Science.gov

Sample records for electron-doped high-tc superconductors

  1. Effect of disorder on the pairing properties of electron-doped high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Jiang, Hong-Min; Li, Jian-Xin

    2007-08-01

    The effect of disorder on pairing properties in the mixed dx2-y2+is - and dx2-y2+idxy -wave pairing states in electron-doped high- Tc cuprates is investigated by self-consistently solving the Bogoliubov-de Gennes equations. It is found that the dominant dx2-y2 -wave component will give way to the s -wave component, while the dxy -wave component will have the same magnitude as the dx2-y2 -wave component with the increase of disorder strength. In real space, the dxy -wave component competes locally with the dx2-y2 -wave component, while the s -wave component does not seem to show such competition with the latter. Both transitions from the dx2-y2 -wave pairing to the mixed dx2-y2+is -wave pairing and to the mixed dx2-y2+idxy -wave pairing can result in the absence of zero-bias peaks in the local tunneling spectra, but it has a U-shaped form for the former and a V-shaped form for the latter. These results may serve to probe the pairing symmetry in the electron-doped cuprates.

  2. Effect of Strong Correlations on the High Energy Anomaly in Hole- and Electron-Doped High-Tc Superconductors

    SciTech Connect

    Moritz, B.; Schmitt, F.; Meevasana, W.; Johnston, S.; Motoyama, E.M.; Greven, M.; Lu, D.H.; Kim, C.; Scalettar, R.T.; Shen, Z.-X.; Devereaux, T.P.; /SLAC, SIMES

    2010-02-15

    Recently, angle-resolved photoemission spectroscopy (ARPES) has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy 'waterfall' or high energy anomaly (HEA). This paper demonstrates, using a combination of new ARPES measurements and quantum Monte Carlo simulations, that the HEA is not simply the byproduct of matrix element effects, but rather represents a cross-over from a quasi-particle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character, in both hole- and electron-doped cuprates. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. the 'waterfall'-like behavior, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole- and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying both hole and electron doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram.

  3. Spin Dynamics in the electron-doped high-Tc superconductors Pr0.88LaCe0.12CuO4-δ

    NASA Astrophysics Data System (ADS)

    Dai, Pengcheng

    2007-03-01

    We briefly review results of recent neutron scattering experiments designed to probe the evolution of antiferromagnetic (AF) order and spin dynamics in the electron- doped Pr0.88LaCe0.12CuO4-δ (PLCCO) as the system is tuned from its as-grown non-superconducting AF state into an optimally doped superconductor (Tc = 27.5 K) without static AF order [1-3]. For under doped materials, a quasi-two- dimensional spin-density wave was found to coexist with three- dimensional AF order and superconductivity. In addition, the low-energy spin excitations follow Bose statistics. In the case of optimally doped material, we have discovered a magnetic resonance intimately related to superconductivity analogous to the resonance in hole-doped materials. On the other hand, the low energy spin excitations have very weak temperature dependence and do not follow Bose statistics, in sharp contrast to the as-grown nonsuperconducting materials. 1 Stephen D. Wilson, Pengcheng Dai, Shiliang Li, Songxue Chi, H. J. Kang, and J. W. Lynn, Nature (London) 442, 59 (2006). 2 Stephen D. Wilson, Shiliang Li, Hyungje Woo, Pengcheng Dai, H. A. Mook, C. D. Frost, S. Komiya, and Y. Ando, Phys. Rev. Lett. 96, 157001 (2006). 3. Stephen D. Wilson, Shiliang Li, Pengcheng Dai, Wei Bao, J. H. Chung, H. J. Kang, S.-H. Lee, S. Komiya, and Y. Ando, Phys. Rev. B 74, 144514 (2006).

  4. Internal static electric and magnetic field at the copper cite in a single crystal of the electron-doped high-Tc superconductor Pr1.85Ce0.15CuO4 -y

    NASA Astrophysics Data System (ADS)

    Wu, Guoqing; Zamborszky, F.; Reyes, A. P.; Kuhns, P. L.; Greene, R. L.; Clark, W. G.

    2014-12-01

    We report 63 ,65Cu -NMR spectroscopy and Knight shift measurements on a single crystal of the electron-doped high-Tc superconductor Pr1.85Ce0.15CuO4 -y with an applied magnetic field (H ) up to 26.42 T. A very small NQR frequency is obtained with the observation of the spectrum, which shows an extremely wide continuous distribution of it that becomes significantly narrower below 20 K at H ∥c where the superconductivity is completely suppressed, indicating a significant change in the charge distribution at the Cu site, while the corresponding change at H ⊥c is negligible when the superconductivity is present or not fully suppressed. The Knight shift and central linewidth are proportional to the applied magnetic field with a high anisotropy. We find that the magnitude of the internal static magnetic field at the copper is dominated by the anisotropic Cu2 + 3 d orbital contributions, while its weak temperature dependence is mainly determined by the isotropic contact hyperfine coupling to the paramagnetic Pr3 + spins, which also gives rise to the full distribution of the internal static magnetic field at the copper for H ⊥c . This internal static electric and magnetic field environment at the copper is very different from that in the hole-doped cuprates, and may provide new insight into the understanding of high-Tc superconductivity. Other experimental techniques are needed to verify whether the observed significant narrowing of the charge distribution at the Cu site with H ∥c is caused by the charge ordering [E. H. da Silva Neto et al., Science (to be published, 2014)] or a new type of charge modulation.

