

2018-01-01

We present experimental evidence for (a) multiphase superconductivity and (b) coexistence of magnetism and superconductivity in a single structural phase of lithiated iron selenide hydroxide [(L i1 -xF ex )OH]FeSe. Magnetic field modulated microwave spectroscopy data confirms superconductivity with at least two distinct transition temperatures attributed to well-defined superconducting phases at TSC 1=40 ±2 K and TSC 2=35 ±2 K. Magnetometry data for the upper critical fields reveal a change in the magnetic order (TM=12 K) below TSC 1 and TSC 2 that is consistent with ferromagnetism. This occurs because the superconducting coherence length is much smaller than the structural coherence length, allowing for several different electronic and magnetic states on a single crystallite. The results give insight into the physics of complex multinary materials, where several phenomena governed by different characteristic length scales coexist.

Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata

DOE Office of Scientific and Technical Information (OSTI.GOV)

Som, Sumit; Ghosh, Surajit; Seth, Sudeshna

2013-11-15

Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A and M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9–27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loopmore » consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.« less

Low gravity phase separator

NASA Technical Reports Server (NTRS)

Smoot, G. F.; Pope, W. L.; Smith, L. (Inventor)

1977-01-01

An apparatus is described for phase separating a gas-liquid mixture as might exist in a subcritical cryogenic helium vessel for cooling a superconducting magnet at low gravity such as in planetary orbit, permitting conservation of the liquid and extended service life of the superconducting magnet.

Strong enhancement of s -wave superconductivity near a quantum critical point of Ca 3 Ir 4 Sn 13

DOE PAGES

Biswas, P. K.; Guguchia, Z.; Khasanov, R.; ...

2015-11-11

We repormore » t microscopic studies by muon spin rotation/relaxation as a function of pressure of the Ca 3 Ir 4 Sn 13 and Sr 3Ir 4Sn 13 system displaying superconductivity and a structural phase transition associated with the formation of a charge density wave (CDW). Our findings show a strong enhancement of the superfluid density and a dramatic increase of the pairing strength above a pressure of ≈ 1.6 GPa giving direct evidence of the presence of a quantum critical point separating a superconducting phase coexisting with CDW from a pure superconducting phase. The superconducting order parameter in both phases has the same s-wave symmetry. In spite of the conventional phonon-mediated BCS character of the weakly correlated (Ca 1-xSr x) 3Ir 4Sn 13 system the dependence of the effective superfluid density on the critical temperature puts this compound in the “Uemura” plot close to unconventional superconductors. This system exemplifies that conventional BCS superconductors in the presence of competing orders or multi-band structure can also display characteristics of unconventional superconductors.« less

Orbitally limited pair-density-wave phase of multilayer superconductors

NASA Astrophysics Data System (ADS)

Möckli, David; Yanase, Youichi; Sigrist, Manfred

2018-04-01

We investigate the magnetic field dependence of an ideal superconducting vortex lattice in the parity-mixed pair-density-wave phase of multilayer superconductors within a circular cell Ginzburg-Landau approach. In multilayer systems, due to local inversion symmetry breaking, a Rashba spin-orbit coupling is induced at the outer layers. This combined with a perpendicular paramagnetic (Pauli) limiting magnetic field stabilizes a staggered layer dependent pair-density-wave phase in the superconducting singlet channel. The high-field pair-density-wave phase is separated from the low-field BCS phase by a first-order phase transition. The motivating guiding question in this paper is: What is the minimal necessary Maki parameter αM for the appearance of the pair-density-wave phase of a superconducting trilayer system? To address this problem we generalize the circular cell method for the regular flux-line lattice of a type-II superconductor to include paramagnetic depairing effects. Then, we apply the model to the trilayer system, where each of the layers are characterized by Ginzburg-Landau parameter κ0 and a Maki parameter αM. We find that when the spin-orbit Rashba interaction compares to the superconducting condensation energy, the orbitally limited pair-density-wave phase stabilizes for Maki parameters αM>10 .

Topological order and thermal equilibrium in polariton condensates

NASA Astrophysics Data System (ADS)

Caputo, Davide; Ballarini, Dario; Dagvadorj, Galbadrakh; Sánchez Muñoz, Carlos; de Giorgi, Milena; Dominici, Lorenzo; West, Kenneth; Pfeiffer, Loren N.; Gigli, Giuseppe; Laussy, Fabrice P.; Szymańska, Marzena H.; Sanvitto, Daniele

2018-02-01

The Berezinskii-Kosterlitz-Thouless phase transition from a disordered to a quasi-ordered state, mediated by the proliferation of topological defects in two dimensions, governs seemingly remote physical systems ranging from liquid helium, ultracold atoms and superconducting thin films to ensembles of spins. Here we observe such a transition in a short-lived gas of exciton-polaritons, bosonic light-matter particles in semiconductor microcavities. The observed quasi-ordered phase, characteristic for an equilibrium two-dimensional bosonic gas, with a decay of coherence in both spatial and temporal domains with the same algebraic exponent, is reproduced with numerical solutions of stochastic dynamics, proving that the mechanism of pairing of the topological defects (vortices) is responsible for the transition to the algebraic order. This is made possible thanks to long polariton lifetimes in high-quality samples and in a reservoir-free region. Our results show that the joint measurement of coherence both in space and time is required to characterize driven-dissipative phase transitions and enable the investigation of topological ordering in open systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Seung Sae; Yu, Jung Ho; Lu, Di

Long-range order and phase transitions in two-dimensional (2D) systems—such as magnetism, superconductivity, and crystallinity—have been important research topics for decades. The issue of 2D crystalline order has reemerged recently, with the development of exfoliated atomic crystals. Understanding the dimensional limit of crystalline phases, with different types of bonding and synthetic techniques, is at the foundation of low-dimensional materials design. We study ultrathin membranes of SrTiO 3, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released after synthesis by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO 3 membrane lattice collapsesmore » below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length is analogous to the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) transition. Finally, the transition is likely driven by chemical bond breaking at the 2D layer-3D bulk interface, defining an effective dimensional phase boundary for coherent crystalline lattices.« less

A quantum diffractor for thermal flux

NASA Astrophysics Data System (ADS)

José Martínez-Pérez, Maria; Giazotto, Francesco

2014-04-01

Macroscopic phase coherence between weakly coupled superconductors leads to peculiar interference phenomena. Among these, magnetic flux-driven diffraction might be produced, in full analogy to light diffraction through a rectangular slit. This can be experimentally revealed by the electric current and, notably, also by the heat current transmitted through the circuit. The former was observed more than 50 years ago and represented the first experimental evidence of the phase-coherent nature of the Josephson effect, whereas the second one was still lacking. Here we demonstrate the existence of heat diffraction by measuring the modulation of the electronic temperature of a small metallic electrode nearby-contacted to a thermally biased short Josephson junction subjected to an in-plane magnetic field. The observed temperature dependence exhibits symmetry under magnetic flux reversal, and clear resemblance with a Fraunhofer-like modulation pattern. Our approach, joined to widespread methods for phase-biasing superconducting circuits, might represent an effective tool for controlling the thermal flux in nanoscale devices.

Method for producing microcomposite powders using a soap solution

DOEpatents

Maginnis, Michael A.; Robinson, David A.

1996-01-01

A method for producing microcomposite powders for use in superconducting and non-superconducting applications. A particular method to produce microcomposite powders for use in superconducting applications includes the steps of: (a) preparing a solution including ammonium soap; (b) dissolving a preselected amount of a soluble metallic such as silver nitrate in the solution including ammonium soap to form a first solution; (c) adding a primary phase material such as a single phase YBC superconducting material in particle form to the first solution; (d) preparing a second solution formed from a mixture of a weak acid and an alkyl-mono-ether; (e) adding the second solution to the first solution to form a resultant mixture; (f) allowing the resultant mixture to set until the resultant mixture begins to cloud and thicken into a gel precipitating around individual particles of the primary phase material; (g) thereafter drying the resultant mixture to form a YBC superconducting material/silver nitrate precursor powder; and (h) calcining the YBC superconducting material/silver nitrate precursor powder to convert the silver nitrate to silver and thereby form a YBC/silver microcomposite powder wherein the silver is substantially uniformly dispersed in the matrix of the YBC material.

CDW order and unconventional s-wave superconductivity in Ba1-xNaxTi2Sb2O

NASA Astrophysics Data System (ADS)

Kamusella, Sirko; Doan, Phuong; Goltz, Til; Luetkens, Hubertus; Sarkar, Rajib; Guloy, Arnold; Klauss, Hans-Henning

2014-12-01

Due to its anticuprate Ti2O layer and its fascinating phase diagram with a large coexistence area of superconductivity and a density wave phase, the new class of titanium based superconductors attracts great scientific interest. In this paper we report μSR investigation on powder samples of Ba1-xNaxTi2Sb2O (x = 0, 0.15, 0.25). Our results exhibit both the presence of a charge density wave and superconductivity in Ba1-xNaxTi2Sb2O. The superconducting order parameter, extracted from a vortex state analysis using the numeric Ginzburg-Landau model, is compatible with a s-wave symmetry. In the universal Uemura classification of superconductors this compound is at the verge of unconventional superconductivity.

Search for Superconductivity in Micrometeorites

PubMed Central

Guénon, S.; Ramírez, J. G.; Basaran, Ali C.; Wampler, J.; Thiemens, M.; Taylor, S.; Schuller, Ivan K.

2014-01-01

We have developed a very sensitive, highly selective, non-destructive technique for screening inhomogeneous materials for the presence of superconductivity. This technique, based on phase sensitive detection of microwave absorption is capable of detecting 10−12 cc of a superconductor embedded in a non-superconducting, non-magnetic matrix. For the first time, we apply this technique to the search for superconductivity in extraterrestrial samples. We tested approximately 65 micrometeorites collected from the water well at the Amundsen-Scott South pole station and compared their spectra with those of eight reference materials. None of these micrometeorites contained superconducting compounds, but we saw the Verwey transition of magnetite in our microwave system. This demonstrates that we are able to detect electro-magnetic phase transitions in extraterrestrial materials at cryogenic temperatures. PMID:25476841

Critical current and electric transport properties of superconducting epitaxial Nb(Ti)N submicron structures

NASA Astrophysics Data System (ADS)

Klimov, A.; Słysz, W.; Guziewicz, M.; Kolkovsky, V.; Wegrzecki, M.; Bar, J.; Marchewka, M.; Seredyński, B.

2016-12-01

Critical current and current-voltage characteristics of epitaxial Nb(Ti)N submicron ultrathin structures were measured as function of temperature. For 700-nm-wide bridge we found current-driven vortex de-pinning at low temperatures and thermally activated flux flow closer to the transition temperature, as the limiting factors for the critical current density. For 100-nm-wide meander we observed combination of phase-slip activation and vortex-anti-vortex pair (VAP) thermal excitation. Our Nb(Ti)N meander structure demonstrates high de-pairing critical current densities 107 A/cm2 at low temperatures, but the critical currents are much smaller due to presence of the local constrictions.

A superconducting large-angle magnetic suspension

NASA Technical Reports Server (NTRS)

Downer, James R.; Anastas, George V., Jr.; Bushko, Dariusz A.; Flynn, Frederick J.; Goldie, James H.; Gondhalekar, Vijay; Hawkey, Timothy J.; Hockney, Richard L.; Torti, Richard P.

1992-01-01

SatCon Technology Corporation has completed a Small Business Innovation Research (SBIR) Phase 2 program to develop a Superconducting Large-Angle Magnetic Suspension (LAMS) for the NASA Langley Research Center. The Superconducting LAMS was a hardware demonstration of the control technology required to develop an advanced momentum exchange effector. The Phase 2 research was directed toward the demonstration for the key technology required for the advanced concept CMG, the controller. The Phase 2 hardware consists of a superconducting solenoid ('source coils') suspended within an array of nonsuperconducting coils ('control coils'), a five-degree-of-freedom positioning sensing system, switching power amplifiers, and a digital control system. The results demonstrated the feasibility of suspending the source coil. Gimballing (pointing the axis of the source coil) was demonstrated over a limited range. With further development of the rotation sensing system, enhanced angular freedom should be possible.

A superconducting large-angle magnetic suspension

NASA Astrophysics Data System (ADS)

Downer, James R.; Anastas, George V., Jr.; Bushko, Dariusz A.; Flynn, Frederick J.; Goldie, James H.; Gondhalekar, Vijay; Hawkey, Timothy J.; Hockney, Richard L.; Torti, Richard P.

1992-12-01

SatCon Technology Corporation has completed a Small Business Innovation Research (SBIR) Phase 2 program to develop a Superconducting Large-Angle Magnetic Suspension (LAMS) for the NASA Langley Research Center. The Superconducting LAMS was a hardware demonstration of the control technology required to develop an advanced momentum exchange effector. The Phase 2 research was directed toward the demonstration for the key technology required for the advanced concept CMG, the controller. The Phase 2 hardware consists of a superconducting solenoid ('source coils') suspended within an array of nonsuperconducting coils ('control coils'), a five-degree-of-freedom positioning sensing system, switching power amplifiers, and a digital control system. The results demonstrated the feasibility of suspending the source coil. Gimballing (pointing the axis of the source coil) was demonstrated over a limited range. With further development of the rotation sensing system, enhanced angular freedom should be possible.

Nano-patterned superconducting surface for high quantum efficiency cathode

DOEpatents

Hannon, Fay; Musumeci, Pietro

2017-03-07

A method for providing a superconducting surface on a laser-driven niobium cathode in order to increase the effective quantum efficiency. The enhanced surface increases the effective quantum efficiency by improving the laser absorption of the surface and enhancing the local electric field. The surface preparation method makes feasible the construction of superconducting radio frequency injectors with niobium as the photocathode. An array of nano-structures are provided on a flat surface of niobium. The nano-structures are dimensionally tailored to interact with a laser of specific wavelength to thereby increase the electron yield of the surface.

Superconductivity in ion-beam-mixed layered Au-Si thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jisrawi, N.M.; McLean, W.L.; Stoffel, N.G.

The superconducting properties of thin films made by mixing alternating layers of Au and Si using ion-beam bombardment correlate with the formation of metastable metallic phases in what is otherwise a simple eutectic system. Transmission-electron-microscopy measurements reveal the superconducting phases to be amorphous. Compound formation and the nature of Au-Si bonding in these metastable phases are demonstrated from x-ray photoelectron spectroscopy and from a previous study of x-ray-absorption spectroscopy. After mixing with a beam of Xe ions, multilayered films with an average nominal composition Au{sub {ital x}}Si{sub 1{minus}{ital x}}, where {ital x}=0.2, 0.4, 0.5, 0.72, and 0.8, exhibited superconducting transitionmore » temperatures in the range 0.2--1.2 K. A double transition feature in the magnetic field dependence of the resistivity is attributed to the formation of more than one metastable metallic phase in the same sample as the ion dose increases.« less

Microwave photonics with superconducting quantum circuits

NASA Astrophysics Data System (ADS)

Gu, Xiu; Kockum, Anton Frisk; Miranowicz, Adam; Liu, Yu-xi; Nori, Franco

2017-11-01

In the past 20 years, impressive progress has been made both experimentally and theoretically in superconducting quantum circuits, which provide a platform for manipulating microwave photons. This emerging field of superconducting quantum microwave circuits has been driven by many new interesting phenomena in microwave photonics and quantum information processing. For instance, the interaction between superconducting quantum circuits and single microwave photons can reach the regimes of strong, ultra-strong, and even deep-strong coupling. Many higher-order effects, unusual and less familiar in traditional cavity quantum electrodynamics with natural atoms, have been experimentally observed, e.g., giant Kerr effects, multi-photon processes, and single-atom induced bistability of microwave photons. These developments may lead to improved understanding of the counterintuitive properties of quantum mechanics, and speed up applications ranging from microwave photonics to superconducting quantum information processing. In this article, we review experimental and theoretical progress in microwave photonics with superconducting quantum circuits. We hope that this global review can provide a useful roadmap for this rapidly developing field.

Theory of superconductivity in a three-orbital model of Sr2RuO4

NASA Astrophysics Data System (ADS)

Wang, Q. H.; Platt, C.; Yang, Y.; Honerkamp, C.; Zhang, F. C.; Hanke, W.; Rice, T. M.; Thomale, R.

2013-10-01

In conventional and high transition temperature copper oxide and iron pnictide superconductors, the Cooper pairs all have even parity. As a rare exception, Sr2RuO4 is the first prime candidate for topological chiral p-wave superconductivity, which has time-reversal breaking odd-parity Cooper pairs known to exist before only in the neutral superfluid 3He. However, there are several key unresolved issues hampering the microscopic description of the unconventional superconductivity. Spin fluctuations at both large and small wave vectors are present in experiments, but how they arise and drive superconductivity is not yet clear. Spontaneous edge current is expected but not observed conclusively. Specific experiments point to highly band- and/or momentum-dependent energy gaps for quasiparticle excitations in the superconducting state. Here, by comprehensive functional renormalization group calculations with all relevant bands, we disentangle the various competing possibilities. In particular, we show the small wave vector spin fluctuations, driven by a single two-dimensional band, trigger p-wave superconductivity with quasi-nodal energy gaps.

Dissipative phases across the superconductor-to-insulator transition

PubMed Central

Couëdo, F.; Crauste, O.; Drillien, A. A.; Humbert, V.; Bergé, L.; Marrache-Kikuchi, C. A.; Dumoulin, L.

2016-01-01

Competing phenomena in low dimensional systems can generate exotic electronic phases, either through symmetry breaking or a non-trivial topology. In two-dimensional (2D) systems, the interplay between superfluidity, disorder and repulsive interactions is especially fruitful in this respect although both the exact nature of the phases and the microscopic processes at play are still open questions. In particular, in 2D, once superconductivity is destroyed by disorder, an insulating ground state is expected to emerge, as a result of a direct superconductor-to-insulator quantum phase transition. In such systems, no metallic state is theoretically expected to survive to the slightest disorder. Here we map out the phase diagram of amorphous NbSi thin films as functions of disorder and film thickness, with two metallic phases in between the superconducting and insulating ones. These two dissipative states, defined by a resistance which extrapolates to a finite value in the zero temperature limit, each bear a specific dependence on disorder. We argue that they originate from an inhomogeneous destruction of superconductivity, even if the system is morphologically homogeneous. Our results suggest that superconducting fluctuations can favor metallic states that would not otherwise exist. PMID:27786260

Interplay between superconductivity and magnetism in iron-based superconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chubukov, Andrey V

2015-06-10

This proposal is for theoretical work on strongly correlated electron systems, which are at the center of experimental and theoretical activities in condensed-matter physics. The interest to this field is driven fascinating variety of observed effects, universality of underlying theoretical ideas, and practical applications. I propose to do research on Iron-based superconductors (FeSCs), which currently attract high attention in the physics community. My goal is to understand superconductivity and magnetism in these materials at various dopings, the interplay between the two, and the physics in the phase in which magnetism and superconductivity co-exist. A related goal is to understand themore » origin of the observed pseudogap-like behavior in the normal state. My research explores the idea that superconductivity is of electronic origin and is caused by the exchange of spin-fluctuations, enhanced due to close proximity to antiferromagnetism. The multi-orbital/multi-band nature of FeSCs opens routes for qualitatively new superconducting states, particularly the ones which break time-reversal symmetry. By all accounts, the coupling in pnictdes is below the threshold for Mott physics and I intend to analyze these systems within the itinerant approach. My plan is to do research in two stages. I first plan to address several problems within weak-coupling approach. Among them: (i) what sets stripe magnetic order at small doping, (ii) is there a preemptive instability into a spin-nematic state, and how stripe order affects fermions; (iii) is there a co-existence between magnetism and superconductivity and what are the system properties in the co-existence state; (iv) how superconductivity emerges despite strong Coulomb repulsion and can the gap be s-wave but with nodes along electron FSs, (v) are there complex superconducting states, like s+id, which break time reversal symmetry. My second goal is to go beyond weak coupling and derive spin-mediated, dynamic interaction between fermions, understand what sets the upper scale for attractive interaction, compute T_c, and then obtain and solve matrix non-linear gap equation for spin-mediated pairing and study various feedbacks from the pairing on fermions on ARPES spectra, optical and thermal conductivity, and other observables, The problems I have chosen are quite generic, and the understanding of magnetically-mediated superconductivity in the strong-coupling regime will not only advance the theory of superconductivity in FeSCs, but will contribute to a generic understanding of the pairing of fermions near quantum-critical points -- the problems ranging from s-wave pairing by soft optical phonons to to color superconductivity of quarks mediated by a gluon exchange.« less

Quantum criticality at the superconductor-insulator transition revealed by specific heat measurements

PubMed Central

Poran, S.; Nguyen-Duc, T.; Auerbach, A.; Dupuis, N.; Frydman, A.; Bourgeois, Olivier

2017-01-01

The superconductor–insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, cp, measurements. Here we use a unique highly sensitive experiment to measure cp of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition. PMID:28224994

Quantum criticality at the superconductor-insulator transition revealed by specific heat measurements.

PubMed

Poran, S; Nguyen-Duc, T; Auerbach, A; Dupuis, N; Frydman, A; Bourgeois, Olivier

2017-02-22

The superconductor-insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, c p , measurements. Here we use a unique highly sensitive experiment to measure c p of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition.

Metallurgical technologies, energy conversion, and magnetohydrodynamic flows

NASA Astrophysics Data System (ADS)

Branover, Herman; Unger, Yeshajahu

The present volume discusses metallurgical applications of MHD, R&D on MHD devices employing liquid working medium for process applications, electromagnetic (EM) modulation of molten metal flow, EM pump performance of superconducting MHD devices, induction EM alkali-metal pumps, a physical model for EM-driven flow in channel-induction furnaces, grain refinement in Al alloys via EM vibrational method, dendrite growth of solidifying metal in dc magnetic field, MHD for mass and heat transfer in single-crystal melt growth, inverse EM shaping, and liquid-metal MHD development in Israel. Also discussed are the embrittlement of steel by lead, an open cycle MHD disk generator, the acceleration of gas-liquid piston flows for molten-metal MHD generators, MHD flow around a cylinder, new MHD drag coefficients, liquid-metal MHD two-phase flow, and two-phase liquid gas mixers for MHD energy conversion. (No individual items are abstracted in this volume)

Competing Quantum Orderings in Cuprate Superconductors: A Minimal Model

NASA Astrophysics Data System (ADS)

Martin, Ivar; Ortiz, Gerardo; Balatsky, A. V.; Bishop, A. R.

2001-03-01

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra, and local density of states measurable by STM.

CO2-laser ablation of Bi-Sr-Ca-Cu oxide by millisecond pulse lengths

NASA Astrophysics Data System (ADS)

Meskoob, M.; Honda, T.; Safari, A.; Wachtman, J. B.; Danforth, S.; Wilkens, B. J.

1990-03-01

We have achieved ablation of Bi-Sr-Ca-Cu oxide from single targets of superconducting pellets by CO2-laser pulses of l ms length to grow superconducting thin films. Upon annealing, the 6000-Å thin films have a Tc (onset) of 90 K and zero resistance at 78 K. X-ray diffraction patterns indicate the growth of single-phase thin films. This technique allows growth of uniform single-phase superconducting thin films of lateral area greater than 1 cm2.

Quantum Device Applications of Mesoscopic Superconductivity

NASA Astrophysics Data System (ADS)

Hakonen, P. J.

2006-08-01

A brief account is given on the possibilities of mesoscopic superconductivity in low-noise amplifier and detector applications. In particular, three devices will be described: 1) Bloch oscillating transistor (BOT), 2) Inductively-read superconducting Cooper pair transistor (L-SET), and 3) Quantum capacitive phase detector (C-SET). The BOT is a low-noise current amplifier while the L-SET and C-SET act as ultra-sensitive charge and phase detectors, respectively. The basic operating principles and the main characteristics of these devices will be reviewed and discussed.

Drive the Dirac electrons into Cooper pairs in SrxBi2Se3.

PubMed

Du, Guan; Shao, Jifeng; Yang, Xiong; Du, Zengyi; Fang, Delong; Wang, Jinghui; Ran, Kejing; Wen, Jinsheng; Zhang, Changjin; Yang, Huan; Zhang, Yuheng; Wen, Hai-Hu

2017-02-15

Topological superconductors are a very interesting and frontier topic in condensed matter physics. Despite the tremendous efforts in exploring topological superconductivity, its presence is however still under heavy debate. The Dirac electrons have been proven to exist on the surface of a topological insulator. It remains unclear whether and how the Dirac electrons fall into Cooper pairing in an intrinsic superconductor with the topological surface states. Here we show the systematic study of scanning tunnelling microscope/spectroscopy on the possible topological superconductor Sr x Bi 2 Se 3 . We first demonstrate that only the intercalated Sr atoms can induce superconductivity. Then we show the full superconducting gaps without any in-gap density of states as expected theoretically for a bulk topological superconductor. Finally, we find that the surface Dirac electrons will simultaneously condense into the superconducting state within the superconducting gap. This vividly demonstrates how the surface Dirac electrons are driven into Cooper pairs.

Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces.

PubMed

Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

2016-07-01

Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2-x Sr x CuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices.

A hidden pseudogap under the 'dome' of superconductivity in electron-doped high-temperature superconductors.

PubMed

Alff, L; Krockenberger, Y; Welter, B; Schonecke, M; Gross, R; Manske, D; Naito, M

2003-04-17

The ground state of superconductors is characterized by the long-range order of condensed Cooper pairs: this is the only order present in conventional superconductors. The high-transition-temperature (high-T(c)) superconductors, in contrast, exhibit more complex phase behaviour, which might indicate the presence of other competing ground states. For example, the pseudogap--a suppression of the accessible electronic states at the Fermi level in the normal state of high-T(c) superconductors-has been interpreted as either a precursor to superconductivity or as tracer of a nearby ground state that can be separated from the superconducting state by a quantum critical point. Here we report the existence of a second order parameter hidden within the superconducting phase of the underdoped (electron-doped) high-T(c) superconductor Pr2-xCe(x)CuO4-y and the newly synthesized electron-doped material La2-xCe(x)CuO4-y (ref. 8). The existence of a pseudogap when superconductivity is suppressed excludes precursor superconductivity as its origin. Our observation is consistent with the presence of a (quantum) phase transition at T = 0, which may be a key to understanding high-T(c) superconductivity. This supports the picture that the physics of high-T(c) superconductors is determined by the interplay between competing and coexisting ground states.

Self-optimized superconductivity attainable by interlayer phase separation at cuprate interfaces

PubMed Central

Misawa, Takahiro; Nomura, Yusuke; Biermann, Silke; Imada, Masatoshi

2016-01-01

Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood. Solving microscopic models suitable for cuprates, we demonstrate that, at an interface between a Mott insulator and an overdoped nonsuperconducting metal, the superconducting amplitude is always pinned at the optimum achieved in the bulk, independently of the carrier concentration in the metal. This is in contrast to the dome-like dependence in bulk superconductors but consistent with the astonishing independence of the critical temperature from the carrier density x observed at the interfaces of La2CuO4 and La2−xSrxCuO4. Furthermore, we identify a self-organization mechanism as responsible for the pinning at the optimum amplitude: An emergent electronic structure induced by interlayer phase separation eludes bulk phase separation and inhomogeneities that would kill superconductivity in the bulk. Thus, interfaces provide an ideal tool to enhance and stabilize superconductivity. This interfacial example opens up further ways of shaping superconductivity by suppressing competing instabilities, with direct perspectives for designing devices. PMID:27482542

Landau-Zener interferometry in a Cooper pair box

NASA Astrophysics Data System (ADS)

Sillanpää, Mika; Lehtinen, Teijo; Paila, Antti; Makhlin, Yuriy; Hakonen, Pertti

2006-03-01

Quantum-mechanical systems having two crossing energy levels are ubiquitous in nature. The rate v = d (E1- E0)/dt at which such levels in a driven system approach each other determines the probability PLZ of a Landau-Zener (LZ) tunneling between them. The traditional treatment of the LZ process, however, ignores quantum-mechanical interference. Here we report an observation of phase-sensitive interference between consecutive LZ tunneling attempts in an artificial two-state system, a superconducting charge qubit. We interpret the experiment in terms of a multi-pass analog to the optical Mach- Zehnder interferometer: The beam splitting occurs by LZ tunneling at the charge degeneracy, while the arms of the Mach- Zehnder interferometer in energy space are represented by the ground and excited state. In accord with theory, we observe constructive interference when the Stokes phase φS picked up during the LZ interaction, and the dynamical phase of one drive period φ= (E1- E0) dt satisfy the condition: (φ- 2 φS) = m .2π. Our LZ interferometer can be used as a high-resolution detector for phase and charge owing to interferometric sensitivity- enhancement.

Acoustic properties of quasi-one-dimensional organic conductor (TMTSF)2ClO4 in the relaxed state: Superconductivity and FISDW anomalies.

NASA Astrophysics Data System (ADS)

Langlois, Alexandre; Poirier, Mario; Bourbonnais, Claude; Bechgaard, Klaus

2008-03-01

Through competing electronic instabilities, the anion sublattice plays an important role in the rich phase diagram of the Bechgaard salts. In the quasi-one-dimensional organic conductor (TMTSF)2ClO4, anion ordering at 24 K affects the nesting properties of the Fermi surface and controls the stability of the superconducting phase below 1.2 K at ambient pressure. Moreover, the field induced spin density wave phases FISDW, one of the several features induced by a magnetic field in this compound, are also sensitive to the symmetry of the anions. In order to address the coupling issue between the lattice and these electronic instabilities, we have performed the first ultrasonic measurements on (TMTSF)2ClO4 in the relaxed state below 4 K using longitudinal and transverses waves (30-500 MHz). If low-frequency vibrating reed experiments have revealed magneto-elastic anomalies in the FISDW phases [1], the superconducting one was never investigated by similar techniques. We report anomalies in the ultrasonic velocity and attenuation for the superconducting and the FISDW phases. The coupling of these phases to the lattice is discussed in relation with the known T-B phase diagram. [1] X.D. Shi et al., Phys. Rev. B. 50, 1984 (1994).

Ceramic superconductor/metal composite materials employing the superconducting proximity effect

DOEpatents

Holcomb, Matthew J.

2002-01-01

Superconducting composite materials having particles of superconducting material disposed in a metal matrix material with a high electron-boson coupling coefficient (.lambda.). The superconducting particles can comprise any type of superconductor including Laves phase materials, Chevrel phase materials, A15 compounds, and perovskite cuprate ceramics. The particles preferably have dimensions of about 10-500 nanometers. The particles preferably have dimensions larger than the superconducting coherence length of the superconducting material. The metal matrix material has a .lambda. greater than 0.2, preferably the .lambda. is much higher than 0.2. The metal matrix material is a good proximity superconductor due to its high .lambda.. When cooled, the superconductor particles cause the metal matrix material to become superconducting due to the proximity effect. In cases where the particles and the metal matrix material are chemically incompatible (i.e., reactive in a way that destroys superconductivity), the particles are provided with a thin protective metal coating. The coating is chemically compatible with the particles and metal matrix material. High Temperature Superconducting (HTS) cuprate ceramic particles are reactive and therefore require a coating of a noble metal resistant to oxidation (e.g., silver, gold). The proximity effect extends through the metal coating. With certain superconductors, non-noble metals can be used for the coating.

NASA Office of Aeronautics and Space Technology Summer Workshop. Volume 10: Basic research panel

NASA Technical Reports Server (NTRS)

1975-01-01

Possible research experiments using the space transportation system are identified based on user requirements. Opportunity driven research areas include quantum electronics, cryogenics system technology, superconducting devices and detectors, and photo-induced reactions. Mission driven research requirements were examined and ranked based on inputs from the user group.

Antiferroic electronic structure in the nonmagnetic superconducting state of the iron-based superconductors

PubMed Central

Shimojima, Takahiro; Malaeb, Walid; Nakamura, Asuka; Kondo, Takeshi; Kihou, Kunihiro; Lee, Chul-Ho; Iyo, Akira; Eisaki, Hiroshi; Ishida, Shigeyuki; Nakajima, Masamichi; Uchida, Shin-ichi; Ohgushi, Kenya; Ishizaka, Kyoko; Shin, Shik

2017-01-01

A major problem in the field of high-transition temperature (Tc) superconductivity is the identification of the electronic instabilities near superconductivity. It is known that the iron-based superconductors exhibit antiferromagnetic order, which competes with the superconductivity. However, in the nonmagnetic state, there are many aspects of the electronic instabilities that remain unclarified, as represented by the orbital instability and several in-plane anisotropic physical properties. We report a new aspect of the electronic state of the optimally doped iron-based superconductors by using high–energy resolution angle-resolved photoemission spectroscopy. We find spectral evidence for the folded electronic structure suggestive of an antiferroic electronic instability, coexisting with the superconductivity in the nonmagnetic state of Ba1−xKxFe2As2. We further establish a phase diagram showing that the antiferroic electronic structure persists in a large portion of the nonmagnetic phase covering the superconducting dome. These results motivate consideration of a key unknown electronic instability, which is necessary for the achievement of high-Tc superconductivity in the iron-based superconductors. PMID:28875162

Antiferroic electronic structure in the nonmagnetic superconducting state of the iron-based superconductors.

PubMed

Shimojima, Takahiro; Malaeb, Walid; Nakamura, Asuka; Kondo, Takeshi; Kihou, Kunihiro; Lee, Chul-Ho; Iyo, Akira; Eisaki, Hiroshi; Ishida, Shigeyuki; Nakajima, Masamichi; Uchida, Shin-Ichi; Ohgushi, Kenya; Ishizaka, Kyoko; Shin, Shik

2017-08-01

A major problem in the field of high-transition temperature ( T c ) superconductivity is the identification of the electronic instabilities near superconductivity. It is known that the iron-based superconductors exhibit antiferromagnetic order, which competes with the superconductivity. However, in the nonmagnetic state, there are many aspects of the electronic instabilities that remain unclarified, as represented by the orbital instability and several in-plane anisotropic physical properties. We report a new aspect of the electronic state of the optimally doped iron-based superconductors by using high-energy resolution angle-resolved photoemission spectroscopy. We find spectral evidence for the folded electronic structure suggestive of an antiferroic electronic instability, coexisting with the superconductivity in the nonmagnetic state of Ba 1- x K x Fe 2 As 2 . We further establish a phase diagram showing that the antiferroic electronic structure persists in a large portion of the nonmagnetic phase covering the superconducting dome. These results motivate consideration of a key unknown electronic instability, which is necessary for the achievement of high- T c superconductivity in the iron-based superconductors.

