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Sample records for induced superconducting state

  1. Possible Electric-Field-Induced Superconducting States in Doped Silicene

    PubMed Central

    Zhang, Li-Da; Yang, Fan; Yao, Yugui

    2015-01-01

    Silicene has been synthesized recently, with experimental evidence showing possible superconductivity in the doped case. The noncoplanar low-buckled structure of this material inspires us to study the pairing symmetry of the doped system under a perpendicular external electric field. Our study reveals that the electric field induces an interesting quantum phase transition from the singlet chiral d + id′-wave superconducting phase to the triplet f-wave one. The emergence of the f-wave pairing results from the sublattice-symmetry-breaking caused by the electric field and the ferromagnetic-like intra-sublattice spin correlations at low dopings. Due to the enhanced density of states, the superconducting critical temperature of the system is enhanced by the electric field remarkably. Furthermore, we design a particular dc SQUID experiment to detect the quantum phase transition predicted here. Our results, if confirmed, will inject a new vitality to the familiar Si-based industry through adopting doped silicene as a tunable platform to study different types of exotic unconventional superconductivities. PMID:25644143

  2. Proximity-induced superconductivity in nanowires: minigap state and differential magnetoresistance oscillations.

    PubMed

    Wang, Jian; Shi, Chuntai; Tian, Mingliang; Zhang, Qi; Kumar, Nitesh; Jain, J K; Mallouk, T E; Chan, M H W

    2009-06-19

    We study proximity-induced superconductivity in gold nanowires as a function of the length of the nanowire, magnetic field, and excitation current. Short nanowires exhibit a sharp superconducting transition, whereas long nanowires show nonzero resistance. At intermediate lengths, however, we observe two sharp transitions; the normal and superconducting regions are separated by what we call the minigap phase. Additionally, we detect periodic oscillations in the differential magnetoresistance. We suggest that the minigap phase as well as the periodic oscillations originate from a coexistence of proximity-induced superconductivity with a normal region near the center of the wire, created either by temperature or the application of a magnetic field.

  3. Impurity-Induced Local Magnetism and Density of States in the Superconducting State of YBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Ouazi, S.; Bobroff, J.; Alloul, H.; Le Tacon, M.; Blanchard, N.; Collin, G.; Julien, M. H.; Horvatić, M.; Berthier, C.

    2006-03-01

    O17 NMR is used to probe the local influence of nonmagnetic Zn and magnetic Ni impurities in the superconducting state of optimally doped high TC YBa2Cu3O7. Zn and Ni induce a staggered paramagnetic polarization, similar to that evidenced above TC, with a typical extension ξ=3 cell units for Zn and ξ≥3 for Ni. In addition, Zn is observed to induce a local density of states near the Fermi energy in its neighborhood, which also decays over about 3 cell units. Its magnitude decreases sharply with increasing temperature. This allows direct comparison with the STM observations done in BiSCCO.

  4. Measurement-Induced State Transitions in a Superconducting Qubit: Beyond the Rotating Wave Approximation

    NASA Astrophysics Data System (ADS)

    Sank, Daniel; Chen, Zijun; Khezri, Mostafa; Kelly, J.; Barends, R.; Campbell, B.; Chen, Y.; Chiaro, B.; Dunsworth, A.; Fowler, A.; Jeffrey, E.; Lucero, E.; Megrant, A.; Mutus, J.; Neeley, M.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Vainsencher, A.; White, T.; Wenner, J.; Korotkov, Alexander N.; Martinis, John M.

    2016-11-01

    Many superconducting qubit systems use the dispersive interaction between the qubit and a coupled harmonic resonator to perform quantum state measurement. Previous works have found that such measurements can induce state transitions in the qubit if the number of photons in the resonator is too high. We investigate these transitions and find that they can push the qubit out of the two-level subspace, and that they show resonant behavior as a function of photon number. We develop a theory for these observations based on level crossings within the Jaynes-Cummings ladder, with transitions mediated by terms in the Hamiltonian that are typically ignored by the rotating wave approximation. We find that the most important of these terms comes from an unexpected broken symmetry in the qubit potential. We confirm the theory by measuring the photon occupation of the resonator when transitions occur while varying the detuning between the qubit and resonator.

  5. Multiple superconducting states induced by pressure in Mo3Sb7

    NASA Astrophysics Data System (ADS)

    Feng, Yejun; Wang, Yishu; Palmer, A.; Li, Ling; Silevitch, D. M.; Calder, S.; Rosenbaum, T. F.

    2017-03-01

    Tuning competing ordering mechanisms with hydrostatic pressure in the 4 d intermetallic compound Mo3Sb7 reveals an intricate interplay of structure, magnetism, and superconductivity. Synchrotron x-ray diffraction and magnetic susceptibility measurements, both employing diamond anvil cell technologies, link a first-order structural phase transition to a doubling of the superconducting transition temperature. In contrast to the spin-dimer picture for Mo3Sb7 , we deduce from x-ray absorption near-edge structure and dc magnetization measurements at ambient pressure that Mo3Sb7 should possess only very small, itinerant magnetic moments. The pressure evolution of the superconducting transition temperature strongly suggests its enhancement is due to a difference in the phonon density-of-states with changed crystal symmetry.

  6. 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.

  7. Geometry and magnetic-state induced phenomena in S/F nanohybrids: unusual flux pinning effects and bistable superconductivity

    NASA Astrophysics Data System (ADS)

    Villegas, Javier E.

    2009-03-01

    Superconducting/Ferromagnetic (S/F) hybrids exhibit a plethora of induced effects and novel physical properties, due to the interplay between the competing S and F orders. We will show a few examples of those, in a series of experiments on a simple hybrid system: a S thin film with an array of F nanodots. Changing the array geometry, the nanodots size or their magnetic-state allows to investigate a large variety of physical phenomena. We will focus on two of them: flux pinning effects and stray-magnetic-field induced manipulation of superconductivity. We will firstly consider geometry induced effects; in particular, we will compare the pinning properties of periodic, quasiperiodic, and fractal arrays [1]. Secondly, we will discuss the effects induced by particular nanodot magnetic-states. We will show experiments on the interaction between flux quanta and nanodot magnetic vortices, which can be used to obtain switchable flux pinning potentials [2]. Finally, we will describe an experiment in which the magnetic reversal events of the nanodot magnetic vortices are imprinted into the transport properties of a superconducting thin film [3]. This yields a very unusual hysteretic magnetoresistance. This effect is induced by the stray magnetic fields from the nanodots, which drive the superconducting-to-normal transition of the hybrid depending on the magnetic history. [4pt] [1] J.E. Villegas et al., Phys. Rev. Lett. 97, 027002 (2006). [0pt] [2] J.E. Villegas et al., Phys. Rev. B 77, 134510 (2008). [0pt] [3] J.E. Villegas et al., Phys. Rev. Lett. 99, 227001 (2007).

  8. Towards inducing superconductivity into graphene

    NASA Astrophysics Data System (ADS)

    Efetov, Dmitri K.

    Graphenes transport properties have been extensively studied in the 10 years since its discovery in 2004, with ground-breaking experimental observations such as Klein tunneling, fractional quantum Hall effect and Hofstadters butterfly. Though, so far, it turned out to be rather poor on complex correlated electronic ground states and phase transitions, despite various theoretical predictions. The purpose of this thesis is to help understanding the underlying theoretical and experimental reasons for the lack of strong electronic interactions in graphene, and, employing graphenes high tunability and versatility, to identify and alter experimental parameters that could help to induce stronger correlations. In particular graphene holds one last, not yet experimentally discovered prediction, namely exhibiting intrinsic superconductivity. With its vanishingly small Fermi surface at the Dirac point, graphene is a semi-metal with very weak electronic interactions. Though, if it is doped into the metallic regime, where the size of the Fermi surface becomes comparable to the size of the Brillouin zone, the density of states becomes sizeable and electronic interactions are predicted to be dramatically enhanced, resulting in competing correlated ground states such as superconductivity, magnetism and charge density wave formation. Following these predictions, this thesis first describes the creation of metallic graphene at high carrier doping via electrostatic doping techniques based on electrolytic gates. Due to graphenes surface only properties, we are able to induce carrier densities above n>1014 cm-2 (epsilonF>1eV) into the chemically inert graphene. While at these record high carrier densities we yet do not observe superconductivity, we do observe fundamentally altered transport properties as compared to semi-metallic graphene. Here, detailed measurements of the low temperature resistivity reveal that the electron-phonon interactions are governed by a reduced, density

  9. Theory on Superconducting Transition from Pseudogap State

    NASA Astrophysics Data System (ADS)

    Yanase, Youichi; Jujo, Takanobu; Yamada, Kosaku

    2000-11-01

    The anomalous properties of High-T c cuprates are investigated both in the normal state and in the superconducting state. In particular, we pay attention to the pseudogap in the normal state and the phase transition from the pseudogap state to the superconducting state. The pseudogap phenomena observed in cuprates are naturally understood as a precursor of the strong coupling superconductivity. We have previously shown by using the self-consistent T-matrix calculation that the pseudogap is a result of the strong superconducting fluctuations which are accompanied by the strong coupling superconductivity in quasi-two dimensional systems [J. Phys. Soc. Jpn. 68 (1999) 2999]. We extend the scenario to the superconducting state. The close relation between the pseudogap state and the superconducting state is pointed out. Once the superconducting phase transition occurs, the superconducting order parameter rapidly grows rather than the result of BCS theory. With the rapid growth of the order parameter, the gap structure becomes sharp, while it is remarkably broad in the pseudogap state. The characteristic energy scale of the gap does not change. These results well explain the phase transition observed in the spectroscopic measurements. Further, we calculate the magnetic and transport properties which show the pseudogap phenomena. The comprehensive understanding of the NMR, the neutron scattering, the optical conductivity and the London penetration depth is obtained both in the pseudogap state and in the superconducting state.

  10. Induced gap in topological materials from the superconducting proximity effect

    NASA Astrophysics Data System (ADS)

    Chiu, Ching-Kai; Cole, William

    Topological superconductivity has been of considerable interest lately, with several proposed experimental realizations in solid state systems. A heterostructure of s-wave superconductor and 3D topological insulator is one of the more promising platforms, with topological superconductivity realized on the ''naked'' surface of the topological insulator through the superconducting proximity effect. We theoretically study the induced superconducting gap on the naked surface. Adjusting the Fermi level above the bulk gap (which is the case in experiments), our results for the induced superconducting gap are in agreement with that probed in thin topological insulators (<10nm) in the experiments (Nat. Phys. 10, 943-950 (2014) and Phys. Rev. Lett. 112, 217001 (2014)). We further predict the gap in thick topological insulators (>10nm). This work is supported by LPS-MPO-CMTC, Microsoft Q, and JQI-NSF-PFC.

  11. Field-Induced Superconductivity in Electric Double Layer Transistors

    NASA Astrophysics Data System (ADS)

    Ueno, Kazunori; Shimotani, Hidekazu; Yuan, Hongtao; Ye, Jianting; Kawasaki, Masashi; Iwasa, Yoshihiro

    2014-03-01

    Electric field tuning of superconductivity has been a long-standing issue in solid state physics since the invention of the field-effect transistor (FET) in 1960. Owing to limited available carrier density in conventional FET devices, electric-field-induced superconductivity was believed to be possible in principle but impossible in practice. However, in the past several years, this limitation has been overcome by the introduction of an electrochemical concept, and electric-field-induced superconductivity has been realized. In the electric double layer (EDL) formed at the electrochemical interfaces, an extremely high electric field is generated and hence high-density charge carriers sufficient to induce superconductivity exist and are collectively used as a charge accumulation device known as an EDL capacitor. Field-induced superconductivity has been used to establish the relationship between Tc and carrier density and can now be used to search for new superconductors. Here, we review electric-field-induced superconductivity using an FET device, with a particular focus on the latest advances in EDL transistors.

  12. Localization of Metal-Induced Gap States at the Metal-Insulator Interface: Origin of Flux Noise in SQUIDs and Superconducting Qubits

    NASA Astrophysics Data System (ADS)

    Choi, Sangkook; Lee, Dung-Hai; Louie, Steven G.; Clarke, John

    2010-03-01

    The origin of magnetic flux noise in dc Superconducting Quantum Interference Devices (SQUIDs) with a power spectrum scaling as 1/f (f is frequency) has been a puzzle for over 25 years. This noise limits both the low frequency performance of SQUIDs and the decoherence time of flux-sensitive superconducting qubits, making scaling-up for quantum computing problematic. Recent calculations and experiments indicate that the noise is generated by electrons that randomly reverse their spin directions. Their areal density of ˜ 5 x 10^17 m-2 is relatively insensitive to the nature of the superconductor and substrate. Here, we propose that the local magnetic moments originate in metal-induced gap states (MIGSs) localized by potential disorder at the metal-insulator interface. MIGSs are particularly sensitive to such disorder, so that the localized states have a Coulomb repulsion sufficiently large to make them singly occupied. Our calculations demonstrate that a modest level of disorder generates the required areal density of localized moments. This result suggests that magnetic flux noise could be reduced by fabricating superconductor-insulator interfaces with less disorder. Support: NSF DMR07-05941, US DOE De-AC02-05CH11231, Samsung Foundation, Teragrid, NERSC.

  13. Superconductivity of metal-induced surface reconstructions on silicon

    NASA Astrophysics Data System (ADS)

    Uchihashi, Takashi

    2016-11-01

    Recent progress in superconducting metal-induced surface reconstructions on silicon is reviewed, mainly focusing on the results of the author’s group. After a brief introduction of an ultrahigh-vacuum (UHV)-low-temperature (LT)-compatible electron transport measurement system, direct observation of the zero resistance state for the Si(111)-(\\sqrt{7} × \\sqrt{3} )-In surface is described, which demonstrates the existence of a superconducting transition in this class of two-dimensional (2D) materials. The measurement and analysis of the temperature dependence of the critical current density indicate that a surface atomic step works as a Josephson junction. This identification is further confirmed by LT-scanning tunneling microscopy (STM) observation of Josephson vortices trapped at atomic steps on the Si(111)-(\\sqrt{7} × \\sqrt{3} )-In surface. These experiments reveal unique features of metal-induced surface reconstructions on silicon that may be utilized to explore novel superconductivity.

  14. Dirac-fermion-induced parity mixing in superconducting topological insulators

    NASA Astrophysics Data System (ADS)

    Mizushima, Takeshi; Yamakage, Ai; Sato, Masatoshi; Tanaka, Yukio

    2014-11-01

    We self-consistently study surface states of superconducting topological insulators. We clarify that, if a topologically trivial bulk s -wave pairing symmetry is realized, parity mixing of the pair potential near the surface is anomalously enhanced by surface Dirac fermions, opening an additional surface gap larger than the bulk one. In contrast to classical s -wave superconductors, the resulting surface density of state hosts an extra coherent peak at the induced gap besides a conventional peak at the bulk gap. We also find that no such extra peak appears for odd-parity superconductors with a cylindrical Fermi surface. Our calculation suggests that the simple U-shaped scanning tunneling microscope spectrum in CuxBi2Se3 does not originate from s -wave superconductivity, but can be explained by odd-parity superconductivity with a cylindrical Fermi surface.

  15. Electric-field-induced superconductivity in an insulator.

    PubMed

    Ueno, K; Nakamura, S; Shimotani, H; Ohtomo, A; Kimura, N; Nojima, T; Aoki, H; Iwasa, Y; Kawasaki, M

    2008-11-01

    Electric field control of charge carrier density has long been a key technology to tune the physical properties of condensed matter, exploring the modern semiconductor industry. One of the big challenges is to increase the maximum attainable carrier density so that we can induce superconductivity in field-effect-transistor geometry. However, such experiments have so far been limited to modulation of the critical temperature in originally conducting samples because of dielectric breakdown. Here we report electric-field-induced superconductivity in an insulator by using an electric-double-layer gating in an organic electrolyte. Sheet carrier density was enhanced from zero to 10(14) cm(-2) by applying a gate voltage of up to 3.5 V to a pristine SrTiO(3) single-crystal channel. A two-dimensional superconducting state emerged below a critical temperature of 0.4 K, comparable to the maximum value for chemically doped bulk crystals, indicating this method as promising for searching for unprecedented superconducting states.

  16. Electric Field Induced Superconductivity in Layered Materials

    NASA Astrophysics Data System (ADS)

    Ye, J. T.; Craciun, M. F.; Russo, S.; Morpurgo, M. F.; Kasahara, Y.; Yuan, H. T.; Shimotani, H.; Iwasa, Y.

    2011-03-01

    Using electric double layer (EDL) gating, large amount of carriers can be accumulated on a broad range of materials, which provides new opportunities in effectively manipulating their electronic properties in complementary with the chemical doping. In searching for novel transport phenomena, layered materials are advantageous because atomically flat surface can be easily fabricated using the graphene techniques. We used layered material: ZrNCl and graphite to act as the channel of EDL transistors. For both ZrNCl and graphene, we achieved high carrier density up to 1014 cm-2 , electrostatically. For graphene, we studied the high carrier density transport for graphene of 1-3 layers. Transport properties at the high carrier density exhibit clear layer dependence governed by the intrinsic band structures of graphene and its multi-layers. For ZrNCl EDL transistor, we observed metallic states at gate voltage higher than 3.5 V followed by gate-induced superconductivity after metal-insulator transition when the transistor was cooled down to about 15 K.

  17. Commensurate states in quasicrystalline superconducting networks

    SciTech Connect

    Jing, X. ); Zhang, Z. , P.O. Box 8730, Beijing, China Institute of Physics, Chinese Academy of Sciences, Beijing, China)

    1989-09-01

    By using the theory of de Gennes and Alexander, the commensurate states of the fluxoid configuration on the phase boundaries of superconducting networks with the Fibonacci pattern are studied explicitly for one- and two-strip geometries. The case in which the network contains three tiles with irrational ratios of areas is also studied. Our numerical results strongly indicate that the amplitude of the wave function of a commensurate state has two-cycle self-similar behavior. The locations of the magnetic field where the commensurate states may occur in an {ital M}-strip network are also predicted.

  18. Controlling coherent state superpositions with superconducting circuits

    NASA Astrophysics Data System (ADS)

    Vlastakis, Brian Michael

    Quantum computation requires a large yet controllable Hilbert space. While many implementations use discrete quantum variables such as the energy states of a two-level system to encode quantum information, continuous variables could allow access to a larger computational space while minimizing the amount of re- quired hardware. With a toolset of conditional qubit-photon logic, we encode quantum information into the amplitude and phase of coherent state superpositions in a resonator, also known as Schrddinger cat states. We achieve this using a superconducting transmon qubit with a strong off-resonant coupling to a waveguide cavity. This dispersive interaction is much greater than decoherence rates and higher-order nonlinearites and therefore allows for simultaneous control of over one hundred photons. Furthermore, we combine this experiment with fast, high-fidelity qubit state readout to perform composite qubit-cavity state tomography and detect entanglement between a physical qubit and a cat-state encoded qubit. These results have promising applications for redundant encoding in a cavity state and ultimately quantum error correction with superconducting circuits.

  19. Qubit lattice coherence induced by electromagnetic pulses in superconducting metamaterials

    PubMed Central

    Ivić, Z.; Lazarides, N.; Tsironis, G. P.

    2016-01-01

    Quantum bits (qubits) are at the heart of quantum information processing schemes. Currently, solid-state qubits, and in particular the superconducting ones, seem to satisfy the requirements for being the building blocks of viable quantum computers, since they exhibit relatively long coherence times, extremely low dissipation, and scalability. The possibility of achieving quantum coherence in macroscopic circuits comprising Josephson junctions, envisioned by Legett in the 1980’s, was demonstrated for the first time in a charge qubit; since then, the exploitation of macroscopic quantum effects in low-capacitance Josephson junction circuits allowed for the realization of several kinds of superconducting qubits. Furthermore, coupling between qubits has been successfully achieved that was followed by the construction of multiple-qubit logic gates and the implementation of several algorithms. Here it is demonstrated that induced qubit lattice coherence as well as two remarkable quantum coherent optical phenomena, i.e., self-induced transparency and Dicke-type superradiance, may occur during light-pulse propagation in quantum metamaterials comprising superconducting charge qubits. The generated qubit lattice pulse forms a compound ”quantum breather” that propagates in synchrony with the electromagnetic pulse. The experimental confirmation of such effects in superconducting quantum metamaterials may open a new pathway to potentially powerful quantum computing. PMID:27403780

  20. Pressure-induced superconductivity in topological parent compound Bi2Te3

    PubMed Central

    Zhang, J. L.; Zhang, S. J.; Weng, H. M.; Zhang, W.; Yang, L. X.; Liu, Q. Q.; Feng, S. M.; Wang, X. C.; Yu, R. C.; Cao, L. Z.; Wang, L.; Yang, W. G.; Liu, H. Z.; Zhao, W. Y.; Zhang, S. C.; Dai, X.; Fang, Z.; Jin, C. Q.

    2011-01-01

    We report a successful observation of pressure-induced superconductivity in a topological compound Bi2Te3 with Tc of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the hole-type carrier in the pressure-induced superconducting Bi2Te3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi2Te3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor. PMID:21173267

  1. Pressure-induced superconductivity in Bi single crystals

    NASA Astrophysics Data System (ADS)

    Li, Yufeng; Wang, Enyu; Zhu, Xiyu; Wen, Hai-Hu

    2017-01-01

    Measurements on resistivity and magnetic susceptibility have been carried out for Bi single crystals under pressures up to 10.5 GPa. The temperature dependent resistivity shows a semimetallic behavior at ambient and low pressures (below about 1.6 GPa). This is followed by an upturn of resistivity in the low temperature region when the pressure is increased, which is explained as a semiconductor behavior. This feature gradually gets enhanced up to a pressure of about 2.52 GPa. Then a nonmonotonic temperature dependent resistivity appears upon further increasing pressure, which is accompanied by a strong suppression to the low temperature resistivity upturn. Simultaneously, a superconducting transition occurs at about 3.92 K under a pressure of about 2.63 GPa. With further increasing pressure, a second superconducting transition emerges at about 7 K under about 2.8 GPa. For these two superconducting states, the superconductivity induced magnetic screening volumes are quite large. As the pressure further increases to 8.1 GPa, we observe the third superconducting transition at about 8.2 K. The resistivity measurements under magnetic field allow us to determine the upper critical fields μ0Hc 2 of the superconducting phases. The upper critical field for the phase with Tc=3.92 K is extremely low. Based on the Werthamer-Helfand-Hohenberg (WHH) theory, the estimated value of μ0Hc 2 for this phase is about 0.103 T, while the upper critical field for the phase with Tc=7 K is very high with a value of about 4.56 T. Finally, we present a pressure dependent phase diagram of Bi single crystals. Our results reveal the interesting and rich physics in bismuth single crystals under high pressure.

  2. Metal-insulator transition near a superconducting state

    NASA Astrophysics Data System (ADS)

    Kaveh, M.; Mott, N. F.

    1992-03-01

    We show that when the metal-insulation transition occurs near a superconducting state it results in a different critical behavior from that of amorphous metals or uncompensated doped semiconductors. This difference results from the enhancement of the effective electron-electron interaction caused by fluctuations to the superconducting state. This explains the recent experiments of Micklitz and co-workers on amorphous superconducting mixtures Ga-Ar and Bi-Kr.

  3. Magnetic field effect on the pressure-induced superconducting state in the hole-doped two-leg ladder compound Sr2 Ca12 Cu24 O41

    NASA Astrophysics Data System (ADS)

    Nakanishi, T.; Motoyama, N.; Mitamura, H.; Takeshita, N.; Takahashi, H.; Eisaki, H.; Uchida, S.; Môri, N.

    2005-08-01

    We report electrical resistivity on a single crystal of the hole-doped two-leg ladder compound Sr2Ca12Cu24O41 , which becomes superconducting with Tc˜5K only at pressures above ˜3.0GPa . Measurements were performed at nearly hydrostatic pressures up to 5.7GPa and low temperatures down to 100mK under static magnetic fields up to 20T parallel to the a axis (along the ladder rungs) and up to 7T parallel to both the b axis (perpendicular to the ladder plane) and the c axis (along the ladder legs). A clear difference in the resistive upper critical field Hc2(T) is observed among these three directions, confirming that this system has a highly anisotropic superconducting ground state. Also, Hc2(T) parallel to the ladder plane is found to exceed the Pauli limit by a factor of more than 2, suggesting either a strong spin-orbit scattering or spin-triplet pairing. Furthermore, it is implied, from measurements of resistivity versus angle of magnetic field in the bc plane, that another superconducting phase is stable below around 3K only when the magnetic field is applied exactly along a certain direction that is ±35° from the ladder direction.

  4. Two-band superconductivity of bulk and surface states in Ag thin films on Nb

    NASA Astrophysics Data System (ADS)

    Tomanic, Tihomir; Schackert, Michael; Wulfhekel, Wulf; Sürgers, Christoph; Löhneysen, Hilbert v.

    2016-12-01

    We use epitaxial strain to spatially tune the bottom of the surface-state band ESS of Ag(111) islands on Nb(110). Bulk and surface-state contributions to the Ag(111) local density of states (LDOS) can be separated with scanning tunneling spectroscopy. For thick islands (≈20 nm), the Ag surface states are decoupled from the Ag bulk states and the superconductive gap induced by proximity to Nb is due to bulk states only. However, for thin islands (3-4 nm), surface-state electrons develop superconducting correlations as identified by a complete energy gap in the LDOS when ESS is smaller than but close to the Fermi level. The induced superconductivity in this case is of a two-band nature and appears to occur when the surface-state wave function reaches down to the Ag/Nb interface.

  5. Electrostatically induced superconductivity at the surface of WS₂.

    PubMed

    Jo, Sanghyun; Costanzo, Davide; Berger, Helmuth; Morpurgo, Alberto F

    2015-02-11

    We investigate transport through ionic liquid gated field effect transistors (FETs) based on exfoliated crystals of semiconducting WS2. Upon electron accumulation, at surface densities close to, or just larger than, 10(14) cm(-2), transport exhibits metallic behavior with the surface resistivity decreasing pronouncedly upon cooling. A detailed characterization as a function of temperature and magnetic field clearly shows the occurrence of a gate-induced superconducting transition below a critical temperature Tc ≈ 4 K, a finding that represents the first demonstration of superconductivity in tungsten-based semiconducting transition metal dichalcogenides. We investigate the nature of superconductivity and find significant inhomogeneity, originating from the local detaching of the frozen ionic liquid from the WS2 surface. Despite the inhomogeneity, we find that in all cases where a fully developed zero resistance state is observed, different properties of the devices exhibit a behavior characteristic of a Berezinskii-Kosterlitz-Thouless transition, as it could be expected in view of the two-dimensional nature of the electrostatically accumulated electron system.

  6. STM imaging of vortex cores states in superconducting graphene

    NASA Astrophysics Data System (ADS)

    Ji, Yu; Ovadia, Maoz; Hoffman, Jennifer; Lee, Gil-Ho; Philip Kim Collaboration; Wenjing Fang Collaboration

    Graphene becomes superconducting via the proximity effect when it comes in good contact with a superconductor. In the presence of a magnetic field, superconducting vortices will form and will each contain Andreev bound states. If the normal electrons in the vortices have a Dirac dispersion and they are surface bound states, the zero modes of the Dirac dispersion are then Majorana fermions. We investigate the electronic properties of graphene on superconducting NbN and search for these vortex bound states using our home built low temperature scanning tunneling microscope. Harvard University.

  7. Induced spectral gap and pairing correlations from superconducting proximity effect

    NASA Astrophysics Data System (ADS)

    Chiu, Ching-Kai; Cole, William S.; Das Sarma, S.

    2016-09-01

    We theoretically consider superconducting proximity effect, using the Bogoliubov-de Gennes (BdG) theory, in heterostructure sandwich-type geometries involving a normal s -wave superconductor and a nonsuperconducting material with the proximity effect being driven by Cooper pairs tunneling from the superconducting slab to the nonsuperconducting slab. Applications of the superconducting proximity effect may rely on an induced spectral gap or induced pairing correlations without any spectral gap. We clarify that in a nonsuperconducting material the induced spectral gap and pairing correlations are independent physical quantities arising from the proximity effect. This is a crucial issue in proposals to create topological superconductivity through the proximity effect. Heterostructures of three-dimensional topological insulator (TI) slabs on conventional s -wave superconductor (SC) substrates provide a platform, with proximity-induced topological superconductivity expected to be observed on the "naked" top surface of a thin TI slab. We theoretically study the induced superconducting gap on this naked surface. In addition, we compare against the induced spectral gap in heterostructures of SC with a normal metal or a semiconductor with strong spin-orbit coupling and a Zeeman splitting potential (another promising platform for topological superconductivity). We find that for any model for the non-SC metal (including metallic TI) the induced spectral gap on the naked surface decays as L-3 as the thickness (L ) of the non-SC slab is increased in contrast to the slower 1 /L decay of the pairing correlations. Our distinction between proximity-induced spectral gap (with its faster spatial decay) and pairing correlation (with its slower spatial decay) has important implications for the currently active search for topological superconductivity and Majorana fermions in various superconducting heterostructures.

  8. Pair-breaking effects by parallel magnetic field in electric-field-induced surface superconductivity

    NASA Astrophysics Data System (ADS)

    Nabeta, Masahiro; Tanaka, Kenta K.; Onari, Seiichiro; Ichioka, Masanori

    2016-11-01

    We study paramagnetic pair-breaking in electric-field-induced surface superconductivity, when magnetic field is applied parallel to the surface. The calculation is performed by Bogoliubov-de Gennes theory with s-wave pairing, including the screening effect of electric fields by the induced carriers near the surface. Due to the Zeeman shift by applied fields, electronic states at higher-level sub-bands become normal-state-like. Therefore, the magnetic field dependence of Fermi-energy density of states reflects the multi-gap structure in the surface superconductivity.

  9. Yu-Shiba-Rusinov states and topological superconductivity in Ising paired superconductors

    NASA Astrophysics Data System (ADS)

    Sharma, Girish; Tewari, Sumanta

    2016-09-01

    An unusual form of superconductivity, called Ising superconductivity, has recently been uncovered in mono- and few-layered transition metal dichalcogenides. This 2D superconducting state is characterized by the so-called Ising spin-orbit coupling (SOC), which produces strong oppositely oriented effective Zeeman fields perpendicular to the 2D layer in opposite momentum space valleys. We examine the Yu-Shiba-Rusinov (YSR) bound states localized at magnetic impurities in Ising superconductors and show that the unusual SOC manifests itself in unusually strong anisotropy in magnetic field response observable in STM experiments. For a chain of magnetic impurities with moments parallel to the plane of Ising superconductors we show that the low energy YSR band hosts topological superconductivity and Majorana excitations as a direct manifestation of topological effects induced by Ising spin-orbit coupling.

  10. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs

    PubMed Central

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Rüegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; Morenzoni, Elvezio

    2015-01-01

    The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p  3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p  7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc  1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5  p  7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs. PMID:26346548

  11. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs.

    PubMed

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K; Rüegg, Christian; Susner, Michael A; Sefat, Athena S; Zhigadlo, Nikolai D; Morenzoni, Elvezio

    2015-09-08

    The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 < or ~  p < or ~ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.

  12. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs

    SciTech Connect

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; Luetkens, Hubertus; Amato, Alex; Biswas, Pabitra K.; Ruegg, Christian; Susner, Michael A.; Sefat, Athena S.; Zhigadlo, Nikolai D.; Morenzoni, Elvezio

    2015-09-08

    We report that the recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5≲ p ≲ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc3.2 as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.

  13. Pressure-induced electronic phase separation of magnetism and superconductivity in CrAs

    DOE PAGES

    Khasanov, Rustem; Guguchia, Zurab; Eremin, Ilya; ...

    2015-09-08

    We report that the recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreasesmore » upon increasing the pressure. In the intermediate pressure region (3.5≲ p ≲ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc3.2 as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.« less

  14. Theory of superconductivity by the edge states in graphene

    NASA Astrophysics Data System (ADS)

    Sasaki, Ken-Ichi; Suzuki, Masahiro; Saito, Riichiro

    2008-03-01

    Superconductivity in graphite intercalation compound and carbon nanotubes has been attracting much attention due to its high superconducting transition temperature above 10 K. However, the density of states (DOS) near the Fermi energy of graphene is not sufficient to explain the observed high transition temperature. Thus, the mechanism of the superconductivity is an important issue. The STS measurements (Kobayashi et al., PRB73,125415, Niimi et al., PRB73,085421) show an anomalous DOS near the Fermi level of graphene which is relevant to localized edge states. The edge states significantly enhance the local DOS near the zigzag edge. Thus, it is valuable to examine the effect of the edge states on the superconductivity. Using the Eliashberg equation, we obtain an appreciable transition temperature for the edge states. We found that the effects of the Coulomb interaction and Fermi energy position are sensitive to the formation of superconducting gap. We will discuss the condition for observing the edge state superconductivity. (Sasaki et al., J. Phys. Soc. Jpn. 76, 033702 (2007))

  15. Gate-induced superconductivity in atomically thin MoS2 crystals.

    PubMed

    Costanzo, Davide; Jo, Sanghyun; Berger, Helmuth; Morpurgo, Alberto F

    2016-04-01

    When thinned down to the atomic scale, many layered van der Waals materials exhibit an interesting evolution of their electronic properties, whose main aspects can be accounted for by changes in the single-particle bandstructure. Phenomena driven by interactions are also observed, but identifying experimentally systematic trends in their thickness dependence is challenging. Here, we explore the evolution of gate-induced superconductivity in exfoliated MoS2 multilayers ranging from bulk-like to individual monolayers. We observe a clear transition for all thicknesses down to the ultimate atomic limit, providing the first demonstration of gate-induced superconductivity in atomically thin exfoliated crystals. Additionally, we characterize the superconducting state by measuring the critical temperature TC and magnetic field BC in a large number of multilayer devices while decreasing their thickness. We find that the superconducting properties exhibit a pronounced reduction in TC and BC when going from bilayers to monolayers, for which we discuss possible microscopic mechanisms.

  16. [A quest for a new superconducting state

    SciTech Connect

    Collman, J.P.; Little, W.A.

    1993-12-31

    The authors report on progress of work for the past twelve months, and the work which is planned for the coming year. They have been working on the theory of the long range proximity effect discovered experimentally on Bi-Ag-Tl(2223) sandwiches during the period of the previous grant. This has led to the prediction of a novel effect which they refer to as a ``pair echo`` which occurs in these sandwiches and is analogous to the familiar ``spin echo`` seen in certain NMR experiments. Experimentally, they have extended the measurements of the proximity effect to lower temperatures and to other superconductors. They have completed high resolution studies of the thermal difference optical reflectance of the high {Tc} superconductor Tl(2223), for temperatures both above and below the transition temperature, over a photon energy range from 0.3 eV to 5.3 eV. A striking anomaly in this thermal difference spectrum has been found near 1.6 eV, which appears below {Tc} and scales in magnitude with temperature like {Delta}(T){sup 2} where {Delta}(T) is a BCS gap. This is precisely the kind of effect which they had hoped to find, based on a Holstein-like mechanism in these materials, and which they had predicted in a paper on ``Gap Modulation``. The proper interpretation of the effect observed should reveal the mechanism responsible for the superconductivity of the cuprates. They have completed a search for the, so-called Zhang-modes in the above high {Tc} superconductor, Tl(2223) over the same energy range, 0.3 eV to 5.3 eV. These modes are predicted to exist if the proper description of the ground state of the system is that of a Hubbard model.

  17. Engineering entangled microwave photon states through multiphoton interactions between two cavity fields and a superconducting qubit

    PubMed Central

    Zhao, Yan-Jun; Wang, Changqing; Zhu, Xiaobo; Liu, Yu-xi

    2016-01-01

    It has been shown that there are not only transverse but also longitudinal couplings between microwave fields and a superconducting qubit with broken inversion symmetry of the potential energy. Using multiphoton processes induced by longitudinal coupling fields and frequency matching conditions, we design a universal algorithm to produce arbitrary superpositions of two-mode photon states of microwave fields in two separated transmission line resonators, which are coupled to a superconducting qubit. Based on our algorithm, we analyze the generation of evenly-populated states and NOON states. Compared to other proposals with only single-photon process, we provide an efficient way to produce entangled microwave photon states when the interactions between superconducting qubits and microwave fields are in the strong and ultrastrong regime. PMID:27033558

  18. Change of surface critical current in the surface superconductivity and mixed states of superconducting niobium

    NASA Astrophysics Data System (ADS)

    Aburas, Muhamad; Pautrat, Alain; Bellido, Natalia

    2017-01-01

    A systematic study of irreversible magnetization was performed in bulk niobium after different surface treatments. Starting with smooth surfaces and abrading them, a strong increase of the critical current is observed up to an apparent limiting value. An impressive change of the critical current is also observed in the surface superconductivity (SSC) state, reaching values of the same order of magnitude as in the mixed state. We explain also the observation of strong SSC for magnetic fields perpendicular to large facets in terms of nucleation of superconductivity along bumps of a corrugated surface.

  19. Entangled Coherent States Generation in two Superconducting LC Circuits

    SciTech Connect

    Chen Meiyu; Zhang Weimin

    2008-11-07

    We proposed a novel pure electronic (solid state) device consisting of two superconducting LC circuits coupled to a superconducting flux qubit. The entangled coherent states of the two LC modes is generated through the measurement of the flux qubit states. The interaction of the flux qubit and two LC circuits is controlled by the external microwave control lines. The geometrical structure of the LC circuits is adjustable and makes a strong coupling between them achievable. This entangled coherent state generator can be realized by using the conventional microelectronic fabrication techniques which increases the feasibility of the experiment.

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    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.

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

    PubMed Central

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

    2016-01-01

    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. PMID:27708255

  2. 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.

  3. Superconducting analogue of the parafermion fractional quantum Hall states

    NASA Astrophysics Data System (ADS)

    Vaezi, Abolhassan

    2014-03-01

    Read and Rezayi Zk parafermion wavefunctions describe ν = 2 + k /(kM + 2) fractional quantum Hall (FQH) states. These states support non-Abelian excitations from which protected quantum gates can be designed. However, there is no experimental evidence for these non-Abelian anyons to date. In this talk, we discuss the ν = 2 / k FQH-superconductor heterostructure and through analytical and numerical calculations we argue that it can yield the superconducting analogue of the Zk parafermion FQH state. The resulting topological state has a gapless chiral edge state with Zk parafermion conformal field theory description. For instance, we find that a ν = 2 / 3 FQH in proximity to a superconductor produces a Z3 parafermion superconducting state. This state can host Fibonacci anyons capable of performing universal quantum computation through braiding operations. We finally discuss our experimental proposal for realizing parafermion superconductors. Reference: arXiv:1307.8069

  4. Multistable current states in high-temperature superconducting composites

    NASA Astrophysics Data System (ADS)

    Romanovskii, V. R.

    2016-09-01

    Conditions for current instabilities that arise in high-temperature superconducting composites with essentially nonlinear dependences of the critical current densities and resistivity on the temperature and magnetic induction have been studied. The analysis has been conducted in terms of zero-dimensional models, which has made it possible to formulate general physical mechanisms behind the formation of currents states in superconducting composites according to the external magnetic field induction, cooling conditions, and the properties of the superconductor and cladding. The possible existence of current and temperature stable steps, as well as stable steps of the electric field strength, in the absence of the superconducting-normal transition, has been demonstrated. Reasons for instabilities under multistable current states have been discussed.

  5. Magnetoelectric Andreev Effect due to Proximity-Induced Nonunitary Triplet Superconductivity in Helical Metals

    NASA Astrophysics Data System (ADS)

    Tkachov, G.

    2017-01-01

    Noncentrosymmetric superconductors exhibit the magnetoelectric effect, which manifests itself in the appearance of the magnetic spin polarization in response to a dissipationless electric current (supercurrent). While much attention has been dedicated to the thermodynamic version of this phenomenon (Edelstein effect), nonequilibrium transport magnetoelectric effects have not been explored yet. We propose the magnetoelectric Andreev effect (MAE), which consists in the generation of spin-polarized triplet Andreev conductance by an electric supercurrent. The MAE stems from the spin polarization of the Cooper-pair condensate due to a supercurrent-induced nonunitary triplet pairing. We propose the realization of such a nonunitary pairing and MAE in superconducting proximity structures based on two-dimensional helical metals—strongly spin-orbit-coupled electronic systems with the Dirac spectrum such as the topological surface states. Our results uncover an unexplored route towards electrically controlled superconducting spintronics and are a smoking gun for induced unconventional superconductivity in spin-orbit-coupled materials.

  6. Superconductivity and metallic behavior in PbxCyOδ structures prepared by focused electron beam induced deposition

    NASA Astrophysics Data System (ADS)

    Winhold, M.; Weirich, P. M.; Schwalb, C. H.; Huth, M.

    2014-10-01

    Focused electron beam induced deposition as a direct-write approach possesses great potential to meet the demands for superconducting nanostructure fabrication especially regarding its 3D patterning capabilities combined with the high resolution in the nanometer regime. So far, however, it was not possible to fabricate superconducting structures with this technique. In this work, we present a lead-based superconductor prepared by focused electron beam induced deposition by dissociation of the precursor tetraethyllead. The as-grown structures exhibit metallic behavior and a minimum resistivity in the normal state of ρ = 16 μΩcm at T = 9 K followed by a superconducting transition at Tc = 7.2 K.

  7. Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures.

    PubMed

    Wan, Zhong; Kazakov, Aleksandr; Manfra, Michael J; Pfeiffer, Loren N; West, Ken W; Rokhinson, Leonid P

    2015-06-11

    Search for Majorana fermions renewed interest in semiconductor-superconductor interfaces, while a quest for higher-order non-Abelian excitations demands formation of superconducting contacts to materials with fractionalized excitations, such as a two-dimensional electron gas in a fractional quantum Hall regime. Here we report induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures and development of highly transparent semiconductor-superconductor ohmic contacts. Supercurrent with characteristic temperature dependence of a ballistic junction has been observed across 0.6 μm, a regime previously achieved only in point contacts but essential to the formation of well separated non-Abelian states. High critical fields (>16 T) in NbN contacts enables investigation of an interplay between superconductivity and strongly correlated states in a two-dimensional electron gas at high magnetic fields.

  8. Induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures

    PubMed Central

    Wan, Zhong; Kazakov, Aleksandr; Manfra, Michael J.; Pfeiffer, Loren N.; West, Ken W.; Rokhinson, Leonid P.

    2015-01-01

    Search for Majorana fermions renewed interest in semiconductor–superconductor interfaces, while a quest for higher-order non-Abelian excitations demands formation of superconducting contacts to materials with fractionalized excitations, such as a two-dimensional electron gas in a fractional quantum Hall regime. Here we report induced superconductivity in high-mobility two-dimensional electron gas in gallium arsenide heterostructures and development of highly transparent semiconductor–superconductor ohmic contacts. Supercurrent with characteristic temperature dependence of a ballistic junction has been observed across 0.6 μm, a regime previously achieved only in point contacts but essential to the formation of well separated non-Abelian states. High critical fields (>16 T) in NbN contacts enables investigation of an interplay between superconductivity and strongly correlated states in a two-dimensional electron gas at high magnetic fields. PMID:26067452

  9. Decoherence in Superconducting Qubits from Surface Magnetic States

    NASA Astrophysics Data System (ADS)

    Hover, David; Sendelbach, Steven; Kittel, Achim; Mueck, Michael; McDermott, Robert

    2008-03-01

    Unpaired spins in amorphous surface oxides can act as a source of decoherence in superconducting and other solid-state qubits. A density of surface spins can give rise to low-frequency magnetic flux noise, which in turn leads to dephasing of the qubit state. In addition, magnetic surface states can couple to high-frequency resonant magnetic fields, and thereby contribute to energy relaxation of the qubit. We present the results of low-frequency measurements of the nonlinear and imaginary spin susceptibility of surface magnetic states in superconducting devices at millikelvin temperatures. In addition, we describe high-frequency magnetic resonance measurements that directly probe the surface spin density of states. We present calculations that connect the measurement results to qubit energy relaxation and dephasing times.

  10. Superconductivity

    DTIC Science & Technology

    1989-07-01

    SUPERCONDUCTIVITY HIGH-POWER APPLICATIONS Electric power generation/transmission Energy storage Acoustic projectors Weapon launchers Catapult Ship propulsion • • • Stabilized...temperature superconductive shields could be substantially enhanced by use of high-Tc materials. 27 28 NRAC SUPERCONDUCTIVITY SHIP PROPULSION APPLICATIONS...motor shown in the photograph. As a next step in the evolution of electric-drive ship propulsion technology, DTRC has proposed to scale up the design

  11. Pressure-induced superconductivity in quasi-2D CeRhIn5

    PubMed

    Hegger; Petrovic; Moshopoulou; Hundley; Sarrao; Fisk; Thompson

    2000-05-22

    CeRhIn5 is a new heavy-electron material that crystallizes in a quasi-2D structure that can be viewed as alternating layers of CeIn3 and RhIn2 stacked sequentially along the tetragonal c axis. Application of hydrostatic pressure induces a first-order-like transition from an unconventional antiferromagnetic state to a superconducting state with T(c) = 2.1 K.

  12. Ground State Properties and Localized Excited States around a Magnetic Impurity Described by the Anisotropic s- d Interaction in Superconductivity

    NASA Astrophysics Data System (ADS)

    Yoshioka, Tomoki; Ohashi, Yoji

    1998-04-01

    We investigate the electronic state around a magnetic impurity in thesuperconductivity in order to clarify how the anisotropy of thes-d interaction works in the presence of the superconductingenergy gap. Using the numerical renormalization group method, weobtain regions induced by the anisotropy where two localizedexcited states with different energies appear at the same time; theycannot obtain as far as the isotropic interaction is considered. Thismeans that the anisotropy of the s-d interaction works relevantlyin some cases in the superconducting state. We also examine whether ornot the bound state energy for the anisotropic and antiferromagnetics-d interaction is scaled by T K/Δ (T K: Kondotemperature, Δ: superconducting order parameter), and find thatit does not hold in the regions with two bound states.

  13. Gate-induced superconductivity in two-dimensional atomic crystals

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro

    2016-09-01

    Two-dimensional (2D) crystals are attracting growing interest in condensed matter physics, since these systems exhibit not only rich electronic and photonic properties but also exotic electronic phase transitions including superconductivity and charge density wave. Moreover, owing to the recent development of transfer methods after exfoliation and electric-double-layer transistors, superconducting 2D atomic crystals, the thicknesses of which are below 1-2 nm, have been successfully obtained. Here, we present a topical review on the recent discoveries of 2D crystalline superconductors by ionic-liquid gating and a series of their novel properties. In particular, we highlight two topics; quantum metallic states (or possible metallic ground states) and superconductivity robust against in-plane magnetic fields. These phenomena can be discussed with the effects of weakened disorder and/or broken spacial inversion symmetry leading to valley-dependent spin-momentum locking (spin-valley locking). These examples suggest the superconducting 2D crystals are new platforms for investigating the intrinsic quantum phases as well as exotic nature in 2D superconductors.

  14. Electronic thermal conductivity in a superconducting vortex state

    NASA Astrophysics Data System (ADS)

    Adachi, H.; Miranovic, P.; Ichioka, M.; Machida, K.

    2007-10-01

    The longitudinal component of the electronic thermal conductivity κxx in a superconducting vortex state is calculated as a function of magnetic field B. Calculations are performed by taking account of the spatial dependence of normal Green's function g, which was neglected in the previous studies using the Brandt-Pesch-Tewordt method. We discuss the possibility of using κxx(B) as a probe of the pair potential symmetry.

  15. Superconductivity

    NASA Astrophysics Data System (ADS)

    Yeo, Yung K.

    Many potential high-temperature superconductivity (HTS) military applications have been demonstrated by low-temperature superconductivity systems; they encompass high efficiency electric drives for naval vessels, airborne electric generators, energy storage systems for directed-energy weapons, electromechanical launchers, magnetic and electromagnetic shields, and cavity resonators for microwave and mm-wave generation. Further HST applications in militarily relevant fields include EM sensors, IR focal plane arrays, SQUIDs, magnetic gradiometers, high-power sonar sources, and superconducting antennas and inertial navigation systems. The development of SQUID sensors will furnish novel magnetic anomaly detection methods for ASW.

  16. Thermal study of vortex states in mesoscopic superconducting disks

    NASA Astrophysics Data System (ADS)

    Ong, Florian; Bourgeois, Olivier; Skipetrov, Sergey; Chaussy, Jacques

    2007-03-01

    We present low temperature highly sensitive heat capacity C measurements [1,2] of aluminum disks with diameters close to ξ(T), the superconducting coherence length. C(T) scans under fixed perpendicular magnetic fields H reveal a quasiperiodic modulation of the height δC of the C jump at the superconducting to normal phase transition. This behavior is due to transitions between several arrangements of vortices in the disks. Indeed giant vortex states or multivortex states can be observed, with a vorticity (an integer equal to the number of vortices threading a single disk) depending on H, T, and on the size of the disks. Heat capacity measurements enable to study phase transitions between such states, without contacting or biasing them. Thus phase boudaries in the H-T plane can be drawn in all the superconducting region. [1] O. Bourgeois, F. Ong, S.E. Skipetrov, and J. Chaussy, Phys. Rev. Lett. 94, 057007 (2005) [2] F.R. Ong, O. Bourgeois, S.E. Skipetrov, and J. Chaussy, Phys. Rev. B 74, 140503(R) (2006)

  17. Giant superconductivity-induced modulation of the ferromagnetic magnetization in a cuprate-manganite superlattice.

    PubMed

    Hoppler, J; Stahn, J; Niedermayer, Ch; Malik, V K; Bouyanfif, H; Drew, A J; Rössle, M; Buzdin, A; Cristiani, G; Habermeier, H-U; Keimer, B; Bernhard, C

    2009-04-01

    Artificial multilayers offer unique opportunities for combining materials with antagonistic orders such as superconductivity and ferromagnetism and thus to realize novel quantum states. In particular, oxide multilayers enable the utilization of the high superconducting transition temperature of the cuprates and the versatile magnetic properties of the colossal-magnetoresistance manganites. However, apart from exploratory work, the in-depth investigation of their unusual properties has only just begun. Here we present neutron reflectometry measurements of a [Y(0.6)Pr(0.4)Ba(2)Cu(3)O(7) (10 nm)/La(2/3)Ca(1/3)MnO(3) (10 nm)](10) superlattice, which reveal a surprisingly large superconductivity-induced modulation of the vertical ferromagnetic magnetization profile. Most surprisingly, this modulation seems to involve the density rather than the orientation of the magnetization and is highly susceptible to the strain, which is transmitted from the SrTiO(3) substrate. We outline a possible explanation of this unusual superconductivity-induced phenomenon in terms of a phase separation between ferromagnetic and non-ferromagnetic nanodomains in the La(2/3)Ca(1/3)MnO(3) layers.

  18. Electromagnetically induced transparency with amplification in superconducting circuits.

    PubMed

    Joo, Jaewoo; Bourassa, Jérôme; Blais, Alexandre; Sanders, Barry C

    2010-08-13

    We show that controlling relative phases of electromagnetic fields driving an atom with a Δ-configuration energy-level structure enables optical susceptibility to be engineered in novel ways. In particular, relative-phase control can yield electromagnetically induced transparency but with the benefit that the transparency window is sandwiched between an absorption and an amplification band rather than between two absorption bands in typical electromagnetically induced transparency. We show that this new phenomenon is achievable for a microwave field interacting with a fluxonium superconducting circuit.

  19. Shooting quasiparticles from Andreev bound states in a superconducting constriction

    SciTech Connect

    Riwar, R.-P.; Houzet, M.; Meyer, J. S.; Nazarov, Y. V.

    2014-12-15

    A few-channel superconducting constriction provides a set of discrete Andreev bound states that may be populated with quasiparticles. Motivated by recent experimental research, we study the processes in an a.c. driven constriction whereby a quasiparticle is promoted to the delocalized states outside the superconducting gap and flies away. We distinguish two processes of this kind. In the process of ionization, a quasiparticle present in the Andreev bound state is transferred to the delocalized states leaving the constriction. The refill process involves two quasiparticles: one flies away while another one appears in the Andreev bound state. We notice an interesting asymmetry of these processes. The electron-like quasiparticles are predominantly emitted to one side of the constriction while the hole-like ones are emitted to the other side. This produces a charge imbalance of accumulated quasiparticles, that is opposite on opposite sides of the junction. The imbalance may be detected with a tunnel contact to a normal metal lead.

  20. Emergence of nanoscale inhomogeneity in the superconducting state of a homogeneously disordered conventional superconductor

    PubMed Central

    Kamlapure, Anand; Das, Tanmay; Ganguli, Somesh Chandra; Parmar, Jayesh B.; Bhattacharyya, Somnath; Raychaudhuri, Pratap

    2013-01-01

    The notion of spontaneous formation of an inhomogeneous superconducting state is at the heart of most theories attempting to understand the superconducting state in the presence of strong disorder. Using scanning tunneling spectroscopy and high resolution scanning transmission electron microscopy, we experimentally demonstrate that under the competing effects of strong homogeneous disorder and superconducting correlations, the superconducting state of a conventional superconductor, NbN, spontaneously segregates into domains. Tracking these domains as a function of temperature we observe that the superconducting domains persist across the bulk superconducting transition, Tc, and disappear close to the pseudogap temperature, T*, where signatures of superconducting correlations disappear from the tunneling spectrum and the superfluid response of the system. PMID:24132046

  1. Pair density wave superconducting states and statistical mechanics of dimers

    NASA Astrophysics Data System (ADS)

    Soto Garrido, Rodrigo Andres

    The following thesis is divided in two main parts. Chapters 2, 3 and 4 are devoted to the study of the so called pair-density-wave (PDW) superconducting state and some of its connections to electronic liquid crystal (ELC) phases, its topological aspects in a one dimensional model and its appearance in a quasi-one dimensional system. On the other hand, chapter 5 is focused on the investigation of the classical statistical mechanics properties of dimers, in particular, the dimer model on the Aztec diamond graph and its relation with the octahedron equation. In chapter 2 we present a theory of superconducting states where the Cooper pairs have a nonzero center-of-mass momentum, inhomogeneous superconducting states known as a pair-density-waves (PDWs) states. We show that in a system of spin-1/2 fermions in two dimensions in an electronic nematic spin-triplet phase where rotational symmetry is broken in both real and spin space PDW phases arise naturally in a theory that can be analysed using controlled approximations. We show that several superfluid phases that may arise in this phase can be treated within a controlled BCS mean field theory, with the strength of the spin-triplet nematic order parameter playing the role of the small parameter of this theory. We find that in a spin-triplet nematic phase, in addition to a triplet p-wave and spin-singlet d-wave (or s depending on the nematic phase) uniform superconducting states, it is also possible to have a d-wave (or s) PDW superconductor. The PDW phases found here can be either unidirectional, bidirectional, or tridirectional depending on the spin-triplet nematic phase and which superconducting channel is dominant. In addition, a triple-helix state is found in a particular channel. We show that these PDW phases are present in the weak-coupling limit, in contrast to the usual Fulde-Ferrell-Larkin-Ovchinnikov phases, which require strong coupling physics in addition to a large magnetic field (and often both). In chapter

  2. Theory of spin-fluctuation induced superconductivity in iron-based superconductors

    SciTech Connect

    Zhang, Junhua

    2011-01-01

    In this dissertation we focus on the investigation of the pairing mechanism in the recently discovered high-temperature superconductor, iron pnictides. Due to the proximity to magnetic instability of the system, we considered short-range spin fluctuations as the major mediating source to induce superconductivity. Our calculation supports the magnetic fluctuations as a strong candidate that drives Cooper-pair formation in this material. We find the corresponding order parameter to be of the so-called ss-wave type and show its evolution with temperature as well as the capability of supporting high transition temperature up to several tens of Kelvin. On the other hand, our itinerant model calculation shows pronounced spin correlation at the observed antiferromagnetic ordering wave vector, indicating the underlying electronic structure in favor of antiferromagnetic state. Therefore, the electronic degrees of freedom could participate both in the magnetic and in the superconducting properties. Our work shows that the interplay between magnetism and superconductivity plays an important role to the understanding of the rich physics in this material. The magnetic-excitation spectrum carries important information on the nature of magnetism and the characteristics of superconductivity. We analyze the spin excitation spectrum in the normal and superconducting states of iron pnictides in the magnetic scenario. As a consequence of the sign-reversed gap structure obtained in the above, a spin resonance mode appears below the superconducting transition temperature. The calculated resonance energy, scaled with the gap magnitude and the magnetic correlation length, agrees well with the inelastic neutron scattering (INS) measurements. More interestingly, we find a common feature of those short-range spin fluctuations that are capable of inducing a fully gapped ss state is the momentum anisotropy with elongated span along the direction transverse to the antiferromagnetic momentum

  3. Anomalous vortex state of superconducting LuNi2B2C

    NASA Astrophysics Data System (ADS)

    Price, A. N.; Miller, R. I.; Kiefl, R. F.; Chakhalian, J. A.; Dunsiger, S. R.; Morris, G. D.; Sonier, J. E.; Canfield, P. C.

    2002-06-01

    Muon spin rotation has been used to investigate the magnetic-field distribution in the vortex state of superconducting LuNi2B2C (Tc~16 K). Data for the magnetic field range 0.06Hc2<~H<~0.23Hc2 are fitted to a nonlocal London model. The temperature dependence of the vortex core radius shows a clear Kramer-Pesch effect due to depopulation of bound states within the cores. Also, the penetration depth and core radius vary substantially with applied magnetic field, suggesting the presence of anomalous field-induced quasiparticles and vortex-vortex interactions.

  4. Superconductivity:

    NASA Astrophysics Data System (ADS)

    Sacchetti, N.