  5. High-Tc superconductivity in weakly electron-doped HfNCl

    NASA Astrophysics Data System (ADS)

    Pamuk, Betül; Mauri, Francesco; Calandra, Matteo

    2017-07-01

    We investigate the magnetic and superconducting properties in electron-doped LixHfNCl . HfNCl is a band insulator that undergoes an insulator to superconductor transition upon doping at x ≈0.13 . The persistence of the insulating state for x <0.13 is due to an Anderson transition probably related to Li disorder. In the metallic and superconducting phase, LixHfNCl is a prototype two-dimensional two-valley electron gas with parabolic bands. By performing a model random phase approximation approach as well as first-principles range-separated Heyd-Scuseria-Ernzerhof (HSE06) calculations, we find that the spin susceptibility χs is strongly enhanced in the low-doping regime by the electron-electron interaction. Furthermore, in the low-doping limit, the exchange interaction renormalizes the intervalley electron-phonon coupling and results in a strong increase of the superconducting critical temperature for x <0.15 . On the contrary, for x >0.15 , Tc is approximately constant, in agreement with experiments. At x =0.055 we found that Tc can be as large as 40 K, suggesting that the synthesis of cleaner samples of LixHfNCl could remove the Anderson insulating state competing with superconductivity and generate a high-Tc superconductor.

  6. Raman Scattering in HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Thomsen, Christian; Cardona, Manuel

    The following sections are included: * INTRODUCTION * Theory * Light scattering by phonons * Electronic scattering * Instrumentation * VIBRATIONAL ANALYSIS AND LATTICE DYNAMICS * Optical Modes of RBa2Cu3O7-δ * Symmetry analysis of the ěc{k} = 0 modes * Lattice dynamical calculation for RBa2Cu3O7 and RBa2Cu3O6 * The Bismuth and Thallium Compounds * The Zurich Superconductors * EXPERIMENTAL RESULTS ON RBa2Cu3O7-δ * Raman Scattering by Phonons * Single crystals of YBa2Cu3O7-δ * Ceramic materials, impurity phases, and thin films * Oxygen deficiency * Isotope effect * Electronic scattering and the gap problem * Scattering by magnons * Bismuth and CuO2-Based Materials: Single-Crystal Spectra and Phonon Assignments * Thallium and CuO2 Based Materials * The Zurich Oxides * BRIEF COMPARISON WITH IR DATA * CONSEQUENCES CONCERNING THE MECHANISM OF HIGH-TC SUPERCONDUCTIVITY AND CONCLUSIONS * ACKNOWLEDGEMENTS * REFERENCES

  7. Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors.

    PubMed

    Sunagawa, Masanori; Ishiga, Toshihiko; Tsubota, Koji; Jabuchi, Taihei; Sonoyama, Junki; Iba, Keita; Kudo, Kazutaka; Nohara, Minoru; Ono, Kanta; Kumigashira, Hiroshi; Matsushita, Tomohiro; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Wakita, Takanori; Muraoka, Yuji; Yokoya, Takayoshi

    2014-03-14

    Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with Tc = 45 K, which is the highest Tc found for the AEFe2As2 bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-Tc superconductors.

  8. High-Tc superconductors in the two-dimensional limit:

    PubMed

    Choy; Kwon; Park

    1998-06-05

    The free modulation of interlayer distance in a layered high-transition temperature (high-Tc) superconductor is of crucial importance not only for the study of the superconducting mechanism but also for the practical application of high-Tc superconducting materials. Two-dimensional (2D) superconductors were achieved by intercalating a long-chain organic compound into bismuth-based high-Tc cuprates. Although the intercalation of the organic chain increased the interlayer distance remarkably, to tens of angstroms, the superconducting transition temperature of the intercalate was nearly the same as that of the pristine material, suggesting the 2D nature of the high-Tc superconductivity.