Peculiar phase diagram with isolated superconducting regions in ThFeAsN1‑x O x

NASA Astrophysics Data System (ADS)

Li, Bai-Zhuo; Wang, Zhi-Cheng; Wang, Jia-Lu; Zhang, Fu-Xiang; Wang, Dong-Ze; Zhang, Feng-Yuan; Sun, Yu-Ping; Jing, Qiang; Zhang, Hua-Fu; Tan, Shu-Gang; Li, Yu-Ke; Feng, Chun-Mu; Mei, Yu-Xue; Wang, Cao; Cao, Guang-Han

2018-06-01

ThFeAsN1‑x O x () system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T c value decreases rapidly to below 2 K for , and surprisingly, superconductivity re-appears in the range of with a maximum of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is , which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN1‑x O x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

Stability and superconducting properties of GaH5 at high pressure

NASA Astrophysics Data System (ADS)

Ning, Yan-Li; Yang, Wen-Hua; Zang, Qing-Jun; Lu, Wen-Cai

2017-11-01

Using genetic algorithm (GA) method combined with first-principles calculations, the structures, dynamical and thermodynamic stabilities of GaH5 were studied. The calculated results suggested that at the pressure range 150-400 GPa, the P21/m phase of GaH5 is the most favorable phase and dynamically stable, but thermodynamically it is unstable and can decompose into GaH3 and H2. The superconducting property of GaH5 was further calculated, and the predicted superconducting transformation temperature Tc of GaH5 P21/m phase is about 35.63 K at 250 GPa. Besides, we compared the GaH5 and GaH3 superconducting properties, and found that GaH3-Pm-3n structure has a larger DOS near Fermi level than GaH5-P21/m structure, which may be the main reason causing higher Tc of GaH3 than GaH5.

Duality picture of Superconductor-insulator transitions on Superconducting nanowire.

PubMed

Makise, Kazumasa; Terai, Hirotaka; Tominari, Yukihiro; Tanaka, Shukichi; Shinozaki, Bunju

2016-06-17

In this study, we investigated the electrical transport properties of niobium titanium nitride (NbTiN) nanowire with four-terminal geometries to clarify the superconducting phase slip phenomena and superconducting-insulator transitions (SIT) for one-dimensional superconductors. We fabricated various nanowires with different widths and lengths from epitaxial NbTiN films using the electron beam lithography method. The temperature dependence of resistance R(T) below the superconducting transition temperature Tc was analyzed using thermal activation phase slip (TAPS) and quantum phase slip (QPS) theories. Although the accuracy of experimental data at low temperatures can deviate when using the TAPS model, the QPS model thoroughly represents the R(T) characteristic with resistive tail at low temperatures. From the analyses of data on Tc, we found that NbTiN nanowires exhibit SIT because of the change in the ratio of kinetic inductance energy and QPS amplitude energy with respect to the flux-charge duality theory.

Current-phase relations in low carrier density graphene Josephson junctions

NASA Astrophysics Data System (ADS)

Kratz, Philip; Amet, Francois; Watson, Christopher; Moler, Kathryn; Ke, Chung; Borzenets, Ivan; Watanabe, Kenji; Taniguchi, Takashi; Deacon, Russell; Yamamoto, Michihisa; Bomze, Yuriy; Tarucha, Seigo; Finkelstein, Gleb

Ideal Dirac semimetals have the unique property of being gate tunable to arbitrarily low electron and hole carrier concentrations near the Dirac point, without suffering from conduction channel pinch-off or Fermi level pinning to band edges and deep-level charge traps, which are common in typical semiconductors. SNS junctions, where N is a Dirac semimetal, can provide a versatile platform for studying few-mode superconducting weak links, with potential device applications for superconducting logic and qubits. We will use an inductive readout technique, scanning superconducting quantum interference device (SQUID) magnetometry, to measure the current-phase relations of high-mobility graphene SNS junctions as a function of temperature and carrier density, complementing magnetic Fraunhofer diffraction analysis from transport measurements which previously have assumed sinusoidal current-phase relations for junction Andreev modes. Deviations from sinusoidal behavior convey information about resonant scattering processes, dissipation, and ballistic modes in few-mode superconducting weak links.

Oxygen stabilization induced enhancement in J(sub c) and T(sub c) of superconducting oxides

NASA Technical Reports Server (NTRS)

Wu, M. K.; Chen, J. T.; Huang, C. Y.

1990-01-01

In an attempt to enhance the electrical and mechanical properties of the high temperature superconducting oxides, high T(sub c) composites were prepared composed of the 123 compounds and AgO. The presence of extra oxygen due to the decomposition of AgO at high temperature is found to stabilize the superconducting 123 phase. Ag is found to serve as clean flux for grain growth and precipitates as pinning center. Consequently, almost two orders of magnitude enhancement in critical current densities were also observed in these composites. In addition, these composites also show much improvement in workability and shape formation. On the other hand, proper oxygen treatment of Y5Ba6Cu11Oy was found to possibly stabilize superconducting phase with T(sub c) near 250 K. I-V, ac susceptibility, and electrical resistivity measurements indicate the existence of this ultra high T(sub c) phase in this compound. Detailed structure, microstructure, electrical, magnetic and thermal studies of the superconducting composites and the ultra high T(sub c) compound are presented and discussed.

Oxygen stabilization induced enhancement in superconducting characteristics of high-Tc oxides

NASA Technical Reports Server (NTRS)

Wu, M. K.; Chen, J. T.; Huang, C. Y.

1991-01-01

In an attempt to enhance the electrical and mechanical properties of the high temperature superconducting oxides, high T(sub c) composites were prepared composed of the 123 compounds and AgO. The presence of extra oxygen due to the decomposition of AgO at high temperature is found to stabilize the superconducting 123 phase. Ag is found to serve as clean flux for grain growth and precipitates as pinning center. Consequently, almost two orders of magnitude enhancement in critical current densities were also observed in these composites. In addition, these composites also show much improvement in workability and shape formation. On the other hand, proper oxygen treatment of Y5Ba6Cu11Oy was found to possibly stabilize superconducting phase with T(sub c) near 250 K. I-V, ac susceptibility, and electrical resistivity measurements indicate the existence of this ultra high T(sub c) phase in this compound. Detailed structure, microstructure, electrical, magnetic and thermal studies of the superconducting composites and the ultra high T(sub c) compound are presented and discussed.

Direct observation of ballistic Andreev reflection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klapwijk, T. M., E-mail: t.m.klapwijk@tudelft.nl; Ryabchun, S. A.

2014-12-15

An overview is presented of experiments on ballistic electrical transport in inhomogeneous superconducting systems which are controlled by the process of Andreev reflection. The initial experiments based on the coexistence of a normal phase and a superconducting phase in the intermediate state led to the concept itself. It was followed by a focus on geometrically inhomogeneous systems like point contacts, which provided a very clear manifestation of the energy and direction dependence of the Andreev reflection process. The point contacts have recently evolved towards the atomic scale owing to the use of mechanical break-junctions, revealing a very detailed dependence ofmore » Andreev reflection on the macroscopic phase of the superconducting state. In present-day research, the superconducting in homogeneity is constructed by clean room technology and combines superconducting materials, for example, with low-dimensional materials and topological insulators. Alternatively, the superconductor is combined with nano-objects, such as graphene, carbon nanotubes, or semiconducting nanowires. Each of these “inhomogeneous systems” provides a very interesting range of properties, all rooted in some manifestation of Andreev reflection.« less

Magneto-transport properties of Co3O4 nanoparticles added (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ superconducting phase

NASA Astrophysics Data System (ADS)

Mumtaz, M.; Baig, Mirza Hassan; Waqee-ur-Rehman, M.; Nasir Khan, M.

2018-05-01

Solid-state reaction method was used to synthesize Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconducting phase and sol-gel method was used to prepare cobalt oxide (Co3O4) magnetic nanoparticles. These Co3O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (Co3O4)x/CuTl-1223; x = 0-2.00 wt.% nanoparticles-superconductor composites. The effects of Co3O4 nanoparticles on crystal structure, phase formation, phase purity and infield superconducting transport properties of CuTl-1223 phase were investigated at different operating temperatures and external applied magnetic fields. The crystal structure and phase formation of Co3O4 nanoparticles and CuTl-1223 superconductor were determined by X-ray diffraction (XRD) technique. XRD peaks of Co3O4 nanoparticles were well indexed according to FCC crystal structure and the average particle size of 70 nm was calculated by using Debye-Scherer's formula. The unaltered crystal structure of host CuTl-1223 superconducting phase (i.e. Tetragonal) with the addition of Co3O4 nanoparticles indicated the dispersion of nanoparticles at inter-granular sites. Temperature dependent magneto-transport superconducting properties of (Co3O4)x/CuTl-1223 composites were investigated by zero field cooled (ZFC) and field cooled (FC) magnetic moment versus temperature (M-T) measurements. The onset transition temperatures {TcOnset (K)} was decreased along with the suppression of diamagnetic amplitude of CuTl-1223 superconducting phase with the addition of magnetic Co3O4 nanoparticles. Temperature dependent magnetic hysteresis (M-H loops) measurements of (Co3O4)x/CuTl-1223 composites were carried out at different operating temperatures from 5 K to 150 K. Critical current density (Jc) was calculated from M-H loops measurements by using Bean's model. Like the suppression of TcOnset (K) values, Jc was also decreased with the inclusion of Co3O4 nanoparticles. It was also observed that variation of Jc with H followed the power law Jc = βH-α at low operating temperatures 5 K and 20 K only.

Formation of Nanofoam carbon and re-emergence of Superconductivity in compressed CaC6.

PubMed

Li, Yan-Ling; Luo, Wei; Chen, Xiao-Jia; Zeng, Zhi; Lin, Hai-Qing; Ahuja, Rajeev

2013-11-26

Pressure can tune material's electronic properties and control its quantum state, making some systems present disconnected superconducting region as observed in iron chalcogenides and heavy fermion CeCu2Si2. For CaC6 superconductor (Tc of 11.5 K), applying pressure first Tc increases and then suppresses and the superconductivity of this compound is eventually disappeared at about 18 GPa. Here, we report a theoretical finding of the re-emergence of superconductivity in heavily compressed CaC6. The predicted phase III (space group Pmmn) with formation of carbon nanofoam is found to be stable at wide pressure range with a Tc up to 14.7 K at 78 GPa. Diamond-like carbon structure is adhered to the phase IV (Cmcm) for compressed CaC6 after 126 GPa, which has bad metallic behavior, indicating again departure from superconductivity. Re-emerged superconductivity in compressed CaC6 paves a new way to design new-type superconductor by inserting metal into nanoporous host lattice.

Superconductivity and hybrid soft modes in Ti Se 2

DOE PAGES

Maschek, M.; Rosenkranz, S.; Hott, R.; ...

2016-12-12

The interplay between superconductivity and charge-density-wave (CDW) order plays a central role in the layered transition-metal dichalcogenides. 1 T-TiSe 2 forms a prime example, featuring superconducting domes on intercalation as well as under applied pressure. Here, we present high energy-resolution inelastic x-ray scattering measurements of the CDW soft phonon mode in intercalated Cu xTiSe 2 and pressurized 1 T-TiSe 2 along with detailed ab-initio calculations for the lattice dynamical properties and phonon-mediated superconductivity. We find that the intercalation-induced superconductivity can be explained by a solely phonon-mediated pairing mechanism, while this is not possible for the superconducting phase under pressure. Wemore » argue that a hybridization of phonon and exciton modes in the pairing mechanism is necessary to explain the full observed temperature-pressure-intercalation phase diagram. Finally, these results indicate that 1 T-TiSe 2 under pressure is close to the elusive state of the excitonic insulator.« less

Scanning laser microscope for imaging nanostructured superconductors

NASA Astrophysics Data System (ADS)

Ishida, Takekazu; Arai, Kohei; Akita, Yukio; Miyanari, Mitsunori; Minami, Yusuke; Yotsuya, Tsutomu; Kato, Masaru; Satoh, Kazuo; Uno, Mayumi; Shimakage, Hisashi; Miki, Shigehito; Wang, Zhen

2010-10-01

The nanofabrication of superconductors yields various interesting features in superconducting properties. A variety of different imaging techniques have been developed for probing the local superconducting profiles. A scanning pulsed laser microscope has been developed by the combination of the XYZ piezo-driven stages and an optical fiber with an aspheric focusing lens. The scanning laser microscope is used to understand the position-dependent properties of a superconducting MgB 2 stripline of length 100 μm and width of 3 μm under constant bias current. Our results show that the superconducting stripline can clearly be seen in the contour image of the scanning laser microscope on the signal voltage. It is suggested from the observed image that the inhomogeneity is relevant in specifying the operating conditions such as detection efficiency of the sensor.

Possible superconductivity in the Bismuth IV solid phase under pressure.

PubMed

Valladares, Ariel A; Rodríguez, Isaías; Hinojosa-Romero, David; Valladares, Alexander; Valladares, Renela M

2018-04-13

The first successful theory of superconductivity was the one proposed by Bardeen, Cooper and Schrieffer in 1957. This breakthrough fostered a remarkable growth of the field that propitiated progress and questionings, generating alternative theories to explain specific phenomena. For example, it has been argued that Bismuth, being a semimetal with a low number of carriers, does not comply with the basic hypotheses underlying BCS and therefore a different approach should be considered. Nevertheless, in 2016 based on BCS we put forth a prediction that Bi at ambient pressure becomes a superconductor at 1.3 mK. A year later an experimental group corroborated that in fact Bi is a superconductor with a transition temperature of 0.53 mK, a result that eluded previous work. So, since Bi is superconductive in almost all the different structures and phases, the question is why Bi-IV has been elusive and has not been found yet to superconduct? Here we present a study of the electronic and vibrational properties of Bi-IV and infer its possible superconductivity using a BCS approach. We predict that if the Bi-IV phase structure were cooled down to liquid helium temperatures it would also superconduct at a T c of 4.25 K.

Suppression of Magnetic Order before the Superconducting Dome in MnP

NASA Astrophysics Data System (ADS)

Yano, Shin-ichiro; Lançon, Diane; Rønnow, Henrik M.; Hansen, Thomas C.; Ressouche, Eric; Qureshi, Navid; Ouladdiaf, Bachir; Gardner, Jason S.

2018-02-01

We have performed neutron diffraction experiments on the manganese superconductor, MnP, under applied pressure. Higher harmonics of the previously reported double helix (2δ and 3δ) at ambient pressure were observed and a new magnetic phases was discovered as hydrostatic pressure was applied to a polycrystalline sample below the pressure required to induce superconductivity. The double helix magnetic structure is suppressed by 0.7 GPa. A new incommensurate magnetic structure with propagation vector ˜ (0.25,0.25,0.125) was found at 1.5 GPa. The application of higher pressures results in the quenching of the incommensurate phase and broad, diffuse magnetic scattering develops before the superconducting phase. Single crystal studies complement the polycrystalline data confirming the magnetic propagation vector in the low pressure phase.

Time-reversal and rotation symmetry breaking superconductivity in Dirac materials

NASA Astrophysics Data System (ADS)

Chirolli, Luca; de Juan, Fernando; Guinea, Francisco

2017-05-01

We consider mixed symmetry superconducting phases in Dirac materials in the odd-parity channel, where pseudoscalar and vector order parameters can coexist due to their similar critical temperatures when attractive interactions are of a finite range. We show that the coupling of these order parameters to unordered magnetic dopants favors the condensation of time-reversal symmetry breaking (TRSB) phases, characterized by a condensate magnetization, rotation symmetry breaking, and simultaneous ordering of the dopant moments. We find a rich phase diagram of mixed TRSB phases characterized by peculiar bulk quasiparticles, with Weyl nodes and nodal lines, and distinctive surface states. These findings are consistent with recent experiments on NbxBi2Se3 that report evidence of point nodes, nematicity, and TRSB superconductivity induced by Nb magnetic moments.

High-Field Superconductivity on Iron Chalcogenide FeSe

NASA Astrophysics Data System (ADS)

Shi, Anlu; Kitagawa, Shunsaku; Ishida, Kenji; Böhmer, Anna E.; Meingast, Christoph; Wolf, Thomas

2018-06-01

We have performed ac-susceptibility and 77Se-NMR measurements on single-crystal FeSe in the field range from 12.5 to 14.75 T below 1.6 K in order to investigate the superconducting properties of the B phase. Our results show that although superconductivity persists beyond the A-B transition line (H*), the broadening of the 77Se-NMR linewidth arising from the superconducting diamagnetic effect decreases at around H*, suggesting that superconducting character is changed at H*.

A graph-theoretical representation of multiphoton resonance processes in superconducting quantum circuits

DOE PAGES

Jooya, Hossein Z.; Reihani, Kamran; Chu, Shih-I

2016-11-21

We propose a graph-theoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a single-mode resonator in arbitrary coupling strength regimes beyond rotating-wave approximation. We define colored-weighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. In conclusion, the intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields.

High- T c Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, J. P.; Ye, G. Z.; Shahi, P.

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (T c). However, high-T c superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in another high-T c phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-T c superconducting phase transforms into high-T c phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstratingmore » dominant hole carriers in striking contrast to other FeSe-derived high-T c systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviours, evidencing strongly enhanced interband spin fluctuations in the high-T c phase. These results in FeSe highlight similarities with high-T c phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.« less

High- T c Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

DOE PAGES

Sun, J. P.; Ye, G. Z.; Shahi, P.; ...

2017-04-07

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (T c). However, high-T c superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in another high-T c phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-T c superconducting phase transforms into high-T c phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstratingmore » dominant hole carriers in striking contrast to other FeSe-derived high-T c systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviours, evidencing strongly enhanced interband spin fluctuations in the high-T c phase. These results in FeSe highlight similarities with high-T c phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.« less

Superconductivity in metastable phases of phosphorus-hydride compounds under high pressure

NASA Astrophysics Data System (ADS)

Flores Livas, Jose; Amsler, Maximilian; Sanna, Antonio; Heil, Christoph; Boeri, Lilia; Profeta, Gianni; Wolverton, Crhis; Goedecker, Stefan; Gross, E. K. U.

Recently, compressed phosphine was reported to metallize at pressures above 45 GPa, reaching a superconducting transition temperature (Tc) of 100 K at 200 GPa. However, neither the exact composition nor the crystal structure of the superconducting phase have been conclusively determined. In this work the phase diagram of PHn (n = 1 , 2 , 3 , 4 , 5 , 6) was extensively explored by means of ab initio crystal structure prediction methods. The results do not support the existence of thermodynamically stable PHn compounds, which exhibit a tendency for elemental decomposition at high pressure even when vibrational contributions to the free energies are taken into account. Although the lowest energy phases of PH1 , 2 , 3 display Tc's comparable to experiments, it remains questionable if the measured values of Tc can be fully attributed to a phase-pure compound of PHn. This work was done within the NCCR MARVEL project.

Evaluating the phase diagram of superconductors with asymmetric spin populations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mannarelli, Massimo; Nardulli, Giuseppe; Ruggieri, Marco

2006-09-15

The phase diagram of a nonrelativistic fermionic system with imbalanced state populations interacting via a short-range S-wave attractive interaction is analyzed in the mean-field approximation. We determine the energetically favored state for different values of the mismatch between the two Fermi spheres in the weak- and strong-coupling regimes considering both homogeneous and nonhomogeneous superconductive states. We find that the homogeneous superconductive phase persists for values of the population imbalance that increase with increasing coupling strength. In the strong-coupling regime and for large population differences the energetically stable homogeneous phase is characterized by one gapless mode. We also find that themore » inhomogeneous superconductive phase characterized by the condensate {delta}(x){approx}{delta} exp(iq{center_dot}x) is energetically favored in a range of values of the chemical-potential mismatch that shrinks to zero in the strong-coupling regime.« less

Susceptibility measurements on the superconducting properties of Nb-Ge alloys

NASA Technical Reports Server (NTRS)

Rathz, T. J.

1981-01-01

A susceptibility apparatus to measure superconducting properties of samples made in the MSFC Drop Tube was used to measure the transition temperature (Tc) and susceptibilities of Nb and Nb Ge Alloys prepared in bulk spherical (2-4 mm diameter) form using a 32 m drop tube in which containerless low gravity solidification could take place. Results indicate that a drop tube processing environment was beneficial for increasing the Tc of the superconducting phase of the material over that of arc melted material. The increase in Tc is found to be related to the amount of solidification of the total sample that took place before reaching the bottom of the drop tube. In phase and quadrature phase measurements of the specimen's susceptibility indicated that some improvement in homogeneity takes place in drop tube processing. These phase measurements also indicated little or no shielding of a lower Tc phase by a higher Tc filamentary structure.

Evolution of structure and superconductivity in Ba(Ni 1 -xCox)2As2

NASA Astrophysics Data System (ADS)

Eckberg, Chris; Wang, Limin; Hodovanets, Halyna; Kim, Hyunsoo; Campbell, Daniel J.; Zavalij, Peter; Piccoli, Philip; Paglione, Johnpierre

2018-06-01

The effects of Co substitution on Ba (Ni1-xCox) 2As2 (0 ≤x ≤0.251 ) single crystals grown out of Pb flux are investigated via transport, magnetic, and thermodynamic measurements. BaNi2As2 exhibits a first-order tetragonal to triclinic structural phase transition at Ts=137 K upon cooling, and enters a superconducting phase below Tc=0.7 K. The structural phase transition is sensitive to cobalt content and is suppressed completely by x ≥0.133 . The superconducting critical temperature, Tc, increases continuously with x , reaching a maximum of Tc=2.3 K at x =0.083 and then decreases monotonically until superconductivity is no longer observable well into the tetragonal phase. In contrast to similar BaNi2As2 substitutional studies, which show an abrupt change in Tc at the triclinic-tetragonal boundary that extends far into the tetragonal phase, Ba (Ni1-xCox) 2As2 exhibits a domelike phase diagram centered around the zero-temperature tetragonal-triclinic boundary. Together with an anomalously large heat capacity jump Δ Ce/γ T ˜2.2 near optimal doping, the smooth evolution of Tc in the Ba (Ni1-xCox) 2As2 system suggests a mechanism for pairing enhancement other than phonon softening.

Electronic phase diagram of disordered Co doped BaFe2As2-δ

NASA Astrophysics Data System (ADS)

Kurth, F.; Iida, K.; Trommler, S.; Hänisch, J.; Nenkov, K.; Engelmann, J.; Oswald, S.; Werner, J.; Schultz, L.; Holzapfel, B.; Haindl, S.

2013-02-01

Superconducting and normal state transport properties in iron pnictides are sensitive to disorder and impurity scattering. By investigation of Ba(Fe1-xCox)2As2-δ thin films with varying Co concentrations we demonstrate that in the dirty limit the superconducting dome in the electronic phase diagram of Ba(Fe1-xCox)2As2-δ shifts towards lower doping concentrations, which differs significantly from observations in single crystals. We show that especially in the underdoped regime superconducting transition temperatures higher than 27 K are possible.

Nematicity, magnetism and superconductivity in FeSe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohmer, Anna E.; Kreisel, Andreas

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of thesemore » phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. In conclusion, the experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.« less

Nematicity, magnetism and superconductivity in FeSe.

PubMed

Böhmer, Anna E; Kreisel, Andreas

2018-01-17

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c , ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.

Nematicity, magnetism and superconductivity in FeSe

NASA Astrophysics Data System (ADS)

Böhmer, Anna E.; Kreisel, Andreas

2018-01-01

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.

Pressure-induced superconductivity in semimetallic 1 T -TiTe2 and its persistence upon decompression

NASA Astrophysics Data System (ADS)

Dutta, U.; Malavi, P. S.; Sahoo, S.; Joseph, B.; Karmakar, S.

2018-02-01

Pristine 1 T -TiTe2 single crystal has been studied for resistance and magnetoresistance behavior under quasihydrostatic and nonhydrostatic compressions. While the semimetallic state is retained in nearly hydrostatic pressures, small nonhydrostatic compression leads to an abrupt change in low-temperature resistance, a signature of possible charge density wave (CDW) ordering, that eventually collapses above 6.2 GPa. Superconductivity emerges at ˜5 GPa, rapidly increasing to a critical temperature (Tc) of 5.3 K at 12 GPa, irrespective of pressure condition. Pressure studies thus evidence that 1 T -TiTe2 exhibits superconductivity irrespective of the formation of the CDW-like state, implying the existence of phase-separated domains. Most surprisingly, the superconducting state persists upon decompression, establishing a novel phase diagram with suppressed P scale. The pressure quenchable superconductivity, of multiband nature and relatively high upper critical field, makes 1 T -TiTe2 unique among other layered dichalcogenides.

Nematicity, magnetism and superconductivity in FeSe

DOE PAGES

Bohmer, Anna E.; Kreisel, Andreas

2017-12-15

Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of thesemore » phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. In conclusion, the experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.« less

Pressure-induced superconductivity in the iron-based ladder material BaFe2S3.

PubMed

Takahashi, Hiroki; Sugimoto, Akira; Nambu, Yusuke; Yamauchi, Touru; Hirata, Yasuyuki; Kawakami, Takateru; Avdeev, Maxim; Matsubayashi, Kazuyuki; Du, Fei; Kawashima, Chizuru; Soeda, Hideto; Nakano, Satoshi; Uwatoko, Yoshiya; Ueda, Yutaka; Sato, Taku J; Ohgushi, Kenya

2015-10-01

All the iron-based superconductors identified so far share a square lattice composed of Fe atoms as a common feature, despite having different crystal structures. In copper-based materials, the superconducting phase emerges not only in square-lattice structures but also in ladder structures. Yet iron-based superconductors without a square-lattice motif have not been found, despite being actively sought out. Here, we report the discovery of pressure-induced superconductivity in the iron-based spin-ladder material BaFe2S3, a Mott insulator with striped-type magnetic ordering below ∼120 K. On the application of pressure this compound exhibits a metal-insulator transition at about 11 GPa, followed by the appearance of superconductivity below Tc = 14 K, right after the onset of the metallic phase. Our findings indicate that iron-based ladder compounds represent promising material platforms, in particular for studying the fundamentals of iron-based superconductivity.

Control of magnetic, nonmagnetic, and superconducting states in annealed Ca(Fe 1–xCo x)₂As₂

DOE PAGES

Ran, S.; Bud'ko, S. L.; Straszheim, W. E.; ...

2012-06-22

We have grown single-crystal samples of Co substituted CaFe₂As₂ using an FeAs flux and systematically studied the effects of annealing/quenching temperature on the physical properties of these samples. Whereas the as-grown samples (quenched from 960°C) all enter the collapsed tetragonal phase upon cooling, annealing/quenching temperatures between 350 and 800°C can be used to tune the system to low-temperature antiferromagnetic/orthorhomic or superconducting states as well. The progression of the transition temperature versus annealing/quenching temperature (T-T anneal) phase diagrams with increasing Co concentration shows that, by substituting Co, the antiferromagnetic/orthorhombic and the collapsed tetragonal phase lines are separated and bulk superconductivity ismore » revealed. We established a 3D phase diagram with Co concentration and annealing/quenching temperature as two independent control parameters. At ambient pressure, for modest x and T anneal values, the Ca(Fe₁₋ xCox)₂As₂ system offers ready access to the salient low-temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and nonmagnetic/collapsed tetragonal.« less

Direct observation of in-plane anisotropy of the superconducting critical current density in Ba (Fe1-xCox) 2As2 crystals

NASA Astrophysics Data System (ADS)

Hecher, J.; Ishida, S.; Song, D.; Ogino, H.; Iyo, A.; Eisaki, H.; Nakajima, M.; Kagerbauer, D.; Eisterer, M.

2018-01-01

The phase diagram of iron-based superconductors exhibits structural transitions, electronic nematicity, and magnetic ordering, which are often accompanied by an electronic in-plane anisotropy and a sharp maximum of the superconducting critical current density (Jc) near the phase boundary of the tetragonal and the antiferromagnetic-orthorhombic phase. We utilized scanning Hall-probe microscopy to visualize the Jc of twinned and detwinned Ba (Fe1-xCox) 2As2 (x =5 %-8 % ) crystals to compare the electronic normal state properties with superconducting properties. We find that the electronic in-plane anisotropy continues into the superconducting state. The observed correlation between the electronic and the Jc anisotropy agrees qualitatively with basic models, however, the Jc anisotropy is larger than predicted from the resistivity data. Furthermore, our measurements show that the maximum of Jc at the phase boundary does not vanish when the crystals are detwinned. This shows that twin boundaries are not responsible for the large Jc, suggesting an exotic pinning mechanism.

Tunnelling spectroscopy of gate-induced superconductivity in MoS2

NASA Astrophysics Data System (ADS)

Costanzo, Davide; Zhang, Haijing; Reddy, Bojja Aditya; Berger, Helmuth; Morpurgo, Alberto F.

2018-06-01

The ability to gate-induce superconductivity by electrostatic charge accumulation is a recent breakthrough in physics and nanoelectronics. With the exception of LaAlO3/SrTiO3 interfaces, experiments on gate-induced superconductors have been largely confined to resistance measurements, which provide very limited information about the superconducting state. Here, we explore gate-induced superconductivity in MoS2 by performing tunnelling spectroscopy to determine the energy-dependent density of states (DOS) for different levels of electron density n. In the superconducting state, the DOS is strongly suppressed at energy smaller than the gap Δ, which is maximum (Δ 2 meV) for n of 1 × 1014 cm-2 and decreases monotonously for larger n. A perpendicular magnetic field B generates states at E < Δ that fill the gap, but a 20% DOS suppression of superconducting origin unexpectedly persists much above the transport critical field. Conversely, an in-plane field up to 10 T leaves the DOS entirely unchanged. Our measurements exclude that the superconducting state in MoS2 is fully gapped and reveal the presence of a DOS that vanishes linearly with energy, the explanation of which requires going beyond a conventional, purely phonon-driven Bardeen-Cooper-Schrieffer mechanism.

Tuner control system of Spoke012 SRF cavity for C-ADS injector I

NASA Astrophysics Data System (ADS)

Liu, Na; Sun, Yi; Wang, Guang-Wei; Mi, Zheng-Hui; Lin, Hai-Ying; Wang, Qun-Yao; Liu, Rong; Ma, Xin-Peng

2016-09-01

A new tuner control system for spoke superconducting radio frequency (SRF) cavities has been developed and applied to cryomodule I of the C-ADS injector I at the Institute of High Energy Physics, Chinese Academy of Sciences. We have successfully implemented the tuner controller based on Programmable Logic Controller (PLC) for the first time and achieved a cavity tuning phase error of ±0.7° (about ±4 Hz peak to peak) in the presence of electromechanical coupled resonance. This paper presents preliminary experimental results based on the PLC tuner controller under proton beam commissioning. Supported by Proton linac accelerator I of China Accelerator Driven sub-critical System (Y12C32W129)

Coherent Oscillations inside a Quantum Manifold Stabilized by Dissipation

NASA Astrophysics Data System (ADS)

Touzard, S.; Grimm, A.; Leghtas, Z.; Mundhada, S. O.; Reinhold, P.; Axline, C.; Reagor, M.; Chou, K.; Blumoff, J.; Sliwa, K. M.; Shankar, S.; Frunzio, L.; Schoelkopf, R. J.; Mirrahimi, M.; Devoret, M. H.

2018-04-01

Manipulating the state of a logical quantum bit (qubit) usually comes at the expense of exposing it to decoherence. Fault-tolerant quantum computing tackles this problem by manipulating quantum information within a stable manifold of a larger Hilbert space, whose symmetries restrict the number of independent errors. The remaining errors do not affect the quantum computation and are correctable after the fact. Here we implement the autonomous stabilization of an encoding manifold spanned by Schrödinger cat states in a superconducting cavity. We show Zeno-driven coherent oscillations between these states analogous to the Rabi rotation of a qubit protected against phase flips. Such gates are compatible with quantum error correction and hence are crucial for fault-tolerant logical qubits.

Unconventional slowing down of electronic recovery in photoexcited charge-ordered La 1/3Sr 2/3FeO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yi; Hoffman, Jason; Rowland, Clare E.

Ordered electronic phases are intimately related to emerging phenomena such as high Tc superconductivity and colossal magnetoresistance. The coupling of electronic charge with other degrees of freedom such as lattice and spin are of central interest in correlated systems. Their correlations have been intensively studied from femtosecond to picosecond time scales, while the dynamics of ordered electronic phases beyond nanoseconds are usually assumed to follow a trivia thermally driven recovery. Here, we report an unusual slowing down of electronic phases across a first-order phase transition, far beyond thermal relaxation time. Following optical excitation, the recovery time of both transient opticalmore » reflectivity and x-ray diffraction intensity from a charge-ordered superstructure in a La 1/3Sr 2/3FeO 3 thin film increases by orders of magnitude longer than the independently measured lattice cooling time when the sample temperature approaches the phase transition temperature. The combined experimental and theoretical investigations show that the slowing down of electronic recovery corresponds to the pseudo-critical dynamics that originates from magnetic interactions close to a weakly first-order phase transition. As a result, this extraordinary long electronic recovery time exemplifies an interplay of ordered electronic phases with magnetism beyond thermal processes in correlated systems.« less

Unconventional slowing down of electronic recovery in photoexcited charge-ordered La 1/3Sr 2/3FeO 3

DOE PAGES

Zhu, Yi; Hoffman, Jason; Rowland, Clare E.; ...