    In this paper a short historical account of the discovery of superconductivity and of its gradual development is given. The physical interpretation of its various aspects took about forty years (from 1911 to 1957) to reach a successful description of this phenomenon in terms of a microscopic theory At the very end it seemed that more or less everything could be reasonably interpreted even if modifications and refinements of the original theory were necessary. In 1986 the situation changed abruptly when a cautious but revolutionary paper appeared showing that superconductivity was found in certain ceramic oxides at temperatures above those up to then known. A rush of frantic experimental activity started world-wide and in less than one year it was shown that superconductivity is a much more widespread phenomenon than deemed before and can be found at temperatures well above the liquid air boiling point. The complexity and the number of the substances (mainly ceramic oxides) involved call for a sort of modern alchemy if compounds with the best superconducting properties are to be manufactured. We don't use the word alchemy in a deprecatory sense but just to emphasise that till now nobody can say why these compounds are what they are: superconductors.

  5. Proximity induced superconductivity in the 3D topological insulator HgTe probed with scanning SQUID microscope

    NASA Astrophysics Data System (ADS)

    Sochnikov, Ilya; Kirtley, John R.; Moler, Kathryn A.; Maier, Luis; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens W.

    2014-03-01

    Inducing superconductivity on the surface of a 3D topological insulator is important for novel broken symmetry phases. However, it is difficult to assess the existence of the surface superconductivity with a single experimental technique. We have used a scanning SQUID microscope to characterize the magnetic properties of hybrid structures made of the 3D topological insulator HgTe and superconducting Nb. The magnetic response of superconducting rings with exotic Josephson junctions reveals the current-phase relation, while measurements of bilayer HgTe/Nb disks reveal the total superfluid density of the hybrid structure. We analyze the degree of skew in the current-phase relation to determine the relative contribution of surface states, and discuss other contributions to the current-phase relation. This work sets an agenda for discussion of the prospects for detection of new broken symmetry phases in 3D topological insulators.

  6. Superconducting state parameters of monovalent and polyvalent amorphous

    SciTech Connect

    Sonvane, Y. A.; Patel, H. P. Thakor, P. B.

    2015-08-28

    In the present study deals, we have calculated superconducting state parameter (SSP) like electron-phonon coupling strength λ, coulomb pseudo potential, μ*, transition temperature Tc, isotope effect exponent α and effective interaction strength N{sub 0}V of monovalent (Li), divalent (Zn), trivalent (In) and tetravalent (Pb) amorphous. To carry out this work we have used our newly constructed model pseudo potential to describe electron ion interaction along with three different local field correction functions like Hartree, Taylor and Sarkar et al. The present results are found in good agreement with other available theoretical as well as experimental data.

  7. 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.

  8. Photon-induced thermal effects in superconducting coplanar waveguide resonators

    NASA Astrophysics Data System (ADS)

    Wang, Yiwen; Zhou, Pinjia; Wei, Lianfu; Li, Haijie; Zhang, Beihong; Zhang, Miao; Wei, Qiang; Fang, Yurong; Cao, Chunhai

    2013-10-01

    We experimentally investigated the optical responses of a superconducting niobium resonator. It was found that, with increasing radiation power, the resonance frequency increases monotonically below around 500 mK, decreases monotonically above around 1 K, and exhibits a nonmonotonic behavior at around 700 mK. These observations show that one can operate the irradiated resonator in three temperature regimes, depending on whether two-level system (TLS) effects or kinetic inductance effects dominate. Furthermore, we found that the optical responses at ultra-low temperatures can be qualitatively regarded as a photon-induced thermalization effect of TLSs, which could be utilized to achieve thermal sensitive photon detections.

  9. Control of switching between metastable superconducting states in δ-MoN nanowires

    PubMed Central

    Buh, Jože; Kabanov, Viktor; Baranov, Vladimir; Mrzel, Aleš; Kovič, Andrej; Mihailovic, Dragan

    2015-01-01

    The superconducting state in one-dimensional nanosystems is very delicate. While fluctuations of the phase of the superconducting wave function lead to the spontaneous decay of persistent supercurrents in thin superconducting wires and nanocircuits, discrete phase-slip fluctuations can also lead to more exotic phenomena, such as the appearance of metastable superconducting states in current-bearing wires. Here we show that switching between different metastable superconducting states in δ-MoN nanowires can be very effectively manipulated by introducing small amplitude electrical noise. Furthermore, we show that deterministic switching between metastable superconducting states with different numbers of phase-slip centres can be achieved in both directions with small electrical current pulse perturbations of appropriate polarity. The observed current-controlled bi-stability is in remarkable agreement with theoretically predicted trajectories of the system switching between different limit cycle solutions of a model one-dimensional superconductor. PMID:26687762

  10. Quantized levitation states of superconducting multiple-ring systems

    SciTech Connect

    Haley, S.B.; Fink, H.J.

    1996-02-01

    The quantized levitation, trapped, and suspension states of a magnetic microsphere held in equilibrium by two fixed superconducting (SC) microrings are calculated by minimizing the free energy of the system. Each state is a discrete function of two independent fluxoid quantum numbers of the rings. When the radii of the SC rings are of the same order as the Ginzburg-Landau coherence length {xi}({ital T}), the system exhibits a small set of gravity and temperature-dependent levels. The levels of a weakly magnetized particle are sensitive functions of the gravitational field, indicating potential application as an accelerometer, and for trapping small magnetic particles in outer space or on Earth. The equilibrium states of a SC ring levitated by another SC ring are also calculated. {copyright} {ital 1996 The American Physical Society.}

  11. Superconductivity in the non-magnetic state of iron under pressure.

    PubMed

    Shimizu, K; Kimura, T; Furomoto, S; Takeda, K; Kontani, K; Onuki, Y; Amaya, K

    2001-07-19

    Ferromagnetism and superconductivity are thought to compete in conventional superconductors, although in principle it is possible for any metal to become a superconductor in its non-magnetic state at a sufficiently low temperature. At pressures above 10 GPa, iron is known to transform to a non-magnetic structure and the possibility of superconductivity in this state has been predicted. Here we report that iron does indeed become superconducting at temperatures below 2 K at pressures between 15 and 30 GPa. The transition to the superconducting state is confirmed by both a drop in resistivity and observation of the Meissner effect.

  12. Cooper-pair insulator phase in superconducting amorphous Bi films induced by nanometer-scale thickness variations

    NASA Astrophysics Data System (ADS)

    Hollen, S. M.; Nguyen, H. Q.; Rudisaile, E.; Stewart, M. D., Jr.; Shainline, J.; Xu, J. M.; Valles, J. M., Jr.

    2011-08-01

    Ultrathin films near the quantum insulator-superconductor transition (IST) can exhibit Cooper-pair transport in their insulating state. This Cooper-pair insulator (CPI) state is achieved in amorphous Bi films evaporated onto substrates with a topography varying on lengths slightly greater than the superconducting coherence length. We present evidence that this topography induces film thickness and corresponding superconducting coupling constant variations that promote Cooper-pair island formation. Analyses of many thickness-tuned ISTs show that weak links between superconducting islands dominate the transport. In particular, the IST occurs when the link resistance approaches the resistance quantum for pairs. These results support conjectures that the CPI is an inhomogeneous state of matter.

  13. Magnetic-field-induced superconductivity in a two-dimensional organic conductor.

    PubMed

    Uji, S; Shinagawa, H; Terashima, T; Yakabe, T; Terai, Y; Tokumoto, M; Kobayashi, A; Tanaka, H; Kobayashi, H

    2001-04-19

    The application of a sufficiently strong magnetic field to a superconductor will, in general, destroy the superconducting state. Two mechanisms are responsible for this. The first is the Zeeman effect, which breaks apart the paired electrons if they are in a spin-singlet (but not a spin-triplet) state. The second is the so-called 'orbital' effect, whereby the vortices penetrate into the superconductors and the energy gain due to the formation of the paired electrons is lost. For the case of layered, two-dimensional superconductors, such as the high-Tc copper oxides, the orbital effect is reduced when the applied magnetic field is parallel to the conducting layers. Here we report resistance and magnetic-torque experiments on single crystals of the quasi-two-dimensional organic conductor lambda-(BETS)2FeCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene. We find that for magnetic fields applied exactly parallel to the conducting layers of the crystals, superconductivity is induced for fields above 17 T at a temperature of 0.1 K. The resulting phase diagram indicates that the transition temperature increases with magnetic field, that is, the superconducting state is further stabilized with magnetic field.

  14. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: On Superconductivity State in Pure Graphene

    NASA Astrophysics Data System (ADS)

    Mousavi, Hamze

    2010-10-01

    We study theoretically the possibility of superconductivity state in pure graphene within the extended attractive Hubbard model. In the absence of disorder, when we use the local attractive interaction potential, U ⋍ 5t, where t is hopping term, pure graphene can be in superconductivity state.

  15. Superconductivity in HfTe5 across weak to strong topological insulator transition induced via pressures

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Long, Y. J.; Zhao, L. X.; Nie, S. M.; Zhang, S. J.; Weng, Y. X.; Jin, M. L.; Li, W. M.; Liu, Q. Q.; Long, Y. W.; Yu, R. C.; Gu, C. Z.; Sun, F.; Yang, W. G.; Mao, H. K.; Feng, X. L.; Li, Q.; Zheng, W. T.; Weng, H. M.; Dai, X.; Fang, Z.; Chen, G. F.; Jin, C. Q.

    2017-03-01

    Recently, theoretical studies show that layered HfTe5 is at the boundary of weak & strong topological insulator (TI) and might crossover to a Dirac semimetal state by changing lattice parameters. The topological properties of 3D stacked HfTe5 are expected hence to be sensitive to pressures tuning. Here, we report pressure induced phase evolution in both electronic & crystal structures for HfTe5 with a culmination of pressure induced superconductivity. Our experiments indicated that the temperature for anomaly resistance peak (Tp) due to Lifshitz transition decreases first before climbs up to a maximum with pressure while the Tp minimum corresponds to the transition from a weak TI to strong TI. The HfTe5 crystal becomes superconductive above ~5.5 GPa where the Tp reaches maximum. The highest superconducting transition temperature (Tc) around 5 K was achieved at 20 GPa. Crystal structure studies indicate that HfTe5 transforms from a Cmcm phase across a monoclinic C2/m phase then to a P-1 phase with increasing pressure. Based on transport, structure studies a comprehensive phase diagram of HfTe5 is constructed as function of pressure. The work provides valuable experimental insights into the evolution on how to proceed from a weak TI precursor across a strong TI to superconductors.

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

    DOE PAGES

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

    2015-11-16

    Polarized Raman scattering spectra of superconducting KxFe2-ySe2 and nonsuperconducting K0.8Fe1.8Co0.2Se2 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 K0.8Fe1.8Co0.2Se2 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-induced anharmonic effects. It is shown that change of Raman mode energymore » with temperature is dominantly driven by thermal expansion of the crystal lattice. Abrupt change of the A1g mode energy near TC was observed in KxFe2-ySe2 , whereas it is absent in 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 critical temperature.« less

  17. Superconductivity in HfTe5 across weak to strong topological insulator transition induced via pressures

    PubMed Central

    Liu, Y.; Long, Y. J.; Zhao, L. X.; Nie, S. M.; Zhang, S. J.; Weng, Y. X.; Jin, M. L.; Li, W. M.; Liu, Q. Q.; Long, Y. W.; Yu, R. C.; Gu, C. Z.; Sun, F.; Yang, W. G.; Mao, H. K.; Feng, X. L.; Li, Q.; Zheng, W. T.; Weng, H. M.; Dai, X.; Fang, Z.; Chen, G. F.; Jin, C. Q.

    2017-01-01

    Recently, theoretical studies show that layered HfTe5 is at the boundary of weak & strong topological insulator (TI) and might crossover to a Dirac semimetal state by changing lattice parameters. The topological properties of 3D stacked HfTe5 are expected hence to be sensitive to pressures tuning. Here, we report pressure induced phase evolution in both electronic & crystal structures for HfTe5 with a culmination of pressure induced superconductivity. Our experiments indicated that the temperature for anomaly resistance peak (Tp) due to Lifshitz transition decreases first before climbs up to a maximum with pressure while the Tp minimum corresponds to the transition from a weak TI to strong TI. The HfTe5 crystal becomes superconductive above ~5.5 GPa where the Tp reaches maximum. The highest superconducting transition temperature (Tc) around 5 K was achieved at 20 GPa. Crystal structure studies indicate that HfTe5 transforms from a Cmcm phase across a monoclinic C2/m phase then to a P-1 phase with increasing pressure. Based on transport, structure studies a comprehensive phase diagram of HfTe5 is constructed as function of pressure. The work provides valuable experimental insights into the evolution on how to proceed from a weak TI precursor across a strong TI to superconductors. PMID:28300156

  18. Superconducting plate in a transverse magnetic field: New state

    SciTech Connect

    Batyev, E. G.

    2012-07-15

    A model is proposed for describing Cooper pairs near the transition (in temperature and magnetic field) point when their spacing is larger than their size. The essence of the model is as follows: the Ginzburg-Landau functional is written in operator form in terms of field operators of the Bose type so that the average value of the density operator gives the concentration of Cooper pairs, and the same Ginzburg-Landau expression is obtained for the Bose condensate. The model is applied to a superconducting plate with a thickness smaller than the size of a pair in a transverse magnetic field near its upper critical value H{sub c2}. A new state is discovered that is energetically more advantageous in a certain interval in the vicinity of the transition point as compared to the Abrikosov vortex state. The wavefunction of the system in this state is of the type of the Laughlin function used in the fractional quantum Hall effect (naturally, as applied to Cooper pairs as Bose particles in our case) and corresponds to a homogeneous incompressible fluid. The energy of this state is proportional to the first power of quantity (1 - H/H{sub c2}) in contrast to the energy of the vortex state containing the square of this quantity. The interval of the existence of the new state is the larger, the dirtier the sample.

  19. Properties of the superconducting state in compressed sulphur

    NASA Astrophysics Data System (ADS)

    Durajski, A. P.; Szczę[sgrave]niak, R.; Jarosik, M. W.

    2012-08-01

    The thermodynamic properties of the superconducting state in sulphur at pressure 160 GPa have been determined. It has been shown that: (i) the critical value of the Coulomb pseudopotential is equal to 0.127; (ii) the critical temperature (T C = 17 K) should be calculated by using the modified Allen-Dynes formula; (iii) the effective electron-electron interaction is attractive in the range of frequencies from zero to the frequency slightly lesser than the maximum phonon frequency (∼0.85Ωmax); (iv) the dimensionless ratios: 2Δ(0)/k B T C , ΔC(T C )/C N (T C ) and ? are equal to: 3.7, 1.65 and 0.16, respectively; (v) the ratio of the effective to bare electron mass reaches maximum of 1.77 for T = T C .

  20. Superconducting and normal-state properties of novel materials

    SciTech Connect

    Crespi, Vincent Henry

    1994-09-01

    Interest in solid state physics naturally gravitates towards novel systems such as the copper oxide superconductors or the alkali-doped fullerenes. This paper tackles high temperature superconductivity by extension of the BCS theory for ordinary superconductors, in particular, incorporation of anharmonicity in phonon dynamics and anisotropy in electron-phonon coupling. These refinements can account for many anomalous properties of the cuprates. Phonon anharmonicity is consistent with a small isotope effect at optimal doping and a larger isotope effect in suboptimal systems. Anisotropy in the interaction, a plausible consequence of certain anharmonic models, can circumvent objections to electron-phonon coupling based on transport measurements. Such anisotropy is consistent with gap anisotropy and strong temperature dependence of Hall coefficient. In contrast to cuprates, the doped fullerenes appear understandable within the standard model of single electron band theory and BCS theory. Microscopic parameters derivable from transport and critical field measurements yield a self-consistent picture of a disordered Type-2 BCS superconductor. Isotope effects imply that superconductivity is mediated by carbon phonons opposed to alkali atom vibrations. The novel properties of the fullerenes are generally traceable to their microscopic heterogeneity, being a collection of tightly bound but weakly overlapping molecules. Separation of electronic regimes into weak intermolecular overlap and strong carbon-carbon on-ball bonds yields a superconductor with both a large density of states and a high phonon frequency, properties consistent with a relatively high {Tc}. Disordered nature of intermolecular overlap produces a large residual resistivity and a universal dependence to the Hall coefficient. This disorder is also consistent with the anomalously large carbon isotope effect for heterogeneous isotopic substitution.

  1. Superconductivity and magnetic field induced spin density waves in the (TMTTF)2X family

    NASA Astrophysics Data System (ADS)

    Balicas, L.; Behnia, K.; Kang, W.; Canadell, E.; Auban-Senzier, P.; Jérome, D.; Ribault, M.; Fabre, J. M.

    1994-10-01

    We report magnetotransport measurements in the quasi one dimensional (Q-1-D) organic conductor (TMTTF)2Br at pressures up to 26 kbar, clown to 0.45 K in magnetic fields up to 19 T along the c^{ast} direction. It is found that a superconducting ground state is stabilized under 26 kbar at T_C = 0.8 K. No magnetic field induced spin density wave (FISDW) transitions are observed below 19T unlike other Q-1-D superconductors pertaining to the selenium series. The computed amplitude of the interchain coupling along transverse directions is unable to explain the missing; FISDW instability.

  2. Characterizing and reducing microfabrication-induced loss in superconducting devices, Part II: Xmon qubits

    NASA Astrophysics Data System (ADS)

    Megrant, Anthony; Dunsworth, A.; Quintana, C.; Kelly, J.; Barends, R.; Campbell, B.; Chen, Y.; Chen, Z.; Chiaro, B.; Fowler, A.; Jeffrey, E.; Mutus, J.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T.; Martinis, J. M.

    Microfabrication-induced loss has previously been shown to limit the coherence times of both planar and 3-D superconducting qubits. Energy loss in these qubits arises from interactions with two-level state defects which are located in thin lossy surface dielectrics. More recently, we have identified a major source of this loss and then substantially improved this decoherence channel using a novel resonator structure for characterization and improvement. I will report on recent measurements of Xmon qubits with substantially improved coherence times due to our new fabrication process.

  3. Hedgehog Excitations and their Superconducting Cores in the Antiferromagnetic State of SO(5) Materials

    NASA Astrophysics Data System (ADS)

    Goldbart, Paul M.

    1998-03-01

    Zhang's SO(5) approach to the physics of high-temperature superconducting materials(S.-C. Zhang, Science 275), 1089 (1997). contains the possibility that the antiferromagnetic state should support novel excitations that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region(P. M. Goldbart, Antiferromagnetic hedgehogs with superconducting cores); cond- mat/9711088 (UIUC Preprint P-97-10-030-iii).. Neither singular nor topologically stable, in contrast with their hedgehog cousins in pure antiferromagnetism, these excitations are what hedgehogs become when antiferromagnetic order is permitted to `` escape'' toward superconductivity---a central element in Zhang's approach. We describe the structure of antiferromagnetic hedgehog excitations with superconducting cores within the context of Zhang's approach to high-temperature superconducting materials, and touch upon a number of the experimental implications that these excitations engender.

  4. Unconventional superconductivity induced in Nb films by adsorbed chiral molecules

    NASA Astrophysics Data System (ADS)

    Alpern, H.; Katzir, E.; Yochelis, S.; Katz, N.; Paltiel, Y.; Millo, O.

    2016-11-01

    Motivated by recent observations of chiral-induced magnetization and spin-selective transport we studied the effect of chiral molecules on conventional BCS superconductors. By applying scanning tunneling spectroscopy, we demonstrate that the singlet-pairing s-wave order parameter of Nb is significantly altered upon adsorption of chiral polyalanine alpha-helix molecules on its surface. The tunneling spectra exhibit zero-bias conductance peaks embedded inside gaps or gap-like features, suggesting the emergence of unconventional triplet-pairing components with either d-wave or p-wave symmetry at the Nb organic-molecules interface, as corroborated by simulations. These results may open a way for realizing simple superconducting spintronics devices.

  5. Shock-induced synthesis of high temperature superconducting materials

    DOEpatents

    Ginley, D.S.; Graham, R.A.; Morosin, B.; Venturini, E.L.

    1987-06-18

    It has now been determined that the unique features of the high pressure shock method, especially the shock-induced chemical synthesis technique, are fully applicable to high temperature superconducting materials. Extraordinarily high yields are achievable in accordance with this invention, e.g., generally in the range from about 20% to about 99%, often in the range from about 50% to about 90%, lower and higher yields, of course, also being possible. The method of this invention involves the application of a controlled high pressure shock compression pulse which can be produced in any conventional manner, e.g., by detonation of a high explosive material, the impact of a high speed projectile or the effect of intense pulsed radiation sources such as lasers or electron beams. Examples and a discussion are presented.

  6. Resistive current state of a wide superconducting film

    NASA Astrophysics Data System (ADS)

    Zolochevskii, I. V.

    2011-12-01

    The current-voltage characteristics (CVCs) of vortex superconducting films are investigated in a wide temperature range. It is shown for the first time that the experimental CVCs and their parameters are described well enough by asymptotic formulas within the theory of the vortex resistive state of Aslamazov-Lempitsky (AL). It is established that for wide films, the critical current of which corresponds to the AL theory, the differential resistance of a linear segment of a CVC does not depend on temperature that agrees with the model of the vortex resistive state of AL. In the range of much higher temperatures, where the critical current is Ic(T)∝(1-T/Tc)3/2, the decrease of the differential resistance with increasing the temperature is observed that corresponds to predictions of the AL theory. However, in the close vicinity of Tc the increase of the differential resistance of a linear vortex segment of CVCs was found at T → Tc. This effect does not have an explanation in modern theories of a vortex state.

  7. Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid.

    PubMed

    Yu, Deshui; Valado, María Martínez; Hufnagel, Christoph; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer

    2016-12-06

    Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa.

  8. Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid

    PubMed Central

    Yu, Deshui; Valado, María Martínez; Hufnagel, Christoph; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer

    2016-01-01

    Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa. PMID:27922087

  9. Quantum State Transmission in a Superconducting Charge Qubit-Atom Hybrid

    NASA Astrophysics Data System (ADS)

    Yu, Deshui; Valado, María Martínez; Hufnagel, Christoph; Kwek, Leong Chuan; Amico, Luigi; Dumke, Rainer

    2016-12-01

    Hybrids consisting of macroscopic superconducting circuits and microscopic components, such as atoms and spins, have the potential of transmitting an arbitrary state between different quantum species, leading to the prospective of high-speed operation and long-time storage of quantum information. Here we propose a novel hybrid structure, where a neutral-atom qubit directly interfaces with a superconducting charge qubit, to implement the qubit-state transmission. The highly-excited Rydberg atom located inside the gate capacitor strongly affects the behavior of Cooper pairs in the box while the atom in the ground state hardly interferes with the superconducting device. In addition, the DC Stark shift of the atomic states significantly depends on the charge-qubit states. By means of the standard spectroscopic techniques and sweeping the gate voltage bias, we show how to transfer an arbitrary quantum state from the superconducting device to the atom and vice versa.

  10. Superconductivity in the system MoxCyGazOδ prepared by focused ion beam induced deposition

    NASA Astrophysics Data System (ADS)

    Weirich, P. M.; Schwalb, C. H.; Winhold, M.; Huth, M.

    2014-05-01

    We have prepared the new amorphous superconductor MoxCyGazOδ with a maximum critical temperature Tc of 3.8 K by the direct-write nano-patterning technique of focused (gallium) ion beam induced deposition (FIBID) using Mo(CO)6 as precursor gas. From a detailed analysis of the temperature-dependent resistivity and the upper critical field, we found clear evidence for proximity of the samples to a disorder-induced metal-insulator transition. We observed a strong dependence of Tc on the deposition parameters and identified clear correlations between Tc, the localization tendency visible in the resistance data and the sample composition. By an in-situ feedback-controlled optimization process in the FIB-induced growth, we were able to identify the beam parameters which lead to samples with the largest Tc-value and sharpest transition into the superconducting state.

  11. Superconducting state in bromium halide at high pressure

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, R.; Zemła, T. P.; Szczȩśniak, D.

    2016-08-01

    The thermodynamic properties of the superconducting state in bromium halide (HBr) compound have been analyzed in the framework of the Eliashberg formalism. In particular, for the range of the pressure (p) from 140 GPa to 200 GPa, it has been shown that the critical temperature increases significantly: TC(p) ∈ < 28.8 , 55.1 > K, whereas the Coulomb pseudopotential (μ⋆) is equal to 0.1. Together with the increase of p, the values of the thermodynamic parameters such as: the ratio of the energy gap at the temperature of zero Kelvin to the critical temperature (RΔ ≡ 2 Δ (0) /kB TC), the ratio of the specific heat jump at the critical temperature to the electronic specific heat of the normal state (RC ≡ ΔC (TC) /CN (TC)), and the ratio related to the thermodynamic critical field (RH ≡TC CN (TC) / HC2 (0)) increasingly deviate from the predictions of the BCS model: RΔ(p) ∈ < 3.79 , 4.05 >, RC(p) ∈ < 1.94 , 2.27 >, and RH(p) ∈ < 0.157 , 0.147 >. It should be noted that the increase of μ⋆ visibly lowers TC and significantly reduces the difference between the results of the Eliashberg and BCS theory.

  12. The mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds

    NASA Astrophysics Data System (ADS)

    Deguchi, Keita; Demura, Satoshi; Okazaki, Hiroyuki; Denholme, Saleem; Fujioka, Masaya; Ozaki, Toshinori; Yamaguchi, Takahide; Takeya, Hiroyuki; Takano, Yoshihiko

    2013-03-01

    We have clarified the mechanism of alcoholic beverage induced superconductivity in Fe-chalcogenide compounds. Previously we reported that the bulk superconductivity in Fe-based compounds Fe(Te, Se) and Fe(Te, S) is achieved by heating in alcoholic beverages. However, the exact mechanism of how they act to enhance the superconductivity in the compounds remains unsolved. To understand the effect of alcoholic beverage treatment, we investigated the mechanism using a technology of metabolomic analysis. We found that weak acid in alcoholic beverages has the ability to deintercalate the excess Fe, which is not in favor of superconductivity. In this presentation, we will discuss the systematic mechanism to induce superconductivity in Fe-chalcogenide compounds.

  13. Induced Superconductivity in the Three-Dimensional Topological Insulator HgTe

    NASA Astrophysics Data System (ADS)

    Maier, Luis; Oostinga, Jeroen B.; Knott, Daniel; Brüne, Christoph; Virtanen, Pauli; Tkachov, Grigory; Hankiewicz, Ewelina M.; Gould, Charles; Buhmann, Hartmut; Molenkamp, Laurens W.

    2012-11-01

    A strained and undoped HgTe layer is a three-dimensional topological insulator, in which electronic transport occurs dominantly through its surface states. In this Letter, we present transport measurements on HgTe-based Josephson junctions with Nb as a superconductor. Although the Nb-HgTe interfaces have a low transparency, we observe a strong zero-bias anomaly in the differential resistance measurements. This anomaly originates from proximity-induced superconductivity in the HgTe surface states. In the most transparent junction, we observe periodic oscillations of the differential resistance as a function of an applied magnetic field, which correspond to a Fraunhofer-like pattern. This unambiguously shows that a precursor of the Josephson effect occurs in the topological surface states of HgTe.

  14. Induced Superconductivity in the Quantum Spin Hall Edge

    NASA Astrophysics Data System (ADS)

    Ren, Hechen; Hart, Sean; Wagner, Timo; Leubner, Philipp; Muehlbauer, Mathias; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens; Yacoby, Amir

    2014-03-01

    Two-dimensional topological insulators have a gapped bulk and helical edge states, making it a quantum spin Hall insulator. Combining such edge states with superconductivity can be an excellent platform for observing and manipulating localized Majorana fermions. In the context of condensed matter, these are emergent electronic states that obey non-Abelian statistics and hence support fault-tolerant quantum computing. To realize such theoretical constructions, an essential step is to show these edge channels are capable of carrying coherent supercurrent. In our experiment, we fabricate Josephson junctions with HgTe/HgCdTe quantum wells, a two-dimensional material that becomes a quantum spin Hall insulator when the quantum well is thicker than 6.3 nm and the bulk density is depleted. In this regime, we observe supercurrents whose densities are confined to the edges of the junctions, with edge widths ranging from 180 nm to 408 nm. To verify the topological nature of these edges, we measure identical junctions with HgTe/HgCdTe quantum wells thinner than 6.3 nm and observe only uniform supercurrent density across the junctions. This research is supported by Microsoft Corporation Project Q, the NSF DMR-1206016, the DOE SCGF Program, the German Research Foundation, and EU ERC-AG program.

  15. Pressure induced Superconductivity in the Charge Density Wave Compound Tritelluride

    SciTech Connect

    Hamlin, J.J.; Zocco, D.A.; Sayles, T.A.; Maple, M.B.; Chu, J.-H.; Fisher, I.R.; /Stanford U., Geballe Lab.

    2010-02-15

    A series of high-pressure electrical resistivity measurements on single crystals of TbTe{sub 3} reveal a complex phase diagram involving the interplay of superconducting, antiferromagnetic and charge density wave order. The onset of superconductivity reaches a maximum of almost 4 K (onset) near {approx} 12.4 GPa.

  16. Alcoholic beverages induce superconductivity in FeTe1 - xSx

    NASA Astrophysics Data System (ADS)

    Deguchi, K.; Mizuguchi, Y.; Kawasaki, Y.; Ozaki, T.; Tsuda, S.; Yamaguchi, T.; Takano, Y.

    2011-05-01

    We found that hot alcoholic beverages were effective in inducing superconductivity in FeTe0.8S0.2. Heating the FeTe0.8S0.2 compound in various alcoholic beverages enhances the superconducting properties compared to a pure water-ethanol mixture as a control. Heating with red wine for 24 h leads to the largest shielding volume fraction of 62.4% and the highest zero resistivity temperature of 7.8 K. Some components present in alcoholic beverages, other than water and ethanol, have the ability to induce superconductivity in the FeTe0.8S0.2 compound.

  17. The Nature of the Superconducting State in Rutheno-Cuprates

    NASA Astrophysics Data System (ADS)

    Chu, C. W.; Xue, Y. Y.; Lorenz, B.; Meng, R. L.

    The magnetism and superconductivity (SC) of rutheno-cuprates RuSr2L-Cu2O_{8-delta} (Ru1212) and RuSr2(L,Ce)2Cu2O_{10+delta} (Ru1222) were investigated, where L = Gd or Eu. The normal state carrier concentration p, the Tc, the intragrain penetration depth λ, and the diamagnetic field-cooled magnetization were measured in various annealed rutheno-cuprate samples. The p varies with annealing only slightly (from 0.09 to 0.12 holes/CuO2), but the intragrain Tc by a factor of 2.3 (from 17 to 40 K). The 1/λ (2), on the other hand, was enhanced more than tenfold (from 0.3 to 6 μm-2). The data are in disagreement with both the universal Tc vs. p and Tc vs. 1/λ (2) proposed for bulk cuprates. These, together with the unusually large d T_{{c}}/dH ≈ 100 K/T observed in both Ru1212 and Ru1222, suggest that even the intragrain SC of rutheno-cuprates is granular. A Josephson-junction-array model was then proposed to interpret the data. The memory effect observed in Ru1222 far above the main magnetic transition temperature further suggests that the root of the granularity may be a phase separation, resulting in the mesoscopic ferromagnetic and antiferromagnetic species in these rutheno-cuprates.

  18. Ideal charge-density-wave order in the high-field state of superconducting YBCO.

    PubMed

    Jang, H; Lee, W-S; Nojiri, H; Matsuzawa, S; Yasumura, H; Nie, L; Maharaj, A V; Gerber, S; Liu, Y-J; Mehta, A; Bonn, D A; Liang, R; Hardy, W N; Burns, C A; Islam, Z; Song, S; Hastings, J; Devereaux, T P; Shen, Z-X; Kivelson, S A; Kao, C-C; Zhu, D; Lee, J-S

    2016-12-20

    The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field ([Formula: see text]) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to [Formula: see text], given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an "ideal" disorder-free cuprate.

  19. Ideal charge-density-wave order in the high-field state of superconducting YBCO

    DOE PAGES

    Jang, H.; Lee, W. -S.; Nojiri, H.; ...

    2016-12-05

    Here, the existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (Hc2) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well asmore » significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to Hc2, given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an “ideal” disorder-free cuprate.« less

  20. Ideal charge-density-wave order in the high-field state of superconducting YBCO

    SciTech Connect

    Jang, H.; Lee, W. -S.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Nie, L.; Maharaj, A. V.; Gerber, S.; Liu, Y. -J.; Mehta, A.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Burns, C. A.; Islam, Z.; Song, S.; Hastings, J.; Devereaux, T. P.; Shen, Z. -X.; Kivelson, S. A.; Kao, C. -C.; Zhu, D.; Lee, J. -S.

    2016-12-05

    Here, the existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (Hc2) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to Hc2, given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an “ideal” disorder-free cuprate.

  1. Ideal charge-density-wave order in the high-field state of superconducting YBCO

    PubMed Central

    Jang, H.; Lee, W.-S.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Nie, L.; Maharaj, A. V.; Gerber, S.; Liu, Y.-J.; Mehta, A.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Burns, C. A.; Islam, Z.; Song, S.; Hastings, J.; Devereaux, T. P.; Shen, Z.-X.; Kivelson, S. A.; Kao, C.-C.; Zhu, D.; Lee, J.-S.

    2016-01-01

    The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (Hc2) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to Hc2, given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an “ideal” disorder-free cuprate. PMID:27930313

  2. Unconventional superconductivity and interaction induced Fermi surface reconstruction in the two-dimensional Edwards model

    NASA Astrophysics Data System (ADS)

    Cho, Dai-Ning; Sykora, Steffen

    We study the possibility of unconventional superconducting pairing in the framework of a novel two-dimensional quantum transport model, where the charge carriers are strongly affected by the correlations and fluctuations of a background medium, described by bosonic degrees of freedom. Using the projective renormalization method (PRM) we find in the half-filled band case an interplay between stable superconducting solutions and a charge-density wave order parameter which determines the ground state in the limit of large bosonic energies. The superconducting pairing mainly appears on a new hole-like Fermi surface, which is formed nearby the center of the Brillouin zone due to strong renormalization of the original fermionic band. In the superconducting state, the Fermi surface splits into two disconnected parts, which are characterized by different sign of the superconducting order parameter.

  3. Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides.

    PubMed

    Ang, R; Wang, Z C; Chen, C L; Tang, J; Liu, N; Liu, Y; Lu, W J; Sun, Y P; Mori, T; Ikuhara, Y

    2015-01-27

    Interplay among various collective electronic states such as charge density wave and superconductivity is of tremendous significance in low-dimensional electron systems. However, the atomistic and physical nature of the electronic structures underlying the interplay of exotic states, which is critical to clarifying its effect on remarkable properties of the electron systems, remains elusive, limiting our understanding of the superconducting mechanism. Here, we show evidence that an ordering of selenium and sulphur atoms surrounding tantalum within star-of-David clusters can boost superconductivity in a layered chalcogenide 1T-TaS2-xSex, which undergoes a superconducting transition in the nearly commensurate charge density wave phase. Advanced electron microscopy investigations reveal that such an ordered superstructure forms only in the x area, where the superconductivity manifests, and is destructible to the occurrence of the Mott metal-insulator transition. The present findings provide a novel dimension in understanding the relationship between lattice and electronic degrees of freedom.

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

    SciTech Connect

    Opačić, M.; Lazarević, N.; Šćepanović, M.; Ryu, Hyejin; Lei, Hechang; Petrovic, C.; Popović, Z. V.

    2015-11-16

    Polarized Raman scattering spectra of superconducting KxFe2-ySe2 and nonsuperconducting K0.8Fe1.8Co0.2Se2 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 K0.8Fe1.8Co0.2Se2 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-induced 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 A1g mode energy near TC was observed in KxFe2-ySe2 , whereas it is absent in 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 critical temperature.

  5. Electrical Conductivity through a Single Atomic Step Measured with the Proximity-Induced Superconducting Pair Correlation

    NASA Astrophysics Data System (ADS)

    Kim, Howon; Lin, Shi-Zeng; Graf, Matthias J.; Miyata, Yoshinori; Nagai, Yuki; Kato, Takeo; Hasegawa, Yukio

    2016-09-01

    Local disordered nanostructures in an atomically thick metallic layer on a semiconducting substrate play significant and decisive roles in transport properties of two-dimensional (2D) conductive systems. We measured the electrical conductivity through a step of monoatomic height in a truly microscopic manner by using as a signal the superconducting pair correlation induced by the proximity effect. The transport property across a step of a one-monolayer Pb surface metallic phase, formed on a Si(111) substrate, was evaluated by inducing the pair correlation around the local defect and measuring its response, i.e., the reduced density of states at the Fermi energy using scanning tunneling microscopy. We found that the step resistance has a significant contribution to the total resistance on a nominally flat surface. Our study also revealed that steps in the 2D metallic layer terminate the propagation of the pair correlation. Superconductivity is enhanced between the first surface step and the superconductor-normal-metal interface by reflectionless tunneling when the step is located within a coherence length.

  6. State preservation by repetitive error detection in a superconducting quantum circuit

    NASA Astrophysics Data System (ADS)

    Kelly, J.; Barends, R.; Fowler, A. G.; Megrant, A.; Jeffrey, E.; White, T. C.; Sank, D.; Mutus, J. Y.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Hoi, I.-C.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Vainsencher, A.; Wenner, J.; Cleland, A. N.; Martinis, John M.

    2015-03-01

    Quantum computing becomes viable when a quantum state can be protected from environment-induced error. If quantum bits (qubits) are sufficiently reliable, errors are sparse and quantum error correction (QEC) is capable of identifying and correcting them. Adding more qubits improves the preservation of states by guaranteeing that increasingly larger clusters of errors will not cause logical failure--a key requirement for large-scale systems. Using QEC to extend the qubit lifetime remains one of the outstanding experimental challenges in quantum computing. Here we report the protection of classical states from environmental bit-flip errors and demonstrate the suppression of these errors with increasing system size. We use a linear array of nine qubits, which is a natural step towards the two-dimensional surface code QEC scheme, and track errors as they occur by repeatedly performing projective quantum non-demolition parity measurements. Relative to a single physical qubit, we reduce the failure rate in retrieving an input state by a factor of 2.7 when using five of our nine qubits and by a factor of 8.5 when using all nine qubits after eight cycles. Additionally, we tomographically verify preservation of the non-classical Greenberger-Horne-Zeilinger state. The successful suppression of environment-induced errors will motivate further research into the many challenges associated with building a large-scale superconducting quantum computer.

  7. Characterizing and reducing microfabrication-induced loss in superconducting devices, Part I: Resonators

    NASA Astrophysics Data System (ADS)

    Dunsworth, Andrew; Megrant, A.; Chen, Z.; Quintana, C.; Burkett, B.; Kelly, J.; Barends, R.; Fowler, A.; Jeffrey, E.; White, T.; Sank, D.; Mutus, J.; Campbell, B.; Chen, Y.; Chiaro, B.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Vainsencher, A.; Wenner, J.; Martinis, J. M.

    Planar and 3D superconducting qubits have previously been shown to be limited by microfabrication induced loss. Using finite element simulations, we have identified a major source of this decoherence in superconducting qubits. Furthermore, we experimentally verified this dominant loss channel using a novel resonator based approach, which we call 'Hydra' resonators. We fully characterized and then substantially reduced this loss channel using these Hydra resonators. I will report on these measurements and their implications on improving the coherence of superconducting qubits. This work is supported by Google inc.

  8. Superconducting state of Ca xMo 6S 8 at ambient pressure

    NASA Astrophysics Data System (ADS)

    Geantet, Christophe; Horyn, Roman; Padiou, Jean; Pen˜a, Octavio; Sergent, Marcel

    1988-06-01

    Experimental evidence is given for superconductivity of Ca xMo 6S 8 at ambient pressure. Crystal structure, susceptibility, magnetization and resistivity measurements on single crystals for x≦ 1.0 are reported. Calcium deficiencies stabilize the rhombohedral structure and inhibit the structural transition which ordinarily suppresses the superconducting state indivalent M(2+)Mo 6S 8 Chevrel phases; M(2+) =Eu, Ba, Ca, Sr.

  9. Superconductivity in topological insulator Sb2Te3 induced by pressure.

    PubMed

    Zhu, J; Zhang, J L; Kong, P P; Zhang, S J; Yu, X H; Zhu, J L; Liu, Q Q; Li, X; Yu, R C; Ahuja, R; Yang, W G; Shen, G Y; Mao, H K; Weng, H M; Dai, X; Fang, Z; Zhao, Y S; Jin, C Q

    2013-01-01

    Topological superconductivity is one of most fascinating properties of topological quantum matters that was theoretically proposed and can support Majorana Fermions at the edge state. Superconductivity was previously realized in a Cu-intercalated Bi2Se3 topological compound or a Bi2Te3 topological compound at high pressure. Here we report the discovery of superconductivity in the topological compound Sb2Te3 when pressure was applied. The crystal structure analysis results reveal that superconductivity at a low-pressure range occurs at the ambient phase. The Hall coefficient measurements indicate the change of p-type carriers at a low-pressure range within the ambient phase, into n-type at higher pressures, showing intimate relation to superconducting transition temperature. The first principle calculations based on experimental measurements of the crystal lattice show that Sb2Te3 retains its Dirac surface states within the low-pressure ambient phase where superconductivity was observed, which indicates a strong relationship between superconductivity and topology nature.

  10. Features of inhomogeneous current state in wide superconducting films

    SciTech Connect

    D'yachenko, A.I.; Tarenkov, V.Y.; Stupakov, V.V.

    1982-04-01

    A dc superconducting-transformer circuit is used to investigate the features of the current-voltage characteristics (CVC) of thin aluminum films of width W>>lambda/sub perpendicular/. It is shown that in contrast to narrow channels, where phase-slippage centers are realized, the steplike structure of the CVC results in this case from the inhomogeneous entry of the vortex strings.

  11. Signatures of Induced Superconductivity in NbTi Contacted InAs Quantum Wells

    NASA Astrophysics Data System (ADS)

    McFadden, Anthony; Shabani, Javad; Shojaei, Borzoyeh; Lee, Joon Sue; Palmstrøm, Chris

    We have studied electrical transport through InAs quantum wells grown by MBE with unannealed superconducting NbTi contacts deposited ex-situ and patterned by optical photolithography. Characterization of the InAs 2DEG's without superconducting contacts yields typical mobilities greater than 100,000 cm2/Vs at a density of 4e11 cm-2. NbTi-InAs-NbTi (SNS) and NbTi-InAs (SN) devices with dimensions greater than 1 µm are fabricated using optical lithography. Although the dimensions of the fabricated SNS devices are too large to observe a supercurrent, signatures of superconductivity induced in the InAs are present. We observe two superconducting critical temperatures: one of the NbTi leads (Tc~8K), and a second (Tc <4.5K) attributed to superconductivity induced in the InAs channel. dI/dV vs V spectroscopy on SNS junctions below the second critical temperature shows a conductance maximum at zero applied voltage while conductance minima appear at finite bias voltage which is attributed to the presence of an induced superconducting gap in the InAs quantum well. This work has been supported by Microsoft research.

  12. Magnetic field-induced superconductivity in the ferromagnet URhGe.

    PubMed

    Lévy, F; Sheikin, I; Grenier, B; Huxley, A D

    2005-08-26

    In several metals, including URhGe, superconductivity has recently been observed to appear and coexist with ferromagnetism at temperatures well below that at which the ferromagnetic state forms. However, the material characteristics leading to such a state of coexistence have not yet been fully elucidated. We report that in URhGe there is a magnetic transition where the direction of the spin axis changes when a magnetic field of 12 tesla is applied parallel to the crystal b axis. We also report that a second pocket of superconductivity occurs at low temperature for a range of fields enveloping this magnetic transition, well above the field of 2 tesla at which superconductivity is first destroyed. Our findings strongly suggest that excitations in which the spins rotate stimulate superconductivity in the neighborhood of a quantum phase transition under high magnetic field.

  13. Volcanic materials superconductivity in desert areas of the states of Sonora and Baja California

    NASA Astrophysics Data System (ADS)

    Holguín, Aldo

    2017-01-01

    Research was conducted to find materials in their natural state at room temperature and exhibit the effects of superconductivity in the volcanic region of deserts Altar in Sonora and Baja California Norte. 100 were collected at random samples of materials from different parts of the region and underwent tests to determine their electromagnetic parameters of electrical resistance, magnetism, temperature and conductivity. Only it has been found that the effects of superconductivity in them is only present at very low temperatures corroborating what has been done in other investigations, however no indication that there is a material or combination of materials that can produce the effects of superconductivity other temperatures so it is suggested to continue the search for such materials and / or develop a technique at room temperature to allow mimic the behavior of atoms when superconductivity occurs at.

  14. Pressure induced superconductivity in CaFe2As2.

    PubMed

    Torikachvili, Milton S; Bud'ko, Sergey L; Ni, Ni; Canfield, Paul C

    2008-08-01

    CaFe2As2 has been found to be exceptionally sensitive to the application of hydrostatic pressure and can be tuned to reveal all the salient features associated with FeAs superconductivity without introducing any disorder. The ambient pressure, 170 K, structural/magnetic, first-order phase transition is suppressed to 128 K by 3.5 kbar. At 5.5 kbar a new transition is detected at 104 K, increasing to above 300 K by 19 kbar. A low temperature, superconducting dome (T(c) approximately 12 K) is centered around 5 kbar, extending down to 2.3 kbar and up to 8.6 kbar. This superconducting phase appears to exist when the low pressure transition is suppressed sufficiently, but before the high pressure transition has reduced the resistivity too dramatically.

  15. Pressure Induced Superconductivity in CaFe2As2

    SciTech Connect

    Milton S. Torikachvili; Sergey L. Bud'ko; Ni Ni; Paul Canfield

    2008-08-01

    CaFe{sub 2}As{sub 2} has been found to be exceptionally sensitive to the application of hydrostatic pressure and can be tuned to reveal all the salient features associated with FeAs superconductivity without introducing any disorder. The ambient pressure, 170 K, structural/magnetic, first-order phase transition is suppressed to 128 K by 3.5 kbar. At 5.5 kbar a new transition is detected at 104 K, increasing to above 300 K by 19 kbar. A low temperature, superconducting dome (T{sub c} {approx} 12 K) is centered around 5 kbar, extending down to 2.3 kbar and up to 8.6 kbar. This superconducting phase appears to exist when the low pressure transition is suppressed sufficiently, but before the high pressure transition has reduced the resistivity too dramatically.

  16. Controllable Quantum States Mesoscopic Superconductivity and Spintronics (MS+S2006)

    NASA Astrophysics Data System (ADS)

    Takayanagi, Hideaki; Nitta, Junsaku; Nakano, Hayato

    2008-10-01

    Mesoscopic effects in superconductors. Tunneling measurements of charge imbalance of non-equilibrium superconductors / R. Yagi. Influence of magnetic impurities on Josephson current in SNS junctions / T. Yokoyama. Nonlinear response and observable signatures of equilibrium entanglement / A. M. Zagoskin. Stimulated Raman adiabatic passage with a Cooper pair box / Giuseppe Falci. Crossed Andreev reflection-induced giant negative magnetoresistance / Francesco Giazotto -- Quantum modulation of superconducting junctions. Adiabatic pumping through a Josephson weak link / Fabio Taddei. Squeezing of superconducting qubits / Kazutomu Shiokawa. Detection of Berrys phases in flux qubits with coherent pulses / D. N. Zheng. Probing entanglement in the system of coupled Josephson qubits / A. S. Kiyko. Josephson junction with tunable damping using quasi-particle injection / Ryuta Yagi. Macroscopic quantum coherence in rf-SQUIDs / Alexey V. Ustinov. Bloch oscillations in a Josephson circuit / D. Esteve. Manipulation of magnetization in nonequilibrium superconducting nanostructures / F. Giazotto -- Superconducting qubits. Decoherence and Rabi oscillations in a qubit coupled to a quantum two-level system / Sahel Ashhab. Phase-coupled flux qubits: CNOT operation, controllable coupling and entanglement / Mun Dae Kim. Characteristics of a switchable superconducting flux transformer with a DC-SQUID / Yoshihiro Shimazu. Characterization of adiabatic noise in charge-based coherent nanodevices / E. Paladino -- Unconventional superconductors. Threshold temperatures of zero-bias conductance peak and zero-bias conductance dip in diffusive normal metal/superconductor junctions / Iduru Shigeta. Tunneling conductance in 2DEG/S junctions in the presence of Rashba spin-orbit coupling / T. Yokoyama. Theory of charge transport in diffusive ferromagnet/p-wave superconductor junctions / T. Yokoyama. Theory of enhanced proximity effect by the exchange field in FS bilayers / T. Yokoyama. Theory of

  17. Randomly distributed spin induced suppression of superconducting properties in Gd-123

    NASA Astrophysics Data System (ADS)

    Biswas, B.; Haldar, S.; Mukherjee, I.; Kumar Ghosh, Ajay

    2017-02-01

    Suppression of superconducting property in presence of inhomogeneous spin distribution in GdBa2Cu3-xCoxO6.9 has been studied. A superconducting sample without Co exhibits superconducting transition at 56.1 K. The current-voltage (I-V) characteristics exhibit nonlinear to linear transformation above a certain temperature. Two other samples (i) with Co and (ii) without Cu are found to be nonsuperconducting with very high resistive in nature at lower temperature. Localization length decreases with the increase in Co substitution. Suppression of the superconducting transition has been attributed to the change in the magnetic fluctuations induced by the randomness in spin substitution. An exponent has been extracted to understand the current-voltage behaviour. Kosterlitz-Thouless (KT) transition may be affected strongly by the shifting of magnetic fluctuations.

  18. Doping-induced superconductivity of ZrB2 and HfB2

    NASA Astrophysics Data System (ADS)

    Barbero, N.; Shiroka, T.; Delley, B.; Grant, T.; Machado, A. Â. J. Â. S.; Fisk, Z.; Ott, H.-R.; Mesot, J.

    2017-03-01

    Unlike the widely studied s -type two-gap superconductor MgB2, the chemically similar compounds ZrB2 and HfB2 do not superconduct above 1 K. Yet it has been shown that small amounts of self or extrinsic doping (in particular with vanadium), can induce superconductivity in these materials. Based on results of different macroscopic and microscopic measurements, including magnetometry, nuclear magnetic resonance (NMR), resistivity, and muon-spin rotation (μ+SR ), we present a comparative study of Zr0.96V0.04B2 and Hf0.97V0.03B2 . Their key magnetic and superconducting features are determined and the results are considered within the theoretical framework of multiband superconductivity proposed for MgB2. Detailed Fermi surface (FS) and electronic structure calculations reveal the difference between MgB2 and transition-metal diborides.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

    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.

  20. 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

  1. Ideal charge-density-wave order in the high-field state of superconducting YBCO

    NASA Astrophysics Data System (ADS)

    Jang, H.; Lee, W.-S.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Nie, L.; Maharaj, A. V.; Gerber, S.; Liu, Y.-J.; Mehta, A.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Burns, C. A.; Islam, Z.; Song, S.; Hastings, J.; Devereaux, T. P.; Shen, Z.-X.; Kivelson, S. A.; Kao, C.-C.; Zhu, D.; Lee, J.-S.

    2016-12-01

    The existence of charge-density-wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the CDW ground state has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to only a dozen unit cells or less. Here we explore the field-induced 3D CDW correlations in extremely pure detwinned crystals of YBa2Cu3O2 (YBCO) ortho-II and ortho-VIII at magnetic fields in excess of the resistive upper critical field (Hc2Hc2) where superconductivity is heavily suppressed. We observe that the 3D CDW is unidirectional and possesses a long in-plane correlation length as well as significant correlations between neighboring CuO2 planes. It is significant that we observe only a single sharply defined transition at a critical field proportional to Hc2Hc2, given that the field range used in this investigation overlaps with other high-field experiments including quantum oscillation measurements. The correlation volume is at least two to three orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground state of an “ideal” disorder-free cuprate.

  2. Skyrmions in a Density-Wave State: A Mechanism for Chiral Superconductivity

    NASA Astrophysics Data System (ADS)

    Chakravarty, Sudip; Hsu, Chen-Hsuan

    Broken symmetry states characterizing density waves of higher angular momentum in correlated electronic systems are intriguing objects. In the scheme of characterization by angular momentum, conventional charge and spin density waves correspond to zero angular momentum. Here we explore a class of exotic density wave states that have topological properties observed in recently discovered topological insulators. These rich topological density wave states deserve closer attention in not only high temperature superconductors but in other correlated electron states, as in heavy fermions, of which an explicit example will be discussed. The state discussed has non-trivial charge 2e skyrmionic spin texture. These skyrmions can condense into a charged superfluid. Alternately, they can fractionalize into merons and anti-merons. The fractionalized particles that are confined in skyrmions in the insulating phase, can emerge at a deconfined quantum critical point, which separates the insulating and the superconducting phases. These fractional particles form a two-component spin-singlet chiral (dx2-y2 ± idxy) wave superconducting state that breaks time reversal symmetry. Possible connections of this exotic order to the superconducting state in the heavy-fermion material URu2Si2 are suggested. The direct evidence of such a chiral superconducting state is polar Kerr effect that was observed recently.

  3. Microtraps for neutral atoms using superconducting structures in the critical state

    SciTech Connect

    Emmert, A.; Brune, M.; Raimond, J.-M.; Nogues, G.; Lupascu, A.; Haroche, S.

    2009-12-15

    Recently demonstrated superconducting atom chips provide a platform for trapping atoms and coupling them to solid-state quantum systems. Controlling these devices requires a full understanding of the supercurrent distribution in the trapping structures. For type-II superconductors, this distribution is hysteretic in the critical state due to the partial penetration of the magnetic field in the thin superconducting film through pinned vortices. We report here an experimental observation of this memory effect. Our results are in good agreement with the predictions of the Bean model of the critical state without adjustable parameters. The memory effect allows to write and store permanent currents in micron-sized superconducting structures and paves the way toward engineered trapping potentials.

  4. Evidence for defect-induced superconductivity up to 49 K in (C a1 -xRx) F e2A s2

    NASA Astrophysics Data System (ADS)

    Deng, L. Z.; Lv, B.; Zhao, K.; Wei, F. Y.; Xue, Y. Y.; Wu, Z.; Chu, C. W.

    2016-02-01

    To explore the origin of the unusual nonbulk superconductivity with a Tc up to 49 K reported in the rare-earth-doped CaF e2A s2 , the chemical composition, magnetization, specific heat, resistivity, and annealing effect are systematically investigated on nominal (C a1 -xRx) F e2A s2 single crystals with different x and R =La , Ce, Pr, and Nd. All display a doping-independent Tc once superconductivity is induced, a doping-dependent low field superconducting volume fraction f , and a large magnetic anisotropy η in the superconducting state, suggesting a rather inhomogeneous superconducting state in an otherwise microscale homogenous superconductor. The wavelength dispersive spectroscopy and specific heat show the presence of defects that are closely related to f , regardless of the R involved. The magnetism further reveals that the defects are mainly superparamagnetic clusters for R =Ce , Pr, and Nd with strong intercluster interactions, implying that defects are locally self-organized. Annealing at 500 °C, without varying the doping level x , suppresses f profoundly but not the Tc. The above observations provide evidence for the crucial role of defects in the occurrence of the unusually high Tc˜49 K in (C a1 -xRx) F e2A s2 and are consistent with the interface-enhanced superconductivity recently proposed.

  5. Evolution of spin excitations into the superconducting state in FeTe1-xSex

    NASA Astrophysics Data System (ADS)

    Lumsden, M. D.; Christianson, A. D.; Goremychkin, E. A.; Nagler, S. E.; Mook, H. A.; Stone, M. B.; Abernathy, D. L.; Guidi, T.; MacDougall, G. J.; de La Cruz, C.; Sefat, A. S.; McGuire, M. A.; Sales, B. C.; Mandrus, D.

    2010-03-01

    The origin of the superconducting state in the recently discovered Fe-based materials is the subject of intense scrutiny. Neutron scattering and NMR (ref. 8) measurements have already demonstrated a strong correlation between magnetism and superconductivity. A central unanswered question concerns the nature of the normal-state spin fluctuations that may be responsible for the pairing. Here we present inelastic neutron scattering measurements from large single crystals of superconducting and non-superconducting Fe1+yTe1-xSex. These measurements indicate a spin fluctuation spectrum dominated by two-dimensional incommensurate excitations extending to energies greater than 250meV. Most importantly, the spin excitations in Fe1+yTe1-xSex have four-fold symmetry about the (1, 0) wavevector (square-lattice (π,π) point). Moreover, the excitations are described by the identical wavevector and can be characterized by the same model as the normal-state spin excitations in the high-TC cuprates. These results demonstrate commonality between the magnetism in these classes of materials, which perhaps extends to a common origin for superconductivity.

  6. Scanning tunneling spectroscopy of the vortex state in NbSe 2 using a superconducting tip

    NASA Astrophysics Data System (ADS)

    Rodrigo, J. G.; Crespo, V.; Vieira, S.

    2008-04-01

    The vortex electronic structure in the multiband superconductor NbSe2 is studied by means of scanning tunneling spectroscopy (STS) using a superconducting tip. The use of a superconducting tip (Pb) as a probe provides an enhancement of the different features related to the DOS of NbSe2 in the tunneling conductance curves. This use allows the observation of rich patterns of electronic states in the conductance images around the vortex cores in a wide range of temperature, as well as the simultaneous acquisition of Josephson current images in the vortex state.