  9. High -Tc superlight bipolarons in novel superconductors

    NASA Astrophysics Data System (ADS)

    Alexandrov, Sasha

    2003-03-01

    Over the last decade, several competing models of high-temperature superconductivity (HTSC) have been proposed, none of which have succeeded to explain high values of the superconducting critical temperature Tc without adjustable parameters. Most of the proposed models are based on the short-range electron-electron correlations or/and on a short-range electron-phonon interaction. However, in the cuprates the screening is poor due to the low carrier density, layered crystal structure, and high ionicity of the lattice. Here we develop further a model of HTSC, which explicitly takes into account the long-range origin of both types of interaction [1]. The long-range electron-phonon (Froehlich) interaction binds carriers into real space pairs-small bipolarons with surprisingly low mass but sufficient binding energy, while the long-range Coulomb repulsion keeps them from forming larger clusters. We analytically solve this multi-polaron "Froelich-Coulomb" model of oxides for a zigzag ladder and a perovskite layer [2]. The model numerically explains high Tc values in the cuprates without any fitting parameters. It describes other key features of the cuprates such as the isotope effect on the effective mass, pseudogap, the normal state diamagnetism, anomalous upper critical field, and spectral functions measured in tunnelling and photoemission. We argue that strong coupling of carriers with high-frequency phonons and low Fermi energies is the cause of high critical temperatures of novel superconductors. [1] A.S. Alexandrov, in Models and Phenomenology for Conventional and High-temperature Superconductivity (Course CXXXVI of the International School of Physics`Enrico Fermi'), eds. G. Iadonisi, J.R. Schrieffer and M.L. Chiofalo, (IOS Press, Amsterdam), p. 309 (1998). [2] A.S. Alexandrov and P.E. Kornilovitch, J. Phys.: Condens. Matter 14 (2002) 5337. * Mailing address: Department of Physics, Loughborough University, Loughborough LE11 3TU, United Kingdom; E-mail: a

  10. Peltier effect in the mixed state of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Logvenov, G. Yu.; Ryazanov, V. V.; Ustinov, A. V.; Huebener, R. P.

    1991-04-01

    The Peltier and Seebeck effects in the mixed state of high- Tc superconductors are proportional to the resistivity due to flux motion. Therefore, both effects also show the broadening of the transition regime characteristic for these superconductors. The origin of the Peltier effect is discussed in detail, and the validity of the Thomson relation is confirmed, as expected.

  11. High Tc composite silver/oxide superconductors

    NASA Technical Reports Server (NTRS)

    Curreri, P. A.; Peters, P. N.; Sisk, R. C.; Wu, M. K.; Huang, C. Y.

    1990-01-01

    Factors involved in the strong flux pinning effect of high-Tc YBa2Cu3O7/AgO (Y-123/AgO) composite and other REE-123/AgO composites were investigated. Samples of superconducting REE-123 and REE-123/AgO (where REE was Nd, Sm, Eu, Gd, Dy, Ho, Er, or Y) were prepared and used to obtain magnetic moments, critical field, and microstructure data. The optimum heat treatment conditions for the formation of strong flux-pinning REE-123/AgO composites were found to be different for different REE-123 compounds. It was found that the annealing temperature depends on the ionic size of the REE, with larger rare-earth ions requiring higher temperature. It was also found that strong flux-pinning REE-123/AgO composites form only in a narrow annealing temperature range.

  12. High Tc composite silver/oxide superconductors

    NASA Technical Reports Server (NTRS)

    Curreri, P. A.; Peters, P. N.; Sisk, R. C.; Wu, M. K.; Huang, C. Y.

    1990-01-01

    Factors involved in the strong flux pinning effect of high-Tc YBa2Cu3O7/AgO (Y-123/AgO) composite and other REE-123/AgO composites were investigated. Samples of superconducting REE-123 and REE-123/AgO (where REE was Nd, Sm, Eu, Gd, Dy, Ho, Er, or Y) were prepared and used to obtain magnetic moments, critical field, and microstructure data. The optimum heat treatment conditions for the formation of strong flux-pinning REE-123/AgO composites were found to be different for different REE-123 compounds. It was found that the annealing temperature depends on the ionic size of the REE, with larger rare-earth ions requiring higher temperature. It was also found that strong flux-pinning REE-123/AgO composites form only in a narrow annealing temperature range.

  13. High Tc superconductors - Composite wire fabrication

    NASA Astrophysics Data System (ADS)

    Jin, S.; Sherwood, R. C.; van Dover, R. B.; Tiefel, T. H.; Johnson, D. W., Jr.

    1987-07-01

    The fabrication of fine-wire, composite superconductors consisting of a high-conductivity normal metal shell, such as Ag or Cu/Ni/Au, and a superconducting core of Ba2YCu3O oxide is described. The functions of the normal metal shell and the importance of using the proper diffusion barrier metals are discussed. A resistivity-temperature curve for the composite wire Ag/Ba2YCu3O7 is examined, and the compound inside the finished wire is analyzed using X-ray diffraction. It is observed that the zero-field critical current density of the wire at 77 K is about 175 A/sq cm and the superconducting core is continuous and retains phase composition after wire drawing and heat treatment. The supplying of oxygen to the core of the long wire during heat treatments is studied. The data reveal that it is possible to process ceramic superconductors into a desirable composite wire form.