2018-05-04

Ordered electronic phases are intimately related to emerging phenomena such as high Tc superconductivity and colossal magnetoresistance. The coupling of electronic charge with other degrees of freedom such as lattice and spin are of central interest in correlated systems. Their correlations have been intensively studied from femtosecond to picosecond time scales, while the dynamics of ordered electronic phases beyond nanoseconds are usually assumed to follow a trivia thermally driven recovery. Here, we report an unusual slowing down of electronic phases across a first-order phase transition, far beyond thermal relaxation time. Following optical excitation, the recovery time of both transient opticalmore » reflectivity and x-ray diffraction intensity from a charge-ordered superstructure in a La 1/3Sr 2/3FeO 3 thin film increases by orders of magnitude longer than the independently measured lattice cooling time when the sample temperature approaches the phase transition temperature. The combined experimental and theoretical investigations show that the slowing down of electronic recovery corresponds to the pseudo-critical dynamics that originates from magnetic interactions close to a weakly first-order phase transition. As a result, this extraordinary long electronic recovery time exemplifies an interplay of ordered electronic phases with magnetism beyond thermal processes in correlated systems.« less

Classification of "multipole" superconductivity in multiorbital systems and its implications

NASA Astrophysics Data System (ADS)

Nomoto, T.; Hattori, K.; Ikeda, H.

2016-11-01

Motivated by a growing interest in multiorbital superconductors with spin-orbit interactions, we perform the group-theoretical classification of various unconventional superconductivity emerging in symmorphic O , D4, and D6 space groups. The generalized Cooper pairs, which we here call "multipole" superconductivity, possess spin-orbital coupled (multipole) degrees of freedom, instead of the conventional spin singlet/triplet in single-orbital systems. From the classification, we obtain the following key consequences, which have never been focused in the long history of research in this field: (1) A superconducting gap function with Γ9⊗Γ9 in D6 possesses nontrivial momentum dependence different from the usual spin-1/2 classification. (2) Unconventional gap structure can be realized in the BCS approximation of purely local (onsite) interactions irrespective of attraction/repulsion. It implies the emergence of an electron-phonon (e-ph) driven unconventional superconductivity. (3) Reflecting symmetry of orbital basis functions there appear not symmetry protected but inevitable line nodes/gap minima, and thus, anisotropic s -wave superconductivity can be naturally explained even in the absence of competing fluctuations.

Enhancement and sign change of magnetic correlations in a driven quantum many-body system

NASA Astrophysics Data System (ADS)

Görg, Frederik; Messer, Michael; Sandholzer, Kilian; Jotzu, Gregor; Desbuquois, Rémi; Esslinger, Tilman

2018-01-01

Periodic driving can be used to control the properties of a many-body state coherently and to realize phases that are not accessible in static systems. For example, exposing materials to intense laser pulses makes it possible to induce metal-insulator transitions, to control magnetic order and to generate transient superconducting behaviour well above the static transition temperature. However, pinning down the mechanisms underlying these phenomena is often difficult because the response of a material to irradiation is governed by complex, many-body dynamics. For static systems, extensive calculations have been performed to explain phenomena such as high-temperature superconductivity. Theoretical analyses of driven many-body Hamiltonians are more challenging, but approaches have now been developed, motivated by recent observations. Here we report an experimental quantum simulation in a periodically modulated hexagonal lattice and show that antiferromagnetic correlations in a fermionic many-body system can be reduced, enhanced or even switched to ferromagnetic correlations (sign reversal). We demonstrate that the description of the many-body system using an effective Floquet-Hamiltonian with a renormalized tunnelling energy remains valid in the high-frequency regime by comparing the results to measurements in an equivalent static lattice. For near-resonant driving, the enhancement and sign reversal of correlations is explained by a microscopic model of the system in which the particle tunnelling and magnetic exchange energies can be controlled independently. In combination with the observed sufficiently long lifetimes of the correlations in this system, periodic driving thus provides an alternative way of investigating unconventional pairing in strongly correlated systems experimentally.

Enhancement and sign change of magnetic correlations in a driven quantum many-body system.

PubMed

Görg, Frederik; Messer, Michael; Sandholzer, Kilian; Jotzu, Gregor; Desbuquois, Rémi; Esslinger, Tilman

2018-01-24

Periodic driving can be used to control the properties of a many-body state coherently and to realize phases that are not accessible in static systems. For example, exposing materials to intense laser pulses makes it possible to induce metal-insulator transitions, to control magnetic order and to generate transient superconducting behaviour well above the static transition temperature. However, pinning down the mechanisms underlying these phenomena is often difficult because the response of a material to irradiation is governed by complex, many-body dynamics. For static systems, extensive calculations have been performed to explain phenomena such as high-temperature superconductivity. Theoretical analyses of driven many-body Hamiltonians are more challenging, but approaches have now been developed, motivated by recent observations. Here we report an experimental quantum simulation in a periodically modulated hexagonal lattice and show that antiferromagnetic correlations in a fermionic many-body system can be reduced, enhanced or even switched to ferromagnetic correlations (sign reversal). We demonstrate that the description of the many-body system using an effective Floquet-Hamiltonian with a renormalized tunnelling energy remains valid in the high-frequency regime by comparing the results to measurements in an equivalent static lattice. For near-resonant driving, the enhancement and sign reversal of correlations is explained by a microscopic model of the system in which the particle tunnelling and magnetic exchange energies can be controlled independently. In combination with the observed sufficiently long lifetimes of the correlations in this system, periodic driving thus provides an alternative way of investigating unconventional pairing in strongly correlated systems experimentally.

Peculiar phase diagram with isolated superconducting regions in ThFeAsN1-x O x.

PubMed

Li, Bai-Zhuo; Wang, Zhi-Cheng; Wang, Jia-Lu; Zhang, Fu-Xiang; Wang, Dong-Ze; Zhang, Feng-Yuan; Sun, Yu-Ping; Jing, Qiang; Zhang, Hua-Fu; Tan, Shu-Gang; Li, Yu-Ke; Feng, Chun-Mu; Mei, Yu-Xue; Wang, Cao; Cao, Guang-Han

2018-06-27

ThFeAsN 1-x O x ([Formula: see text]) system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at [Formula: see text] K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T c value decreases rapidly to below 2 K for [Formula: see text], and surprisingly, superconductivity re-appears in the range of [Formula: see text] with a maximum [Formula: see text] of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is [Formula: see text], which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN 1-x O x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

119Sn-NMR investigations on superconducting Ca 3Ir 4Sn 13: Evidence for multigap superconductivity

DOE PAGES

Sarkar, R.; Petrovic, C.; Bruckner, F.; ...

2015-09-25

In this study, we report bulk superconductivity (SC) in Ca 3Ir 4Sn 13 by means of 119Sn nuclear magnetic resonance (NMR) experiments. Two classical signatures of BCS superconductivity in spin-lattice relaxation rate (1/T 1), namely the Hebel–Slichter coherence peak just below the T c, and the exponential decay in the superconducting phase, are evident. The noticeable decrease of 119Sn Knight shift below T c indicates spin-singlet superconductivity. The temperature dependence of the spin-lattice relaxation rate 119(1/T 1) is convincingly described by the multigap isotropic superconducting gap. NMR experiments do not witness any sign of enhanced spin fluctuations.

Perturbation theory of a superconducting 0 - π impurity quantum phase transition.

PubMed

Žonda, M; Pokorný, V; Janiš, V; Novotný, T

2015-03-06

A single-level quantum dot with Coulomb repulsion attached to two superconducting leads is studied via the perturbation expansion in the interaction strength. We use the Nambu formalism and the standard many-body diagrammatic representation of the impurity Green functions to formulate the Matsubara self-consistent perturbation expansion. We show that at zero temperature second order of the expansion in its spin-symmetric version yields a nearly perfect agreement with the numerically exact calculations for the position of the 0 - π phase boundary at which the Andreev bound states reach the Fermi energy as well as for the values of single-particle quantities in the 0-phase. We present results for phase diagrams, level occupation, induced local superconducting gap, Josephson current, and energy of the Andreev bound states with the precision surpassing any (semi)analytical approaches employed thus far.

Macroscopic phase separation of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-x Se x revealed by μSR.

PubMed

Nikitin, A M; Grinenko, V; Sarkar, R; Orain, J-C; Salis, M V; Henke, J; Huang, Y K; Klauss, H-H; Amato, A; Visser, A de

2017-12-12

The compound Sr 0.5 Ce 0.5 FBiS 2 belongs to the intensively studied family of layered BiS 2 superconductors. It attracts special attention because superconductivity at T sc  = 2.8 K was found to coexist with local-moment ferromagnetic order with a Curie temperature T C  = 7.5 K. Recently it was reported that upon replacing S by Se T C drops and ferromagnetism becomes of an itinerant nature. At the same time T sc increases and it was argued superconductivity coexists with itinerant ferromagnetism. Here we report a muon spin rotation and relaxation study (μSR) conducted to investigate the coexistence of superconductivity and ferromagnetic order in Sr 0.5 Ce 0.5 FBiS 2-x Se x with x = 0.5 and 1.0. By inspecting the muon asymmetry function we find that both phases do not coexist on the microscopic scale, but occupy different sample volumes. For x = 0.5 and x = 1.0 we find a ferromagnetic volume fraction of ~8 % and ~30 % at T = 0.25 K, well below T C  = 3.4 K and T C  = 3.3 K, respectively. For x = 1.0 (T sc  = 2.9 K) the superconducting phase occupies most (~64 %) of the remaining sample volume, as shown by transverse field experiments that probe the Gaussian damping due to the vortex lattice. We conclude ferromagnetism and superconductivity are macroscopically phase separated.

Transport spectroscopy of induced superconductivity in the three-dimensional topological insulator HgTe

NASA Astrophysics Data System (ADS)

Wiedenmann, Jonas; Liebhaber, Eva; Kübert, Johannes; Bocquillon, Erwann; Burset, Pablo; Ames, Christopher; Buhmann, Hartmut; Klapwijk, Teun M.; Molenkamp, Laurens W.

2017-10-01

The proximity-induced superconducting state in the three-dimensional topological insulator HgTe has been studied using electronic transport of a normal metal-superconducting point contact as a spectroscopic tool (Andreev point-contact spectroscopy). By analyzing the conductance as a function of voltage for various temperatures, magnetic fields, and gate voltages, we find evidence, in equilibrium, for an induced order parameter in HgTe of 70 µeV and a niobium order parameter of 1.1 meV. To understand the full conductance curve as a function of applied voltage we suggest a non-equilibrium-driven transformation of the quantum transport process where the relevant scattering region and equilibrium reservoirs change with voltage. This change implies that the spectroscopy probes the superconducting correlations at different positions in the sample, depending on the bias voltage.

Circulation and Directional Amplification in the Josephson Parametric Converter

NASA Astrophysics Data System (ADS)

Hatridge, Michael

Nonreciprocal transport and directional amplification of weak microwave signals are fundamental ingredients in performing efficient measurements of quantum states of flying microwave light. This challenge has been partly met, as quantum-limited amplification is now regularly achieved with parametrically-driven, Josephson-junction based superconducting circuits. However, these devices are typically non-directional, requiring external circulators to separate incoming and outgoing signals. Recently this limitation has been overcome by several proposals and experimental realizations of both directional amplifiers and circulators based on interference between several parametric processes in a single device. This new class of multi-parametrically driven devices holds the promise of achieving a variety of desirable characteristics simultaneously- directionality, reduced gain-bandwidth constraints and quantum-limited added noise, and are good candidates for on-chip integration with other superconducting circuits such as qubits.

Hysteretic Flux Response and Nondegenerate Gain of Flux-Driven Josephson Parametric Amplifiers

NASA Astrophysics Data System (ADS)

Pogorzalek, Stefan; Fedorov, Kirill G.; Zhong, Ling; Goetz, Jan; Wulschner, Friedrich; Fischer, Michael; Eder, Peter; Xie, Edwar; Inomata, Kunihiro; Yamamoto, Tsuyoshi; Nakamura, Yasunobu; Marx, Achim; Deppe, Frank; Gross, Rudolf

2017-08-01

Josephson parametric amplifiers (JPAs) have become key devices in quantum science and technology with superconducting circuits. In particular, they can be utilized as quantum-limited amplifiers or as a source of squeezed microwave fields. Here, we report on the detailed measurements of five flux-driven JPAs exhibiting a hysteretic dependence of the resonant frequency on the applied magnetic flux. We model the measured characteristics by numerical simulations based on the two-dimensional potential landscape of the dc superconducting quantum interference devices, which provide the JPA nonlinearity for a nonzero screening parameter βL>0 and demonstrate excellent agreement between the numerical results and the experimental data. Furthermore, we study the nondegenerate response of different JPAs and accurately describe the experimental results with our theory.

Fe-vacancy and superconductivity in FeSe-based superconductors

NASA Astrophysics Data System (ADS)

Wang, C. H.; Chen, T. K.; Chang, C. C.; Lee, Y. C.; Wang, M. J.; Huang, K. C.; Wu, P. M.; Wu, M. K.

2018-06-01

This review summarizes recent advancements in FeSe and related systems. The FeSe and related superconductors are currently receiving considerable attention for the high Tcs observed and for many similar features to the high Tc cuprate superconductors. These similarities suggest that understanding the FeSe based compounds could potentially help our understanding of the cuprates. We shall first review the common features observed in the FeSe-based system. It was found that with a careful control of material synthesizing processes, numerous rich phases have been observed in the FeSe-based system. Detailed studies show that the Fe-vacancy ordered phases found in the FeSe based compounds, which are non-superconducting Mott insulators, are the parent compounds of the superconductors. Superconductivity emerges from the parent phases by disordering the Fe vacancy order, often by a simple annealing treatment. Recent high temperature X-ray diffraction experiments show that the degree of structural distortion associated with the disorder of Fe-vacancy is closely related to volume fraction of the superconductivity observed. These results suggest the strong lattice to spin coupling are important for the occurrence of superconductivity in FeSe based superconductors.

Influence of chemical etching and heat-treatment on the structure and superconducting properties of YGdBCO coated conductors

NASA Astrophysics Data System (ADS)

Wang, M. J.; Wang, W. T.; Liu, L.; Huo, B. L.; Yang, X.; Cheng, C. H.; Zhao, Y.

2017-07-01

The effects of chemical etching (to remove metal stabilizer layers) and novel heat treatment process on the structure and superconducting properties of YGdBCO CCs for preparing a superconducting joint were studied. After removing the Cu stabilizer layer with the FeCl3 alcohol solution, the mixture of NH3.H2O and H2O2 was used to remove Ag stabilizer layer with various conditions such as etching temperature and time. Due to the decomposition of YGdBCO at high temperature, few secondary phases such as YGd211 and BaCuO2 were detected after partial melting. It is interested to note that these secondary phases were not detected after recrystallization at a relatively lower temperature. According to the pseudo-binary phase diagrams of Lee [1], the peritectic reaction of YGd211 was occurred and the YGd123 particle was aligned again along c-axis. Additionally, the oxygenation annealing process was indispensable to restore the degraded superconducting properties of YGdBCO CCs caused by the oxygen diffusion out of itself during heat treatment process. The above results were favorable to prepare the superconducting joint of YGdBCO CCs in our future work.

Superconductivity, phase separation, and charge-transfer instability in the U = infinity limit of the three-band model of the CuO sub 2 planes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grilli, M.; Raimondi, R.; Castellani, C.

1991-07-08

The {ital U}={infinity} limit of the three-band Hubbard model with nearest-neighbor repulsion {ital V} is studied using the slave-boson approach and the large-{ital N} expansion technique to order 1/{ital N}. A charge-transfer instability is found as in weak-coupling theory. The charge-transfer instability is always associated with a diverging compressibility leading to a phase separation. Near the phase-separation, charge-transfer-instability region we find superconducting instabilities in the {ital s}- and {ital d}-wave channel. The requirement for superconductivity is that {ital V} be on the scale of the Cu-O hopping as suggested by Varma, Schmitt-Rink, and Abrahams.

Development of high Tc (greater than 100 K) Bi, Tl and Y-based materials as superconducting circuit elements

NASA Technical Reports Server (NTRS)

Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

1993-01-01

Results on this project over the past three years have shown that the Bi and Tl-based superconducting materials in bulk form are noticeably different from the Y-based 123 material in that superconductivity is considerably harder to achieve, maintain and reproduce. This is due primarily to the difficulty in obtaining the higher Tc phase in pure form since it commonly co-exists with other undesirable, lower Tc phases. In particular, it has been found that long processing times for calcining and firing (20 - 200 hrs.) and close control of temperatures which are very near the melting point are required in order to obtain higher proportions of the desirable, high Tc (2223) phase.

Publisher's Note: High-temperature superconductivity stabilized by electron-hole interband coupling in collapsed tetragonal phase of KFe 2 As 2 under high pressure [Phys. Rev. B 91 , 060508(R) (2015)

DOE PAGES

Nakajima, Yasuyuki; Wang, Renxiong; Metz, Tristin; ...

2015-03-09

Here, we report a high-pressure study of simultaneous low-temperature electrical resistivity and Hall effect measurements on high quality single-crystalline KFe 2As 2 using designer diamond anvil cell techniques with applied pressures up to 33 GPa. In the low pressure regime, we show that the superconducting transition temperature T c finds a maximum onset value of 7 K near 2 GPa, in contrast to previous reports that find a minimum T c and reversal of pressure dependence at this pressure. Upon applying higher pressures, this T c is diminished until a sudden drastic enhancement occurs coincident with a first-order structural phasemore » transition into a collapsed tetragonal phase. The appearance of a distinct superconducting phase above 13 GPa is also accompanied by a sudden reversal of dominant charge carrier sign, from hole- to electron-like, which agrees with our band calculations predicting the emergence of an electron pocket and diminishment of hole pockets upon Fermi surface reconstruction. Our results suggest the high-temperature superconducting phase in KFe 2As 2 is substantially enhanced by the presence of nested electron and hole pockets, providing the key ingredient of high-T c superconductivity in iron pnictide superconductors.« less

Superconducting thermal neutron detectors

NASA Astrophysics Data System (ADS)

Merlo, V.; Pietropaolo, A.; Celentano, G.; Cirillo, M.; Lucci, M.; Ottaviani, I.; Salvato, M.; Scherillo, A.; Schooneveld, E. M.; Vannozzi, A.

2016-09-01

A neutron detection concept is presented that is based on superconductive niobium nitride (NbN) strips coated by a boron (B) layer. The working principle is well described by a hot spot mechanism: upon the occurrence of the nuclear reactions n + 10B → α + 7Li + 2.8 MeV, the energy released by the secondary particles into the strip induces a superconducting-normal state transition. The latter is recognized as a voltage signal which is the evidence of the incident neutron. The above described detection principle has been experimentally assessed and verified by irradiating the samples with a pulsed neutron beam at the ISIS spallation neutron source (UK). It is found that the boron coated superconducting strips, kept at a temperature T below 11K and current-biased below the critical current IC, are driven into the normal state upon thermal neutron irradiation. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed and compared to those of a borated Nb superconducting strip.

Drive the Dirac electrons into Cooper pairs in SrxBi2Se3

PubMed Central

Du, Guan; Shao, Jifeng; Yang, Xiong; Du, Zengyi; Fang, Delong; Wang, Jinghui; Ran, Kejing; Wen, Jinsheng; Zhang, Changjin; Yang, Huan; Zhang, Yuheng; Wen, Hai-Hu

2017-01-01

Topological superconductors are a very interesting and frontier topic in condensed matter physics. Despite the tremendous efforts in exploring topological superconductivity, its presence is however still under heavy debate. The Dirac electrons have been proven to exist on the surface of a topological insulator. It remains unclear whether and how the Dirac electrons fall into Cooper pairing in an intrinsic superconductor with the topological surface states. Here we show the systematic study of scanning tunnelling microscope/spectroscopy on the possible topological superconductor SrxBi2Se3. We first demonstrate that only the intercalated Sr atoms can induce superconductivity. Then we show the full superconducting gaps without any in-gap density of states as expected theoretically for a bulk topological superconductor. Finally, we find that the surface Dirac electrons will simultaneously condense into the superconducting state within the superconducting gap. This vividly demonstrates how the surface Dirac electrons are driven into Cooper pairs. PMID:28198378

Phase competition and anomalous thermal evolution in high-temperature superconductors

NASA Astrophysics Data System (ADS)

Yu, Zuo-Dong; Zhou, Yuan; Yin, Wei-Guo; Lin, Hai-Qing; Gong, Chang-De

2017-07-01

The interplay of competing orders is relevant to high-temperature superconductivity known to emerge upon suppression of a parent antiferromagnetic order typically via charge doping. How such interplay evolves at low temperature—in particular at what doping level the zero-temperature quantum critical point (QCP) is located—is still elusive because it is masked by the superconducting state. The QCP had long been believed to follow a smooth extrapolation of the characteristic temperature T* for the strange normal state well above the superconducting transition temperature. However, recently the T* within the superconducting dome was reported to unexpectedly exhibit back-bending likely in the cuprate Bi2Sr2CaCu2O8 +δ . Here we show that the original and revised phase diagrams can be understood in terms of weak and moderate competitions, respectively, between superconductivity and a pseudogap state such as d -density or spin-density wave, based on both Ginzburg-Landau theory and the realistic t -t'-t''-J -V model for the cuprates. We further found that the calculated temperature and doping-level dependence of the quasiparticle spectral gap and Raman response qualitatively agrees with the experiments. In particular, the T* back-bending can provide a simple explanation of the observed anomalous two-step thermal evolution dominated by the superconducting gap and the pseudogap, respectively. Our results imply that the revised phase diagram is likely to take place in high-temperature superconductors.

Low cost, formable, high T(sub c) superconducting wire

NASA Technical Reports Server (NTRS)

Smialek, James L. (Inventor)

1991-01-01

A ceramic superconductivity part such as a wire is produced through the partial oxidation of a specially formulated copper alloy in the core. The alloys contain low level quantities of rare earth and alkaline earth dopant elements. Upon oxidation at high temperature, superconducting oxide phases are formed as a thin film.

Unconventional superconductivity and quantum criticality in the heavy fermions CeIrSi3 and CeRhSi3

NASA Astrophysics Data System (ADS)

Landaeta, J. F.; Subero, D.; Catalá, D.; Taylor, S. V.; Kimura, N.; Settai, R.; Īnuki, Y.; Sigrist, M.; Bonalde, I.

2018-03-01

In most strongly correlated electron systems superconductivity appears nearby a magnetic quantum critical point (QCP) which is believed to cause unconventional behaviors. In order to explore this physics, we present here a study of the heavy-fermion superconductors CeIrSi3 and CeRhSi3 carried out using a newly developed system for high-resolution magnetic penetration-depth measurements under pressure. Superconductivity in CeIrSi3 shows a change from an excitation spectrum with a line-nodal gap to one which is entirely gapful when pressure is close but not yet at the QCP. In contrast, CeRhSi3 does not possess a T =0 quantum phase transition and the superconducting phase remains for all accessible pressures with a nodal gap. Combining both results suggests that in these compounds unconventional superconducting behaviors are rather connected with the coexisting antiferromagnetic order. This study provides another viewpoint on the interplay of superconductivity, magnetism, and quantum criticality in CeIrSi3 and CeRhSi3 and maybe in other heavy fermions.

Pressure-induced zigzag phosphorus chain and superconductivity in boron monophosphide.

PubMed

Zhang, Xinyu; Qin, Jiaqian; Liu, Hanyu; Zhang, Shiliang; Ma, Mingzhen; Luo, Wei; Liu, Riping; Ahuja, Rajeev

2015-03-04

We report on the prediction of the zinc-blende structure BP into a novel C2/m phase from 113 to 208 GPa which possesses zigzag phosphorus chain structure, followed by another P42/mnm structure above 208 GPa above using the particle-swarm search method. Strong electron-phonon coupling λ in compressed BP is found, in particular for C2/m phase with the zigzag phosphorus chain, which has the highest λ (0.56-0.61) value among them, leading to its high superconducting critical temperature Tc (9.4 K-11.5 K), which is comparable with the 4.5 K to 13 K value of black phosphorus phase I (orthorhombic, Cmca). This is the first system in the boron phosphides which shows superconductivity from the present theoretical calculations. Our results show that pressure-induced zigzag phosphorus chain in BP exhibit higher superconducting temperature TC, opening a new route to search and design new superconductor materials with zigzag phosphorus chains.

Giant phonon anomaly associated with superconducting fluctuations in the pseudogap phase of cuprates

DOE PAGES

Liu, Ye-Hua; Konik, Robert M.; Rice, T. M.; ...

2016-01-20

The pseudogap in underdoped cuprates leads to significant changes in the electronic structure, and was later found to be accompanied by anomalous fluctuations of superconductivity and certain lattice phonons. Here we propose that the Fermi surface breakup due to the pseudogap, leads to a breakup of the pairing order into two weakly coupled sub-band amplitudes, and a concomitant low energy Leggett mode due to phase fluctuations between them. This increases the temperature range of superconducting fluctuations containing an overdamped Leggett mode. In this range inter-sub-band phonons show strong damping due to resonant scattering into an intermediate state with a pairmore » of overdamped Leggett modes. In the ordered state, the Leggett mode develops a finite energy, changing the anomalous phonon damping into an anomaly in the dispersion. Finally, this proposal explains the intrinsic connection between the anomalous pseudogap phase, enhanced superconducting fluctuations and giant anomalies in the phonon spectra.« less

Enhancement of superconductivity under pressure and the magnetic phase diagram of tantalum disulfide single crystals

PubMed Central

Abdel-Hafiez, M.; Zhao, X.-M.; Kordyuk, A. A.; Fang, Y.-W.; Pan, B.; He, Z.; Duan, C.-G.; Zhao, J.; Chen, X.-J.

2016-01-01

In low-dimensional electron systems, charge density waves (CDW) and superconductivity are two of the most fundamental collective quantum phenomena. For all known quasi-two-dimensional superconductors, the origin and exact boundary of the electronic orderings and superconductivity are still attractive problems. Through transport and thermodynamic measurements, we report on the field-temperature phase diagram in 2H-TaS2 single crystals. We show that the superconducting transition temperature (Tc) increases by one order of magnitude from temperatures at 0.98 K up to 9.15 K at 8.7 GPa when the Tc becomes very sharp. Additionally, the effects of 8.7 GPa illustrate a suppression of the CDW ground state, with critically small Fermi surfaces. Below the Tc the lattice of magnetic flux lines melts from a solid-like state to a broad vortex liquid phase region. Our measurements indicate an unconventional s-wave-like picture with two energy gaps evidencing its multi-band nature. PMID:27534898

Mesoscopic superconductivity and high spin polarization coexisting at metallic point contacts on Weyl semimetal TaAs

PubMed Central

Aggarwal, Leena; Gayen, Sirshendu; Das, Shekhar; Kumar, Ritesh; Süß, Vicky; Felser, Claudia; Shekhar, Chandra; Sheet, Goutam

2017-01-01

A Weyl semimetal is a topologically non-trivial phase of matter that hosts mass-less Weyl fermions, the particles that remained elusive for more than 80 years since their theoretical discovery. The Weyl semimetals exhibit unique transport properties and remarkably high surface spin polarization. Here we show that a mesoscopic superconducting phase with critical temperature Tc=7 K can be realized by forming metallic point contacts with silver (Ag) on single crystals of TaAs, while neither Ag nor TaAs are superconductors. Andreev reflection spectroscopy of such point contacts reveals a superconducting gap of 1.2 meV that coexists with a high transport spin polarization of 60% indicating a highly spin-polarized supercurrent flowing through the point contacts on TaAs. Therefore, apart from the discovery of a novel mesoscopic superconducting phase, our results also show that the point contacts on Weyl semimetals are potentially important for applications in spintronics. PMID:28071685

Inhomogeneities and superconductivity in poly-phase Fe-Se-Te systems

NASA Astrophysics Data System (ADS)

Hartwig, S.; Schäfer, N.; Schulze, M.; Landsgesell, S.; Abou-Ras, D.; Blum, Ch. G. F.; Wurmehl, S.; Sokolowski, A.; Büchner, B.; Prokeš, K.

2018-02-01

The impact of synthesis conditions, post-preparation heating procedure, aging and influence of pressure on the superconducting properties of FeSe0.4Te0.6 crystals is reported. Two FeSe0.4Te0.6 single crystals were used in the study, prepared from stoichiometric melt but cooled down with very different cooling rates, and investigated using magnetic bulk and electrical-resistivity methods. The fast-cooled crystal contains large inclusions of Fe3Se2.1Te1.8 and exhibits bulk superconductivity in its as-prepared state, while the other is homogeneous and shows only traces of superconductivity. AC susceptibility measurements under hydrostatic pressure show that the superconducting transition temperature of the inhomogeneous crystal increases from 12.3 K at ambient pressure to Tsc = 17.9 K at 9 kbar. On the other hand, neither pressure nor mechanically-induced stress is sufficient to induce superconductivity in the homogeneous crystal. However, an additional heat treatment at 673 K followed by fast cooling down and/or long-term aging at ambient conditions leads to the appearance of bulk superconductivity also in the latter sample. This sample remains homogeneous on a scale down to few μm but shows an additional magnetic phase transition around 130 K suggesting that it must be inhomogeneous. For comparison also Fe3Se2.1Te1.8 polycrystals have been prepared and their magnetic properties have been studied. It appears that this phase is not superconducting by itself. It is concluded that nano-scale inhomogeneities that appear in the FeSexTe1-x system due to a spinodal decomposition in the solid state are necessary for bulk superconductivity, possibly due to minor changes in the crystal structure and microstructure. Macroscopic inclusions quenched by fast cooling from high temperatures lead obviously to strain and hence variations in the lattice constants, an effect that is further supported by application of pressure/stress.

Multiband superconductivity in BiS2-based layered compounds

NASA Astrophysics Data System (ADS)

Griffith, M. A.; Puel, T. O.; Continentino, M. A.; Martins, G. B.

2017-08-01

A mean-field treatment is presented of a square lattice two-orbital-model for \\text{Bi}{{\\text{S}}2} taking into account intra- and inter-orbital superconductivity. A rich phase diagram involving both types of superconductivity is presented as a function of the ratio between the couplings of electrons in the same and different orbitals (η ={{\\text{V}}\\text{XX}}/{{\\text{V}}\\text{XY}} ) and electron doping x. With the help of a quantity we call orbital-mixing ratio, denoted as R(φ ) , the phase diagram is analyzed using a simple and intuitive picture based on how R(φ ) varies as electron doping increases. The predictive power of R(φ ) suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.

Tunneling probe of fluctuating superconductivity in disordered thin films

NASA Astrophysics Data System (ADS)

Dentelski, David; Frydman, Aviad; Shimshoni, Efrat; Dalla Torre, Emanuele G.

2018-03-01

Disordered thin films close to the superconductor-insulator phase transition (SIT) hold the key to understanding quantum phase transition in strongly correlated materials. The SIT is governed by superconducting quantum fluctuations, which can be revealed, for example, by tunneling measurements. These experiments detect a spectral gap, accompanied by suppressed coherence peaks, on both sides of the transition. Here we describe the insulating side in terms of a fluctuating superconducting field with finite-range correlations. We perform a controlled diagrammatic resummation and derive analytic expressions for the tunneling differential conductance. We find that short-range superconducting fluctuations suppress the coherence peaks even in the presence of long-range correlations. Our approach offers a quantitative description of existing measurements on disordered thin films and accounts for tunneling spectra with suppressed coherence peaks.

Phonons and superconductivity in fcc and dhcp lanthanum

NASA Astrophysics Data System (ADS)

Baǧcı, S.; Tütüncü, H. M.; Duman, S.; Srivastava, G. P.

2010-04-01

We have investigated the structural and electronic properties of lanthanum in the face-centered-cubic (fcc) and double hexagonal-close-packed (dhcp) phases using a generalized gradient approximation of the density functional theory and the ab initio pseudopotential method. It is found that double hexagonal-close-packed is the more stable phase for lanthanum. Differences in the density of states at the Fermi level between these two phases are pointed out and discussed in detail. Using the calculated lattice constant and electronic band structure for both phases, a linear response approach based on the density functional theory has been applied to study phonon modes, polarization characteristics of phonon modes, and electron-phonon interaction. Our phonon results show a softening behavior of the transverse acoustic branch along the Γ-L direction and the Γ-M direction for face-centered-cubic and double hexagonal-close-packed phases, respectively. Thus, the transverse-phonon linewidth shows a maximum at the zone boundary M(L) for the double hexagonal-close-packed phase (face-centered-cubic phase), where the transverse-phonon branch exhibits a dip. The electron-phonon coupling parameter λ is found to be 0.97 (1.06) for the double hexagonal-close-packed phase (face-centered-cubic phase), and the superconducting critical temperature is estimated to be 4.87 (dhcp) and 5.88 K (fcc), in good agreement with experimental values of around 5.0 (dhcp) and 6.0 K (fcc). A few superconducting parameters for the double hexagonal-close-packed phase have been calculated and compared with available theoretical and experimental results. Furthermore, the calculated superconducting parameters for both phases are compared between each other in detail.

Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS

DOE PAGES

Lai, Xiaofang; Liu, Ying; Lu, Xujie; ...

2016-08-08

Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change ofmore » anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Lastly, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS.« less

Pressure-induced phase transitions and correlation between structure and superconductivity in iron-based superconductor Ce(O(0.84)F(0.16))FeAs.

PubMed

Zhao, Jinggeng; Liu, Haozhe; Ehm, Lars; Dong, Dawei; Chen, Zhiqiang; Liu, Qingqing; Hu, Wanzheng; Wang, Nanlin; Jin, Changqing

2013-07-15

High-pressure angle-dispersive X-ray diffraction experiments on iron-based superconductor Ce(O(0.84)F(0.16))FeAs were performed up to 54.9 GPa at room temperature. A tetragonal to tetragonal isostructural phase transition starts at about 13.9 GPa, and a new high-pressure phase has been found above 33.8 GPa. At pressures above 19.9 GPa, Ce(O(0.84)F(0.16))FeAs completely transforms to a high-pressure tetragonal phase, which remains in the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure tetragonal phase. The structure analysis shows a discontinuity in the pressure dependences of the Fe-As and Ce-(O, F) bond distances, as well as the As-Fe-As and Ce-(O, F)-Ce bond angles in the transition region, which correlates with the change in T(c) of this compound upon compression. The isostructural phase transition in Ce(O(0.84)F(0.16))FeAs leads to a drastic drop in the superconducting transition temperature T(c) and restricts the superconductivity at low temperature. For the 1111-type iron-based superconductors, the structure evolution and following superconductivity changes under compression are related to the radius of lanthanide cations in the charge reservoir layer.