  7. Measuring and Suppressing Quantum State Leakage in a Superconducting Qubit

    NASA Astrophysics Data System (ADS)

    Chen, Zijun; Kelly, Julian; Quintana, Chris; Barends, R.; Campbell, B.; Chen, Yu; Chiaro, B.; Dunsworth, A.; Fowler, A. G.; Lucero, E.; Jeffrey, E.; Megrant, A.; Mutus, J.; Neeley, M.; Neill, C.; O'Malley, P. J. J.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Korotkov, A. N.; Martinis, John M.

    2016-01-01

    Leakage errors occur when a quantum system leaves the two-level qubit subspace. Reducing these errors is critically important for quantum error correction to be viable. To quantify leakage errors, we use randomized benchmarking in conjunction with measurement of the leakage population. We characterize single qubit gates in a superconducting qubit, and by refining our use of derivative reduction by adiabatic gate pulse shaping along with detuning of the pulses, we obtain gate errors consistently below 1 0-3 and leakage rates at the 1 0-5 level. With the control optimized, we find that a significant portion of the remaining leakage is due to incoherent heating of the qubit.

  8. Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal

    PubMed Central

    Nair, Sunil; Stockert, O.; Witte, U.; Nicklas, M.; Schedler, R.; Kiefer, K.; Thompson, J. D.; Bianchi, A. D.; Fisk, Z.; Wirth, S.; Steglich, F.

    2010-01-01

    The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity. PMID:20457945

  9. Magnetism and superconductivity driven by identical 4f states in a heavy-fermion metal

    SciTech Connect

    Thompson, Joe E; Nair, S; Stockert, O; Witte, U; Nicklas, M; Schedler, R; Bianchi, A; Fisk, Z; Wirth, S; Steglich, K

    2009-01-01

    The apparently inimical relationship between magnetism and superconductivity has come under increasing scrutiny in a wide range of material classes, where the free energy landscape conspires to bring them in close proximity to each other. Particularly enigmatic is the case when these phases microscopically interpenetrate, though the manner in which this can be accomplished remains to be fully comprehended. Here, we present combined measurements of elastic neutron scattering, magnetotransport, and heat capacity on a prototypical heavy fermion system, in which antiferromagnetism and superconductivity are observed. Monitoring the response of these states to the presence of the other, as well as to external thermal and magnetic perturbations, points to the possibility that they emerge from different parts of the Fermi surface. Therefore, a single 4f state could be both localized and itinerant, thus accounting for the coexistence of magnetism and superconductivity.

  10. Superconductivity in molecular crystals induced by charge injection.

    PubMed

    Schön, J H; Kloc, C; Batlogg, B

    2000-08-17

    Progress in the field of superconductivity is often linked to the discovery of new classes of materials, with the layered copper oxides being a particularly impressive example. The superconductors known today include a wide spectrum of materials, ranging in complexity from simple elemental metals, to alloys and binary compounds of metals, to multi-component compounds of metals and chalcogens or metalloids, doped fullerenes and organic charge-transfer salts. Here we present a new class of superconductors: insulating organic molecular crystals that are made metallic through charge injection. The first examples are pentacene, tetracene and anthracene, the last having the highest transition temperature, at 4 K. We anticipate that many other organic molecular crystals can also be made superconducting by this method, which will lead to surprising findings in the vast composition space of molecular crystals.

  11. Quench of superconducting magnet induced by mechanical disturbance using impact hammer

    SciTech Connect

    Ninomiya, A.; Inada, T.; Akiba, K.; Kanda, Y.; Uriu, Y.; Ishigohka, T.

    1996-07-01

    In an epoxy-impregnated superconducting magnet, triggers of quench are considered to be conductor motion or epoxy cracking which succeed the temperature rise of the conductor induced by friction between conductor and epoxy or conductor and conductor. A more direct method which makes a quench would be hitting the magnet with mechanical hammer. To the authors` knowledge, there are very few papers which treat this type of quench. So they have carried out a quench experiment triggered by mechanical impact induced by dropping a weight. They have investigated the relation between magnitude of the mechanical disturbance and the behavior of the superconducting magnet. They have also investigated the relation between the impact energy and the structural change of superconducting magnet using an ultrasonic transfer function which they have already proposed as a quench detection method.

  12. Local geometric phase and quantum-state tomography for a superconducting qubit threaded by a magnetic flux

    NASA Astrophysics Data System (ADS)

    Kang, Kicheon

    2014-02-01

    We investigate the local geometric phase induced by Faraday's law of induction in a superconducting charge qubit threaded by an Aharonov-Bohm flux. A quantum-state reconstruction scheme, which is based on measurement of three complementary quantities, that is, the extra charge and two local currents, is introduced. We find that, while the variation of the local phase with magnetic field is determined by Faraday's law, incorporation of the time-reversal symmetry enables complete determination of the local phase. This procedure clearly demonstrates that the local geometric phase is a physical quantity (aside from a global phase factor), in contrast to the standard description of the Aharonov-Bohm effect.

  13. Skyrmion-induced bound states in a p -wave superconductor

    NASA Astrophysics Data System (ADS)

    Pöyhönen, Kim; Westström, Alex; Pershoguba, Sergey S.; Ojanen, Teemu; Balatsky, Alexander V.

    2016-12-01

    In s -wave systems, it has been theoretically shown that a ferromagnetic film hosting a skyrmion can induce a bound state embedded in the opposite-spin continuum. In this work, we consider a case of skyrmion-induced state in a p -wave superconductor. We find that the skyrmion induces a bound state that generally resides within the spectral gap and is isolated from all other states, in contrast to the case of conventional superconductors. To this end, we derive an approximate expression for the T matrix, through which we calculate the spin-polarized local density of states which is observable in scanning tunneling microscopy measurements. We find the unique spectroscopic features of the skyrmion-induced bound state and discuss how our predictions could be employed as experimental probes for p -wave superconducting states.

  14. Superconductivity and metallic behavior in Pb{sub x}C{sub y}O{sub δ} structures prepared by focused electron beam induced deposition

    SciTech Connect

    Winhold, M. Weirich, P. M.; Schwalb, C. H.; Huth, M.

    2014-10-20

    Focused electron beam induced deposition as a direct-write approach possesses great potential to meet the demands for superconducting nanostructure fabrication especially regarding its 3D patterning capabilities combined with the high resolution in the nanometer regime. So far, however, it was not possible to fabricate superconducting structures with this technique. In this work, we present a lead-based superconductor prepared by focused electron beam induced deposition by dissociation of the precursor tetraethyllead. The as-grown structures exhibit metallic behavior and a minimum resistivity in the normal state of ρ = 16 μΩcm at T = 9 K followed by a superconducting transition at T{sub c} = 7.2 K.

  15. Topological Quantum Phase Transition and Superconductivity Induced by Pressure in the Bismuth Tellurohalide BiTeI.

    PubMed

    Qi, Yanpeng; Shi, Wujun; Naumov, Pavel G; Kumar, Nitesh; Sankar, Raman; Schnelle, Walter; Shekhar, Chandra; Chou, Fang-Cheng; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A

    2017-03-06

    A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor bismuth tellurohalide BiTeI with giant Rashba spin splitting. In this work, evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted topological quantum phase transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr, while resistivity at higher temperatures still exhibits semiconducting behavior. Theoretical calculations suggest that superconductivity may develop from the multivalley semiconductor phase. The superconducting transition temperature, Tc , increases with applied pressure and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa for BiTeBr), followed by a slow decrease. The results demonstrate that BiTeX (X = I, Br) compounds with nontrivial topology of electronic states display new ground states upon compression.

  16. Current-induced SQUID behavior of superconducting Nb nano-rings.

    PubMed

    Sharon, Omri J; Shaulov, Avner; Berger, Jorge; Sharoni, Amos; Yeshurun, Yosef

    2016-06-20

    The critical temperature in a superconducting ring changes periodically with the magnetic flux threading it, giving rise to the well-known Little-Parks magnetoresistance oscillations. Periodic changes of the critical current in a superconducting quantum interference device (SQUID), consisting of two Josephson junctions in a ring, lead to a different type of magnetoresistance oscillations utilized in detecting extremely small changes in magnetic fields. Here we demonstrate current-induced switching between Little-Parks and SQUID magnetoresistance oscillations in a superconducting nano-ring without Josephson junctions. Our measurements in Nb nano-rings show that as the bias current increases, the parabolic Little-Parks magnetoresistance oscillations become sinusoidal and eventually transform into oscillations typical of a SQUID. We associate this phenomenon with the flux-induced non-uniformity of the order parameter along a superconducting nano-ring, arising from the superconducting leads ('arms') attached to it. Current enhanced phase slip rates at the points with minimal order parameter create effective Josephson junctions in the ring, switching it into a SQUID.

  17. Current-induced SQUID behavior of superconducting Nb nano-rings

    PubMed Central

    Sharon, Omri J.; Shaulov, Avner; Berger, Jorge; Sharoni, Amos; Yeshurun, Yosef

    2016-01-01

    The critical temperature in a superconducting ring changes periodically with the magnetic flux threading it, giving rise to the well-known Little-Parks magnetoresistance oscillations. Periodic changes of the critical current in a superconducting quantum interference device (SQUID), consisting of two Josephson junctions in a ring, lead to a different type of magnetoresistance oscillations utilized in detecting extremely small changes in magnetic fields. Here we demonstrate current-induced switching between Little-Parks and SQUID magnetoresistance oscillations in a superconducting nano-ring without Josephson junctions. Our measurements in Nb nano-rings show that as the bias current increases, the parabolic Little-Parks magnetoresistance oscillations become sinusoidal and eventually transform into oscillations typical of a SQUID. We associate this phenomenon with the flux-induced non-uniformity of the order parameter along a superconducting nano-ring, arising from the superconducting leads (‘arms’) attached to it. Current enhanced phase slip rates at the points with minimal order parameter create effective Josephson junctions in the ring, switching it into a SQUID. PMID:27321733

  18. Current-induced SQUID behavior of superconducting Nb nano-rings

    NASA Astrophysics Data System (ADS)

    Sharon, Omri J.; Shaulov, Avner; Berger, Jorge; Sharoni, Amos; Yeshurun, Yosef

    2016-06-01

    The critical temperature in a superconducting ring changes periodically with the magnetic flux threading it, giving rise to the well-known Little-Parks magnetoresistance oscillations. Periodic changes of the critical current in a superconducting quantum interference device (SQUID), consisting of two Josephson junctions in a ring, lead to a different type of magnetoresistance oscillations utilized in detecting extremely small changes in magnetic fields. Here we demonstrate current-induced switching between Little-Parks and SQUID magnetoresistance oscillations in a superconducting nano-ring without Josephson junctions. Our measurements in Nb nano-rings show that as the bias current increases, the parabolic Little-Parks magnetoresistance oscillations become sinusoidal and eventually transform into oscillations typical of a SQUID. We associate this phenomenon with the flux-induced non-uniformity of the order parameter along a superconducting nano-ring, arising from the superconducting leads (‘arms’) attached to it. Current enhanced phase slip rates at the points with minimal order parameter create effective Josephson junctions in the ring, switching it into a SQUID.

  19. Oxidation induced superconductivity and Mo/Cu charge equilibrium in Mo0.3Cu0.7Sr2ErCu2Oy

    NASA Astrophysics Data System (ADS)

    Marik, Sourav; Santos-Garcia, A. J. D.; Labrugere, Christine; Morán, Emilio; Toulemonde, O.; Alario-Franco, M. A.

    2015-04-01

    A detailed study of the structure-composition-properties correlation is reported for the as-prepared (AP) and two oxygenated (oxygenation carried out at ambient pressure and under high pressure) Mo0.3Cu0.7Sr2ErCu2Oy samples. Their crystal structures were characterized by combining the x-ray/neutron powder diffraction (NPD) and electron diffraction techniques. All the samples show tetragonal symmetry, crystallizing in the P4/mmm space group. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2ErCu2Oy system associated with an oxidation reaction leading from a non-superconducting to a superconducting state has also been investigated by means of x-ray photoelectron spectroscopy (XPS). XPS measurements show the predominance of the MoV oxidation state over the MoVI one in the AP sample; annealing under flowing oxygen enhances both the MoVI and CuII amounts. The AP sample shows the existence of ferromagnetic clusters originated from the short-range magnetic correlations of the paramagnetic MoV cations. On the other hand, all the oxygenated samples are not magnetic but superconducting. The high-pressure oxygenated sample shows the highest superconducting transition temperature of TC = 84 K. A partial oxygen ordering in the (Mo/Cu)O1+δ chain and a decrease in the charge transfer energy after oxygenation induces superconductivity in the oxygenated samples.

  20. Type-1.5 superconducting state from an intrinsic proximity effect in two-band superconductors.

    PubMed

    Babaev, Egor; Carlström, Johan; Speight, Martin

    2010-08-06

    We show that in multiband superconductors, even an extremely small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vortices by producing long-range intervortex attraction. This type of vortex interaction results in an unusual response to low magnetic fields leading to phase separation into domains of two-component Meissner states and vortex droplets.

  1. Supercooling of the normal state of a type I superconductor in the presence of surface superconductivity

    SciTech Connect

    Berezin, V. A. Khlyustikov, I. N.

    2009-05-15

    Supercooling of the normal state of lead single crystals is studied experimentally in the range of surface superconductivity. The supercooling field is plotted on the phase diagram of the superconductor. The experimental data are compared with the results of theoretical calculations.

  2. Induced Superconductivity In Bi2 Se3 Nanostructures By Anneal Doping Of Palladium

    NASA Astrophysics Data System (ADS)

    Mlack, Jerome T.; Rahman, Atikur; Drichko, Natalia; Markovic, Nina

    Utilizing thermal annealing at temperatures in excess of 100 Celsius we induce superconductivity in Bi2Se3 by palladium doping. Changes in the material structure are analyzed using a combination of AFM, optical microscopy and Raman spectroscopy. The absorption of Pd results in superconductivity in the material with a transition temperature below 1K. The differential conductance as a function of temperature and magnetic field reveals multiple transitions in the material at several applied currents. This work was supported under the National Science Foundation Grant Nos. DGE-1232825 (J.T.M.) and DMR-1106167.

  3. Characterization and reduction of microfabrication-induced decoherence in superconducting quantum circuits

    NASA Astrophysics Data System (ADS)

    Quintana, C. M.; Megrant, A.; Chen, Z.; Dunsworth, A.; Chiaro, B.; Barends, R.; Campbell, B.; Chen, Yu; Hoi, I.-C.; Jeffrey, E.; Kelly, J.; Mutus, J. Y.; O'Malley, P. J. J.; Neill, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Cleland, A. N.; Martinis, John M.

    2014-08-01

    Many superconducting qubits are highly sensitive to dielectric loss, making the fabrication of coherent quantum circuits challenging. To elucidate this issue, we characterize the interfaces and surfaces of superconducting coplanar waveguide resonators and study the associated microwave loss. We show that contamination induced by traditional qubit lift-off processing is particularly detrimental to quality factors without proper substrate cleaning, while roughness plays at most a small role. Aggressive surface treatment is shown to damage the crystalline substrate and degrade resonator quality. We also introduce methods to characterize and remove ultra-thin resist residue, providing a way to quantify and minimize remnant sources of loss on device surfaces.

  4. Superconducting quantum criticality of topological surface states at three loops

    NASA Astrophysics Data System (ADS)

    Zerf, Nikolai; Lin, Chien-Hung; Maciejko, Joseph

    2016-11-01

    The semimetal-superconductor quantum phase transition on the two-dimensional (2D) surface of a 3D topological insulator is conjectured to exhibit an emergent N =2 supersymmetry, based on a one-loop renormalization group (RG) analysis in the ɛ expansion. We provide additional support for this conjecture by performing a three-loop RG analysis and showing that the supersymmetric fixed point found at this order survives the extrapolation to 2D. We compute critical exponents to order ɛ3, obtaining the more accurate value ν ≈0.985 for the correlation length exponent and confirming that the fermion and boson anomalous dimensions remain unchanged beyond one loop, as expected from non-renormalization theorems in supersymmetric theories. We further couple the system to a dynamical U(1) gauge field, and argue that the transition becomes fluctuation-induced first order in an appropriate type-I regime. We discuss implications of this result for quantum phase transitions between certain symmetry-preserving correlated surface states of 3D topological insulators.

  5. Normal-state charge dynamics in doped BaFe2As2: Roles of doping and necessary ingredients for superconductivity

    PubMed Central

    Nakajima, M.; Ishida, S.; Tanaka, T.; Kihou, K.; Tomioka, Y.; Saito, T.; Lee, C. H.; Fukazawa, H.; Kohori, Y.; Kakeshita, T.; Iyo, A.; Ito, T.; Eisaki, H.; Uchida, S.

    2014-01-01

    In high-transition-temperature superconducting cuprates and iron arsenides, chemical doping plays an important role in inducing superconductivity. Whereas in the cuprate case, the dominant role of doping is to inject charge carriers, the role for the iron arsenides is complex owing to carrier multiplicity and the diversity of doping. Here, we present a comparative study of the in-plane resistivity and the optical spectrum of doped BaFe2As2, which allows for separation of coherent (itinerant) and incoherent (highly dissipative) charge dynamics. The coherence of the system is controlled by doping, and the doping evolution of the charge dynamics exhibits a distinct difference between electron and hole doping. It is found in common with any type of doping that superconductivity with high transition temperature emerges when the normal-state charge dynamics maintains incoherence and when the resistivity associated with the coherent channel exhibits dominant temperature-linear dependence. PMID:25077444

  6. Possible Superconductivity Induced by Strong Spin-Orbit Coupling in Carrier Doped Iridium Oxides Insulators

    NASA Astrophysics Data System (ADS)

    Nishiguchi, Kazutaka; Shirakawa, Tomonori; Watanabe, Hiroshi; Arita, Ryotaro; Yunoki, Seiji

    2014-03-01

    5 d transition metal oxide Sr2IrO4 and its relevant Iridium oxides have attracted much interest because of exotic properties arising from highly entangled spin and orbital degrees of freedom due to strong spin-orbit coupling (SOC). Sr2IrO4 crystalizes in the layered perovskite structure, similar to cuprates. Five 5 d electrons in Ir occupy its t2 g orbitals which are split by strong SOC, locally inducing an effective total angular momentum Jeff = 1 / 2 , analogous to a S = 1 / 2 state in cuprates. Because of the similarities to cuprates, the possibility of superconductivity (SC) in Iridium oxides has been expected theoretically once mobile carriers are introduced into the Jeff = 1 / 2 antiferromagnetic insulator. To study theoretically possible SC in carrier doped Sr2IrO4, we investigate a three-orbital Hubbard model with SOC. By solving the Eliashberg equation in the random phase approximation, we find that Jeff = 1 / 2 antiferromagnetic fluctuations favor dx2 -y2-wave SC with a mixture of singlet and triplet Cooper pairings. We will also discuss the particle-hole asymmetry of the SC induced by electron and hole doping.

  7. Coherent population transfer between uncoupled or weakly coupled states in ladder-type superconducting qutrits

    PubMed Central

    Xu, H. K.; Song, C.; Liu, W. Y.; Xue, G. M.; Su, F. F.; Deng, H.; Tian, Ye; Zheng, D. N.; Han, Siyuan; Zhong, Y. P.; Wang, H.; Liu, Yu-xi; Zhao, S. P.

    2016-01-01

    Stimulated Raman adiabatic passage offers significant advantages for coherent population transfer between uncoupled or weakly coupled states and has the potential of realizing efficient quantum gate, qubit entanglement and quantum information transfer. Here we report on the realization of the process in the superconducting Xmon and phase qutrits—two ladder-type three-level systems in which the ground state population is coherently transferred to the second excited state via the dark state subspace. We demonstrate that the population transfer efficiency is no less than 96% and 67% for the two devices, which agree well with the numerical simulation of the master equation. Population transfer via stimulated Raman adiabatic passage is significantly more robust against variations of the experimental parameters compared with that via the conventional resonant π pulse method. Our work opens up a new venue for exploring the process for quantum information processing using the superconducting artificial atoms. PMID:27009972

  8. Field-induced superconducting phase of FeSe in the BCS-BEC cross-over.

    PubMed

    Kasahara, Shigeru; Watashige, Tatsuya; Hanaguri, Tetsuo; Kohsaka, Yuhki; Yamashita, Takuya; Shimoyama, Yusuke; Mizukami, Yuta; Endo, Ryota; Ikeda, Hiroaki; Aoyama, Kazushi; Terashima, Taichi; Uji, Shinya; Wolf, Thomas; von Löhneysen, Hilbert; Shibauchi, Takasada; Matsuda, Yuji

    2014-11-18

    Fermi systems in the cross-over regime between weakly coupled Bardeen-Cooper-Schrieffer (BCS) and strongly coupled Bose-Einstein-condensate (BEC) limits are among the most fascinating objects to study the behavior of an assembly of strongly interacting particles. The physics of this cross-over has been of considerable interest both in the fields of condensed matter and ultracold atoms. One of the most challenging issues in this regime is the effect of large spin imbalance on a Fermi system under magnetic fields. Although several exotic physical properties have been predicted theoretically, the experimental realization of such an unusual superconducting state has not been achieved so far. Here we show that pure single crystals of superconducting FeSe offer the possibility to enter the previously unexplored realm where the three energies, Fermi energy εF, superconducting gap Δ, and Zeeman energy, become comparable. Through the superfluid response, transport, thermoelectric response, and spectroscopic-imaging scanning tunneling microscopy, we demonstrate that εF of FeSe is extremely small, with the ratio Δ/εF ~ 1(~0.3) in the electron (hole) band. Moreover, thermal-conductivity measurements give evidence of a distinct phase line below the upper critical field, where the Zeeman energy becomes comparable to εF and Δ. The observation of this field-induced phase provides insights into previously poorly understood aspects of the highly spin-polarized Fermi liquid in the BCS-BEC cross-over regime.

  9. Evolution of superconducting gap and metallic ground state in cuprates from transport

    NASA Astrophysics Data System (ADS)

    Taillefer, Louis

    2006-03-01

    We report on fundamental characteristics of the ground state of cuprates in the limit of T=0, for both normal and superconducting states, obtained from transport measurements on high-quality single crystals of YBCO and Tl-2201, as a function of hole concentration. The superconducting gap is extracted from thermal conductivity; it is found to scale with the superconducting transition temperature throughout the overdoped regime, with a gap-to-Tc ratio of 5 [1]. The normal state is accessed by suppressing superconductivity with magnetic fields up to 60 T and is characterized by the limiting behavior of its electrical resistivity; while carrier localization is observed in YBCO at low temperature for carrier concentrations p below 0.1 hole/planar Cu, at p=0.1 and above the material remains highly metallic down to T=0 [2]. This shows that the non-superconducting state of underdoped cuprates, deep in the pseudogap phase, is remarkably similar to that of strongly overdoped cuprates, e.g. at p=0.3. We compare these results with similar measurements on other cuprates and discuss their implication for our understanding of the cuprate phase diagram. [1] In collaboration with: D.G. Hawthorn, S.Y. Li, M. Sutherland, E. Boaknin, R.W. Hill, C. Proust, F. Ronning, M. Tanatar, J. Paglione, D. Peets, R. Liang, D.A. Bonn, W.N. Hardy, and N.N. Kolesnikov. [2] In collaboration with: C. Proust, M. Sutherland, N. Doiron- Leyraud, S.Y. Li, R. Liang, D.A. Bonn, W.N. Hardy, N.E. Hussey, S. Adachi, S. Tajima, J. Levallois, and M. Narbone.

  10. Commensurate states on incommensurate lattices. [for superconducting arrays in magnetic fields

    NASA Technical Reports Server (NTRS)

    Grest, Gary S.; Chaikin, Paul M.; Levine, Dov

    1988-01-01

    A simple one-dimensional model related to flux quantization on superconducting networks or charged particles on a substrate is proposed to investigate whether commensurate states can exist on incommensurate lattices. For both periodic and quasi-crystalline patterns, a set of low-energy states is found which is related to decimation symmetry and periodicity. It is suggested that the present quasi-periodic arrays which possess a decimation operation can be generalized to more-dimensional quasi-crystalline systems.

  11. Potential benefits of superconductivity to transportation in the United States

    NASA Astrophysics Data System (ADS)

    Rote, Donald M.; Johnson, Larry R.

    Research in U.S. transportation applications of superconductors is strongly motivated by a number of potential national benefits. These include the reduction of dependence on petroleum-based fuels, energy savings, substantially reduced air and noise pollution, increased customer convenience, and reduced maintenance costs. Current transportation technology offers little flexibility to switch to alternative fuels, and efforts to achieve the other benefits are confounded by growing congestion at airports and on urban roadways. A program has been undertaken to identify possible applications of the emerging superconducting applications to transportation and to evaluate potential national benefits. The current phase of the program will select the most promising applications for a more detailed subsequent study. Transportation modes being examined include highway and industrial vehicles, as well as rail, sea, air transport and pipelines. Three strategies are being considered: (1) replacing present components with those employing superconductors, (2) substituting new combinations of components or systems for present systems, and (3) developing completely new technologies. Distinctions are made between low-, medium-, and near-room-temperature superconductors. The most promising applications include magnetically levitated passenger and freight vehicles; replacement of drive systems in locomotives, self-propelled rail cars, and ships; and electric vehicles inductively coupled to electrified roadways.

  12. Gate-induced superconductivity in a solution-processed organic polymer film

    NASA Astrophysics Data System (ADS)

    Schön, J. H.; Dodabalapur, A.; Bao, Z.; Kloc, Ch.; Schenker, O.; Batlogg, B.

    2001-03-01

    The electrical and optical properties of conjugated polymers have received considerable attention in the context of potentially low-cost replacements for conventional metals and inorganic semiconductors. Charge transport in these organic materials has been characterized in both the doped-metallic and the semiconducting state, but superconductivity has not hitherto been observed in these polymers. Here we report a distinct metal-insulator transition and metallic levels of conductivity in a polymer field-effect transistor. The active material is solution-cast regioregular poly(3-hexylthiophene), which forms relatively well ordered films owing to self-organization, and which yields a high charge carrier mobility (0.05-0.1cm2V-1s-1) at room temperature. At temperatures below ~2.35K with sheet carrier densities exceeding 2.5 × 1014cm-2, the polythiophene film becomes superconducting. The appearance of superconductivity seems to be closely related to the self-assembly properties of the polymer, as the introduction of additional disorder is found to suppress superconductivity. Our findings therefore demonstrate the feasibility of tuning the electrical properties of conjugated polymers over the largest range possible-from insulating to superconducting.

  13. Pressure induced superconductivity on the border of magnetic order in MnP.

    PubMed

    Cheng, J-G; Matsubayashi, K; Wu, W; Sun, J P; Lin, F K; Luo, J L; Uwatoko, Y

    2015-03-20

    We report the discovery of superconductivity on the border of long-range magnetic order in the itinerant-electron helimagnet MnP via the application of high pressure. Superconductivity with T(sc)≈1  K emerges and exists merely near the critical pressure P(c)≈8  GPa, where the long-range magnetic order just vanishes. The present finding makes MnP the first Mn-based superconductor. The close proximity of superconductivity to a magnetic instability suggests an unconventional pairing mechanism. Moreover, the detailed analysis of the normal-state transport properties evidenced non-Fermi-liquid behavior and the dramatic enhancement of the quasiparticle effective mass near P(c) associated with the magnetic quantum fluctuations.

  14. Pressure-induced superconductivity in CaC2

    PubMed Central

    Li, Yan-Ling; Luo, Wei; Zeng, Zhi; Lin, Hai-Qing; Mao, Ho-kwang; Ahuja, Rajeev

    2013-01-01

    Carbon can exist as isolated dumbbell, 1D chain, 2D plane, and 3D network in carbon solids or carbon-based compounds, which attributes to its rich chemical binding way, including sp-, sp2-, and sp3-hybridized bonds. sp2-hybridizing carbon always captures special attention due to its unique physical and chemical property. Here, using an evolutionary algorithm in conjunction with ab initio method, we found that, under compression, dumbbell carbon in CaC2 can be polymerized first into 1D chain and then into ribbon and further into 2D graphite sheet at higher pressure. The C2/m structure transforms into an orthorhombic Cmcm phase at 0.5 GPa, followed by another orthorhombic Immm phase, which is stabilized in a wide pressure range of 15.2–105.8 GPa and then forced into MgB2-type phase with wide range stability up to at least 1 TPa. Strong electron–phonon coupling λ in compressed CaC2 is found, in particular for Immm phase, which has the highest λ value (0.562–0.564) among them, leading to its high superconducting critical temperature Tc (7.9∼9.8 K), which is comparable with the 11.5 K value of CaC6. Our results show that calcium not only can stabilize carbon sp2 hybridization at a larger range of pressure but also can contribute in superconducting behavior, which would further ignite experimental and theoretical interest in alkaline–earth metal carbides to uncover their peculiar physical properties under extreme conditions. PMID:23690580

  15. Frequency dispersion of nonlinear response of thin superconducting films in the Berezinskii-Kosterlitz-Thouless state

    DOE PAGES

    Dietrich, Scott; Mayer, William; Byrnes, Sean; ...

    2015-02-20

    The effects of microwave radiation on transport properties of atomically thin La2-xSrxCuO₄ films were studied in the 0.1-20 GHz frequency range. Resistance changes induced by microwaves were investigated at different temperatures (8–15 K) near the superconducting transition. A strong decrease of the nonlinear response is observed within a few GHz of a cutoff frequency νcut ≈ 2GHz. The expected frequency dependence vastly underestimates the sharpness of this drop. Numerical simulations that assume ac response to follow dc V-I characteristics of the films reproduce well the low frequency behavior, but fail above νcut. Thus, high-frequency radiation is much less effective inmore » inducing vortex-antivortex dissociation in the oscillating superconducting condensate.« less

  16. Frequency dispersion of nonlinear response of thin superconducting films in the Berezinskii-Kosterlitz-Thouless state

    SciTech Connect

    Dietrich, Scott; Mayer, William; Byrnes, Sean; Vitkalov, Sergey; Sergeev, A.; Bollinger, Anthony T.; Božović, Ivan

    2015-02-20

    The effects of microwave radiation on transport properties of atomically thin La2-xSrxCuO₄ films were studied in the 0.1-20 GHz frequency range. Resistance changes induced by microwaves were investigated at different temperatures (8–15 K) near the superconducting transition. A strong decrease of the nonlinear response is observed within a few GHz of a cutoff frequency νcut ≈ 2GHz. The expected frequency dependence vastly underestimates the sharpness of this drop. Numerical simulations that assume ac response to follow dc V-I characteristics of the films reproduce well the low frequency behavior, but fail above νcut. Thus, high-frequency radiation is much less effective in inducing vortex-antivortex dissociation in the oscillating superconducting condensate.

  17. Induced Superconductivity and Engineered Josephson Tunneling Devices in Epitaxial (111)-Oriented Gold/Vanadium Heterostructures.

    PubMed

    Wei, Peng; Katmis, Ferhat; Chang, Cui-Zu; Moodera, Jagadeesh S

    2016-04-13

    We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing.

  18. Possible light-induced superconductivity in K3C60 at high temperature.

    PubMed

    Mitrano, M; Cantaluppi, A; Nicoletti, D; Kaiser, S; Perucchi, A; Lupi, S; Di Pietro, P; Pontiroli, D; Riccò, M; Clark, S R; Jaksch, D; Cavalleri, A

    2016-02-25

    The non-equilibrium control of emergent phenomena in solids is an important research frontier, encompassing effects such as the optical enhancement of superconductivity. Nonlinear excitation of certain phonons in bilayer copper oxides was recently shown to induce superconducting-like optical properties at temperatures far greater than the superconducting transition temperature, Tc (refs 4-6). This effect was accompanied by the disruption of competing charge-density-wave correlations, which explained some but not all of the experimental results. Here we report a similar phenomenon in a very different compound, K3C60. By exciting metallic K3C60 with mid-infrared optical pulses, we induce a large increase in carrier mobility, accompanied by the opening of a gap in the optical conductivity. These same signatures are observed at equilibrium when cooling metallic K3C60 below Tc (20 kelvin). Although optical techniques alone cannot unequivocally identify non-equilibrium high-temperature superconductivity, we propose this as a possible explanation of our results.

  19. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5

    DOE PAGES

    Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; ...

    2016-06-27

    The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc2, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with fieldmore » reveals that the electron-electron scattering (or transport mass m*) of those unpaired electrons diverges as H→Hc2 from below, in the same way that it does in the normal state as H→Hc2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H*=Hc2 even from inside the superconducting state. In conclusion, the fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.« less

  20. Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn5

    NASA Astrophysics Data System (ADS)

    Paglione, Johnpierre; Tanatar, M. A.; Reid, J.-Ph.; Shakeripour, H.; Petrovic, C.; Taillefer, Louis

    2016-07-01

    The thermal conductivity κ of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H , for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc 2, κ /T is found to increase as T →0 , just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ /T with field reveals that the electron-electron scattering (or transport mass m⋆) of those unpaired electrons diverges as H →Hc 2 from below, in the same way that it does in the normal state as H →Hc 2 from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn5 at H⋆=Hc 2 even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k -space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.

  1. Anomalous metallic state and anisotropic multiband superconductivity in Nb3Pd0.7Se7

    NASA Astrophysics Data System (ADS)

    Zhang, Q. R.; Rhodes, D.; Zeng, B.; Besara, T.; Siegrist, T.; Johannes, M. D.; Balicas, L.

    2013-07-01

    We report the discovery of superconductivity in Nb3PdxSe7 with an x-dependent superconducting transition temperature as high as Tc≃2.1 K for x≃0.7 (middle point of the resistive transition). Needlelike single crystals display anisotropic upper-critical fields with an anisotropy γ=Hc2b/Hc2a as large as 6 between fields applied along their needle axis (or b axis) or along the a axis. As for the Fe based superconductors γ is temperature-dependent, suggesting that Nb3Pd0.7Se7 is a multiband superconductor. This is supported by band structure calculations which reveal a Fermi surface composed of quasi-one-dimensional and quasi-two-dimensional sheets of hole character, as well as three-dimensional sheets of both hole and electron character. Remarkably, Hc2b is observed to saturate at Hc2b(T→0K)≃14.1 T which is 4.26×Hp where Hp is the Pauli-limiting field in the weak-coupling regime. The synthesis procedure yields additional crystals belonging to the Nb2PdxSe5 phase which also becomes superconducting when the fraction of Pd is varied. For both phases we find that superconductivity condenses out of an anomalous metallic state, i.e., displaying ∂ρ/∂T<0 above Tc similarly to what is observed in the pseudogap phase of the underdoped cuprates. An anomalous metallic state, low-dimensionality, multiband character, extremely high and anisotropic Hc2's are all ingredients for unconventional superconductivity.

  2. Monte Carlo study of an unconventional superconducting phase in iridium oxide J(eff)=1/2 Mott insulators induced by carrier doping.

    PubMed

    Watanabe, Hiroshi; Shirakawa, Tomonori; Yunoki, Seiji

    2013-01-11

    Based on a microscopic theoretical study, we show that novel superconductivity is induced by carrier doping in layered perovskite Ir oxides where a strong spin-orbit coupling causes an effective total angular momentum J(eff)=1/2 Mott insulator. Using a variational Monte Carlo method, we find an unconventional superconducting state in the ground state phase diagram of a t(2g) three-orbital Hubbard model on the square lattice. This superconducting state is characterized by a d(x(2)-y(2))-wave "pseudospin singlet" formed by the J(eff)=1/2 Kramers doublet, which thus contains interorbital as well as both singlet and triplet components of t(2g) electrons. The superconducting state is found stable only by electron doping, but not by hole doping, for the case of carrier doped Sr2IrO4. We also study an effective single-orbital Hubbard model to discuss the similarities to high-T(c) cuprate superconductors and the multiorbital effects.

  3. Pressure-induced superconductivity in thin films of boron-doped carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Haruyama, Junji; Nakamura, Jin; Reppert, Jason; Rao, Apparao; Sano, Hirotaka; Iye, Yasuhiro

    2010-03-01

    We have reported that thin films of slightly boron-doped single-walled carbon nanotubes (B-SWNTs) can be superconductor at Tc of 12K [1]. Here, based on this, we show creation of paperlike thin film (Buckypaper) consisting of pseudo-two-dimensional network of B-SWNTs within weakly intertube van der Waals coupling (IVDWC) state. It was formed by sufficiently dissolving as-grown ropes of B-SWNTs and densely assembling them on silicon substrate. We find that superconducting transition temperature Tc of 8 K under absent pressure can be induced up to 19 K by applying a small pressure to the film and that a frequency in the radial breathing phonon drastically increases with applying pressure [2]. Discussion about IVDWC and distribution of B-SWNTs diameter imply the strong correlation. References [1] N. Murata, J. Haruyama, J. Reppert, A. M. Rao, T. Koretsune, S. Saito, Phys. Rev. Lett. 101, 027002 (2008) [2] J. Nakamura, J. Haruyama, M. Tachibana, J. Reppert,A. Rao, H. Sano, Y. Iye et al., Appl.Phys.Lett. 95, 142503 (2009)

  4. Dirac surface states and nature of superconductivity in Noncentrosymmetric BiPd

    PubMed Central

    Sun, Zhixiang; Enayat, Mostafa; Maldonado, Ana; Lithgow, Calum; Yelland, Ed; Peets, Darren C.; Yaresko, Alexander; Schnyder, Andreas P.; Wahl, Peter

    2015-01-01

    In non-magnetic bulk materials, inversion symmetry protects the spin degeneracy. If the bulk crystal structure lacks a centre of inversion, however, spin–orbit interactions lift the spin degeneracy, leading to a Rashba metal whose Fermi surfaces exhibit an intricate spin texture. In superconducting Rashba metals a pairing wavefunction constructed from these complex spin structures will generally contain both singlet and triplet character. Here we examine the possible triplet components of the order parameter in noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric superconductor macroscopic characterization, atomic-scale ultra-low-temperature scanning tunnelling spectroscopy, and relativistic first-principles calculations. While the superconducting state of BiPd appears topologically trivial, consistent with Bardeen–Cooper–Schrieffer theory with an order parameter governed by a single isotropic s-wave gap, we show that the material exhibits Dirac-cone surface states with a helical spin polarization. PMID:25818338

  5. Topological Superconducting State of Lead Nanowires in an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Rodrigo, J. G.; Crespo, V.; Suderow, H.; Vieira, S.; Guinea, F.

    2012-12-01

    Superconductors with an odd number of bands crossing the Fermi energy have topologically protected Andreev states at interfaces, including Majorana states in one-dimensional geometries. We propose here that repeated indentation of a Pb tip on a Pb substrate can lead to nanowires such that the resulting superconducting system has novel topological properties. We have analyzed a number of conductance curves obtained in different nanowires, and observe, in a few cases, very peculiar dependence of the critical current on magnetic field. In these cases, the form of multiple Andreev reflections observed at finite voltages are compatible with topological superconductivity. The nanowires give a low number of 1D channels, large spin orbit coupling, and a sizable Zeeman energy, provided that the applied magnetic field is higher than the Pb bulk critical field.

  6. Proximity-Induced Shiba States in a Molecular Junction

    NASA Astrophysics Data System (ADS)

    Island, Joshua O.; Gaudenzi, Rocco; de Bruijckere, Joeri; Burzurí, Enrique; Franco, Carlos; Mas-Torrent, Marta; Rovira, Concepció; Veciana, Jaume; Klapwijk, Teun M.; Aguado, Ramón; van der Zant, Herre S. J.

    2017-03-01

    Superconductors containing magnetic impurities exhibit intriguing phenomena derived from the competition between Cooper pairing and Kondo screening. At the heart of this competition are the Yu-Shiba-Rusinov (Shiba) states which arise from the pair breaking effects a magnetic impurity has on a superconducting host. Hybrid superconductor-molecular junctions offer unique access to these states but the added complexity in fabricating such devices has kept their exploration to a minimum. Here, we report on the successful integration of a model spin 1 /2 impurity, in the form of a neutral and stable all organic radical molecule, in proximity-induced superconducting break junctions. Our measurements reveal excitations which are characteristic of a spin-induced Shiba state due to the radical's unpaired spin strongly coupled to a superconductor. By virtue of a variable molecule-electrode coupling, we access both the singlet and doublet ground states of the hybrid system which give rise to the doublet and singlet Shiba excited states, respectively. Our results show that Shiba states are a robust feature of the interaction between a paramagnetic impurity and a proximity-induced superconductor where the excited state is mediated by correlated electron-hole (Andreev) pairs instead of Cooper pairs.

  7. Superconductivity in the liquid-dimer valence-bond state

    SciTech Connect

    Ioffe, L.B.; Larkin, A.I. )

    1989-10-01

    Introducing an unambiguous prescription which converts singlet dimers into quasidipoles, we describe the low-energy excitations in the liquid-dimer state as fluctuations of the average dipole moment. The exchange of these fluctuations leads to a long-range interaction between holes in this state. This interaction favors the two-particle Bose condensate and destroys the order parameter of the one-particle Bose condensate even at zero temperature.

  8. Emergence of superconductivity from the dynamically heterogeneous insulating state in La(2-x)Sr(x)CuO4.

    PubMed

    Shi, Xiaoyan; Logvenov, G; Bollinger, A T; Božović, I; Panagopoulos, C; Popović, Dragana

    2013-01-01

    A central issue for copper oxides is the nature of the insulating ground state at low carrier densities and the emergence of high-temperature superconductivity from that state with doping. Even though this superconductor-insulator transition (SIT) is a zero-temperature transition, measurements are not usually carried out at low temperatures. Here we use magnetoresistance to probe both the insulating state at very low temperatures and the presence of superconducting fluctuations in La(2-x)Sr(x)CuO(4) films, for doping levels that range from the insulator to the superconductor (x  =  0.03-0.08). We observe that the charge glass behaviour, characteristic of the insulating state, is suppressed with doping, but it coexists with superconducting fluctuations that emerge already on the insulating side of the SIT. The unexpected quenching of the superconducting fluctuations by the competing charge order at low temperatures provides a new perspective on the mechanism for the SIT.

  9. Strain induced superconductivity in the parent compound BaFe2As2.

    PubMed

    Engelmann, J; Grinenko, V; Chekhonin, P; Skrotzki, W; Efremov, D V; Oswald, S; Iida, K; Hühne, R; Hänisch, J; Hoffmann, M; Kurth, F; Schultz, L; Holzapfel, B

    2013-01-01

    The discovery of superconductivity with a transition temperature, Tc, up to 65 K in single-layer FeSe (bulk Tc=8 K) films grown on SrTiO3 substrates has attracted special attention to Fe-based thin films. The high Tc is a consequence of the combined effect of electron transfer from the oxygen-vacant substrate to the FeSe thin film and lattice tensile strain. Here we demonstrate the realization of superconductivity in the parent compound BaFe2As2 (no bulk Tc) just by tensile lattice strain without charge doping. We investigate the interplay between strain and superconductivity in epitaxial BaFe2As2 thin films on Fe-buffered MgAl2O4 single crystalline substrates. The strong interfacial bonding between Fe and the FeAs sublattice increases the Fe-Fe distance due to the lattice misfit, which leads to a suppression of the antiferromagnetic spin density wave and induces superconductivity with bulk Tc≈10 K. These results highlight the role of structural changes in controlling the phase diagram of Fe-based superconductors.

  10. Ir doping-induced superconductivity in the SmFeAsO system.

    PubMed

    Chen, Yong Liang; Cheng, Cui Hua; Cui, Ya Jing; Zhang, Han; Zhang, Yong; Yang, Ye; Zhao, Yong

    2009-08-05

    The 5d transition metal Ir is successfully doped for Fe in SmFeAsO to induce superconductivity with T(c) = 16 K at a doping level of approximately 15 atom %. Ir doping decreases the As-Fe-As bond angle, beta; this behavior is different from the change in beta for the system with doping charges in the charge-reservoir layers.

  11. High-temperature superconductivity in space-charge regions of lanthanum cuprate induced by two-dimensional doping

    NASA Astrophysics Data System (ADS)

    Baiutti, F.; Logvenov, G.; Gregori, G.; Cristiani, G.; Wang, Y.; Sigle, W.; van Aken, P. A.; Maier, J.

    2015-10-01

    The exploitation of interface effects turned out to be a powerful tool for generating exciting material properties. Such properties include magnetism, electronic and ionic transport and even superconductivity. Here, instead of using conventional homogeneous doping to enhance the hole concentration in lanthanum cuprate and achieve superconductivity, we replace single LaO planes with SrO dopant planes using atomic-layer-by-layer molecular beam epitaxy (two-dimensional doping). Electron spectroscopy and microscopy, conductivity measurements and zinc tomography reveal such negatively charged interfaces to induce layer-dependent superconductivity (Tc up to 35 K) in the space-charge zone at the side of the planes facing the substrate, where the strontium (Sr) profile is abrupt. Owing to the growth conditions, the other side exhibits instead a Sr redistribution resulting in superconductivity due to conventional doping. The present study represents a successful example of two-dimensional doping of superconducting oxide systems and demonstrates its power in this field.

  12. Pressure-induced superconductivity in beta- Na (0.33) V(2)O(5) beyond charge ordering.

    PubMed

    Yamauchi, T; Ueda, Y; Môri, N

    2002-07-29

    We report the discovery of a new superconducting phase in highly correlated 3d electron systems. The compound is beta-vanadium bronze, beta- Na0.33V 2O5, in which the charge-ordered phase collapses under hydrostatic high pressure and a pressure-induced superconducting phase appears around T(S C)=8 K, P=8 GPa. This report presents the first observation not only of superconductivity in vanadium oxides but also of a phase transition from charge ordered to superconducting on a pressure-temperature (P- T) plane. The phase diagrams seem to have universal aspects across the classes of materials. This indicates a profound physics of superconductivity in highly correlated electron systems.

  13. Free energy surfaces in the superconducting mixed state

    NASA Technical Reports Server (NTRS)

    Finnemore, D. K.; Fang, M. M.; Bansal, N. P.; Farrell, D. E.

    1989-01-01

    The free energy surface for Tl2Ba2Ca2Cu3O1O has been measured as a function of temperature and magnetic field to determine the fundamental thermodynamic properties of the mixed state. The change in free energy, G(H)-G(O), is found to be linear in temperature over a wide range indicating that the specific heat is independent of field.

  14. Magnon-phonon coupling and implications for charge-density wave states and superconductivity in cuprates

    NASA Astrophysics Data System (ADS)

    Struzhkin, Viktor V.; Chen, Xiao-Jia

    2016-10-01

    The mechanism of high-temperature superconductivity of copper oxides (cuprates) remains unsolved puzzle in condensed matter physics. The cuprates represent extremely complicated system, showing fascinating variety of quantum phenomena and rich phase diagram as a function of doping. In the suggested "superconducting glue" mechanisms, phonon and spin excitations are invoked most frequently, and it appears that only spin excitations cover the energy scale required to justify very high transition temperature Tc ˜ 165 K (as in mercury-based triple layer cuprates compressed to 30 GPa). It appears that pressure is quite important variable helping to boost the Tc record by almost 30°. Pressure may be also considered as a clean tuning parameter, helping to understand the underlying balance of various energy scales and ordered states in cuprates. In this paper, a review of mostly our work on cuprates under pressure will be given, with the emphasis on the interactions between phonon and spin excitations. It appears that there is a strong coupling between superexchange interaction and stretching in-plane oxygen vibrations, which may give rise to a variety of complex phenomena, including the charge-density wave state intertwined with superconductivity and attracting a lot of interest recently.

  15. Heavy-fermion superconductivity in the quadrupole ordered state of PrV2Al20.

    PubMed

    Tsujimoto, Masaki; Matsumoto, Yosuke; Tomita, Takahiro; Sakai, Akito; Nakatsuji, Satoru

    2014-12-31

    PrV2Al20 is a rare example of a heavy-fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic Γ3 ground doublet. Here, we report that a high-quality single crystal of PrV2Al20 exhibits superconductivity at Tc=50  mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy-fermion character of the superconductivity is evident from the specific heat jump of ΔC/T∼0.3  J/mol K(2) and the effective mass m*/m0∼140 estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at TQ=0.75  K and T*=0.65  K associated with quadrupole and octupole degrees of freedom of the Γ3 doublet. In the ordered state, the specific heat C/T shows a T(3) dependence, indicating the gapless mode associated with the quadrupole order, the octupole order, or both. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.

  16. Superconducting/magnetic Three-state Nanodevice for Memory and Reading Applications

    NASA Astrophysics Data System (ADS)

    Del Valle, J.; Gomez, A.; Gonzalez, E. M.; Osorio, M. R.; Granados, D.; Vicent, J. L.

    2015-10-01

    We present a simple nanodevice that can operate in two modes: i) non-volatile three-state memory and ii) reading device. The nanodevice can retain three well defined states -1, 0 and +1 and can operate in a second mode as a sensor for external magnetic fields. The nanodevice is fabricated with an array of ordered triangular-shaped nanomagnets embedded in a superconducting thin film gown on Si substrates. The device runs based on the combination of superconducting vortex ratchet effect (superconducting film) with the out of plane magnetization (nanomagnets). The input signals are ac currents and the output signal are dc voltages. The memory mode is realized without applying a magnetic field and the nanomagnet stray magnetic fields govern the effect. In the sensor mode an external magnetic field is applied. The main characteristic of this mode is that the output signal is null for a precise value of the external magnetic field that only depends on the fabrication characteristics of the nanodevice.

  17. Relaxation of the resistive superconducting state in boron-doped diamond films

    NASA Astrophysics Data System (ADS)

    Kardakova, A.; Shishkin, A.; Semenov, A.; Goltsman, G. N.; Ryabchun, S.; Klapwijk, T. M.; Bousquet, J.; Eon, D.; Sacépé, B.; Klein, Th.; Bustarret, E.

    2016-02-01

    We report a study of the relaxation time of the restoration of the resistive superconducting state in single crystalline boron-doped diamond using amplitude-modulated absorption of (sub-)THz radiation (AMAR). The films grown on an insulating diamond substrate have a low carrier density of about 2.5 ×1021cm-3 and a critical temperature of about 2 K . By changing the modulation frequency we find a high-frequency rolloff which we associate with the characteristic time of energy relaxation between the electron and the phonon systems or the relaxation time for nonequilibrium superconductivity. Our main result is that the electron-phonon scattering time varies clearly as T-2, over the accessible temperature range of 1.7 to 2.2 K. In addition, we find, upon approaching the critical temperature Tc, evidence for an increasing relaxation time on both sides of Tc.

  18. Fully gapped superconducting state in Au2Pb: A natural candidate for topological superconductor

    NASA Astrophysics Data System (ADS)

    Yu, Y. J.; Xu, Y.; Xing, Y.; Zhang, J.; Ying, T. P.; Hong, X. C.; Wang, M. X.; Zhang, X.; Jia, S.; Wang, J.; Li, S. Y.

    2016-12-01

    We measured the ultra-low-temperature specific heat and thermal conductivity of the Au2Pb single crystal, a possible three-dimensional Dirac semimetal with a superconducting transition temperature Tc ≈ 1.05 \\text{K} . The electronic specific heat can be fitted by a two-band s-wave model, which gives the gap amplitudes Δ1(0)/k B T c = 1.41 and Δ2(0)/k B T c = 5.25. From the thermal conductivity measurements, a negligible residual linear term κ_0/T in zero field and a slow field dependence of κ_0/T at low field are obtained. These results suggest that Au2Pb has a fully gapped superconducting state in the bulk, which is a necessary condition for topological superconductors if Au2Pb is indeed one.

  19. Pressure Induced Enhancement of Superconductivity in LaRu2P2.

    PubMed

    Li, Baoxuan; Lu, Pengchao; Liu, Jianzhong; Sun, Jian; Li, Sheng; Zhu, Xiyu; Wen, Hai-Hu

    2016-04-18

    To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan's theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors.

  20. Pressure Induced Enhancement of Superconductivity in LaRu2P2

    PubMed Central

    Li, Baoxuan; Liu, Jianzhong; Sun, Jian; Li, Sheng; Zhu, Xiyu; Wen, Hai-Hu

    2016-01-01

    To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan’s theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors. PMID:27086696

  1. Pressure Induced Enhancement of Superconductivity in LaRu2P2

    NASA Astrophysics Data System (ADS)

    Li, Baoxuan; Lu, Pengchao; Liu, Jianzhong; Sun, Jian; Li, Sheng; Zhu, Xiyu; Wen, Hai-Hu

    2016-04-01

    To explore new superconductors beyond the copper-based and iron-based systems is very important. The Ru element locates just below the Fe in the periodic table and behaves like the Fe in many ways. One of the common thread to induce high temperature superconductivity is to introduce moderate correlation into the system. In this paper, we report the significant enhancement of superconducting transition temperature from 3.8 K to 5.8 K by using a pressure only of 1.74 ± 0.05 GPa in LaRu2P2 which has an iso-structure of the iron-based 122 superconductors. The ab-initio calculation shows that the superconductivity in LaRu2P2 at ambient pressure can be explained by the McMillan’s theory with strong electron-phonon coupling. However, it is difficult to interpret the enhancement of Tc versus pressure within this picture. Detailed analysis of the pressure induced evolution of resistivity and upper critical field Hc2(T) reveals that the increase of Tc with pressure may be accompanied by the involvement of extra electron-boson interaction. This suggests that the Ru-based system has some commonality as the Fe-based superconductors.

  2. Magnetic-field-induced criticality in superconducting two-leg ladders

    NASA Astrophysics Data System (ADS)

    Vekua, Temo

    2017-03-01

    We study magnetic-field-induced critical singularities in the superconducting phase of the hole-doped Hubbard model of repulsively interacting electrons, defined on a two-leg ladder. We argue that, provided the low-energy spin excitations in doped ladders carry electric charge, the low-temperature thermodynamic quantities, such as the specific-heat coefficient and magnetic susceptibility, will show logarithmic singularities in the quantum critical regime. This behavior is in drastic contrast to the magnetic-field-induced criticality in undoped Mott insulator ladders, which is governed by the zero-scale-factor universality with its hallmark square-root singularities.

  3. Critical state stability in type-II superconductors and superconducting--normal-metal composites

    SciTech Connect

    Mints, R.G.; Rakhmanov, A.L.

    1981-07-01

    This review is devoted to the problem of critical state stability in hard superconductors and superconducting normal composites. An introduction is given to the properties of hard and composite superconductors, and to the qualitative nature of the physical processes that occur in these materials in the critical state. The dynamics of the development of instabilities of various kinds are treated in detail. Stability criteria are obtained and discussed, and theory is compared with experiment. The interaction between flux jumps and plastic strain jerks and the training phenomenon in superconductors are also covered.

  4. Proximity-induced superconductivity effect in a double-stranded DNA

    SciTech Connect

    Simchi, Hamidreza; Esmaeilzadeh, Mahdi Mazidabadi, Hossein

    2014-02-07

    We study the proximity-induced superconductivity effect in a double-stranded DNA by solving the Bogoliubov-de Gennes equations and taking into account the effect of thermal fluctuations of the twist angle between neighboring base pairs. We show that the electron conductance is spin-dependent and the conductance of spin up (down) increases (decreases) due to the spin-orbit coupling (SOC). It is found that, for T < 100 K, the band gap energy is temperature-independent and it decreases due to the SOC. In addition, by solving the Bogoliubov-de Gennes equations and local gap parameter equation self-consistently, we find the critical temperature at which transition to superconductivity can take place.

  5. Superconductive quantum interference magnetometer with high sensitivity achieved by an induced resonance

    SciTech Connect

    Vettoliere, A.; Granata, C.

    2014-08-15

    A fully integrated low noise superconducting quantum interference device (SQUID) in a magnetometer configuration is presented. An intrinsic high voltage responsivity as high as 500 μV/Φ{sub 0} has been obtained by introducing a resonance in the voltage – magnetic flux characteristic. This resonance is induced by an integrated superconducting coil surrounding the pick-up coil and connected to one end of the SQUID output. The SQUID magnetometer exhibits a spectral density of magnetic field noise as low as 3 fT/Hz{sup 1/2}. In order to verify the suitability of the magnetometer, measurements of bandwidth and slew rate have been performed and compared with those of the same device without the resonance and with additional positive feedback. Due to their good characteristics such devices can be employed in a large number of applications including biomagnetism.

  6. Superconductive quantum interference magnetometer with high sensitivity achieved by an induced resonance.

    PubMed

    Vettoliere, A; Granata, C

    2014-08-01

    A fully integrated low noise superconducting quantum interference device (SQUID) in a magnetometer configuration is presented. An intrinsic high voltage responsivity as high as 500 μV/Φ0 has been obtained by introducing a resonance in the voltage - magnetic flux characteristic. This resonance is induced by an integrated superconducting coil surrounding the pick-up coil and connected to one end of the SQUID output. The SQUID magnetometer exhibits a spectral density of magnetic field noise as low as 3 fT/Hz(1/2). In order to verify the suitability of the magnetometer, measurements of bandwidth and slew rate have been performed and compared with those of the same device without the resonance and with additional positive feedback. Due to their good characteristics such devices can be employed in a large number of applications including biomagnetism.

  7. Properties of an excitonic insulator in the superconducting state

    SciTech Connect

    Batyev, E. G.

    2012-01-15

    The properties of an excitonic insulator with embedded (nondissipative) current are studied using the self-consistent field approximation, in which the wavefunction of the system has the form of the known Bardeen-Cooper-Schrieffer trial function with time-dependent coefficients; the equations for these coefficients are derived. Such a formulation holds for the homogeneous case (in the absence of a coordinate dependence). We consider two problems: (i) time evolution of the system in the case when an embedded current exists at the initial instant; and (ii) the response of the system to an abrupt perturbation (the vector potential changes jumpwise from zero to a certain finite value). In both cases, the state of the system depends on time, but some characteristics (e.g., undamped current) tend to a constant value. For a weak perturbation, the system behaves as an insulator. If the perturbation is not small (on the order of the gap in the spectrum), nonlinear effects lead to substantial differences: a certain part of the embedded current is preserved in the former case, while the initial current in the latter case acquires a certain addition.