  14. Semiconductor/High-Tc-Superconductor Hybrid ICs

    NASA Technical Reports Server (NTRS)

    Burns, Michael J.

    1995-01-01

    Hybrid integrated circuits (ICs) containing both Si-based semiconducting and YBa(2)Cu(3)O(7-x) superconducting circuit elements on sapphire substrates developed. Help to prevent diffusion of Cu from superconductors into semiconductors. These hybrid ICs combine superconducting and semiconducting features unavailable in superconducting or semiconducting circuitry alone. For example, complementary metal oxide/semiconductor (CMOS) readout and memory devices integrated with fast-switching Josephson-junction super-conducting logic devices and zero-resistance interconnections.

  15. Semiconductor/High-Tc-Superconductor Hybrid ICs

    NASA Technical Reports Server (NTRS)

    Burns, Michael J.

    1995-01-01

    Hybrid integrated circuits (ICs) containing both Si-based semiconducting and YBa(2)Cu(3)O(7-x) superconducting circuit elements on sapphire substrates developed. Help to prevent diffusion of Cu from superconductors into semiconductors. These hybrid ICs combine superconducting and semiconducting features unavailable in superconducting or semiconducting circuitry alone. For example, complementary metal oxide/semiconductor (CMOS) readout and memory devices integrated with fast-switching Josephson-junction super-conducting logic devices and zero-resistance interconnections.

  16. Rugged Low-Resistance Contacts To High-Tc Superconductors

    NASA Technical Reports Server (NTRS)

    Caton, Randall; Selim, Raouf; Byvik, Charles E.; Buoncristiani, A. Martin

    1992-01-01

    Newly developed technique involving use of gold makes possible to fabricate low-resistance contacts with rugged connections to high-Tc superconductors. Gold diffused into specimen of superconducting material by melting gold beads onto surface of specimen, making strong mechanical contacts. Shear strength of gold bead contacts greater than epoxy or silver paste. Practical use in high-current-carrying applications of new high-Tc materials, including superconducting magnets, long-wavelength sensors, electrical ground planes at low temperatures, and efficient transmission of power.

  17. Rugged Low-Resistance Contacts To High-Tc Superconductors

    NASA Technical Reports Server (NTRS)

    Caton, Randall; Selim, Raouf; Byvik, Charles E.; Buoncristiani, A. Martin

    1992-01-01

    Newly developed technique involving use of gold makes possible to fabricate low-resistance contacts with rugged connections to high-Tc superconductors. Gold diffused into specimen of superconducting material by melting gold beads onto surface of specimen, making strong mechanical contacts. Shear strength of gold bead contacts greater than epoxy or silver paste. Practical use in high-current-carrying applications of new high-Tc materials, including superconducting magnets, long-wavelength sensors, electrical ground planes at low temperatures, and efficient transmission of power.

  18. Measurements of the rf surface resistance of high- Tc superconductors

    SciTech Connect

    Delayen, J.R.; Bohn, C.L.; Roche, C.T.

    1990-01-01

    An experimental program is being conducted to assess the applicability of high-{Tc} superconductors for use in high power rf and microwave devices. The program involves the measurement of the rf surface resistance of high-{Tc} samples at frequencies between 0.15 and 40 GHz and rf surface magnetic fields as high as 640 gauss. Polycrystalline samples were found to have surface resistances which increase monotonically with rf-field amplitude, saturating at high field at a few percent of the normal-state surface resistance just above {Tc}. 13 refs., 2 figs., 1 tab.

  19. Induction magnetometer using a high-Tc superconductor coil

    NASA Astrophysics Data System (ADS)

    Sasada, Ichiro

    2010-05-01

    An induction magnetometer consisting of a search coil and an inverting operational amplifier is simple in structure and in signal transferring mechanism from the magnetic field input to the voltage output. Because this magnetometer is based on Faraday's law of induction, it has a lower cutoff frequency r/(2πL), where r is the resistance of the coil and L is its inductance. An attempt has been made to lower the cutoff frequency of the induction magnetometer by using a high-Tc superconductor coil. With a pancake coil (inner diameter ≈18 cm and outer diameter ≈23 cm, 92 turns, 3.23 mH) made of a Bismuth strontium calcium copper oxide (BSCCO) superconductor tape of 5 mm in width and 0.23 mm in thickness, the cutoff frequency achieved was 1.7 Hz which is much lower than that obtained with a bulky copper search coil which is typically in the range of 10-20 Hz. In the experiment, an inverting amplifier was made with a complementary metal-oxide semiconductor operational amplifier and was immersed in liquid nitrogen together with a BSCCO high-Tc superconducting coil. Discussion is made on the resolution of the induction magnetometer using a high-Tc superconductor search coil.