Two-dimensional limit of crystalline order in perovskite membrane films

PubMed Central

Hong, Seung Sae; Yu, Jung Ho; Lu, Di; Marshall, Ann F.; Hikita, Yasuyuki; Cui, Yi; Hwang, Harold Y.

2017-01-01

Long-range order and phase transitions in two-dimensional (2D) systems—such as magnetism, superconductivity, and crystallinity—have been important research topics for decades. The issue of 2D crystalline order has reemerged recently, with the development of exfoliated atomic crystals. Understanding the dimensional limit of crystalline phases, with different types of bonding and synthetic techniques, is at the foundation of low-dimensional materials design. We study ultrathin membranes of SrTiO3, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released after synthesis by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO3 membrane lattice collapses below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length is analogous to the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) transition. The transition is likely driven by chemical bond breaking at the 2D layer-3D bulk interface, defining an effective dimensional phase boundary for coherent crystalline lattices. PMID:29167822

Two-dimensional limit of crystalline order in perovskite membrane films

DOE PAGES

Hong, Seung Sae; Yu, Jung Ho; Lu, Di; ...

2017-11-17

Long-range order and phase transitions in two-dimensional (2D) systems—such as magnetism, superconductivity, and crystallinity—have been important research topics for decades. The issue of 2D crystalline order has reemerged recently, with the development of exfoliated atomic crystals. Understanding the dimensional limit of crystalline phases, with different types of bonding and synthetic techniques, is at the foundation of low-dimensional materials design. We study ultrathin membranes of SrTiO 3, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released after synthesis by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO 3 membrane lattice collapsesmore » below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length is analogous to the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) transition. Finally, the transition is likely driven by chemical bond breaking at the 2D layer-3D bulk interface, defining an effective dimensional phase boundary for coherent crystalline lattices.« less

Ginzburg-Landau Theory for Flux Phase and Superconductivity in t-J Model

NASA Astrophysics Data System (ADS)

Kuboki, Kazuhiro

2018-02-01

Ginzburg-Landau (GL) equations and GL free energy for flux phase and superconductivity are derived microscopically from the t-J model on a square lattice. Order parameter (OP) for the flux phase has direct coupling to a magnetic field, in contrast to the superconducting OP which has minimal coupling to a vector potential. Therefore, when the flux phase OP has unidirectional spatial variation, staggered currents would flow in a perpendicular direction. The derived GL theory can be used for various problems in high-Tc cuprate superconductors, e.g., states near a surface or impurities, and the effect of an external magnetic field. Since the GL theory derived microscopically directly reflects the electronic structure of the system, e.g., the shape of the Fermi surface that changes with doping, it can provide more useful information than that from phenomenological GL theories.

Superconducting resonator used as a beam phase detector.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharamentov, S. I.; Pardo, R. C.; Ostroumov, P. N.

2003-05-01

Beam-bunch arrival time has been measured for the first time by operating superconducting cavities, normally part of the linac accelerator array, in a bunch-detecting mode. The very high Q of the superconducting cavities provides high sensitivity and allows for phase-detecting low-current beams. In detecting mode, the resonator is operated at a very low field level comparable to the field induced by the bunched beam. Because of this, the rf field in the cavity is a superposition of a 'pure' (or reference) rf and the beam-induced signal. A new method of circular phase rotation (CPR), allowing extraction of the beam phasemore » information from the composite rf field was developed. Arrival time phase determination with CPR is better than 1{sup o} (at 48 MHz) for a beam current of 100 nA. The electronics design is described and experimental data are presented.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petković, Ivana; Lollo, A.; Glazman, L. I.

The properties of one-dimensional superconductors are strongly influenced by topological fluctuations of the order parameter, known as phase slips, which cause the decay of persistent current in superconducting rings and the appearance of resistance in superconducting wires. Despite extensive work, quantitative studies of phase slips have been limited by uncertainty regarding the order parameter’s free-energy landscape. Here we show detailed agreement between measurements of the persistent current in isolated flux-biased rings and Ginzburg–Landau theory over a wide range of temperature, magnetic field and ring size; this agreement provides a quantitative picture of the free-energy landscape. Furthermore, we also demonstrate thatmore » phase slips occur deterministically as the barrier separating two competing order parameter configurations vanishes. These results will enable studies of quantum and thermal phase slips in a well-characterized system and will provide access to outstanding questions regarding the nature of one-dimensional superconductivity.« less

Bosonic Confinement and Coherence in Disordered Nanodiamond Arrays.

PubMed

Zhang, Gufei; Samuely, Tomas; Du, Hongchu; Xu, Zheng; Liu, Liwang; Onufriienko, Oleksandr; May, Paul W; Vanacken, Johan; Szabó, Pavol; Kačmarčík, Jozef; Yuan, Haifeng; Samuely, Peter; Dunin-Borkowski, Rafal E; Hofkens, Johan; Moshchalkov, Victor V

2017-11-28

In the presence of disorder, superconductivity exhibits short-range characteristics linked to localized Cooper pairs which are responsible for anomalous phase transitions and the emergence of quantum states such as the bosonic insulating state. Complementary to well-studied homogeneously disordered superconductors, superconductor-normal hybrid arrays provide tunable realizations of the degree of granular disorder for studying anomalous quantum phase transitions. Here, we investigate the superconductor-bosonic dirty metal transition in disordered nanodiamond arrays as a function of the dispersion of intergrain spacing, which ranges from angstroms to micrometers. By monitoring the evolved superconducting gaps and diminished coherence peaks in the single-quasiparticle density of states, we link the destruction of the superconducting state and the emergence of bosonic dirty metallic state to breaking of the global phase coherence and persistence of the localized Cooper pairs. The observed resistive bosonic phase transitions are well modeled using a series-parallel circuit in the framework of bosonic confinement and coherence.

The happy marriage between electron-phonon superconductivity and Mott physics in Cs3C60: A first-principle phase diagram

NASA Astrophysics Data System (ADS)

Capone, Massimo; Nomura, Yusuke; Sakai, Shiro; Giovannetti, Gianluca; Arita, Ryotaro

The phase diagram of doped fullerides like Cs3C60 as a function of the spacing between fullerene molecules is characterized by a first-order transition between a Mott insulator and an s-wave superconductor with a dome-shaped behavior of the critical temperature. By means of an ab-initio modeling of the bandstructure, the electron-phonon interaction and the interaction parameter and a Dynamical Mean-Field Theory solution, we reproduce the phase diagram and demonstrate that phonon superconductivity benefits from strong correlations confirming earlier model predictions. The role of correlations is manifest also in infrared measurements carried out by L. Baldassarre. The superconducting phase shares many similarities with ''exotic'' superconductors with electronic pairing, suggesting that the anomalies in the ''normal'' state, rather than the pairing glue, can be the real common element unifying a wide family of strongly correlated superconductors including cuprates and iron superconductors

Crystal growth and annealing study of fragile, non-bulk superconductivity in YFe 2Ge 2

DOE PAGES

Kim, H.; Ran, S.; Mun, E. D.; ...

2015-02-05

In this study, we investigated the occurrence and nature of superconductivity in single crystals of YFe 2Ge 2 grown out of Sn flux by employing X-ray diffraction, electrical resistivity and specific heat measurements. We found that the residual resistivity ratio (RRR) of single crystals can be greatly improved, reaching as high as ~60, by decanting the crystals from the molten Sn at ~350°C and/or by annealing at temperatures between 550°C and 600°C. We found that the samples with RRR ≳ 34 showed resistive signatures of superconductivity with the onset of the superconducting transition T c ≈ 1.4K. RRR values varymore » between 35 and 65 with, on average, no systematic change in value T c, indicating that the systematic changes in RRR do not lead to comparable changes in T c. Specific heat measurements on samples that showed the clear resistive signatures of a superconducting transition did not show any signature of a superconducting phase transition, which suggests that the superconductivity observed in this compound is either some sort of filamentary, strain-stabilized superconductivity associated with small amounts of stressed YFe 2Ge 2 (perhaps at twin boundaries or dislocations) or is a second crystallographic phase that is present at level below detection capability of conventional powder X-ray techniques.« less

High-Temperature-Superconductor Films In Microwave Circuits

NASA Technical Reports Server (NTRS)

Bhasin, K. B.; Warner, J. D.; Romanofsky, R. R.; Heinen, V. O.; Chorey, C. M.

1993-01-01

Report discusses recent developments in continuing research on fabrication and characterization of thin films of high-temperature superconducting material and incorporation of such films into microwave circuits. Research motivated by prospect of exploiting superconductivity to reduce electrical losses and thereby enhancing performance of such critical microwave components as ring resonators, filters, transmission lines, phase shifters, and feed lines in phased-array antennas.

Quantum Multicriticality near the Dirac-Semimetal to Band-Insulator Critical Point in Two Dimensions: A Controlled Ascent from One Dimension

NASA Astrophysics Data System (ADS)

Roy, Bitan; Foster, Matthew S.

2018-01-01

We compute the effects of generic short-range interactions on gapless electrons residing at the quantum critical point separating a two-dimensional Dirac semimetal and a symmetry-preserving band insulator. The electronic dispersion at this critical point is anisotropic (Ek=±√{v2kx2+b2ky2 n } with n =2 ), which results in unconventional scaling of thermodynamic and transport quantities. Because of the vanishing density of states [ϱ (E )˜|E |1 /n ], this anisotropic semimetal (ASM) is stable against weak short-range interactions. However, for stronger interactions, the direct Dirac-semimetal to band-insulator transition can either (i) become a fluctuation-driven first-order transition (although unlikely in a particular microscopic model considered here, the anisotropic honeycomb lattice extended Hubbard model) or (ii) get avoided by an intervening broken-symmetry phase. We perform a controlled renormalization group analysis with the small parameter ɛ =1 /n , augmented with a 1 /n expansion (parametrically suppressing quantum fluctuations in the higher dimension) by perturbing away from the one-dimensional limit, realized by setting ɛ =0 and n →∞ . We identify charge density wave (CDW), antiferromagnet (AFM), and singlet s -wave superconductivity as the three dominant candidates for broken symmetry. The onset of any such order at strong coupling (˜ɛ ) takes place through a continuous quantum phase transition across an interacting multicritical point, where the ordered phase, band insulator, Dirac, and anisotropic semimetals meet. We also present the phase diagram of an extended Hubbard model for the ASM, obtained via the controlled deformation of its counterpart in one dimension. The latter displays spin-charge separation and instabilities to CDW, spin density wave, and Luther-Emery liquid phases at arbitrarily weak coupling. The spin density wave and Luther-Emery liquid phases deform into pseudospin SU(2)-symmetric quantum critical points separating the ASM from the AFM and superconducting orders, respectively. Our phase diagram shows an intriguing interplay among CDW, AFM, and s -wave paired states that can be germane for a uniaxially strained optical honeycomb lattice for ultracold fermion atoms, or the organic compound α -(BEDT -TTF )2I3 .

Cuprate phase diagram and the influence of nanoscale inhomogeneities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaki, N.; Yang, H. -B.; Rameau, J. D.

2017-11-01

The phase diagram associated with high-Tc superconductors is complicated by an array of different ground states. The parent material represents an antiferromagnetic insulator but with doping superconductivity becomes possible with transition temperatures previously thought unattainable. The underdoped region of the phase diagram is dominated by the so-called pseudogap phenomena, whereby in the normal state the system mimics superconductivity in its spectral response but does not show the complete loss of resistivity associated with the superconducting state. An understanding of this regime presents one of the great challenges for the field. In the present study we revisit the structure of themore » phase diagram as determined in photoemission studies. By careful analysis of the role of nanoscale inhomogeneities in the overdoped region, we are able to more carefully separate out the gaps due to the pseudogap phenomena from the gaps due to the superconducting transition. Within a mean-field description, we are thus able to link the magnitude of the doping-dependent pseudogap directly to the Heisenberg exchange interaction term, J Sigma s(i)s(j), contained in the t - J model. This approach provides a clear indication that the pseudogap is associated with spin singlet formation.« less

Cuprate phase diagram and the influence of nanoscale inhomogeneities

DOE PAGES

Zaki, Nader; Yang, Hongbo -B.; Rameau, Jon D.; ...

2017-11-28

The phase diagram associated with high-T c superconductors is complicated by an array of different ground states. The parent material represents an antiferromagnetic insulator but with doping superconductivity becomes possible with transition temperatures previously thought unattainable. The underdoped region of the phase diagram is dominated by the so-called pseudogap phenomena, whereby in the normal state the system mimics superconductivity in its spectral response but does not show the complete loss of resistivity associated with the superconducting state. An understanding of this regime presents one of the great challenges for the field. In the present study we revisit the structure ofmore » the phase diagram as determined in photoemission studies. By careful analysis of the role of nanoscale inhomogeneities in the overdoped region, we are able to more carefully separate out the gaps due to the pseudogap phenomena from the gaps due to the superconducting transition. Within a mean-field description, we are thus able to link the magnitude of the doping-dependent pseudogap directly to the Heisenberg exchange interaction term, JΣs is j, contained in the t-J model. This approach provides a clear indication that the pseudogap is associated with spin singlet formation.« less

Cuprate phase diagram and the influence of nanoscale inhomogeneities

NASA Astrophysics Data System (ADS)

Zaki, N.; Yang, H.-B.; Rameau, J. D.; Johnson, P. D.; Claus, H.; Hinks, D. G.

2017-11-01

The phase diagram associated with high-Tc superconductors is complicated by an array of different ground states. The parent material represents an antiferromagnetic insulator but with doping superconductivity becomes possible with transition temperatures previously thought unattainable. The underdoped region of the phase diagram is dominated by the so-called pseudogap phenomena, whereby in the normal state the system mimics superconductivity in its spectral response but does not show the complete loss of resistivity associated with the superconducting state. An understanding of this regime presents one of the great challenges for the field. In the present study we revisit the structure of the phase diagram as determined in photoemission studies. By careful analysis of the role of nanoscale inhomogeneities in the overdoped region, we are able to more carefully separate out the gaps due to the pseudogap phenomena from the gaps due to the superconducting transition. Within a mean-field description, we are thus able to link the magnitude of the doping-dependent pseudogap directly to the Heisenberg exchange interaction term, J ∑sisj , contained in the t -J model. This approach provides a clear indication that the pseudogap is associated with spin singlet formation.

Origin of Pressure-induced Superconducting Phase in K xFe 2-ySe 2 studied by Synchrotron X-ray Diffraction and Spectroscopy

DOE PAGES

Yamamoto, Yoshiya; Yamaoka, Hitoshi; Tanaka, Masashi; ...

2016-08-08

Pressure dependence of the electronic and crystal structures of K xFe 2–ySe 2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change ofmore » Fermi surface topology. Lastly, our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.« less

Origin of Pressure-induced Superconducting Phase in KxFe2-ySe2 studied by Synchrotron X-ray Diffraction and Spectroscopy

NASA Astrophysics Data System (ADS)

Yamamoto, Yoshiya; Yamaoka, Hitoshi; Tanaka, Masashi; Okazaki, Hiroyuki; Ozaki, Toshinori; Takano, Yoshihiko; Lin, Jung-Fu; Fujita, Hidenori; Kagayama, Tomoko; Shimizu, Katsuya; Hiraoka, Nozomu; Ishii, Hirofumi; Liao, Yen-Fa; Tsuei, Ku-Ding; Mizuki, Jun'Ichiro

2016-08-01

Pressure dependence of the electronic and crystal structures of KxFe2-ySe2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change of Fermi surface topology. Our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.

Towards phase-coherent caloritronics in superconducting circuits

NASA Astrophysics Data System (ADS)

Fornieri, Antonio; Giazotto, Francesco

2017-10-01

The emerging field of phase-coherent caloritronics (from the Latin word calor, heat) is based on the possibility of controlling heat currents by using the phase difference of the superconducting order parameter. The goal is to design and implement thermal devices that can control energy transfer with a degree of accuracy approaching that reached for charge transport by contemporary electronic components. This can be done by making use of the macroscopic quantum coherence intrinsic to superconducting condensates, which manifests itself through the Josephson effect and the proximity effect. Here, we review recent experimental results obtained in the realization of heat interferometers and thermal rectifiers, and discuss a few proposals for exotic nonlinear phase-coherent caloritronic devices, such as thermal transistors, solid-state memories, phase-coherent heat splitters, microwave refrigerators, thermal engines and heat valves. Besides being attractive from the fundamental physics point of view, these systems are expected to have a vast impact on many cryogenic microcircuits requiring energy management, and possibly lay the first stone for the foundation of electronic thermal logic.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gyenis, András; Feldman, Benjamin E.; Randeria, Mallika T.

Layered material structures play a key role in enhancing electron–electron interactions to create correlated metallic phases that can transform into unconventional superconducting states. The quasi-two-dimensional electronic properties of such compounds are often inferred indirectly through examination of bulk properties. Here we use scanning tunneling microscopy to directly probe in cross-section the quasi-two-dimensional electronic states of the heavy fermion superconductor CeCoIn 5. Our measurements reveal the strong confined nature of quasiparticles, anisotropy of tunneling characteristics, and layer-by-layer modulated behavior of the precursor pseudogap gap phase. In the interlayer coupled superconducting state, the orientation of line defects relative to the d-wave ordermore » parameter determines whether in-gap states form due to scattering. Spectroscopic imaging of the anisotropic magnetic vortex cores directly characterizes the short interlayer superconducting coherence length and shows an electronic phase separation near the upper critical in-plane magnetic field, consistent with a Pauli-limited first-order phase transition into a pseudogap phase.« less

Towards phase-coherent caloritronics in superconducting circuits.

PubMed

Fornieri, Antonio; Giazotto, Francesco

2017-10-06

The emerging field of phase-coherent caloritronics (from the Latin word calor, heat) is based on the possibility of controlling heat currents by using the phase difference of the superconducting order parameter. The goal is to design and implement thermal devices that can control energy transfer with a degree of accuracy approaching that reached for charge transport by contemporary electronic components. This can be done by making use of the macroscopic quantum coherence intrinsic to superconducting condensates, which manifests itself through the Josephson effect and the proximity effect. Here, we review recent experimental results obtained in the realization of heat interferometers and thermal rectifiers, and discuss a few proposals for exotic nonlinear phase-coherent caloritronic devices, such as thermal transistors, solid-state memories, phase-coherent heat splitters, microwave refrigerators, thermal engines and heat valves. Besides being attractive from the fundamental physics point of view, these systems are expected to have a vast impact on many cryogenic microcircuits requiring energy management, and possibly lay the first stone for the foundation of electronic thermal logic.

Method of forming low cost, formable High T(subc) superconducting wire

NASA Technical Reports Server (NTRS)

Smialek, James L. (Inventor)

1989-01-01

A ceramic superconductivity part, such as a wire, is produced through the partial oxidation of a specially formulated copper alloy in a core. The alloys contains low level of quantities of rare earth and alkaline earth dopant elements. Upon oxidation at high temperatures, and superconducting oxide phases are formed as a thin film.

Power superconducting power transmission cable

DOEpatents

Ashworth, Stephen P.

2003-06-10

The present invention is for a compact superconducting power transmission cable operating at distribution level voltages. The superconducting cable is a conductor with a number of tapes assembled into a subconductor. These conductors are then mounted co-planarly in an elongated dielectric to produce a 3-phase cable. The arrangement increases the magnetic field parallel to the tapes thereby reducing ac losses.

Power superconducting power transmission cable

DOEpatents

Ashworth, Stephen P.

2003-01-01

The present invention is for a compact superconducting power transmission cable operating at distribution level voltages. The superconducting cable is a conductor with a number of tapes assembled into a subconductor. These conductors are then mounted co-planarly in an elongated dielectric to produce a 3-phase cable. The arrangement increases the magnetic field parallel to the tapes thereby reducing ac losses.

Unusual superconducting state at 49 K in electron-doped CaFe2As2 at ambient pressure

PubMed Central

Lv, Bing; Deng, Liangzi; Gooch, Melissa; Wei, Fengyan; Sun, Yanyi; Meen, James K.; Xue, Yu-Yi; Lorenz, Bernd; Chu, Ching-Wu

2011-01-01

We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe2As2 via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at 49 K, which has a low critical field < 4 Oe, and the other at 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe2As2 (or Ae122), where Ae = Ca, Sr, or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (Tc) only up to 38 K and pressurization has been reported to produce superconductivity with a Tc up to 30 K. The unusual 49 K phase detected will be discussed. PMID:21911404

Anomalous anisotropic compression behavior of superconducting CrAs under high pressure

PubMed Central

Yu, Zhenhai; Wu, Wei; Hu, Qingyang; Zhao, Jinggeng; Li, Chunyu; Yang, Ke; Cheng, Jinguang; Luo, Jianlin; Wang, Lin; Mao, Ho-kwang

2015-01-01

CrAs was observed to possess the bulk superconductivity under high-pressure conditions. To understand the superconducting mechanism and explore the correlation between the structure and superconductivity, the high-pressure structural evolution of CrAs was investigated using the angle-dispersive X-ray diffraction (XRD) method. The structure of CrAs remains stable up to 1.8 GPa, whereas the lattice parameters exhibit anomalous compression behaviors. With increasing pressure, the lattice parameters a and c both demonstrate a nonmonotonic change, and the lattice parameter b undergoes a rapid contraction at ∼0.18−0.35 GPa, which suggests that a pressure-induced isostructural phase transition occurs in CrAs. Above the phase transition pressure, the axial compressibilities of CrAs present remarkable anisotropy. A schematic band model was used to address the anomalous compression behavior of CrAs. The present results shed light on the structural and related electronic responses to high pressure, which play a key role toward understanding the superconductivity of CrAs. PMID:26627230

Colossal thermomagnetic response in chiral d-wave superconductor URu2Si2

NASA Astrophysics Data System (ADS)

Matsuda, Yuji

The heavy-fermion compound URu2Si2 exhibits unconventional superconductivity at Tc = 1.45 K deep inside the so-called hidden order phase. An intriguing aspect is that this system has been suggested to be a candidate of a chiral d-wave superconductor, and possible Weyl-type topological superconducting states have been discussed recently. Here we report on the observation of a highly unusual Nernst signal due to the superconducting fluctuations above Tc. The Nernst coefficient is anomalously enhanced (by a factor of ~106) as compared with the theoretically expected value of the Gaussian fluctuations. This colossal Nernst effect intimately reflects the highly unusual superconducting state of URu2Si2. The results invoke possible chiral or Berry-phase fluctuations associated with the broken time-reversal symmetry of the superconducting order parameter. In collaboration with T. Yamashita, Y. Shimoyama, H. Sumiyoshi (Kyoto), S. Fujimoto (Osaka), T. Shibauchi (Tokyo), Y. Haga (JAEA), T. D. Matsuda (TMU) , Y. Onuki (Ryukyus), A. Levchenko (Wisconsin-Madison).

Metal-Insulator Transition in Copper Oxides Induced by Apex Displacements

NASA Astrophysics Data System (ADS)

Acharya, Swagata; Weber, Cédric; Plekhanov, Evgeny; Pashov, Dimitar; Taraphder, A.; Van Schilfgaarde, Mark

2018-04-01

High temperature superconductivity has been found in many kinds of compounds built from planes of Cu and O, separated by spacer layers. Understanding why critical temperatures are so high has been the subject of numerous investigations and extensive controversy. To realize high temperature superconductivity, parent compounds are either hole doped, such as La2 CuO4 (LCO) with Sr (LSCO), or electron doped, such as Nd2 CuO4 (NCO) with Ce (NCCO). In the electron-doped cuprates, the antiferromagnetic phase is much more robust than the superconducting phase. However, it was recently found that the reduction of residual out-of-plane apical oxygen dramatically affects the phase diagram, driving those compounds to a superconducting phase. Here we use a recently developed first-principles method to explore how displacement of the apical oxygen (AO) in LCO affects the optical gap, spin and charge susceptibilities, and superconducting order parameter. By combining quasiparticle self-consistent GW (QS GW) and dynamical mean-field theory (DMFT), we show that LCO is a Mott insulator, but small displacements of the apical oxygen drive the compound to a metallic state through a localization-delocalization transition, with a concomitant maximum in d -wave order parameter at the transition. We address the question of whether NCO can be seen as the limit of LCO with large apical displacements, and we elucidate the deep physical reasons why the behavior of NCO is so different from the hole-doped materials. We shed new light on the recent correlation observed between Tc and the charge transfer gap, while also providing a guide towards the design of optimized high-Tc superconductors. Further, our results suggest that strong correlation, enough to induce a Mott gap, may not be a prerequisite for high-Tc superconductivity.

Nonlinear heat transport in ferromagnetic-quantum dot-superconducting systems

NASA Astrophysics Data System (ADS)

Hwang, Sun-Yong; Sánchez, David

2018-03-01

We analyze the heat current traversing a quantum dot sandwiched between a ferromagnetic and a superconducting electrode. The heat flow generated in response to a voltage bias presents rectification as a function of the gate potential applied to the quantum dot. Remarkably, in the thermally driven case the heat shows a strong diode effect with large asymmetry ratios that can be externally tuned with magnetic fields or spin-polarized tunneling. Our results thus demonstrate the importance of hybrid systems as promising candidates for thermal applications.

Superconductivity and bandwidth-controlled Mott metal-insulator transition in 1T-TaS2-xSex

NASA Astrophysics Data System (ADS)

Ang, R.; Miyata, Y.; Ieki, E.; Nakayama, K.; Sato, T.; Liu, Y.; Lu, W. J.; Sun, Y. P.; Takahashi, T.

2013-09-01

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) of layered chalcogenide 1T-TaS2-xSex to elucidate the electronic states especially relevant to the occurrence of superconductivity. We found a direct evidence for a Ta-5d-derived electron pocket associated with the superconductivity, which is fragile against a Mott-gap opening observed in the insulating ground state for S-rich samples. In particular, a strong electron-electron interaction-induced Mott gap driven by a Ta 5d orbital also exists in the metallic ground state for Se-rich samples, while finite ARPES intensity near the Fermi level likely originating from a Se 4p orbital survives, indicative of the orbital-selective nature of the Mott transition. Present results suggest that effective electron correlation and p-d hybridization play a crucial role to tune the superconductivity and Mott metal-insulator transition.

Antiferromagnetism and superconductivity in layered organic conductors: Variational cluster approach.

PubMed

Sahebsara, P; Sénéchal, D

2006-12-22

The kappa-(ET)2X layered conductors (where ET stands for BEDT-TTF) are studied within the dimer model as a function of the diagonal hopping t' and Hubbard repulsion U. Antiferromagnetism and d-wave superconductivity are investigated at zero temperature using variational cluster perturbation theory (VCPT). For large U, Néel antiferromagnetism exists for t' < t(c2)', with t(c2)' approximately 0.9. For fixed t', as U is decreased (or pressure increased), a d(x2-y2) superconducting phase appears. When U is decreased further, then a d(xy) order takes over. There is a critical value of t(c1)' approximately 0.8 of t' beyond which the AF and dSC phases are separated by the Mott disordered phase.

Unconventional superconductivity in heavy-fermion compounds

DOE PAGES

White, B. D.; Thompson, J. D.; Maple, M. B.

2015-02-27

Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion com- pounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates andmore » iron-based superconductors. Lastly, we conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.« less

Ferromagnetic superconductors: A vortex phase in ternary rare-earth compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuper, C.G.; Revzen, M.; Ron, A.

1980-06-09

It is shown that the generalized Ginzburg-Landau free-energy functional of Blount and Varma admits self-consistent solutions with quantized-flux vortices, magnetized in a region about the cores. There is a temperature range where the new phase has a lower free energy than either the pure superconducting or ferromagnetic phases; it represents true coexistence of ferromagnetism and superconductivity. The main features of the specific heat and magnetic properties of some rare-earth ternary compounds can be explained qualitatively.

Simultaneous measurement of pressure evolution of crystal structure and superconductivity in FeSe[subscript 0.92] using designer diamonds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uhoya, Walter; Tsoi, Georgiy; Vohra, Yogesh

Simultaneous high-pressure X-ray diffraction and electrical resistance measurements have been carried out on a PbO-type {alpha}-FeSe{sub 0.92} compound to a pressure of 44 GPa and temperatures down to 4 K using designer diamond anvils at synchrotron source. A ambient temperature, a structural phase transition from a tetragonal (P4/nmm) phase to an orthorhombic (Pbnm) phase is observed at 11 GPa and the Pbnm phase persists up to 74 GPa. The superconducting transition temperature (T{sub c}) increases rapidly with pressure reaching a maximum of {approx}28 K at {approx}6 GPa and decreases at higher pressures, disappearing completely at 14.6 GPa. Simultaneous pressure-dependent X-raymore » diffraction and resistance measurements at low temperatures show superconductivity only in a low-pressure orthorhombic (Cmma) phase of the {alpha}-FeSe{sub 0.92}. Upon increasing pressure at 10 K near T{sub c}, crystalline phases change from a mixture of orthorhombic (Cmma) and hexagonal (P63/mmc) phases to a high-pressure orthorhombic (Pbnm) phase near 6.4 GPa where T{sub c} is maximum.« less

Experimental formation of a fractional vortex in a superconducting bi-layer

NASA Astrophysics Data System (ADS)

Tanaka, Y.; Yamamori, H.; Yanagisawa, T.; Nishio, T.; Arisawa, S.

2018-05-01

We report the experimental formation of a fractional vortex generated by using a thin superconducting bi-layer in the form of a niobium bi-layer, observed as a magnetic flux distribution image taken by a scanning superconducting quantum interference device (SQUID) microscope. Thus, we demonstrated that multi-component superconductivity can be realized by an s-wave conventional superconductor, because, in these superconductors, the magnetic flux is no longer quantized as it is destroyed by the existence of an inter-component phase soliton (i-soliton).

Structural differences between superconducting and non-superconducting CaCuO2/SrTiO3 interfaces

NASA Astrophysics Data System (ADS)

Zarotti, Francesca; Di Castro, Daniele; Felici, Roberto; Balestrino, Giuseppe

2018-06-01

A study of the interface structure of superconducting and non-superconducting CaCuO2/SrTiO3 heterostructures grown on NdGaO3(110) substrates is reported. Using the combination of high resolution x-ray reflectivity and surface diffraction, the crystallographic structure of superconducting and non-superconducting samples has been investigated. The analysis has demonstrated the excellent sharpness of the CaCuO2/SrTiO3 interface (roughness smaller than one perovskite unit cell). Furthermore, we were able to discriminate between the superconducting and the non-superconducting phase. In the former case, we found an increase of the spacing between the topmost Ca plane of CaCuO2 block and the first TiO2 plane of the overlaying STO block, relative to the non-superconducting case. These results are in agreement with the model that foresees a strong oxygen incorporation in the interface Ca plane in the superconducting heterostructures.

Uniaxial-Strain-Orientation Dependence of the Competition between Mott and Charge Ordered Phases and their Corresponding Superconductivity of β-(BDA-TTP)2I3

NASA Astrophysics Data System (ADS)

Nuruzzaman, Md.; Yokogawa, Keiichi; Yoshino, Harukazu; Yoshimoto, Haruo; Kikuchi, Koichi; Kaihatsu, Takayuki; Yamada, Jun-ichi; Murata, Keizo

2012-12-01

We studied the electronic transport properties of the charge transfer salt β-(BDA-TTP)2I3 [BDA-TTP: 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] by applying uniaxial strains along the three crystallographic axes, and obtained three corresponding temperature-pressure phase diagrams. Three phase diagrams were quite dependent on the direction of compression. Following the preceding paper by Kikuchi et al., we speculate that the insulating states are of 1/2-filled Mott insulators for the a- and b-axes compressions, and of 1/4-filled charge ordered states for the c-axis compression as well as hydrostatic pressure. The superconducting phase under uniaxial strain was realized with Tc = 5 K at 1.9 GPa along the a-axis and with Tc = 5.6 K at 1.75 GPa along the b-axis. Superconductivity was also reproduced with a Tc of 9.5 K at 1.0 GPa for the c-axis compressions in the range of 0.85 to 1.53 GPa as previously reported. We studied tentative measurement on upper critical fields, Bc2's of these superconductivities and found that the extrapolated values, Bc2(0)'s, exceeded Pauli-limit by about 2--3 times. However, at least in terms of Bc2, the difference in superconductivity associated with two different insulating states was not clear.

Processing study of high temperature superconducting Y-Ba-Cu-O ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Safari, A.; Wachtman, J.B. Jr.; Ward, C.

Processing of the YBa{sub 2}Cu{sub 3}O{sub 6+x} superconducting phase by employing different precursor powder preparation techniques (ball milling, attrition milling) and samples formed by different sintering conditions are discussed. The superconducting phase has been identified by powder x-ray diffraction. The effect of different powder processing and pressing conditions on the structure, density, resistivity and a.c. magnetic susceptibility were studied. Though there is no variation in T{sub c} for all the samples, attrition milled samples show a much lower resistance and less temperature dependence compared to ball milled samples above the superconducting transition temperature up to room temperature. Ball milled samplesmore » were loosely packed with more voids compared to attrition milled samples which are more densely packed with a needle-like structure.« less

Vertical temperature boundary of the pseudogap under the superconducting dome in the phase diagram of Bi 2 Sr 2 CaCu 2 O 8 + δ

DOE PAGES

Loret, B.; Sakai, S.; Benhabib, S.; ...