  8. Surface superconductivity in thin cylindrical Bi nanowire.

    PubMed

    Tian, Mingliang; Wang, Jian; Ning, Wei; Mallouk, Thomas E; Chan, Moses H W

    2015-03-11

    The physical origin and the nature of superconductivity in nanostructured Bi remains puzzling. Here, we report transport measurements of individual cylindrical single-crystal Bi nanowires, 20 and 32 nm in diameter. In contrast to nonsuperconducting Bi nanoribbons with two flat surfaces, cylindrical Bi nanowires show superconductivity below 1.3 K. However, their superconducting critical magnetic fields decrease with their diameter, which is the opposite of the expected behavior for thin superconducting wires. Quasiperiodic oscillations of magnetoresistance were observed in perpendicular fields but were not seen in the parallel orientation. These results can be understood by a model of surface superconductivity with an enhanced surface-to-bulk volume in small diameter wires, where the superconductivity originates from the strained surface states of the nanowires due to the surface curvature-induced stress.

  9. The effects of disorder on the normal state and superconducting properties of Nb3Sn

    NASA Astrophysics Data System (ADS)

    Mentink, M. G. T.; Dhalle, M. M. J.; Dietderich, D. R.; Godeke, A.; Hellman, F.; ten Kate, H. H. J.

    2017-02-01

    The effect of disorder on the normal state resistivity and the superconducting properties of Nb{}3Sn is explored in a combination of ab initio calculations and microscopic theory. The crystal symmetry is calculated to be preferentially tetragonal at a normal state resistivity below 27.0 ± 1.4 μ {{Ω }}{cm}, and preferentially cubic above this value, which is shown to be consistent with the experimentally observed transition point. The phonon density of states, the Eliashberg spectrum {α }2(ω )F(ω ), the electron-phonon coupling constant, the characteristic frequency, the critical temperature T c, and the upper critical magnetic field at 0 K {H}{{c}2}(0) are calculated over a large normal state resistivity range and shown to be consistent with experimental observations. The high degree of consistency between the calculation results and experimental observations is a strong indication that the calculation approach utilized here, a combination of ab initio calculations and microscopic theory, is a useful tool for understanding the superconducting and normal state properties of Nb{}3Sn.

  10. Thermally activated phase slips from metastable states in mesoscopic superconducting rings

    NASA Astrophysics Data System (ADS)

    Petkovic, Ivana; Lollo, Anthony; Harris, Jack

    In equilibrium, a flux-biased superconducting ring at low temperature can occupy any of several metastable states. The particular state that the ring occupies depends on the history of the applied flux, as different states are separated from each other by flux-dependent energy barriers. There is a critical value of the applied flux at which a given barrier goes to zero, the state becomes unstable, and the system transition into another state. In recent experiments performed on arrays of rings we showed that this transition occurs close to the critical flux predicted by Ginzburg-Landau theory. Here, we will describe experiments in which we have extended these measurements to an individual ring in order to study the thermal activation of the ring over a barrier that has been tuned close to zero. We measure the statistics of transitions as function of temperature and ramp rate.

  11. Superconductivity induced by U doping in the SmFeAsO system

    NASA Astrophysics Data System (ADS)

    Huang, Bo; Yang, Jijun; Tang, Jun; Liao, Jiali; Yang, Yuanyou; Liu, Ning; Mu, Gang; Hu, Tao; Shen, Xiaoping; Feng, Donglai

    2013-02-01

    Through partial substitution of Sm by U in SmFeAsO, a different member of the family of iron-based superconductors was successfully synthesized. X-ray diffraction measurements show that the lattice constants along the a and c axes are both squeezed through U doping, indicating a successful substitution of U at the Sm site. The parent compound shows a strong resistivity anomaly near 150 K, associated with spin-density-wave instability. U doping suppresses this instability and leads to a transition to the superconducting state at temperatures up to 49 K. Magnetic measurements confirm the bulk superconductivity in this system. For the sample with a doping level of x=0.2, the external magnetic field suppresses the onset temperature very slowly, indicating a rather high upper critical field. In addition, the Hall effect measurements show that U clearly dopes electrons into the material.

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

    PubMed Central

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

    2015-01-01

    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. PMID:25737341

  13. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1+yTe1-xSex [How does annealing in chalcogen vapor induce superconductivity in Fe1+yTe-xSex?

    DOE PAGES

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; ...

    2015-02-01

    Recent investigations have shown that Fe1+yTe1-xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1+yTe1-xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥ 1) complexes. We show thatmore » the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.« less

  14. Charge ordered normal ground state and its interplay with superconductivity in the underdoped cuprates

    NASA Astrophysics Data System (ADS)

    Sebastian, Suchitra

    2015-03-01

    Over the last few years, evidence has gradually built for a charge ordered normal ground state in the underdoped region of the cuprate high temperature superconductors. I will address the electronic structure of the normal ground state of the underdoped cuprates as accessed by quantum oscillations, and relate it to complementary measurements by other experimental techniques. The interplay of the charge ordered ground state with the antinodal gapped pseudogap state, and overarching magnetic and superconducting correlations will be further explored. This work was performed in collaboration with N. Harrison, G. G. Lonzarich, B. J. Ramshaw, B. S. Tan, P. A. Goddard, F. F. Balakirev, C. H. Mielke, R. Liang, D. A. Bonn, and W. N. Hardy

  15. Effective theory of the T- and P-breaking superconducting state

    NASA Technical Reports Server (NTRS)

    Wen, X. G.; Zee, A.

    1989-01-01

    An effective theory of superconductivity based on a microscopic theory of the T- and P-breaking spin-liquid state is proposed. There are two independent gauge invariances broken by two separate condensates. The theory may be useful for phenomenological calculations. In particular, it is found that the H(c1) are different for magnetic fields with opposite orientations. It is also found that the polarization of an electromagnetic wave is rotated after reflection from these T- and P-breaking superconductors.

  16. Measurements of the nonradiative states of optically illuminated semiconductors by a superconducting tunnel junction

    SciTech Connect

    Iguchi, I.; Kasai, Y.

    1986-08-18

    A novel technique which utilizes a superconducting tunnel junction as a phonon detector is introduced to detect nonequilibrium phonons from the nonradiative states in optically illuminated semiconductors such as Si or GaAs. The method proved to have very high sensitivity for phonon detection with a large S-italic/N-italic ratio. The detected phonon signal as a function of wavelength of the light for GaAs exhibited modulated structures below the band-gap energy consistent with the presence of an EL2 level.

  17. The Use of a Solid State Analog Television Transmitter as a Superconducting Electron Gun Power Amplifier

    SciTech Connect

    J.G. Kulpin, K.J. Kleman, R.A. Legg

    2012-07-01

    A solid state analog television transmitter designed for 200 MHz operation is being commissioned as a radio frequency power amplifier on the Wisconsin superconducting electron gun cavity. The amplifier consists of three separate radio frequency power combiner cabinets and one monitor and control cabinet. The transmitter employs rugged field effect transistors built into one kilowatt drawers that are individually hot swappable at maximum continuous power output. The total combined power of the transmitter system is 33 kW at 200 MHz, output through a standard coaxial transmission line. A low level radio frequency system is employed to digitally synthesize the 200 MHz signal and precisely control amplitude and phase.

  18. Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe2

    PubMed Central

    Guan, Syu-You; Chen, Peng-Jen; Chu, Ming-Wen; Sankar, Raman; Chou, Fangcheng; Jeng, Horng-Tay; Chang, Chia-Seng; Chuang, Tien-Ming

    2016-01-01

    The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level (EF) combined with fully gapped bulk superconductivity. We report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe2. Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point at E ≅ 1.0 eV, of which the inner TSS and the partial outer TSS cross EF, on the Pb-terminated surface of this fully gapped superconductor. This discovery reveals PbTaSe2 as a promising candidate for TSC. PMID:28138520

  19. Superconducting topological surface states in the noncentrosymmetric bulk superconductor PbTaSe2.

    PubMed

    Guan, Syu-You; Chen, Peng-Jen; Chu, Ming-Wen; Sankar, Raman; Chou, Fangcheng; Jeng, Horng-Tay; Chang, Chia-Seng; Chuang, Tien-Ming

    2016-11-01

    The search for topological superconductors (TSCs) is one of the most urgent contemporary problems in condensed matter systems. TSCs are characterized by a full superconducting gap in the bulk and topologically protected gapless surface (or edge) states. Within each vortex core of TSCs, there exists the zero-energy Majorana bound states, which are predicted to exhibit non-Abelian statistics and to form the basis of the fault-tolerant quantum computation. To date, no stoichiometric bulk material exhibits the required topological surface states (TSSs) at the Fermi level (EF) combined with fully gapped bulk superconductivity. We report atomic-scale visualization of the TSSs of the noncentrosymmetric fully gapped superconductor PbTaSe2. Using quasi-particle scattering interference imaging, we find two TSSs with a Dirac point at E ≅ 1.0 eV, of which the inner TSS and the partial outer TSS cross EF, on the Pb-terminated surface of this fully gapped superconductor. This discovery reveals PbTaSe2 as a promising candidate for TSC.

  20. Superconductivity from Emerging Magnetic Moments.

    PubMed

    Hoshino, Shintaro; Werner, Philipp

    2015-12-11

    Multiorbital Hubbard models are shown to exhibit a spatially isotropic spin-triplet superconducting phase, where equal-spin electrons in different local orbitals are paired. This superconducting state is stabilized in the spin-freezing crossover regime, where local moments emerge in the metal phase, and the pairing is substantially assisted by spin anisotropy. The phase diagram features a superconducting dome below a non-Fermi-liquid metallic region and next to a magnetically ordered phase. We suggest that this type of fluctuating-moment-induced superconductivity, which is not originating from fluctuations near a quantum critical point, may be realized in spin-triplet superconductors such as strontium ruthenates and uranium compounds.

  1. Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa2Cu3O6.48.

    PubMed

    Mankowsky, R; Fechner, M; Först, M; von Hoegen, A; Porras, J; Loew, T; Dakovski, G L; Seaberg, M; Möller, S; Coslovich, G; Keimer, B; Dhesi, S S; Cavalleri, A

    2017-07-01

    Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. The empty chain Cu dy(2)-z(2) orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.

  2. Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa2Cu3O6.48

    PubMed Central

    Mankowsky, R.; Fechner, M.; Först, M.; von Hoegen, A.; Porras, J.; Loew, T.; Dakovski, G. L.; Seaberg, M.; Möller, S.; Coslovich, G.; Keimer, B.; Dhesi, S. S.; Cavalleri, A.

    2017-01-01

    Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBa2Cu3O6+x induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO2 planes. The empty chain Cu dy2-z2 orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu L-edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions. PMID:28345009

  3. kz Dependent Electronic Structure Studies of CaC6 and Inter Layer State Driven Superconductivity

    NASA Astrophysics Data System (ADS)

    Kyung, Wonshik; Kim, Yeongkwan; Han, Garam; Leem, Choonshik; Kim, Chul; Koh, Yoonyoung; Kim, Beomyoung; Kim, Yeongwook; Kim, Junsung; Kim, Keunsu; Rotenberg, Eli; Denlinger, Jonathan; Kim, Changyoung; Yonsei University Team; Postech Collaboration; Advanced light source Collaboration

    2015-03-01

    We performed angle-resolved photoemission experiments on CaC6 and measured kz dependent electronic structures to investigate the interlayer states. The results reveal a spherical interlayer Fermi surface centered at the Γ point. We also find the graphene driven band possesses a weak kz dispersion. The overall electronic structure shows a peculiar single graphene layer periodicity in the kz direction although CaC6 unit cell is supposed to contain three graphene layers. This suggests that c-axis ordering of Ca has little effect on the electronic structure of CaC6. In addition to CaC6, we also studied the non-superconducting BaC6. For BaC6, the graphene band Dirac point energy is smaller than that of CaC6. Based on data from CaC6 and BaC6, we rule out Cxy phonon mode as the origin of the superconductivity in CaC6, which strongly suggests interlayer state driven supercondutivity.

  4. Field-induced reentrant superconductivity in thin films of nodal superconductors

    NASA Astrophysics Data System (ADS)

    Hachiya, M.; Aoyama, K.; Ikeda, R.

    2013-08-01

    Previous work on nodal d-wave superconductors has shown that a Fulde-Ferrell-Larkin-Ovchinnikov- (FFLO-) like superconducting (SC) state, which is modulated along the film plane, can be realized with no magnetic field when quasiparticles acquire an additional linear term in the wave vector in their dispersion. In the present work, the stability of such a modulated SC state in an artificial film against an applied magnetic field is studied. As a reflection of the presence of two FFLO-like states of different origins, one close to zero field and the other at the high-field end, in a single field vs temperature phase diagram of thin films, the conventional SC state, which is uniform along the film plane, generally tends to appear as a reentrant ordered phase bounded by the normal phase in lower fields.

  5. The Kohn-Luttinger mechanism and phase diagram of the superconducting state in the Shubin-Vonsovsky model

    SciTech Connect

    Kagan, M. Yu.; Val'kov, V. V.; Mitskan, V. A.; Korovuskin, M. M.

    2013-10-15

    Using the Shubin-Vonsovsky model in the weak-coupling regime W > U > V (W is the bandwidth, U is the Hubbard onsite repulsion, and V is the Coulomb interaction at neighboring sites) based on the Kohn-Luttinger mechanism, we determined the regions of the existence of the superconducting phases with the d{sub xy}, p, s, and d{sub x{sup 2}-y{sup 2}} symmetry types of the order parameter. It is shown that the effective interaction in the Cooper channel considerably depends not only on single-site but also on intersite Coulomb correlations. This is demonstrated by the example of the qualitative change and complication of the phase diagram of the superconducting state. The superconducting (SC) phase induction mechanism is determined taking into account polarization contributions in the second-order perturbation theory in the Coulomb interaction. The results obtained for the angular dependence of the superconducting gap in different channels are compared with angule-resolved photoemission spectroscopy (ARPES) results. The influence of long-range hops in the phase diagram and critical superconducting transition temperature in different channels is analyzed. The conditions for the appearance of the Kohn-Luttinger superconductivity with the d{sub x{sup 2}-y{sup 2}} symmetry and high critical temperatures T{sub c} {approx} 100 K near the half-filling are determined.

  6. Hybrid superconducting neutron detectors

    SciTech Connect

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

    2015-03-16

    A neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction, {sup 10}B + n → α + {sup 7}Li, with α and Li ions generating a hot spot on the current-biased Nb strip which in turn 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 = 8 K and current-biased below the critical current I{sub c}, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the superconducting state, thus resetting the detector. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed.

  7. Hybrid superconducting neutron detectors

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    A neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction, 10B + n → α + 7Li, with α and Li ions generating a hot spot on the current-biased Nb strip which in turn 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 = 8 K and current-biased below the critical current Ic, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the superconducting state, thus resetting the detector. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed.

  8. Origin of Pressure-induced Superconducting Phase in KxFe2−ySe2 studied by Synchrotron X-ray Diffraction and Spectroscopy

    PubMed Central

    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

    2016-01-01

    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. PMID:27499373

  9. An indication of magnetic-field-induced superconductivity in a bifunctional layered organic conductor, kappa-(BETS)(2)FeBr(4).

    PubMed

    Fujiwara, Hideki; Kobayashi, Hayao; Fujiwara, Emiko; Kobayashi, Akiko

    2002-06-19

    Hybrid systems consisting of the conducting layers of organic donor molecules and the magnetic layers of inorganic anions have been focused on as possible bifunctional materials, whose conducting properties can be tuned by controlling the magnetic state of the anion layers on an application of magnetic field. Here we report the magnetoresistance of the antiferromagnetic organic superconductor, kappa-(BETS)2FeBr4 [BETS = bis(ethylenedithio)tetraselenafulvalene], consisting of the two-dimensional superconducting layers of the BETS semications and the insulating layers of the FeBr4- anions. Due to the metamagnetic nature of the Fe3+ spin system, characteristic resistivity decrease was observed just below the antiferromagnetic superconductor-to-ferromagnetic metal transition at 1.6 T. Furthermore, an indication of the onsets of the magnetic-field-induced superconductivity was discovered around 12.5 T.

  10. Electric field-induced superconducting transition of insulating FeSe thin film at 35 K.

    PubMed

    Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-04-12

    It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 10(15) cm(-2) (the average volume density of 1.7 × 10(21) cm(-3)), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials.

  11. Electric field-induced superconducting transition of insulating FeSe thin film at 35 K

    PubMed Central

    Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-01-01

    It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 1015 cm–2 (the average volume density of 1.7 × 1021 cm–3), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials. PMID:27035956

  12. Probing the dynamics of Andreev states in a coherent Normal/Superconducting ring

    PubMed Central

    Chiodi, F.; Ferrier, M.; Tikhonov, K.; Virtanen, P.; Heikkilä, T. T.; Feigelman, M.; Guéron, S.; Bouchiat, H.

    2011-01-01

    The supercurrent that establishes between two superconductors connected through a normal N mesoscopic link is carried by quasiparticule states localized within the link, the “Andreev bound states (ABS)”. Whereas the dc properties of this supercurrent in SNS junctions are now well understood, its dynamical properties are still an unresolved issue. In this letter we probe this dynamics by inductively coupling an NS ring to a multimode superconducting resonator, thereby implementing both a phase bias and current detection at high frequency. Whereas at very low temperatures we essentially measure the phase derivative of the supercurrent, at higher temperature we find a surprisingly strong frequency dependence in the current response of the ring: the ABS do not follow adiabatically the phase modulation. This experiment also illustrates a new tool to probe the fundamental time scales of phase coherent systems that are decoupled from macroscopic normal contacts and thermal baths. PMID:22355522

  13. Probing the dynamics of Andreev states in a coherent normal/superconducting ring.

    PubMed

    Chiodi, F; Ferrier, M; Tikhonov, K; Virtanen, P; Heikkilä, T T; Feigelman, M; Guéron, S; Bouchiat, H

    2011-01-01

    The supercurrent that establishes between two superconductors connected through a normal N mesoscopic link is carried by quasiparticule states localized within the link, the "Andreev bound states (ABS)". Whereas the dc properties of this supercurrent in SNS junctions are now well understood, its dynamical properties are still an unresolved issue. In this letter we probe this dynamics by inductively coupling an NS ring to a multimode superconducting resonator, thereby implementing both a phase bias and current detection at high frequency. Whereas at very low temperatures we essentially measure the phase derivative of the supercurrent, at higher temperature we find a surprisingly strong frequency dependence in the current response of the ring: the ABS do not follow adiabatically the phase modulation. This experiment also illustrates a new tool to probe the fundamental time scales of phase coherent systems that are decoupled from macroscopic normal contacts and thermal baths.

  14. Ambient-Pressure Bulk Superconductivity Deep in the Magnetic State of CeRhIn5

    SciTech Connect

    Paglione,J.; Ho, P.; Maple, M.; Tanatar, M.; Taillefer, L.; Lee, Y.; Petrovic, C.

    2008-01-01

    Specific heat, magnetic susceptibility and electrical transport measurements were performed at ambient pressure on high-quality single crystal specimens of CeRhIn5 down to ultra-low temperatures. We report signatures of an anomaly observed in all measured quantities consistent with a bulk phase transition to a superconducting state at T{sub c}=110 mK. Occurring far below the onset of antiferromagnetism at T{sub N}=3.8 K, this transition appears to involve a significant portion of the available low-temperature density of electronic states, exhibiting an entropy change in line with that found in other members of the 115 family of superconductors tuned away from quantum criticality.

  15. Superconducting state in the atomic metallic hydrogen just above the pressure of the molecular dissociation

    NASA Astrophysics Data System (ADS)

    Szcze&şacute; niak, R.; Szcze&şacute; niak, D.; Drzazga, E. A.

    2012-11-01

    Above the pressure of ˜500 GPa, the molecular metallic hydrogen gets converted into the atomic phase. The properties of the superconducting state in the metallic hydrogen just above the molecular-atomic phase transition have been examined in the paper (p=539 GPa). The numerical calculations have been conducted in the framework of the Eliashberg formalism. It has been stated that the critical temperature (TC) is equal to 360 K when the Coulomb pseudopotential takes the value of 0.1. In the considered case, TC considerably exceeds the value calculated with the help of the McMillan or Allen-Dynes formula. The remaining thermodynamic parameters significantly diverge from the canonical values predicted by the BCS theory. In particular: RΔ≡2Δ(0)/kBTC=4.95, RC≡ΔC(TC)/CN(TC)=2.78, and RH≡TCCN(TC)/HC2(0)=0.126.

  16. Microscopically derived multi-component Ginzburg-Landau theories for s + is superconducting state

    NASA Astrophysics Data System (ADS)

    Garaud, Julien; Silaev, Mihail; Babaev, Egor

    2017-02-01

    Starting with the generic Ginzburg-Landau expansion from a microscopic N-band model, we focus on the case of a 3-band model which was suggested to be relevant to describe some iron-based superconductors. This can lead to the so-called s + is superconducting state that breaks time-reversal symmetry due to the competition between different pairing channels. Of particular interest in that context, is the case of an interband dominated pairing with repulsion between different bands. For that case we consider in detail the relevant reduced two-component Ginzburg-Landau theory. We provide detailed analysis of the ground state, length scales and topological properties of that model. Prepared for the proceedings of Vortex IX conference in Rhodes (Sept. 2015).

  17. A method of studying the Bogoliubov-de Gennes equations for the superconducting vortex lattice state.

    PubMed

    Han, Qiang

    2010-01-27

    In this paper, we present a method to construct the eigenspace of the tight-binding electrons moving on a 2D square lattice with nearest-neighbor hopping in the presence of a perpendicular uniform magnetic field which imposes (quasi-)periodic boundary conditions for the wavefunctions in the magnetic unit cell. Exact unitary transformations are put forward to correlate the discrete eigenvectors of the 2D electrons with those of the Harper equation. The cyclic tridiagonal matrix associated with the Harper equation is then tridiagonalized by another unitary transformation. The obtained truncated eigenbasis is utilized to expand the Bogoliubov-de Gennes equations for the superconducting vortex lattice state, which shows the merit of our method in studying large-sized systems. To test our method, we have applied our results to study the vortex lattice state of an s-wave superconductor.

  18. Magnetic field induced lattice ground states from holography

    NASA Astrophysics Data System (ADS)

    Bu, Yan-Yan; Erdmenger, Johanna; Shock, Jonathan P.; Strydom, Migael

    2013-03-01

    We study the holographic field theory dual of a probe SU(2) Yang-Mills field in a background (4 + 1)-dimensional asymptotically Anti-de Sitter space. We find a new ground state when a magnetic component of the gauge field is larger than a critical value. The ground state forms a triangular Abrikosov lattice in the spatial directions perpendicular to the magnetic field. The lattice is composed of superconducting vortices induced by the condensation of a charged vector operator. We perform this calculation both at finite temperature and at zero temperature with a hard wall cutoff dual to a confining gauge theory. The study of this state may be of relevance to both holographic condensed matter models as well as to heavy ion physics. The results shown here provide support for the proposal that such a ground state may be found in the QCD vacuum when a large magnetic field is present.

  19. Coherent-state storage and retrieval between superconducting cavities using parametric frequency conversion

    SciTech Connect

    Sirois, A. J.; Castellanos-Beltran, M. A.; DeFeo, M. P.; Ranzani, L.; Lecocq, F.; Simmonds, R. W.; Teufel, J. D.; Aumentado, J.

    2015-04-27

    In superconducting quantum information, machined aluminum superconducting cavities have proven to be a well-controlled, low-dissipation electromagnetic environment for quantum circuits such as qubits. They can possess large internal quality factors, Q{sub int} > 10{sup 8}, and present the possibility of storing quantum information for times far exceeding those of microfabricated circuits. However, in order to be useful as a storage element, these cavities require a fast “read/write” mechanism—in other words, they require tunable coupling between other systems of interest such as other cavity modes and qubits, as well as any associated readout hardware. In this work, we demonstrate these qualities in a simple dual cavity architecture in which a low-Q “readout” mode is parametrically coupled to a high-Q “storage” mode, allowing us to store and retrieve classical information. Specifically, we employ a flux-driven Josephson junction-based coupling scheme to controllably swap coherent states between two cavities, demonstrating full, sequenced control over the coupling rates between modes.

  20. Fast generation of W states of superconducting qubits with multiple Schrödinger dynamics.

    PubMed

    Kang, Yi-Hao; Chen, Ye-Hong; Wu, Qi-Cheng; Huang, Bi-Hua; Song, Jie; Xia, Yan

    2016-11-09

    In this paper, we present a protocol to generate a W state of three superconducting qubits (SQs) by using multiple Schrödinger dynamics. The three SQs are respective embedded in three different coplanar waveguide resonators (CPWRs), which are coupled to a superconducting coupler (SCC) qubit at the center of the setups. With the multiple Schrödinger dynamics, we build a shortcuts to adiabaticity (STA), which greatly accelerates the evolution of the system. The Rabi frequencies of the laser pulses being designed can be expressed by the superpositions of Gaussian functions via the curves fitting, so that they can be realized easily in experiments. What is more, numerical simulation result shows that the protocol is robust against control parameters variations and decoherence mechanisms, such as the dissipations from the CPWRs and the energy relaxation. In addition, the influences of the dephasing are also resisted on account of the accelerating for the dynamics. Thus, the performance of the protocol is much better than that with the conventional adiabatic passage techniques when the dephasing is taken into account. We hope the protocol could be implemented easily in experiments with current technology.

  1. Fast generation of W states of superconducting qubits with multiple Schrödinger dynamics

    PubMed Central

    Kang, Yi-Hao; Chen, Ye-Hong; Wu, Qi-Cheng; Huang, Bi-Hua; Song, Jie; Xia, Yan

    2016-01-01

    In this paper, we present a protocol to generate a W state of three superconducting qubits (SQs) by using multiple Schrödinger dynamics. The three SQs are respective embedded in three different coplanar waveguide resonators (CPWRs), which are coupled to a superconducting coupler (SCC) qubit at the center of the setups. With the multiple Schrödinger dynamics, we build a shortcuts to adiabaticity (STA), which greatly accelerates the evolution of the system. The Rabi frequencies of the laser pulses being designed can be expressed by the superpositions of Gaussian functions via the curves fitting, so that they can be realized easily in experiments. What is more, numerical simulation result shows that the protocol is robust against control parameters variations and decoherence mechanisms, such as the dissipations from the CPWRs and the energy relaxation. In addition, the influences of the dephasing are also resisted on account of the accelerating for the dynamics. Thus, the performance of the protocol is much better than that with the conventional adiabatic passage techniques when the dephasing is taken into account. We hope the protocol could be implemented easily in experiments with current technology. PMID:27827422

  2. Thermodynamic investigations of high-pressure superconducting state in CaLi2 at 45 GPa

    NASA Astrophysics Data System (ADS)

    Szczȩśniak, R.; Szczȩśniak, D.

    2012-05-01

    The thermodynamic properties of the high-pressure superconducting phase in CaLi2 have been studied. A pressure value of 45 GPa has been chosen, at which the critical temperature reaches the maximum (TC=12.9 K). The following results have been obtained. (i) The critical temperature cannot be calculated using the classical analytical formulas (McMillan or Allen-Dynes). (ii) The critical value of the Coulomb pseudopotential is high: μC⋆=0.23. Generalizing the results, the function μC⋆(p) has a high value (μC⋆(p)>0.15) in practically the entire pressure range from 28 to 60 GPa. (iii) The remaining fundamental thermodynamic parameters differ from the Bardeen, Cooper, and Schrieffer (BCS) values. In particular, the zero-temperature energy gap to the critical temperature: R1≡2Δ(0)/kBTC=3.95; the ratio of the specific heat for superconducting (CS) and the normal (CN) state: R2≡(CS(TC)-CN(TC))/CN(TC)=2.01; and the parameter connected with the zero-temperature thermodynamic critical field: R3=TCCN(TC)/HC2(0)=0.158. Finally, it has been shown that the value of the electronic effective mass is high: me⋆/me>2.

  3. 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.

  4. Microwave characterization of normal and superconducting states of MOCVD made YBCO tapes

    NASA Astrophysics Data System (ADS)

    Wosik, Jarek; Krupka, Jerzy; Qin, Kuang; Ketharnath, Dhivya; Galstyan, Eduard; Selvamanickam, Venkat

    2017-03-01

    We have used a microwave, non-contact, non-destructive, dielectric resonator (DR) technique to characterize complex conductivity of different quality YBCO/Hastelloy tapes for the purpose of exploring such a technique as a potential quality control method for fabrication of YBCO tapes. The tapes were deposited at different temperatures on Hastelloy-supported oxide buffer layers using the MOCVD technique. The buffer stack consisted of aluminum oxide (Al2O3), yttrium oxide (Y2O3), and textured ion beam assisted deposition-MgO and LaMnO3 layers. Two dielectric resonators (DRs), the single post DR, consisting of high-permittivity barium zirconium titanate ceramic operating at 13 GHz in quasi-TE01δ mode, and the rod DR, consisting of rutile single crystal disk operating at 9.4 GHz in-TE011 mode, were designed to meet sensitivity requirements for characterization of conductivity of the superconductor at normal and superconducting states, respectively. For calculations of complex conductivity from experimental data of Q-factor and resonant frequency shift, a commercial electromagnetic simulator HFSS, based on finite elements analysis, was used. The theoretical Q-factor and resonant frequency on conductivity functions obtained from full wave numerical simulations of microwave fields were matched with the experimental data to determine conductivity of the YBCO tapes in both normal and superconducting states. In addition, for comparison purposes, 280 nm thick high-quality YBCO epitaxial film deposited on a dielectric substrate was also characterized, including frequency dependence of the complex conductivity. Discussion about feasibility of using DR microwave techniques as a quality control tool via measurements of conductivity versus temperature slope of the YBCO/Hastelloy tape in normal state is included. Also, microwave conductivity values of Hastelloy substrate as a function of temperature are reported.

  5. Efficient Bell state analyzer for time-bin qubits with fast-recovery WSi superconducting single photon detectors.

    PubMed

    Valivarthi, R; Lucio-Martinez, I; Rubenok, A; Chan, P; Marsili, F; Verma, V B; Shaw, M D; Stern, J A; Slater, J A; Oblak, D; Nam, S W; Tittel, W

    2014-10-06

    We experimentally demonstrate a high-efficiency Bell state measurement for time-bin qubits that employs two superconducting nanowire single-photon detectors with short dead-times, allowing projections onto two Bell states, |ψ⁻〉 and |ψ⁺〉. Compared to previous implementations for time-bin qubits, this yields an increase in the efficiency of Bell state analysis by a factor of thirty.

  6. Superconducting properties of the s (±)-wave state: Fe-based superconductors.

    PubMed

    Bang, Yunkyu; Stewart, G R

    2017-02-13

    Although the pairing mechanism of Fe-based superconductors (FeSCs) has not yet been settled with consensus with regard to the pairing symmetry and the superconducting (SC) gap function, the vast majority of experiments support the existence of spin-singlet sign-changing s-wave SC gaps on multi-bands ([Formula: see text]-wave state). This multi-band [Formula: see text]-wave state is a very unique gap state per se and displays numerous unexpected novel SC properties, such as a strong reduction of the coherence peak, non-trivial impurity effects, nodal-gap-like nuclear magnetic resonance signals, various Volovik effects in the specific heat (SH) and thermal conductivity, and anomalous scaling behaviors with a SH jump and condensation energy versus T c, etc. In particular, many of these non-trivial SC properties can easily be mistaken as evidence for a nodal-gap state such as a d-wave gap. In this review, we provide detailed explanations of the theoretical principles for the various non-trivial SC properties of the [Formula: see text]-wave pairing state, and then critically compare the theoretical predictions with experiments on FeSCs. This will provide a pedagogical overview of to what extent we can coherently understand the wide range of different experiments on FeSCs within the [Formula: see text]-wave gap model.

  7. Superconducting properties of the s ±-wave state: Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Bang, Yunkyu; Stewart, G. R.

    2017-03-01

    Although the pairing mechanism of Fe-based superconductors (FeSCs) has not yet been settled with consensus with regard to the pairing symmetry and the superconducting (SC) gap function, the vast majority of experiments support the existence of spin-singlet sign-changing s-wave SC gaps on multi-bands ({{s}+/- } -wave state). This multi-band {{s}+/- } -wave state is a very unique gap state per se and displays numerous unexpected novel SC properties, such as a strong reduction of the coherence peak, non-trivial impurity effects, nodal-gap-like nuclear magnetic resonance signals, various Volovik effects in the specific heat (SH) and thermal conductivity, and anomalous scaling behaviors with a SH jump and condensation energy versus T c, etc. In particular, many of these non-trivial SC properties can easily be mistaken as evidence for a nodal-gap state such as a d-wave gap. In this review, we provide detailed explanations of the theoretical principles for the various non-trivial SC properties of the {{s}+/- } -wave pairing state, and then critically compare the theoretical predictions with experiments on FeSCs. This will provide a pedagogical overview of to what extent we can coherently understand the wide range of different experiments on FeSCs within the {{s}+/- } -wave gap model.

  8. Study of vortex states and dynamics in mesoscopic superconducting samples with MFM

    NASA Astrophysics Data System (ADS)

    Polshyn, Gregory; Naibert, Tyler; Chua, Victor; Budakian, Raffi

    Vortex states in superconducting (SC) structures, their dynamics and ways to manipulate them are topics of great interest. We report a new method of magnetic force microscopy (MFM) that allows the study of vortex states in mesoscopic SC samples. For the case of a SC ring, which is biased to a half-integer flux quantum, the flux modulation through the ring caused by the motion of the magnetic tip drives the ring between two consecutive fluxoid states. The corresponding current switching in the ring produces strong position-dependent forces on the cantilever. In the regime where the frequency of the thermally activated jumps between fluxoid states is close to the frequency of the cantilever, large changes in the cantilever frequency and dissipation are observed. This effect may be understood as a stochastic resonance (SR) process. These changes in the cantilever's mechanical properties are used to ``image'' the barrier energies between fluxoid states. Additionally, SR imaging of the barrier energies are used to study the effect of the locally applied magnetic field from the MFM tip on the barrier heights. We report the results of measurements for Al rings. Further, the same imaging technique can be applied to more sophisticated SC structures such as arrays of Josephson junctions.

  9. First results from solid state neutral particle analyzer on experimental advanced superconducting tokamak

    NASA Astrophysics Data System (ADS)

    Zhang, J. Z.; Zhu, Y. B.; Zhao, J. L.; Wan, B. N.; Li, J. G.; Heidbrink, W. W.

    2016-11-01

    Full function integrated, compact solid state neutral particle analyzers (ssNPA) based on absolute extreme ultraviolet silicon photodiode have been successfully implemented on the experimental advanced superconducting tokamak to measure energetic particle. The ssNPA system has been operated in advanced current mode with fast temporal and spatial resolution capabilities, with both active and passive charge exchange measurements. It is found that the ssNPA flux signals are increased substantially with neutral beam injection (NBI). The horizontal active array responds to modulated NBI beam promptly, while weaker change is presented on passive array. Compared to near-perpendicular beam, near-tangential beam brings more passive ssNPA flux and a broader profile, while no clear difference is observed on active ssNPA flux and its profile. Significantly enhanced intensities on some ssNPA channels have been observed during ion cyclotron resonant heating.

  10. First results from solid state neutral particle analyzer on experimental advanced superconducting tokamak.

    PubMed

    Zhang, J Z; Zhu, Y B; Zhao, J L; Wan, B N; Li, J G; Heidbrink, W W

    2016-11-01

    Full function integrated, compact solid state neutral particle analyzers (ssNPA) based on absolute extreme ultraviolet silicon photodiode have been successfully implemented on the experimental advanced superconducting tokamak to measure energetic particle. The ssNPA system has been operated in advanced current mode with fast temporal and spatial resolution capabilities, with both active and passive charge exchange measurements. It is found that the ssNPA flux signals are increased substantially with neutral beam injection (NBI). The horizontal active array responds to modulated NBI beam promptly, while weaker change is presented on passive array. Compared to near-perpendicular beam, near-tangential beam brings more passive ssNPA flux and a broader profile, while no clear difference is observed on active ssNPA flux and its profile. Significantly enhanced intensities on some ssNPA channels have been observed during ion cyclotron resonant heating.

  11. Superconductive microstrip exhibiting negative differential resistivity

    DOEpatents

    Huebener, R.P.; Gallus, D.E.

    1975-10-28

    A device capable of exhibiting negative differential electrical resistivity over a range of values of current and voltage is formed by vapor- depositing a thin layer of a material capable of exhibiting superconductivity on an insulating substrate, establishing electrical connections at opposite ends of the deposited strip, and cooling the alloy into its superconducting range. The device will exhibit negative differential resistivity when biased in the current- induced resistive state.

  12. Anisotropic superconducting states in a CuO{sub 2} layer

    SciTech Connect

    Dickinson, P.H.

    1993-12-31

    The high-temperature superconductors share CuO{sub 2} layers as structural elements in which the Coulomb repulsion between holes on the Cu site is very large. As a result, the authors choose to model the system with a three-band Hubbard model including the Cu 3d(x{sup 2}{minus}y{sup 2}) and the O 2p(x,y) orbitals. The Coulomb repulsion on the Cu site is treated in the U {r_arrow} {infinity} limit using the slave boson formalism. They expand this model`s Lagrangian in a large N expansion considering terms up to order 1/N. The angle-resolved spectral weight determined from the resulting Green`s functions suggests that within this picture higher order corrections in 1/N are necessary for good agreement with the corresponding angle-resolved photoemission data. They phenomenologically add spin-dependent Heisenberg interactions between neighboring Cu sites and neighboring Cu and O sites. These interactions form the basis of a nonretarded calculation of the superconducting state. For an interaction between neighboring Cu spins only, the lowest energy solution possesses d(x{sup 2}{minus}y{sup 2}) symmetry. The use of a three-band model leads to the possibility of the addition of an interaction between Cu and O spins. The resulting novel {open_quotes}d + idp{close_quotes} superconducting state involves pairing of carriers in Cu orbitals both with themselves and with holes on the O orbitals. This additional pairing removes the node in the d-wave state at T = 0 by an amount which depends on the Cu-O coupling parameter; however, the mixed symmetry state occurs only for a narrow range of coupling parameters. The angle-resolved photo-emission and tunneling results are calculated and compared to experimental findings. As a function of decreasing temperature, symmetry arguments require transition to a d-wave state before transition to the d + idp state. A BCS analysis is performed on a tight-binding model.

  13. Large Dispersive Shift of Cavity Resonance Induced by a Superconducting Flux Qubit in the Straddling Regime

    NASA Astrophysics Data System (ADS)

    Inomata, Kunihiro; Yamamoto, Tsuyoshi; Billangeon, Pierre-M.; Lin, Zhirong; Nakamura, Yasunobu; Tsai, Jaw-Shen; Koshino, Kazuki

    2013-03-01

    We demonstrate enhancement of the dispersive frequency shift in a coplanar waveguide resonator induced by a capacitively coupled superconducting flux qubit in the straddling regime. The magnitude of the observed shift, 80 MHz for the qubit-resonator detuning of 5 GHz, is quantitatively explained by the generalized Rabi model which takes into account the contribution of the qubit higher energy levels. By applying the enhanced dispersive shift to the qubit readout, we achieved 90 % contrast of the Rabi oscillations which is mainly limited by the energy relaxation of the qubit. We also discuss the qubit readout using a Josephson parametric amplifier. This work was supported by the MEXT Kakenhi ``Quantum Cybernetics'', the JSPS through its FIRST Program, and the NICT Commissioned Research.

  14. Supercurrent-induced skyrmion dynamics and tunable Weyl points in chiral magnet with superconductivity

    NASA Astrophysics Data System (ADS)

    Takashima, Rina; Fujimoto, Satoshi

    2016-12-01

    Recent studies show superconductivity provides new perspectives on spintronics. We study a heterostructure composed of an s -wave superconductor and a cubic chiral magnet that stabilizes a topological spin texture, a skyrmion. We propose a supercurrent-induced spin torque, which originates from the spin-orbit coupling, and we show that the spin torque can drive a skyrmion in an efficient way that reduces Joule heating. We also study the band structure of Bogoliubov quasiparticles and show the existence of Weyl points, whose positions can be controlled by the magnetization. This results in an effective magnetic field acting on the Weyl quasiparticles in the presence spin textures. Furthermore, the tilt of the Weyl cones can also be tuned by the strength of the spin-orbit coupling, and we propose a possible realization of type-II Weyl points.

  15. Thermoelectric instability induced by single pulses and alternating currents in second-generation superconducting tapes

    NASA Astrophysics Data System (ADS)

    Degtyarenko, P. N.; Dul'kin, I. N.; Fisher, L. M.; Kalinov, A. V.; Voloshin, I. F.; Yampol'skii, V. A.

    2011-02-01

    We have studied current flow instabilities in a second-generation superconducting tapes and the transition of the tapes into the resistive state. Contrary to the usual quasisteady instability regimes, here we consider the adiabatic case in which the sample is heated rapidly. Two kinds of measurements of the current-voltage characteristics (CVC) have been made, specifically, with excitation of the tape by a single sinusoidal current pulse I (t)=I0sin(ωt) at different amplitudes I0 and by a continuous ac current. The main results were obtained for current amplitudes I0 exceeding the critical current Ic. We find that the dynamic CVC are essentially reversible for low amplitudes, whereas they become irreversible and acquire an N-shape for higher current amplitudes. The dynamic CVC change radically if the dissipated energy attains a threshold value Wth roughly equal to 5mJ/cm for our tapes. When this energy is reached, the tape undergoes a transition to the resistive state owing to formation of normal domains. The development of the instability with steady ac currents was studied at relatively small amplitudes such that the energy dissipated per half cycle is much lower than Wth. Even in this case, a tape undergoes a transition to the resistive state because of energy accumulation (heat pumping). With this pumping, the transition takes place after a definite number of ac cycles, when the total accumulated energy reaches the same threshold value Wth. The specific features of the dynamic CVC are interpreted qualitatively, with the appearance of resistive domains taken into account. Estimates based on the CVC agree well with our experimental data. These results can be useful in the design of superconducting fault current limiters.

  16. High-temperature superconductivity in space-charge regions of lanthanum cuprate induced by two-dimensional doping.

    PubMed

    Baiutti, F; Logvenov, G; Gregori, G; Cristiani, G; Wang, Y; Sigle, W; van Aken, P A; Maier, J

    2015-10-20

    The exploitation of interface effects turned out to be a powerful tool for generating exciting material properties. Such properties include magnetism, electronic and ionic transport and even superconductivity. Here, instead of using conventional homogeneous doping to enhance the hole concentration in lanthanum cuprate and achieve superconductivity, we replace single LaO planes with SrO dopant planes using atomic-layer-by-layer molecular beam epitaxy (two-dimensional doping). Electron spectroscopy and microscopy, conductivity measurements and zinc tomography reveal such negatively charged interfaces to induce layer-dependent superconductivity (Tc up to 35 K) in the space-charge zone at the side of the planes facing the substrate, where the strontium (Sr) profile is abrupt. Owing to the growth conditions, the other side exhibits instead a Sr redistribution resulting in superconductivity due to conventional doping. The present study represents a successful example of two-dimensional doping of superconducting oxide systems and demonstrates its power in this field.

  17. High-temperature superconductivity in space-charge regions of lanthanum cuprate induced by two-dimensional doping

    PubMed Central

    Baiutti, F.; Logvenov, G.; Gregori, G.; Cristiani, G.; Wang, Y.; Sigle, W.; van Aken, P. A.; Maier, J.

    2015-01-01

    The exploitation of interface effects turned out to be a powerful tool for generating exciting material properties. Such properties include magnetism, electronic and ionic transport and even superconductivity. Here, instead of using conventional homogeneous doping to enhance the hole concentration in lanthanum cuprate and achieve superconductivity, we replace single LaO planes with SrO dopant planes using atomic-layer-by-layer molecular beam epitaxy (two-dimensional doping). Electron spectroscopy and microscopy, conductivity measurements and zinc tomography reveal such negatively charged interfaces to induce layer-dependent superconductivity (Tc up to 35 K) in the space-charge zone at the side of the planes facing the substrate, where the strontium (Sr) profile is abrupt. Owing to the growth conditions, the other side exhibits instead a Sr redistribution resulting in superconductivity due to conventional doping. The present study represents a successful example of two-dimensional doping of superconducting oxide systems and demonstrates its power in this field. PMID:26481902

  18. Anomalous Eu valence state and superconductivity in undoped Eu3Bi2S4F4.

    PubMed

    Zhai, Hui-Fei; Zhang, Pan; Wu, Si-Qi; He, Chao-Yang; Tang, Zhang-Tu; Jiang, Hao; Sun, Yun-Lei; Bao, Jin-Ke; Nowik, Israel; Felner, Israel; Zeng, Yue-Wu; Li, Yu-Ke; Xu, Xiao-Feng; Tao, Qian; Xu, Zhu-An; Cao, Guang-Han

    2014-10-29

    We have synthesized a novel europium bismuth sulfofluoride, Eu3Bi2S4F4, by solid-state reactions in sealed evacuated quartz ampules. The compound crystallizes in a tetragonal lattice (space group I4/mmm, a = 4.0771(1) Å, c = 32.4330(6) Å, and Z = 2), in which CaF2-type Eu3F4 layers and NaCl-like BiS2 bilayers stack alternately along the crystallographic c axis. There are two crystallographically distinct Eu sites, Eu(1) and Eu(2) at the Wyckoff positions 4e and 2a, respectively. Our bond valence sum calculation, based on the refined structural data, indicates that Eu(1) is essentially divalent, while Eu(2) has an average valence of ∼ +2.64(5). This anomalous Eu valence state is further confirmed and supported, respectively, by Mössbauer and magnetization measurements. The Eu(3+) components donate electrons into the conduction bands that are mainly composed of Bi 6px and 6py states. Consequently, the material itself shows metallic conduction and superconducts at 1.5 K without extrinsic chemical doping.

  19. Gluon effects on the equation of state of color superconducting strange stars

    NASA Astrophysics Data System (ADS)

    Ferrer, E. J.; de la Incera, V.; Paulucci, L.

    2015-08-01

    Compact astrophysical objects are a window for the study of strongly interacting nuclear matter given the conditions in their interiors, which are not reproduced in a laboratory environment. Much has been debated about their composition with possibilities ranging from a simple mixture of mostly protons and neutrons to deconfined quark matter. Recent observations on the mass of two pulsars, PSR J 1614 -2230 and PSR J 0348 +0432 , have posed a great restriction on their composition, since the equation of state must be hard enough to support masses of about at least two solar masses. The onset of quarks tends to soften the equation of state, but it can get substantially stiffer since in the high-dense medium a repulsive vector interaction channel is opened. Nevertheless, we show that once gluon effects are considered, the equation of state of strange stars formed by quark matter in the color-flavor-locked (CFL) phase of color superconductivity becomes softer decreasing the maximum stellar mass that can be reached. This may indicate that strange stars made entirely of CFL matter can only be favored if other interactions, as the one corresponding to the vector channel, are taken into consideration and are large enough.

  20. New Steady-State Quiescent High-Confinement Plasma in an Experimental Advanced Superconducting Tokamak

    NASA Astrophysics Data System (ADS)

    Hu, J. S.; Sun, Z.; Guo, H. Y.; Li, J. G.; Wan, B. N.; Wang, H. Q.; Ding, S. Y.; Xu, G. S.; Liang, Y. F.; Mansfield, D. K.; Maingi, R.; Zou, X. L.; Wang, L.; Ren, J.; Zuo, G. Z.; Zhang, L.; Duan, Y. M.; Shi, T. H.; Hu, L. Q.; East Team

    2015-02-01

    A critical challenge facing the basic long-pulse high-confinement operation scenario (H mode) for ITER is to control a magnetohydrodynamic (MHD) instability, known as the edge localized mode (ELM), which leads to cyclical high peak heat and particle fluxes at the plasma facing components. A breakthrough is made in the Experimental Advanced Superconducting Tokamak in achieving a new steady-state H mode without the presence of ELMs for a duration exceeding hundreds of energy confinement times, by using a novel technique of continuous real-time injection of a lithium (Li) aerosol into the edge plasma. The steady-state ELM-free H mode is accompanied by a strong edge coherent MHD mode (ECM) at a frequency of 35-40 kHz with a poloidal wavelength of 10.2 cm in the ion diamagnetic drift direction, providing continuous heat and particle exhaust, thus preventing the transient heat deposition on plasma facing components and impurity accumulation in the confined plasma. It is truly remarkable that Li injection appears to promote the growth of the ECM, owing to the increase in Li concentration and hence collisionality at the edge, as predicted by GYRO simulations. This new steady-state ELM-free H -mode regime, enabled by real-time Li injection, may open a new avenue for next-step fusion development.

  1. Preparation of Schrödinger cat states of a cavity field via coupling to a superconducting charge qubit

    NASA Astrophysics Data System (ADS)

    Freitas, Dagoberto S.; Nemes, M. C.

    2014-05-01

    We extend the approach in Ref. 5 [Y.-X. Liu, L. F. Wei and F. Nori, Phys. Rev. A 71 (2005) 063820] for preparing superposition states of a cavity field interacting with a superconducting charge qubit. We study effects of the nonlinearity on the creation of such states. We show that the main contribution of nonlinear effects is to shorten the time necessary to build the superposition.

  2. Clarification as to why alcoholic beverages have the ability to induce superconductivity in Fe1+dTe1-xSx

    NASA Astrophysics Data System (ADS)

    Deguchi, K.; Sato, D.; Sugimoto, M.; Hara, H.; Kawasaki, Y.; Demura, S.; Watanabe, T.; Denholme, S. J.; Okazaki, H.; Ozaki, T.; Yamaguchi, T.; Takeya, H.; Soga, T.; Tomita, M.; Takano, Y.

    2012-08-01

    To elucidate the mechanism as to why alcoholic beverages can induce superconductivity in Fe1+dTe1-xSx samples, we performed component analysis and found that a weak acid such as an organic acid has the ability to induce superconductivity. Inductively coupled plasma spectroscopy was performed on weak acid solutions post-annealing. We found that the mechanism of inducement of superconductivity in Fe1+dTe1-xSx is the deintercalation of excess Fe from the interlayer sites.

  3. Superconducting and normal-state properties of APd2As2 (A = Ca, Sr, Ba) single crystals

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Kim, H.; Tanatar, M. A.; Prozorov, R.; Johnston, D. C.

    2013-06-01

    The synthesis and crystallography, magnetic susceptibility χ, magnetization M, specific heat Cp, in-plane electrical resistivity ρ, and in-plane magnetic penetration depth measurements are reported for single crystals of APd2As2 (A = Ca, Sr, Ba) versus temperature T and magnetic field H. The crystals were grown using PdAs self-flux. CaPd2As2 and SrPd2As2 crystallize in a collapsed body-centered tetragonal ThCr2Si2-type structure (I4/mmm), whereas BaPd2As2 crystallizes in the primitive tetragonal CeMg2Si2-type structure (P4/mmm), in agreement with literature data. The ρ(T) data exhibit metallic behavior for all three compounds. Bulk superconductivity is reported for CaPd2As2 and SrPd2As2 below Tc=1.27 and 0.92 K, respectively, whereas only a trace of superconductivity is found in BaPd2As2. No other phase transitions were observed. The χ(T) and M(H) data reveal anisotropic diamagnetism in the normal state, with χc>χab for CaPd2As2 and BaPd2As2, and χc<χab for SrPd2As2. The normal and superconducting state data indicate that CaPd2As2 and SrPd2As2 are conventional type-II nodeless s-wave electron-phonon superconductors. The electronic superconducting state heat capacity data for CaPd2As2, which has an extremely sharp heat capacity jump at Tc, are analyzed using our recent elaboration of the α-model of the BCS theory of superconductivity, which indicates that the s-wave gap in this compound is anisotropic in momentum space.

  4. Controllable generation of two-mode-entangled states in two-resonator circuit QED with a single gap-tunable superconducting qubit

    NASA Astrophysics Data System (ADS)

    Ma, Sheng-Li; Li, Zhen; Fang, Ai-Ping; Li, Peng-Bo; Gao, Shao-Yan; Li, Fu-Li

    2014-12-01

    We study controllable generation of two-mode-entangled states in a circuit QED setup, which consists of two spatially separated superconducting transmission line resonators and a single gap-tunable superconducting qubit. Two sharp coupling sidebands are induced when the artificial atom is suitably driven by a bichromatic microwave field. The two resonators can have squeezing-type interactions with the qubit via the coupling sidebands. If the two resonators are not degenerate, we show that the two resonators can be cooled down into the two-mode squeezed vacuum via dissipation of the qubit. The generation of the two-mode squeezed state is based on a dissipative state-engineering process, which explores the energy relaxation of the qubit as a resource. Moreover, the scheme does not need both the specific preparation of the initial state and the designed special dynamical process of the system. If the resonators are degenerate, we show that entangled coherent states of the resonators can be generated by use of the unitary dynamical evolution process of the system and the state-projection measurement. Moreover, macro entangled coherent states of the resonators with huge photons can in principle be created if the resonators and the qubit have sufficiently long lifetimes. The present scheme has two remarkable features: (1) only a single qubit is used in the generation of the two-mode squeezed state; and (2) the ultrastrong coupling condition and initializing the resonators in coherent states are not required. These make the present scheme more simple and feasible in experimental implementation.

  5. Proximity-induced high-temperature superconductivity in the topological insulators Bi₂Se₃ and Bi₂Te₃.

    PubMed

    Zareapour, Parisa; Hayat, Alex; Zhao, Shu Yang F; Kreshchuk, Michael; Jain, Achint; Kwok, Daniel C; Lee, Nara; Cheong, Sang-Wook; Xu, Zhijun; Yang, Alina; Gu, G D; Jia, Shuang; Cava, Robert J; Burch, Kenneth S

    2012-01-01

    Interest in the superconducting proximity effect has been reinvigorated recently by novel optoelectronic applications as well as by the possible emergence of the elusive Majorana fermion at the interface between topological insulators and superconductors. Here we produce high-temperature superconductivity in Bi(2)Se(3) and Bi(2)Te(3) via proximity to Bi(2)Sr(2)CaCu(2)O(8+δ), to access higher temperature and energy scales for this phenomenon. This was achieved by a new mechanical bonding technique that we developed, enabling the fabrication of high-quality junctions between materials, unobtainable by conventional approaches. We observe proximity-induced superconductivity in Bi(2)Se(3) and Bi(2)Te(3) persisting up to at least 80 K-a temperature an order of magnitude higher than any previous observations. Moreover, the induced superconducting gap in our devices reaches values of 10 mV, significantly enhancing the relevant energy scales. Our results open new directions for fundamental studies in condensed matter physics and enable a wide range of applications in spintronics and quantum computing.

  6. Superconductivity in anti-post-Perovskite vanadium compounds.

    PubMed

    Wang, Bosen; Ohgushi, Kenya

    2013-11-29

    Superconductivity, which is a quantum state induced by spontaneous gauge symmetry breaking, frequently emerges in low-dimensional materials. Hence, low dimensionality has long been considered as necessary to achieve high superconducting transition temperatures (TC). The recently discovered post-perovskite (ppv) MgSiO3, which constitutes the Earth's lowermost mantle (D" layer), has attracted significant research interest due to its importance in geoscience. The ppv structure has a peculiar two-dimensional character and is expected to be a good platform for superconductivity. However, hereunto, no superconductivity has been observed in isostructural materials, despite extensive investigation. Here, we report the discovery of superconductivity with a maximum TC of 5.6 K in V3PnNx (Pn = P, As) phases with the anti-ppv structure, where the anion and cation positions are reversed with respect to the ppv structure. This discovery stimulates further explorations of new superconducting materials with ppv and anti-ppv structures.

  7. Electric-field-induced superconductivity in electrochemically etched ultrathin FeSe films on SrTiO3 and MgO

    NASA Astrophysics Data System (ADS)

    Shiogai, J.; Ito, Y.; Mitsuhashi, T.; Nojima, T.; Tsukazaki, A.

    2016-01-01

    Among the recently discovered iron-based superconductors, ultrathin films of FeSe grown on SrTiO3 substrates have uniquely evolved into a high-transition-temperature (Tc) superconducting material. The mechanisms for the high-Tc superconductivity are under debate, with the superconducting gap mainly characterized with in situ analysis for FeSe films grown by molecular beam epitaxy. Here, we investigate the high-Tc superconductivity in ultrathin FeSe using an alternative top-down electrochemical etching technique in a three-terminal transistor configuration. In addition to the high-temperature superconductivity in FeSe on SrTiO3, the electrochemically etched ultrathin FeSe transistor on MgO also exhibits superconductivity around 40 K, implying that the application of an electric field effectively contributes to the high-Tc superconductivity in ultrathin FeSe regardless of substrate material. Moreover, the observable critical thickness for the high-Tc superconductivity is expanded up to 10 unit cells under an applied electric field and the insulator-superconductor transition is electrostatically controlled. The present demonstration implies that the modification of charge imbalance of holes and electrons by the electric-field effect plays a crucial role in inducing high-Tc superconductivity in FeSe-based electric double-layer transistors.

  8. Tartaric acid in red wine as one of the key factors to induce superconductivity in FeTe0.8S0.2

    NASA Astrophysics Data System (ADS)

    Deguchi, Keita; Okuda, Tohru; Hara, Hiroshi; Demura, Satoshi; Watanabe, Tohru; Okazaki, Hiroyuki; Fujioka, Masaya; Denholme, Saleem James; Ozaki, Toshinori; Yamaguchi, Takahide; Takeya, Hiroyuki; Saito, Fumie; Hisamoto, Masashi; Takano, Yoshihiko

    2013-04-01

    We investigated the key factor of superconductivity in FeTe1-xSx induced by alcoholic beverages. To understand the reason why red wine shows larger shielding volume fraction than the other alcoholic beverages, the red wine dependence of superconductivity was performed. All the samples heated in red wine made from different grapes shows large shielding volume fraction compared with the samples heated in water and other alcoholic beverages. The shielding volume fraction of the red wine samples is proportional to the concentration of tartaric acid. We found that tartaric acid is one of the key factors to induce superconductivity in FeTe1-xSx.