  20. Vortex Pinning in the High-Tc Superconductor YBa2Cu3O6+x

    DTIC Science & Technology

    2009-09-24

    vortex pinning and dissipation in high-Tc superconductors with potential for DOD applications (e.g. for use in efficient filters for high-frequency...Final Performance Report 3. DATES COVERED (From - To) 15-05-2005 to 31-12-2008 4. TITLE AND SUBTITLE Vortex Pinning in the High-Tc Superconductor ...optimized for the study of superconductors . The microscope was first used to study the vortex liquid state in the cuprate high-Tc superconductor

  1. Activation of high- Tc superconductors due to neutron irradiation

    NASA Astrophysics Data System (ADS)

    Shitamichi, T.; Nakano, M.; Terai, T.; Yamawaki, M.; Hoshiya, T.

    2003-10-01

    For actual application of high- Tc superconductors (HTSC), the improvement of Jc is required. It has been reported that pinning centers in the HTSC increase Jc. Particle beam irradiation is one of the most effective methods to introduce strong pinning centers into HTSC for Jc enhancement. In particular, neutron irradiation is very effective for bulk materials, although the activation might be an important problem. In this study, activation of HTSCs was analysed by using the computer code, ORIGEN-II. The contribution of impurities in Bi 2Sr 2CaCu 2O 8+ x (Bi-2212) to 1 cm dose equivalent occupies about 15%. In RE-123 family, Y, La, Nd, Sm. Gd, Dy, Ho and Yb gave low activation. In the case of U-doped Y-123, about 75% of the activity is from the contribution of the fission products.

  2. Doping dependence of fluctuation diamagnetism in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Sarkar, Kingshuk; Banerjee, Sumilan; Mukerjee, Subroto; Ramakrishnan, T. V.

    2016-02-01

    Using a recently proposed Ginzburg-Landau-like lattice free energy functional due to Banerjee et al. (2011) we calculate the fluctuation diamagnetism of high-Tc superconductors as a function of doping, magnetic field and temperature. We analyse the pairing fluctuations above the superconducting transition temperature in the cuprates, ranging from the strong phase fluctuation dominated underdoped limit to the more conventional amplitude fluctuation dominated overdoped regime. We show that a model where the pairing scale increases and the superfluid density decreases with underdoping produces features of the observed magnetization in the pseudogap region, in good qualitative and reasonable quantitative agreement with the experimental data. In particular, we explicitly show that even when the pseudogap has a pairing origin the magnetization actually tracks the superconducting dome instead of the pseudogap temperature, as seen in experiment. We discuss the doping dependence of the 'onset' temperature for fluctuation diamagnetism and comment on the role of vortex core-energy in our model.

  3. Magnetically-related properties of bismuth containing high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Vezzoli, Gary C.; Chen, M. F.; Craver, F.; Safari, A.; Moon, B. M.; Lalevic, B.; Burke, Terence; Shoga, M.

    1990-08-01

    The effect of magnetic fields to 15 T on electrical resistance has been measured for the BiSrCaCuO superconductor at precise temperatures during the transition to the superconducting state from pre-onset conditions to essentially zero resistance conditions. The results show that the temperature at which the magnetic field causes a divergence in the resistance versus 1000/ T curve is approximately the same temperature as the value at which, during cooling, the positive Hall coefficient begins its abrupt descent to zero. This temperature gives the best measure of Tc. It is also shown that small oscillations of low frequency start near onset conditions, the amplitude of which at a given temperature is B-field dependent. Additionally, Hall effect studies as a function of temperature at 4 T in three separate experiments (including high Tc BiSrCaCu PbO of > 90% theoretical density) show that sharp delta-function-like peaks in + RH are observed near Tc and are superimposed on a broader maximum. The Hall data are explicable in terms of exciton formation and ionization. The bound holes associated with these excitons are believed to be the mediators producing Cooper-pairing, and scale very well with Tc for all the known high Tc oxides.