2017-09-25

We combine electronic Raman scattering experiments with cellular dynamical mean field theory and present evidence of the pseudogap in the superconducting state of various hole-doped cuprates. In Bi 2 Sr 2 CaCu 2 O 8 + δ we also track the superconducting pseudogap hallmark, a peak-dip feature, as a function of temperature T and doping p , well beyond the optimal one. We show that, at all temperatures under the superconducting dome, the pseudogap disappears at the doping p c , between 0.222 and 0.226, where also the normal-state pseudogap collapses at a Lifshitz transition. This demonstrates that the superconductingmore » pseudogap boundary forms a vertical line in the T - p phase diagram.« less

Effect of disorder on the pressure-induced superconducting state of CeAu 2Si 2

NASA Astrophysics Data System (ADS)

Ren, Z.; Giriat, G.; Scheerer, G. W.; Lapertot, G.; Jaccard, D.

2015-03-01

CeAu2Si2 is a newly discovered pressure-induced heavy fermion superconductor, which shows very unusual interplay between superconductivity and magnetism under pressure. Here we compare the results of high-pressure measurements on single-crystalline CeAu2Si2 samples with different levels of disorder. It is found that while the magnetic properties are essentially sample independent, superconductivity is rapidly suppressed when the residual resistivity of the sample increases. We show that the depression of bulk Tc can be well understood in terms of pair breaking by nonmagnetic disorder, which strongly suggests an unconventional pairing state in pressurized CeAu2Si2 . Furthermore, increasing the level of disorder leads to the emergence of another phase transition at T* within the magnetic phase, which might be in competition with superconductivity.

Phase competition and anomalous thermal evolution in high-temperature superconductors

DOE PAGES

Yu, Zuo-Dong; Zhou, Yuan; Yin, Wei-Guo; ...

2017-07-12

The interplay of competing orders is relevant to high-temperature superconductivity known to emerge upon suppression of a parent antiferromagnetic order typically via charge doping. How such interplay evolves at low temperature—in particular at what doping level the zero-temperature quantum critical point (QCP) is located—is still elusive because it is masked by the superconducting state. The QCP had long been believed to follow a smooth extrapolation of the characteristic temperature T * for the strange normal state well above the superconducting transition temperature. However, recently the T * within the superconducting dome was reported to unexpectedly exhibit back-bending likely in themore » cuprate Bi 2 Sr 2 CaCu 2 O 8 + δ . We show that the original and revised phase diagrams can be understood in terms of weak and moderate competitions, respectively, between superconductivity and a pseudogap state such as d -density or spin-density wave, based on both Ginzburg-Landau theory and the realistic t - t ' - t ' ' - J - V model for the cuprates. We further found that the calculated temperature and doping-level dependence of the quasiparticle spectral gap and Raman response qualitatively agrees with the experiments. Particularly, the T * back-bending can provide a simple explanation of the observed anomalous two-step thermal evolution dominated by the superconducting gap and the pseudogap, respectively. These results imply that the revised phase diagram is likely to take place in high-temperature superconductors.« less

Quantum interference in an interfacial superconductor.

PubMed

Goswami, Srijit; Mulazimoglu, Emre; Monteiro, Ana M R V L; Wölbing, Roman; Koelle, Dieter; Kleiner, Reinhold; Blanter, Ya M; Vandersypen, Lieven M K; Caviglia, Andrea D

2016-10-01

The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (T c ; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-T c superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir1−xRux)O3

PubMed Central

Gunasekera, J.; Harriger, L.; Dahal, A.; Heitmann, T.; Vignale, G.; Singh, D. K.

2015-01-01

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1−xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund’s orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems. PMID:26647965

Fractional statistics and quantum scaling properties of the integrable Penson-Kolb-Hubbard chain

NASA Astrophysics Data System (ADS)

Vitoriano, Carlindo; Coutinho-Filho, M. D.

2010-09-01

We investigate the ground-state and low-temperature properties of the integrable version of the Penson-Kolb-Hubbard chain. The model obeys fractional statistical properties, which give rise to fractional elementary excitations and manifest differently in the four regions of the phase diagram U/t versus n , where U is the Coulomb coupling, t is the correlated hopping amplitude, and n is the particle density. In fact, we can find local pair formation, fractionalization of the average occupation number per orbital k , or U - and n -dependent average electric charge per orbital k . We also study the scaling behavior near the U -driven quantum phase transitions and characterize their universality classes. Finally, it is shown that in the regime of parameters where local pair formation is energetically more favorable, the ground state exhibits power-law superconductivity; we also stress that above half filling the pair-hopping term stabilizes local Cooper pairs in the repulsive- U regime for U

Magnetic fluctuations driven insulator-to-metal transition in Ca(Ir(1-x)Rux)O3.

PubMed

Gunasekera, J; Harriger, L; Dahal, A; Heitmann, T; Vignale, G; Singh, D K

2015-12-09

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1-xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund's orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems.

Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point.

PubMed

Lederer, Samuel; Schattner, Yoni; Berg, Erez; Kivelson, Steven A

2017-05-09

Using determinantal quantum Monte Carlo, we compute the properties of a lattice model with spin [Formula: see text] itinerant electrons tuned through a quantum phase transition to an Ising nematic phase. The nematic fluctuations induce superconductivity with a broad dome in the superconducting [Formula: see text] enclosing the nematic quantum critical point. For temperatures above [Formula: see text], we see strikingly non-Fermi liquid behavior, including a "nodal-antinodal dichotomy" reminiscent of that seen in several transition metal oxides. In addition, the critical fluctuations have a strong effect on the low-frequency optical conductivity, resulting in behavior consistent with "bad metal" phenomenology.

Role of vertex corrections in the matrix formulation of the random phase approximation for the multiorbital Hubbard model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Altmeyer, Michaela; Guterding, Daniel; Hirschfeld, P. J.

2016-12-21

In the framework of a multiorbital Hubbard model description of superconductivity, a matrix formulation of the superconducting pairing interaction that has been widely used is designed to treat spin, charge, and orbital fluctuations within a random phase approximation (RPA). In terms of Feynman diagrams, this takes into account particle-hole ladder and bubble contributions as expected. It turns out, however, that this matrix formulation also generates additional terms which have the diagrammatic structure of vertex corrections. Furthermore we examine these terms and discuss the relationship between the matrix-RPA superconducting pairing interaction and the Feynman diagrams that it sums.

Elliptical vortex and oblique vortex lattice in the FeSe superconductor based on the nematicity and mixed superconducting orders

NASA Astrophysics Data System (ADS)

Lu, Da-Chuan; Lv, Yang-Yang; Li, Jun; Zhu, Bei-Yi; Wang, Qiang-Hua; Wang, Hua-Bing; Wu, Pei-Heng

2018-03-01

The electronic nematic phase is characterized as an ordered state of matter with rotational symmetry breaking, and has been well studied in the quantum Hall system and the high-Tc superconductors, regardless of cuprate or pnictide family. The nematic state in high-Tc systems often relates to the structural transition or electronic instability in the normal phase. Nevertheless, the electronic states below the superconducting transition temperature is still an open question. With high-resolution scanning tunneling microscope measurements, direct observation of vortex core in FeSe thin films revealed the nematic superconducting state by Song et al. Here, motivated by the experiment, we construct the extended Ginzburg-Landau free energy to describe the elliptical vortex, where a mixed s-wave and d-wave superconducting order is coupled to the nematic order. The nematic order induces the mixture of two superconducting orders and enhances the anisotropic interaction between the two superconducting orders, resulting in a symmetry breaking from C4 to C2. Consequently, the vortex cores are stretched into an elliptical shape. In the equilibrium state, the elliptical vortices assemble a lozenge-like vortex lattice, being well consistent with experimental results.

Full superconducting dome of strong Ising protection in gated monolayer WS2.

PubMed

Lu, Jianming; Zheliuk, Oleksandr; Chen, Qihong; Leermakers, Inge; Hussey, Nigel E; Zeitler, Uli; Ye, Jianting

2018-04-03

Many recent studies show that superconductivity not only exists in atomically thin monolayers but can exhibit enhanced properties such as a higher transition temperature and a stronger critical field. Nevertheless, besides being unstable in air, the weak tunability in these intrinsically metallic monolayers has limited the exploration of monolayer superconductivity, hindering their potential in electronic applications (e.g., superconductor-semiconductor hybrid devices). Here we show that using field effect gating, we can induce superconductivity in monolayer WS 2 grown by chemical vapor deposition, a typical ambient-stable semiconducting transition metal dichalcogenide (TMD), and we are able to access a complete set of competing electronic phases over an unprecedented doping range from band insulator, superconductor, to a reentrant insulator at high doping. Throughout the superconducting dome, the Cooper pair spin is pinned by a strong internal spin-orbit interaction, making this material arguably the most resilient superconductor in the external magnetic field. The reentrant insulating state at positive high gating voltages is attributed to localization induced by the characteristically weak screening of the monolayer, providing insight into many dome-like superconducting phases observed in field-induced quasi-2D superconductors.

Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe.

PubMed

Sun, J P; Matsuura, K; Ye, G Z; Mizukami, Y; Shimozawa, M; Matsubayashi, K; Yamashita, M; Watashige, T; Kasahara, S; Matsuda, Y; Yan, J-Q; Sales, B C; Uwatoko, Y; Cheng, J-G; Shibauchi, T

2016-07-19

The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ∼15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ∼6 GPa the sudden enhancement of superconductivity (Tc≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates.

Structural and magnetic phase diagram of CrAs and its relationship with pressure-induced superconductivity

DOE PAGES

Shen, Yao; Wang, Qisi; Hao, Yiqing; ...

2016-02-01

In this paper, we use neutron diffraction to study the structure and magnetic phase diagram of the newly discovered pressure-induced superconductor CrAs. Unlike most magnetic unconventional superconductors where the magnetic moment direction barely changes upon doping, here we show that CrAs exhibits a spin reorientation from the ab plane to the ac plane, along with an abrupt drop of the magnetic propagation vector at a critical pressure (P c ≈ 0.6 GPa). This magnetic phase transition, accompanied by a lattice anomaly, coincides with the emergence of bulk superconductivity. With further increasing pressure, the magnetic order completely disappears near the optimalmore » T c regime (P ≈ 0.94 GPa). Moreover, the Cr magnetic moments tend to be aligned antiparallel between nearest neighbors with increasing pressure toward the optimal superconductivity regime. Finally, our findings suggest that the noncollinear helimagnetic order is strongly coupled to structural and electronic degrees of freedom, and that the antiferromagnetic correlations between nearest neighbors might be essential for superconductivity.« less

Spin-liquid polymorphism in a correlated electron system on the threshold of superconductivity.

PubMed

Zaliznyak, Igor; Savici, Andrei T; Lumsden, Mark; Tsvelik, Alexei; Hu, Rongwei; Petrovic, Cedomir

2015-08-18

We report neutron scattering measurements which reveal spin-liquid polymorphism in an "11" iron chalcogenide superconductor. It occurs when a poorly metallic magnetic state of FeTe is tuned toward superconductivity by substitution of a small amount of tellurium with isoelectronic sulfur. We observe a liquid-like magnetic response, which is described by the coexistence of two disordered magnetic phases with different local structures whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in undoped, nonsuperconducting FeTe, which preserves the C4 symmetry of the underlying square lattice and is favored at high temperatures, whereas the other is the antiferromagnetic plaquette phase with broken C4 symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest the coexistence of and competition between two distinct liquid states, and a liquid-liquid phase transformation between these states, in the electronic spin system of FeTe(1-x)(S,Se)(x). We have thus discovered the remarkable physics of competing spin-liquid polymorphs in a correlated electron system approaching superconductivity. Our results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors. In particular, the phase with lower C2 local symmetry, whose emergence precedes superconductivity, naturally accounts for a propensity for forming electronic nematic states which have been observed experimentally, in cuprate and iron-based superconductors alike.

Spin-liquid polymorphism in a correlated electron system on the threshold of superconductivity

PubMed Central

Zaliznyak, Igor; Savici, Andrei T.; Lumsden, Mark; Tsvelik, Alexei; Hu, Rongwei; Petrovic, Cedomir

2015-01-01

We report neutron scattering measurements which reveal spin-liquid polymorphism in an “11” iron chalcogenide superconductor. It occurs when a poorly metallic magnetic state of FeTe is tuned toward superconductivity by substitution of a small amount of tellurium with isoelectronic sulfur. We observe a liquid-like magnetic response, which is described by the coexistence of two disordered magnetic phases with different local structures whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in undoped, nonsuperconducting FeTe, which preserves the C4 symmetry of the underlying square lattice and is favored at high temperatures, whereas the other is the antiferromagnetic plaquette phase with broken C4 symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest the coexistence of and competition between two distinct liquid states, and a liquid–liquid phase transformation between these states, in the electronic spin system of FeTe1−x(S,Se)x. We have thus discovered the remarkable physics of competing spin-liquid polymorphs in a correlated electron system approaching superconductivity. Our results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors. In particular, the phase with lower C2 local symmetry, whose emergence precedes superconductivity, naturally accounts for a propensity for forming electronic nematic states which have been observed experimentally, in cuprate and iron-based superconductors alike. PMID:26240327

Superconductivity in the Sn-Ba-Sr-Y-Cu-O system

NASA Technical Reports Server (NTRS)

Aleksandrov, K. S.; Khrustalev, B. P.; Krivomazov, S. N.; Petrov, M. I.; Vasilyev, A. D.; Zwegintsev, S. A.

1991-01-01

After the discovery of high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides were synthesized. Here, researchers report the results of the search for superconductivity in the compounds based on tin which has a lone electron pair like Bi, Tl, and Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3O(sub x), Sn1Ba1Ca1Cu3O(sub x), Sn1Ba1Mg1Cu3O(sub x), Sn1Sr1Ca1Cu3O(sub x), Sn1Sr1Mg1Cu3O(sub x), and Sn1Ca1Mg1Cu3O(sub x). The initial components were oxides and carbonates of the appropriate elements. A standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3O(sub x) showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3O(sub x) was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperature undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3O(sub x) ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase, two-valent cations Ba and Sr were partially substituted by univalent (K) and three-valent ones (Y).

Composition and annealing effects on superconductivity in sintered and arc-melted Fe1+εTe0.5Se0.5

NASA Astrophysics Data System (ADS)

Foreman, M. M.; Ponti, G.; Mozaffari, S.; Markert, J. T.

2018-03-01

We present the results of x-ray diffraction, electrical resistivity, and ac magnetic susceptibility measurements on specimens of the “11”-structure superconductor Fe1+εTe0.50Se0.50 (0 ≤ ε ≤ 0.15). Samples were initially either sintered in sealed quartz tubes or melted in a zirconium-gettered arc furnace. Sintered samples were fired two to three times at temperatures of 425°C, 600°C, or 675°C, while arc-melted samples were studied both asmelted and after annealing at 650°C. X-ray diffraction data show a predominant PbO-type tetragonal phase, with a secondary hexagonal NiAs-type phase; for sintered specimens annealed at 600°C, the secondary phase decreases as ε increases over the range 0 ≤ ε ≤ 0.10, with the composition Fe1.10Te0.5Se0.5 exhibiting x-ray phase purity. A higher annealing temperature of 675°C provided such tetragonal phase purity at the composition Fe1.05Te0.5Se0.5. The resistive superconducting transition temperature Tc was nearly independent of the iron concentration 1+ε, suggesting a single superconducting phase, while the magnetic screening fraction varied greatly with concentration and conditions, peaking at ɛ = 0.07, indicating that the amount of superconducting phase is strongly dependent on conditions. We propose that the behaviour can also be viewed in terms of an electron-doped, chalcogen-deficient stoichiometry.

New Developments in Nb3Sn PIT Strand: The Effects of Titanium and Second Phase Additions on the Superconducting Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Motowidlo, L.R.; Ghosh, A.; Distin, J.

2011-08-03

We report the effect of titanium on the transport properties of multifilament PIT strand. In addition, the effect of second phase yttrium additions on the microstructure and the bulk pinning force are reported for PIT Nb{sub 3}Sn mono-core wires. High resolution SEM, EDS, magnetization, and transport measurements were utilized to evaluate the superconducting properties.

Implementing an ancilla-free 1→M economical phase-covariant quantum cloning machine with superconducting quantum-interference devices in cavity QED

NASA Astrophysics Data System (ADS)

Yu, Long-Bao; Zhang, Wen-Hai; Ye, Liu

2007-09-01

We propose a simple scheme to realize 1→M economical phase-covariant quantum cloning machine (EPQCM) with superconducting quantum interference device (SQUID) qubits. In our scheme, multi-SQUIDs are fixed into a microwave cavity by adiabatic passage for their manipulation. Based on this model, we can realize the EPQCM with high fidelity via adiabatic quantum computation.

Universal phase diagrams with superconducting domes for electronic flat bands

NASA Astrophysics Data System (ADS)

Löthman, Tomas; Black-Schaffer, Annica M.

2017-08-01

Condensed matter systems with flat bands close to the Fermi level generally exhibit, due to their very large density of states, extraordinarily high critical ordering temperatures of symmetry-breaking orders, such as superconductivity and magnetism. Here we show that the critical temperatures follow one of two universal curves with doping away from a flat band depending on the ordering channel, which completely dictates both the general order competition and the phase diagram. Notably, we find that orders in the particle-particle channel (superconducting orders) survive decisively farther than orders in the particle-hole channel (magnetic or charge orders) because the channels have fundamentally different polarizabilities. Thus, even if a magnetic or charge order initially dominates, superconducting domes are still likely to exist on the flanks of flat bands. We apply these general results to both the topological surface flat bands of rhombohedral ABC-stacked graphite and to the Van Hove singularity of graphene.

Photoemission and muon spin relaxation spectroscopy of the iron-based Rb0.77Fe1.61Se2 superconductor: Crucial role of the cigar-shaped Fermi surface

NASA Astrophysics Data System (ADS)

Maletz, J.; Zabolotnyy, V. B.; Evtushinsky, D. V.; Yaresko, A. N.; Kordyuk, A. A.; Shermadini, Z.; Luetkens, H.; Sedlak, K.; Khasanov, R.; Amato, A.; Krzton-Maziopa, A.; Conder, K.; Pomjakushina, E.; Klauss, H.-H.; Rienks, E. D. L.; Büchner, B.; Borisenko, S. V.

2013-10-01

In this study, we investigate the electronic and magnetic properties of Rb0.77Fe1.61Se2 (Tc = 32.6 K) in normal and superconducting states by means of photoemission and μSR spectroscopies as well as band-structure calculations. We demonstrate that the unusual behavior of these materials is the result of separation into metallic (˜12%) and insulating (˜88%) phases. Only the former becomes superconducting and has a usual electronic structure of electron-doped FeSe slabs. Our results thus imply that the antiferromagnetic insulating phase is just a by-product of Rb intercalation and its magnetic properties have no direct relation to the superconductivity. Instead, we find that also in this class of iron-based compounds, the key ingredient for superconductivity is a certain proximity of a Van Hove singularity to the Fermi level.

Structure and superconductivity in (Bi(0.35)Cu(0.65))Sr2YCu2O7 and related materials

NASA Technical Reports Server (NTRS)

Jennings, R. A.; Williams, S. P.; Greaves, C.

1995-01-01

The recently reported (Bi/Cu)Sr2YCu2O7 phase has been studied by time of flight powder neutron diffraction. The proposed 1212 structure has been confirmed and refinements have shown the oxygen in the (Bi/Cu)O layer is displaced by 0.78 A from the ideal (1/2,1/2,0) site (P4/mmm space group) along /100/. Bond Valence Sum calculations have suggested oxidation states of Bi(5+) and Cu(2+) for the cations in the (Bi/Cu)O layers. The material is non-superconducting and all attempts to induce superconductivity have been unsuccessful. Work on the related material (Ce/Cu)Sr2YCu2O7 has shown the ideal Ce content to be 0.5 Ce per formula unit. The introduction of Ba (10%) onto the Sr site dramatically increases phase stability and also induces superconductivity (62 K).

Nanoscale phase separation of antiferromagnetic order and superconductivity in K0.75Fe1.75Se2

PubMed Central

Yuan, R. H.; Dong, T.; Song, Y. J.; Zheng, P.; Chen, G. F.; Hu, J. P.; Li, J. Q.; Wang, N. L.

2012-01-01

We report an in-plane optical spectroscopy study on the iron-selenide superconductor K0.75Fe1.75Se2. The measurement revealed the development of a sharp reflectance edge below Tc at frequency much smaller than the superconducting energy gap on a relatively incoherent electronic background, a phenomenon which was not seen in any other Fe-based superconductors so far investigated. Furthermore, the feature could be noticeably suppressed and shifted to lower frequency by a moderate magnetic field. Our analysis indicates that this edge structure arises from the development of a Josephson-coupling plasmon in the superconducting condensate. Together with the transmission electron microscopy analysis, our study yields compelling evidence for the presence of nanoscale phase separation between superconductivity and magnetism. The results also enable us to understand various seemingly controversial experimental data probed from different techniques. PMID:22355735

Casimir energy for two and three superconducting coupled cavities: Numerical calculations

NASA Astrophysics Data System (ADS)

Rosa, L.; Avino, S.; Calloni, E.; Caprara, S.; De Laurentis, M.; De Rosa, R.; Esposito, Giampiero; Grilli, M.; Majorana, E.; Pepe, G. P.; Petrarca, S.; Puppo, P.; Rapagnani, P.; Ricci, F.; Rovelli, C.; Ruggi, P.; Saini, N. L.; Stornaiolo, C.; Tafuri, F.

2017-11-01

In this paper we study the behavior of the Casimir energy of a "multi-cavity" across the transition from the metallic to the superconducting phase of the constituting plates. Our analysis is carried out in the framework of the ARCHIMEDES experiment, aiming at measuring the interaction of the electromagnetic vacuum energy with a gravitational field. For this purpose it is foreseen to modulate the Casimir energy of a layered structure composing a multy-cavity coupled system by inducing a transition from the metallic to the superconducting phase. This implies a thorough study of the behavior of the cavity, in which normal metallic layers are alternated with superconducting layers, across the transition. Our study finds that, because of the coupling between the cavities, mainly mediated by the transverse magnetic modes of the radiation field, the variation of energy across the transition can be very large.

Topological Dirac line nodes and superconductivity coexist in SnSe at high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xuliang; Lu, Pengchao; Wang, Xuefei

2017-10-01

We report on the discovery of a pressure-induced topological and superconducting phase of SnSe, a material which attracts much attention recently due to its superior thermoelectric properties. In situ high-pressure electrical transport and synchrotron x-ray diffraction measurements show that the superconductivity emerges along with the formation of a CsCl-type structural phase of SnSe above around 27 GPa, with a maximum critical temperature of 3.2 K at 39 GPa. Based on ab initio calculations, this CsCl-type SnSe is predicted to be a Dirac line-node (DLN) semimetal in the absence of spin-orbit coupling, whose DLN states are protected by the coexistence ofmore » time-reversal and inversion symmetries. These results make CsCl-type SnSe an interesting model platform with simple crystal symmetry to study the interplay of topological physics and superconductivity.« less

Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high temperature superconductor La 2-x(Sr;Ba) xCuO 4

DOE PAGES

Wagman, J. J.; Carlo, Jeremy P.; Gaudet, J.; ...

2016-03-14

We present time-of-flight neutron-scattering measurements on single crystals of La 2-xBa xCuO 4 (LBCO) with 0 ≤ x ≤ 0.095 and La 2-xSr xCuO 4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high temperature cuprate superconductivity, ranging from insulating, three dimensional commensurate long range antiferromagnetic order for x ≤ 0.02 to two dimensional (2D) incommensurate antiferromagnetism co-existing with superconductivity for x ≥ 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear resonant enhancement of the inelastic scattering coincident with the low energy crossingsmore » of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore we show that the low temperature, low energy magnetic spectral weight is substantially larger for samples with non-superconducting ground states relative to any of the samples with superconducting ground states. Lastly spin gaps, suppression of low energy magnetic spectral weight, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO« less

Electron pairing without superconductivity

NASA Astrophysics Data System (ADS)

Levy, Jeremy

Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. Support from AFOSR, ONR, ARO, NSF, DOE and NSSEFF is gratefully acknowledged.

Recent Topics of Organic Superconductors

NASA Astrophysics Data System (ADS)

Ardavan, Arzhang; Brown, Stuart; Kagoshima, Seiichi; Kanoda, Kazushi; Kuroki, Kazuhiko; Mori, Hatsumi; Ogata, Masao; Uji, Shinya; Wosnitza, Jochen

2012-01-01

Recent developments in research into superconductivity in organic materials are reviewed. In the epoch-defining quasi-one-dimensional TMTSF superconductors with Tc ˜ 1 K, Tc decreases monotonically with increasing pressure, as do signatures of spin fluctuations in the normal state, providing good evidence for magnetically-mediated pairing. Upper critical fields exceed the Zeeman-limiting field by several times, suggesting triplet pairing or a transition to an inhomogeneous superconducting state at high magnetic fields, while triplet pairing is ruled out at low fields by NMR Knight-shift measurements. Evidence for a spatially inhomogeneous superconducting state, Fulde--Ferrel--Larkin--Ovchinnikov state, which has long been sought in various superconducting systems, is now captured by thermodynamic and transport measurements for clean and highly two-dimensional BEDT-TTF and BETS superconductors. Some of the layered superconductors also serve as model systems for Mott physics on anisotropic triangular lattice. For example, the Nernst effect and the pseudo-gap behavior in NMR relaxation are enhanced near to the Mott transition. In the case of increasing spin frustration, the superconducting transition temperature is depressed, and antiferromagnetic ordering is eliminated altogether in the adjacent Mott insulating phase. There is an increasing number of materials exhibiting superconductivity in competition or cooperation with charge order. Theoretical studies shed light on the role of spin and/or charge fluctuations for superconductivity appearing under conditions close to those of correlation-induced insulating phases in the diversity of organic materials.

Nematic and chiral superconductivity induced by odd-parity fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Fengcheng; Martin, Ivar

Recent experiments indicate that superconductivity in Bi 2Se 3 intercalated with Cu, Nb, or Sr is nematic with rotational symmetry breaking. Motivated by this observation, we present a model study of nematic and chiral superconductivity induced by odd-parity fluctuations. Additionally, we show that odd-parity fluctuations in the two-component E u representation of D 3d crystal point group can generate attractive interaction in both the even-parity s-wave and odd-parity E-u pairing channels, but repulsive interaction in other odd-parity pairing channels. Coulomb repulsion can suppress s-wave pairing relative to E u pairing, and thus the latter can have a higher critical temperature.more » E u pairing has two distinct phases: a nematic phase and a chiral phase, both of which can be realized in our model. Finally, when s-wave and E u pairings have similar instability temperature, we find an intermediate phase in which both types of pairing coexist.« less

Nematic and chiral superconductivity induced by odd-parity fluctuations

DOE PAGES

Wu, Fengcheng; Martin, Ivar

2017-10-09

Recent experiments indicate that superconductivity in Bi 2Se 3 intercalated with Cu, Nb, or Sr is nematic with rotational symmetry breaking. Motivated by this observation, we present a model study of nematic and chiral superconductivity induced by odd-parity fluctuations. Additionally, we show that odd-parity fluctuations in the two-component E u representation of D 3d crystal point group can generate attractive interaction in both the even-parity s-wave and odd-parity E-u pairing channels, but repulsive interaction in other odd-parity pairing channels. Coulomb repulsion can suppress s-wave pairing relative to E u pairing, and thus the latter can have a higher critical temperature.more » E u pairing has two distinct phases: a nematic phase and a chiral phase, both of which can be realized in our model. Finally, when s-wave and E u pairings have similar instability temperature, we find an intermediate phase in which both types of pairing coexist.« less

Highly oriented Bi-based thin films with zero resistance at 106 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kula, W.; Sobolewski, R.; Gorecka, J.

1991-03-01

This paper reports on fabrication and characterization of nearly single-phase superconducting Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} thin films. The films were dc magnetron sputtered from heavily Pb-doped (Pb/Bi molar ratios up to 1.25), sintered targets on unheated MgO, SrTiO{sub 3}, CaNdAlO{sub 4}, and SrLaAlO{sub 4} single crystals. For the films grown on the (100) oriented MgO substrate, less than 1 hour of annealing in air at 870{degrees} C was sufficient to obtain more than 90% of the 110-K-phase material, with highly c-axis oriented crystalline structure and zero resistivity at 106 K. The films fabricated on the other substrates alsomore » exhibited a narrow superconducting transition and were fully superconducting above 100 K, but they consisted of a mixed-phase material with a large percentage of the 80 K phase.« less

Superconductivity in metal coated graphene

NASA Astrophysics Data System (ADS)

Uchoa, Bruno; Castro Neto, Antonio

2007-03-01

Graphene, a single atomic layer of graphite, is a two dimensional (2D) zero gap insulator with a high electronic mobility between nearest neighbor carbon sites. The unique electronic properties of graphene, from the semi-metallic behavior to the observation of an anomalous quantum Hall effect and a zero field quantized minimum of conductivity derive from the relativistic nature of its quasiparticles. By doping graphene, it behaves in several aspects as a conventional Fermi liquid, where electrons may form Cooper pairs by coupling with a bosonic mode. In this talk, we develop a mean-field phenomenology of superconductivity in a honeycomb lattice. We predict the possibility of two distinct phases, a singlet s-wave phase and a novel p+ip wave phase in the singlet channel. At half filling, the p+ip phase is gapless and superconductivity is a hidden order. We propose a few possible sources of Cooper pairing instability in graphene coated with alkaline and transition metals, and similar low dimensional graphene based devices.

Intense beam production of highly charged heavy ions by the superconducting electron cyclotron resonance ion source SECRAL.

PubMed

Zhao, H W; Sun, L T; Zhang, X Z; Guo, X H; Cao, Y; Lu, W; Zhang, Z M; Yuan, P; Song, M T; Zhao, H Y; Jin, T; Shang, Y; Zhan, W L; Wei, B W; Xie, D Z

2008-02-01

There has been increasing demand to provide higher beam intensity and high enough beam energy for heavy ion accelerator and some other applications, which has driven electron cyclotron resonance (ECR) ion source to produce higher charge state ions with higher beam intensity. One of development trends for highly charged ECR ion source is to build new generation ECR sources by utilization of superconducting magnet technology. SECRAL (superconducting ECR ion source with advanced design in Lanzhou) was successfully built to produce intense beams of highly charged ion for Heavy Ion Research Facility in Lanzhou (HIRFL). The ion source has been optimized to be operated at 28 GHz for its maximum performance. The superconducting magnet confinement configuration of the ion source consists of three axial solenoid coils and six sextupole coils with a cold iron structure as field booster and clamping. An innovative design of SECRAL is that the three axial solenoid coils are located inside of the sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. For 28 GHz operation, the magnet assembly can produce peak mirror fields on axis of 3.6 T at injection, 2.2 T at extraction, and a radial sextupole field of 2.0 T at plasma chamber wall. During the commissioning phase at 18 GHz with a stainless steel chamber, tests with various gases and some metals have been conducted with microwave power less than 3.5 kW by two 18 GHz rf generators. It demonstrates the performance is very promising. Some record ion beam intensities have been produced, for instance, 810 e microA of O(7+), 505 e microA of Xe(20+), 306 e microA of Xe(27+), and so on. The effect of the magnetic field configuration on the ion source performance has been studied experimentally. SECRAL has been put into operation to provide highly charged ion beams for HIRFL facility since May 2007.

Intense beam production of highly charged heavy ions by the superconducting electron cyclotron resonance ion source SECRAL (invited)a)

NASA Astrophysics Data System (ADS)

Zhao, H. W.; Sun, L. T.; Zhang, X. Z.; Guo, X. H.; Cao, Y.; Lu, W.; Zhang, Z. M.; Yuan, P.; Song, M. T.; Zhao, H. Y.; Jin, T.; Shang, Y.; Zhan, W. L.; Wei, B. W.; Xie, D. Z.

2008-02-01

There has been increasing demand to provide higher beam intensity and high enough beam energy for heavy ion accelerator and some other applications, which has driven electron cyclotron resonance (ECR) ion source to produce higher charge state ions with higher beam intensity. One of development trends for highly charged ECR ion source is to build new generation ECR sources by utilization of superconducting magnet technology. SECRAL (superconducting ECR ion source with advanced design in Lanzhou) was successfully built to produce intense beams of highly charged ion for Heavy Ion Research Facility in Lanzhou (HIRFL). The ion source has been optimized to be operated at 28GHz for its maximum performance. The superconducting magnet confinement configuration of the ion source consists of three axial solenoid coils and six sextupole coils with a cold iron structure as field booster and clamping. An innovative design of SECRAL is that the three axial solenoid coils are located inside of the sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. For 28GHz operation, the magnet assembly can produce peak mirror fields on axis of 3.6T at injection, 2.2T at extraction, and a radial sextupole field of 2.0T at plasma chamber wall. During the commissioning phase at 18GHz with a stainless steel chamber, tests with various gases and some metals have been conducted with microwave power less than 3.5kW by two 18GHz rf generators. It demonstrates the performance is very promising. Some record ion beam intensities have been produced, for instance, 810eμA of O7+, 505eμA of Xe20+, 306eμA of Xe27+, and so on. The effect of the magnetic field configuration on the ion source performance has been studied experimentally. SECRAL has been put into operation to provide highly charged ion beams for HIRFL facility since May 2007.

Cooling of Compact Stars with Nucleon Superfluidity and Quark Superconductivity

NASA Astrophysics Data System (ADS)

Noda, Tsuneo; Hashimoto, Masa-aki; Yasutake, Nobutoshi; Maruyama, Toshiki; Tatsumi, Toshitaka

We show a cooling scenario of compact stars to satisfy recent observations of compact stars. The central density of compact stars can exceed the nuclear density, and it is considered that many hadronic phases appear at such a density. It is discussed that neutron superfluidity (1S0 for lower density, and 3P2 for higher density) and proton superfluidity/superconductivity (1S0) appears in all compact stars. And some "Exotic" states are considered to appear in compact stars, such as meson condensation, hyperon mixing, deconfinement of quarks and quark colour superconductivity. These exotic states appear at the density region above the threshold densities of each state. We demonstrate the thermal evolution of isolated compact stars, adopting the effects of nucleon superfluidity and quark colour superconductivity. We assume large gap energy (Δ > 10 MeV) for colour superconducting quark phase, and include the effects of nucleon superfluidity with parametrised models. We simulate the cooling history of compact stars, and shows that the heavier star does not always cool faster than lighter one, which is determined by the parameters of neutron 3P2 superfluidity.