  9. Local density of states and its mesoscopic fluctuations near the transition to a superconducting state in disordered systems

    NASA Astrophysics Data System (ADS)

    Burmistrov, I. S.; Gornyi, I. V.; Mirlin, A. D.

    2016-05-01

    We develop a theory of the local density of states (LDOS) of disordered superconductors, employing the nonlinear sigma-model formalism and the renormalization-group framework. The theory takes into account the interplay of disorder and interaction couplings in all channels, treating the systems with short-range and Coulomb interactions on equal footing. We explore two-dimensional systems that would be Anderson insulators in the absence of interaction and two- or three-dimensional systems that undergo an Anderson transition in the absence of interaction. We evaluate both the average tunneling density of states and its mesoscopic fluctuations which are related to the LDOS multifractality in normal disordered systems. The obtained average LDOS shows a pronounced depletion around the Fermi energy, both in the metallic phase (i.e., above the superconducting critical temperature Tc) and in the insulating phase near the superconductor-insulator transition (SIT). The fluctuations of the LDOS are found to be particularly strong for the case of short-range interactions, especially, in the regime when Tc is enhanced by Anderson localization. On the other hand, the long-range Coulomb repulsion reduces the mesoscopic LDOS fluctuations. However, also in a model with Coulomb interaction, the fluctuations become strong when the systems approach the SIT.

  10. 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.

  11. PREFACE: Superconducting materials Superconducting materials

    NASA Astrophysics Data System (ADS)

    Charfi Kaddour, Samia; Singleton, John; Haddad, Sonia

    2011-11-01

    and by invited authors selected by the editor. We are grateful to IUPAP, ICTP and the European Office of Aerospace Research and Development, Air Force Office of Scientific Research, United States Air Force Laboratory. We would like to acknowledge the authors for their careful work, and finally we thank Dr L Smith the publisher of Journal of Physics: Condensed Matter for her patience and help. Superconducting materials contents Raman spectrum in the pseudogap phase of the underdoped cuprates: effect of phase coherence and the signature of the KT-type superconducting transitionTao Li and Haijun Liao Pressure effects on Dirac fermions in α-(BEDT-TTF)2I3Takahiro Himura, Takao Morinari and Takami Tohyama Effect of Zn doping in hole-type 1111 phase (Pr, Sr)FeAsOXiao Lin, Chenyi Shen, Chen Lv, Jianjian Miao, Hao Tan, Guanghan Cao and Zhu-An Xu Superconductivity and ferromagnetism in EuFe2(As1 - xPx)2*Guanghan Cao, Shenggao Xu, Zhi Ren, Shuai Jiang, Chunmu Feng and Zhu'an Xu OInhomogeneous superconductivity in organic conductors: the role of disorder and magnetic fieldS Haddad, S Charfi-Kaddour and J-P Pouget

  12. Nonequilibrium superconducting states with temporal periodic structures under high quasiparticle injection

    SciTech Connect

    CHEN Shi-gang; CHEN Xiao-lan; WANG You-qin

    1984-07-01

    Based on the Scalapino-Huberman ..mu..* model, the possibility of temporally oscillating structures appearing in a superconducting film under high quasiparticle injection is discussed. The range of parameters in which these structures may occur is also given.

  13. Gapless helical superconductivity on the surface of a three-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Ozfidan, Isil; Han, Jinsen; Maciejko, Joseph

    2016-12-01

    Recent angle-resolved photoemission experiments have observed a proximity-induced superconducting gap in the helical surface states of a thin film of the three-dimensional topological insulator Bi2Se3 grown on a superconducting NbSe2 substrate. The superconducting coherence peaks in the electronic density of states are strongly suppressed when the topological insulator is doped with magnetic Mn impurities, which was interpreted as the complete destruction of helical superconductivity in the topological surface states. Motivated by these experiments, we explore a different possibility: gapless helical superconductivity, where a gapless electronic density of states coexists with a nonzero helical superconducting order parameter. We study a model of superconducting Dirac fermions coupled to random magnetic impurities within the Abrikosov-Gor'kov framework, and find finite regions of gapless helical superconductivity in the phase diagram of the system for both proximity-induced and intrinsic superconductivity. For the latter, we derive universal rates of suppression of the superconducting transition temperature due to magnetic scattering and, for a Fermi level at the Dirac point, a universal rate of increase of the quantum critical attraction strength.

  14. Oxide-based platform for reconfigurable superconducting nanoelectronics

    NASA Astrophysics Data System (ADS)

    Veazey, Joshua P.; Cheng, Guanglei; Irvin, Patrick; Cen, Cheng; Bogorin, Daniela F.; Bi, Feng; Huang, Mengchen; Bark, Chung-Wung; Ryu, Sangwoo; Cho, Kwang-Hwan; Eom, Chang-Beom; Levy, Jeremy

    2013-09-01

    We report quasi-1D superconductivity at the interface of LaAlO3 and SrTiO3. The material system and nanostructure fabrication method supply a new platform for superconducting nanoelectronics. Nanostructures having line widths w ˜ 10 nm are formed from the parent two-dimensional electron liquid using conductive atomic force microscope lithography. Nanowire cross-sections are small compared to the superconducting coherence length in LaAlO3/SrTiO3, placing them in the quasi-1D regime. Broad superconducting transitions versus temperature and finite resistances in the superconducting state well below Tc ≈ 200 mK are observed, suggesting the presence of fluctuation- and heating-induced resistance. The superconducting resistances and V-I characteristics are tunable through the use of a back gate. Four-terminal resistances in the superconducting state show an unusual dependence on the current path, varying by as much as an order of magnitude. This new technology, i.e., the ability to ‘write’ gate-tunable superconducting nanostructures on an insulating LaAlO3/SrTiO3 ‘canvas’, opens possibilities for the development of new families of reconfigurable superconducting nanoelectronics.

  15. General Conditions for Proximity-Induced Odd-Frequency Superconductivity in Two-Dimensional Electronic Systems.

    PubMed

    Triola, Christopher; Badiane, Driss M; Balatsky, Alexander V; Rossi, E

    2016-06-24

    We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s-wave superconductor with Rashba spin-orbit coupling exhibits odd-frequency superconducting pairing. Our results allow the identification of a new class of systems among van der Waals heterostructures in which odd-frequency superconductivity should be present.

  16. Control of magnetic, nonmagnetic, and superconducting states in annealed Ca(Fe1–xCox)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-Tanneal) 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 is revealed.more » 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 Tanneal 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

  17. Field-dependent critical state of high-Tc superconducting strip simultaneously exposed to transport current and perpendicular magnetic field

    SciTech Connect

    Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe

    2013-12-15

    We present an exact analytical approach for arbitrary field-dependent critical state of high-T{sub c} superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the I{sub a}-B{sub a} plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.

  18. Hard Superconducting Gap in InSb Nanowires.

    PubMed

    Gül, Önder; Zhang, Hao; de Vries, Folkert K; van Veen, Jasper; Zuo, Kun; Mourik, Vincent; Conesa-Boj, Sonia; Nowak, Michał P; van Woerkom, David J; Quintero-Pérez, Marina; Cassidy, Maja C; Geresdi, Attila; Koelling, Sebastian; Car, Diana; Plissard, Sébastien R; Bakkers, Erik P A M; Kouwenhoven, Leo P

    2017-04-12

    Topological superconductivity is a state of matter that can host Majorana modes, the building blocks of a topological quantum computer. Many experimental platforms predicted to show such a topological state rely on proximity-induced superconductivity. However, accessing the topological properties requires an induced hard superconducting gap, which is challenging to achieve for most material systems. We have systematically studied how the interface between an InSb semiconductor nanowire and a NbTiN superconductor affects the induced superconducting properties. Step by step, we improve the homogeneity of the interface while ensuring a barrier-free electrical contact to the superconductor and obtain a hard gap in the InSb nanowire. The magnetic field stability of NbTiN allows the InSb nanowire to maintain a hard gap and a supercurrent in the presence of magnetic fields (∼0.5 T), a requirement for topological superconductivity in one-dimensional systems. Our study provides a guideline to induce superconductivity in various experimental platforms such as semiconductor nanowires, two-dimensional electron gases, and topological insulators and holds relevance for topological superconductivity and quantum computation.

  19. Influence of disorder on the local density of states in high- T(c) superconducting thin films

    PubMed

    Cren; Roditchev; Sacks; Klein; Moussy; Deville-Cavellin; Lagues

    2000-01-03

    Using a low temperature scanning tunneling microscope in the spectroscopic mode, we find that the disorder in a Bi(2)Sr(2)CaCu(2)O(8+delta) thin film modifies dramatically the quasiparticle local density of states. Small, but well-defined superconducting regions, coexisting with dominating semiconducting areas, show well-pronounced gap structures, similar to those observed previously in high-quality single crystals. Surprisingly, between these two regions, the detailed shape of the quasiparticle spectrum is virtually identical to the pseudogap previously observed at temperatures T>T(c), or in the vortex core, at 4.2 K. Thus, the role of the disorder in destroying the superconducting phase is comparable to that of the magnetic field or thermal fluctuations.

  20. Momentum dependence of the superconducting gap and in-gap states in MgB2 multiband superconductor

    DOE PAGES

    Mou, Daixiang; Jiang, Rui; Taufour, Valentin; ...

    2015-06-29

    We use tunable laser-based angle-resolved photoemission spectroscopy to study the electronic structure of the multiband superconductor MgB2. These results form the baseline for detailed studies of superconductivity in multiband systems. We find that the magnitude of the superconducting gap on both σ bands follows a BCS-like variation with temperature with Δ0 ~ 7meV. Furthermore, the value of the gap is isotropic within experimental uncertainty and in agreement with a pure s-wave pairing symmetry. We observe in-gap states confined to kF of the σ band that occur at some locations of the sample surface. As a result, the energy of thismore » excitation, ~ 3 meV, was found to be somewhat larger than the previously reported gap on π Fermi sheet and therefore we cannot exclude the possibility of interband scattering as its origin.« less

  1. Probing the density of states of two-level tunneling systems in silicon oxide films using superconducting lumped element resonators

    SciTech Connect

    Skacel, S. T.; Kaiser, Ch.; Wuensch, S.; Siegel, M.; Rotzinger, H.; Lukashenko, A.; Jerger, M.; Weiss, G.; Ustinov, A. V.

    2015-01-12

    We have investigated dielectric losses in amorphous silicon oxide (a-SiO) thin films under operating conditions of superconducting qubits (mK temperatures and low microwave powers). For this purpose, we have developed a broadband measurement setup employing multiplexed lumped element resonators using a broadband power combiner and a low-noise amplifier. The measured temperature and power dependences of the dielectric losses are in good agreement with those predicted for atomic two-level tunneling systems (TLS). By measuring the losses at different frequencies, we found that the TLS density of states is energy dependent. This had not been seen previously in loss measurements. These results contribute to a better understanding of decoherence effects in superconducting qubits and suggest a possibility to minimize TLS-related decoherence by reducing the qubit operation frequency.

  2. Quantum state transfer and controlled-phase gate on one-dimensional superconducting resonators assisted by a quantum bus

    PubMed Central

    Hua, Ming; Tao, Ming-Jie; Deng, Fu-Guo

    2016-01-01

    We propose a quantum processor for the scalable quantum computation on microwave photons in distant one-dimensional superconducting resonators. It is composed of a common resonator R acting as a quantum bus and some distant resonators rj coupled to the bus in different positions assisted by superconducting quantum interferometer devices (SQUID), different from previous processors. R is coupled to one transmon qutrit, and the coupling strengths between rj and R can be fully tuned by the external flux through the SQUID. To show the processor can be used to achieve universal quantum computation effectively, we present a scheme to complete the high-fidelity quantum state transfer between two distant microwave-photon resonators and another one for the high-fidelity controlled-phase gate on them. By using the technique for catching and releasing the microwave photons from resonators, our processor may play an important role in quantum communication as well. PMID:26907366

  3. Pressure-induced metallization of dense (H₂S)₂H₂ with high-Tc superconductivity.

    PubMed

    Duan, Defang; Liu, Yunxian; Tian, Fubo; Li, Da; Huang, Xiaoli; Zhao, Zhonglong; Yu, Hongyu; Liu, Bingbing; Tian, Wenjing; Cui, Tian

    2014-11-10

    The high pressure structures, metallization, and superconductivity of recently synthesized H2-containing compounds (H2S)2H2 are elucidated by ab initio calculations. The ordered crystal structure with P1 symmetry is determined, supported by the good agreement between theoretical and experimental X-ray diffraction data, equation of states, and Raman spectra. The Cccm structure is favorable with partial hydrogen bond symmetrization above 37 GPa. Upon further compression, H2 molecules disappear and two intriguing metallic structures with R3m and Im-3m symmetries are reconstructive above 111 and 180 GPa, respectively. The predicted metallization pressure is 111 GPa, which is approximately one-third of the currently suggested metallization pressure of bulk molecular hydrogen. Application of the Allen-Dynes-modified McMillan equation for the Im-3m structure yields high Tc values of 191 K to 204 K at 200 GPa, which is among the highest values reported for H2-rich van der Waals compounds and MH3 type hydride thus far.

  4. Superconducting optical modulator

    NASA Astrophysics Data System (ADS)

    Bunt, Patricia S.; Ference, Thomas G.; Puzey, Kenneth A.; Tanner, David B.; Tache, Nacira; Varhue, Walter J.

    2000-12-01

    An optical modulator based on the physical properties of high temperature superconductors has been fabricated and tested. The modulator was constructed form a film of Yttrium Barium Copper Oxide (YBCO) grown on undoped silicon with a buffer layer of Yttria Stabilized Zirconia. Standard lithographic procedures were used to pattern the superconducting film into a micro bridge. Optical modulation was achieved by passing IR light through the composite structure normal to the micro bridge and switching the superconducting film in the bridge region between the superconducting and non-superconducting states. In the superconducting state, IR light reflects from the superconducting film surface. When a critical current is passed through the micro bridge, it causes the film in this region to switch to the non-superconducting state allowing IR light to pass through it. Superconducting materials have the potential to switch between these two states at speeds up to 1 picosecond using electrical current. Presently, fiber optic transmission capacity is limited by the rate at which optical data can be modulated. The superconducting modulator, when combined with other components, may have the potential to increase the transmission capacity of fiber optic lines.

  5. Pressure-induced superconductivity in Ba0.5Sr0.5Fe2As2.

    PubMed

    Tsoi, Georgiy M; Malone, Walter; Uhoya, Walter; Mitchell, Jonathan E; Vohra, Yogesh K; Wenger, Lowell E; Sefat, Athena S; Weir, S T

    2012-12-12

    High-pressure electrical resistance measurements have been performed on single crystal Ba(0.5)Sr(0.5)Fe(2)As(2) platelets to pressures of 16 GPa and temperatures down to 10 K using designer diamond anvils under quasi-hydrostatic conditions with an insulating steatite pressure medium. The resistance measurements show evidence of pressure-induced superconductivity with an onset transition temperature at ∼31 K and zero resistance at ∼22 K for a pressure of 3.3 GPa. The transition temperature decreases gradually with increasing pressure before completely disappearing for pressures above 12 GPa. The present results provide experimental evidence that a solid solution of two 122-type materials, i.e., Ba(1-x)Sr(x)Fe(2)As(2) (0 < x < 1), can also exhibit superconductivity under high pressure.

  6. Josephson effect and nonequilibrium superconductivity in superconducting tunnel structures

    NASA Astrophysics Data System (ADS)

    Rudenko, E. M.

    2012-04-01

    Nonequilibrium superconductivity induced by tunnel current injection of quasiparticles is studied. It is found that an instability in the form of a negative voltage jump in the oscillator current-voltage characteristic (CVC), which leads to an inhomogeneous state, as well as the spatial structure of the inhomogeneous state are very sensitive to low magnetic fields. The shape of the CVC of low-resistance tunnel junctions for bias voltages V ≈ 2Δ/e depends strongly on the junction dimensions and barrier transparency. These results are interpreted in terms of Josephson vortices (fluxons) in a tunnel oscillator. Studies of the nonequilibrium phenomena, with the Josephson properties of low-resistance tunnel structures taken into account, reveal a number of new effects, such as nonequilibrium suppression of the energy gap at bias voltages V < 2Δ/e, the possible existence of an entire series of instabilities of the nonequilibrium superconducting state during tunnel injection, and inhomogeneity in the tunnel injector effect.

  7. Substitution effects on superconducting and normal state properties in (Mo1-xTx)3Sb7, where T = Ru and Fe

    NASA Astrophysics Data System (ADS)

    Tran, V. H.

    2016-12-01

    The effects of Ru- and Fe-doping on the physical properties of Mo3Sb7 were studied by measuring ac-susceptibility, dc-magnetization, electrical resistivity and specific heat. It is found that single-phased (Mo{}1-xRu x )3Sb7 and (Mo{}1-xFe x )3Sb7 samples are obtained for the concentrations x ≤slant 0.1. In this concentration range, the lattice parameter shrinks with increasing dopant content. The substitution effects on the superconducting and normal state properties are completely different between two investigated systems. In the Ru-based solid solution alloys, the substitution enhances the superconducting parameters T c and H c2 and also benefits the spin-gap opening at {T}* ˜ 50 K. In contrast, in the Fe-substituted samples, there is a depression of both T c and H c2, accompanied by vanishing spin-gap and low-dimensional magnetic correlation. The substitution of the Mo atoms by Ru and Fe atoms suppresses the cubic-tetragonal distortion, but presumably favours the magnetic field to induce a magnetic order below T *.

  8. Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe.

    PubMed

    Jung, Soon-Gil; Kang, Ji-Hoon; Park, Eunsung; Lee, Sangyun; Lin, Jiunn-Yuan; Chareev, Dmitriy A; Vasiliev, Alexander N; Park, Tuson

    2015-11-09

    We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors.

  9. Optical Probe of the Superconducting Normal Mixed State in a Magnetic Penetration Thermometer

    NASA Technical Reports Server (NTRS)

    Stevenson, T. R.; Balvin, M. A.; Bandler, S. R.; Denis, K. L.; Lee, S. -J.; Nagler, P. C.; Smith, S. J.

    2016-01-01

    Using ultraviolet photon pulses, we have probed the internal behavior of a molybdenum-gold Magnetic Penetration Thermometer (MPT) that we designed for x-ray microcalorimetry. In this low-temperature detector, the diamagnetic response of a superconducting MoAu bilayer is used to sense temperature changes in response to absorbed photons. We have previously described an approximate model that explains the high responsivity of the detector to temperature changes as a consequence of a Meissner transition of the molybdenum-gold film in the magnetic field applied by the superconducting circuit used to bias the detector. We compare measurements of MPT heat capacity and thermal conductance, derived from UV photon pulse data, to our model predictions for the thermodynamic properties of the sensor and for the electron cooling obtained by quasiparticle recombination. Our data on electron cooling power is also relevant to the operation of other superconducting detectors, such as Microwave Kinetic Inductance Detectors.

  10. Universal quenching of the superconducting state of two-dimensional nanosize Pb-island structures

    NASA Astrophysics Data System (ADS)

    Kim, Jungdae; Fiete, Gregory A.; Nam, Hyoungdo; MacDonald, A. H.; Shih, Chih-Kang

    2011-07-01

    We systematically address superconductivity of Pb nano-islands with different thicknesses and lateral sizes via a scanning tunneling microscopy/spectroscopy (STM/STS). Reduction of the superconducting gap (Δ) is observed even when the island is larger than the bulk coherence length (ξ) and becomes very fast below ˜50-nm lateral size. The suppression of Δ with size depends to a good approximation only on the volume of the island and is independent of its shape. Theoretical analysis indicates that the universal quenching behavior is primarily manifested by the mean number of electronic orbitals within the pairing energy window.

  11. Observation of a Spin Gap in the Normal State of Superconducting Mo3Sb7

    NASA Astrophysics Data System (ADS)

    Tran, Vinh Hung; Miiller, Wojciech; Bukowski, Zbigniew

    2008-04-01

    Magnetization, specific heat, and electrical resistivity measurements have been performed on the superconductor Mo3Sb7. Two kinds of transitions are observed at 2.3 and 50 K, respectively. The former is superconducting transition, while the latter is attributed to spin-gap formation. From the analysis of the experimental data, excitation gap, intra- and interdimer interactions are estimated as Δ/kb˜120K, J0/kB˜150K, and J1/kB˜55K. The electronic structure calculations using the LSDA approximation show nesting property in the Fermi surface, favoring the superconductivity.

  12. Superconducting Bi2Te: Pressure-induced universality in the (Bi2)m(Bi2Te3)n series

    DOE PAGES

    Stillwell, Ryan L.; Jeffries, Jason R.; Jenei, Zsolt; ...

    2016-03-09

    Using high-pressure magnetotransport techniques we have discovered superconductivity in Bi2Te, a member of the infinitely adaptive (Bi2)m(Bi2Te3)n series, whose end members, Bi and Bi2Te3, can be tuned to display topological surface states or superconductivity. Bi2Te has a maximum Tc = 8.6 K at P = 14.5 GPa and goes through multiple high pressure phase transitions, ultimately collapsing into a bcc structure that suggests a universal behavior across the series. High-pressure magnetoresistance and Hall measurements suggest a semi-metal to metal transition near 5.4 GPa, which accompanies the hexagonal to intermediate phase transition seen via x-ray diffraction measurements. In addition, the linearitymore » of Hc2 (T) exceeds the Werthamer-Helfand-Hohenberg limit, even in the extreme spin-orbit scattering limit, yet is consistent with other strong spin-orbit materials. Furthermore, considering these results in combination with similar reports on strong spin-orbit scattering materials seen in the literature, we suggest the need for a new theory that can address the unconventional nature of their superconducting states.« less

  13. Three energy scales in the superconducting state of hole-doped cuprates detected by electronic Raman scattering

    DOE PAGES

    Benhabib, S.; Gu, G. D.; Gallais, Y.; ...

    2015-10-06

    We explore by electronic Raman scattering the superconducting state of the Bi2Sr2CaCu2O8+δ (Bi-2212) crystal by performing a fine-tuned doping study. We find three distinct energy scales in A1g, B1g, and B2g symmetries which show three distinct doping dependencies. Above p=0.22, the three energies merge; below p=0.12, the A1g scale is no longer detectable, while the B1g and B2g scales become constant in energy. In between, the A1g and B1g scales increase monotonically with underdoping, while the B2g one exhibits a maximum at p=0.16. The three superconducting energy scales appear to be a universal feature of hole-doped cuprates. Furthermore, we proposemore » that the nontrivial doping dependencies of the three scales originate from the Fermi-surface changes and reveal competing orders inside the superconducting dome.« less

  14. Three energy scales in the superconducting state of hole-doped cuprates detected by electronic Raman scattering

    SciTech Connect

    Benhabib, S.; Gu, G. D.; Gallais, Y.; Cazayous, M.; Measson, M. -A.; Zhong, R. D.; Schneeloch, J.; Forget, A.; Colson, D.; Sacuto, A.

    2015-10-06

    We explore by electronic Raman scattering the superconducting state of the Bi2Sr2CaCu2O8+δ (Bi-2212) crystal by performing a fine-tuned doping study. We find three distinct energy scales in A1g, B1g, and B2g symmetries which show three distinct doping dependencies. Above p=0.22, the three energies merge; below p=0.12, the A1g scale is no longer detectable, while the B1g and B2g scales become constant in energy. In between, the A1g and B1g scales increase monotonically with underdoping, while the B2g one exhibits a maximum at p=0.16. The three superconducting energy scales appear to be a universal feature of hole-doped cuprates. Furthermore, we propose that the nontrivial doping dependencies of the three scales originate from the Fermi-surface changes and reveal competing orders inside the superconducting dome.

  15. Superconducting transmission line particle detector

    DOEpatents

    Gray, K.E.

    1988-07-28

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non- superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propagating in a superconducting transmission line are used to resolve N/sup 2/ ambiguity of charged particle events. 6 figs.

  16. Superconducting transmission line particle detector

    DOEpatents

    Gray, Kenneth E.

    1989-01-01

    A microvertex particle detector for use in a high energy physic collider including a plurality of parallel superconducting thin film strips separated from a superconducting ground plane by an insulating layer to form a plurality of superconducting waveguides. The microvertex particle detector indicates passage of a charged subatomic particle by measuring a voltage pulse measured across a superconducting waveguide caused by the transition of the superconducting thin film strip from a superconducting to a non-superconducting state in response to the passage of a charged particle. A plurality of superconducting thin film strips in two orthogonal planes plus the slow electromagnetic wave propogating in a superconducting transmission line are used to resolve N.sup.2 ambiguity of charged particle events.

  17. Diamagnetic susceptibility near the surface or twinning plane at the transition to the superconducting state

    NASA Astrophysics Data System (ADS)

    Burmistrov, S. N.; Dubovskii, L. B.

    1983-10-01

    Besides the well-known bulk fluctuation contribution to the diamagnetic susceptibility there is an additional surface contribution with the singularity at TSH exceeding the superconducting bulk transition temperature Tc( H). The results obtained allow to explain the anomalous behavior of the diamagnetic susceptibility found by Khaikin and Khlyustikov.

  18. Pressure-induced superconductivity in the giant Rashba system BiTeI

    NASA Astrophysics Data System (ADS)

    VanGennep, D.; Linscheid, A.; Jackson, D. E.; Weir, S. T.; Vohra, Y. K.; Berger, H.; Stewart, G. R.; Hennig, R. G.; Hirschfeld, P. J.; Hamlin, J. J.

    2017-03-01

    At ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to  ∼40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with T c values as high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute T c and find that our data is consistent with phonon-mediated superconductivity.

  19. Pressure-induced superconductivity in the giant Rashba system BiTeI.

    PubMed

    VanGennep, D; Linscheid, A; Jackson, D E; Weir, S T; Vohra, Y K; Berger, H; Stewart, G R; Hennig, R G; Hirschfeld, P J; Hamlin, J J

    2017-03-08

    At ambient pressure, BiTeI exhibits a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to  ∼40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with T c values as high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute T c and find that our data is consistent with phonon-mediated superconductivity.

  20. Enhanced Superconductivity in Restacked TaS2 Nanosheets.

    PubMed

    Pan, Jie; Guo, Chenguang; Song, Changsheng; Lai, Xiaofang; Li, Hui; Zhao, Wei; Zhang, Hui; Mu, Gang; Bu, Kejun; Lin, Tianquan; Xie, Xiaoming; Chen, Mingwei; Huang, Fuqiang

    2017-04-05

    Since interface superconductivity was discovered at the interface between two insulating layers LaAlO3 and SrTiO3, such interface-induced superconducting systems have been a research hotspot in superconductivity. Here, we report homogeneous interfaces formed by stacking chemically exfoliated monolayer TaS2 nanosheets randomly. Enhanced superconductivity of Tc = 3 K is observed, compared with 0.8 K of parent 2H-TaS2. The measurement of heat capacity shows the increase of electronic specific-heat coefficient γ of restacked TaS2 nanosheets compared to parent 2H-TaS2 crystals. Density functional theory calculations indicate that increase and delocalization of electron states near the Fermi surface due to the homogeneous interfaces effects could account for the enhanced superconductivity.

  1. Competition between intrinsic and extrinsic effects in the quenching of the superconducting state in Fe(Se,Te) thin films

    NASA Astrophysics Data System (ADS)

    Leo, Antonio; Marra, Pasquale; Grimaldi, Gaia; Citro, Roberta; Kawale, Shrikant; Bellingeri, Emilio; Ferdeghini, Carlo; Pace, Sandro; Nigro, Angela

    2016-02-01

    We report the first experimental observation of the quenching of the superconducting state in current-voltage characteristics of an iron-based superconductor, namely, in Fe(Se,Te) thin films. Based on available theoretical models, our analysis suggests the presence of an intrinsic flux-flow electronic instability along with non-negligible extrinsic thermal effects. The coexistence and competition of these two mechanisms classify the observed instability as halfway between those of low-temperature and of high-temperature superconductors, where thermal effects are, respectively, largely negligible or predominant.

  2. Nodal Quasiparticle Lifetime in the Superconducting State of Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Corson, J.; Orenstein, J.; Oh, Seongshik; O'Donnell, J.; Eckstein, J. N.

    2000-09-01

    We have measured the complex conductivity σ of a Bi2Sr2CaCu2O8+δ thin film between 0.2 and 0.8 THz. We find σ in the superconducting state to be well described as the sum of contributions from quasiparticles, condensate, and order parameter fluctuations which draw 30% of the spectral weight from the condensate. An analysis based on this decomposition yields a quasiparticle scattering rate on the order of kBT/ħ for temperatures below Tc.

  3. Emerging superconductivity hidden beneath charge-transfer insulators

    PubMed Central

    Krockenberger, Yoshiharu; Irie, Hiroshi; Matsumoto, Osamu; Yamagami, Keitaro; Mitsuhashi, Masaya; Tsukada, Akio; Naito, Michio; Yamamoto, Hideki

    2013-01-01

    In many of today's most interesting materials, strong interactions prevail upon the magnetic moments, the electrons, and the crystal lattice, forming strong links between these different aspects of the system. Particularly, in two-dimensional cuprates, where copper is either five- or six-fold coordinated, superconductivity is commonly induced by chemical doping which is deemed to be mandatory by destruction of long-range antiferromagnetic order of 3d9 Cu2+ moments. Here we show that superconductivity can be induced in Pr2CuO4, where copper is four-fold coordinated. We induced this novel quantum state of Pr2CuO4 by realizing pristine square-planar coordinated copper in the copper-oxygen planes, thus, resulting in critical superconducting temperatures even higher than by chemical doping. Our results demonstrate new degrees of freedom, i.e., coordination of copper, for the manipulation of magnetic and superconducting order parameters in quantum materials. PMID:23887134

  4. Developments of the theory of spin fluctuations and spin fluctuation-induced superconductivity

    PubMed Central

    Moriya, Tôru

    2006-01-01

    Theory of spin fluctuations as developed in the past 30 years have played important roles in the theory of magnetism in metals, particularly in elucidating the properties around the magnetic instability or quantum critical points. Recently the theory has been extended to deal with the spin fluctuaion-mediated superconductivity with anisotropic order parameters in strongly correlated electron systems. These theoretical developments are briefly reviewed and the high temperature superconductivity of cuprates and organic and heavy electron superconductors are discussed in the light of these theories. PMID:25792765

  5. General conditions for proximity induced odd-frequency superconductivity in two-dimensional electronic systems

    NASA Astrophysics Data System (ADS)

    Rossi, Enrico; Triola, Christopher; Badiane, Driss; Balatsky, Alexander V.

    We obtain the general conditions for the emergence of odd-frequency superconducting pairing in a two-dimensional (2D) electronic system proximity-coupled to a superconductor, making minimal assumptions about both the 2D system and the superconductor. Using our general results we show that a simple heterostructure formed by a monolayer of a group VI transition metal dichalcogenide, such as molybdenum disulfide, and an s-wave superconductor with Rashba spin-orbit coupling will exhibit odd-frequency superconducting pairing. Work supported by US DOE BES E304, KAW, ACS-PRF-53581-DNI5, and NSF-DMR-1455233.

  6. Development of a ferromagnetic component in the superconducting state of Fe-excess Fe1.12Te1-xSex by electronic charge redistribution

    PubMed Central

    Li, Wen-Hsien; Karna, Sunil K.; Hsu, Han; Li, Chi-Yen; Lee, Chi-Hung; Sankar, Raman; Cheng Chou, Fang

    2015-01-01

    The general picture established so far for the links between superconductivity and magnetic ordering in iron chalcogenide Fe1+y(Te1-xSex) is that the substitution of Se for Te directly drives the system from the antiferromagnetic end into the superconducting regime. Here, we report on the observation of a ferromagnetic component that developed together with the superconducting transition in Fe-excess Fe1.12Te1-xSex crystals using neutron and x-ray diffractions, resistivity, magnetic susceptibility and magnetization measurements. The superconducting transition is accompanied by a negative thermal expansion of the crystalline unit cell and an electronic charge redistribution, where a small portion of the electronic charge flows from around the Fe sites toward the Te/Se sites. First-principles calculations show consistent results, revealing that the excess Fe ions play a more significant role in affecting the magnetic property in the superconducting state than in the normal state and the occurrence of an electronic charge redistribution through the superconducting transition. PMID:26077466

  7. Temperature dependence of the superconductivity-induced collective mode in the c-axis infrared spectra of bilayer cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Munzar, D.; Chaloupka, J.; Bernhard, C.; Dubroka, A.; Vašátko, J.

    2010-12-01

    The low-temperature spectra of the c-axis infrared conductivity of bilayer high-Tc cuprate superconductors (HTCS) exhibit two superconductivity-induced modes [Li Yu et al., Phys. Rev. Lett. 100 (2008) 177004; and references therein]. Both can be understood in terms of a microscopic theory developed recently [J. Chaloupka, C. Bernhard, D. Munzar, Phys. Rev. B 79 (2009) 184513]. Here we summarize the elements of the theory and report on the temperature dependence (TD) of the low-energy mode and of the total optical spectral weight (SW). The calculated TD of the mode is consistent with experiment but the trends of the SW are not.

  8. Search for pressure-induced superconductivity in CeFeAsO and CeFePO iron pnictides

    SciTech Connect

    Zocco, D. A.; Baumbach, R. E.; Hamlin, J. J.; Janoschek, M.; Lum, I. K.; McGuire, Michael A; Safa-Sefat, Athena; Sales, Brian C; Jin, Rongying; Mandrus, David; Jeffries, J. R.; Weir, S. T.; Vohra, Y. K.; Maple, M. B.

    2011-01-01

    The CeFeAsO and CeFePO iron pnictide compounds were studied via electrical transport measurements under high pressure. In CeFeAsO polycrystals, the magnetic phases involving the Fe and Ce ions coexist for hydrostatically applied pressures up to 15 GPa, and with no signs of pressure-induced superconductivity up to 50 GPa for the less hydrostatic pressure techniques. For the CeFePO single crystals, pressure further stabilizes the Kondo screening of the Ce 4f-electron magnetic moments.

  9. Vortex-glass transformation within the surface superconducting state of β-phase Mo1-x Re x alloys

    NASA Astrophysics Data System (ADS)

    Sundar, Shyam; Chattopadhyay, M. K.; Sharath Chandra, L. S.; Rawat, R.; Roy, S. B.

    2017-02-01

    We have performed an experimental study on the temperature dependence of electrical resistivity ρ(T) and heat capacity C(T) of the Mo{}1-xRe x (x=0.20,0.25) alloy superconductors in different magnetic fields. In the presence of applied magnetic field, the electrical resistivity of these alloys goes to zero at a temperature well above the bulk superconducting transition temperature obtained with the help of heat capacity measurements in the same magnetic field. Our study indicates the presence of a surface superconducting state in these alloys, where the flux lines are pinned in the surface sheath of the superconductor. The configuration of the flux lines (two-dimensional pancake-like) in the surface sheath is understood in the realm of the flux-spot model. Experimental evidence in support of the surface mixed-state state or ‘Kulik vortex-state’ and the occurrence of a vortex-liquid to vortex-glass transition is presented.

  10. Pressure-induced exotic states in rare earth hexaborides

    NASA Astrophysics Data System (ADS)

    Sun, Liling; Wu, Qi

    2016-08-01

    Finding the exotic phenomena in strongly correlated electron systems (SCESs) and understanding the corresponding microphysics have long been the research frontiers of condensed matter physics. The remarkable examples for the intriguing phenomena discovered in past years include unconventional superconductivity, heavy Fermion behaviors, giant magneto-resistance and so on. A fascinating type of rare earth hexaboride RB6 (R  =  Sm, Yb, Eu and Ce) belongs to a strongly correlated electron system (SCES), but shows unusual ambient-pressure and high-pressure behaviors beyond the phenomena mentioned above. Particularly, the recent discovery of the coexistence of an unusual metallic surface state and an insulating bulk state in SmB6, known to be a Kondo insulator decades ago, by theoretical calculations and many experimental measurements creates new interest for the investigation of the RB6. This significant progress encourages people to revisit the RB6 with an attempt to establish a new physics that links the SCES and the unusual metallic surface state which is a common feature of a topological insulator (TI). It is well known that pressure has the capability of tuning the electronic structure and modifying the ground state of solids, or even inducing a quantum phase transition which is one of the kernel issues in studies of SCESs. In this brief review, we will describe the progress in high pressure studies on the RB6 based on our knowledge and research interests, mainly focusing on the pressure-induced phenomena in YbB6 and SmB6, especially on the quantum phase transitions and their connections with the valence state of the rare earth ions. Moreover, some related high-pressure results obtained from CeB6 and EuB6 are also included. Finally, a summary is given in the conclusions and perspectives section.

  11. Pressure-induced exotic states in rare earth hexaborides.

    PubMed

    Sun, Liling; Wu, Qi

    2016-08-01

    Finding the exotic phenomena in strongly correlated electron systems (SCESs) and understanding the corresponding microphysics have long been the research frontiers of condensed matter physics. The remarkable examples for the intriguing phenomena discovered in past years include unconventional superconductivity, heavy Fermion behaviors, giant magneto-resistance and so on. A fascinating type of rare earth hexaboride RB6 (R  =  Sm, Yb, Eu and Ce) belongs to a strongly correlated electron system (SCES), but shows unusual ambient-pressure and high-pressure behaviors beyond the phenomena mentioned above. Particularly, the recent discovery of the coexistence of an unusual metallic surface state and an insulating bulk state in SmB6, known to be a Kondo insulator decades ago, by theoretical calculations and many experimental measurements creates new interest for the investigation of the RB6. This significant progress encourages people to revisit the RB6 with an attempt to establish a new physics that links the SCES and the unusual metallic surface state which is a common feature of a topological insulator (TI). It is well known that pressure has the capability of tuning the electronic structure and modifying the ground state of solids, or even inducing a quantum phase transition which is one of the kernel issues in studies of SCESs. In this brief review, we will describe the progress in high pressure studies on the RB6 based on our knowledge and research interests, mainly focusing on the pressure-induced phenomena in YbB6 and SmB6, especially on the quantum phase transitions and their connections with the valence state of the rare earth ions. Moreover, some related high-pressure results obtained from CeB6 and EuB6 are also included. Finally, a summary is given in the conclusions and perspectives section.

  12. Experimental investigation of the role of the triplet pairing in the superconducting spin-valve effect

    NASA Astrophysics Data System (ADS)

    Leksin, P. V.; Kamashev, A. A.; Garif'yanov, N. N.; Validov, A. A.; Fominov, Ya. V.; Schumann, J.; Kataev, V. E.; Büchner, B.; Garifullin, I. A.

    2016-11-01

    An important role of the morphology of a superconducting layer in the superconducting spin-valve effect has been established. The triplet pairing induced by the superconductor/ferromagnet proximity effect has been experimentally investigated for samples CoO x /Py1/Cu/Py2/Cu/Pb (where Py = Ni0.81Fe0.19) with a smooth superconducting layer. The optimization of the parameters of this structure has demonstrated a complete switching between the normal and superconducting states with a change in the relative orientation of magnetizations of the ferromagnetic layers from the antiparallel to orthogonal orientation. A pure triplet contribution has been observed for the sample with a permalloy layer thickness at which the superconducting spin-valve effect vanishes. A direct comparison of the experimental data with the theoretical calculation of the temperature of the transition to the superconducting state has been performed for the first time.

  13. Superconductivity emerging from a suppressed large magnetoresistant state in tungsten ditelluride.

    PubMed

    Kang, Defen; Zhou, Yazhou; Yi, Wei; Yang, Chongli; Guo, Jing; Shi, Youguo; Zhang, Shan; Wang, Zhe; Zhang, Chao; Jiang, Sheng; Li, Aiguo; Yang, Ke; Wu, Qi; Zhang, Guangming; Sun, Liling; Zhao, Zhongxian

    2015-07-23

    The recent discovery of large magnetoresistance in tungsten ditelluride provides a unique playground to find new phenomena and significant perspective for potential applications. The large magnetoresistance effect originates from a perfect balance of hole and electron carriers, which is sensitive to external pressure. Here we report the suppression of the large magnetoresistance and emergence of superconductivity in pressurized tungsten ditelluride via high-pressure synchrotron X-ray diffraction, electrical resistance, magnetoresistance and alternating current magnetic susceptibility measurements. Upon increasing pressure, the positive large magnetoresistance effect is gradually suppressed and turned off at a critical pressure of 10.5 GPa, where superconductivity accordingly emerges. No structural phase transition is observed under the pressure investigated. In situ high-pressure Hall coefficient measurements at low temperatures demonstrate that elevating pressure decreases the population of hole carriers but increases that of the electron ones. Significantly, at the critical pressure, a sign change of the Hall coefficient is observed.

  14. Superconductivity emerging from a suppressed large magnetoresistant state in tungsten ditelluride

    PubMed Central

    Kang, Defen; Zhou, Yazhou; Yi, Wei; Yang, Chongli; Guo, Jing; Shi, Youguo; Zhang, Shan; Wang, Zhe; Zhang, Chao; Jiang, Sheng; Li, Aiguo; Yang, Ke; Wu, Qi; Zhang, Guangming; Sun, Liling; Zhao, Zhongxian

    2015-01-01

    The recent discovery of large magnetoresistance in tungsten ditelluride provides a unique playground to find new phenomena and significant perspective for potential applications. The large magnetoresistance effect originates from a perfect balance of hole and electron carriers, which is sensitive to external pressure. Here we report the suppression of the large magnetoresistance and emergence of superconductivity in pressurized tungsten ditelluride via high-pressure synchrotron X-ray diffraction, electrical resistance, magnetoresistance and alternating current magnetic susceptibility measurements. Upon increasing pressure, the positive large magnetoresistance effect is gradually suppressed and turned off at a critical pressure of 10.5 GPa, where superconductivity accordingly emerges. No structural phase transition is observed under the pressure investigated. In situ high-pressure Hall coefficient measurements at low temperatures demonstrate that elevating pressure decreases the population of hole carriers but increases that of the electron ones. Significantly, at the critical pressure, a sign change of the Hall coefficient is observed. PMID:26203807

  15. Berezinskii-Kosterlitz-Thouless transition to the superconducting state of heavy-fermion superlattices.

    PubMed

    She, Jian-Huang; Balatsky, Alexander V

    2012-08-17

    We propose an explanation of the superconducting transitions discovered in the heavy-fermion superlattices by Mizukami et al. [Nature Phys. 7, 849 (2011)] in terms of Berezinskii-Kosterlitz-Thouless (BKT) transition. We observe that the effective mass mismatch between the heavy-fermion superconductor and the normal metal regions provides an effective barrier that enables quasi-2D superconductivity in such systems. We show that the resistivity data, both with and without magnetic field, are consistent with BKT transition. Furthermore, we study the influence of a nearby magnetic quantum critical point on the vortex system and find that the vortex core energy can be significantly reduced due to magnetic fluctuations. Further reduction of the gap with decreasing number of layers is understood as a result of pair breaking effect of Yb ions at the interface.

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

    PubMed

    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

    2016-03-15

    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.

  17. 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.

  18. Review of High Power Density Superconducting Generators: Present State and Prospects for Incorporating YBCO Windings

    DTIC Science & Technology

    2005-01-01

    efficient cryocoolers such as Stirling and Pulse Tube cryocoolers . Stirling cryocoolers have been used by the military for decades for sensor cool- ing...but these cryocoolers are too small for cooling the lar- ger volume associated with superconducting power applications. Large Stirling and Pulse Tube...Air Force contract for a laser application is a lightweight Stirling cryocooler weighing only 19 lbs and delivering 16 W of refrigeration at 80 K [39

  19. Using a Superconducting Resonator with Frequency-Compensated Tunable Coupling to Transfer a Quantum State Deterministically and Directly

    NASA Astrophysics Data System (ADS)

    Wenner, James; Neill, C.; Quintana, C.; Campbell, B.; Chen, Z.; Chiaro, B.; Dunsworth, A.; O'Malley, P.; Vainsencher, A.; White, T.; Barends, R.; Chen, Y.; Fowler, A.; Jeffrey, E.; Kelly, J.; Lucero, E.; Megrant, A.; Mutus, J.; Neeley, M.; Roushan, P.; Sank, D.; Martinis, John M.

    Deterministic direct quantum state transfer between devices on different chips requires the ability to transfer quantum states between traveling qubits and fixed logic qubits. Reflections must be minimized to avoid energy loss and phase interference; this requires tunable coupling to an inter-chip line while the two devices are at equal frequencies. To achieve this, we use a 6GHz superconducting coplanar resonator with tunable coupling to a 50 Ohm transmission line. We compensate for the resulting shift in resonator frequency by simultaneously tuning a second SQUID. We measure the device coherence and demonstrate the ability to release a single-frequency shaped pulse into the transmission line, efficiently capture a shaped pulse, and deterministically and directly transfer a quantum state.

  20. Model Evidence of a Superconducting State with a Full Energy Gap in Small Cuprate Islands

    NASA Astrophysics Data System (ADS)

    Black-Schaffer, Annica M.; Golubev, Dmitri S.; Bauch, Thilo; Lombardi, Floriana; Fogelström, Mikael

    2013-05-01

    We investigate subdominant order parameters stabilizing at low temperatures in nanoscale high-Tc cuprate islands, motivated by the recent observation of a fully gapped state in nanosized YBa2Cu3O7-δ [D. Gustafsson et al., Nature Nanotech. 8, 25 (2013)]. Using complementary quasiclassical and tight-binding Bogoliubov-de Gennes methods, we show on distinctly different properties dependent on the symmetry being dx2-y2+is or dx2-y2+idxy. We find that a surface-induced dx2-y2+is phase creates a global spectroscopic gap which increases with an applied magnetic field, consistent with experimental observation.

  1. The interplay between topological p-wave superconductivity and odd-frequency pairing in superconducting proximity systems

    NASA Astrophysics Data System (ADS)

    Stanev, Valentin; Galitski, Victor

    2014-03-01

    We study the proximity-induced superconductivity in semiconductor nanowires. The interplay between superconductivity and spin-orbit coupling plays a crucial role in proposals for creating Majorana fermions in semiconducting heterostructures. To further elucidate the physics of such devices we employ the quasiclassical Green's functions methods. We show that the spatial variations of the superconducting order parameter leads to non-trivial effects in the nanowire. We demonstrate the appearance of odd-frequency pairing correlations close to the boundaries, and discuss their effect on the density of states. Work supported by DOE-BES (DESC0001911) and Simons Foundation.

  2. Interlayer-state-driven superconductivity in CaC6 studied by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Kyung, Wonshik; Kim, Yeongkwan; Han, Garam; Leem, Choonshik; Kim, Chul; Koh, Yoonyoung; Kim, Beomyoung; Kim, Youngwook; Kim, Jun Sung; Kim, Keun Su; Rotenberg, Eli; Denlinger, Jonathan D.; Kim, Changyoung

    2015-12-01

    We performed angle-resolved photoemission experiments on CaC6 and measured kz-dependent electronic structures to investigate the interlayer states. The results reveal a spherical interlayer Fermi surface centered at the Γ point. We also find that the graphene-driven band possesses a weak kz dispersion. The overall electronic structure shows a peculiar single-graphene-layer periodicity in the kz direction although the CaC6 unit cell is supposed to contain three graphene layers. This suggests that the c -axis ordering of Ca has little effect on the electronic structure of CaC6. In addition to CaC6, we also studied the a low-temperature superconductor BaC6. For BaC6, the graphene-band Dirac-point energy is smaller than that of CaC6. Based on data from CaC6 and BaC6, we rule out the Cx y phonon mode as the origin of the superconductivity in CaC6, which strongly suggests interlayer-state-driven superconductivity.

  3. Non-BCS superconducting state in yttrium hydride at a record low value of the external pressure

    NASA Astrophysics Data System (ADS)

    Jarosik, Marcin W.; Szczȩśniak, Radosław; Wrona, Izabela A.; Kostrzewa, Małgorzata

    2017-01-01

    The ab initio calculations suggest that YH3 compound is a superconductor with the maximum value of the critical temperature (TC) for the record low external pressure equal to 17.7 GPa. Due to the high value of the electron-phonon coupling constant, the thermodynamic properties of the superconducting state in YH3 have been determined in the framework of the Eliashberg formalism. It has been shown that TC changes in the range from 45.91K to 27.29 K, for the value of the Coulomb pseudopotential μ⋆ ∈ < 0.1 , 0.3 > . The parameters of the superconducting phase differ significantly from the values predicted by the BCS theory due to the significant strong-coupling and retardation effects: kBTC /ωln ∈ < 0.138 , 0.082 > , where ωln denotes the logarithmic phonon frequency. In particular, the dimensionless ratios: RΔ = 2 Δ (0) /kBTC , RC = Δ C (TC) /CN (TC) and RH =TCCN (TC) /HC2(0) take the following values: RΔ ∈ < 4.38 , 4.20 > , RC ∈ < 2.18 , 2.02 > and RH ∈ < 0.151 , 0.168 > . The symbol Δ represents the order parameter, Δ C is the specific heat jump, CN is the specific heat of the normal state, and HC is the thermodynamic critical field.

  4. Modulation of superconducting critical temperature in niobium film by using all-solid-state electric-double-layer transistor

    SciTech Connect

    Tsuchiya, Takashi E-mail: TERABE.Kazuya@nims.go.jp; Moriyama, Satoshi; Terabe, Kazuya E-mail: TERABE.Kazuya@nims.go.jp; Aono, Masakazu

    2015-07-06

    An all-solid-state electric-double-layer transistor (EDLT) was fabricated for electrical modulation of the superconducting critical temperature (T{sub c}) of Nb film epitaxially grown on α-Al{sub 2}O{sub 3} (0001) single crystal. In an experiment, T{sub c} was modulated from 8.33 to 8.39 K while the gate voltage (V{sub G}) was varied from 2.5 to −2.5 V. The specific difference of T{sub c} for the applied V{sub G} was 12 mK/V, which is larger than that of an EDLT composed of ionic liquid. A T{sub c} enhancement of 300 mK was found at the Li{sub 4}SiO{sub 4}/Nb film interface and is attributed to an increase in density of states near the Fermi level due to lattice constant modulation. This solid electrolyte gating method should enable development of practical superconducting devices highly compatible with other electronic devices.

  5. Longitudinal spin fluctuations and superconductivity in ferromagnetic ZrZn2 from Ab initio calculations.

    PubMed

    Santi, G; Dugdale, S B; Jarlborg, T

    2001-12-10

    The recent discovery of superconductivity coexisting with weak itinerant ferromagnetism in the d-electron intermetallic compound ZrZn2 strongly suggests spin-fluctuation mediated superconductivity. Ab initio electronic structure calculations of the Fermi surface and generalized susceptibilities are performed to investigate the viability of longitudinal spin-fluctuation-induced spin-triplet superconductivity in the ferromagnetic state. The critical temperature is estimated to be of the order of 1 K. Additionally, it is shown that in spite of a strong electron-phonon coupling ( lambda(ph) = 0.7), conventional s-wave superconductivity is inhibited by the presence of strong spin fluctuations.

  6. Measurement-induced Nonlocality for Gaussian States

    NASA Astrophysics Data System (ADS)

    Ma, Ruifen; Hou, Jinchuan; Qi, Xiaofei

    2017-04-01

    We establish an analytic formula of measurement-induced nonlocality (MIN) for two-mode squeezed thermal states and mixed thermal states. Different from the quantum discord case, we show that there is no Gaussian version of MIN by Gaussian positive operator valued measurements.

  7. Status report on the design and construction of the Superconducting Source for Ions at the National Superconducting Cyclotron Laboratory/Michigan State University

    SciTech Connect

    Zavodszky, P.A.; Arend, B.; Cole, D.; DeKamp, J.; Machicoane, G.; Marti, F.; Miller, P.; Moskalik, J.; Ottarson, J.; Vincent, J.; Zeller, A.; Kazarinov, N.Yu.

    2006-03-15

    A status report of the design and fabrication of a new, fully superconducting electron cyclotron resonance ion source will be presented. The Superconducting Source for Ions (SuSI) first will operate at 18+14.5 GHz microwave frequencies. A short description of the magnet structure and the injection and extraction hardware will be presented. Several innovative solutions are described, which will allow maximum flexibility in tuning SuSI in order to match the acceptance of the coupled cyclotrons. Details of an ultrahigh temperature inductive oven construction are given as well as a description of the low-energy beam transport line.

  8. Superconductivity in carbon nanomaterials

    NASA Astrophysics Data System (ADS)

    Dlugon, Katarzyna

    The purpose of this thesis is to explain the phenomenon of superconductivity in carbon nanomaterials such as graphene, fullerenes and carbon nanotubes. In the introductory chapter, there is a description of superconductivity and how it occurs at critical temperature (Tc) that is characteristic and different to every superconducting material. The discovery of superconductivity in mercury in 1911 by Dutch physicist Heike Kamerlingh Onnes is also mentioned. Different types of superconductors, type I and type II, low and high temperatures superconductors, as well as the BCS theory that was developed in 1957 by Bardeen, Cooper, and Schrieffer, are also described in detail. The BCS theory explains how Cooper's pairs are formed and how they are responsible for the superconducting properties of many materials. The following chapters explain superconductivity in doped fullerenes, graphene and carbon nanotubes, respectively. There is a thorough explanation followed by many examples of different types of carbon nanomaterials in which small changes in chemical structure cause significant changes in superconducting properties. The goal of this research was not only to take into consideration well known carbon based superconductors but also to search for the newest available materials such as the fullerene nanowhiskers discovered quite recently. There is also a presentation of fairly new ideas about inducing superconductivity in a monolayer of graphene which is more challenging than inducing superconductivity in graphite by simply intercalating metal atoms between its graphene sheets. An effort has been taken to look for any available information about carbon nanomaterials that have the potential to superconduct at room temperature, mainly because discovery of such materials would be a real revolution in the modern world, although no such materials have been discovered yet.

  9. Robust preparation of four-qubit decoherence-free states for superconducting quantum interference devices against collective amplitude damping

    NASA Astrophysics Data System (ADS)

    Shao, Xiao-Qiang; Zheng, Tai-Yu; Zhang, Shou

    2013-11-01

    Based on the quantum Zeno dynamics, we present an approach for deterministic preparation of arbitrary four-qubit decoherence-free state of superconducting quantum interference devices with respective to collective amplitude damping in a decoherence-free way, namely, not only the form of the target state is free of decoherence, but also the whole process for preparation. The operation is fast and convenient since we only need to manipulate three weak laser pulses sequentially. Other decoherence effects such as cavity decay and the spontaneous emission of qubits are also taken into account in virtue of master equation, and the strictly numerical simulation signifies the final fidelity is high corresponding to the current experimental technology.

  10. Closing a quantum feedback loop inside a cryostat: Autonomous state preparation and long-time memory of a superconducting qubit

    NASA Astrophysics Data System (ADS)

    Andersen, Christian Kraglund; Kerckhoff, Joseph; Lehnert, Konrad W.; Chapman, Benjamin J.; Mølmer, Klaus

    2016-01-01

    We propose to use a nonlinear resonator for projective readout, classical memory, and feedback for a superconducting qubit. Keeping the classical controller at cryogenic temperatures sidesteps many of the inefficiencies inherent in two-way communication between temperature stages in typical systems with room-temperature controllers, and avoids increasing the cryogenic heat load. This controller may find a broad range of uses in multiqubit systems, but here we analyze two specific demonstrative cases in single qubit control. In the first case, the nonlinear controller is used to initialize the qubit in a definite eigenstate. And in the second case, the qubit's state is read into the controller's classical memory and used to reinstate the measured state after the qubit has decayed. We analyze the properties of this system and we show simulations of the time evolution for the full system dynamics.

  11. Superconductivity Induced by Oxygen Doping in Y2 O2 Bi.

    PubMed

    Cheng, Xiyue; Gordon, Elijah E; Whangbo, Myung-Hwan; Deng, Shuiquan

    2017-04-03

    When doped with oxygen, the layered Y2 O2 Bi phase becomes a superconductor. This finding raises questions about the sites for doped oxygen, the mechanism of superconductivity, and practical guidelines for discovering new superconductors. We probed these questions in terms of first-principles calculations for undoped and O-doped Y2 O2 Bi. The preferred sites for doped O atoms are the centers of Bi4 squares in the Bi square net. Several Bi 6p x/y bands of Y2 O2 Bi are raised in energy by oxygen doping because the 2p x/y orbitals of the doped oxygen make antibonding possible with the 6p x/y orbitals of surrounding Bi atoms. Consequently, the condition necessary for the "flat/steep" band model for superconductivity is satisfied in O-doped Y2 O2 Bi.

  12. Solid-state circuit breaker with current-limiting characteristic using a superconducting coil

    DOEpatents

    Boenig, H.J.

    1982-08-16

    A thyristor bridge interposes an ac source and a load. A series connected DC source and superconducting coil within the bridge biases the thyristors thereof so as to permit bidirectional ac current flow therethrough under normal operating conditions. Upon a fault condition a control circuit triggers the thyristors so as to reduce ac current flow therethrough to zero in less than two eyeles and to open the bridge thereafter. Upon a temporary overload condition the control circuit triggers the thyristors so as to limit ac current flow therethrough to an acceptable level.

  13. Solid-state circuit breaker with current limiting characteristic using a superconducting coil

    DOEpatents

    Boenig, Heinrich J.