  4. Towards a complete Fermi surface in underdoped high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    The discovery of magnetic quantum oscillations in underdoped high Tc superconductors raised many questions, and initiated a quest to understand the origin of the Fermi surface the like of which had not been seen since the very first discovery of quantum oscillations in elemental bismuth. While studies of the Fermi surface of materials are today mostly assisted by computer codes for calculating the electronic band structure, this was not the case in the underdoped high Tc materials. The Fermi surface was shown to reconstructed into small pockets, yet there was no hint of a viable order parameter. Crucial clues to understanding the origin of the Fermi surface were provided by the small value of the observed Fermi surface cross-section, the negative Hall coefficient and the small electronic heat capacity at high magnetic fields. We also know that the magnetic fields were likely to be too weak to destroy the pseudogap and that vortex pinning effects could be seen to persist to high magnetic fields at low temperatures. I will show that the Fermi surface that appears to fit best with the experimental observations is a small electron pocket formed by connecting the nodal `Fermi arcs' seen in photoemission experiments, corresponding to a density-wave state with two different orthogonal ordering vectors. The existence of such order has subsequently been detected by x-ray scattering experiments, thereby strengthening the case for charge ordering being responsible for reconstructing the Fermi surface. I will discuss new efforts to understand the relationship between the charge ordering and the pseudogap state, discussing the fate of the quasiparticles in the antinodal region and the dimensionality of the Fermi surface. The author acknowledges contributions from Suchitra Sebastian, Brad Ramshaw, Mun Chan, Yu-Te Hsu, Mate Hartstein, Gil Lonzarich, Beng Tan, Arkady Shekhter, Fedor Balakirev, Ross McDonald, Jon Betts, Moaz Altarawneh, Zengwei Zhu, Chuck Mielke, James Day, Doug

  5. Bosonization Theorem and a Model of High-Tc Superconductor.

    NASA Astrophysics Data System (ADS)

    Ren, Hai-Cang

    1996-03-01

    For a purely fermionic system on a lattice, there exists a different, but well defined system on the same lattice, consisting both of bona fide fermions and bosons with an interaction depending on a parameter G characterizing on-site repulsion between particles(R. Friedberg, T. D. Lee and H. C. Ren, Phys. Rev. B50, 10190 (1994).). The energy spectrum and the scattering matrix of the former are identical to those in the finite-energy sector of the latter in the hard-core limit, G→∞. This theorem is particularly useful for the description of a fermionic system whose low-lying spectrum consists of bosonic resonances. We argue that the high-Tc superconductors belong to this category and the long-range order in the superphase can be identified with the condensation of resonance bosons. A short coherence length, results from μSR experiments, measurements of the Hall number and the anomalous behavior of H_c2 near T=0 can be understood in terms of this resonance-boson model(R. Friedberg, T. D. Lee and H. C. Ren, Phys. Rev. B42, 4122 (1990).). We have also examined the possibility of a bosonic d-wave resonance(O.Tchernyshyov, A.S.Blaer and H.Ren, in the current Proceedings.). In this case, the bosonization theorem predicts coexistence of an s-wave bosonic condensate and a d-wave gap parameter for fermions.

  6. Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors.

    PubMed

    Li, Gang; Yan, Binghai; Thomale, Ronny; Hanke, Werner

    2015-05-27

    Recent theoretical studies employing density-functional theory have predicted BaBiO3 (when doped with electrons) and YBiO3 to become a topological insulator (TI) with a large topological gap (~0.7 eV). This, together with the natural stability against surface oxidation, makes the Bismuth-Oxide family of special interest for possible applications in quantum information and spintronics. The central question, we study here, is whether the hole-doped Bismuth Oxides, i.e. Ba(1-x)K(x)BiO3 and BaPb(1-x)Bi(x)O3, which are "high-Tc" bulk superconducting near 30 K, additionally display in the further vicinity of their Fermi energy EF a topological gap with a Dirac-type of topological surface state. Our electronic structure calculations predict the K-doped family to emerge as a TI, with a topological gap above EF. Thus, these compounds can become superconductors with hole-doping and potential TIs with additional electron doping. Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac cone below EF for further hole doping, which manifests these systems to be candidates for both electron- and hole-doped topological insulators.

  7. Fermi surface reconstruction in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Taillefer, Louis

    2009-03-01

    The recent observation of quantum oscillations in underdoped high-Tc superconductors (1), combined with their negative Hall coefficient at low temperature (2), reveals that the Fermi surface of hole-doped cuprates includes a small electron pocket. This strongly suggests that the large hole Fermi surface characteristic of the overdoped regime undergoes a reconstruction caused by the onset of some order which breaks translational symmetry. Here we consider the possibility that this order is ``stripe'' order, a form of combined charge / spin modulation observed most clearly in materials like Eu- doped and Nd-doped LSCO. In these materials, the onset of stripe order coincides with major changes in transport properties (3), providing strong evidence that stripe order is indeed the cause of Fermi-surface reconstruction. We identify the critical doping where this reconstruction occurs and show that the temperature dependence of transport coefficients at that doping is typical of metals at a quantum critical point (4). We discuss an interpretation of the pseudogap as a fluctuating precursor of the stripe-ordered phase.This work was performed in collaboration with L. Balicas, D.A. Bonn, J. Chang, O. Cyr-Choinière, R. Daou, N. Doiron- Leyraud, W.N. Hardy, N.E. Hussey, F. Lalibert'e, D. LeBoeuf, S.Y. Li, R. Liang, C. Proust, H. Takagi, and J.S. Zhou.(1) N. Doiron-Leyraud et al., Nature 447, 565 (2007).(2) D. LeBoeuf et al., Nature 450, 533 (2007).(3) R. Daou et al., Nature Physics, in press (DOI 10.1038/nphys1109); http://arXiv.org/abs/0806.2881.(4) R. Daou et al., to be published; http://arXiv.org/abs/0810.4280.