Superconductivity in dense carbon-based materials

DOE PAGES

Lu, Siyu; Liu, Hanyu; Naumov, Ivan I.; ...

2016-03-08

Guided by a simple strategy in searching of new superconducting materials we predict that high temperature superconductivity can be realized in classes of high-density materials having strong sp 3 chemical bonding and high lattice symmetry. Here, we examine in detail sodalite carbon frameworks doped with simple metals such as Li, Na, and Al. Though such materials share some common features with doped diamond, their doping level is not limited and the density of states at the Fermi level in them can be as high as that in the renowned MgB 2. Altogether, with other factors, this boosts the superconducting temperaturemore » (T c) in the materials investigated to higher levels compared to doped diamond. For example, the superconducting T c of sodalite-like NaC 6 is predicted to be above 100 K. This phase and a series of other sodalite-based superconductors are predicted to be metastable phases but are dynamically stable. In owing to the rigid carbon framework of these and related dense carbon-materials, these doped sodalite-based structures could be recoverable as potentially useful superconductors.« less

Imaging phase slip dynamics in micron-size superconducting rings

NASA Astrophysics Data System (ADS)

Polshyn, Hryhoriy; Naibert, Tyler R.; Budakian, Raffi

2018-05-01

We present a scanning probe technique for measuring the dynamics of individual fluxoid transitions in multiply connected superconducting structures. In these measurements, a small magnetic particle attached to the tip of a silicon cantilever is scanned over a micron-size superconducting ring fabricated from a thin aluminum film. We find that near the superconducting transition temperature of the aluminum, the dissipation and frequency of the cantilever changes significantly at particular locations where the tip-induced magnetic flux penetrating the ring causes the two lowest-energy fluxoid states to become nearly degenerate. In this regime, we show that changes in the cantilever frequency and dissipation are well-described by a stochastic resonance (SR) process, wherein small oscillations of the cantilever in the presence of thermally activated phase slips (TAPS) in the ring give rise to a dynamical force that modifies the mechanical properties of the cantilever. Using the SR model, we calculate the average fluctuation rate of the TAPS as a function of temperature over a 32-dB range in frequency, and we compare it to the Langer-Ambegaokar-McCumber-Halperin theory for TAPS in one-dimensional superconducting structures.

Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.

PubMed

Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q

2016-09-01

Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.

Persistent ferromagnetism and topological phase transition at the interface of a superconductor and a topological insulator.

PubMed

Qin, Wei; Zhang, Zhenyu

2014-12-31

At the interface of an s-wave superconductor and a three-dimensional topological insulator, Majorana zero modes and Majorana helical states have been proposed to exist respectively around magnetic vortices and geometrical edges. Here we first show that randomly distributed magnetic impurities at such an interface will induce bound states that broaden into impurity bands inside (but near the edges of) the superconducting gap, which remains open unless the impurity concentration is too high. Next we find that an increase in the superconducting gap suppresses both the oscillation magnitude and the period of the Ruderman-Kittel-Kasuya-Yosida interaction between two magnetic impurities. Within a mean-field approximation, the ferromagnetic Curie temperature is found to be essentially independent of the superconducting gap, an intriguing phenomenon due to a compensation effect between the short-range ferromagnetic and long-range antiferromagnetic interactions. The existence of robust superconductivity and persistent ferromagnetism at the interface allows realization of a novel topological phase transition from a nonchiral to a chiral superconducting state at sufficiently low temperatures, providing a new platform for topological quantum computation.

Superconductivity-induced features in the electronic Raman spectrum of monolayer graphene

NASA Astrophysics Data System (ADS)

García-Ruiz, A.; Mucha-Kruczyński, M.; Fal'ko, V. I.

2018-04-01

Using the continuum model, we investigate theoretically the contribution of the low-energy electronic excitations to the Raman spectrum of superconducting monolayer graphene. We consider superconducting phases characterised by an isotropic order parameter in a single valley and find a Raman peak at a shift set by the size of the superconducting gap. The height of this peak is proportional to the square root of the gap and the third power of the Fermi level, and we estimate its quantum efficiency as I ˜10-14 .

System and method for cooling a superconducting rotary machine

DOEpatents

Ackermann, Robert Adolf [Schenectady, NY; Laskaris, Evangelos Trifon [Schenectady, NY; Huang, Xianrui [Clifton Park, NY; Bray, James William [Niskayuna, NY

2011-08-09

A system for cooling a superconducting rotary machine includes a plurality of sealed siphon tubes disposed in balanced locations around a rotor adjacent to a superconducting coil. Each of the sealed siphon tubes includes a tubular body and a heat transfer medium disposed in the tubular body that undergoes a phase change during operation of the machine to extract heat from the superconducting coil. A siphon heat exchanger is thermally coupled to the siphon tubes for extracting heat from the siphon tubes during operation of the machine.

The Pressure Coefficients of the Superconducting Order Parameters at the Ground State of Ferromagnetic Superconductors

NASA Astrophysics Data System (ADS)

Konno, R.; Hatayama, N.; Chaudhury, R.

2014-04-01

We investigated the pressure coefficients of the superconducting order parameters at the ground state of ferromagnetic superconductors based on the microscopic single band model by Linder et al. The superconducting gaps (i) similar to the ones seen in the thin film of A2 phase in liquid 3He and (ii) with the line node were used. This study shows that we would be able to estimate the pressure coefficients of the superconducting and magnetic order parameters at the ground state of ferromagnetic superconductors.

Superconductivity in the Penson-Kolb Model on a Triangular Lattice

NASA Astrophysics Data System (ADS)

Ptok, A.; Mierzejewski, M.

2008-07-01

We investigate properties of the two-dimensional Penson-Kolb model with repulsive pair hopping interaction. In the case of a bipartite square lattice this interaction may lead to the η-type pairing, when the phase of superconducting order parameter changes from one lattice site to the neighboring one. We show that this interaction may be responsible for the onset of superconductivity also for a triangular lattice. We discuss the spatial dependence of the superconducting order parameter and demonstrate that the total momentum of the paired electrons is determined by the lattice geometry.

Probing the strongly driven spin-boson model in a superconducting quantum circuit.

PubMed

Magazzù, L; Forn-Díaz, P; Belyansky, R; Orgiazzi, J-L; Yurtalan, M A; Otto, M R; Lupascu, A; Wilson, C M; Grifoni, M

2018-04-11

Quantum two-level systems interacting with the surroundings are ubiquitous in nature. The interaction suppresses quantum coherence and forces the system towards a steady state. Such dissipative processes are captured by the paradigmatic spin-boson model, describing a two-state particle, the "spin", interacting with an environment formed by harmonic oscillators. A fundamental question to date is to what extent intense coherent driving impacts a strongly dissipative system. Here we investigate experimentally and theoretically a superconducting qubit strongly coupled to an electromagnetic environment and subjected to a coherent drive. This setup realizes the driven Ohmic spin-boson model. We show that the drive reinforces environmental suppression of quantum coherence, and that a coherent-to-incoherent transition can be achieved by tuning the drive amplitude. An out-of-equilibrium detailed balance relation is demonstrated. These results advance fundamental understanding of open quantum systems and bear potential for the design of entangled light-matter states.

Quantum phases in circuit QED with a superconducting qubit array

PubMed Central

Zhang, Yuanwei; Yu, Lixian; Liang, J. -Q; Chen, Gang; Jia, Suotang; Nori, Franco

2014-01-01

Circuit QED on a chip has become a powerful platform for simulating complex many-body physics. In this report, we realize a Dicke-Ising model with an antiferromagnetic nearest-neighbor spin-spin interaction in circuit QED with a superconducting qubit array. We show that this system exhibits a competition between the collective spin-photon interaction and the antiferromagnetic nearest-neighbor spin-spin interaction, and then predict four quantum phases, including: a paramagnetic normal phase, an antiferromagnetic normal phase, a paramagnetic superradiant phase, and an antiferromagnetic superradiant phase. The antiferromagnetic normal phase and the antiferromagnetic superradiant phase are new phases in many-body quantum optics. In the antiferromagnetic superradiant phase, both the antiferromagnetic and superradiant orders can coexist, and thus the system possesses symmetry. Moreover, we find an unconventional photon signature in this phase. In future experiments, these predicted quantum phases could be distinguished by detecting both the mean-photon number and the magnetization. PMID:24522250

Synthesis of superconducting Nb 3Sn coatings on Nb substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barzi, E.; Franz, S.; Reginato, F.

In the present work the electrochemical and thermal syntheses of superconductive Nb 3Sn films are investigated. The Nb 3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm 2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb 3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of aboutmore » 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb 3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb 3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.« less

Synthesis of superconducting Nb 3Sn coatings on Nb substrates

DOE PAGES

Barzi, E.; Franz, S.; Reginato, F.; ...

2015-12-01

In the present work the electrochemical and thermal syntheses of superconductive Nb 3Sn films are investigated. The Nb 3Sn phase is obtained by electrodeposition of Sn layers and Cu intermediate layers onto Nb substrates followed by high temperature diffusion in inert atmosphere. Electrodeposition was performed from aqueous solutions at current densities in the 20 to 50 mA/cm 2 range and at temperatures between 40 and 50°C. Subsequent thermal treatments were realized to obtain the Nb 3Sn superconductive phase. Glow discharge optical emission spectrometry (GDOES) demonstrated that after thermal treatment interdiffusion of Nb and Sn occurred across a thickness of aboutmore » 13 μm. Scanning Electron Microscopy (SEM) allowed accurately measuring the thickness of the Nb 3Sn phase, whose average for the various types of film samples was between 5.7 and 8.0 μm. X-ray diffraction (XRD) patterns confirmed the presence of a cubic Nb 3Sn phase (A15 structure) having (210) preferred orientation. The maximum obtained T c was 17.68 K and the B c20 ranged between 22.5 T and 23.8 T. With the procedure described in the present paper, coating complex shapes cost-effectively becomes possible, which is typical of electrochemical techniques. Furthermore, this approach can be implemented in classical wire processes such as "Jelly Roll" or "Rod in Tube", or directly used for producing superconducting surfaces. In conclusion, the potential of this method for Superconducting Radiofrequency (SRF) structures is also outlined.« less

0-π phase-controllable thermal Josephson junction

NASA Astrophysics Data System (ADS)

Fornieri, Antonio; Timossi, Giuliano; Virtanen, Pauli; Solinas, Paolo; Giazotto, Francesco

2017-05-01

Two superconductors coupled by a weak link support an equilibrium Josephson electrical current that depends on the phase difference ϕ between the superconducting condensates. Yet, when a temperature gradient is imposed across the junction, the Josephson effect manifests itself through a coherent component of the heat current that flows opposite to the thermal gradient for |ϕ| < π/2 (refs 2-4). The direction of both the Josephson charge and heat currents can be inverted by adding a π shift to ϕ. In the static electrical case, this effect has been obtained in a few systems, for example via a ferromagnetic coupling or a non-equilibrium distribution in the weak link. These structures opened new possibilities for superconducting quantum logic and ultralow-power superconducting computers. Here, we report the first experimental realization of a thermal Josephson junction whose phase bias can be controlled from 0 to π. This is obtained thanks to a superconducting quantum interferometer that allows full control of the direction of the coherent energy transfer through the junction. This possibility, in conjunction with the completely superconducting nature of our system, provides temperature modulations with an unprecedented amplitude of ∼100 mK and transfer coefficients exceeding 1 K per flux quantum at 25 mK. Then, this quantum structure represents a fundamental step towards the realization of caloritronic logic components such as thermal transistors, switches and memory devices. These elements, combined with heat interferometers and diodes, would complete the thermal conversion of the most important phase-coherent electronic devices and benefit cryogenic microcircuits requiring energy management, such as quantum computing architectures and radiation sensors.

Quantum and superconducting fluctuations effects in disordered Nb 1- xTa x thin films above Tc

NASA Astrophysics Data System (ADS)

Giannouri, M.; Papastaikoudis, C.

1999-05-01

Disordered Nb 1- xTa x thin films are prepared with e-gun coevaporation. The influence of the β-phase of tantalum in the critical temperature Tc is observed as a function of the substrate temperature. The measurements of transverse magnetoresistance at various isothermals are interpreted in terms of weak-localization and superconducting fluctuations. From the fitting procedure, the phase breaking rate τφ-1 and the Larkin parameter βL are estimated as a function of temperature. Conclusions about the dominant inelastic scattering mechanisms at various temperature regions as well as for the dominant mechanism of superconducting fluctuations near the transition temperature are extracted.

Phase Sensitive Measurements of Ferromagnetic Josephson Junctions for Cryogenic Memory Applications

NASA Astrophysics Data System (ADS)

Niedzielski, Bethany Maria

A Josephson junction is made up of two superconducting layers separated by a barrier. The original Josephson junctions, studied in the early 1960's, contained an insulating barrier. Soon thereafter, junctions with normal-metal barriers were also studied. Ferromagnetic materials were not even theoretically considered as a barrier layer until around 1980, due to the competing order between ferromagnetic and superconducting systems. However, many exciting physical phenomena arise in hybrid superconductor/ferromagnetic devices, including devices where the ground state phase difference between the two superconductors is shifted by pi. Since their experimental debut in 2001, so-called pi junctions have been demonstrated by many groups, including my own, in systems with a single ferromagnetic layer. In this type of system, the phase of the junction can be set to either 0 or pi depending on the thickness of the ferromagnetic layer. Of interest, however, is the ability to control the phase of a single junction between the 0 and pi states. This was theoretically shown to be possible in a system containing two ferromagnetic layers (spin-valve junctions). If the materials and their thicknesses are properly chosen to manipulate the electron pair correlation function, then the phase state of a spin-valve Josephson junction should be capable of switching between the 0 and ? phase states when the magnetization directions of the two ferromagnetic layers are oriented in the antiparallel and parallel configurations, respectively. Such a phase-controllable junction would have immediate applications in cryogenic memory, which is a necessary component to an ultra-low power superconducting computer. A fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. The goal of this work was to experimentally verify this prediction for a phase-controllable ferromagnetic Josephson junction. To address this complicated system, first, studies of junctions with only a single ferromagnetic junction were required to determine the 0-pi transition thickness of that material, the decay of the critical current through the junction with thickness, and the switching field of the material. The materials studied included NiFeMo, NiFe, Ni, and NiFeCo. Additionally, roughness studies of several different superconducting base electrodes and normal metal buffer and spacer layers were performed to determine the optimum junction layers. The ferromagnetic layers used were on the order of 1-2 nm thick, so a smooth growth template is imperative to maintain continuous films with in-plane magnetizations. Lastly, single junction spin-valve samples were studied. We are not equipped to measure the phase of a single junction, but series of samples where one ferromagnetic layer is systematically varied in thickness can inform the proper thicknesses needed for 0-pi switching based on relative critical current values between the parallel and antiparallel magnetic configurations. Utilizing this background information, two spin-valve samples were incorporated in a superconducting loop so that the relative phase of the two junctions could be investigated. Through this process, the first phase-controllable ferromagnetic Josephson junctions were experimentally demonstrated using phase-sensitive measurement techniques. This provided the proof of concept for the Josephson Magnetic Random Access Memory (JMRAM), a superconducting memory system in development at Northrop Grumman, with whom we collaborate on this work. Phase-controllable systems were successfully demonstrated using two different magnetic material stacks and verified with several analysis techniques.

Field-induced reentrant superconductivity driven by quantum tricritical fluctuations in URhGe

NASA Astrophysics Data System (ADS)

Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Hattori, T.; Kambe, S.; Araki, S.

2018-05-01

We review our 59Co NMR study in a URhGe single crystal doped with 10% cobalt. The spin-spin relaxation time (T2) measurements have revealed a divergence of electronic spin fluctuations in the vicinity of a field-induced tricritical point (TCP) locating around 13 T. The fluctuations is developed in the same limited field region around the TCP as that where a reentrant superconductivity (RSC) is observed in URhGe. The finding strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC.

Unusual phonon density of states and response to superconducting transition in In-doped topological crystalline insulator Pb 0.5Sn 0.5Te

DOE PAGES

Ran, Keijing; Tranquada, John M.; Zhong, Ruidan; ...

2018-06-30

Here, we present inelastic neutron scattering results of phonons in (Pb 0.5Sn 0.5) 1–xIn xTe powders, with x = 0, and 0.3.The x = 0 sample is a topological crystalline insulator, and the x = 0 . 3 sample is a superconductor with a bulk superconducting transition temperature T c of 4.7 K. In both samples, we observe unexpected van Hove singularities in the phonon density of states at energies of 1– 2.5 meV, suggestive of local modes. On cooling the superconducting sample through T c, there is an enhancement of these features for energies below twice the superconducting-gap energy.more » We further note that the superconductivity in (Pb 0.5Sn 0.5) 1–xIn xTe occurs in samples with normal-state resistivities of order 10 mΩ cm, indicative of bad-metal behavior. Calculations based on density functional theory suggest that the superconductivity is easily explainable in terms of electron-phonon coupling; however, they completely miss the low-frequency modes and do not explain the large resistivity. While the bulk superconducting state of (Pb 0.5Sn 0.5) 0.7In 0.3Te appears to be driven by phonons, a proper understanding will require ideas beyond simple BCS theor« less

Unusual phonon density of states and response to superconducting transition in In-doped topological crystalline insulator Pb 0.5Sn 0.5Te

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ran, Keijing; Tranquada, John M.; Zhong, Ruidan

Here, we present inelastic neutron scattering results of phonons in (Pb 0.5Sn 0.5) 1–xIn xTe powders, with x = 0, and 0.3.The x = 0 sample is a topological crystalline insulator, and the x = 0 . 3 sample is a superconductor with a bulk superconducting transition temperature T c of 4.7 K. In both samples, we observe unexpected van Hove singularities in the phonon density of states at energies of 1– 2.5 meV, suggestive of local modes. On cooling the superconducting sample through T c, there is an enhancement of these features for energies below twice the superconducting-gap energy.more » We further note that the superconductivity in (Pb 0.5Sn 0.5) 1–xIn xTe occurs in samples with normal-state resistivities of order 10 mΩ cm, indicative of bad-metal behavior. Calculations based on density functional theory suggest that the superconductivity is easily explainable in terms of electron-phonon coupling; however, they completely miss the low-frequency modes and do not explain the large resistivity. While the bulk superconducting state of (Pb 0.5Sn 0.5) 0.7In 0.3Te appears to be driven by phonons, a proper understanding will require ideas beyond simple BCS theor« less

Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors.

PubMed

Meng, Qingyou; Varney, Christopher N; Fangohr, Hans; Babaev, Egor

2017-01-25

It was recently proposed to use the stray magnetic fields of superconducting vortex lattices to trap ultracold atoms for building quantum emulators. This calls for new methods for engineering and manipulating of the vortex states. One of the possible routes utilizes type-1.5 superconducting layered systems with multi-scale inter-vortex interactions. In order to explore the possible vortex states that can be engineered, we present two phase diagrams of phenomenological vortex matter models with multi-scale inter-vortex interactions featuring several attractive and repulsive length scales. The phase diagrams exhibit a plethora of phases, including conventional 2D lattice phases, five stripe phases, dimer, trimer, and tetramer phases, void phases, and stable low-temperature disordered phases. The transitions between these states can be controlled by the value of an applied external field.

Effects of short-range order on electronic properties of Zr-Ni glasses as seen from low-temperature specific heat

NASA Astrophysics Data System (ADS)

Kroeger, D. M.; Koch, C. C.; Scarbrough, J. O.; McKamey, C. G.

1984-02-01

Measurements of the low-temperature specific heat Cp of liquid-quenched Zr-Ni glasses for a large number of compositions in the range from 55 to 74 at.% Zr revealed an unusual composition dependence of the density of states at the Fermi level, N(EF). Furthermore, for some compositions the variation of Cp near the superconducting transition temperature Tc indicated the presence of two superconducting phases, i.e., two superconducting transitions were detected. Comparison of the individual Tc's in phase-separated samples to the composition dependence of Tc for all of the samples suggests that amorphous phases with compositions near 60 and 66.7 at.% Zr occur. We discuss these results in terms of an "association model" for liquid alloys (due to Sommer), in which associations of unlike atoms with definite stoichiometries are assumed to exist in equilibrium with unassociated atoms. We conclude that in the composition range studied, associate clusters with the compositions Zr3Ni2 and Zr2Ni occur. In only a few cases are the clusters sufficiently large, compared with the superconducting coherence length, for separate superconducting transitions to be observed. The variation of N(EF) with composition is discussed, as well as the effects of this chemical short-range ordering on the crystallization behavior and glass-forming tendency.

Fluctuation spectroscopy: From Rayleigh-Jeans waves to Abrikosov vortex clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varlamov, A. A.; Galda, A.; Glatz, A.

Superconducting (SC) fluctuations, discovered in the late 1960s, have constituted an important research area in superconductivity as they are manifest in a variety of phenomena. Indeed, the underlying physics of SC fluctuations makes it possible to elucidate the fundamental properties of the superconducting state. The interest in SC fluctuation phenomena was further enhanced with the discovery of cuprate high-temperature superconductors (HTSs). In these materials, superconducting fluctuations appear over a wide range of temperatures due to the superconductors extremely short coherence lengths and low effective dimensionality of the electron systems. These strong fluctuations lead to anomalous properties of the normal statemore » in some HTS materials. Within the framework of the phenomenological Ginzburg-Landau theory, and more extensively in the diagrammatic microscopic approach based on BCS theory, SC fluctuations as well as other quantum contributions (weak localization, etc.) enabled a new way to investigate and characterize disordered electron systems, granular metals, Josephson structures, artificial superlattices, and others. The characteristic feature of SC fluctuations is its strong dependence on temperature and magnetic field in the vicinity of the superconducting phase transition. This dependence allows the separation of fluctuation effects from other contributions and provides information about the microscopic parameters of a material, in particular, the critical temperature and the zero-temperature critical magnetic field. As such, SC fluctuations are very sensitive to the relaxation processes that break phase coherence and can be used as a versatile characterization instrument for SCs: Fluctuation spectroscopy has emerged as a powerful tool for studying the properties of superconducting systems on a quantitative level. Here the physics of SC fluctuations is reviewed, commencing from a qualitative description of thermodynamic fluctuations close to the critical temperature and quantum fluctuations at zero temperature in the vicinity of the second critical field. The analysis of the latter allows us to present fluctuation formation as a fragmentation of the Abrikosov lattice. Finally, this review highlights a series of experimental findings followed by microscopic description and numerical analysis of the effects of fluctuations on numerous properties of superconductors in the entire phase diagram and beyond the superconducting phase.« less

Fluctuation spectroscopy: From Rayleigh-Jeans waves to Abrikosov vortex clusters

DOE PAGES

Varlamov, A. A.; Galda, A.; Glatz, A.

2018-03-27

Superconducting (SC) fluctuations, discovered in the late 1960s, have constituted an important research area in superconductivity as they are manifest in a variety of phenomena. Indeed, the underlying physics of SC fluctuations makes it possible to elucidate the fundamental properties of the superconducting state. The interest in SC fluctuation phenomena was further enhanced with the discovery of cuprate high-temperature superconductors (HTSs). In these materials, superconducting fluctuations appear over a wide range of temperatures due to the superconductors extremely short coherence lengths and low effective dimensionality of the electron systems. These strong fluctuations lead to anomalous properties of the normal statemore » in some HTS materials. Within the framework of the phenomenological Ginzburg-Landau theory, and more extensively in the diagrammatic microscopic approach based on BCS theory, SC fluctuations as well as other quantum contributions (weak localization, etc.) enabled a new way to investigate and characterize disordered electron systems, granular metals, Josephson structures, artificial superlattices, and others. The characteristic feature of SC fluctuations is its strong dependence on temperature and magnetic field in the vicinity of the superconducting phase transition. This dependence allows the separation of fluctuation effects from other contributions and provides information about the microscopic parameters of a material, in particular, the critical temperature and the zero-temperature critical magnetic field. As such, SC fluctuations are very sensitive to the relaxation processes that break phase coherence and can be used as a versatile characterization instrument for SCs: Fluctuation spectroscopy has emerged as a powerful tool for studying the properties of superconducting systems on a quantitative level. Here the physics of SC fluctuations is reviewed, commencing from a qualitative description of thermodynamic fluctuations close to the critical temperature and quantum fluctuations at zero temperature in the vicinity of the second critical field. The analysis of the latter allows us to present fluctuation formation as a fragmentation of the Abrikosov lattice. Finally, this review highlights a series of experimental findings followed by microscopic description and numerical analysis of the effects of fluctuations on numerous properties of superconductors in the entire phase diagram and beyond the superconducting phase.« less

Fluctuation spectroscopy: From Rayleigh-Jeans waves to Abrikosov vortex clusters

NASA Astrophysics Data System (ADS)

Varlamov, A. A.; Galda, A.; Glatz, A.

2018-01-01

Superconducting (SC) fluctuations, discovered in the late 1960s, have constituted an important research area in superconductivity as they are manifest in a variety of phenomena. Indeed, the underlying physics of SC fluctuations makes it possible to elucidate the fundamental properties of the superconducting state. The interest in SC fluctuation phenomena was further enhanced with the discovery of cuprate high-temperature superconductors (HTSs). In these materials, superconducting fluctuations appear over a wide range of temperatures due to the superconductors extremely short coherence lengths and low effective dimensionality of the electron systems. These strong fluctuations lead to anomalous properties of the normal state in some HTS materials. Within the framework of the phenomenological Ginzburg-Landau theory, and more extensively in the diagrammatic microscopic approach based on BCS theory, SC fluctuations as well as other quantum contributions (weak localization, etc.) enabled a new way to investigate and characterize disordered electron systems, granular metals, Josephson structures, artificial superlattices, and others. The characteristic feature of SC fluctuations is its strong dependence on temperature and magnetic field in the vicinity of the superconducting phase transition. This dependence allows the separation of fluctuation effects from other contributions and provides information about the microscopic parameters of a material, in particular, the critical temperature and the zero-temperature critical magnetic field. As such, SC fluctuations are very sensitive to the relaxation processes that break phase coherence and can be used as a versatile characterization instrument for SCs: Fluctuation spectroscopy has emerged as a powerful tool for studying the properties of superconducting systems on a quantitative level. Here the physics of SC fluctuations is reviewed, commencing from a qualitative description of thermodynamic fluctuations close to the critical temperature and quantum fluctuations at zero temperature in the vicinity of the second critical field. The analysis of the latter allows us to present fluctuation formation as a fragmentation of the Abrikosov lattice. This review highlights a series of experimental findings followed by microscopic description and numerical analysis of the effects of fluctuations on numerous properties of superconductors in the entire phase diagram and beyond the superconducting phase.

Apparatus and method for critical current measurements

DOEpatents

Martin, Joe A.; Dye, Robert C.

1992-01-01

An apparatus for the measurement of the critical current of a superconductive sample, e.g., a clad superconductive sample, the apparatus including a conductive coil, a means for maintaining the coil in proximity to a superconductive sample, an electrical connection means for passing a low amplitude alternating current through the coil, a cooling means for maintaining the superconductive sample at a preselected temperature, a means for passing a current through the superconductive sample, and, a means for monitoring reactance of the coil, is disclosed, together with a process of measuring the critical current of a superconductive material, e.g., a clad superconductive material, by placing a superconductive material into the vicinity of the conductive coil of such an apparatus, cooling the superconductive material to a preselected temperature, passing a low amplitude alternating current through the coil, the alternating current capable of generating a magnetic field sufficient to penetrate, e.g., any cladding, and to induce eddy currents in the superconductive material, passing a steadily increasing current through the superconductive material, the current characterized as having a different frequency than the alternating current, and, monitoring the reactance of the coil with a phase sensitive detector as the current passed through the superconductive material is steadily increased whereby critical current of the superconductive material can be observed as the point whereat a component of impedance deviates.

Glass-Derived Superconductive Ceramic

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Farrell, D. E.

1992-01-01

Critical superconducting-transition temperature of 107.2 K observed in specimen made by annealing glass of composition Bi1.5Pb0.5Sr2Ca2Cu3Ox for 243 h at 840 degrees C. PbO found to lower melting temperature and viscosity of glass, possibly by acting as fluxing agent. Suggested partial substitution of lead into bismuth oxide planes of crystalline phase having Tc of 110 K stabilizes this phase and facilitates formation of it.

High-temperature superconducting phase of HBr under pressure predicted by first-principles calculations

NASA Astrophysics Data System (ADS)

Gu, Qinyan; Lu, Pengchao; Xia, Kang; Sun, Jian; Xing, Dingyu

2017-08-01

The high pressure phases of HBr are explored with an ab initio crystal structure search. By taking into account the contribution of zero-point energy (ZPE), we find that the P 4 /n m m phase of HBr is thermodynamically stable in the pressure range from 150 to 200 GPa. The superconducting critical temperature (Tc) of P 4 /n m m HBr is evaluated to be around 73 K at 170 GPa, which is the highest record so far among binary halogen hydrides. Its Tc can be further raised to around 95K under 170 GPa if half of the bromine atoms in the P 4 /n m m HBr are substituted by the lighter chlorine atoms. Our study shows that, in addition to lower mass, higher coordination number, shorter bonds, and more highly symmetric environment for the hydrogen atoms are important factors to enhance the superconductivity in hydrides.

Holographic superconductor on a novel insulator

NASA Astrophysics Data System (ADS)

Ling, Yi; Liu, Peng; Wu, Jian-Pin; Wu, Meng-He

2018-01-01

We construct a holographic superconductor model, based on a gravity theory, which exhibits novel metal-insulator transitions. We investigate the condition for the condensation of the scalar field over the parameter space, and then focus on the superconductivity over the insulating phase with a hard gap, which is supposed to be Mott-like. It turns out that the formation of the hard gap in the insulating phase benefits the superconductivity. This phenomenon is analogous to the fact that the pseudogap phase can promote the pre-pairing of electrons in high {T}{{c}} cuprates. We expect that this work can shed light on understanding the mechanism of high {T}{{c}} superconductivity from the holographic side. Supported by Natural Science Foundation of China (11575195, 11775036, 11305018), Y.L. also acknowledges the support from Jiangxi young scientists (JingGang Star) program and 555 talent project of Jiangxi Province. J. P. Wu is also supported by Natural Science Foundation of Liaoning Province (201602013)

Phase Stability and Superconductivity of Compressed Argon-Hydrogen Compounds from First-Principles

NASA Astrophysics Data System (ADS)

Ishikawa, Takahiro; Nakanishi, Akitaka; Shimizu, Katsuya; Oda, Tatsuki

2017-12-01

We present the phase stability and superconductivity of Ar-H compounds under high pressure predicted by first-principles calculations and a genetic algorithm technique for crystal structure search. We found that insulating ArH4, earlier predicted to be metalized at 350 GPa, survives up to 700 GPa owing to the transition into a new phase Pnma at around 250 GPa and then decomposes into metallic ArH2 and pure solid hydrogen. At around 1500 GPa, the bonding form of ArH2 is changed by the dissociation of H2 molecules at the interstitial site of the argon lattice, and antibonding orbitals are partially filled, which causes an increase in the density of states at the Fermi level. Results showed that electron-phonon coupling is enhanced and the superconducting critical temperature is increased from 0.2 to 67 K.

Improved Magnetron Stability and Reduced Noise in Efficient Transmitters for Superconducting Accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kazakevich, G.; Johnson, R.; Lebedev, V.

State of the art high-current superconducting accelerators require efficient RF sources with a fast dynamic phase and power control. This allows for compensation of the phase and amplitude deviations of the accelerating voltage in the Superconducting RF (SRF) cavities caused by microphonics, etc. Efficient magnetron transmitters with fast phase and power control are attractive RF sources for this application. They are more cost effective than traditional RF sources such as klystrons, IOTs and solid-state amplifiers used with large scale accelerator projects. However, unlike traditional RF sources, controlled magnetrons operate as forced oscillators. Study of the impact of the controlling signalmore » on magnetron stability, noise and efficiency is therefore important. This paper discusses experiments with 2.45 GHz, 1 kW tubes and verifies our analytical model which is based on the charge drift approximation.« less

Modelling nonlinearity in superconducting split ring resonator and its effects on metamaterial structures

NASA Astrophysics Data System (ADS)

Mazdouri, Behnam; Mohammad Hassan Javadzadeh, S.

2017-09-01

Superconducting materials are intrinsically nonlinear, because of nonlinear Meissner effect (NLME). Considering nonlinear behaviors, such as harmonic generation and intermodulation distortion (IMD) in superconducting structures, are very important. In this paper, we proposed distributed nonlinear circuit model for superconducting split ring resonators (SSRRs). This model can be analyzed by using Harmonic Balance method (HB) as a nonlinear solver. Thereafter, we considered a superconducting metamaterial filter which was based on split ring resonators and we calculated fundamental and third-order IMD signals. There are good agreement between nonlinear results from proposed model and measured ones. Additionally, based on the proposed nonlinear model and by using a novel method, we considered nonlinear effects on main parameters in the superconducting metamaterial structures such as phase constant (β) and attenuation factor (α).