    1984-01-01

    A thyristor bridge interposes an ac source and a load. A series connected DC source and superconducting coil within the bridge biases the thyristors thereof so as to permit bidirectional ac current flow therethrough under normal operating conditions. Upon a fault condition a control circuit triggers the thyristors so as to reduce ac current flow therethrough to zero in less than two cycles and to open the bridge thereafter. Upon a temporary overload condition the control circuit triggers the thyristors so as to limit ac current flow therethrough to an acceptable level.

  14. Transition between different quantum states in a mesoscopic system: The superconducting ring

    SciTech Connect

    Horane, E.M.; Castro, J.I.; Buscaglia, G.C.; Lopez, A.

    1996-04-01

    We investigate the thermodynamic properties of a superconducting ring, both analytically and numerically, relying upon the Ginzburg-Landau theory. We find that modulated solutions for the order parameter play a role in describing the thermodynamic transitions between consecutive modes of uniform order parameter, associated with different quantum numbers. Exact expressions for these solutions are given in terms of elliptic functions. We identify the family of energy extrema which, being saddle points of the energy in the functional space of the distributions of the order parameter, represent the energy barrier to be overcome for transitions between different solutions. {copyright} {ital 1996 The American Physical Society.}

  15. Superconducting dome and crossover to an insulating state in [Tl{sub 4}]Tl{sub 1−x}Sn{sub x}Te{sub 3}

    SciTech Connect

    Arpino, K. E.; Wasser, B. D.; McQueen, T. M.

    2015-04-01

    The structural, superconducting, and electronic phase diagram of [Tl{sub 4}]Tl{sub 1−x}Sn{sub x}Te{sub 3} is reported. Magnetization and specific heat measurements show bulk superconductivity exists for 0 ≤ x ≤ 0.4. Resistivity measurements indicate a crossover from a metallic state at x = 0 to a doped insulator at x = 1. Universally, there is a large non-Debye specific heat contribution, characterized by an Einstein temperature of θ{sub E} ≈ 35 K. Density functional theory calculations predict x = 0 to be a topological metal, while x = 1 is a topological crystalline insulator. The disappearance of superconductivity correlates with the transition between these distinct topological states.

  16. Metal optics and superconductivity

    SciTech Connect

    Golovashkin, A.L.

    1989-01-01

    The articles contained in this collection are dedicated to the study of the electron structure of transition metals and superconducting alloys and compounds based on them. The study of the electron structure of materials is one of the central problems of solid-state physics and defines the solution of a number of problems. One of them is the problem of high-temperature superconductivity which has attracted exceptional attention from physicists in connection with the discovery of new classes of ceramic oxides which are superconducting at liquid-nitrogen temperature. The electron structure is one of the three whales on which all of superconductivity rests. It is frequently our ignorance of the electronic properties of a metal, alloy or compound in its normal state which makes it impossible to predict superconductivity in the material, preventing use from calculating the parameters of the superconducting state. There are now a number of effective methods for investigation of the electron structure of the metals and allows. This collection discusses metal optics, tunneling and magnetic measurements in superconductors. These methods are quite informative and allow us to obtain many important electron characteristics and temperature relations. Various characteristics of the superconducting compounds Nb{sub 3}Ge, Nb{sub 3}Al, nb{sub 3}Sn and Nb{sub 3}Ga with A15 structure and NbN with B1 structure, having rather high critical temperatures, are experimentally studied.

  17. Electrostatic separation of superconducting particles from non-superconducting particles and improvement in fuel atomization by electrorheology

    NASA Astrophysics Data System (ADS)

    Chhabria, Deepika

    This thesis has two major topics: (1) Electrostatic Separation of Superconducting Particles from a Mixture of Non-Superconducting Particles. (2) Improvement in fuel atomization by Electrorheology. (1) Based on the basic science research, the interactions between electric field and superconductors, we have developed a new technology, which can separate superconducting granular particles from their mixture with non-superconducting particles. The electric-field induced formation of superconducting balls is important aspect of the interaction between superconducting particles and electric field. When the applied electric field exceeds a critical value, the induced positive surface energy on the superconducting particles forces them to aggregate into balls or cling to the electrodes. In fabrication of superconducting materials, especially HTSC materials, it is common to come across materials with multiple phases: some grains are in superconducting state while the others are not. Our technology is proven to be very useful in separating superconducting grains from the rest non-superconducting materials. To separate superconducting particles from normal conducting particles, we apply a suitable strong electric field. The superconducting particles cling to the electrodes, while normal conducting particles bounce between the electrodes. The superconducting particles could then be collected from the electrodes. To separate superconducting particles from insulating ones, we apply a moderate electric field to force insulating particles to the electrodes to form short chains while the superconducting particles are collected from the middle of capacitor. The importance of this technology is evidenced by the unsuccessful efforts to utilize the Meissner effect to separate superconducting particles from nonsuperconducting ones. Because the Meissner effect is proportional to the particle volume, it has been found that the Meissner effect is not useful when the superconducting

  18. Solid State Thermal Gradient Processing of YTTRIUM(1) BARIUM(2) COPPER(3) OXYGEN(7-X)/SILVER Superconducting Composite Ribbons

    NASA Astrophysics Data System (ADS)

    Kaforey, Monica L.

    The effect of solid state thermal gradient processing on microstructure was examined experimentally and theoretically. The starting material Y_1Ba_2Cu _3Ag_{15} was used to produce Y_1Ba_2Cu_3O_ {7-x}/Ag superconducting composite ribbons. During the low temperature oxidation stage, internal oxidation resulted in the formation of elemental oxides Y_2O_3, BaO, and CuO in Ag. The low temperature oxidation treatment had a very strong influence on the microstructure of the final ribbon, with the tendency for forming Ag bands being stronger in samples subjected to longer oxidation stage treatments. Ag nodules formed at the surfaces due to stress relief and an Ag band formed at the center of samples due to outward solute diffusion in samples that were completely oxidized. Complete oxidation was achieved by heating the samples in flowing oxygen 5^circC/min to 140 ^circC, 0.5^ circC/min to 420^circ C, and holding for 13 hours. The high temperature transformation stage enabled the elemental oxides to transform to the superconducting oxide Y_1Ba_2Cu_3O _{7-x}. During the high temperature transformation treatment, the Ag nodules on the surface spread out to become a surface band of Ag. Coarsening resulted in an increase in the average oxide particle size and a thickening of the Ag bands as the hold time increased, with temperatures in the range of 890^circ C to 900^circC. The superconducting properties of the composite Y_1Ba_2Cu_3O_ {7-x}/Ag ribbons were tested after oxygenation. The samples were found to contain superconducting Y _1Ba_2Cu_3O_{7 -x} with a critical transition temperature in the range of 86 K to 90 K. The samples were found to be unable to support a supercurrent at either 77 K or 4.2 K. The use of solid state thermal gradient processing to produce textured Y_1Ba_2Cu _3O_{7-x}/Ag composite superconducting ribbons during the high temperature transformation stage was investigated experimentally and theoretically. Experimentally, no significant amount of either

  19. Pressure-induced superconductivity in H2-containing hydride PbH4(H2)2

    PubMed Central

    Cheng, Ya; Zhang, Chao; Wang, Tingting; Zhong, Guohua; Yang, Chunlei; Chen, Xiao-Jia; Lin, Hai-Qing

    2015-01-01

    High pressure structure, stability, metallization, and superconductivity of PbH4(H2)2, a H2-containing compound combining one of the heaviest elements with the lightest element, are investigated by the first-principles calculations. The metallic character is found over the whole studied pressure range, although PbH4(H2)2 is metastable and easily decompose at low pressure. The decomposition pressure point of 133 GPa is predicted above which PbH4(H2)2 is stable both thermodynamically and dynamically with the C2/m symmetry. Interestedly, all hydrogen atoms pairwise couple into H2 quasi-molecules and remain this style up to 400 GPa in the C2/m structure. At high-pressure, PbH4(H2)2 tends to form the Pb-H2 alloy. The superconductivity of Tc firstly rising and then falling is observed in the C2/m PbH4(H2)2. The maximum of Tc is about 107 K at 230 GPa. The softening of intermediate-frequency phonon induced by more inserted H2 molecules is the main origin of the high Tc. The results obtained represent a significant step toward the understanding of the high pressure behavior of metallic hydrogen and hydrogen-rich materials, which is helpful for obtaining the higher Tc. PMID:26559369

  20. NMR investigation of the pressure induced Mott transition to superconductivity in Cs3C60 isomeric compounds

    NASA Astrophysics Data System (ADS)

    Alloul, H.; Ihara, Y.; Mito, T.; Wzietek, P.; Aramini, M.; Pontiroli, D.; Ricco, M.

    2013-07-01

    The discovery in 1991 of high temperature superconductivity (SC) in A3C60 compounds, where A is an alkali ion, has been initially ascribed to a BCS mechanism, with a weak incidence of electron correlations. However various experimental evidences taken for compounds with distinct alkali content established the interplay of strong correlations and Jahn Teller distortions of the C60 ball. The importance of electronic correlations even in A3C60 has been highlighted by the recent discovery of two expanded fulleride Cs3C60 isomeric phases that are Mott insulators at ambient pressure. Both phases undergo a pressure induced first order Mott transition to SC with a (p, T) phase diagram displaying a dome shaped SC, a common situation encountered nowadays in correlated electron systems. NMR experiments allowed us to establish that the bipartite A15 phase displays Néel order at 47K, while magnetic freezing only occurs at lower temperature in the fcc phase. NMR data do permit us to conclude that well above the critical pressure, the singlet superconductivity found for light alkalis is recovered. However deviations from BCS expectations linked with electronic correlations are found near the Mott transition. So, although SC involves an electron-phonon mechanism, correlations have a significant incidence on the electronic properties, as had been anticipated from DMFT calculations.

  1. Pressure-induced superconductivity in H2-containing hydride PbH4(H2)2

    NASA Astrophysics Data System (ADS)

    Cheng, Ya; Zhang, Chao; Wang, Tingting; Zhong, Guohua; Yang, Chunlei; Chen, Xiao-Jia; Lin, Hai-Qing

    2015-11-01

    High pressure structure, stability, metallization, and superconductivity of PbH4(H2)2, a H2-containing compound combining one of the heaviest elements with the lightest element, are investigated by the first-principles calculations. The metallic character is found over the whole studied pressure range, although PbH4(H2)2 is metastable and easily decompose at low pressure. The decomposition pressure point of 133 GPa is predicted above which PbH4(H2)2 is stable both thermodynamically and dynamically with the C2/m symmetry. Interestedly, all hydrogen atoms pairwise couple into H2 quasi-molecules and remain this style up to 400 GPa in the C2/m structure. At high-pressure, PbH4(H2)2 tends to form the Pb-H2 alloy. The superconductivity of Tc firstly rising and then falling is observed in the C2/m PbH4(H2)2. The maximum of Tc is about 107 K at 230 GPa. The softening of intermediate-frequency phonon induced by more inserted H2 molecules is the main origin of the high Tc. The results obtained represent a significant step toward the understanding of the high pressure behavior of metallic hydrogen and hydrogen-rich materials, which is helpful for obtaining the higher Tc.

  2. Superconductive wire

    DOEpatents

    Korzekwa, David A.; Bingert, John F.; Peterson, Dean E.; Sheinberg, Haskell

    1995-01-01

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity.

  3. Superconductive wire

    DOEpatents

    Korzekwa, D.A.; Bingert, J.F.; Peterson, D.E.; Sheinberg, H.

    1995-07-18

    A superconductive article is made by inserting a rigid mandrel into an internal cavity of a first metallic tube, said tube having an interior surface and an exterior surface, said interior surface defining the interior cavity, forming a layer of a superconductive material or superconductive precursor upon the exterior surface of said first metallic tube, machining the layer of superconductive material or superconductive precursor to a predetermined diameter to form an intermediate article configured for insertion into a second metallic tube having an interior diameter corresponding to the predetermined diameter, inserting the machined intermediate article into a second metallic tube having an internal diameter corresponding to the predetermined diameter of the intermediate article to form a composite intermediate article, reducing or ironing the composite intermediate article to a predetermined cross-sectional diameter, and sintering the reduced or ironed composite intermediate article at temperatures and for time sufficient for the superconductive material or superconductive precursor to exhibit superconductivity. 2 figs.

  4. Model of an exotic chiral superconducting phase in a graphene bilayer.

    PubMed

    Hosseini, Mir Vahid; Zareyan, Malek

    2012-04-06

    We theoretically demonstrate the formation of a new type of unconventional superconductivity in graphene materials, which exhibits a gapless property. The studied superconductivity is based on an interlayer pairing of chiral electrons in bilayer graphene, which results in an exotic s-wave spin-triplet condensate order with anomalous thermodynamic properties. These include the possibility of a temperature-induced condensation causing an increase of the pairing gap with increasing temperature and an entropy of the stable superconducting state which can be higher than its value in the normal state. Our study reveals the analogy of the interlayer superconductivity in graphene materials to the color superconductivity in dense quark matter and the gapless pairing states in nuclear matter and ultracold atomic gases.

  5. Superconducting transistor

    DOEpatents

    Gray, Kenneth E.

    1979-01-01

    A superconducting transistor is formed by disposing three thin films of superconducting material in a planar parallel arrangement and insulating the films from each other by layers of insulating oxides to form two tunnel junctions. One junction is biased above twice the superconducting energy gap and the other is biased at less than twice the superconducting energy gap. Injection of quasiparticles into the center film by one junction provides a current gain in the second junction.

  6. Time-resolved spectroscopic study of the KrF laser-induced plasma plume created above an YBaCuO superconducting target

    SciTech Connect

    Girault, C.; Damiani, D.; Aubreton, J.; Catherinot, A.

    1989-07-10

    The laser-induced plasma plume created above an YBaCuO superconducting target by a KrF laser beam (248 nm) is investigated by time-resolved spectroscopy. High-resolution spectra are obtained and ejection velocities of ablated species are deduced from temporal evolution of spatially resolved spectroscopic measurements.

  7. High-efficiency WSi superconducting nanowire single-photon detectors for quantum state engineering in the near infrared

    NASA Astrophysics Data System (ADS)

    Le Jeannic, Hanna; Verma, Varun B.; Cavaillès, Adrien; Marsili, Francesco; Shaw, Matthew D.; Huang, Kun; Morin, Olivier; Nam, Sae Woo; Laurat, Julien

    2016-11-01

    We report on high-efficiency superconducting nanowire single-photon detectors based on amorphous WSi and optimized at 1064 nm. At an operating temperature of 1.8 K, we demonstrated a 93% system detection efficiency at this wavelength with a dark noise of a few counts per second. Combined with cavity-enhanced spontaneous parametric down-conversion, this fiber-coupled detector enabled us to generate narrowband single photons with a heralding efficiency greater than 90% and a high spectral brightness of $0.6\\times10^4$ photons/(s$\\cdot$mW$\\cdot$MHz). Beyond single-photon generation at large rate, such high-efficiency detectors open the path to efficient multiple-photon heralding and complex quantum state engineering.

  8. High-efficiency WSi superconducting nanowire single-photon detectors for quantum state engineering in the near infrared.

    PubMed

    Le Jeannic, Hanna; Verma, Varun B; Cavaillès, Adrien; Marsili, Francesco; Shaw, Matthew D; Huang, Kun; Morin, Olivier; Nam, Sae Woo; Laurat, Julien

    2016-11-15

    We report on high-efficiency superconducting nanowire single-photon detectors based on amorphous tungsten silicide and optimized at 1064 nm. At an operating temperature of 1.8 K, we demonstrated a 93% system detection efficiency at this wavelength with a dark noise of a few counts per second. Combined with cavity-enhanced spontaneous parametric downconversion, this fiber-coupled detector enabled us to generate narrowband single photons with a heralding efficiency greater than 90% and a high spectral brightness of 0.6×104 photons/(s·mW·MHz). Beyond single-photon generation at large rate, such high-efficiency detectors open the path to efficient multiple-photon heralding and complex quantum state engineering.

  9. Generation of three-qubit Greenberger-Horne-Zeilinger state of superconducting qubits via transitionless quantum driving

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Chen, Ye-Hong; Wu, Qi-Cheng; Shi, Zhi-Cheng; Song, Jie; Xia, Yan

    2017-01-01

    We present an efficient scheme to quickly generate three-qubit Greenberger-Horne-Zeilinger (GHZ) states by using three superconducting qubits (SQs) separated by two coplanar waveguide resonators (CPWRs) capacitively. The scheme is based on quantum Zeno dynamics and the approach of transitionless quantum driving to construct shortcuts to adiabatic passage. In order to highlight the advantages, we compare the present scheme with the traditional one with adiabatic passage. The comparison result shows the shortcut scheme is closely related to the adiabatic scheme but is better than it. Moreover, we discuss the influence of various decoherences with numerical simulation. The result proves that the present scheme is less sensitive to the energy relaxation, the decay of CPWRs and the deviations of the experimental parameters the same as the adiabatic passage. However, the shortcut scheme is effective and robust against the dephasing of SQs in comparison with the adiabatic scheme.

  10. Scanning Tunneling Spectroscopy in the Superconducting State and Vortex Cores of the β-Pyrochlore KOs2O6

    NASA Astrophysics Data System (ADS)

    Dubois, C.; Santi, G.; Cuttat, I.; Berthod, C.; Jenkins, N.; Petrović, A. P.; Manuel, A. A.; Fischer, Ø.; Kazakov, S. M.; Bukowski, Z.; Karpinski, J.

    2008-08-01

    We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc=9.6K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31 40 Å, in agreement with the value derived from the upper critical field Hc2. We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported.

  11. Microwave-induced excess quasiparticles in superconducting resonators measured through correlated conductivity fluctuations

    NASA Astrophysics Data System (ADS)

    de Visser, P. J.; Baselmans, J. J. A.; Yates, S. J. C.; Diener, P.; Endo, A.; Klapwijk, T. M.

    2012-04-01

    We have measured the number of quasiparticles and their lifetime in aluminium superconducting microwave resonators. The number of excess quasiparticles below 160 mK decreases from 72 to 17 μm-3 with a 6 dB decrease of the microwave power. The quasiparticle lifetime increases accordingly from 1.4 to 3.5 ms. These properties of the superconductor were measured through the spectrum of correlated fluctuations in the quasiparticle system and condensate of the superconductor, which show up in the resonator amplitude and phase, respectively. Because uncorrelated noise sources vanish, fluctuations in the superconductor can be studied with a sensitivity close to the vacuum noise.

  12. Superconductivity-induced magnetization depletion in a ferromagnet through an insulator in a ferromagnet-insulator-superconductor hybrid oxide heterostructure

    NASA Astrophysics Data System (ADS)

    Prajapat, C. L.; Singh, Surendra; Paul, Amitesh; Bhattacharya, D.; Singh, M. R.; Mattauch, S.; Ravikumar, G.; Basu, S.

    2016-05-01

    Coupling between superconducting and ferromagnetic states in hybrid oxide heterostructures is presently a topic of intense research. Such a coupling is due to the leakage of the Cooper pairs into the ferromagnet. However, tunneling of the Cooper pairs though an insulator was never considered plausible. Using depth sensitive polarized neutron reflectivity we demonstrate the coupling between superconductor and magnetic layers in epitaxial La2/3Ca1/3MnO3 (LCMO)/SrTiO3/YBa2Cu3O7-δ (YBCO) hybrid heterostructures, with SrTiO3 as an intervening oxide insulator layer between the ferromagnet and the superconductor. Measurements above and below the superconducting transition temperature (TSC) of YBCO demonstrate a large modulation of magnetization in the ferromagnetic layer below the TSC of YBCO in these heterostructures. This work highlights a unique tunneling phenomenon between the epitaxial layers of an oxide superconductor (YBCO) and a magnetic layer (LCMO) through an insulating layer. Our work would inspire further investigations on the fundamental aspect of a long range order of the triplet spin-pairing in hybrid structures.

  13. Superconductivity-induced magnetization depletion in a ferromagnet through an insulator in a ferromagnet-insulator-superconductor hybrid oxide heterostructure.

    PubMed

    Prajapat, C L; Singh, Surendra; Paul, Amitesh; Bhattacharya, D; Singh, M R; Mattauch, S; Ravikumar, G; Basu, S

    2016-05-21

    Coupling between superconducting and ferromagnetic states in hybrid oxide heterostructures is presently a topic of intense research. Such a coupling is due to the leakage of the Cooper pairs into the ferromagnet. However, tunneling of the Cooper pairs though an insulator was never considered plausible. Using depth sensitive polarized neutron reflectivity we demonstrate the coupling between superconductor and magnetic layers in epitaxial La2/3Ca1/3MnO3 (LCMO)/SrTiO3/YBa2Cu3O7-δ (YBCO) hybrid heterostructures, with SrTiO3 as an intervening oxide insulator layer between the ferromagnet and the superconductor. Measurements above and below the superconducting transition temperature (TSC) of YBCO demonstrate a large modulation of magnetization in the ferromagnetic layer below the TSC of YBCO in these heterostructures. This work highlights a unique tunneling phenomenon between the epitaxial layers of an oxide superconductor (YBCO) and a magnetic layer (LCMO) through an insulating layer. Our work would inspire further investigations on the fundamental aspect of a long range order of the triplet spin-pairing in hybrid structures.

  14. Local switching of two-dimensional superconductivity using the ferroelectric field effect

    NASA Astrophysics Data System (ADS)

    Takahashi, K. S.; Gabay, M.; Jaccard, D.; Shibuya, K.; Ohnishi, T.; Lippmaa, M.; Triscone, J.-M.

    2006-05-01

    Correlated oxides display a variety of extraordinary physical properties including high-temperature superconductivity and colossal magnetoresistance. In these materials, strong electronic correlations often lead to competing ground states that are sensitive to many parameters-in particular the doping level-so that complex phase diagrams are observed. A flexible way to explore the role of doping is to tune the electron or hole concentration with electric fields, as is done in standard semiconductor field effect transistors. Here we demonstrate a model oxide system based on high-quality heterostructures in which the ferroelectric field effect approach can be studied. We use a single-crystal film of the perovskite superconductor Nb-doped SrTiO3 as the superconducting channel and ferroelectric Pb(Zr,Ti)O3 as the gate oxide. Atomic force microscopy is used to locally reverse the ferroelectric polarization, thus inducing large resistivity and carrier modulations, resulting in a clear shift in the superconducting critical temperature. Field-induced switching from the normal state to the (zero resistance) superconducting state was achieved at a well-defined temperature. This unique system could lead to a field of research in which devices are realized by locally defining in the same material superconducting and normal regions with `perfect' interfaces, the interface being purely electronic. Using this approach, one could potentially design one-dimensional superconducting wires, superconducting rings and junctions, superconducting quantum interference devices (SQUIDs) or arrays of pinning centres.

  15. Local switching of two-dimensional superconductivity using the ferroelectric field effect.

    PubMed

    Takahashi, K S; Gabay, M; Jaccard, D; Shibuya, K; Ohnishi, T; Lippmaa, M; Triscone, J-M

    2006-05-11

    Correlated oxides display a variety of extraordinary physical properties including high-temperature superconductivity and colossal magnetoresistance. In these materials, strong electronic correlations often lead to competing ground states that are sensitive to many parameters--in particular the doping level--so that complex phase diagrams are observed. A flexible way to explore the role of doping is to tune the electron or hole concentration with electric fields, as is done in standard semiconductor field effect transistors. Here we demonstrate a model oxide system based on high-quality heterostructures in which the ferroelectric field effect approach can be studied. We use a single-crystal film of the perovskite superconductor Nb-doped SrTiO3 as the superconducting channel and ferroelectric Pb(Zr,Ti)O3 as the gate oxide. Atomic force microscopy is used to locally reverse the ferroelectric polarization, thus inducing large resistivity and carrier modulations, resulting in a clear shift in the superconducting critical temperature. Field-induced switching from the normal state to the (zero resistance) superconducting state was achieved at a well-defined temperature. This unique system could lead to a field of research in which devices are realized by locally defining in the same material superconducting and normal regions with 'perfect' interfaces, the interface being purely electronic. Using this approach, one could potentially design one-dimensional superconducting wires, superconducting rings and junctions, superconducting quantum interference devices (SQUIDs) or arrays of pinning centres.

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

    PubMed

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

    2016-11-15

    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.

  17. Interface-induced superconductivity at ˜25 K at ambient pressure in undoped CaFe2As2 single crystals

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    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.

  18. Enhancement of superconductivity near the pressure-induced semiconductor-metal transition in the BiS₂-based superconductors LnO₀.₅F₀.₅BiS₂ (Ln = La, Ce, Pr, Nd).

    PubMed

    Wolowiec, C T; White, B D; Jeon, I; Yazici, D; Huang, K; Maple, M B

    2013-10-23

    Measurements of electrical resistivity were performed between 3 and 300 K at various pressures up to 2.8 GPa on the BiS2-based superconductors LnO0.5F0.5BiS2 (Ln=Pr, Nd). At lower pressures, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 exhibit superconductivity with critical temperatures Tc of 3.5 and 3.9 K, respectively. As pressure is increased, both compounds undergo a transition at a pressure Pt from a low Tc superconducting phase to a high Tc superconducting phase in which Tc reaches maximum values of 7.6 and 6.4 K for PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2, respectively. The pressure-induced transition is characterized by a rapid increase in Tc within a small range in pressure of ∼0.3 GPa for both compounds. In the normal state of PrO0.5F0.5BiS2, the transition pressure Pt correlates with the pressure where the suppression of semiconducting behaviour saturates. In the normal state of NdO0.5F0.5BiS2, Pt is coincident with a semiconductor-metal transition. This behaviour is similar to the results recently reported for the LnO0.5F0.5BiS2 (Ln=La, Ce) compounds. We observe that Pt and the size of the jump in Tc between the two superconducting phases both scale with the lanthanide element in LnO0.5F0.5BiS2 (Ln=La, Ce, Pr, Nd).

  19. Feasibility study for reduction of the screening current induced field in a 2G high temperature superconducting coil

    NASA Astrophysics Data System (ADS)

    Hwang, Y. J.; Jang, J. Y.; Ahn, M. C.; Park, Y. G.; Lee, S. G.

    2016-10-01

    This paper reports the effects of thermal energy on reducing the overshoot of the current sweep cycle method to reduce the screening current-induced field (SCF) in a 2G high temperature superconducting (HTS) coil. A disadvantage of the current sweep cycle method is the necessity for large overshoot in the coil current. For a 2G HTS coil, excessive overshooting of the coil current is undesirable (Yanagisawa et al 2012 AIP Conf. Proc. 1434 1373-8). In an effort to circumvent this overshooting problem, the thermal energy effect was investigated in combination with the current sweep cycle method based on experiments in this study. The experimental results show that greater SCF reduction in the HTS coil was obtained upon increasing thermal energy by heater current.

  20. Tunable superconductivity in decorated graphene

    NASA Astrophysics Data System (ADS)

    Han, Zheng; Allain, Adrien; Marty, Laetitia; Bendiab, Nedjma; Toulemonde, Pierre; Strobel, Pierre; Coraux, Johann; Bouchiat, Vincent

    2013-03-01

    Graphene offers an exposed bidimensional gas of high mobility charge carriers with gate tunable density. Its chemical inertness offers an outstanding platform to explore exotic 2D superconductivity. Superconductivity can be induced in graphene by means of proximity effect (by depositing a set of superconducting metal clusters such as lead or tin nanoparticles). The influence of decoration material, density or particles and disorder of graphene will be discussed. In the case of disordered graphene, Tin decoration leads to a gate-tunable superconducting-to-insulator quantum phase transition. Superconductivity in graphene is also expected to occur under strong charge doping (induced either by gating or under chemical decoration, in analogy with graphite intercalated compounds). I will also show preliminary results showing the influence of Calcium intercalation of few layer graphene and progress toward the demonstration of intrinsic superconductivity in such systems. Work supported by EU GRANT FP7-NMP GRENADA.

  1. Time constant of round superconducting structures determined from the time development of the induced magnetic field

    NASA Astrophysics Data System (ADS)

    Takács, S.

    2016-12-01

    It is shown that evaluating the time development of the penetrated magnetic field into the superconductors can be used for the determination of time constant for round structures, too. The calculations are very similar to those used for the flat structures. The method is very simple, both by the practical realization of the experiment and by the evaluation of the time evolution of the penetrated magnetic field above the superconductor. The procedure uses an exponential decrease of the applied magnetic field, which can be easily performed by discharging an external circuit. By determining the position of the maximum of the difference between the penetrated field induction and the applied magnetic field induction, the corresponding time constant can be evaluated by a very simple equation, which is calculated in the paper. The results are very similar to the previous calculations, obtained for the flat superconducting cables. In addition, it is suggested that knowing the time constant of superconducting structures could be in many cases more important both for research aspects and for practical applications.

  2. Break the electron- hole balance and pressure induced superconductivity in Tungsten Ditelluride

    NASA Astrophysics Data System (ADS)

    Song, Fengqi; Pan, Xing-Chen

    Tungsten ditelluride has garnered immense interest due to the recent discovery of titanic unsaturated magnetoresistance up to 60 Tesla and its possible topological metal nature. The titanic unsaturated magnetoresistance is attributed to the perfect compensation between the opposite carriers in this material. Motivated by the small and sensitive Fermi surface of 5d electronic orbitals, we break the electron-hole balance by the application of high pressure. Superconductivity sharply appears at the pressure of 2.5 GPa, quickly reaching a maximum critical temperature of 7 K at around 16.8 GPa, and followed by a monotonic decrease in Tc with increasing pressure exhibiting the typical dome-shaped superconducting phase. What's more, linear magnetoresistance dominates the transport behavior under high pressure instead of semi-classical parabolic magnetoresistance, like in other topological metals. Refence: Nature Commun. 6, 7805 (2015), arXiv 1505, 07968. The authors would like to thank the National Key Projects for Basic Research in China, the National Natural Science Foundation of China , the NSF of Jiangsu Province, the PAPD project, and the Fundamental Research Funds for the Central Universities.

  3. Bulk Superconductivity in Fe1+yTe0.6Se0.4 Induced by Removal of Excess Fe

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Sun, Yue; Zhang, Shuo; Zhuang, Jincheng; Yuan, Feifei; Li, Xiong; Shi, Zhixiang; Yamada, Tatsuhiro; Tsuchiya, Yuji; Tamegai, Tsuyoshi

    2014-06-01

    Experimental evidences from transport, magnetic, and magneto-optical (MO) image measurements confirmed that arsenic (As) vapor annealing was another effective way to induce bulk superconductivity with isotropic, large, and homogenous superconducting critical current density (Jc) in Fe1+yTe0.6Se0.4 single crystal. Since As is an exotic and easily detectable heavy element to Fe1+yTe0.6Se0.4 single crystal, As vapor annealing is very advantageous for the study of annealing mechanism. Detailed micro-structural and elemental analyses exclude the possibility that intercalating or doping effect may happen in the other post-annealing methods, proving that Fe reacts with As on the surface of the crystal and the reaction itself acts as a driving force to drag excess Fe out. The removal of excess Fe results in the good superconductivity performance.

  4. Anisotropic rectifying characteristics induced by the superconducting gap of YBa2Cu3O7-δ/Nb-doped SrTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Zhang, M. J.; Hao, F. X.; Zhang, C.; Liu, X.; Li, X. G.

    2015-11-01

    In this paper, we investigated the anisotropic rectifying characteristics of a YBa2Cu3O7-δ (YBCO)/Nb-doped SrTiO3 heterojunction in magnetic fields of up to 9 T by rotating the junction from H//c to H//ab of the YBCO film. From the temperature and field dependencies of the diffusion potential Vd, we found that the angle-resolved reductions of Vd from its original value, δVd, were induced by the anisotropic superconducting gap Δ of the YBCO. The anisotropic parameter obtained from Δ was close to that obtained from the angular-dependent upper critical fields of the YBCO. This heterojunction is helpful both in investigating the superconducting gap and in designing sensitive superconducting devices.

  5. Band-renormalization effect in coexistent state of d-wave superconducting and antiferromagnetic orders for Hubbard model

    NASA Astrophysics Data System (ADS)

    Sato, R.; Yokoyama, H.

    2016-11-01

    In view of cuprate superconductors, we apply a variational Monte Carlo method to a strongly correlated square-lattice Hubbard (t-t‧-U) model. As a one-body part in a trial wave function, we use a coexistent state of antiferromagnetic (AF) and d-wave superconducting (SC) orders for each of which band-renormalization effect (BRE) is considered independently. We focus on t‧/t and doping-rate (δ) dependence of properties of this state. It is found that the BRE for the AF order causes expansion of the AF area up to δ ∼ 0.2 for a large |t‧/t|. For t‧ / t = 0 (- 0.3), the AF and SC orders are coexistent (mutually exclusive), and the state is unstable toward (stable against) phase separation. This feature of coexistence or exclusion depends on the position of the Fermi surface in the underlying pure AF state, and indicates that antinodal Fermi surfaces are crucial for forming d-wave SC.

  6. Enhancing superconductivity in A3C60 fullerides

    NASA Astrophysics Data System (ADS)

    Kim, Minjae; Nomura, Yusuke; Ferrero, Michel; Seth, Priyanka; Parcollet, Olivier; Georges, Antoine

    2016-10-01

    Motivated by the recent experimental report of a possible light-induced superconductivity in K3C60 at high temperature [Mitrano et al., Nature 530, 451 (2016), 10.1038/nature16522], we investigate theoretical mechanisms for enhanced superconductivity in A3C60 fullerenes. We find that an "interaction imbalance" corresponding to a smaller value of the Coulomb matrix element for two of the molecular orbitals in comparison to the third one, efficiently enhances superconductivity. Furthermore, we perform first-principle calculations of the changes in the electronic structure and in the screened Coulomb matrix elements of K3C60 , brought in by the deformation associated with the pumped T1 u intramolecular mode. We find that an interaction imbalance is indeed induced, with a favorable sign and magnitude for superconductivity enhancement. The physical mechanism responsible for this enhancement consists of a stabilization of the intramolecular states containing a singlet pair, while preserving the orbital fluctuations allowing for a coherent interorbital delocalization of the pair. Other perturbations have also been considered and found to be detrimental to superconductivity. The light-induced deformation and ensuing interaction imbalance is shown to bring superconductivity further into the strong-coupling regime.

  7. Majorana Fermion Induced Non-local Current Correlations in Spin-orbit Coupled Superconducting Wires

    NASA Astrophysics Data System (ADS)

    Liu, Jie; Zhang, Fu-Chun; Law, K. T.

    2014-03-01

    The observation of zero bias conductance peaks in semiconductor wire-superconductor heterostructures has generated great interest, and there is a hot debate on whether the observation is associated with Majorana Fermions (MFs) or other effects which enhance local Andreev reflections. In this work, we study the transport of a normal lead/semiconductor wire-superconductor heterostructure /normal lead junction. We show that when MF end states from the two ends of the wire are strongly coupled, the MF end states can suppress local Andreev reflections and strongly enhance crossed Andreev reflections (CARs), in which an electron from one lead is reflected as a hole in a different lead. In the CAR dominated regime, the current-current correlations between the two leads are strongly enhanced. Moreover, the Fano factor of a normal lead, which is the ratio of the shot noise to the average current, is reduced from 2e to e. Since the CAR associated effects are non-local effects and they cannot be induced by processes which enhance local Andreev reflections, therefore, the measurement of Fano factors and current-current correlations of the normal leads can be used to identify MFs.

  8. H. R. 1009: A Bill to terminate the obligation of funds by the United States for the superconducting super collider project. Introduced in the House of Representatives, One Hundred Third Congress, First Session, February 18, 1993

    SciTech Connect

    Not Available

    1993-01-01

    The purpose of this Bill is to terminate the obligation of funds by the United States for the superconducting super collider project. This Bill states, [open quotes]Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That the United States shall not, after the date of enactment of this Act, obligate any funds for the superconducting super collider project.[close quotes

  9. Persistent Fe moments in the normal-state collapsed-tetragonal phase of the pressure-induced superconductor Ca0.67Sr0.33Fe2As2

    NASA Astrophysics Data System (ADS)

    Jeffries, J. R.; Butch, N. P.; Lipp, M. J.; Bradley, J. A.; Kirshenbaum, K.; Saha, S. R.; Paglione, J.; Kenney-Benson, C.; Xiao, Y.; Chow, P.; Evans, W. J.

    2014-10-01

    Using nonresonant Fe Kβ x-ray emission spectroscopy, we reveal that Sr substitution into CaFe2As2 decouples the Fe moment from the volume collapse transition, yielding a collapsed-tetragonal, paramagnetic normal state out of which superconductivity develops. X-ray diffraction measurements implicate the c-axis lattice parameter as the controlling criterion for the Fe moment, promoting a generic description for the appearance of pressure-induced superconductivity in the alkaline-earth-based 122 ferropnictides (AFe2As2). The evolution of Tc with pressure lends support to theories for superconductivity involving unconventional pairing mediated by magnetic fluctuations.

  10. Superconductivity Bordering Rashba Type Topological Transition

    PubMed Central

    Jin, M. L.; Sun, F.; Xing, L. Y.; Zhang, S. J.; Feng, S. M.; Kong, P. P.; Li, W. M.; Wang, X. C.; Zhu, J. L.; Long, Y. W.; Bai, H. Y.; Gu, C. Z.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Mao, H. K.; Jin, C. Q.

    2017-01-01

    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 close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature TC 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. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity. PMID:28051188

  11. Superconductivity Bordering Rashba Type Topological Transition.

    PubMed

    Jin, M L; Sun, F; Xing, L Y; Zhang, S J; Feng, S M; Kong, P P; Li, W M; Wang, X C; Zhu, J L; Long, Y W; Bai, H Y; Gu, C Z; Yu, R C; Yang, W G; Shen, G Y; Zhao, Y S; Mao, H K; Jin, C Q

    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 close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature TC 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. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.

  12. Superconductivity Bordering Rashba Type Topological Transition

    NASA Astrophysics Data System (ADS)

    Jin, M. L.; Sun, F.; Xing, L. Y.; Zhang, S. J.; Feng, S. M.; Kong, P. P.; Li, W. M.; Wang, X. C.; Zhu, J. L.; Long, Y. W.; Bai, H. Y.; Gu, C. Z.; Yu, R. C.; Yang, W. G.; Shen, G. Y.; Zhao, Y. S.; Mao, H. K.; Jin, C. Q.

    2017-01-01

    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 close then reopen with band inverse. Superconducting transition appears at 8 GPa with a critical temperature TC 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. The Hall Effect measurements reveal an intimate relationship between superconductivity and the unusual change in carrier density that points to possible unconventional superconductivity.

  13. 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 TC 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

  14. Topological Superconductivity in Dirac Semimetals.

    PubMed

    Kobayashi, Shingo; Sato, Masatoshi

    2015-10-30

    Dirac semimetals host bulk band-touching Dirac points and a surface Fermi loop. We develop a theory of superconducting Dirac semimetals. Establishing a relation between the Dirac points and the surface Fermi loop, we clarify how the nontrivial topology of Dirac semimetals affects their superconducting state. We note that the unique orbital texture of Dirac points and a structural phase transition of the crystal favor symmetry-protected topological superconductivity with a quartet of surface Majorana fermions. We suggest the possible application of our theory to recently discovered superconducting states in Cd_{3}As_{2}.

  15. 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

  16. Quantum Memristors with Superconducting Circuits

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    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.

  17. Quantum Memristors with Superconducting Circuits.

    PubMed

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

    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. 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.

  18. Superconductivity in repulsively interacting fermions on a diamond chain: Flat-band-induced pairing

    NASA Astrophysics Data System (ADS)

    Kobayashi, Keita; Okumura, Masahiko; Yamada, Susumu; Machida, Masahiko; Aoki, Hideo

    2016-12-01

    To explore whether a flat-band system can accommodate superconductivity, we consider repulsively interacting fermions on the diamond chain, a simplest possible quasi-one-dimensional system that contains a flat band. Exact diagonalization and the density-matrix renormalization group are used to show that we have a significant binding energy of a Cooper pair with a long-tailed pair-pair correlation in real space when the total band filling is slightly below 1/3, where a filled dispersive band interacts with the flat band that is empty but close to EF. Pairs selectively formed across the outer sites of the diamond chain are responsible for the pairing correlation. At exactly 1/3-filling an insulating phase emerges, where the entanglement spectrum indicates the particles on the outer sites are highly entangled and topological. These come from a peculiarity of the flat band in which "Wannier orbits" are not orthogonalizable.

  19. Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds

    NASA Astrophysics Data System (ADS)

    Chi, Songxue; Uwatoko, Yoshiya; Cao, Huibo; Hirata, Yasuyuki; Hashizume, Kazuki; Aoyama, Takuya; Ohgushi, Kenya

    2016-07-01

    The pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe2Se3 and BaFe2S3 have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe2Se3 the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change. In contrast, the stripe order in BaFe2S3 undergoes a quantum phase transition where an abrupt increase of Néel temperature by more than 50% occurs at about 1 GPa, accompanied by a jump in the ordered moment. With its spin structure unchanged, BaFe2S3 enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true neighbor of superconductivity emerging at higher pressures.

  20. Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds.

    PubMed

    Chi, Songxue; Uwatoko, Yoshiya; Cao, Huibo; Hirata, Yasuyuki; Hashizume, Kazuki; Aoyama, Takuya; Ohgushi, Kenya

    2016-07-22

    The pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe_{2}Se_{3} and BaFe_{2}S_{3} have been studied using neutron diffraction. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe_{2}Se_{3} the ladders are brought much closer to each other by pressure, but the stripe-type magnetic order shows no observable change. In contrast, the stripe order in BaFe_{2}S_{3} undergoes a quantum phase transition where an abrupt increase of Néel temperature by more than 50% occurs at about 1 GPa, accompanied by a jump in the ordered moment. With its spin structure unchanged, BaFe_{2}S_{3} enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true neighbor of superconductivity emerging at higher pressures.

  1. Vortex-State Complex Hall Conductivity of Superconducting YBa2Cu3O7 Epitaxial Films at Radio Frequencies

    NASA Technical Reports Server (NTRS)

    Beam, D. A.; Yeh, N.-C.; Vasquez, R. P.

    1999-01-01

    The first intermediate-frequency measurements of the vortex-state complex Hall conductivity \\sigma_xy of YBa_2CU_3O_7 superconducting epitaxial films are reported. A direct transport measurement technique from dc to 7 MHz was used. The results are analyzed in terms of a phenomenological model, generalized from that for the dc Hall conductivity, with the assumptions that: 1) the sign reversal in the vortex-state Hall conductivity is associated with the different carrier densities within and far away from the vortex cores; 2) the Drude approximation Is applicable; and 3) the anomalous sign reversal occurs in the flux-flow Limit. The temperature, frequency, and magnetic field (B) dependencies of our \\sigma_xy data are in good agreement with the model. The B-dependence of \\sigma_xy reveals that both vortices (\\sigma_xyAv \\propto BA-1) and quasiparticles (sigma_xyAq \\propto B) contribute to the vortex-state Hall conduction. The magnitude of the real part of \\sigma_xy, \\sigma_xyA\\prime, is in good agreement with our model, while that of the imaginary part, \\sigma_xyA\\prime \\prime, is significantly Luger than the theoretical prediction. This may be attributed to the unconventional electronic structures in the vortex core of cuprate superconductors with d-wave or mixed pairing symmetries.

  2. Superconductivity in graphite intercalation compounds

    SciTech Connect

    Smith, Robert P.; Weller, Thomas E.; Howard, Christopher A.; Dean, Mark P. M.; Rahnejat, Kaveh C.; Saxena, Siddharth S.; Ellerby, Mark

    2015-02-26

    This study examines the field of superconductivity in the class of materials known as graphite intercalation compounds which has a history dating back to the 1960s. This paper recontextualizes the field in light of the discovery of superconductivity in CaC₆ and YbC₆ in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.

  3. Magnetic levitation, suspension, and superconductivity: Macroscopic and mesoscopic

    SciTech Connect

    Haley, S.B.; Fink, H.J.

    1996-02-01

    The levitation state of a large magnetic sphere held in equilibrium above a thick superconducting layer in the Meissner state is a single temperature-independent state as long as the maximum magnetic field at the superconducting (SC) surface does not exceed the critical field {ital H}{sub {ital c}}({ital T}). In contrast, a magnetic microsphere trapped by a superconducting microring exhibits very different behavior. When the radius {ital b} of the SC ring is of the same order as the Ginzburg-Landau coherence length {xi}({ital T}), the system exhibits, in general, a small set of distinct, quantized, temperature-dependent levitation and suspension states. For certain discrete values of {ital b} the flux in the ring is quantized, and the levitation and suspension heights are temperature independent. An abrupt temperature induced transition in the suspension height is also found for a special set of parameters. {copyright} {ital 1996 The American Physical Society.}

  4. Superconductivity-induced re-entrance of the orthorhombic distortion in Ba1-xKxFe2As2.

    PubMed

    Böhmer, A E; Hardy, F; Wang, L; Wolf, T; Schweiss, P; Meingast, C

    2015-07-31

    Detailed knowledge of the phase diagram and the nature of the competing magnetic and superconducting phases is imperative for a deeper understanding of the physics of iron-based superconductivity. Magnetism in the iron-based superconductors is usually a stripe-type spin-density-wave, which breaks the tetragonal symmetry of the lattice, and is known to compete strongly with superconductivity. Recently, it was found that in some systems an additional spin-density-wave transition occurs, which restores this tetragonal symmetry, however, its interaction with superconductivity remains unclear. Here, using thermodynamic measurements on Ba1-xKxFe2As2 single crystals, we show that the spin-density-wave phase of tetragonal symmetry competes much stronger with superconductivity than the stripe-type spin-density-wave phase, which results in a novel re-entrance of the latter at or slightly below the superconducting transition.

  5. Large superconducting double-gap, a pronounced pseudogap and evidence for proximity-induced topological superconductivity in the Bi2Te3/Fe1+yTe interfacial superconductor

    NASA Astrophysics Data System (ADS)

    Shen, J. Y.; He, M. Q.; He, Q. L.; Law, K. T.; Sou, I. K.; Lortz, R.; Petrovic, A. P.

    We investigate directional point-contact spectroscopy on a Bi2Te3/ Fe1+yTe heterostructure, fabricated via van der Waals epitaxy, which is interfacial superconducting with an onset TC at 12K and zero resistance below 8K. A large superconducting twin-gap structure is seen down to 0.27K, together with a zero bias conductance peak. The anisotropic smaller gap (Δ1) is around 5 meV at 0.27K and closes at 8K, while the other one (Δ2), as large as 12 meV, is isotropic and eventually evolves into a pseudogap closing at 40K. Both, the two-gap BTK and Dynes models can well reproduce our data, demonstrating Δ1 should be associated with the proximity-induced superconductivity in the topological Bi2Te3 layer, while Δ2 may be attributed to an intrinsically-doped FeTe thin film at the interface. This work was supported by grants from the Research Grants Council of the Hong Kong Special Administrative Region, China (603010, SEGHKUST03).

  6. Heat Capacity and Thermal Conductance Measurements of a Superconducting-Normal Mixed State by Detection of Single 3 eV Photons in a Magnetic Penetration Thermometer

    NASA Technical Reports Server (NTRS)

    Stevenson, T. R.; Balvin, M. A.; Bandler, S. R.; Denis, K. L.; Lee, S.-J.; Nagler, P. C.; Smith, S. J.

    2015-01-01

    We report on measurements of the detected signal pulses in a molybdenum-gold Magnetic Penetration Thermometer (MPT) in response to absorption of one or more 3 eV photons. We designed and used this MPT sensor for x-ray microcalorimetry. In this device, the diamagnetic response of a superconducting MoAu bilayer is used to sense temperature changes in response to absorbed photons, and responsivity is enhanced by a Meissner transition in which the magnetic flux penetrating the sensor changes rapidly to minimize free energy in a mixed superconducting normal state. We have previously reported on use of our MPT to study a thermal phonon energy loss to the substrate when absorbing x-rays. We now describe results of extracting heat capacity C and thermal conductance G values from pulse height and decay time of MPT pulses generated by 3 eV photons. The variation in C and G at temperatures near the Meissner transition temperature (set by an internal magnetic bias field) allow us to probe the behavior in superconducting normal mixed state of the condensation energy and the electron cooling power resulting from quasi-particle recombination and phonon emission. The information gained on electron cooling power is also relevant to the operation of other superconducting detectors, such as Microwave Kinetic Inductance Detectors.

  7. Mestastable State Population in Laser Induced Plasmas

    NASA Technical Reports Server (NTRS)

    Kwong, V. H. S.; Kyriakides, C.; Ward, W. K.

    2006-01-01

    Laser induced plasma has been used as a source of neutrals and ions in the study of astrophysical plasmas. The purity of state of this source is essential in the determination of collision parameters such as the charge transfer rate coefficients between ions and neutrals. We will show that the temperature of the laser induced plasma is a rapidly decreasing function of time. The temperature is initially high but cools off rapidly through collisions with the expanding plasma electrons as the plasma recombines and streams into the vacuum. This rapid expansion of the plasma, similar to a supersonic jet, drastically lowers the internal energy of the neutrals and ions.

  8. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-07-22

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  9. Superconducting Cable

    DOEpatents

    Hughey, Raburn L.; Sinha, Uday K.; Reece, David S.; Muller, Albert C.

    2005-03-08

    In order to provide a flexible oxide superconducting cable which is reduced in AC loss, tape-shaped superconducting wires covered with a stabilizing metal are wound on a flexible former. The superconducting wires are preferably laid on the former at a bending strain of not more than 0.2%. In laying on the former, a number of tape-shaped superconducting wires are laid on a core member in a side-by-side manner, to form a first layer. A prescribed number of tape-shaped superconducting wires are laid on top of the first layer in a side-by-side manner, to form a second layer. The former may be made of a metal, plastic, reinforced plastic, polymer, or a composite and provides flexibility to the superconducting wires and the cable formed therewith.

  10. The role of local repulsion in superconductivity in the Hubbard-Holstein model

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Wang, Bingnan; Teo, Koon Hoo

    2017-01-01

    We examine the superconducting solution in the Hubbard-Holstein model using Dynamical Mean Field Theory. The Holstein term introduces the site-independent Boson fields coupling to local electron density, and has two competing influences on superconductivity: The Boson field mediates the effective electron-electron attraction, which is essential for the S-wave electron pairing; the same coupling to the Boson fields also induces the polaron effect, which makes the system less metallic and thus suppresses superconductivity. The Hubbard term introduces an energy penalty U when two electrons occupy the same site, which is expected to suppress superconductivity. By solving the Hubbard-Holstein model using Dynamical Mean Field theory, we find that the Hubbard U can be beneficial to superconductivity under some circumstances. In particular, we demonstrate that when the Boson energy Ω is small, a weak local repulsion actually stabilizesthe S-wave superconducting state. This behavior can be understood as an interplay between superconductivity, the polaron effect, and the on-site repulsion: As the polaron effect is strong and suppresses superconductivity in the small Ω regime, the weak on-site repulsion reduces the polaron effect and effectively enhances superconductivity. Our calculation elucidates the role of local repulsion in the conventional S-wave superconductors.

  11. Field-induced transition from chiral spin-triplet to mixed-parity Fulde-Ferrell-Larkin-Ovchinnikov superconductivity

    NASA Astrophysics Data System (ADS)

    Romano, Alfonso; Cuoco, Mario; Noce, Canio; Gentile, Paola; Annunziata, Gaetano

    2010-02-01

    We analyze the response to a magnetic field of a two-dimensional spin-triplet superconductor with chiral order parameter when triplet pairing is closely competing with the singlet one. The study is performed via numerical solution of the Bogoliubov-de Gennes equations, assuming that the translational symmetry is broken in one direction by the presence of an interface beyond which superconducting pairing is not effective. We show that as the intensity of the magnetic field is increased above a threshold value, the system undergoes a transition to a spatially inhomogeneous state of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type where chirality disappears and a singlet-triplet mixing takes place along the direction perpendicular to the interface. Subdominant singlet components are found to accompany the triplet dominant ones in both phases. They develop close to the interface at low fields, then turning continuously into oscillating long-range ones as the field is increased. A similar behavior is found for the magnetization. It nucleates at the interface in the chiral phase, then acquiring in the FFLO phase an oscillatory behavior reaching its maximum amplitude at the sites where the dominant triplet component has a node. At these sites, the local spin-resolved density of states exhibits strong resonances, associated with the formation of Andreev bound states, which tend to broaden and decay in intensity as increasingly high magnetic fields are considered.

  12. Superconducting and normal state properties of the systems La1 -xMxPt4Ge12 (M = Ce ,Th )

    NASA Astrophysics Data System (ADS)

    Huang, K.; Yazici, D.; White, B. D.; Jeon, I.; Breindel, A. J.; Pouse, N.; Maple, M. B.

    2016-09-01

    Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La1 -xMxPt4Ge12(M =Ce and Th ) . Superconductivity in LaPt4Ge12 was quickly suppressed with Ce substitution and no evidence for superconductivity was found down to 1.1 K for x >0.2 . Temperature-dependent specific heat data at low temperatures for La1 -xCexPt4Ge12 show a change from power-law to exponential behavior, which may be an indication for multiband superconductivity in LaPt4Ge12 . A similar crossover was observed in the Pr1 -xCexPt4Ge12 system. However, the suppression rates of the superconducting transition temperatures Tc(x ) in the two systems are quite disparate, indicating a difference in the nature of superconductivity, which is conventional in LaPt4Ge12 and unconventional in PrPt4Ge12 . In comparison, a nearly linear and smooth evolution of Tc with increasing Th was observed in the La1 -xThxPt4Ge12 system, with no change of the superconducting energy gap in the temperature dependence of the specific heat, suggesting similar types of superconductivity in both the LaPt4Ge12 and ThPt4Ge12 compounds.

  13. Microwave induced plasma discharge in multi-cell superconducting radio-frequency cavity.

    PubMed

    Ahmed, Shahid; Mammosser, John D

    2015-07-01

    A R&D effort for in situ cleaning of 1.5 GHz Superconducting Radio Frequency (SRF) cavities at room temperature using the plasma processing technique has been initiated at Jefferson Lab. This is a step toward the cleaning of cryomodules installed in the Continuous Electron Beam Accelerator Facility (CEBAF). For this purpose, we have developed an understanding of plasma discharge in a 5-cell CEBAF-type SRF cavity having configurations similar to those in the main accelerator. The focus of this study involves the detailed investigations of developing a plasma discharge inside the cavity volume and avoids the breakdown condition in the vicinity of the ceramic RF window. A plasma discharge of the gas mixture Ar-O2 (90%:10%) can be established inside the cavity volume by the excitation of a resonant 4π/5 TM010-mode driven by a klystron. The absence of any external magnetic field for generating the plasma is suitable for cleaning cavities installed in a complex cryomodule assembly. The procedures developed in these experimental investigations can be applied to any complex cavity structure. Details of these experimental measurements and the observations are discussed in the paper.

  14. Microwave induced plasma discharge in multi-cell superconducting radio-frequency cavity

    SciTech Connect

    Ahmed, Shahid; Mammosser, John D.

    2015-07-15

    A R&D effort for in situ cleaning of 1.5 GHz Superconducting Radio Frequency (SRF) cavities at room temperature using the plasma processing technique has been initiated at Jefferson Lab. This is a step toward the cleaning of cryomodules installed in the Continuous Electron Beam Accelerator Facility (CEBAF). For this purpose, we have developed an understanding of plasma discharge in a 5-cell CEBAF-type SRF cavity having configurations similar to those in the main accelerator. The focus of this study involves the detailed investigations of developing a plasma discharge inside the cavity volume and avoids the breakdown condition in the vicinity of the ceramic RF window. A plasma discharge of the gas mixture Ar–O{sub 2} (90%:10%) can be established inside the cavity volume by the excitation of a resonant 4π/5 TM{sub 010}-mode driven by a klystron. The absence of any external magnetic field for generating the plasma is suitable for cleaning cavities installed in a complex cryomodule assembly. The procedures developed in these experimental investigations can be applied to any complex cavity structure. Details of these experimental measurements and the observations are discussed in the paper.

  15. Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds

    SciTech Connect

    Chi, Songxue; Uwatoko, Yoshiya; Cao, Huibo; Hirata, Yasuyuki; Hashizume, Kazuki; Aoyama, Takuya; Ohgushi, Kenya

    2016-07-21

    We studied the pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFe$_2$Se$_3$ and BaFe$_2$S$_3$ using single crytal neutron diffraction technique. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe$_2$Se$_3$ the ladders are brought much closer to each other by pressure, but the stripe-type of magnetic order shows no observable change. Furthermore, the stripe order in BaFe$_2$S$_3$, undergoes a quantum phase transition where an abrupt increase of $N\\acute{e}el$ temperature by more than 50$\\%$ occurs at about 1 GPa, accompanied by a jump in ordered moment. Finally, with its spin structure unchanged, BaFe$_2$S$_3$ enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true herald for superconductivity emerging at higher pressures.

  16. Magnetic Precursor of the Pressure-Induced Superconductivity in Fe-Ladder Compounds

    DOE PAGES

    Chi, Songxue; Uwatoko, Yoshiya; Cao, Huibo; ...