  8. Recent Photoemission Results for the Electron-Doped Superconductors

    NASA Astrophysics Data System (ADS)

    Matsui, Hiroaki

    2006-03-01

    Recent improvement in the energy and angular resolution of angle-resolved photoemission spectroscopy (ARPES) enabled us to investigate the detailed electronic structure in electron-doped high-temperature superconductors (HTSC), which have a relatively smaller energy-scale of superconductivity compared to hole-doped systems. In this talk, we report our recent ARPES results1,2 focusing on the many-body interaction and the superconducting-gap symmetry in electron-doped HTSC. We have performed high-resolution ARPES measurements on Nd2-xCexCuO4 and observed that the quasiparticle (QP) effective mass around oπ sg&_slash;p is strongly enhanced due to opening of an antiferromagnetic (AF) pseudogap. Both the QP effective mass and the AF pseudogap are strongly anisotropic with the largest magnitude near the hot spot, which is defined as an intersection point of the Fermi surface and the AF zone boundary. Temperature-dependent measurements have revealed that the AF pseudogap survives at temperatures much higher than TN (N'{e}el temperature), possibly due to the short-range AF correlation remaining even above TN. The AF pseudogap gradually decreases with doping and is abruptly filled up near the boundary between the AF and superconducting phases. To study the anisotropy of superconducting gap in electron-doped HTSC, we have performed high-resolution ARPES on Pr0.89LaCe0.11CuO4. We observed that the momentum dependence of superconducting gap is basically consistent with the dx2-y2-wave symmetry, but it obviously deviates from the simple dx2-y2 gap function. The maximum superconducting gap is not observed at the zone boundary as expected from the simple dx2-y2 gap symmetry, but it is located around the hot spot where electrons are thought to be strongly coupled to the AF spin fluctuation. All these ARPES results suggest that the electronic stricture and the superconducting behavior are strongly dominated by the AF interaction in electron-doped HTSC. 1) H. Matsui, K. Terashima

  9. Neutron depolarization effects in a high-Tc superconductor (abstract)

    NASA Astrophysics Data System (ADS)

    Nunes, A. C.; Pickart, S. J.; Crow, L.; Goyette, R.; McGuire, T. R.; Shinde, S.; Shaw, T. M.

    1988-11-01

    Using the polarized beam small-angle neutron scattering spectrometer at the Rhode Island Nuclear Science Center Reactor, we have observed significant depolarization of a neutron beam by passage through polycrystalline high-Tc superconductors, specifically 123 Y-Ba-Cu-O prepared and characterized at the IBM Watson Research Center. We believe that this technique will prove useful in studying aspects of these materials, such as the penetration depth of shielding currents, the presence and structure of trapped flux vortices, and grain size effects on the supercurrent distribution in polycrystalline samples. The two samples showed sharp transitions at 87 and 89 K, and have been studied at temperatures of 77 K; the second sample has also been studied at 4 K. The transition to the superconducting state was monitored by the shift in resonant frequency of a coil surrounding the sample. No measurable depolarization was observed in either sample at 77 K in both the field-cooled and zero-field-cooled states, using applied fields of 0 (nominal), 54, and 1400 Oe. This negative result may be connected with the fact that the material is still in the reversible region as indicated by susceptibility measurements, but it allows an estimate of the upper bound of possible inhomogeneous internal fields, assuming a distance scale for the superconducting regions. For the 10-μm grain size suggested by photomicrographs, this upper bound for the field turns out to be 1.2 kOe, which seems reasonable. At 4 K a significant depolarization was observed when the sample was cooled in low fields and a field of 1400 Oe was subsequently applied. This result suggests that flux lines are penetrating the sample. Further investigations are being carried out to determine the field and temperature dependence of the depolarization, and attempts will be made to model it quantitatively in terms of possible internal field distributions. We are also searching for possible diffraction effects from ordered vortex

  10. Numerical analyses of levitation force and flux creep on high [Tc] superconductor

    SciTech Connect

    Tsuchimoto, M.; Kojima, T.; Takeuchi, H.; Honma, T. . Dept. of Electrical Engineering)

    1993-11-01

    Large levitation force and a stable equilibrium are obtained with a permanent magnet and a bulk high [Tc] superconductor (HTSC). Evaluation of the levitation force is important for many applications, such as magnetically levitated vehicles, magnetic bearing, flywheel and linear drive. Levitation force between a permanent magnet and a high [Tc] superconductor is examined by using two numerical methods. The levitation force to vertical direction is calculated by using the critical state model. Stiffness of restoring force to horizontal direction is calculated by using a frozen-in field model. Numerical solutions agree well with experimental results. Dynamic properties of the levitation force are also analyzed by combining the two methods.