Imaging the coexistence of superconductivity and antiferromagnetism in Fe1+yTe1-xSex (x=0.1) using spin-polarized scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Zhou, Haibiao; Aluru, Ramakrishna; Tsurkan, Vladimir; Loidl, Alois; Deisenhofer, Joachim; Wahl, Peter

Magnetism has been widely thought to play an important role in unconventional superconductivity. In iron chalcogenide Fe1+yTe, the bicollinear antiferromagnetim (AFM) can be suppressed by Se doping, and consequently superconductivity appears. Though a competition between the two orders is expected, their relation has never been shown in details. Here, using spin-polarized scanning tunneling microscopy, we explore their relation at the atomic scale in an Fe1+yTe1-xSex (x=0.1) single crystal with TC = 10 K, in a regime of the phase diagram where a spin-glass phase has been detected. We clearly observe the short-range AFM order with domains of a lateral size of 10 nm embedded in a non-magnetic matrix. In addition we observe a superconducting gap with prominent coherent peaks in differential conductance spectroscopy with a gap size 2 Δ 4 mV. Surprisingly, no correlation between the superconducting properties (gap size and zero bias conductance) and the local AFM order is observed, while the coherence peaks are weakened by the existence of excess iron atoms. Our observations put constraints on theories that are aimed at explaining the relation between magnetism and unconventional superconductivity.

Spin-sensitive interference due to Majorana state on the interface between normal and superconducting leads

NASA Astrophysics Data System (ADS)

Barański, J.; Kobiałka, A.; Domański, T.

2017-02-01

We investigate the subgap spectrum and transport properties of the quantum dot on the interface between the metallic and superconducting leads and additionally side-coupled to the edge of the topological superconducting (TS) chain, hosting the Majorana quasiparticle. Due to the chiral nature of the Majorana states only one spin component of the quantum dot electrons (say \\uparrow ) is directly affected, however the proximity induced on-dot pairing transmits its influence on the opposite spin as well. We investigate the unique interferometric patterns driven by the Majorana quasiparticle that are different for each spin component. We also address the spin-sensitive interplay with the Kondo effect manifested at the same zero-energy and we come to the conclusion that quantum interferometry can unambiguously identify the Majorana quasiparticle.

The road to superconducting spintronics

NASA Astrophysics Data System (ADS)

Eschrig, Matthias

Energy efficient computing has become a major challenge, with the increasing importance of large data centres across the world, which already today have a power consumption comparable to that of Spain, with steeply increasing trend. Superconducting computing is progressively becoming an alternative for large-scale applications, with the costs for cooling being largely outweighed by the gain in energy efficiency. The combination of superconductivity and spintronics - ``superspintronics'' - has the potential and flexibility to develop into such a green technology. This young field is based on the observation that new phenomena emerge at interfaces between superconducting and other, competing, phases. The past 15 years have seen a series of pivotal predictions and experimental discoveries relating to the interplay between superconductivity and ferromagnetism. The building blocks of superspintronics are equal-spin Cooper pairs, which are generated at the interface between superconducting and a ferromagnetic materials in the presence of non-collinear magnetism. Such novel, spin-polarised Cooper pairs carry spin-supercurrents in ferromagnets and thus contribute to spin-transport and spin-control. Geometric Berry phases appear during the singlet-triplet conversion process in structures with non-coplanar magnetisation, enhancing functionality of devices, and non-locality introduced by superconducting order leads to long-range effects. With the successful generation and control of equal-spin Cooper pairs the hitherto notorious incompatibility of superconductivity and ferromagnetism has been not only overcome, but turned synergistic. I will discuss these developments and their extraordinary potential. I also will present open questions posed by recent experiments and point out implications for theory. This work is supported by the Engineering and Physical Science Research Council (EPSRC Grant No. EP/J010618/1).

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary.

PubMed

Potočnik, Anton; Krajnc, Andraž; Jeglič, Peter; Takabayashi, Yasuhiro; Ganin, Alexey Y; Prassides, Kosmas; Rosseinsky, Matthew J; Arčon, Denis

2014-03-03

The alkali fullerides, A(3)C(60) (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs(3)C(60) polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/k(B)T(c) = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/k(B)T(c) decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached.

Size and symmetry of the superconducting gap in the f.c.c. Cs3C60 polymorph close to the metal-Mott insulator boundary

PubMed Central

Potočnik, Anton; Krajnc, Andraž; Jeglič, Peter; Takabayashi, Yasuhiro; Ganin, Alexey Y.; Prassides, Kosmas; Rosseinsky, Matthew J.; Arčon, Denis

2014-01-01

The alkali fullerides, A3C60 (A = alkali metal) are molecular superconductors that undergo a transition to a magnetic Mott-insulating state at large lattice parameters. However, although the size and the symmetry of the superconducting gap, Δ, are both crucial for the understanding of the pairing mechanism, they are currently unknown for superconducting fullerides close to the correlation-driven magnetic insulator. Here we report a comprehensive nuclear magnetic resonance (NMR) study of face-centred-cubic (f.c.c.) Cs3C60 polymorph, which can be tuned continuously through the bandwidth-controlled Mott insulator-metal/superconductor transition by pressure. When superconductivity emerges from the insulating state at large interfullerene separations upon compression, we observe an isotropic (s-wave) Δ with a large gap-to-superconducting transition temperature ratio, 2Δ0/kBTc = 5.3(2) [Δ0 = Δ(0 K)]. 2Δ0/kBTc decreases continuously upon pressurization until it approaches a value of ~3.5, characteristic of weak-coupling BCS theory of superconductivity despite the dome-shaped dependence of Tc on interfullerene separation. The results indicate the importance of the electronic correlations for the pairing interaction as the metal/superconductor-insulator boundary is approached. PMID:24584087

Progress towards 3-cell superconducting traveling wave cavity cryogenic test

NASA Astrophysics Data System (ADS)

Kostin, R.; Avrakhov, P.; Kanareykin, A.; Yakovlev, V.; Solyak, N.

2017-12-01

This paper describes a superconducting L-band travelling wave cavity for electron linacs as an alternative to the 9-cell superconducting standing wave Tesla type cavity. A superconducting travelling wave cavity may provide 20-40% higher accelerating gradient by comparison with conventional cavities. This feature arises from an opportunity to use a smaller phase advance per cell which increases the transit time factor and affords the opportunity to use longer cavities because of its significantly smaller sensitivity to manufacturing errors. Two prototype superconducting travelling wave cavities were designed and manufactured for a high gradient travelling wave demonstration at cryogenic temperature. This paper presents the main milestones achieved towards this test.

In situ/non-contact superfluid density measurement apparatus

NASA Astrophysics Data System (ADS)

Nam, Hyoungdo; Su, Ping-Hsang; Shih, Chih-Kang

2018-04-01

We present a double-coil apparatus designed to operate with in situ capability, which is strongly desired for superconductivity studies on recently discovered two-dimensional superconductors. Coupled with a scanning tunneling microscope, the study of both local and global superconductivity [for superconducting gap and superfluid density (SFD), respectively] is possible on an identical sample without sample degradations due to damage, contamination, or oxidation in an atmosphere. The performance of the double-coil apparatus was tested on atomically clean surfaces of non-superconducting Si(111)-7 × 7 and on superconducting films of 100 nm-thick Pb and 1.4 nm-ultrathin Pb. The results clearly show the normal-to-superconductor phase transition for Pb films with a strong SFD.

Spin liquid polymorphism in a correlated electron system on the threshold of superconductivity

DOE PAGES

Zalinznyak, Igor; Savici, Andrei T.; Lumsden, Mark D.; ...

2015-08-18

We report neutron scattering measurements which reveal spin-liquid polymorphism in an “11” iron chalcogenide superconductor. It occurs when a poorly metallic magnetic state of FeTe is tuned toward superconductivity by substitution of a small amount of tellurium with isoelectronic sulfur. We also observe a liquid-like magnetic response, which is described by the coexistence of two disordered magnetic phases with different local structures whose relative abundance depends on temperature. One is the ferromagnetic (FM) plaquette phase observed in undoped, nonsuperconducting FeTe, which preserves the C 4 symmetry of the underlying square lattice and is favored at high temperatures, whereas the othermore » is the antiferromagnetic plaquette phase with broken C 4 symmetry, which emerges with doping and is predominant at low temperatures. These findings suggest the coexistence of and competition between two distinct liquid states, and a liquid–liquid phase transformation between these states, in the electronic spin system of FeTe 1-x(S,Se) x. We have thus discovered the remarkable physics of competing spin-liquid polymorphs in a correlated electron system approaching superconductivity. These results facilitate an understanding of large swaths of recent experimental data in unconventional superconductors. In particular, the phase with lower C 2 local symmetry, whose emergence precedes superconductivity, naturally accounts for a propensity for forming electronic nematic states which have been observed experimentally, in cuprate and iron-based superconductors alike.« less

Modeling tunneling for the unconventional superconducting proximity effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zareapour, Parisa; Xu, Jianwei; Zhao, Shu Yang F.

Recently there has been reinvigorated interest in the superconducting proximity effect, driven by predictions of the emergence of Majorana fermions. To help guide this search, we have developed a phenomenological model for the tunneling spectra in anisotropic superconductor-normal metal proximity devices. We combine successful approaches used in s-wave proximity and standard d-wave tunneling to reproduce tunneling spectra in d-wave proximity devices, and clarify the origin of various features. Different variations of the pair potential are considered, resulting from the proximity-induced superconductivity. Furthermore, the effective pair potential felt by the quasiparticles is momentum-dependent in contrast to s-wave superconductors. The probabilities ofmore » reflection and transmission are calculated by solving the Bogoliubov equations. Our results are consistent with experimental observations of the unconventional proximity effect and provide important experimental parameters such as the size and length scale of the proximity induced gap, as well as the conditions needed to observe the reduced and full superconducting gaps.« less

Modeling tunneling for the unconventional superconducting proximity effect

DOE PAGES

Zareapour, Parisa; Xu, Jianwei; Zhao, Shu Yang F.; ...

2016-10-12

Recently there has been reinvigorated interest in the superconducting proximity effect, driven by predictions of the emergence of Majorana fermions. To help guide this search, we have developed a phenomenological model for the tunneling spectra in anisotropic superconductor-normal metal proximity devices. We combine successful approaches used in s-wave proximity and standard d-wave tunneling to reproduce tunneling spectra in d-wave proximity devices, and clarify the origin of various features. Different variations of the pair potential are considered, resulting from the proximity-induced superconductivity. Furthermore, the effective pair potential felt by the quasiparticles is momentum-dependent in contrast to s-wave superconductors. The probabilities ofmore » reflection and transmission are calculated by solving the Bogoliubov equations. Our results are consistent with experimental observations of the unconventional proximity effect and provide important experimental parameters such as the size and length scale of the proximity induced gap, as well as the conditions needed to observe the reduced and full superconducting gaps.« less

Imaging of super-fast dynamics and flow instabilities of superconducting vortices

DOE PAGES

Embon, L.; Anahory, Y.; Jelić, Ž. L.; ...

2017-07-20

Quantized magnetic vortices driven by electric current determine key electromagnetic properties of superconductors. And while the dynamic behavior of slow vortices has been thoroughly investigated, the physics of ultrafast vortices under strong currents remains largely unexplored. Here, we use a nanoscale scanning superconducting quantum interference device to image vortices penetrating into a superconducting Pb film at rates of tens of GHz and moving with velocities of up to tens of km/s, which are not only much larger than the speed of sound but also exceed the pair-breaking speed limit of superconducting condensate. These experiments reveal formation of mesoscopic vortex channelsmore » which undergo cascades of bifurcations as the current and magnetic field increase. Our numerical simulations predict metamorphosis of fast Abrikosov vortices into mixed Abrikosov-Josephson vortices at even higher velocities. Our work offers an insight into the fundamental physics of dynamic vortex states of superconductors at high current densities, crucial for many applications.« less

Entropy generation and momentum transfer in the superconductor-normal and normal-superconductor phase transformations and the consistency of the conventional theory of superconductivity

NASA Astrophysics Data System (ADS)

Hirsch, J. E.

2018-05-01

Since the discovery of the Meissner effect, the superconductor to normal (S-N) phase transition in the presence of a magnetic field is understood to be a first-order phase transformation that is reversible under ideal conditions and obeys the laws of thermodynamics. The reverse (N-S) transition is the Meissner effect. This implies in particular that the kinetic energy of the supercurrent is not dissipated as Joule heat in the process where the superconductor becomes normal and the supercurrent stops. In this paper, we analyze the entropy generation and the momentum transfer between the supercurrent and the body in the S-N transition and the N-S transition as described by the conventional theory of superconductivity. We find that it is not possible to explain the transition in a way that is consistent with the laws of thermodynamics unless the momentum transfer between the supercurrent and the body occurs with zero entropy generation, for which the conventional theory of superconductivity provides no mechanism. Instead, we point out that the alternative theory of hole superconductivity does not encounter such difficulties.

Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe

DOE PAGES

Sun, J. P.; Matsuura, K.; Ye, G. Z.; ...

2016-07-19

The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (T c) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of T c has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ~15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ~6 GPa the sudden enhancement of superconductivity (T c ≤ 38.3 K) accompanies a suppressionmore » of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-T c phase above 6 GPa. In conclusion, the obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-T c cuprates.« less

Formation of the 110-K superconducting phase in Pb-doped Bi-Sr-Ca-Cu-O thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kula, W.; Sobolewski, R.; Gorecka, J.

1991-09-15

Investigation of the 110-K Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {ital x}} phase formation in superconducting thin films of Bi-based cuprates is reported. The films were dc magnetron sputtered from single Bi(Pb)-Sr-Ca-Cu-O targets of various stoichiometries, and subsequently annealed in air at high temperatures. The influence of the initial Pb content, annealing conditions, as well as the substrate material on the growth of the 110-K phase was investigated. We found that the films, fully superconducting above 100 K could be reproducibly fabricated on various dielectric substrates from Pb-rich targets by optimizing annealing conditions for each initial Pb/Bi ratio. Heavy Pb dopingmore » considerably accelerated formation of the 110-K phase, reducing the film annealing time to less than 1 h. Films containing, according to the x-ray measurement, more than 90% of the 110-K phase were obtained on MgO substrates, after sputtering from the Bi{sub 2}Pb{sub 2.5}Sr{sub 2}Ca{sub 2.15}Cu{sub 3.3}O{sub {ital x}} target and annealing in air for 1 h at 870 {degree}C. The films were {ital c}-axis oriented, with 4.5-K-wide superconducting transition, and zero resistivity at 106 K. Their critical current density was 2 {times} 10{sup 2} A/cm{sup 2} at 90 K, and above 10{sup 4} A/cm{sup 2} below 60 K. The growth of the 110-K phase on epitaxial substrates, such as CaNdAlO{sub 4} and SrTiO{sub 3}, was considerably deteriorated, and the presence of the 80- and 10-K phases was detected. Nevertheless, the best films deposited on these substrates were fully superconducting at 104 K and exhibited critical current densities above 2 {times} 10{sup 5} A/cm{sup 2} below 60 K{minus}one order of magnitude greater than the films deposited on MgO.« less

Colloquium: High pressure and road to room temperature superconductivity

NASA Astrophysics Data System (ADS)

Gor'kov, Lev P.; Kresin, Vladimir Z.

2018-01-01

This Colloquium is concerned with the superconducting state of new high-Tc compounds containing hydrogen ions (hydrides). Recently superconductivity with the record-setting transition temperature of Tc=203 K was reported for sulfur hydrides under high pressure. In general, high pressure serves as a path finding tool toward novel structures, including those with very high Tc . The field has a rich and interesting history. Currently, it is broadly recognized that superconductivity in sulfur hydrides owes its origin to the phonon mechanism. However, the picture differs from the conventional one in important ways. The phonon spectrum in sulfur hydride is both broad and has a complex structure. Superconductivity arises mainly due to strong coupling to the high-frequency optical modes, although the acoustic phonons also make a noticeable contribution. A new approach is described, which generalizes the standard treatment of the phonon mechanism and makes it possible to obtain an analytical expression for Tc in this phase. It turns out that, unlike in the conventional case, the value of the isotope coefficient (for the deuterium-hydrogen substitution) varies with the pressure and reflects the impact of the optical modes. The phase diagram, that is the pressure dependence of Tc , is rather peculiar. A crucial feature is that increasing pressure results in a series of structural transitions, including the one which yields the superconducting phase with the record Tc of 203 K. In a narrow region near P ≈150 GPa the critical temperature rises sharply from Tc≈120 to ≈200 K . It seems that the sharp structural transition, which produces the high-Tc phase, is a first-order phase transition caused by interaction between the order parameter and lattice deformations. A remarkable feature of the electronic spectrum in the high-Tc phase is the appearance of small pockets at the Fermi level. Their presence leads to a two-gap spectrum, which can, in principle, be observed with the future use of tunneling spectroscopy. This feature leads to nonmonotonic and strongly asymmetric pressure dependence of Tc . Other hydrides, e.g., CaH6 and MgH6 , can be expected to display even higher values of Tc up to room temperature. The fundamental challenge lies in the creation of a structure capable of displaying high Tc at ambient pressure.

Superconducting Continuous Graphene Fibers via Calcium Intercalation.

PubMed

Liu, Yingjun; Liang, Hui; Xu, Zhen; Xi, Jiabin; Chen, Genfu; Gao, Weiwei; Xue, Mianqi; Gao, Chao

2017-04-25

Superconductors are important materials in the field of low-temperature magnet applications and long-distance electrical power transmission systems. Besides metal-based superconducting materials, carbon-based superconductors have attracted considerable attention in recent years. Up to now, five allotropes of carbon, including diamond, graphite, C 60 , CNTs, and graphene, have been reported to show superconducting behavior. However, most of the carbon-based superconductors are limited to small size and discontinuous phases, which inevitably hinders further application in macroscopic form. Therefore, it raises a question of whether continuously carbon-based superconducting wires could be accessed, which is of vital importance from viewpoints of fundamental research and practical application. Here, inspired by superconducting graphene, we successfully fabricated flexible graphene-based superconducting fibers via a well-established calcium (Ca) intercalation strategy. The resultant Ca-intercalated graphene fiber (Ca-GF) shows a superconducting transition at ∼11 K, which is almost 2 orders of magnitude higher than that of early reported alkali metal intercalated graphite and comparable to that of commercial superconducting NbTi wire. The combination of lightness and easy scalability makes Ca-GF highly promising as a lightweight superconducting wire.

Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films.

PubMed

Zhao, Lin; Liang, Aiji; Yuan, Dongna; Hu, Yong; Liu, Defa; Huang, Jianwei; He, Shaolong; Shen, Bing; Xu, Yu; Liu, Xu; Yu, Li; Liu, Guodong; Zhou, Huaxue; Huang, Yulong; Dong, Xiaoli; Zhou, Fang; Liu, Kai; Lu, Zhongyi; Zhao, Zhongxian; Chen, Chuangtian; Xu, Zuyan; Zhou, X J

2016-02-08

The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

Crystalline Symmetry-Protected Majorana Mode in Number-Conserving Dirac Semimetal Nanowires

NASA Astrophysics Data System (ADS)

Zhang, Rui-Xing; Liu, Chao-Xing

2018-04-01

One of the cornerstones for topological quantum computations is the Majorana zero mode, which has been intensively searched in fractional quantum Hall systems and topological superconductors. Several recent works suggest that such an exotic mode can also exist in a one-dimensional (1D) interacting double-wire setup even without long-range superconductivity. A notable instability in these proposals comes from interchannel single-particle tunneling that spoils the topological ground state degeneracy. Here we show that a 1D Dirac semimetal (DSM) nanowire is an ideal number-conserving platform to realize such Majorana physics. By inserting magnetic flux, a DSM nanowire is driven into a 1D crystalline-symmetry-protected semimetallic phase. Interaction enables the emergence of boundary Majorana zero modes, which is robust as a result of crystalline symmetry protection. We also explore several experimental consequences of Majorana signals.

Quantum phase transitions and phase diagram for a one-dimensional p-wave superconductor with an incommensurate potential.

PubMed

Cai, X

2014-04-16

The effect of the incommensurate potential is studied for the one-dimensional p-wave superconductor. It is determined by analyzing various properties, such as the superconducting gap, the long-range order of the correlation function, the inverse participation ratio and the Z2 topological invariant, etc. In particular, two important aspects of the effect are investigated: (1) as disorder, the incommensurate potential destroys the superconductivity and drives the system into the Anderson localized phase; (2) as a quasi-periodic potential, the incommensurate potential causes band splitting and turns the system with certain chemical potential into the band insulator phase. A full phase diagram is also presented in the chemical potential-incommensurate potential strength plane.

Realizing a partial general quantum cloning machine with superconducting quantum-interference devices in a cavity QED

NASA Astrophysics Data System (ADS)

Fang, Bao-Long; Yang, Zhen; Ye, Liu

2009-05-01

We propose a scheme for implementing a partial general quantum cloning machine with superconducting quantum-interference devices coupled to a nonresonant cavity. By regulating the time parameters, our system can perform optimal symmetric (asymmetric) universal quantum cloning, optimal symmetric (asymmetric) phase-covariant cloning, and optimal symmetric economical phase-covariant cloning. In the scheme the cavity is only virtually excited, thus, the cavity decay is suppressed during the cloning operations.

Synthesis and characterization of YBaCu2O5-δ compound

NASA Astrophysics Data System (ADS)

Ehsandoust, A.; Sandoghchi, M.; Mokhtari, P.; Akhavan, M.

2018-05-01

YBaCu2O5 compound as one of the possible microstructures of Y3Ba5Cu8O19 has been synthesized. The X-ray diffraction analysis of this compound indicates that its formation is accompanied with the formation of YBa2Cu3O7-δ. The observed superconductivity around ∼92 K supports this. So, it seems that YBa2Cu3O7-δ is responsible for the observed superconductivity in YBaCu2O5, and this phase is not an independent superconducting phase. Consequently, the overall effect of the YBaCu2O5 formation during the Y3Ba5Cu8O19 fabrication process could be a reduction in Tc.

Crystal Structure and Superconductivity of PH 3 at High Pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Hanyu; Li, Yinwei; Gao, Guoying

2016-02-04

We have performed a systematic structure search on solid PH3 at high pressures using the particle swarm optimization method. At 100–200 GPa, the search led to two structures which along with others have P–P bonds. These structures are structurally and chemically distinct from those predicted for the high-pressure superconducting H2S phase, which has a different topology (i.e., does not contain S–S bonds). Phonon and electron–phonon coupling calculations indicate that both structures are dynamically stable and superconducting. The pressure dependence and critical temperature for the monoclinic (C2/m) phase of 83 K at 200 GPa are in excellent agreement with a recentmore » experimental report.« less

Study of the superconducting properties of the Bi-Ca-Sr-Cu-O system

NASA Technical Reports Server (NTRS)

Khan, Musheer H.; Naqvi, S. M. M. R.; Zia-Ul-haq, S. M.

1991-01-01

High Temperature Superconductivity in the Bi-Ca-Sr-Cu-O System has been observed and has attracted considerable attention in 1988. The 80 K superconductivity phase has been identified to have a composition of Bi2CaSr2Cu2Ox, while the 110 K phase as reported in the literature has a possible composition of Bi2Ca2Sr2Cu3O(x). Researchers present here a study of the electrical properties of bulk samples of the slowly cooled and rapidly quenched 2:1:2:2 system. The samples used in this study were prepared from appropriate amounts of Bi2O3, CuO, SrCO3, CaCO3.

Composition dependence of superconductivity in YBa2(Cu(3-x)Al(x))O(y)

NASA Technical Reports Server (NTRS)

Bansal, N. P.

1993-01-01

Eleven different compositions in the system YBa2(Cu(3-x)Al(x))O(y) (x = 0 to 0.3) have been synthesized and characterized by electrical resistivity measurements, powder X-ray diffraction, and scanning electron microscopy. The superconducting transition temperature T sub c (onset) was almost unaffected by the presence of alumina due to its limited solubility in YBa2Cu3O(7-x). However, T sub c(R = 0) gradually decreased, and the resistive tails became longer with increasing Al2O3 concentration. This was probably due to formation of BaAl2O4 and other impurity phases from chemical decomposition of the superconducting phase by reaction with Al2O3.

Varying Eu2+ magnetic order by chemical pressure in EuFe2(As1-xPx)2

NASA Astrophysics Data System (ADS)

Zapf, S.; Wu, D.; Bogani, L.; Jeevan, H. S.; Gegenwart, P.; Dressel, M.

2011-10-01

Based on low-field magnetization measurements on a series of single crystals, we present a scheme of the Eu2+ spin alignment in EuFe2(As1-xPx)2. We explain observations of the Eu2+ ordering previously reported, reconciling different existing phase diagrams. The magnetic moments of the Eu2+ ions are slightly canted, yielding a ferromagnetic contribution along the c direction that becomes stronger with pressure, until superconductivity sets in. The spin-density wave as well as the superconducting phase coexist with an antiferromagnetic interlayer coupling of the canted spins. Reducing the interlayer distance finally leads to a ferromagnetic Eu2+ interlayer coupling and to the suppression of superconductivity.

Exotic superconducting states in the extended attractive Hubbard model.

PubMed

Nayak, Swagatam; Kumar, Sanjeev

2018-04-04

We show that the extended attractive Hubbard model on a square lattice allows for a variety of superconducting phases, including exotic mixed-symmetry phases with [Formula: see text] and [Formula: see text] symmetries, and a novel [Formula: see text] state. The calculations are performed within the Hartree-Fock Bardeen-Cooper-Schrieffer framework. The ground states of the mean-field Hamiltonian are obtained via a minimization scheme that relaxes the symmetry constraints on the superconducting solutions, hence allowing for a mixing of s-, p- and d-wave order parameters. The results are obtained within the assumption of uniform-density states. Our results show that extended attractive Hubbard model can serve as an effective model for investigating properties of exotic superconductors.

Nuclear magnetic resonance in high magnetic field: Application to condensed matter physics

NASA Astrophysics Data System (ADS)

Berthier, Claude; Horvatić, Mladen; Julien, Marc-Henri; Mayaffre, Hadrien; Krämer, Steffen

2017-05-01

In this review, we describe the potentialities offered by the nuclear magnetic resonance (NMR) technique to explore at a microscopic level new quantum states of condensed matter induced by high magnetic fields. We focus on experiments realised in resistive (up to 34 T) or hybrid (up to 45 T) magnets, which open a large access to these quantum phase transitions. After an introduction on NMR observables, we consider several topics: quantum spin systems (spin-Peierls transition, spin ladders, spin nematic phases, magnetisation plateaus, and Bose-Einstein condensation of triplet excitations), the field-induced charge density wave (CDW) in high-Tc superconductors, and exotic superconductivity including the Fulde-Ferrel-Larkin-Ovchinnikov superconducting state and the field-induced superconductivity due to the Jaccarino-Peter mechanism.

Exotic superconducting states in the extended attractive Hubbard model

NASA Astrophysics Data System (ADS)

Nayak, Swagatam; Kumar, Sanjeev

2018-04-01

We show that the extended attractive Hubbard model on a square lattice allows for a variety of superconducting phases, including exotic mixed-symmetry phases with dx^2-y^2 + i [s + s^*] and dx^2-y^2 + px symmetries, and a novel px + i py state. The calculations are performed within the Hartree-Fock Bardeen-Cooper-Schrieffer framework. The ground states of the mean-field Hamiltonian are obtained via a minimization scheme that relaxes the symmetry constraints on the superconducting solutions, hence allowing for a mixing of s-, p- and d-wave order parameters. The results are obtained within the assumption of uniform-density states. Our results show that extended attractive Hubbard model can serve as an effective model for investigating properties of exotic superconductors.

Decomposition Products of Phosphine Under Pressure: PH 2 Stable and Superconducting?

DOE PAGES

Shamp, Andrew; Terpstra, Tyson; Bi, Tiange; ...

2016-02-17

Evolutionary algorithms (EA) coupled with Density Functional Theory (DFT) calculations have been used to predict the most stable hydrides of phosphorous (PH n, n = 1 - 6) at 100, 150 and 200 GPa. At these pressures phosphine is unstable with respect to decomposition into the elemental phases, as well as PH 2 and H 2. Three metallic PH 2 phases were found to be dynamically stable and superconducting between 100-200 GPa. One of these contains five formula units in the primitive cell and has C2=m symmetry (5FU-C2=m). It is comprised of 1D periodic PH 3-PH-PH 2-PH-PH 3 oligomers. Twomore » structurally related phases consisting of phosphorous atoms that are octahedrally coordinated by four phosphorous atoms in the equatorial positions and two hydrogen atoms in the axial positions (I4=mmm and 2FU-C 2=m) were the most stable phases between 160-200 GPa. Their superconducting critical temperatures (Tc) were computed as being 70 and 76 K, respectively, via the Allen-Dynes modified McMillan formula and using a value of 0.1 for the Coulomb pseudopotential, . Our results suggest that the superconductivity recently observed by Drozdov, Eremets and Troyan when phosphine was subject to pressures of 207 GPa in a diamond anvil cell may result from these, and other, decomposition products of phosphine.« less

Decomposition Products of Phosphine Under Pressure: PH 2 Stable and Superconducting?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shamp, Andrew; Terpstra, Tyson; Bi, Tiange

Evolutionary algorithms (EA) coupled with Density Functional Theory (DFT) calculations have been used to predict the most stable hydrides of phosphorous (PH n, n = 1 - 6) at 100, 150 and 200 GPa. At these pressures phosphine is unstable with respect to decomposition into the elemental phases, as well as PH 2 and H 2. Three metallic PH 2 phases were found to be dynamically stable and superconducting between 100-200 GPa. One of these contains five formula units in the primitive cell and has C2=m symmetry (5FU-C2=m). It is comprised of 1D periodic PH 3-PH-PH 2-PH-PH 3 oligomers. Twomore » structurally related phases consisting of phosphorous atoms that are octahedrally coordinated by four phosphorous atoms in the equatorial positions and two hydrogen atoms in the axial positions (I4=mmm and 2FU-C 2=m) were the most stable phases between 160-200 GPa. Their superconducting critical temperatures (Tc) were computed as being 70 and 76 K, respectively, via the Allen-Dynes modified McMillan formula and using a value of 0.1 for the Coulomb pseudopotential, . Our results suggest that the superconductivity recently observed by Drozdov, Eremets and Troyan when phosphine was subject to pressures of 207 GPa in a diamond anvil cell may result from these, and other, decomposition products of phosphine.« less

Low-energy inelastic response in the superconducting phases of PrOs4Sb12

NASA Astrophysics Data System (ADS)

Setty, Chandan; Wang, Yuxuan; Phillips, Philip W.

2017-08-01

Recent ac susceptibility and polar Kerr effect measurements in the skutterudite superconductor PrOs4Sb12 (POS) (E. M. Levenson-Falk, E. R. Schemm, M. B. Maple, and A. Kapitulnik, arXiv:1609.07535) uncovered the nature of the superconducting double transition from a high-temperature, high-field, time-reversal symmetric phase (or the A phase) to a low-temperature, low-field, time-reversal symmetry-broken phase (or the B phase). Starting from a microscopic model, we derive a Ginzburg-Landau expansion relevant to POS that describes this entrance into the time-reversal symmetry-broken phase along the temperature axis. We also provide a study of the low-energy inelastic (Raman) response in both the A and B phases of POS, and seek additional signatures which could help reveal the exact form of the gap functions previously proposed in these phases. By appropriately manipulating the incoming and scattered light geometries, along with additional subtraction procedures and suitable assumptions, we show that one can access the various irreducible representations contained in the point group describing POS. We demonstrate how to use this technique on example order parameters proposed in POS. Depending on whether there exist nodes along the c axis, we find additional low-energy spectral weight within the superconducting gap in the Eg geometry, a feature that could pinpoint the location of nodes on the Fermi surface.

Europium-based iron pnictides: a unique laboratory for magnetism, superconductivity and structural effects

NASA Astrophysics Data System (ADS)

Zapf, Sina; Dressel, Martin

2017-01-01

Despite decades of intense research, the origin of high-temperature superconductivity in cuprates and iron-based compounds is still a mystery. Magnetism and superconductivity are traditionally antagonistic phenomena; nevertheless, there is basically no doubt left that unconventional superconductivity is closely linked to magnetism. But this is not the whole story; recently, also structural effects related to the so-called nematic phase gained considerable attention. In order to obtain more information about this peculiar interplay, systematic material research is one of the most important attempts, revealing from time to time unexpected effects. Europium-based iron pnictides are the latest example of such a completely paradigmatic material, as they display not only spin-density-wave and superconducting ground states, but also local Eu2+ magnetism at a similar temperature scale. Here we review recent experimental progress in determining the complex phase diagrams of europium-based iron pnictides. The conclusions drawn from the observations reach far beyond these model systems. Thus, although europium-based iron pnictides are very peculiar, they provide a unique platform to study the common interplay of structural-nematic, magnetic and electronic effects in high-temperature superconductors.

Structure and superconductivity in (Bi{sub 0.35}Cu{sub 0.65})Sr{sub 2}YCu{sub 2}O{sub 7} and related materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jennings, R.A.; Williams, S.P.; Greaves, C.

1994-12-31

The recently reported (Bi/Cu)Sr{sub 2}YCu{sub 2}O{sub 7} phase has been studied by time of flight powder neutron diffraction. The proposed 1212 structure has been confirmed and refinements have shown the oxygen in the (Bi/Cu)O layer is displaced by 0.78{angstrom} from the ideal (1/2,1/2,0) site (P4/mmm space group) along (100). Bond Valence Sum calculations have suggested oxidation states of Bi{sup 5+} and Cu{sup 2+} for the cations in the (Bi/Cu)O layers. The material is non-superconducting and all attempts to induce superconductivity have been unsuccessful. Work on the related material (Ce/Cu)Sr{sub 2}YCu{sub 2}O{sub y} has shown the ideal Ce content to bemore » 0.5 Ce per formula unit. The introduction of Ba (10%) onto the Sr site dramatically increases phase stability and also induces superconductivity (62K).« less

Pressure dependence of the charge-density-wave and superconducting states in GdTe 3 ,   TbTe 3 , and DyTe 3

DOE PAGES

Zocco, D. A.; Hamlin, J. J.; Grube, K.; ...