    2016-07-21

    We studied the pressure effects on the antiferromagentic orders in iron-based ladder compounds CsFemore » $$_2$$Se$$_3$$ and BaFe$$_2$$S$$_3$$ using single crytal neutron diffraction technique. With identical crystal structure and similar magnetic structures, the two compounds exhibit highly contrasting magnetic behaviors under moderate external pressures. In CsFe$$_2$$Se$$_3$$ the ladders are brought much closer to each other by pressure, but the stripe-type of magnetic order shows no observable change. Furthermore, the stripe order in BaFe$$_2$$S$$_3$$, undergoes a quantum phase transition where an abrupt increase of $$N\\acute{e}el$$ temperature by more than 50$$\\%$$ occurs at about 1 GPa, accompanied by a jump in ordered moment. Finally, with its spin structure unchanged, BaFe$$_2$$S$$_3$$ enters an enhanced magnetic phase that bears the characteristics of an orbital selective Mott phase, which is the true herald for superconductivity emerging at higher pressures.« less

  17. Superconductivity-related insulating behavior.

    PubMed

    Sambandamurthy, G; Engel, L W; Johansson, A; Shahar, D

    2004-03-12

    We present the results of an experimental study of superconducting, disordered, thin films of amorphous indium oxide. These films can be driven from the superconducting phase to a reentrant insulating state by the application of a perpendicular magnetic field (B). We find that the high-B insulator exhibits activated transport with a characteristic temperature, TI. TI has a maximum value (TpI) that is close to the superconducting transition temperature (Tc) at B=0, suggesting a possible relation between the conduction mechanisms in the superconducting and insulating phases. Tp(I) and Tc display opposite dependences on the disorder strength.

  18. Superconductivity in graphite intercalation compounds

    DOE PAGES

    Smith, Robert P.; Weller, Thomas E.; Howard, Christopher A.; ...

    2015-02-26

    This study examines the field of superconductivity in the class of materials known as graphite intercalation compounds which has a history dating back to the 1960s. This paper recontextualizes the field in light of the discovery of superconductivity in CaC₆ and YbC₆ in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic statesmore » and phonon modes are most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.« less

  19. Multigap superconductivity and barrier-driven resonances in superconducting nanofilms with an inner potential barrier

    NASA Astrophysics Data System (ADS)

    Doria, Mauro M.; Cariglia, Marco; Perali, Andrea

    2016-12-01

    We study the crossover in a zero-temperature superconducting nanofilm from a single to a double superconducting slab induced by a barrier in the middle. We use the Bogoliubov-de Gennes (BdG) equations in the Anderson approximation to show that the single-phase superconducting ground state of this heterostructure is intrinsically multigapped and has a new type of resonance caused by the strength of the barrier, thus distinct from the Thompson-Blatt shape resonance which is caused by tuning the thickness of the film. The simplest theoretical framework able to describe a finite height and very thin tunable insulating potential barrier in the middle is provided by a δ -function potential. In this framework, the even single-particle states are affected by the insulating barrier, whereas the odd ones are not. The new type of resonance, hereafter called barrier-driven resonance, is caused by the crossing of the even single-particle states through the Fermi surface. The lift of the even-odd degeneracy at the barrier reconfigures the pairing interaction and leads to a multigapped superconducting state with barrier-driven resonances.

  20. Normal State Transport in Superconducting Yttrium BARIUM(2) COPPER(3) OXYGEN(7-DELTA) and Semiconducting Praseodymium BARIUM(2) COPPER(3) OXYGEN(7-DELTA)

    NASA Astrophysics Data System (ADS)

    Browning, Valerie Michelle

    1995-01-01

    The discovery, in 1986, of materials with superconducting transition temperatures well above 77 K has generated a renewed interest in potential applications for superconductors. Unfortunately, the widespread use of high temperature superconductors (HTS) has not been realized due to their poor performance in terms of electrical and physical properties. Although the mechanism of high temperature superconductivity remains a mystery, it is hoped that an understanding of the HTS will result in the ability to engineer better quality materials. The normal state of the HTS exhibits several features which are considered unusual. Among these features are a linear temperature dependence of the resistivity and a temperature dependent Hall effect. It is believed that knowledge of the normal state transport properties of the HTS is crucial to understanding superconductivity in these materials. In an effort to better understand the normal state of the these materials, the transport properties of single crystal samples of two members of the superconducting RBa_2Cu_3O _{7-delta} ("123") family were studied (R = yttrium and many of the rare earth elements). Resistivity, Hall effect, and magnetoresistance measurements were performed on a detwinned single crystal sample of YBa_2Cu_3 _{7-delta} (Y 123). Measurements were repeated after various oxygen anneals to study the effects of oxygen inhomogeneities on the sample's transport properties. These results indicate that oxygen inhomogeneities strongly influence the transport properties of this system. A model is presented which takes into account oxygen defects in calculating the resistivity and Hall coefficient. Of the rare earth elements that will form the 123 structure, only PrBa_2Cu _3O_{7-delta} (Pr 123) does not superconduct. Pr 123 exhibits a non-metallic temperature dependent resistivity as opposed to the metallic resistivity exhibited by the superconducting 123 family members. Magnetotransport and magnetization measurements

  1. Superconducting Materials

    NASA Technical Reports Server (NTRS)

    1995-01-01

    After working with Lewis Research Center and Jet Propulsion Laboratory, Superconducting Technologies, Inc. (STI) adapted NASA requirements and refined its own standard production recipe. STI uses high temperature superconducting (HTS) materials in its basic products: high quality thin films, circuits and components. Applications include microwave circuits for radar to reduce interference.

  2. Order, disorder, and tunable gaps in the spectrum of Andreev bound states in a multiterminal superconducting device

    NASA Astrophysics Data System (ADS)

    Yokoyama, Tomohiro; Reutlinger, Johannes; Belzig, Wolfgang; Nazarov, Yuli V.

    2017-01-01

    We consider the spectrum of Andreev bound states (ABSs) in an exemplary four-terminal superconducting structure where four chaotic cavities are connected by quantum point contacts to the terminals and to each other forming a ring. We nickname the resulting device 4T-ring. Such a tunable device can be realized in a 2D electron gas-superconductor or a graphene-based hybrid structure. We concentrate on the limit of a short structure and large conductance of the point contacts where there are many ABS in the device forming a quasicontinuous spectrum. The energies of the ABS can be tuned by changing the superconducting phases of the terminals. We observe the opening and closing of gaps in the spectrum upon changing the phases. This concerns the usual proximity gap that separates the levels from zero energy as well as less usual "smile" gaps that split the levels of the quasicontinuous spectrum. We demonstrate a remarkable crossover in the overall spectrum that occurs upon changing the ratio of conductances of the inner and outer point contacts. At big values of the ratio (closed limit), the levels exhibit a generic behavior expected for the spectrum of a disordered system manifesting level repulsion and Brownian "motion" upon changing the phases. At small values of the ratio (open limit), the levels are squeezed into narrow bunches separated by wide smile gaps. Each bunch consists of almost degenerate ABS formed by Andreev reflection between two adjacent terminals. We study in detail the properties of the spectrum in the limit of a small ratio, paying special attention to the crossings of bunches. We distinguish two types of crossings: (i) with a regular phase dependence of the levels and (ii) crossings where the Brownian motion of the levels leads to an apparently irregular phase dependence. We work out a perturbation theory that explains the observations both at a detailed level of random scattering in the device and at a phenomenological level of positively defined

  3. Superconducting structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2003-04-01

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  4. Superconducting Structure

    DOEpatents

    Kwon, Chuhee; Jia, Quanxi; Foltyn, Stephen R.

    2005-09-13

    A superconductive structure including a dielectric oxide substrate, a thin buffer layer of a superconducting material thereon; and, a layer of a rare earth-barium-copper oxide superconducting film thereon the thin layer of yttrium-barium-copper oxide, the rare earth selected from the group consisting of samarium, gadolinium, ytterbium, erbium, neodymium, dysprosium, holmium, lutetium, a combination of more than one element from the rare earth group and a combination of one or more elements from the rare earth group with yttrium, the buffer layer of superconducting material characterized as having chemical and structural compatibility with the dielectric oxide substrate and the rare earth-barium-copper oxide superconducting film is provided.

  5. Equilibrium intermediate-state patterns in a type-I superconducting slab in an arbitrarily oriented applied magnetic field

    DOE PAGES

    Clem, John; Prozorov, Ruslan; Wijngaarden, Rinke J.

    2013-09-04

    The equilibrium topology of superconducting and normal domains in flat type-I superconductors is investigated. Important improvements with respect to previous work are that (1) the energy of the external magnetic field, as deformed by the presence of superconducting domains, is calculated in the same way for three different topologies and (2) calculations are made for arbitrary orientation of the applied field. A phase diagram is presented for the minimum-energy topology as a function of applied field magnitude and angle. For small (large) applied fields, normal (superconducting) tubes are found, while for intermediate fields, parallel domains have a lower energy. Themore » range of field magnitudes for which the superconducting-tubes structure is favored shrinks when the field is more in-plane oriented.« less

  6. Equilibrium intermediate-state patterns in a type-I superconducting slab in an arbitrarily oriented applied magnetic field

    SciTech Connect

    Clem, John; Prozorov, Ruslan; Wijngaarden, Rinke J.

    2013-09-04

    The equilibrium topology of superconducting and normal domains in flat type-I superconductors is investigated. Important improvements with respect to previous work are that (1) the energy of the external magnetic field, as deformed by the presence of superconducting domains, is calculated in the same way for three different topologies and (2) calculations are made for arbitrary orientation of the applied field. A phase diagram is presented for the minimum-energy topology as a function of applied field magnitude and angle. For small (large) applied fields, normal (superconducting) tubes are found, while for intermediate fields, parallel domains have a lower energy. The range of field magnitudes for which the superconducting-tubes structure is favored shrinks when the field is more in-plane oriented.

  7. Fully gapped topological surface states in Bi2Se3 films induced by a d-wave high-temperature superconductor

    NASA Astrophysics Data System (ADS)

    Wang, Eryin; Ding, Hao; Fedorov, Alexei V.; Yao, Wei; Li, Zhi; Lv, Yan-Feng; Zhao, Kun; Zhang, Li-Guo; Xu, Zhijun; Schneeloch, John; Zhong, Ruidan; Ji, Shuai-Hua; Wang, Lili; He, Ke; Ma, Xucun; Gu, Genda; Yao, Hong; Xue, Qi-Kun; Chen, Xi; Zhou, Shuyun

    2013-10-01

    Topological insulators are a new class of material, that exhibit robust gapless surface states protected by time-reversal symmetry. The interplay of such symmetry-protected topological surface states and symmetry-broken states (for example, superconductivity) provides a platform for exploring new quantum phenomena and functionalities, such as one-dimensional chiral or helical gapless Majorana fermions, and Majorana zero modes that may find application in fault-tolerant quantum computation. Inducing superconductivity on the topological surface states is a prerequisite for their experimental realization. Here, by growing high-quality topological insulator Bi2Se3 films on a d-wave superconductor Bi2Sr2CaCu2O8+δ using molecular beam epitaxy, we are able to induce high-temperature superconductivity on the surface states of Bi2Se3 films with a large pairing gap up to 15meV. Interestingly, distinct from the d-wave pairing of Bi2Sr2CaCu2O8+δ, the proximity-induced gap on the surface states is nearly isotropic and consistent with predominant s-wave pairing as revealed by angle-resolved photoemission spectroscopy. Our work could provide a critical step towards the realization of the long sought Majorana zero modes.

  8. First observation of a new zonal-flow cycle state in the H-mode transport barrier of the experimental advanced superconducting Tokamak

    SciTech Connect

    Xu, G. S.; Wang, H. Q.; Wan, B. N.; Guo, H. Y.; Zhang, W.; Chang, J. F.; Wang, L.; Chen, R.; Liu, S. C.; Ding, S. Y.; Shao, L. M.; Xiong, H.; Naulin, V.; Diamond, P. H.; Tynan, G. R.; Xu, M.; Yan, N.; Zhao, H. L.

    2012-12-15

    A new turbulence-flow cycle state has been discovered after the formation of a transport barrier in the H-mode plasma edge during a quiescent phase on the EAST superconducting tokamak. Zonal-flow modulation of high-frequency-broadband (0.05-1 MHz) turbulence was observed in the steep-gradient region leading to intermittent transport events across the edge transport barrier. Good confinement (H{sub 98y,2} {approx} 1) has been achieved in this state, even with input heating power near the L-H transition threshold. A novel model based on predator-prey interaction between turbulence and zonal flows reproduced this state well.

  9. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

    DOE PAGES

    Guguchia, Z.; Amato, A.; Kang, J.; ...

    2015-11-09

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. Contrasting with other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperaturemore » behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.« less

  10. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

    PubMed Central

    Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P. K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; Morenzoni, E.; Fernandes, Rafael M.; Khasanov, R.

    2015-01-01

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap. PMID:26548650

  11. Bulk Superconductivity Induced by In-Plane Chemical Pressure Effect in Eu0.5La0.5FBiS2-xSex

    NASA Astrophysics Data System (ADS)

    Jinno, Gen; Jha, Rajveer; Yamada, Akira; Higashinaka, Ryuji; Matsuda, Tatsuma D.; Aoki, Yuji; Nagao, Masanori; Miura, Osuke; Mizuguchi, Yoshikazu

    2016-12-01

    We have investigated the Se substitution effect on the superconductivity of optimally doped BiS2-based superconductor Eu0.5La0.5FBiS2. Eu0.5La0.5FBiS2-xSex samples with x = 0-1 were synthesized. With increasing x, in-plane chemical pressure is enhanced. For x ≥ 0.6, superconducting transitions with a large shielding volume fraction are observed in magnetic susceptibility measurements, and the highest Tc is 3.8 K for x = 0.8. From low-temperature electrical resistivity measurements, a zero-resistivity state is observed for all the samples, and the highest Tc is observed for x = 0.8. With increasing Se concentration, the characteristic electrical resistivity changes from semiconducting-like to metallic, suggesting that the emergence of bulk superconductivity is linked with the enhanced metallicity. A superconductivity phase diagram of the Eu0.5La0.5FBiS2-xSex superconductor is established.

  12. Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor

    NASA Astrophysics Data System (ADS)

    Guguchia, Z.; Amato, A.; Kang, J.; Luetkens, H.; Biswas, P. K.; Prando, G.; von Rohr, F.; Bukowski, Z.; Shengelaya, A.; Keller, H.; Morenzoni, E.; Fernandes, Rafael M.; Khasanov, R.

    2015-11-01

    The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.

  13. Possible weakly first-order superconducting transition induced by magnetic excitations in the YBCO system: A fluctuation conductivity study

    NASA Astrophysics Data System (ADS)

    Hneda, Marlon Luiz; da Silva Berchon, Luciano; Pureur, Paulo; das Neves Vieira, Valdemar; Jaeckel, Sandra Teixeira; Dias, Fábio Teixeira; Menegotto Costa, Rosângela

    2017-04-01

    Fluctuation conductivity is experimentally studied in the genuine critical region near the superconducting transition of YBa2Cu3O7 - δ, YBa2Cu2.985Fe0.015O7 - δ and Y0.95Ca0.05Ba2Cu3O7 - δ single crystal samples. Two fluctuation regimes where the electrical conductivity diverges as a power-law of the reduced temperature were systematically observed. In the first regime, farther from the critical temperature Tc, the transition behaves as predicted by the thermodynamics of the three dimensional-XY (3D-XY) universality class characteristic of a second-order phase transition. In the asymptotic regime closer to Tc a power-law regime characterized by a much smaller exponent is observed. The smallest value ever reported for the fluctuation conductivity exponent in the high-Tc superconductors is obtained for the Fe- and Ca-doped systems. We suggest that the regime beyond 3D-XY is a crossover towards a weakly first-order transition induced by internal magnetic excitations.

  14. RVB states in doped band insulators from Coulomb forces: theory and a case study of superconductivity in BiS2 layers

    NASA Astrophysics Data System (ADS)

    Baskaran, G.

    2016-12-01

    Doped band insulators, HfNCl, WO3, diamond, Bi2Se3, BiS2 families, STO/LAO interface, gate doped SrTiO3, MoS2 and so on are unusual superconductors. With an aim to build a general theory for superconductivity in doped band insulators, we focus on the BiS2 family which was discovered by Mizuguchi et al in 2012. While maximum Tc is only ˜11 K in {{LaO}}1-{{x}}{{{F}}}{{x}}{{BiS}}2, a number of experimental results are puzzling and anomalous in the sense that they resemble high T c and unconventional superconductors. Using a two orbital model of Usui, Suzuki and Kuroki, we show that the uniform low density free Fermi sea in {{LaO}}{0,5}{{{F}}}0.5{{BiS}}2 is unstable towards formation of the next nearest neighbor Bi-S-Bi diagonal valence bond (charged -2e Cooper pair) and their Wigner crystallization. Instability to this novel state of matter is caused by unscreened nearest neighbor coulomb repulsions (V ˜ 1 eV) and a hopping pattern with sulfur mediated diagonal next nearest neighbor Bi-S-Bi hopping t’ ˜ 0.88 eV, as well as larger than nearest neighbor Bi-Bi hopping, t ˜ 0.16 eV. Wigner crystals of Cooper pairs quantum melt for doping around x = 0.5 and stabilize certain resonating valence bond states and superconductivity. We study a few variational RVB states and suggest that BiS2 family members are latent high Tc superconductors, but challenged by competing orders and the fragile nature of many body states sustained by unscreened Coulomb forces. One of our superconducting states has d XY symmetry and a gap. We also predict a 2d Bose metal or vortex liquid normal state, as charged -2e valence bonds survive in the normal state.

  15. Influence of spin-polarized current on superconductivity and the realization of large magnetoresistance.

    PubMed

    Miao, Guo-Xing; Yoon, Kapsoo; Santos, Tiffany S; Moodera, Jagadeesh S

    2007-06-29

    The superconducting state can be influenced by injecting spin-polarized current in a controlled manner by properly tailoring the interfacial transmittivity between a ferromagnet (F) and a superconductor (S), resulting in a large magnetoresistance of over 1100% for a F/I/S/I/F multilayer system (I insulator). Because of the competition between ferromagnetism and superconductivity, the superconducting transition temperature (T(C)) in the spin-parallel configuration is shifted below that in the spin antiparallel configuration. The T(C) shift is attributed to ferromagnet-induced nonequilibrium spin carriers in the superconductors.

  16. Steady-state entanglement of harmonic oscillators via dissipation in a single superconducting artificial atom

    NASA Astrophysics Data System (ADS)

    Wang, Fei; Nie, Wei; Feng, Xunli; Oh, C. H.

    2016-07-01

    The correlated emission lasing (CEL) is experimentally demonstrated in harmonic oscillators coupled via a single three-level artificial atom [Phys. Rev. Lett. 115, 223603 (2015), 10.1103/PhysRevLett.115.223603] in which two-mode entanglement only exists in a certain time period when the harmonic oscillators are resonant with the atomic transitions. Here we examine this system and show that it is possible to obtain the steady-state entanglement when the two harmonic oscillators are resonant with Rabi sidebands. Applying dressed atomic states and Bogoliubov-mode transformation, we obtain the analytical results of the variance sum of a pair of Einstein-Podolsky-Rosen (EPR)-like operators. The stable entanglement originates from the dissipation process of the Bogoliubov modes because the atomic system can act as a reservoir in dressed state representation. We also show that the entanglement is robust against the dephasing rates of the superconducing atom, which is expected to have important applications in quantum information processing.

  17. Control of magnetic, nonmagnetic, and superconducting states in annealed Ca(Fe1–xCox)₂As₂

    SciTech Connect

    Ran, S.; Bud'ko, S. L.; Straszheim, W. E.; Soh, J.; Kim, M. G.; Kreyssig, A.; Goldman, A. I.; Canfield, P. C.

    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-Tanneal) 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 is 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 Tanneal 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.

  18. Large enhancement of superconducting transition temperature of SrBi3 induced by Na substitution for Sr

    PubMed Central

    Iyo, Akira; Yanagi, Yousuke; Kinjo, Tatsuya; Nishio, Taichiro; Hase, Izumi; Yanagisawa, Takashi; Ishida, Shigeyuki; Kito, Hijiri; Takeshita, Nao; Oka, Kunihiko; Yoshida, Yoshiyuki; Eisaki, Hiroshi

    2015-01-01

    The Matthias rule, which is an empirical correlation between the superconducting transition temperature (Tc) and the average number of valence electrons per atom (n) in alloys and intermetallic compounds, has been used in the past as a guiding principle to search for new superconductors with higher Tc. The intermetallic compound SrBi3 (AuCu3 structure) exhibits a Tc of 5.6 K. An ab-initio electronic band structure calculation for SrBi3 predicted that Tc increases on decreasing the Fermi energy, i.e., on decreasing n, because of a steep increase in the density of states. In this study, we demonstrated that high-pressure (~ 3 GPa) and low-temperature ( < 350 °C) synthesis conditions enables the substitution of Na for about 40 at.% of Sr. With a consequent decrease in n, the Tc of (Sr,Na)Bi3 increases to 9.0 K. A new high-Tc peak is observed in the oscillatory dependence of Tc on n in compounds with the AuCu3 structure. We have shown that the oscillatory dependence of Tc is in good agreement with the band structure calculation. Our experiments reaffirm the importance of controlling the number of electrons in intermetallic compounds. PMID:25965162

  19. Pressure-induced metallization of dense (H2S)2H2 with high-Tc superconductivity

    PubMed Central

    Duan, Defang; Liu, Yunxian; Tian, Fubo; Li, Da; Huang, Xiaoli; Zhao, Zhonglong; Yu, Hongyu; Liu, Bingbing; Tian, Wenjing; Cui, Tian

    2014-01-01

    The high pressure structures, metallization, and superconductivity of recently synthesized H2-containing compounds (H2S)2H2 are elucidated by ab initio calculations. The ordered crystal structure with P1 symmetry is determined, supported by the good agreement between theoretical and experimental X-ray diffraction data, equation of states, and Raman spectra. The Cccm structure is favorable with partial hydrogen bond symmetrization above 37 GPa. Upon further compression, H2 molecules disappear and two intriguing metallic structures with R3m and Im-3m symmetries are reconstructive above 111 and 180 GPa, respectively. The predicted metallization pressure is 111 GPa, which is approximately one-third of the currently suggested metallization pressure of bulk molecular hydrogen. Application of the Allen-Dynes-modified McMillan equation for the Im-3m structure yields high Tc values of 191 K to 204 K at 200 GPa, which is among the highest values reported for H2-rich van der Waals compounds and MH3 type hydride thus far. PMID:25382349

  20. Pressure-induced metallization of dense (H2S)2H2 with high-Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Duan, Defang; Liu, Yunxian; Tian, Fubo; Li, Da; Huang, Xiaoli; Zhao, Zhonglong; Yu, Hongyu; Liu, Bingbing; Tian, Wenjing; Cui, Tian

    2014-11-01

    The high pressure structures, metallization, and superconductivity of recently synthesized H2-containing compounds (H2S)2H2 are elucidated by ab initio calculations. The ordered crystal structure with P1 symmetry is determined, supported by the good agreement between theoretical and experimental X-ray diffraction data, equation of states, and Raman spectra. The Cccm structure is favorable with partial hydrogen bond symmetrization above 37 GPa. Upon further compression, H2 molecules disappear and two intriguing metallic structures with R3m and Im-3m symmetries are reconstructive above 111 and 180 GPa, respectively. The predicted metallization pressure is 111 GPa, which is approximately one-third of the currently suggested metallization pressure of bulk molecular hydrogen. Application of the Allen-Dynes-modified McMillan equation for the Im-3m structure yields high Tc values of 191 K to 204 K at 200 GPa, which is among the highest values reported for H2-rich van der Waals compounds and MH3 type hydride thus far.

  1. Superconductivity with Rashba spin-orbit coupling and magnetic field.

    PubMed

    Loder, Florian; Kampf, Arno P; Kopp, Thilo

    2013-09-11

    Two-dimensional electron systems at oxide interfaces are often influenced by a Rashba type spin-orbit coupling, which is tunable by a transverse electric field. Ferromagnetism near the interface can simultaneously induce strong local magnetic fields. This combination of spin-orbit coupling and magnetism leads to asymmetric two-sheeted Fermi surfaces, on which either intra- or inter-band pairing is favored. The superconducting order parameters are derived within a microscopic pairing model realizing both the Bardeen-Cooper-Schrieffer superconductor with inter-band pairing and a mixed parity state with finite-momentum intra-band pairing. We present a phase diagram for the superconducting groundstates and analyze the density of states, the spectra, and the momentum distribution functions of the different phases. The results are discussed in the context of superconductivity and ferromagnetism at LaAlO3-SrTiO3 interfaces and superconductors with broken inversion symmetry.

  2. Fulde-Ferrell-Larkin-Ovchinnikov states in a superconducting ring with magnetic fields: Phase diagram and the first-order phase transitions

    NASA Astrophysics Data System (ADS)

    Yoshii, Ryosuke; Takada, Satoshi; Tsuchiya, Shunji; Marmorini, Giacomo; Hayakawa, Hisao; Nitta, Muneto

    2015-12-01

    We find the angular Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states (or the twisted kink crystals) in which a phase and an amplitude of a pair potential modulate simultaneously in a quasi-one-dimensional superconducting ring with a static Zeeman magnetic field applied on the ring and static Aharonov-Bohm magnetic flux penetrating the ring. The superconducting ring with magnetic flux produces a persistent current, whereas the Zeeman split of Fermi energy results in the spatial modulation of the pair potential. We show that these two magnetic fields stabilize the FFLO phase in a large parameter region of the magnetic fields. We further draw the phase diagram with the two kinds of first-order phase transitions; one corresponds to phase slips separating the Aharonov-Bohm magnetic flux, and the other separates the number of peaks of the pair amplitude for the Zeeman magnetic field.

  3. Uniaxial linear resistivity of superconducting La1.905Ba0.095CuO4 induced by an external magnetic field

    NASA Astrophysics Data System (ADS)

    Wen, Jinsheng; Jie, Qing; Li, Qiang; Hücker, M.; v. Zimmermann, M.; Han, Su Jung; Xu, Zhijun; Singh, D. K.; Konik, R. M.; Zhang, Liyuan; Gu, Genda; Tranquada, J. M.

    2012-04-01

    We present an experimental study of the anisotropic resistivity of superconducting La2-xBaxCuO4 with x=0.095 and transition temperature Tc=32 K. In a magnetic field perpendicular to the CuO2 layers H⊥, we observe that the resistivity perpendicular to the layers ρ⊥ becomes finite at a temperature consistent with previous studies on very similar materials; however, the onset of finite parallel resistivity ρ∥ occurs at a much higher temperature. This behavior contradicts conventional theory, which predicts that ρ⊥ and ρ∥ should become finite at the same temperature. Voltage versus current measurements near the threshold of voltage detectability indicate linear behavior perpendicular to the layers, becoming nonlinear at higher currents, while the behavior is nonlinear from the onset parallel to the layers. These results, in the presence of moderate H⊥, appear consistent with superconducting order parallel to the layers with voltage fluctuations between the layers due to thermal noise. In search of uncommon effects that might help to explain this behavior, we have performed diffraction measurements that provide evidence for H⊥-induced charge- and spin-stripe order. The field-induced decoupling of superconducting layers is similar to the decoupled phase observed previously in La2-xBaxCuO4 with x=1/8 in zero field.

  4. Thermodynamics of the magnetic-field-induced "normal" state in an underdoped high Tc superconductor

    NASA Astrophysics Data System (ADS)

    Riggs, Scott Chandler

    High magnetic fields are used to kill superconductivity and probe what happens to system when it cannot reach the ideal ground state, i.e. what is the normal-state ground state? Early work in High-Tc, where the application of magnetic field destroyed the zero resistance state and recovered a resistivity value that connected continuously with the zero field curve, lead people to believe this magnetic-field-induced-state had fully driven the system normal, revealing the true underlying ground state, without any vestige of superconductivity. Many experiments done in this region of phase space have results interpreted as coming from the low energy ground state excitations. With the emergence of ultra-clean crystals in a unique family of hole doped high-Tc superconductors, YBa2Cu3O 7-delta, YBCO, a new and highly unexpected phenomena of quantum oscillations were discovered, and they followed the standard Liftshitz-Kosevich (LK) theory for a normal metal. The results suddenly made the problem of high-T c appear to be analogous to superconductivity in the organics, which is brought about by a wave-vector nesting and Fermi surface reconstruction. The only problem, it appeared, that needed to be reconciled was with Angle Resolved Photo-Emission Spectroscopy (ARPES) and Scanning Tunneling Microscopy (STM) data that claimed to see no such Fermi surface, instead only "arcs", a set of disconnected segments in the Brillouin zone which quasiparticle peaks are observed at the Fermi energy, which in a mean field description does not allow for a continuous Fermi surface contour. These two discrepancies led to the "arc vs pocket" debate, which is still unresolved. The other kink in the quantum oscillation armor is that, to this date, quantum oscillations in the hole-doped cuprates have only been seen in YBCO, the only cuprate structure to have CuO chains, which conduct and are located in between two CuO2 superconducting planes in the unit cell. In an attempt to reconcile the "arc vs

  5. Unconventional superconductivity in heavy-fermion compounds

    SciTech Connect

    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 and 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.

  6. 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

  7. Unconventional superconductivity in heavy-fermion compounds

    NASA Astrophysics Data System (ADS)

    White, B. D.; Thompson, J. D.; Maple, M. B.

    2015-07-01

    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 compounds 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 and iron-based superconductors. 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.

  8. Levitation force on a permanent magnet over a superconducting plane: Modified critical-state model

    SciTech Connect

    Yang, Z.J.

    1997-08-01

    The authors consider a model system of a permanent magnet above a semi-infinite superconductor. They introduce a modified critical-state model, and carry out derivations of the levitation force acting on the magnet. A key feature of the modification allows the current density to be less than the critical value. The theoretical results show an exponential relationship between the force and the distance. Analytical expressions are developed for permanent magnets in the form of a point dipole, a tip of a magnetic force microscope, and a cylindrical magnet. In the latter case, the exponential relationship has been observed in numerous experiments but without previous interpretation.

  9. Thickness-modulated tungsten–carbon superconducting nanostructures grown by focused ion beam induced deposition for vortex pinning up to high magnetic fields

    PubMed Central

    Serrano, Ismael García; Sesé, Javier; Guillamón, Isabel; Suderow, Hermann; Vieira, Sebastián; Ibarra, Manuel Ricardo

    2016-01-01

    We report efficient vortex pinning in thickness-modulated tungsten–carbon-based (W–C) nanostructures grown by focused ion beam induced deposition (FIBID). By using FIBID, W–C superconducting films have been created with thickness modulation properties exhibiting periodicity from 60 to 140 nm, leading to a strong pinning potential for the vortex lattice. This produces local minima in the resistivity up to high magnetic fields (2.2 T) in a broad temperature range due to commensurability effects between the pinning potential and the vortex lattice. The results show that the combination of single-step FIBID fabrication of superconducting nanostructures with built-in artificial pinning landscapes and the small intrinsic random pinning potential of this material produces strong periodic pinning potentials, maximizing the opportunities for the investigation of fundamental aspects in vortex science under changing external stimuli (e.g., temperature, magnetic field, electrical current). PMID:28144519

  10. Quasiparticle Excitations in the Superconducting State of FeSe Probed by Thermal Hall Conductivity in the Vicinity of the BCS-BEC Crossover

    NASA Astrophysics Data System (ADS)

    Watashige, Tatsuya; Arsenijević, Stevan; Yamashita, Takuya; Terazawa, Daiki; Onishi, Takafumi; Opherden, Lars; Kasahara, Shigeru; Tokiwa, Yoshifumi; Kasahara, Yuichi; Shibauchi, Takasada; von Löhneysen, Hilbert; Wosnitza, Jochen; Matsuda, Yuji

    2017-01-01

    There is growing evidence that the superconducting semimetal FeSe (Tc ˜ 8 K) is in the crossover regime between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein-condensate (BEC) limits. We report on longitudinal and transverse thermal conductivities, κxx and κxy, respectively, in magnetic fields up to 20 T. The field dependences of κxx and κxy imply that a highly anisotropic small superconducting gap forms at the electron Fermi-surface pocket whereas a more isotropic and larger gap forms at the hole pocket. Below ˜1.0 K, both κxx and κxy exhibit distinct anomalies (kinks) at the upper critical field Hc2 and at a field H* slightly below Hc2. The analysis of the thermal Hall angle (κxy/κxx) indicates a change of the quasiparticle scattering rate at H*. These results provide strong support to the previous suggestion that above H* a distinct field-induced superconducting phase emerges with an unprecedented large spin imbalance.

  11. Identification of Plasma Parameters and Optimization of Magnetic Sensors in the Superconducting Steady-State Tokamak-1 Using Neural Networks

    SciTech Connect

    Sengupta, A.; Ranjan, P

    2001-01-15

    In this paper, we examine the possibility of using a multilayered feedforward neural network to extract tokamak plasma parameters from magnetic measurements as an improvement over the traditional methodology of function parametrization. It is also used to optimize the number and locations of the magnetic diagnostics designed for the tokamak. This work has been undertaken with the specific purpose of application of the neural network technique to the newly designed (and currently under fabrication) Superconducting Steady-State Tokamak-1 (SST-1). The magnetic measurements will be utilized to achieve real-time control of plasma shape, position, and some global profiles. A trained neural network is tested, and the results of parameter identification are compared with function parametrization. Both techniques appear well suited for the purpose, but a definite improvement with neural networks is observed. Although simulated measurements are used in this work, confidence regarding the network performance with actual experimental data is ensured by testing the network's noise tolerance with Gaussian noise of up to 10%. Finally, three possible methods of ranking the diagnostics in decreasing order of importance are suggested, and the neural network is used to optimize the number and locations of the magnetic sensors designed for SST-1. The results from the three methods are compared with one another and also with function parametrization. Magnetic probes within the plasma-facing side of the outboard limiter have been ranked high. Function parametrization and one of the neural network methods show a distinct tendency to favor the probes in the remote regions of the vacuum vessel, proving the importance of redundancy. Fault tolerance of the optimized network is tested. The results obtained should, in the long run, help in the decision regarding the final effective set of magnetic diagnostics to be used in SST-1 for reconstruction of the control parameters.

  12. Unusual nature of ferromagnetism coexisting with superconductivity in UGe2.

    PubMed

    Nishioka, T; Motoyama, G; Nakamura, S; Kadoya, H; Sato, N K

    2002-06-10

    We report the discovery of a jump in the magnetization of a macroscopic single crystalline sample of UGe2 that shows coexistence of ferromagnetism and superconductivity. In particular, we observe that the jump occurs at regular intervals of field and only at very low temperatures. This novel feature implies that the magnetic field induces a sudden change of the direction of the magnetization between two equivalent easy axes of magnetization even in a macroscopic sample. We ascribe it to a field-tuned resonant tunneling between quantum spin states, and we propose that the size of a magnetic domain is smaller than a superconducting coherence length.

  13. SUPERCONDUCTING VANADIUM BASE ALLOY

    DOEpatents

    Cleary, H.J.

    1958-10-21

    A new vanadium-base alloy which possesses remarkable superconducting properties is presented. The alloy consists of approximately one atomic percent of palladium, the balance being vanadium. The alloy is stated to be useful in a cryotron in digital computer circuits.

  14. Superconducting thermometer for cryogenics

    NASA Technical Reports Server (NTRS)

    White, F. A.

    1977-01-01

    Digital electronic device uses superconducting filaments as sensors. Simple solid-state circuitry combined with filaments comprise highly-reliable temperature monitor. Device has ability to track very fast thermal transients and "on/off" output is adaptable to remote sensing and telemetry.

  15. Critical current density and microstructural state of an internal tin multifilamentary superconducting wire

    NASA Astrophysics Data System (ADS)

    Dietderich, D. R.; Glazer, J.; Lea, C.; Hassenzahl, W. V.; Morris, J. W., Jr.

    1984-09-01

    The critical current density (J sub c) of internal tin wires is increased when low-temperature diffusion heat treatments are performed prior to a high temperature reaction. To determine the variation of J sub c with prereaction heat treatments a copper-stabilized IGC internal tin wire with an outside diameter of 0.267mm was studied. The wire has 2 to 2.5 micron diameter filameters, and within the Ta barrier, the area ratio of the copper matrix and Sn core to Nb is about 2.2. Due to the character of the Cu-Sn phase diagram, heat treatments at a series of temperatures below the Nb3Sn reaction temperature affect the local Sn concentration in the matrix about the Nb filaments. The variation in J sub c resulting from these heat treatments is a consequence of the microstructural state of the conductor and the morphology of the Nb3Sn layer produced. The results of this work show that the internal tin and bronze-processed wires have different J sub c (H) characteristics. The two processes have comparable critical currents at high fields, suggesting the same H sub c2, while at low fields the internal tin wire is superior, suggesting a better grain morphology.

  16. Evidence for a spin pseudogap in the normal state of superconducting Mo3Sb7

    NASA Astrophysics Data System (ADS)

    Tran, V. H.; Hillier, A. D.; Adroja, D. T.; Bukowski, Z.; Miiller, W.

    2009-12-01

    Using muon spin relaxation (μSR) and inelastic neutron scattering (INS) we have investigated the normal state of the superconductor Mo3Sb7 and the reference compound Ru3Sn7. The μSR experiments on Ru3Sn7 reveal static and relatively slow dynamic relaxations, which are ascribed to a random static nuclear dipole field and thermally activated muon motion, respectively. INS experiments on Ru3Sn7, on the other hand, reveal three phononic excitations at 11, 18 and 23 meV, substantiating the assertion of Einstein and Debye oscillations derived from the specific heat and electrical resistivity data. The distinct difference in the μSR as well as INS spectra between Ru3Sn7 and Mo3Sb7 provides strong evidence for a magnetic/electronic nature of the phase transition at T* = 50 K in the Mo-based compound. On the basis of the μSR and INS data, the energy spin pseudogap of 150(10) K was estimated. The observed weak magnetism in the dynamic susceptibility χ''(Q,ω) and residual longitudinal field relaxation at 5 K imply a static ordering or quantum fluctuations.

  17. Time-Resolved Photoexcitation of the Superconducting Two-Gap State in MgB2 Thin Films

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Khafizov, M.; Satrapinsky, L.; Kúš, P.; Plecenik, A.; Sobolewski, Roman

    2003-11-01

    Femtosecond pump-probe studies show that carrier dynamics in MgB2 films is governed by the sub-ps electron-phonon (e-ph) relaxation present at all temperatures, the few-ps e-ph process well pronounced below 70K, and the sub-ns superconducting relaxation below Tc. The amplitude of the superconducting component versus temperature follows the superposition of the isotropic dirty gap and the three-dimensional π gap dependences, closing at two different Tc values. The time constant of the few-ps relaxation exhibits a double divergence at temperatures corresponding to the Tc's of the two gaps.

  18. Superconducting tensor gravity gradiometer

    NASA Technical Reports Server (NTRS)

    Paik, H. J.

    1981-01-01

    The employment of superconductivity and other material properties at cryogenic temperatures to fabricate sensitive, low-drift, gravity gradiometer is described. The device yields a reduction of noise of four orders of magnitude over room temperature gradiometers, and direct summation and subtraction of signals from accelerometers in varying orientations are possible with superconducting circuitry. Additional circuits permit determination of the linear and angular acceleration vectors independent of the measurement of the gravity gradient tensor. A dewar flask capable of maintaining helium in a liquid state for a year's duration is under development by NASA, and a superconducting tensor gravity gradiometer for the NASA Geodynamics Program is intended for a LEO polar trajectory to measure the harmonic expansion coefficients of the earth's gravity field up to order 300.

  19. Gate-Induced Superconductivity in Layered-Material-Based Electric Double Layer Transistors

    NASA Astrophysics Data System (ADS)

    Ye, J. T.; Zhang, Y. J.; Matsuhashi, Y.; Craciun, M. F.; Russo, S.; Kasahara, Y.; Morpurgo, A. F.; Iwasa, Y.

    2012-12-01

    High carrier density part of many materials could be accessed by a variation of the field effect transistor technique: electric double layer transistor. Carrier density regime of n~1014 cm-2 can be easily accessed electrostatically realizing effective doping without chemical modification. In this study, we utilized micro-cleavage on a number of interesting layered materials. And realized high carrier density state and high performance transport on atomically flat surfaces.

  20. Pressure dependence of the charge-density-wave and superconducting states in GdTe3, TbTe3, and DyTe3

    DOE PAGES

    Zocco, D. A.; Hamlin, J. J.; Grube, K.; ...

    2015-05-14

    Here, we present electrical resistivity and ac-susceptibility measurements of GdTe3, TbTe3 and DyTe3 performed under pressure. An upper charge-density-wave (CDW) is suppressed at a rate of dTCW,1/dP~ –85K/GPa. For TbTe3 and DyTe3, a second CDW below TCDW,2 increases with pressure until it reaches the TCDW,1(P) line. For GdTe3, 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 TbTe3 provide compelling evidence for bulk SC in the low-pressure region of the phase diagram. We provide measurements ofmore » superconducting critical fields and discuss the origin of a high-pressure superconducting phase occurring above 5 GPa.« less

  1. 2D superconductivity by ionic gating

    NASA Astrophysics Data System (ADS)

    Iwasa, Yoshi

    2D superconductivity is attracting a renewed interest due to the discoveries of new highly crystalline 2D superconductors in the past decade. Superconductivity at the oxide interfaces triggered by LaAlO3/SrTiO3 has become one of the promising routes for creation of new 2D superconductors. Also, the MBE grown metallic monolayers including FeSe are also offering a new platform of 2D superconductors. In the last two years, there appear a variety of monolayer/bilayer superconductors fabricated by CVD or mechanical exfoliation. Among these, electric field induced superconductivity by electric double layer transistor (EDLT) is a unique platform of 2D superconductivity, because of its ability of high density charge accumulation, and also because of the versatility in terms of materials, stemming from oxides to organics and layered chalcogenides. In this presentation, the following issues of electric filed induced superconductivity will be addressed; (1) Tunable carrier density, (2) Weak pinning, (3) Absence of inversion symmetry. (1) Since the sheet carrier density is quasi-continuously tunable from 0 to the order of 1014 cm-2, one is able to establish an electronic phase diagram of superconductivity, which will be compared with that of bulk superconductors. (2) The thickness of superconductivity can be estimated as 2 - 10 nm, dependent on materials, and is much smaller than the in-plane coherence length. Such a thin but low resistance at normal state results in extremely weak pinning beyond the dirty Boson model in the amorphous metallic films. (3) Due to the electric filed, the inversion symmetry is inherently broken in EDLT. This feature appears in the enhancement of Pauli limit of the upper critical field for the in-plane magnetic fields. In transition metal dichalcogenide with a substantial spin-orbit interactions, we were able to confirm the stabilization of Cooper pair due to its spin-valley locking. This work has been supported by Grant-in-Aid for Specially

  2. Superconductivity in a chiral nanotube

    NASA Astrophysics Data System (ADS)

    Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.

    2017-02-01

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity--unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

  3. Superconductivity in a chiral nanotube.

    PubMed

    Qin, F; Shi, W; Ideue, T; Yoshida, M; Zak, A; Tenne, R; Kikitsu, T; Inoue, D; Hashizume, D; Iwasa, Y

    2017-02-16

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity-unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures.

  4. Pressure-induced change of the electronic state in the tetragonal phase of CaFe2As2

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Yui; Ikeda, Shugo; Kuse, Tetsuji; Kobayashi, Hisao

    2014-07-01

    We have investigated the electronic states of single-crystal CaFe2As2 under hydrostatic pressure using 57Fe Mössbauer spectroscopy and magnetization measurements. The center shift and the quadrupole splitting were refined from observed 57Fe Mössbauer spectra using the single-crystalline sample under pressure at room temperature. A discontinuous decrease in the pressure dependence of the refined center shift was observed at 0.33 GPa without any anomaly in the pressure dependence of the refined quadrupole splitting, indicating a purely electronic state change in CaFe2As2 with a tetragonal structure. Such a change is shown to be reflected in the peak-like anomalies observed in the pressure dependences of the magnetic susceptibility at 0.26 GPa above 150 K. Our results reveal that this pressure-induced electronic state change suppresses the tetragonal-to-orthorhombic structural phase transition accompanied by an antiferromagnetic ordering. We further observed superconductivity in CaFe2As2 below ˜8 K around 0.33 GPa although our sample was not in a single phase at this pressure. These findings suggest that the electronic state change observed in CaFe2As2 with the tetragonal structure is relevant to the appearance of the pressure-induced superconductivity in AFe2As2.

  5. Electrostatic electron-doping yields superconductivity in LaOBiS2

    NASA Astrophysics Data System (ADS)

    Uesugi, Eri; Nishiyama, Saki; Goto, Hidenori; Ota, Hiromi; Kubozono, Yoshihiro

    2016-12-01

    Electrostatic carrier-doping is attracting serious attention as a meaningful technique for producing interesting electronic states in two-dimensional (2D) layered materials. Ionic-liquid gating can provide the critical carrier density required to induce the metal-insulator transition and superconductivity. However, the physical properties of only a few materials have been controlled by the electrostatic carrier-doping during the past decade. Here, we report an observation of superconductivity in a 2D layered material, LaOBiS2, achieved by the electrostatic electron-doping. The electron doping of LaOBiS2 induced metallic conductivity in the normally insulating LaOBiS2, ultimately led to superconductivity. The superconducting transition temperature, Tc, was 3.6 K, higher than the 2.7 K seen in LaO1-xFxBiS2 with an electron-doped BiS2 layer. A rapid drop in resistance (R) was observed at low temperature, which disappeared with the application of high magnetic fields, implying a superconducting state. This study reveals that electron-doping is an important technique for inducing superconductivity in 2D layered BiS2 materials.

  6. Magnetic Field Reentrant Superconductivity in Aluminum Nanowires

    NASA Astrophysics Data System (ADS)

    Bretz-Sullivan, Terence; Goldman, Allen

    Reentrance to the superconducting state through the application of a magnetic field to quasi-one dimensional superconductors driven resistive by current, is counter to the expected properties of superconductors. It was not until recently that a microscopic mechanism explaining the phenomenon was proposed in which superconductivity and phase slip driven dissipation coexist in a non-equilibrium state. Here we present additional results of magnetic field induced reentrance into the superconducting state in quasi-one-dimensional aluminum nanowires with an in-plane magnetic field both transverse to, and along the wire axis. The reentrant behavior is seen in the magnetic field dependence of the I-V characteristic and resistance vs. temperature, and in the wire's magnetoresistance at 450mK. This work was supported by DOE Basic Energy Sciences Grant DE-FG02-02ER46004. Samples were fabricated at the Minnesota Nanofabrication Center. Parts of this work were carried out in the University of Minnesota Characterization Facility, a member of the Materials Research Facilities Network (www.mrfn.org) funded via the NSF MRSEC program.

  7. Superconductivity in MgB 2

    NASA Astrophysics Data System (ADS)

    Akimitsu, Jun; Muranaka, Takahiro

    2003-05-01

    We recently discovered that the intermetallic compound magnesium diboride (MgB2) exhibits the highest superconducting transition temperature (Tc=39 K) of all the metallic superconductors. In this paper we report on the basic superconducting characteristics of MgB2 and the current status of the research for the unanswered problem in this superconductivity. Especially, we review the several reports for the superconducting gap (Δ) by the spectroscopic measurements. Moreover we introduce the research into its anisotropic parameter (γ), which is important for the understanding of this superconducting states in this material.

  8. New research in Superconductivity

    NASA Astrophysics Data System (ADS)

    Khorrami, Mona

    2013-03-01

    Superconductors are materials that have no resistance to electricity's flow; they are one of the last great frontiers of scientific discovery. The theories that explain superconductor behavior seem to be constantly under review. In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes When he cooled it to the temperature of liquid helium, 4 degrees Kelvin (-452F, -269C), its resistance suddenly disappeared. It was necessary for Onnes to come within 4 degrees of the coldest temperature that is theoretically attainable to witness the phenomenon of superconductivity. In 1933 German researchers Walther Meissner and Robert Ochsenfeld discovered that a superconducting material will repel a magnetic field. A magnet moving by a conductor induces currents in the conductor, but, in a superconductor the induced currents exactly mirror the field that would have otherwise penetrated the superconducting material - causing the magnet to be repulsed. This phenomenon is known as strong diamagnetism and is today often referred to as the ``Meissner effect'' (an eponym). Later on the theory developed by American physicists John Bardeen, Leon Cooper, and John Schrieffer together with extensions and refinements of the theory, which followed in the years after 1957, succeeded in explaining in considerable detail the properties of superconductors.

  9. Magnetic order on a topological insulator surface with warping and proximity-induced superconductivity

    NASA Astrophysics Data System (ADS)

    Mendler, Daniel; Kotetes, Panagiotis; Schön, Gerd

    2015-04-01

    We determine the nature of the magnetic order on the surface of a topological insulator (TI) which develops due to hexagonal warping and the resulting Fermi surface (FS) nesting in the presence of a repulsive Hubbard interaction. For this purpose we investigate the spin susceptibility and derive a Landau theory to compare the different accessible phases. For a nearly hexagonal FS and sufficiently strong interaction the magnetic ground state is formed by a skyrmion lattice, i.e., by a superposition of three helical spin density waves which preserves C3 symmetry. The magnetic ground state is topologically nontrivial with a nonzero skyrmion charge, which can be stabilized and controlled by an applied magnetic field. By bringing the TI in proximity to a conventional superconductor one can engineer a C3-symmetric topological superconductor. We explore the modification of the phase diagram as well as the mutual influence between the skyrmion structure and a multipolar distribution of supercurrents, which can provide information about the underlying skyrmion charge.

  10. Investigation of Precursor Superconducting State in YBa2Cu3O7-δ through In-Plane Optical Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Kegan; Kamiya, Keisuke; Nakajima, Masamichi; Miyasaka, Shigeki; Tajima, Setsuko

    2017-02-01

    A precursor of superconductivity has been searched in the in-plane optical spectra of underdoped YBa2Cu3Oy, in which the previous c-axis optical spectra showed the presence of superconducting carriers at a temperature far above Tc [Uykur et al., Phys. Rev. Lett. 112, 127003 (2014)][Dubroka et al., Phys. Rev. Lett. 106, 047006 (2011)]. By carefully subtracting the normal component from the imaginary part of conductivity σ2(ω), we found a clear in-plane response of superconducting condensate at the temperature consistent with the c-axis optical data. This confirms that the precursory superconductivity developing with decreasing doping level is an intrinsic phenomenon in the cuprates.

  11. Proximity fingerprint of s{plus_minus} superconductivity.

    SciTech Connect

    Koshelev, A. E.; Stanev, V.

    2011-01-01

    We suggest a straightforward and unambiguous test to identify possible opposite signs of the superconducting order parameter in different bands proposed for iron-based superconductors (s{sub {+-}}-state). We consider the proximity effect in a weakly coupled sandwich composed of a s{sub {+-}}-superconductor and a thin layer of the s-wave superconductor. In such system the s-wave order parameter is coupled differently with different s{sub {+-}}-gaps and it typically aligns with one of these gaps. This forces the other s{sub {+-}}-gap to be anti-aligned with the s-wave gap. In such situation the aligned band induces a peak in the s-wave density of states (DoS), while the anti-aligned band induces a dip. Observation of such contact-induced negative feature in the s-wave DoS would provide a definite proof for s{sub {+-}}-superconductivity.

  12. Pinning of a single Abrikosov vortex in superconducting Nb thin films using artificially induced pinning sites

    SciTech Connect

    Breitwisch, M.; Finnemore, D. K.

    2000-07-01

    Artificial structures were intentionally introduced into Nb films in order to study the interaction of a single Abrikosov vortex with pinning sites caused by these known defects. A vortex trapped on one of these structures or defects can be induced to move either by thermal depinning or by pushing on the vortex with a transport current in one of the films. The resulting motion, in turn, can be followed by observing the changes in the Fraunhofer-like interference pattern of a cross-strip Josephson junction having the thin film as one leg of the junction. Artificial pinning sites were successfully created by depositing Fe balls on the surface of a previously characterized thin film. Attempts to create artificial pinning sites by depressing the order parameter with a thin strip of Au on the surface of the Nb were not successful. There was no correlation between the location of trapped vortices and the location of the Au line. In a separate measurement, Lorentz-force-depinning studies for several intrinsic pinning sites in the thin film show that a transport current in the top film will depin a vortex in the top film with about one-tenth the current needed in the bottom film to depin the same vortex. (c) 2000 The American Physical Society.

  13. Pinning of a single Abrikosov vortex in superconducting Nb thin films using artificially induced pinning sites

    NASA Astrophysics Data System (ADS)

    Breitwisch, M.; Finnemore, D. K.

    2000-07-01

    Artificial structures were intentionally introduced into Nb films in order to study the interaction of a single Abrikosov vortex with pinning sites caused by these known defects. A vortex trapped on one of these structures or defects can be induced to move either by thermal depinning or by pushing on the vortex with a transport current in one of the films. The resulting motion, in turn, can be followed by observing the changes in the Fraunhofer-like interference pattern of a cross-strip Josephson junction having the thin film as one leg of the junction. Artificial pinning sites were successfully created by depositing Fe balls on the surface of a previously characterized thin film. Attempts to create artificial pinning sites by depressing the order parameter with a thin strip of Au on the surface of the Nb were not successful. There was no correlation between the location of trapped vortices and the location of the Au line. In a separate measurement, Lorentz-force-depinning studies for several intrinsic pinning sites in the thin film show that a transport current in the top film will depin a vortex in the top film with about one-tenth the current needed in the bottom film to depin the same vortex.

  14. Quantifying Surface Loss Induced by Anti-Vortex Hole Arrays in Planar Superconducting Circuits for Quantum Computation

    NASA Astrophysics Data System (ADS)

    Chiaro, B.; Megrant, A.; Dunsworth, A.; Chen, Z.; Campbell, B.; Hoi, I.-C.; Kelly, J.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Vainsencher, A.; Wenner, J.; White, T.; Barends, R.; Chen, Y.; Fowler, A.; Jeffrey, E.; Mutus, J.; Roushan, P.; Sank, D.; Cleland, A. N.; Martinis, J. M.

    2015-03-01

    Two important dissipation sources in superconducting circuits operated at low power are surface loss from two level systems (TLS) and magnetic vortex loss. By patterning the superconducting electrodes with an array of holes, it is possible to reduce or eliminate loss due to magnetic vortices. However, since the highest levels of coherence in planar superconducting circuits have been achieved by improving the electrode-substrate interface, it is natural to expect that adding hole arrays to the electrodes may cause excess surface loss. We present simulations predicting the excess loss magnitude to be < 10 % for typical ground plane hole arrays, but for extreme cases of hole size or placement the loss may be much greater. We confirm the simulation result with measurements of high quality factor resonators (Qi > 106) with and without the hole patterns.

  15. Superconducting Memristors

    NASA Astrophysics Data System (ADS)

    Peotta, Sebastiano; Di Ventra, Massimiliano

    2014-09-01

    In his original work, Josephson predicted that a phase-dependent conductance should be present in superconducting tunnel junctions, an effect difficult to detect, mainly because it is hard to single it out from the usual nondissipative Josephson current. We propose a solution for this problem that consists of using different superconducting materials to realize the two junctions of a superconducting interferometer. According to the Ambegaokar-Baratoff relation the two junctions have different conductances if the critical currents are equal, thus the Josephson current can be suppressed by fixing the magnetic flux in the loop at half of a flux quantum without canceling the phase-dependent conductance. Our proposal can be used to study the phase-dependent conductance, an effect present in principle in all superconducting weak links. From the standpoint of nonlinear circuit theory, such a device is in fact an ideal memristor with possible applications to memories and neuromorphic computing in the framework of ultrafast and low-energy-consumption superconducting digital circuits.

  16. Role of chalcogen vapor annealing in inducing bulk superconductivity in Fe1+yTe1-xSex [How does annealing in chalcogen vapor induce superconductivity in Fe1+yTe-xSex?

    SciTech Connect

    Lin, Wenzhi; Ganesh, P.; Gianfrancesco, Anthony; Berlijn, Tom; Maier, Thomas A.; Kalinin, Sergei V.; Sales, Brian C.; Pan, Minghu

    2015-02-01

    Recent investigations have shown that Fe1+yTe1-xSex can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe1+yTe1-xSex treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTem (m ≥ 1) complexes. We show that the remaining FeTem complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.

  17. Making Superconducting Welds between Superconducting Wires

    NASA Technical Reports Server (NTRS)

    Penanen, Konstantin I.; Eom, Byeong Ho

    2008-01-01

    A technique for making superconducting joints between wires made of dissimilar superconducting metals has been devised. The technique is especially suitable for fabrication of superconducting circuits needed to support persistent electric currents in electromagnets in diverse cryogenic applications. Examples of such electromagnets include those in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems and in superconducting quantum interference devices (SQUIDs). Sometimes, it is desirable to fabricate different parts of a persistent-current-supporting superconducting loop from different metals. For example, a sensory coil in a SQUID might be made of Pb, a Pb/Sn alloy, or a Cu wire plated with Pb/Sn, while the connections to the sensory coil might be made via Nb or Nb/Ti wires. Conventional wire-bonding techniques, including resistance spot welding and pressed contact, are not workable because of large differences between the hardnesses and melting temperatures of the different metals. The present technique is not subject to this limitation. The present technique involves the use (1) of a cheap, miniature, easy-to-operate, capacitor-discharging welding apparatus that has an Nb or Nb/Ti tip and operates with a continuous local flow of gaseous helium and (2) preparation of a joint in a special spark-discharge welding geometry. In a typical application, a piece of Nb foil about 25 m thick is rolled to form a tube, into which is inserted a wire that one seeks to weld to the tube (see figure). The tube can be slightly crimped for mechanical stability. Then a spark weld is made by use of the aforementioned apparatus with energy and time settings chosen to melt a small section of the niobium foil. The energy setting corresponds to the setting of a voltage to which the capacitor is charged. In an experiment, the technique was used to weld an Nb foil to a copper wire coated with a Pb/Sn soft solder, which is superconducting. The joint was evaluated as

  18. Nodal Quasiparticle Lifetime in the Superconducting State of Bi{sub 2}Sr{sub 2}Ca Cu{sub 2}O{sub 8+{delta}}

    SciTech Connect

    Corson, J.; Orenstein, J.; Oh, Seongshik; O'Donnell, J.; Eckstein, J. N.

    2000-09-18

    We have measured the complex conductivity {sigma} of a Bi{sub 2}Sr {sub 2}CaCu{sub 2}O{sub 8+{delta}} thin film between 0.2 and 0.8 THz. We find {sigma} in the superconducting state to be well described as the sum of contributions from quasiparticles, condensate, and order parameter fluctuations which draw 30% of the spectral weight from the condensate. An analysis based on this decomposition yields a quasiparticle scattering rate on the order of k{sub B}T/({Dirac_h}/2{pi}) for temperatures below T{sub c} . (c) 2000 The American Physical Society.

  19. Superconducting magnets

    SciTech Connect

    Willen, E.; Dahl, P.; Herrera, J.

    1985-01-01

    This report provides a self-consistent description of a magnetic field in the aperture of a superconducting magnet and details how this field can be calculated in a magnet with cos theta current distribution in the coils. A description of an apparatus that can be used to measure the field uniformity in the aperture has been given. Finally, a detailed description of the magnet being developed for use in the Superconducting Super Collider is given. When this machine is built, it will be by far the largest application of superconductivity to date and promises to make possible the experimental discoveries needed to understand the basic laws of nature governing the world in which we live.

  20. Antiferromagnetic hedgehogs with superconducting cores

    SciTech Connect

    Goldbart, P.M.; Sheehy, D.E.

    1998-09-01

    Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang{close_quote}s SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to {open_quotes}escape{close_quotes} into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined. {copyright} {ital 1998} {ital The American Physical Society}

  1. Antiferromagnetic hedgehogs with superconducting cores

    NASA Astrophysics Data System (ADS)

    Goldbart, Paul M.; Sheehy, Daniel E.

    1998-09-01

    Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang's SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to ``escape'' into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined.

  2. 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.

  3. Phase slips in superconducting weak links

    SciTech Connect

    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 and 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.

  4. Underdoped superconducting cuprates as topological superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Yuan-Ming; Xiang, Tao; Lee, Dung-Hai

    2014-09-01

    Superconductivity in copper oxide (cuprate) high-transition-temperature superconductors follows from the chemical doping of an antiferromagnetic insulating state. The consensus that the wavefunction of the superconducting carrier, the Cooper pair, has dx2-y2 symmetry has long been reached. This pairing symmetry implies the existence of nodes in the superconducting energy gap. Recently, a series of angle-resolved photoemission spectroscopy experiments have revealed that deeply underdoped cuprates exhibit a particle-hole symmetric superconducting-like energy gap at the momentum-space locations where the dx2-y2 gap nodes are expected. Here we discuss the possibility that this phenomenon is caused by a fully gapped topological superconducting state that coexists with the antiferromagnetic order. If experimentally confirmed, this result will completely change our view of how exactly the high-temperature superconductivity state evolves from the insulating antiferromagnet.

  5. Quasiparticle spin relaxation with superconducting velocity-tunable state in GaAs(100) quantum wells in proximity to s -wave superconductor

    NASA Astrophysics Data System (ADS)

    Yu, T.; Wu, M. W.

    2016-11-01

    We investigate the quasiparticle spin relaxation with superconducting-velocity-tunable state in GaAs (100) quantum wells in proximity to an s -wave superconductor. We first present the influence of the supercurrent on the quasiparticle state in GaAs (100) quantum wells, which can be tuned by the superconducting velocity. Rich features such as the suppressed Cooper pairings, large quasiparticle density and nonmonotonically tunable momentum current can be realized by varying the superconducting velocity. In the degenerate regime, the quasiparticle Fermi surface is composed by two arcs, referred to as Fermi arcs, which are contributed by the electron- and holelike branches. The D'yakonov-Perel' spin relaxation is then explored, and intriguing physics is revealed when the Fermi arc emerges. Specifically, when the order parameter tends to zero, it is found that the branch-mixing scattering is forbidden in the quasielectron band. When the condensation process associated with the annihilation of the quasielectron and quasihole is slow, this indicates that the electron- and holelike Fermi arcs in the quasielectron band are independent. The open structure of the Fermi arc leads to the nonzero angular average of the effective magnetic field due to the spin-orbit coupling, which acts as an effective Zeeman field. This Zeeman field leads to spin oscillations even in the strong-scattering regime. Moreover, in the strong-scattering regime, we show that the open structure of the Fermi arc also leads to the insensitiveness of the spin relaxation to the momentum scattering, in contrast to the conventional motional narrowing situation. Nevertheless, with a finite order parameter, the branch-mixing scattering can be triggered, opening the interbranch spin relaxation channel, which is dominant in the strong-scattering regime. In contrast to the situation with an extremely small order parameter, due to the interbranch channel, the spin oscillations vanish and the spin relaxation

  6. Disbursement of $65 million to the State of Texas for construction of a Regional Medical Technology Center at the former Superconducting Super Collider Site, Waxahachie, Texas

    SciTech Connect

    1995-05-01

    As part of a settlement agreement between the US DOE and the State of Texas, DOE proposes to transfer $65 million of federal funds to the Texas National Research Laboratory Commission (TNLRC) for construction of the Regional Medical Technology Center (RMTC) to be located in Ellis County, Texas. The RMTC would be a state-of-the-art medical facility for proton cancer therapy, operated by the State of Texas in conjunction with the University of Texas Southwestern Medical Center. The RMTC would use the linear accelerator assets of the recently terminated DOE Superconducting Super Collider Project to accelerate protons to high energies for the treatment of cancer patients. The current design provides for treatment areas, examination rooms, support laboratories, diagnostic imaging equipment, and office space as well as the accelerators (linac and synchrotron) and beam steering and shaping components. The potential environmental consequences of the proposed action are expected to be minor.

  7. Superconducting Microelectronics.

    ERIC Educational Resources Information Center

    Henry, Richard W.

    1984-01-01

    Discusses superconducting microelectronics based on the Josephson effect and its advantages over conventional integrated circuits in speed and sensitivity. Considers present uses in standards laboratories (voltage) and in measuring weak magnetic fields. Also considers future applications in superfast computer circuitry using Superconducting…

  8. Granular superconductivity and magnetic-field-driven recovery of macroscopic coherence in a cuprate/manganite multilayer

    NASA Astrophysics Data System (ADS)

    Mallett, B. P. P.; Khmaladze, J.; Marsik, P.; Perret, E.; Cerreta, A.; Orlita, M.; Biškup, N.; Varela, M.; Bernhard, C.

    2016-11-01

    We show that in Pr0.5La0.2Ca0.3MnO3 /YBa2Cu3O7 (PLCMO/YBCO) multilayers the low temperature state of YBCO is very resistive and resembles that of a granular superconductor or a frustrated Josephson-junction network. Notably, a coherent superconducting response can be restored with a large magnetic field which also suppresses the charge-orbital order in PLCMO. This coincidence suggests that the granular superconducting state of YBCO is induced by the charge-orbital order of PLCMO. The coupling mechanism and the nature of the induced inhomogeneous state in YBCO remain to be understood.

  9. Electronic state and superconductivity of YBa2Cu3-xO7-y (M=Al,Zn and Sn) systems

    NASA Technical Reports Server (NTRS)

    Zhao, Y.; Zhang, Q. R.; Zhang, H.

    1990-01-01

    A series of YBa2Cu(3-x)MxO(7-y) (M=Al,Zn and Sn) single phase samples were prepared, and the measurements of the crystal structure, oxygen content, electric resistivity, thermoelectric power, Mossbauer spectrum, XPS and superconductivity were performed. The experimental results of X ray powder diffraction, Mossbauer spectrum and oxygen content show that the Zn(2+) and the Al(3+) occupy the Cu(2) site in Cu-O planes and the Cu(1) site in Cu-O chains respectively, but the Sn(4+) occupies both the Cu(1) sites. As regards the properties in superconducting state, both the Zn(2+) and the Al(3+) depress T(sub c) strongly, but the Sn(4+) does not. As for the electronic transport properties in normal state, the system doped by Al(3+) displays a rapid increase of resistivity and some electron localization-like effects, and the thermoelectric power enhances obviously; the series contained Zn(2+) almost shows no changes of electric resistivity but the sign of the thermoelectric power is reversed. Other results are given and briefly discussed.

  10. Fractal superconductivity near localization threshold

    SciTech Connect

    Feigel'man, M.V.; Ioffe, L.B.; Kravtsov, V.E.; Cuevas, E.

    2010-07-15

    We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk 'poor conductors' in which Fermi energy E{sub F} is located in the region of localized states not so far from the Anderson mobility edge E{sub c}. We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model. Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical wavefunction's correlations is shown to be crucial for the physics of these systems. We identify three distinct phases: 'critical' superconductive state formed at E{sub F} = E{sub c}, superconducting state with a strong pseudo-gap, realized due to pairing of weakly localized electrons and insulating state realized at E{sub F} still deeper inside a localized band. The 'critical' superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gapped state is the presence of two independent energy scales: superconducting gap {Delta}, that is due to many-body correlations and a new 'pseudo-gap' energy scale {Delta}{sub P} which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive T{sub c}. Two gap nature of the pseudo-gapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudo-gapped superconducting state demonstrates anomalous behavior of the optical

  11. Charge 2 e /3 Superconductivity and Topological Degeneracies without Localized Zero Modes in Bilayer Fractional Quantum Hall States

    NASA Astrophysics Data System (ADS)

    Barkeshli, Maissam

    2016-08-01

    It has been recently shown that non-Abelian defects with localized parafermion zero modes can arise in conventional Abelian fractional quantum Hall (FQH) states. Here we propose an alternate route to creating, manipulating, and measuring topologically protected degeneracies in bilayer FQH states coupled to superconductors, without the creation of localized parafermion zero modes. We focus mainly on electron-hole bilayers, with a ±1 /3 Laughlin FQH state in each layer, with boundaries that are proximity coupled to a superconductor. We show that the superconductor induces charge 2 e /3 quasiparticle-pair condensation at each boundary of the FQH state, and that this leads to (i) topologically protected degeneracies that can be measured through charge sensing experiments and (ii) a fractional charge 2 e /3 ac Josephson effect. We demonstrate that an analog of non-Abelian braiding is possible, despite the absence of a localized zero mode. We discuss several practical advantages of this proposal over previous work, and also several generalizations.

  12. The Induction of Euphoric and Dysphoric States with Induced Affect.

    ERIC Educational Resources Information Center

    Sipprelle, R. Carl; Ascough, James C.

    Three induced affect (IA) studies are reported. Their goal was the development of a methodology for inducing and quantifying specific affective states in a controlled setting, with the ultimate purpose of making the detailed study of affective states more feasible. Euphoric by moderate autonomic activation were elicited with cue manipulation in…

  13. Spin-orbit-coupled superconductivity.

    PubMed

    Lo, Shun-Tsung; Lin, Shih-Wei; Wang, Yi-Ting; Lin, Sheng-Di; Liang, C-T

    2014-06-25

    Superconductivity and spin-orbit (SO) interaction have been two separate emerging fields until very recently that the correlation between them seemed to be observed. However, previous experiments concerning SO coupling are performed far beyond the superconducting state and thus a direct demonstration of how SO coupling affects superconductivity remains elusive. Here we investigate the SO coupling in the critical region of superconducting transition on Al nanofilms, in which the strength of disorder and spin relaxation by SO coupling are changed by varying the film thickness. At temperatures T sufficiently above the superconducting critical temperature T(c), clear signature of SO coupling reveals itself in showing a magneto-resistivity peak. When T < T(c), the resistivity peak can still be observed; however, its line-shape is now affected by the onset of the quasi two-dimensional superconductivity. By studying such magneto-resistivity peaks under different strength of spin relaxation, we highlight the important effects of SO interaction on superconductivity.

  14. Superconducting thermoelectric generator

    DOEpatents

    Metzger, J.D.; El-Genk, M.S.

    1994-01-01

    Thermoelectricity is produced by applying a temperature differential to dissimilar electrically conducting or semiconducting materials, thereby producing a voltage that is proportional to the temperature difference. Thermoelectric generators use this effect to directly convert heat into electricity; however, presently-known generators have low efficiencies due to the production of high currents which in turn cause large resistive heating losses. Some thermoelectric generators operate at efficiencies between 4% and 7% in the 800{degrees} to 1200{degrees}C range. According to its major aspects and bradly stated, the present invention is an apparatus and method for producing electricity from heat. In particular, the invention is a thermoelectric generator that juxtaposes a superconducting material and a semiconducting material - so that the superconducting and the semiconducting materials touch - to convert heat energy into electrical energy without resistive losses in the temperature range below the critical temperature of the superconducting material. Preferably, an array of superconducting material is encased in one of several possible configurations within a second material having a high thermal conductivity, preferably a semiconductor, to form a thermoelectric generator.

  15. Global and local superconductivity in boron-doped granular diamond.

    PubMed

    Zhang, Gufei; Turner, Stuart; Ekimov, Evgeny A; Vanacken, Johan; Timmermans, Matias; Samuely, Tomás; Sidorov, Vladimir A; Stishov, Sergei M; Lu, Yinggang; Deloof, Bart; Goderis, Bart; Van Tendeloo, Gustaaf; Van de Vondel, Joris; Moshchalkov, Victor V

    2014-04-02

    Strong granularity-correlated and intragrain modulations of the superconducting order parameter are demonstrated in heavily boron-doped diamond situated not yet in the vicinity of the metal-insulator transition. These modulations at the superconducting state (SC) and at the global normal state (NS) above the resistive superconducting transition, reveal that local Cooper pairing sets in prior to the global phase coherence.

  16. Superconducting Quantum Interference Single-Electron Transistor

    NASA Astrophysics Data System (ADS)

    Enrico, Emanuele; Giazotto, Francesco

    2016-06-01

    We propose the concept of a quantized single-electron source based on the interplay between Coulomb blockade and magnetic flux-controllable superconducting proximity effect. We show that flux dependence of the induced energy gap in the density of states of a nanosized metallic wire can be exploited as an efficient tunable energy barrier which enables charge-pumping configurations with enhanced functionalities. This control parameter strongly affects the charging landscape of a normal metal island with non-negligible Coulombic energy. Under a suitable evolution of a time-dependent magnetic flux the structure behaves like a turnstile for single electrons in a fully electrostatic regime.

  17. Coexistence and interplay of superconductivity and ferromagnetism in URhGe.

    PubMed

    Lévy, F; Sheikin, I; Grenier, B; Marcenat, C; Huxley, A

    2009-04-22

    As ferromagnetism and superconductivity are usually considered to be antagonistic, the discovery of their coexistence in UGe(2), URhGe, UIr and UCoGe has attracted a lot of interest. The mechanism to explain such a state has, however, not yet been fully elucidated. In these compounds superconductivity may be unconventional: Cooper pairs could be formed by electrons with parallel spins and magnetic fluctuations might be involved in the pairing mechanism. URhGe becomes ferromagnetic below a Curie temperature of 9.5 K, with a spontaneous moment aligned to the c-axis. For temperatures below 260 mK and fields lower than 2 T, superconductivity was first observed in 2001. Recently, we discovered a second pocket of superconductivity. This new pocket of superconductivity appears at higher fields applied close to the b-axis, enveloping a sudden magnetic moment rotation transition at H(R) = 12 T. Detailed studies of the field induced metamagnetic transition and superconductivity are presented. The possibility that magnetic fluctuations emerging from a quantum critical point provide the pairing mechanism for superconductivity is discussed.

  18. Scanning SQUID Measurements of Superconducting Proximity Effect in Bi2 Se3 -Nb Heterojunctions

    NASA Astrophysics Data System (ADS)

    Kratz, Philip; Sochnikov, Ilya; Wu, Phillip; Yu, Jung Ho; Koski, Kristie; Cui, Yi; Hammond, Robert; Beasley, Malcolm R.; Kirtley, John R.; Moler, Kathryn A.

    2014-03-01

    In superconductivity induced on the surface of a 3D topological insulator, in contrast to conventional s-wave superconductivity, each vortex core theoretically carries a nondegenerate zero energy state with the properties of a Majorana fermion. The local superfluid density and its characteristic magnetic field penetration depth, critical current and temperature are sensitive metrics for placing limits on the relative contributions of the bulk and surface to a proximitized supercurrent in a topological insulator. Using a scanning SQUID microscope integrated with a quartz tuning fork sensor in a force-sensitive phase-locked loop for simultaneous topography characterization, we study the local superfluid density in Sb-doped Bi2Se3-Nb heterojunctions, prepared by Nb growth through molecular beam epitaxy on solvothermally synthesized Bi2Se3 nanoplates. We observe a suppression of the superconducting diamagnetic susceptibility, consistent with a superconducting proximity effect. We also explore the dependence of the local superfluid density on back gate voltage and temperature.

  19. Calculation of angle-resolved photoemission and tunneling for a CuO[sub 2] layer in the normal and superconducting states

    SciTech Connect

    Dickinson, P.H.; Doniach, S. )

    1993-05-01

    We represent the normal-state electronic structure of a CuO[sub 2] layer in terms of a three-band model having an infinite Cu intrasite Coulomb repulsion. We express the Lagrangian for this model using a slave-boson formalism and approximate it in a large-[ital N] expansion to order 1/[ital N] in the zero-temperature limit. The angle-resolved spectral weight determined from the resulting Green's functions suggests that within this picture higher-order corrections in 1/[ital N] are necessary for good agreement with the corresponding angle-resolved photoemission data. We phenomenologically add spin-dependent Heisenberg interactions between neighboring Cu sites and neighboring Cu and O sites. These interactions form the basis of a nonretarded calculation of the superconducting state. For the case of an interaction between neighboring Cu spins only, the lowest-energy solution possesses [ital d]([ital x][sup 2][minus][ital y][sup 2]) symmetry. The use of a three-band model leads to the possibility of the addition of the interaction between Cu and O spins. The resulting [ital d]+[ital idp] superconducting state involves pairing of carriers in Cu orbitals both with themselves and with holes on the O orbitals. This additional pairing will remove the node in the [ital d]-wave state at [ital T]=0 by an amount that depends on the Cu-O coupling parameter; however, the mixed-symmetry state occurs only for a narrow range of coupling parameters. The angle-resolved photoemission and tunneling results are calculated and compared to experimental findings.

  20. Theory of Laser-Controlled Competing Superconducting and Charge Orders

    NASA Astrophysics Data System (ADS)

    Sentef, M. A.; Tokuno, A.; Georges, A.; Kollath, C.

    2017-02-01

    We investigate the nonequilibrium dynamics of competing coexisting superconducting (SC) and charge-density wave (CDW) orders in an attractive Hubbard model. A time-periodic laser field A →(t ) lifts the SC-CDW degeneracy, since the CDW couples linearly to the field (A →), whereas SC couples in second order (A→2) due to gauge invariance. This leads to a striking resonance: When the photon energy is red detuned compared to the equilibrium single-particle energy gap, CDW is enhanced and SC is suppressed, while this behavior is reversed for blue detuning. Both orders oscillate with an emergent slow frequency, which is controlled by the small amplitude of a third induced order, namely η pairing, given by the commutator of the two primary orders. The induced η pairing is shown to control the enhancement and suppression of the dominant orders. Finally, we demonstrate that light-induced superconductivity is possible starting from a predominantly CDW initial state.

  1. Superconductivity induced by In substitution into the topological crystalline insulator Pb0.5Sn0.5Te

    NASA Astrophysics Data System (ADS)

    Zhong, R. D.; Schneeloch, J. A.; Liu, T. S.; Camino, F. E.; Tranquada, J. M.; Gu, G. D.

    2014-07-01

    Indium substitution turns the topological crystalline insulator (TCI) Pb0.5Sn0.5Te into a possible topological superconductor. To investigate the effect of the indium concentration on the crystal structure and superconducting properties of (Pb0.5Sn0.5)1-xInxTe, we have grown high-quality single crystals using a modified floating-zone method and have performed systematic studies for indium content in the range 0≤x≤0.35. We find that the single crystals retain the rocksalt structure up to the solubility limit of indium (x ˜0.30). Experimental dependencies of the superconducting transition temperature (Tc) and the upper critical magnetic field (Hc2) on the indium content x have been measured. The maximum Tc is determined to be 4.7 K at x =0.30, with μ0Hc2(T =0)≈5 T.

  2. Constructive influence of the induced electron pairing on the Kondo state

    PubMed Central

    Domański, T.; Weymann, I.; Barańska, M.; Górski, G.

    2016-01-01

    Superconducting order and magnetic impurities are usually detrimental to each other. We show, however, that in nanoscopic objects the induced electron pairing can have constructive influence on the Kondo effect originating from the effective screening interactions. Such situation is possible at low temperatures in the quantum dots placed between the conducting and superconducting reservoirs, where the proximity induced electron pairing cooperates with the correlations amplifying the spin-exchange potential. The emerging Abrikosov-Suhl resonance, which is observable in the Andreev conductance, can be significantly enhanced by increasing the coupling to superconducting lead. We explain this intriguing tendency within the Anderson impurity model using: the generalized Schrieffer-Wolff canonical transformation, the second order perturbative treatment of the Coulomb repulsion, and the nonperturbative numerical renormalization group calculations. We also provide hints for experimental observability of this phenomenon. PMID:27009681

  3. Calculation of eddy-currents induced in a compact synchrotron superconducting magnet structure during a current ramp

    SciTech Connect

    Kalsi, S. . Space and Electronics Systems Div.); Heese, R. )

    1991-01-01

    Under DARPA sponsorship, a compact Superconducting X-Ray Light Source (SXSL) is being designed and built by the Brookhaven National Laboratory (BNL) with industry participation from Grumman Corporation and General Dynamics. The SXLS machine employs two 180{degrees} curved 4 telsa superconducting dipole magnets. These magnets are required to produce a dipole field for bending the beam but at the same time they must produce finite amounts of higher multipoles which are required for conditioning the beam. In fact uniformity of the field to less than 1 part in 10,000 must be maintained under all operating conditions. When a superconducting magnet is ramped from zero to full field, the changing magnetic field produces eddy-currents in the magnet structure which in turn can produce undesirable multipoles. This paper discusses a simple method for estimating these eddy-currents and their effect on the field harmonics. The paper present the analysis basis and its application to the SXLS magnet support structure and to the beam chamber components. 5 figs., 1 tab.

  4. Spectroscopic evidence of odd frequency superconducting order

    PubMed Central

    Pal, Avradeep; Ouassou, J. A.; Eschrig, M.; Linder, J.; Blamire, M. G.

    2017-01-01

    Spin filter superconducting S/I/N tunnel junctions (NbN/GdN/TiN) show a robust and pronounced Zero Bias Conductance Peak (ZBCP) at low temperatures, the magnitude of which is several times the normal state conductance of the junction. Such a conductance anomaly is representative of unconventional superconductivity and is interpreted as a direct signature of an odd frequency superconducting order. PMID:28106102

  5. Transition radiation effects in superconducting granules

    NASA Technical Reports Server (NTRS)

    Drukier, A. K.; Valette, C.; Waysand, G.; Peters, F.; Yuan, L. C. L.

    1975-01-01

    The paper examines the use of a superheated superconducting suspension as a transition radiation detector of relativistic charged particles. The suspensions would also be used for detecting low-energy X-ray photons. The DESY experiment for developing such a superconducting detector has been carried out at a 7 GeV electron synchrotron. The detection is shown to be based on the recordable flipping of the state of a single superconducting grain.

  6. Superconductivity in a chiral nanotube

    PubMed Central

    Qin, F.; Shi, W.; Ideue, T.; Yoshida, M.; Zak, A.; Tenne, R.; Kikitsu, T.; Inoue, D.; Hashizume, D.; Iwasa, Y.

    2017-01-01

    Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena such as circular dichiroism for chiral molecules, magnetic Skyrmions in chiral magnets and nonreciprocal carrier transport in chiral conductors. On the other hand, effect of chirality on superconducting transport has not been known. Here we report the nonreciprocity of superconductivity—unambiguous evidence of superconductivity reflecting chiral structure in which the forward and backward supercurrent flows are not equivalent because of inversion symmetry breaking. Such superconductivity is realized via ionic gating in individual chiral nanotubes of tungsten disulfide. The nonreciprocal signal is significantly enhanced in the superconducting state, being associated with unprecedented quantum Little-Parks oscillations originating from the interference of supercurrent along the circumference of the nanotube. The present results indicate that the nonreciprocity is a viable approach toward the superconductors with chiral or noncentrosymmetric structures. PMID:28205518

  7. SUPERCONDUCTING PHOTOINJECTOR

    SciTech Connect

    BEN-ZVI,I.; BURRILL, A.; CALAGA, R.; CHANG, X.; GROVER, R.; GUPTA, R.; HAHN, H.; HAMMONS, L.; KAYRAN, D.; KEWISCH, J.; LAMBIASE, R.; LITVINENKO, V.; MCINTYRE, G.; NAIK, D.; PATE, D.; PHILLIPS, D.; POZDEYEV, E.; RAO, T.; SMEDLEY, J.; THAN, R.; TODD, R.; WEISS, D.; WU, Q.; ZALTSMAN, A.; ET AL.

    2007-08-26

    One of the frontiers in FEL science is that of high power. In order to reach power in the megawatt range, one requires a current of the order of one ampere with a reasonably good emittance. The superconducting laser-photocathode RF gun with a high quantum efficiency photocathode is the most natural candidate to provide this performance. The development of a 1/2 cell superconducting photoinjector designed to operate at up to a current of 0.5 amperes and beam energy of 2 MeV and its photocathode system are the subjects covered in this paper. The main issues are the photocathode and its insertion mechanism, the power coupling and High Order Mode damping. This technology is being developed at BNL for DOE nuclear physics applications such as electron cooling at high energy and electron ion colliders..

  8. Color superconductivity

    SciTech Connect

    Wilczek, F.

    1997-09-22

    The asymptotic freedom of QCD suggests that at high density - where one forms a Fermi surface at very high momenta - weak coupling methods apply. These methods suggest that chiral symmetry is restored and that an instability toward color triplet condensation (color superconductivity) sets in. Here I attempt, using variational methods, to estimate these effects more precisely. Highlights include demonstration of a negative pressure in the uniform density chiral broken phase for any non-zero condensation, which we take as evidence for the philosophy of the MIT bag model; and demonstration that the color gap is substantial - several tens of MeV - even at modest densities. Since the superconductivity is in a pseudoscalar channel, parity is spontaneously broken.

  9. Anisotropic superconducting and normal state magnetic properties of single crystals of RNi*2*B*2*C compounds (R = Y, Gd, Dy, Ho, Er, and Tm)

    SciTech Connect

    Cho, Beongki

    1995-09-26

    The interaction of superconductivity with magnetism has been one of the most interesting and important phenomena in solid state physics since the 1950`s when small amounts of magnetic impurities were incorporated in superconductors. The discovery of the magnetic superconductors RNi2B2C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (Tc) and antiferromagnetic (AF) ordering temperatures (TN) (0 K ≤ Tc ≤ 16 K, 0 K ≤ TN ≤ 20 K) give a good opportunity to observe a variety of interesting phenomena. Single crystals of high quality with appropriate size and mass are crucial in examining the anisotropic intrinsic properties. Single crystals have been grown successfully by an unusual high temperature flux method and characterized thoroughly by X-ray, electrical transport, magnetization, neutron scattering, scanning electron microscopy, and other measurements.

  10. Investigation of the superconducting and normal state properties of the filled-skutterudite system PrPt4Ge12 via chemical substitution

    NASA Astrophysics Data System (ADS)

    Jeon, Inho; Huang, Kevin; Yazici, Duygu; Kanchanavatee, Noravee; White, Benjamin D.; Jang, Sooyoung; Pouse, Naveen; Maple, M. Brian; Ho, Pei-Chun

    We report a systematic chemical substitution study on the unconventional superconductor system PrPt4Ge12, which Sb ions are substituted for Ge. Polycrystalline samples of PrPt4Ge12-x Sbx up to x = 5 were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitutions and evidence for a weak ``rattling'' mode associated with the Pr ions, characterized by a value of ΘE ~ 60 K. As part of a systematic study of the effect of various elemental substitutions on the properties of PrPt4Ge12, measurements of the superconducting and normal state properties of the Pr1-xEuxPt4Ge12 system are currently being performed. This work was supported by the U. S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Grant No. DE-FG02-04-ER46105 (characterization and physical properties measurements), and the National Science Foundation under Grant No. DMR 1206553 (low-temperature measurements).

  11. Superconducting instability of a non-centrosymmetric system

    NASA Astrophysics Data System (ADS)

    Grzybowska, Dorota; Harań, Grzegorz

    2017-03-01

    The Fermi gas approach to the weak-coupling superconductivity in the non-centrosymmetric systems lead to a conclusion of an approximately spin-orbit coupling independent critical temperature of the singlet states as well as the triplet states defined by the order parameter aligned with the antisymmetric spin-orbit coupling vector. We indicate that the above results follow from a simplified approximation of a density of states by a constant Fermi surface value. Such a scenario does not properly account for the spin-split quasiparticle energy spectrum and reduces the spin-orbit coupling influence on superconductivity to the bare pair-breaking effect of a lifted spin degeneracy. Applying the tight-binding model, which captures the primary features of the spin-split energy band, i.e., its enhanced width and the spin-orbit coupling induced redistribution of the spectral weights in the density of states, we calculate the critical temperature of a non-centrosymmetric superconductor. We report a general tendency of the critical temperature to be suppressed by the antisymmetric spin-orbit coupling. We indicate that, the monotonic decrease of the critical temperature may be altered by the spin-orbit coupling induced van Hove singularities which, when driven to the Fermi level, generate maxima in the phase diagram. Extending our considerations to the intermediate-coupling superconductivity we point out that the spin-orbit coupling induced change of the critical temperature depends on the structure of the electronic energy band and both - the strength and symmetry of the pair potential. Finally, we discuss the mixed singlet-triplet state superconducting instability and establish conditions concerning the symmetry of the singlet and triplet counterparts as well as the range of the spin-orbit coupling energy which make such a phase transition possible.

  12. High temperature interface superconductivity

    NASA Astrophysics Data System (ADS)

    Gozar, A.; Bozovic, I.

    2016-02-01

    High-Tc superconductivity at interfaces has a history of more than a couple of decades. In this review we focus our attention on copper-oxide based heterostructures and multi-layers. We first discuss the technique, atomic layer-by-layer molecular beam epitaxy (ALL-MBE) engineering, that enabled High-Tc Interface Superconductivity (HT-IS), and the challenges associated with the realization of high quality interfaces. Then we turn our attention to the experiments which shed light on the structure and properties of interfacial layers, allowing comparison to those of single-phase films and bulk crystals. Both 'passive' hetero-structures as well as surface-induced effects by external gating are discussed. We conclude by comparing HT-IS in cuprates and in other classes of materials, especially Fe-based superconductors, and by examining the grand challenges currently laying ahead for the field.

  13. High temperature interface superconductivity

    DOE PAGES

    Gozar, A.; Bozovic, I.

    2016-01-20

    High-Tc superconductivity at interfaces has a history of more than a couple of decades. In this review we focus our attention on copper-oxide based heterostructures and multi-layers. We first discuss the technique, atomic layer-by-layer molecular beam epitaxy (ALL-MBE) engineering, that enabled High-Tc Interface Superconductivity (HT-IS), and the challenges associated with the realization of high quality interfaces. Then we turn our attention to the experiments which shed light on the structure and properties of interfacial layers, allowing comparison to those of single-phase films and bulk crystals. Both ‘passive’ hetero-structures as well as surface-induced effects by external gating are discussed. Here, wemore » conclude by comparing HT-IS in cuprates and in other classes of materials, especially Fe-based superconductors, and by examining the grand challenges currently laying ahead for the field.« less

  14. High temperature interface superconductivity

    SciTech Connect

    Gozar, A.; Bozovic, I.

    2016-01-20

    High-Tc superconductivity at interfaces has a history of more than a couple of decades. In this review we focus our attention on copper-oxide based heterostructures and multi-layers. We first discuss the technique, atomic layer-by-layer molecular beam epitaxy (ALL-MBE) engineering, that enabled High-Tc Interface Superconductivity (HT-IS), and the challenges associated with the realization of high quality interfaces. Then we turn our attention to the experiments which shed light on the structure and properties of interfacial layers, allowing comparison to those of single-phase films and bulk crystals. Both ‘passive’ hetero-structures as well as surface-induced effects by external gating are discussed. Here, we conclude by comparing HT-IS in cuprates and in other classes of materials, especially Fe-based superconductors, and by examining the grand challenges currently laying ahead for the field.

  15. Superconducting magnet

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Extensive computer based engineering design effort resulted in optimization of a superconducting magnet design with an average bulk current density of approximately 12KA/cm(2). Twisted, stranded 0.0045 inch diameter NbTi superconductor in a copper matrix was selected. Winding the coil from this bundle facilitated uniform winding of the small diameter wire. Test coils were wound using a first lot of the wire. The actual packing density was measured from these. Interwinding voltage break down tests on the test coils indicated the need for adjustment of the wire insulation on the lot of wire subsequently ordered for construction of the delivered superconducting magnet. Using the actual packing densities from the test coils, a final magnet design, with the required enhancement and field profile, was generated. All mechanical and thermal design parameters were then also fixed. The superconducting magnet was then fabricated and tested. The first test was made with the magnet immersed in liquid helium at 4.2K. The second test was conducted at 2K in vacuum. In the latter test, the magnet was conduction cooled from the mounting flange end.

  16. Coexistence of superconductivity and ferromagnetism in the d-band metal ZrZn2.

    PubMed

    Pfleiderer, C; Uhlarz, M; Hayden, S M; Vollmer, R; v Löhneysen, H; Bernhoeft, N R; Lonzarich, G G

    2001-07-05

    It has generally been believed that, within the context of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, the conduction electrons in a metal cannot be both ferromagnetically ordered and superconducting. Even when the superconductivity has been interpreted as arising from magnetic mediation of the paired electrons, it was thought that the superconducting state occurs in the paramagnetic phase. Here we report the observation of superconductivity in the ferromagnetically ordered phase of the d-electron compound ZrZn2. The specific heat anomaly associated with the superconducting transition in this material appears to be absent, and the superconducting state is very sensitive to defects, occurring only in very pure samples. Under hydrostatic pressure superconductivity and ferromagnetism disappear at the same pressure, so the ferromagnetic state appears to be a prerequisite for superconductivity. When combined with the recent observation of superconductivity in UGe2 (ref. 4), our results suggest that metallic ferromagnets may universally become superconducting when the magnetization is small.

  17. Evidence for superconductivity in Li-decorated monolayer graphene.

    PubMed

    Ludbrook, B M; Levy, G; Nigge, P; Zonno, M; Schneider, M; Dvorak, D J; Veenstra, C N; Zhdanovich, S; Wong, D; Dosanjh, P; Straßer, C; Stöhr, A; Forti, S; Ast, C R; Starke, U; Damascelli, A

    2015-09-22

    Monolayer graphene exhibits many spectacular electronic properties, with superconductivity being arguably the most notable exception. It was theoretically proposed that superconductivity might be induced by enhancing the electron-phonon coupling through the decoration of graphene with an alkali adatom superlattice [Profeta G, Calandra M, Mauri F (2012) Nat Phys 8(2):131-134]. Although experiments have shown an adatom-induced enhancement of the electron-phonon coupling, superconductivity has never been observed. Using angle-resolved photoemission spectroscopy (ARPES), we show that lithium deposited on graphene at low temperature strongly modifies the phonon density of states, leading to an enhancement of the electron-phonon coupling of up to λ ≃ 0.58. On part of the graphene-derived π*-band Fermi surface, we then observe the opening of a Δ ≃ 0.9-meV temperature-dependent pairing gap. This result suggests for the first time, to our knowledge, that Li-decorated monolayer graphene is indeed superconducting, with Tc ≃ 5.9 K.

  18. Emergence of superconductivity in heavy-electron materials.

    PubMed

    Yang, Yi-feng; Pines, David

    2014-12-23

    Although the pairing glue for the attractive quasiparticle interaction responsible for unconventional superconductivity in heavy-electron materials has been identified as the spin fluctuations that arise from their proximity to a magnetic quantum critical point, there has been no model to describe their superconducting transition at temperature Tc that is comparable to that found by Bardeen, Cooper, and Schrieffer (BCS) for conventional superconductors, where phonons provide the pairing glue. Here we propose such a model: a phenomenological BCS-like expression for Tc in heavy-electron materials that is based on a simple model for the effective range and strength of the spin-fluctuation-induced quasiparticle interaction and reflects the unusual properties of the heavy-electron normal state from which superconductivity emerges. We show that it provides a quantitative understanding of the pressure-induced variation of Tc in the "hydrogen atoms" of unconventional superconductivity, CeCoIn5 and CeRhIn5, predicts scaling behavior and a dome-like structure for Tc in all heavy-electron quantum critical superconductors, provides unexpected connections between members of this family, and quantifies their variations in Tc with a single parameter.

  19. Emergence of superconductivity in heavy-electron materials

    PubMed Central

    Yang, Yi-feng; Pines, David

    2014-01-01

    Although the pairing glue for the attractive quasiparticle interaction responsible for unconventional superconductivity in heavy-electron materials has been identified as the spin fluctuations that arise from their proximity to a magnetic quantum critical point, there has been no model to describe their superconducting transition at temperature Tc that is comparable to that found by Bardeen, Cooper, and Schrieffer (BCS) for conventional superconductors, where phonons provide the pairing glue. Here we propose such a model: a phenomenological BCS-like expression for Tc in heavy-electron materials that is based on a simple model for the effective range and strength of the spin-fluctuation-induced quasiparticle interaction and reflects the unusual properties of the heavy-electron normal state from which superconductivity emerges. We show that it provides a quantitative understanding of the pressure-induced variation of Tc in the “hydrogen atoms” of unconventional superconductivity, CeCoIn5 and CeRhIn5, predicts scaling behavior and a dome-like structure for Tc in all heavy-electron quantum critical superconductors, provides unexpected connections between members of this family, and quantifies their variations in Tc with a single parameter. PMID:25489102

  20. Different approaches to generate matching effects using arrays in contact with superconducting films.

    NASA Astrophysics Data System (ADS)

    del Valle, J.; Gomez, A.; Luis-Hita, J.; Rollano, V.; Gonzalez, E. M.; Vicent, J. L.

    2017-02-01

    Superconducting films in contact with non-superconducting regular arrays can exhibit commensurability effects between the vortex lattice and the unit cell of the pinning array. These matching effects yield a slowdown of the vortex flow and the corresponding dissipation decrease. The superconducting samples are Nb films grown on Si substrates. We have studied these matching effects with the array on top, embedded or threading the Nb superconducting films and using different materials (Si, Cu, Ni, Py dots and dots fabricated with Co/Pd multilayers). These hybrids allow for studying the contribution of different pinning potentials to the matching effects. The main findings are: (i) Periodic roughness induced in the superconducting film is enough to generate resistivity minima; (ii) A minor effect is achieved by magnetic pinning from periodic magnetic field potentials obtained by dots with out of plane magnetization grown on top of the superconducting film, (iii) In the case of array of magnetic dots embedded in the films, vortex flow probes the magnetic state; i.e. magnetoresistance measurements detect the magnetic state of very small nanomagnets. In addition, we have studied the role played by the local order in the commensurability effects. This was attained using an array that mimics a smectic crystal. We have found that preserving the local order is crucial. If the local order is not retained the magnetoresistance minima vanish.

  1. Dominant Majorana bound energy and critical current enhancement in ferromagnetic-superconducting topological insulator

    NASA Astrophysics Data System (ADS)

    Khezerlou, Maryam; Goudarzi, Hadi; Asgarifar, Samin

    2017-03-01

    Among the potential applications of topological insulators, we theoretically study the coexistence of proximity-induced ferromagnetic and superconducting orders in the surface states of a 3-dimensional topological insulator. The superconducting electron-hole excitations can be significantly affected by the magnetic order induced by a ferromagnet. In one hand, the surface state of the topological insulator, protected by the time-reversal symmetry, creates a spin-triplet and, on the other hand, magnetic order causes to renormalize the effective superconducting gap. We find Majorana mode energy along the ferromagnet/superconductor interface to sensitively depend on the magnitude of magnetization mzfs from superconductor region, and its slope around perpendicular incidence is steep with very low dependency on mzfs. The superconducting effective gap is renormalized by a factor η(mzfs), and Andreev bound state in ferromagnet-superconductor/ferromagnet/ferromagnet-superconductor (FS/F/FS) Josephson junction is more sensitive to the magnitude of magnetizations of FS and F regions. In particular, we show that the presence of mzfs has a noticeable impact on the gap opening in Andreev bound state, which occurs in finite angle of incidence. This directly results in zero-energy Andreev state being dominant. By introducing the proper form of corresponding Dirac spinors for FS electron-hole states, we find that via the inclusion of mzfs, the Josephson supercurrent is enhanced and exhibits almost abrupt crossover curve, featuring the dominant zero-energy Majorana bound states.

  2. Magnetically leviated superconducting bearing

    DOEpatents

    Weinberger, Bernard R.; Lynds, Jr., Lahmer

    1993-01-01

    A magnetically levitated superconducting bearing includes a magnet (2) mounted on a shaft (12) that is rotatable around an axis of rotation and a Type II superconductor (6) supported on a stator (14) in proximity to the magnet (2). The superconductor (6) is positioned so that when it is cooled to its superconducting state in the presence of a magnetic field, it interacts with the magnet (2) to produce an attractive force that levitates the magnet (2) and supports a load on the shaft (12). The interaction between the superconductor (6) and magnet(2) also produces surface screening currents (8) that generate a repulsive force perpendicular to the load. The bearing also has means for maintaining the superconductor at a temperature below its critical temperature (16, 18). The bearing could also be constructed so the magnet (2) is supported on the stator (14) and the superconductor (6) is mounted on the shaft (12). The bearing can be operated by cooling the superconductor (6) to its superconducting state in the presence of a magnetic field.

  3. Topological Superconductivity in CuxBi2Se3

    NASA Astrophysics Data System (ADS)

    Sasaki, Satoshi; Kriener, M.; Segawa, Kouji; Yada, Keiji; Tanaka, Yukio; Sato, Masatoshi; Ando, Yoichi

    2011-11-01

    A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator CuxBi2Se3, which superconducts below ˜3K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting CuxBi2Se3 present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in CuxBi2Se3. In addition, we found an unusual pseudogap that develops below ˜20K and coexists with the topological superconducting state.

  4. Superconducting and mechanical properties of the bulk Bi(pb)SCCO system prepared via solid state and ammonium nitrate precipitation methods

    NASA Astrophysics Data System (ADS)

    Safran, S.; Kılıçarslan, E.; Ozturk, H.; Alp, M.; Akdogan, M.; Asikuzun, E.; Ozturk, O.; Kılıç, A.

    2015-09-01

    We have investigated the effect of preparation method on superconducting and mechanical properties of Bi(Pb)-2223 bulk samples using Bi1.85Pb0.35Sr2Ca2Cu3O10±y stoichiometry. Solid-state reaction and ammonium nitrate precipitation methods have been used for fabrication of the bulk samples. In addition, the effect of annealing time on BSCCO samples have been studied. Structural, electrical, magnetic and microhardness analyses of samples are performed by the X-ray powder diffraction (XRD), the Scanning Electron Microscopy (SEM), DC resistivity, AC susceptibility and Vickers microhardness test. The critical transition temperature, phase purity, surface morphology and crystallinity of the prepared bulk samples are compared with each other. Elasticity (E), brittleness (Bi), fracture toughness (KIC) and yield strength (Y) values are also determined according to annealing time, applied load and production parameters of materials.

  5. Depression of superconducting and antiferromagnetic states in the Dy-rich (U 1- xDy x)Ni 2B 2C solid solutions

    NASA Astrophysics Data System (ADS)

    Gonçalves, António P.; Pereira, Laura C. J.; Kuznietz, Moshe; Almeida, Manuel; Silva, Paulo A. S.; Godinho, Margarida

    2000-06-01

    Polycrystalline Dy-rich (U 1- xDy x)Ni 2B 2C solid solutions ( x=0.97, 0.95, 0.90) were prepared, adopting LuNi 2B 2C-type structure. AC-susceptibility and magnetization studies show that Dy substitution by U (decreasing x) affects the superconducting (SC) and antiferromagnetic (AF) transitions of DyNi 2B 2C [initial magnetic order at 16.3(3) K, AF at 10.4(3) K, SC at ≅6 K], lowering the magnetic transition temperatures, with AF order disappearing for x<0.90. There is no clear evidence for a SC state in the materials down to the lower-temperature limit of 2 K.

  6. Development of density-functional theory for a plasmon-assisted superconducting state: application to lithium under high pressures.

    PubMed

    Akashi, Ryosuke; Arita, Ryotaro

    2013-08-02

    We extend the density-functional theory for superconductors (SCDFT) to take account of the dynamical structure of the screened Coulomb interaction. We construct an exchange-correlation kernel in the SCDFT gap equation on the basis of the random-phase approximation, where electronic collective excitations such as plasmons are properly treated. Through an application to fcc lithium under high pressures, we demonstrate that our new kernel gives higher transition temperatures (T(c)) when the plasmon and phonon cooperatively mediate pairing and it improves the agreement between the calculated and experimentally observed T(c). The present formalism opens the door to nonempirical studies on unconventional electron mechanisms of superconductivity based on density-functional theory.

  7. Microscopic study of the superconducting state of the iron pnictide RbFe2As2 via muon spin rotation

    NASA Astrophysics Data System (ADS)

    Shermadini, Z.; Kanter, J.; Baines, C.; Bendele, M.; Bukowski, Z.; Khasanov, R.; Klauss, H.-H.; Luetkens, H.; Maeter, H.; Pascua, G.; Batlogg, B.; Amato, A.

    2010-10-01

    A study of the temperature and field dependence of the penetration depth λ of the superconductor RbFe2As2(Tc=2.52K) was carried out by means of muon-spin rotation measurements. In addition to the zero-temperature value of the penetration depth λ(0)=267(5)nm , a determination of the upper critical field Bc2(0)=2.6(2)T was obtained. The temperature dependence of the superconducting carrier concentration is discussed within the framework of a multigap scenario. Compared to the other “122” systems which exhibit much higher Fermi level, a strong reduction in the large gap BCS ratio 2Δ/kBTc is observed. This is interpreted as a consequence of the absence of interband processes. Indications of possible pair-breaking effect are also discussed.

  8. Circuit theory of non-equilibrium superconductivity

    NASA Astrophysics Data System (ADS)

    Nazarov, Yuli V.

    2001-04-01

    We give here a short account of a recently developed circuit theory of superconductivity. The theory accounts for decoherence between electrons and holes, twofold nature of the distribution function in the superconducting state and includes arbitrary connectors. We give a simple example and discuss numerical implementation of the theory.

  9. Chalcogen (O2, S, Se, Te) atmosphere annealing induced bulk superconductivity in Fe1+yTe1-xSex single crystal

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Tsuchiya, Y.; Yamada, T.; Taen, T.; Pyon, S.; Shi, Z. X.; Tamegai, T.

    2014-09-01

    We reported a detailed study of Fe1+yTe0.6Se0.4 single crystals annealed in the atmosphere of chalcogens (O2, S, Se, Te). After annealing with appropriate amount of chalcogens, Fe1+yTe0.6Se0.4 single crystals show Tc higher than 14 K with a sharp transition width ∼1 K. Critical current density Jc for the annealed crystals reach a very high value ∼2-4 × 105 A/cm2 under zero field, and is also robust under applied field at low temperatures. Magneto-optical imaging reveal that the Jc is homogeneously distributed in the annealed crystals and isotropic in the ab-plane. Our results show that annealing in the atmosphere of chalcogens can successfully induce bulk superconductivity in Fe1+yTe0.6Se0.4.

  10. Stress state in turbopump bearing induced by shrink fitting

    NASA Technical Reports Server (NTRS)

    Sims, P.; Zee, R.

    1991-01-01

    The stress generated by shrink fitting in bearing-like geometries is studied. The feasibility of using strain gages to determine the strain induced by shrink fitting process is demonstrated. Results from a ring with a uniform cross section reveal the validity of simple stress mechanics calculations for determining the stress state induced in this geometry by shrink fitting.

  11. Superconducting magnet cooling system

    DOEpatents

    Vander Arend, Peter C.; Fowler, William B.

    1977-01-01

    A device is provided for cooling a conductor to the superconducting state. The conductor is positioned within an inner conduit through which is flowing a supercooled liquid coolant in physical contact with the conductor. The inner conduit is positioned within an outer conduit so that an annular open space is formed therebetween. Through the annular space is flowing coolant in the boiling liquid state. Heat generated by the conductor is transferred by convection within the supercooled liquid coolant to the inner wall of the inner conduit and then is removed by the boiling liquid coolant, making the heat removal from the conductor relatively independent of conductor length.

  12. Wavelength-dependent optical enhancement of superconducting interlayer coupling in La1.885Ba0.115CuO4

    DOE PAGES

    Casandruc, E.; Nicoletti, D.; Rajasekaran, S.; ...

    2015-05-05

    We analyze the pump wavelength dependence for the photo-induced enhancement of interlayer coupling in La1.885Ba0.115CuO4, which is promoted by optical melting of the stripe order. In the equilibrium superconducting state (T < TC = 13 K), in which stripes and superconductivity coexist, time-domain THz spectroscopy reveals a photo-induced blue-shift of the Josephson Plasma Resonance after excitation with optical pulses polarized perpendicular to the CuO2 planes. In the striped, non-superconducting state (TC < T < TSO ≃ 40 K) a transient plasma resonance similar to that seen below TC appears from a featureless equilibrium reflectivity. Most strikingly, both these effects becomemore » stronger upon tuning of the pump wavelength from the mid-infrared to the visible, underscoring an unconventional competition between stripe order and superconductivity, which occurs on energy scales far above the ordering temperature.« less

  13. Competition Between the Pseudogap and Superconducting States of Bi2Sr2Ca0.92Y0.08Cu2O8+δ Single Crystals Revealed by Ultrafast Broadband Optical Reflectivity

    NASA Astrophysics Data System (ADS)

    Coslovich, G.; Giannetti, C.; Cilento, F.; Dal Conte, S.; Abebaw, T.; Bossini, D.; Ferrini, G.; Eisaki, H.; Greven, M.; Damascelli, A.; Parmigiani, F.

    2013-03-01

    Ultrafast broadband transient reflectivity experiments are performed to study the interplay between the nonequilibrium dynamics of the pseudogap and the superconducting phases in Bi2Sr2Ca0.92Y0.08Cu2O8+δ. Once superconductivity is established, the relaxation of the pseudogap proceeds ˜2 times faster than in the normal state, and the corresponding transient reflectivity variation changes sign after ˜0.5ps. The results can be described by a set of coupled differential equations for the pseudogap and for the superconducting order parameter. The sign and strength of the coupling term suggest a remarkably weak competition between the two phases, allowing their coexistence.

  14. Superconducting fault current-limiter with variable shunt impedance

    DOEpatents

    Llambes, Juan Carlos H; Xiong, Xuming

    2013-11-19

    A superconducting fault current-limiter is provided, including a superconducting element configured to resistively or inductively limit a fault current, and one or more variable-impedance shunts electrically coupled in parallel with the superconducting element. The variable-impedance shunt(s) is configured to present a first impedance during a superconducting state of the superconducting element and a second impedance during a normal resistive state of the superconducting element. The superconducting element transitions from the superconducting state to the normal resistive state responsive to the fault current, and responsive thereto, the variable-impedance shunt(s) transitions from the first to the second impedance. The second impedance of the variable-impedance shunt(s) is a lower impedance than the first impedance, which facilitates current flow through the variable-impedance shunt(s) during a recovery transition of the superconducting element from the normal resistive state to the superconducting state, and thus, facilitates recovery of the superconducting element under load.

  15. Two-dimensional superconductivity at the interface of a Bi2Te3/FeTe heterostructure.

    PubMed

    He, Qing Lin; Liu, Hongchao; He, Mingquan; Lai, Ying Hoi; He, Hongtao; Wang, Gan; Law, Kam Tuen; Lortz, Rolf; Wang, Jiannong; Sou, Iam Keong

    2014-06-23

    The realization of superconductivity at the interface between a topological insulator and an iron-chalcogenide compound is highly attractive for exploring several recent theoretical predictions involving these two new classes of materials. Here we report transport measurements on a Bi2Te3/FeTe heterostructure fabricated via van der Waals epitaxy, which demonstrate superconductivity at the interface, which is induced by the Bi2Te3 epilayer with thickness even down to one quintuple layer, though there is no clear-cut evidence that the observed superconductivity is induced by the topological surface states. The two-dimensional nature of the observed superconductivity with the highest transition temperature around 12 K was verified by the existence of a Berezinsky-Kosterlitz-Thouless transition and the diverging ratio of in-plane to out-plane upper critical field on approaching the superconducting transition temperature. With the combination of interface superconductivity and Dirac surface states of Bi2Te3, the heterostructure studied in this work provides a novel platform for realizing Majorana fermions.

  16. Strain tolerant microfilamentary superconducting wire

    DOEpatents

    Finnemore, Douglas K.; Miller, Theodore A.; Ostenson, Jerome E.; Schwartzkopf, Louis A.; Sanders, Steven C.

    1993-02-23

    A strain tolerant microfilamentary wire capable of carrying superconducting currents is provided comprising a plurality of discontinuous filaments formed from a high temperature superconducting material. The discontinuous filaments have a length at least several orders of magnitude greater than the filament diameter and are sufficiently strong while in an amorphous state to withstand compaction. A normal metal is interposed between and binds the discontinuous filaments to form a normal metal matrix capable of withstanding heat treatment for converting the filaments to a superconducting state. The geometry of the filaments within the normal metal matrix provides substantial filament-to-filament overlap, and the normal metal is sufficiently thin to allow supercurrent transfer between the overlapped discontinuous filaments but is also sufficiently thick to provide strain relief to the filaments.

  17. Evolution of the Electronic State through the Reduction Annealing in Electron-Doped Pr1.3-xLa0.7CexCuO4+δ (x=0.10) Single Crystals: Antiferromagnetism, Kondo Effect, and Superconductivity

    NASA Astrophysics Data System (ADS)

    Adachi, Tadashi; Mori, Yosuke; Takahashi, Akira; Kato, Masatsune; Nishizaki, Terukazu; Sasaki, Takahiko; Kobayashi, Norio; Koike, Yoji

    2013-06-01

    The evolution of the electronic state through the reduction annealing has been investigated in electron-doped Pr1.3-xLa0.7CexCuO4+δ (x=0.10) single crystals with the so-called T' structure. From the ab-plane and c-axis electrical resistivity measurements in magnetic fields, it has been found that, through the reduction annealing, the strongly localized state of carriers accompanied by the antiferromagnetic (AF) pseudogap in the as-grown crystal changes to a metallic state bringing about the Kondo effect without AF pseudogap and to a superconducting state. These results are able to be understood in terms of a model based on the strong electron correlation. The complete removal of excess oxygen in the T'-cuprates is expected to result in the appearance of superconductivity in a wide range of the Ce concentration including the parent compound of x=0.

  18. Exotic Superconductivity in Correlated Electron Systems

    SciTech Connect

    Mu, Gang; Sandu, Viorel; Li, Wei; Shen, Bing

    2015-05-25

    Over the past decades, the search for high-Tc superconductivity (SC) and its novel superconducting mechanisms is one of the most challenging tasks of condensed matter physicists and material scientists, wherein the most striking achievement is the discovery of high-c and unconventional superconductivity in strongly correlated 3d-electron systems, such as cuprates and iron pnictides/chalcogenides. Those exotic superconductors display the behaviors beyond the scope of the BCS theory (in the SC states) and the Landau-Fermi liquid theory (in the normal states). In general, such exotic superconductivity can be seen as correlated electron systems, where there are strong interplays among charge, spin, orbital, and lattice degrees of freedom. Thus, we focus on the exotic superconductivity in materials with correlated electrons in the present special issue.

  19. Exotic Superconductivity in Correlated Electron Systems

    DOE PAGES

    Mu, Gang; Sandu, Viorel; Li, Wei; ...

    2015-05-25

    Over the past decades, the search for high-Tc superconductivity (SC) and its novel superconducting mechanisms is one of the most challenging tasks of condensed matter physicists and material scientists, wherein the most striking achievement is the discovery of high-c and unconventional superconductivity in strongly correlated 3d-electron systems, such as cuprates and iron pnictides/chalcogenides. Those exotic superconductors display the behaviors beyond the scope of the BCS theory (in the SC states) and the Landau-Fermi liquid theory (in the normal states). In general, such exotic superconductivity can be seen as correlated electron systems, where there are strong interplays among charge, spin, orbital,more » and lattice degrees of freedom. Thus, we focus on the exotic superconductivity in materials with correlated electrons in the present special issue.« less

  20. Proximity-induced minimum radius of superconducting thin rings closed by the Josephson 0 or π junction

    NASA Astrophysics Data System (ADS)

    Barash, Yu. S.

    2017-01-01

    Superconductivity is shown to be completely destroyed in thin mesoscopic or nanoscopic rings closed by the junction with a noticeable interfacial pair breaking and/or a Josephson coupling, if a ring's radius r is less than the minimum radius rmin. The quantity rmin depends on the phase difference χ across the junction, or on the magnetic flux that controls χ in the flux-biased ring. It also depends on the Josephson and interfacial effective coupling constants, and in particular, on whether the ring is closed by the 0 or the π junction. The current-phase relation is substantially modified when the ring's radius exceeds rmin for some of the phase difference values, or slightly goes beyond its maximum. The modified critical temperature Tc and the temperature-dependent supercurrent near Tc are identified here as functions of the ring's radius and the magnetic flux.