2015-05-14

Here, we present electrical resistivity and ac-susceptibility measurements of GdTe 3, TbTe 3 and DyTe 3 performed under pressure. An upper charge-density-wave (CDW) is suppressed at a rate of dT CW,1/dP~ –85K/GPa. For TbTe 3 and DyTe 3, a second CDW below T CDW,2 increases with pressure until it reaches the T CDW,1(P) line. For GdTe 3, the lower CDW emerges as pressure is increased above ~1GPa. As these two CDW states are suppressed with pressure, superconductivity (SC) appears in the three compounds at lower temperatures. Ac-susceptibility experiments performed on TbTe 3 provide compelling evidence for bulk SC in themore » low-pressure region of the phase diagram. We provide measurements of superconducting critical fields and discuss the origin of a high-pressure superconducting phase occurring above 5 GPa.« less

Casting of superconducting composite materials (M-4)

NASA Technical Reports Server (NTRS)

Togano, Kazumasa

1993-01-01

An aluminum-lead-bismuth alloy is a flexible alloy and is promising for easily workable embedded-type, filament-dispersed superconducting wire material. It is difficult to produce homogeneous ingots of this material because it is easily separated into elements when melted on Earth due to the large specific gravity differences. In this experiment, a homogeneous alloy will first be produced in molten state in microgravity. It will then be returned to Earth and processed into a wire or tape form. It will then be dispersed as the second phase in micro texture form into the primary phase of aluminum. Superconducting wire material with high-critical-magnetic-field characteristics will be produced. The texture of the material will be observed, and its performance will be evaluated. In addition to the above alloy, a four-element alloy will be produced from silver, a rare Earth element, barium, and copper. The alloys will be oxidized and drawn into wire after being returned to Earth. The materials are expected to be forerunners in obtaining superconducting wire materials from oxide superconductors.

Structural stability and phase transition of Bi 2 Te 3 under high pressure and low temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, J. L.; Zhang, S. J.; Zhu, J. L.

2017-09-01

Structural stability and phase transition of topological insulator Bi2Te3 were studied via angle-dispersive synchrotron radiation X-ray diffraction under high pressure and low temperature condition. The results manifest that the R-3m phase (phase I) is stable at 8 K over the pressure range up to 10 GPa and phase transition occurs between 8 K and 45 K at 8 GPa. According to the Birch-Murnaghan equation of state, the bulk modulus at ambient pressure B0 was estimated to be 45 ± 3 GPa with the assumption of B0' = 4. The structural robustness of phase I at 8 K suggests that themore » superconductivity below 10 GPa is related to phase I. Topological properties of superconducting Bi2Te3 phase under pressure were discussed.« less

Overview of KSTAR initial operation

NASA Astrophysics Data System (ADS)

Kwon, M.; Oh, Y. K.; Yang, H. L.; Na, H. K.; Kim, Y. S.; Kwak, J. G.; Kim, W. C.; Kim, J. Y.; Ahn, J. W.; Bae, Y. S.; Baek, S. H.; Bak, J. G.; Bang, E. N.; Chang, C. S.; Chang, D. H.; Chavdarovski, I.; Chen, Z. Y.; Cho, K. W.; Cho, M. H.; Choe, W.; Choi, J. H.; Chu, Y.; Chung, K. S.; Diamond, P.; Do, H. J.; Eidietis, N.; England, A. C.; Grisham, L.; Hahm, T. S.; Hahn, S. H.; Han, W. S.; Hatae, T.; Hillis, D.; Hong, J. S.; Hong, S. H.; Hong, S. R.; Humphrey, D.; Hwang, Y. S.; Hyatt, A.; In, Y. K.; Jackson, G. L.; Jang, Y. B.; Jeon, Y. M.; Jeong, J. I.; Jeong, N. Y.; Jeong, S. H.; Jhang, H. G.; Jin, J. K.; Joung, M.; Ju, J.; Kawahata, K.; Kim, C. H.; Kim, D. H.; Kim, Hee-Su; Kim, H. S.; Kim, H. K.; Kim, H. T.; Kim, J. H.; Kim, J. C.; Kim, Jong-Su; Kim, Jung-Su; Kim, Kyung-Min; Kim, K. M.; Kim, K. P.; Kim, M. K.; Kim, S. H.; Kim, S. S.; Kim, S. T.; Kim, S. W.; Kim, Y. J.; Kim, Y. K.; Kim, Y. O.; Ko, W. H.; Kogi, Y.; Kong, J. D.; Kubo, S.; Kumazawa, R.; Kwak, S. W.; Kwon, J. M.; Kwon, O. J.; LeConte, M.; Lee, D. G.; Lee, D. K.; Lee, D. R.; Lee, D. S.; Lee, H. J.; Lee, J. H.; Lee, K. D.; Lee, K. S.; Lee, S. G.; Lee, S. H.; Lee, S. I.; Lee, S. M.; Lee, T. G.; Lee, W. C.; Lee, W. L.; Leur, J.; Lim, D. S.; Lohr, J.; Mase, A.; Mueller, D.; Moon, K. M.; Mutoh, T.; Na, Y. S.; Nagayama, Y.; Nam, Y. U.; Namkung, W.; Oh, B. H.; Oh, S. G.; Oh, S. T.; Park, B. H.; Park, D. S.; Park, H.; Park, H. T.; Park, J. K.; Park, J. S.; Park, K. R.; Park, M. K.; Park, S. H.; Park, S. I.; Park, Y. M.; Park, Y. S.; Patterson, B.; Sabbagh, S.; Saito, K.; Sajjad, S.; Sakamoto, K.; Seo, D. C.; Seo, S. H.; Seol, J. C.; Shi, Y.; Song, N. H.; Sun, H. J.; Terzolo, L.; Walker, M.; Wang, S. J.; Watanabe, K.; Welander, A. S.; Woo, H. J.; Woo, I. S.; Yagi, M.; Yaowei, Y.; Yonekawa, Y.; Yoo, K. I.; Yoo, J. W.; Yoon, G. S.; Yoon, S. W.; KSTAR Team

2011-09-01

Since the successful first plasma generation in the middle of 2008, three experimental campaigns were successfully made for the KSTAR device, accompanied with a necessary upgrade in the power supply, heating, wall-conditioning and diagnostic systems. KSTAR was operated with the toroidal magnetic field up to 3.6 T and the circular and shaped plasmas with current up to 700 kA and pulse length of 7 s, have been achieved with limited capacity of PF magnet power supplies. The mission of the KSTAR experimental program is to achieve steady-state operations with high performance plasmas relevant to ITER and future reactors. The first phase (2008-2012) of operation of KSTAR is dedicated to the development of operational capabilities for a super-conducting device with relatively short pulse. Development of start-up scenario for a super-conducting tokamak and the understanding of magnetic field errors on start-up are one of the important issues to be resolved. Some specific operation techniques for a super-conducting device are also developed and tested. The second harmonic pre-ionization with 84 and 110 GHz gyrotrons is an example. Various parameters have been scanned to optimize the pre-ionization. Another example is the ICRF wall conditioning (ICWC), which was routinely applied during the shot to shot interval. The plasma operation window has been extended in terms of plasma beta and stability boundary. The achievement of high confinement mode was made in the last campaign with the first neutral beam injector and good wall conditioning. Plasma control has been applied in shape and position control and now a preliminary kinetic control scheme is being applied including plasma current and density. Advanced control schemes will be developed and tested in future operations including active profiles, heating and current drives and control coil-driven magnetic perturbation.

Signatures of pair-density wave order via measurement of the current-phase relation in La2-xBaxCuO4 Josephson junctions

NASA Astrophysics Data System (ADS)

Hamilton, David; Weis, Adam; Gu, Genda; van Harlingen, Dale

La2-xBaxCuO4 (LBCO) exhibits a sharp drop in the transition temperature near x = 1 / 8 doping. In this regime, charge, spin and superconducting orders are intertwined and superconductivity is believed to exist in a pair-density wave (PDW) state, an ordered stripe phase characterized by sign changes in the superconducting order parameter between adjacent stripes. We present direct measurements of the current-phase relation (CPR) of Josephson junctions patterned onto crystals of LBCO at x = 1 / 8 and x = 0 . 155 (optimal doping) using a phase-sensitive Josephson interferometry technique. In contrast to the approximately sinusoidal CPR observed at optimal doping, we find the proportion of higher harmonics in the CPR increases at x = 1 / 8 doping, consistent with the formation of a PDW state. In parallel, we are carrying out measurements of the resistance noise in thin films of LBCO of various doping levels to identify features that signify the onset of charge order and changes in the dynamics of charge stripes.

Intertwined Orders in Heavy-Fermion Superconductor CeCoIn 5

DOE PAGES

Kim, Duk Young; Lin, Shi-Zeng; Weickert, Franziska; ...

2016-12-20

The appearance of spin-density-wave (SDW) magnetic order in the low-temperature and high-field corner of the superconducting phase diagram of CeCoIn 5 is unique among unconventional superconductors. The nature of this magnetic $Q$ phase is a matter of current debate. Here, we present the thermal conductivity of CeCoIn 5 in a rotating magnetic field, which reveals the presence of an additional order inside the $Q$ phase that is intimately intertwined with the superconducting d-wave and SDW orders. A discontinuous change of the thermal conductivity within the $Q$ phase, when the magnetic field is rotated about antinodes of the superconducting d-wave ordermore » parameter, demands that the additional order must change abruptly, together with the recently observed switching of the SDW. Lastly, a combination of interactions, where spin-orbit coupling orients the SDW, which then selects the secondary p -wave pair-density-wave component (with an average amplitude of 20% of the primary d-wave order parameter), accounts for the observed behavior.« less

Double-Q spin-density wave in iron arsenide superconductors

DOE PAGES

Allred, J. M.; Taddei, K. M.; Bugaris, D. E.; ...

2016-01-25

Elucidating the nature of the magnetic ground state of iron-based superconductors is of paramount importance in unveiling the mechanism behind their high temperature superconductivity. Until recently, it was thought that superconductivity emerges only from an orthorhombic antiferromagnetic stripe phase, which can in principle be described in terms of either localized or itinerant spins. However, we recently reported that tetragonal symmetry is restored inside the magnetically ordered state of certain hole-doped compounds, revealing the existence of a new magnetic phase at compositions close to the onset of superconductivity. Here, we present Mossbauer data that show that half of the iron sitesmore » in this tetragonal phase are non-magnetic, establishing conclusively the existence of a novel magnetic ground state with a non-uniform magnetization that is inconsistent with localized spins. Instead, this state is naturally explained as the interference between two commensurate spin density waves, a rare example of collinear double-Q magnetic order. Finally, our results demonstrate the itinerant character of the magnetism of the iron pnictides, and the primary role played by magnetic degrees of freedom in determining their phase diagram.« less

Effect of interlayer coupling on the coexistence of antiferromagnetism and superconductivity in Fe pnictide superconductors: A study of Ca0.74 (1 )La0.26 (1 )(Fe1 -xCox)As2 single crystals

NASA Astrophysics Data System (ADS)

Jiang, Shan; Liu, Lian; Schütt, Michael; Hallas, Alannah M.; Shen, Bing; Tian, Wei; Emmanouilidou, Eve; Shi, Aoshuang; Luke, Graeme M.; Uemura, Yasutomo J.; Fernandes, Rafael M.; Ni, Ni

2016-05-01

We report the transport, thermodynamic, muon spin relaxation, and neutron study of the Ca0.74 (1 )La0.26 (1 ) (Fe1 -xCox )As2 single crystals, mapping out the temperature-doping level phase diagram. Upon Co substitution on the Fe site, the structural and magnetic phase transitions in this 112 compound are suppressed and superconductivity up to 20 K occurs. Our measurements of the superconducting and magnetic volume fractions show that these two phases coexist microscopically in the underdoped region, in contrast to the related Ca10(Pt3As8 )((Fe1 -xPtx )2As2 )5 (10-3-8) compound, where coexistence is absent. Supported by model calculations, we discuss the differences in the phase diagrams of the 112 and 10-3-8 compounds in terms of the FeAs interlayer coupling, whose strength is affected by the character of the spacer layer, which is metallic in the 112 compound and insulating in the 10-3-8 compound.

Nature of the superconductor-insulator transition in disordered superconductors.

PubMed

Dubi, Yonatan; Meir, Yigal; Avishai, Yshai

2007-10-18

The interplay of superconductivity and disorder has intrigued scientists for several decades. Disorder is expected to enhance the electrical resistance of a system, whereas superconductivity is associated with a zero-resistance state. Although superconductivity has been predicted to persist even in the presence of disorder, experiments performed on thin films have demonstrated a transition from a superconducting to an insulating state with increasing disorder or magnetic field. The nature of this transition is still under debate, and the subject has become even more relevant with the realization that high-transition-temperature (high-T(c)) superconductors are intrinsically disordered. Here we present numerical simulations of the superconductor-insulator transition in two-dimensional disordered superconductors, starting from a microscopic description that includes thermal phase fluctuations. We demonstrate explicitly that disorder leads to the formation of islands where the superconducting order is high. For weak disorder, or high electron density, increasing the magnetic field results in the eventual vanishing of the amplitude of the superconducting order parameter, thereby forming an insulating state. On the other hand, at lower electron densities or higher disorder, increasing the magnetic field suppresses the correlations between the phases of the superconducting order parameter in different islands, giving rise to a different type of superconductor-insulator transition. One of the important predictions of this work is that in the regime of high disorder, there are still superconducting islands in the sample, even on the insulating side of the transition. This result, which is consistent with experiments, explains the recently observed huge magneto-resistance peak in disordered thin films and may be relevant to the observation of 'the pseudogap phenomenon' in underdoped high-T(c) superconductors.

Entanglement control in a superconducting qubit system by an electromagnetic field

NASA Astrophysics Data System (ADS)

Zhang, Y. Q.; Xu, J. B.

2011-08-01

By making use of the dynamical algebraic method we investigate a quantum system consisting of superconducting qubits interacting with data buses, where the qubits are driven by time-dependent electromagnetic field and obtain an explicit expression of time evolution operator. Furthermore, we explore the entanglement dynamics and the influence of the time-dependent electromagnetic field and the initial state on the entanglement sudden death and birth for the system. It is shown that the entanglement between the qubit and bus as well as the entanglement sudden death and birth can be controlled by the time-dependent electromagnetic field.

Conductor requirements for high-temperature superconducting utility power transformers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pleva, E. F.; Mehrotra, V.; Schwenterly, S W

High-temperature superconducting (HTS) coated conductors in utility power transformers must satisfy a set of operating requirements that are driven by two major considerations-HTS transformers must be economically competitive with conventional units, and the conductor must be robust enough to be used in a commercial manufacturing environment. The transformer design and manufacturing process will be described in order to highlight the various requirements that it imposes on the HTS conductor. Spreadsheet estimates of HTS transformer costs allow estimates of the conductor cost required for an HTS transformer to be competitive with a similarly performing conventional unit.

Frequency-multiplexed bias and readout of a 16-pixel superconducting nanowire single-photon detector array

NASA Astrophysics Data System (ADS)

Doerner, S.; Kuzmin, A.; Wuensch, S.; Charaev, I.; Boes, F.; Zwick, T.; Siegel, M.

2017-07-01

We demonstrate a 16-pixel array of microwave-current driven superconducting nanowire single-photon detectors with an integrated and scalable frequency-division multiplexing architecture, which reduces the required number of bias and readout lines to a single microwave feed line. The electrical behavior of the photon-sensitive nanowires, embedded in a resonant circuit, as well as the optical performance and timing jitter of the single detectors is discussed. Besides the single pixel measurements, we also demonstrate the operation of a 16-pixel array with a temporal, spatial, and photon-number resolution.

Fluxoids behavior in superconducting ladders

NASA Astrophysics Data System (ADS)

Sharon, Omri J.; Haham, Noam; Shaulov, Avner; Yeshurun, Yosef

2018-03-01

The nature of the interaction between fluxoids and between them and the external magnetic field is studied in one-dimensional superconducting networks. An Ising like expression is derived for the energy of a network revealing that fluxoids behave as repulsively interacting objects driven towards the network center by the effective applied field. Competition between these two interactions determines the equilibrium arrangement of fluxoids in the network as a function of the applied field. It is demonstrated that the fluxoids configurations are not always commensurate to the network symmetry. Incommensurate, degenerated configurations may be formed even in networks with an odd number of loops.

Dependence of the critical temperature in overdoped copper oxides on superfluid density

NASA Astrophysics Data System (ADS)

Božović, I.; He, X.; Wu, J.; Bollinger, A. T.

2016-08-01

The physics of underdoped copper oxide superconductors, including the pseudogap, spin and charge ordering and their relation to superconductivity, is intensely debated. The overdoped copper oxides are perceived as simpler, with strongly correlated fermion physics evolving smoothly into the conventional Bardeen-Cooper-Schrieffer behaviour. Pioneering studies on a few overdoped samples indicated that the superfluid density was much lower than expected, but this was attributed to pair-breaking, disorder and phase separation. Here we report the way in which the magnetic penetration depth and the phase stiffness depend on temperature and doping by investigating the entire overdoped side of the La2-xSrxCuO4 phase diagram. We measured the absolute values of the magnetic penetration depth and the phase stiffness to an accuracy of one per cent in thousands of samples; the large statistics reveal clear trends and intrinsic properties. The films are homogeneous; variations in the critical superconducting temperature within a film are very small (less than one kelvin). At every level of doping the phase stiffness decreases linearly with temperature. The dependence of the zero-temperature phase stiffness on the critical superconducting temperature is generally linear, but with an offset; however, close to the origin this dependence becomes parabolic. This scaling law is incompatible with the standard Bardeen-Cooper-Schrieffer description.

Majorana spin liquids, topology, and superconductivity in ladders

NASA Astrophysics Data System (ADS)

Le Hur, Karyn; Soret, Ariane; Yang, Fan

2017-11-01

We theoretically address spin chain analogs of the Kitaev quantum spin model on the honeycomb lattice. The emergent quantum spin-liquid phases or Anderson resonating valence-bond (RVB) states can be understood, as an effective model, in terms of p -wave superconductivity and Majorana fermions. We derive a generalized phase diagram for the two-leg ladder system with tunable interaction strengths between chains allowing us to vary the shape of the lattice (from square to honeycomb ribbon or brickwall ladder). We evaluate the winding number associated with possible emergent (topological) gapless modes at the edges. In the Az phase, as a result of the emergent Z2 gauge fields and π -flux ground state, one may build spin-1/2 (loop) qubit operators by analogy to the toric code. In addition, we show how the intermediate gapless B phase evolves in the generalized ladder model. For the brick-wall ladder, the B phase is reduced to one line, which is analyzed through perturbation theory in a rung tensor product states representation and bosonization. Finally, we show that doping with a few holes can result in the formation of hole pairs and leads to a mapping with the Su-Schrieffer-Heeger model in polyacetylene; a superconducting-insulating quantum phase transition for these hole pairs is accessible, as well as related topological properties.

Reentrant Phase Coherence in Superconducting Nanowire Composites.

PubMed

Ansermet, Diane; Petrović, Alexander P; He, Shikun; Chernyshov, Dmitri; Hoesch, Moritz; Salloum, Diala; Gougeon, Patrick; Potel, Michel; Boeri, Lilia; Andersen, Ole Krogh; Panagopoulos, Christos

2016-01-26

The short coherence lengths characteristic of low-dimensional superconductors are associated with usefully high critical fields or temperatures. Unfortunately, such materials are often sensitive to disorder and suffer from phase fluctuations in the superconducting order parameter which diverge with temperature T, magnetic field H, or current I. We propose an approach to overcome synthesis and fluctuation problems: building superconductors from inhomogeneous composites of nanofilaments. Macroscopic crystals of quasi-one-dimensional Na2-δMo6Se6 featuring Na vacancy disorder (δ ≈ 0.2) are shown to behave as percolative networks of superconducting nanowires. Long-range order is established via transverse coupling between individual one-dimensional filaments, yet phase coherence remains unstable to fluctuations and localization in the zero (T,H,I) limit. However, a region of reentrant phase coherence develops upon raising (T,H,I). We attribute this phenomenon to an enhancement of the transverse coupling due to electron delocalization. Our observations of reentrant phase coherence coincide with a peak in the Josephson energy EJ at nonzero (T,H,I), which we estimate using a simple analytical model for a disordered anisotropic superconductor. Na2-δMo6Se6 is therefore a blueprint for a future generation of nanofilamentary superconductors with inbuilt resilience to phase fluctuations at elevated (T,H,I).

Nucleation of stable superconductivity in YBCO-films

NASA Astrophysics Data System (ADS)

Kötzler, J.

By means of the linear dynamic conductivity, inductively measured on epitaxial films between 30mHz and 30 MHz, the transition line T g (B) to generic superconductivity is studied in fields between B=0 and 19T. It follows closely the melting line T m (B) described recently in terms of a blowout of thermal vortex loops in clean materials. The critical exponents of the correlation length and time near T g (B), however, enem to be dominated by some intrinsic disorder. Columnar defects produced by heavy-ion irradiation up to field-equivalent-doses of B ϕ =10T lead to adisappointing reduction of T g (B→0) while for B>B ϕ the generic line of the pristine film is recovered. These novel results are also discussed in terms of a loop-driven destruction of generic superconductivity.

Superconducting properties of under- and over-doped BaxK1‑xBiO3 perovskite oxide

NASA Astrophysics Data System (ADS)

Szczȩśniak, D.; Kaczmarek, A. Z.; Szczȩśniak, R.; Turchuk, S. V.; Zhao, H.; Drzazga, E. A.

2018-06-01

In this study, we investigate the thermodynamic properties of the BaxK1‑xBiO3 (BKBO) superconductor in the under- (x = 0.5) and over-doped (x = 0.7) regime, within the framework of the Migdal-Eliashberg formalism. The analysis is conducted to verify that the electron-phonon pairing mechanism is responsible for the induction of the superconducting phase in the mentioned compound. In particular, we show that BKBO is characterized by the relatively high critical value of the Coulomb pseudopotential, which changes with doping level and does not follow the Morel-Anderson model. In what follows, the corresponding superconducting band gap size and related dimensionless ratio are estimated to increase with the doping, in agreement with the experimental predictions. Moreover, the effective mass of electrons is found to take on high values in the entire doping and temperature region. Finally, the characteristic dimensionless ratios for the superconducting band gap, the critical magnetic field and the specific heat for the superconducting state are predicted to exceed the limits set within the Bardeen-Cooper-Schrieffer theory, suggesting pivotal role of the strong-coupling and retardation effects in the analyzed compound. Presented results supplement our previous investigations and account for the strong-coupling phonon-mediated character of the superconducting phase in BKBO at any doping level.

Origin of nonlinear transport across the magnetically induced superconductor-metal-insulator transition in two dimensions.

PubMed

Seo, Y; Qin, Y; Vicente, C L; Choi, K S; Yoon, Jongsoo

2006-08-04

We have studied the effect of perpendicular magnetic fields and temperatures on nonlinear electronic transport in amorphous Ta superconducting thin films. The films exhibit a magnetic field-induced metallic behavior intervening the superconductor-insulator transition in the zero temperature limit. We show that the phase-identifying nonlinear transport in the superconducting and metallic phases arises from an intrinsic origin, not from an electron heating effect. The nonlinear transport is found to accompany an extraordinarily long voltage response time.

Low-Frequency Raman Modes of 2H-TaSe2 in the Charge Density Wave Phase

NASA Astrophysics Data System (ADS)

Chowdhury, Sugata; Simpson, J.; Einstein, T. L.; Hight Walker, A. R.; Theoretical Collaboration

With changes in temperatures, tantalum diselenide (2H-TaSe2) , a layered, transition metal chalcogenides (TMD) exhibits unique super-lattice structures. The metallic ground state changes to an incommensurate charge density wave (CDW) state at 122?K followed by a commensurate CDW state at 90?K, and eventually a superconducting state 0.14 K. These phase transitions are driven by strong electron-phonon coupling and favored by the particular form of the Fermi surface of these systems. Here we theoretically studied the structural origin of low-frequency Raman modes of bulk 2H-TaSe2\\ in the CDW phases. Our calculations reveal that changes observed in the Raman modes are associated with the thermal expansion in the basal plane of 2H-TaSe2. The Grüneisen parameters of these two Raman modes increase in the CDW phases. Changes in the lattice parameter ``a'' are large compared to ``c'' which induces strain along the a-axis. We compared our results with experimental data which show low-frequency Raman phonon modes are very sensitive to temperature and are not observed in the metallic room-temperature state. In addition, we found that cation displacement is more than anion in CDW phase. Our results may shed more light on exact nature of the CDW instability and optical properties in this system.

Superconductivity in zirconium-rhodium alloys

NASA Technical Reports Server (NTRS)

Zegler, S. T.

1969-01-01

Metallographic studies and transition temperature measurements were made with isothermally annealed and water-quenched zirconium-rhodium alloys. The results clarify both the solid-state phase relations at the Zr-rich end of the Zr-Rh alloy system and the influence upon the superconducting transition temperature of structure and composition.

Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocharian, Armen N.; Fernando, Gayanath W.; Fang, Kun

Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges andmore » opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.« less

Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator

NASA Astrophysics Data System (ADS)

Manna, S.; Kamlapure, A.; Cornils, L.; Hänke, T.; Hedegaard, E. M. J.; Bremholm, M.; Iversen, B. B.; Hofmann, Ph.; Wiebe, J.; Wiesendanger, R.

2017-01-01

The discovery of high-temperature superconductivity in Fe-based compounds triggered numerous investigations on the interplay between superconductivity and magnetism, and on the enhancement of transition temperatures through interface effects. It is widely believed that the emergence of optimal superconductivity is intimately linked to the suppression of long-range antiferromagnetic (AFM) order, although the exact microscopic picture remains elusive because of the lack of atomically resolved data. Here we present spin-polarized scanning tunnelling spectroscopy of ultrathin FeTe1-xSex (x=0, 0.5) films on bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level, indicating superconducting correlations up to Tc~6 K for one unit cell FeTe grown on Bi2Te3, in contrast to the non-superconducting bulk FeTe. The gap spatially coexists with bi-collinear AFM order. This finding opens perspectives for theoretical studies of competing orders in Fe-based superconductors and for experimental investigations of exotic phases in superconducting layers on topological insulators.

High temperature interfacial superconductivity

DOEpatents

Bozovic, Ivan [Mount Sinai, NY; Logvenov, Gennady [Port Jefferson Station, NY; Gozar, Adrian Mihai [Port Jefferson, NY

2012-06-19

High-temperature superconductivity confined to nanometer-scale interfaces has been a long standing goal because of potential applications in electronic devices. The spontaneous formation of a superconducting interface in bilayers consisting of an insulator (La.sub.2CuO.sub.4) and a metal (La.sub.1-xSr.sub.xCuO.sub.4), neither of which is superconducting per se, is described. Depending upon the layering sequence of the bilayers, T.sub.c may be either .about.15 K or .about.30 K. This highly robust phenomenon is confined to within 2-3 nm around the interface. After exposing the bilayer to ozone, T.sub.c exceeds 50 K and this enhanced superconductivity is also shown to originate from a 1 to 2 unit cell thick interfacial layer. The results demonstrate that engineering artificial heterostructures provides a novel, unconventional way to fabricate stable, quasi two-dimensional high T.sub.c phases and to significantly enhance superconducting properties in other superconductors. The superconducting interface may be implemented, for example, in SIS tunnel junctions or a SuFET.

Theoretical studies of superconductivity in doped BaCoSO

NASA Astrophysics Data System (ADS)

Qin, Shengshan; Li, Yinxiang; Zhang, Qiang; Le, Congcong; Hu, Jiangping

2018-06-01

We investigate superconductivity that may exist in the doped BaCoSO, a multi-orbital Mott insulator with a strong antiferromagnetic ground state. The superconductivity is studied in both t-J type and Hubbard type multi-orbital models by mean field approach and random phase approximation (RPA) analysis. Even if there is no C 4 rotational symmetry, it is found that the system still carries a d-wave like pairing symmetry state with gapless nodes and sign changed superconducting order parameters on Fermi surfaces. The results are largely doping insensitive. In this superconducting state, the three {t_{{2_g}}} orbitals have very different superconducting form factors in momentum space. In particular, the intra-orbital pairing of the {d_{{x^2} - {y^2}}} orbital has an s-wave like pairing form factor. The two methods also predict very different pairing strength on different parts of Fermi surfaces. These results suggest that BaCoSO and related materials can be a new ground to test and establish fundamental principles for unconventional high temperature superconductivity.

Magnetotransport Properties in High-Quality Ultrathin Two-Dimensional Superconducting Mo2C Crystals.

PubMed

Wang, Libin; Xu, Chuan; Liu, Zhibo; Chen, Long; Ma, Xiuliang; Cheng, Hui-Ming; Ren, Wencai; Kang, Ning

2016-04-26

Ultrathin transition metal carbides are a class of developing two-dimensional (2D) materials with superconductivity and show great potentials for electrical energy storage and other applications. Here, we report low-temperature magnetotransport measurements on high-quality ultrathin 2D superconducting α-Mo2C crystals synthesized by a chemical vapor deposition method. The magnetoresistance curves exhibit reproducible oscillations at low magnetic fields for temperature far below the superconducting transition temperature of the crystals. We interpret the oscillatory magnetoresistance as a consequence of screening currents circling around the boundary of triangle-shaped terraces found on the surface of ultrathin Mo2C crystals. As the sample thickness decreases, the Mo2C crystals exhibit negative magnetoresistance deep in the superconducting transition regime, which reveals strong phase fluctuations of the superconducting order parameters associated with the superconductor-insulator transition. Our results demonstrate that the ultrathin superconducting Mo2C crystals provide an interesting system for studying rich transport phenomena in a 2D crystalline superconductor with enhanced quantum fluctuations.

Structure and properties of U alloys with selected d-metals and their hydrides

NASA Astrophysics Data System (ADS)

Sowa, S.; Kim-Ngan, N.-. T. H.; Krupska, M.; Paukov, M.; Buturlim, V.; Havela, L.

2018-05-01

U-Ti and U-Ru alloys with various Ti, Ru concentrations were prepared using an ultrafast-cooling technique (splat cooling). A phase analysis by X-ray diffraction revealed the presence of the bcc γ-U phase developing with increasing concentration of alloying elements, while the concentration of orthorhombic α-U structure decreases. The tetragonally distorted γ° phase, (existing for 8-10 at. % Ru) is followed by pure cubic γ-U phase (for 12, 15% Ru). For Ti, more than 20 at. % is needed to yield pure γ-U phase. The occurrence of superconductivity was investigated by resistivity and specific heat measurements down to 0.4 K in various magnetic fields. All U-T splats studied become superconducting with Tc not exceeding 2.0 K.

RbEu (Fe1-xNix) 4As4 : From a ferromagnetic superconductor to a superconducting ferromagnet

NASA Astrophysics Data System (ADS)

Liu, Yi; Liu, Ya-Bin; Yu, Ya-Long; Tao, Qian; Feng, Chun-Mu; Cao, Guang-Han

2017-12-01

The intrinsically hole-doped RbEuFe4As4 exhibits bulk superconductivity at Tsc=36.5 K and ferromagnetic ordering in the Eu sublattice at Tm=15 K. Here we present a hole-compensation study by introducing extra itinerant electrons via a Ni substitution in the ferromagnetic superconductor RbEuFe4As4 with Tsc>Tm . With the Ni doping, Tsc decreases rapidly, and the Eu-spin ferromagnetism and its Tm remain unchanged. Consequently, the system RbEu (Fe1-xNix) 4As4 transforms into a superconducting ferromagnet with Tm>Tsc for 0.07 ≤x ≤0.08 . The occurrence of superconducting ferromagnets is attributed to the decoupling between Eu2 + spins and superconducting Cooper pairs. The superconducting and magnetic phase diagram is established, which additionally includes a recovered yet suppressed spin-density-wave state.

From antiferromagnetic insulator to correlated metal in pressurized and doped LaMnPO.

PubMed

Simonson, J W; Yin, Z P; Pezzoli, M; Guo, J; Liu, J; Post, K; Efimenko, A; Hollmann, N; Hu, Z; Lin, H-J; Chen, C-T; Marques, C; Leyva, V; Smith, G; Lynn, J W; Sun, L L; Kotliar, G; Basov, D N; Tjeng, L H; Aronson, M C

2012-07-03

Widespread adoption of superconducting technologies awaits the discovery of new materials with enhanced properties, especially higher superconducting transition temperatures T(c). The unexpected discovery of high T(c) superconductivity in cuprates suggests that the highest T(c)s occur when pressure or doping transform the localized and moment-bearing electrons in antiferromagnetic insulators into itinerant carriers in a metal, where magnetism is preserved in the form of strong correlations. The absence of this transition in Fe-based superconductors may limit their T(c)s, but even larger T(c)s may be possible in their isostructural Mn analogs, which are antiferromagnetic insulators like the cuprates. It is generally believed that prohibitively large pressures would be required to suppress the effects of the strong Hund's rule coupling in these Mn-based compounds, collapsing the insulating gap and enabling superconductivity. Indeed, no Mn-based compounds are known to be superconductors. The electronic structure calculations and X-ray diffraction measurements presented here challenge these long held beliefs, finding that only modest pressures are required to transform LaMnPO, isostructural to superconducting host LaFeAsO, from an antiferromagnetic insulator to a metallic antiferromagnet, where the Mn moment vanishes in a second pressure-driven transition. Proximity to these charge and moment delocalization transitions in LaMnPO results in a highly correlated metallic state, the familiar breeding ground of superconductivity.

Onset of superconductivity in sodium and potassium intercalated molybdenum disulphide

NASA Technical Reports Server (NTRS)

Somoano, R. B.; Rembaum, A.

1971-01-01

Molybdenum disulfide in the form of natural crystals or powder has been intercalated at -65 to -70 C with sodium and potassium using the liquid ammonia technique. All intercalated samples were found to show a superconducting transition. A plot of the percent of diamagnetic throw versus temperature indicates the possible existence of two phases in the potassium intercalated molybdenum disulfide. The onset of superconductivity in potassium and sodium intercalated molybdenite powder was found to be approximately 6.2 and approximately 4.5 K, respectively. The observed superconductivity is believed to be due to an increase in electron density as a result of intercalation.