  11. Progress of research of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Tanaka, Shoji

    1991-01-01

    Research in the area of of high T(sub c) superconductors has made great progress in the last few years. New materials were found and the systematic investigation of these materials has contributed to understanding the mechanism of high T(sub c) superconductivity. The critical currents in thin films, bulks, and tapes increased drastically, and the origin of flux pinning will be clarified in the near future. The future of high T(sub c) superconductivity, in both the basic and applied research areas, is very optimistic. Recent activities in research of high T(sub c) superconductivity and superconductors in Japan are overviewed.

  12. Weak Coupling Electron-Phonon for High Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Labbe, J.

    1989-01-01

    Our opinion is that, in the high Tc copper oxides, the electronic correlations are not large enough to allow the localization of the electrons of the half-filled d-p sub-band. Thus, we treat them as itinerant electrons, in a bidimensional structure. And we show that, contrary to a widely held opinion, the electron-phonon interaction can induce high Tc superconductivity in these compounds, even in the weak coupling limit. This is due to the fact that, because of the bidimensionality, the electronic density of states is sharply peaked in the neighbourhood of the Fermi energy. A small coupling between nearest neighbouring CuO2 planes is sufficient to prevent a very large reduction of Tc by the critical fluctuations. The calculated isotope effect is much smaller than usually in the BCS theory. And, in our weak coupling theory, the antiferromagnetic (AF) phase is much more rapidly destabilized by dopping or internal charge transfer than the superconducting phase, which takes place when the AF phase has vanished.

  13. Flux lattice melting in the high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Bishop, D. J.; Gammel, P. L.; Schneemeyer, L. F.

    1989-01-01

    One of the important issues for technological application of the high temperature superconductors is their behavior in a magnetic field. A variety of experiments including electrical transport, mechanical oscillators, and magnetic decoration have suggested that these magnetic properties will make applications more difficult than originally anticipated. These experiments and their results are briefly discussed.

  14. Laser surface interaction of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Chen, C. H.; Mccann, M. P.; Phillips, R. C.

    1991-01-01

    During the past two years, one of the most exciting research fields in science has been the study of the newly discovered high-T(sub c) metal oxide superconductors. Although many theoretical models were proposed, there is no general agreement on any theory to explain these materials. One of the peculiar features of these high-T(sub c) materials is the noninteger number of oxygen atoms. The oxygen content is extremely critical to the superconductive properties. Take YBa2Cu3O(7-x) as an example. Its superconductive properties disappear whenever x is larger than 0.5. The existence of Cu(+ 3) was considered to account for x less than 0.5. However, results from mass spectroscopy of laser desorbed species indicate that significant quantities of oxygen molecules are trapped in the bulk of these high-T(sub c) superconductors. It appears that these trapped oxygen molecules may play key roles in superconductive properties. Preparation of superconductive thin films are considered very important for the applications of these new superconductors for the electronics industry. Fluorescence spectra and ion spectra following laser ablation of high-temperature superconductors were obtained. A real time monitor for preparation of superconductive thin films can possibly be developed.

  15. Measuring Thermal Diffusivity Of A High-Tc Superconductor

    NASA Technical Reports Server (NTRS)

    Powers, Charles E.; Oh, Gloria; Leidecker, Henning

    1992-01-01

    Technique for measuring thermal diffusivity of superconductor of high critical temperature based on Angstrom's temperature-wave method. Peltier junction generates temperature oscillations, which propagate with attenuation up specimen. Thermal diffusivity of specimen calculated from distance between thermocouples and amplitudes and phases of oscillatory components of thermocouple readings.

  16. Measuring Thermal Diffusivity Of A High-Tc Superconductor

    NASA Technical Reports Server (NTRS)

    Powers, Charles E.; Oh, Gloria; Leidecker, Henning

    1992-01-01

    Technique for measuring thermal diffusivity of superconductor of high critical temperature based on Angstrom's temperature-wave method. Peltier junction generates temperature oscillations, which propagate with attenuation up specimen. Thermal diffusivity of specimen calculated from distance between thermocouples and amplitudes and phases of oscillatory components of thermocouple readings.

  17. Photoemission studies of high-tc superconductors: the superconducting gap.

    PubMed

    Shen, Z X; Spicer, W E; King, D M; Dessau, D S; Wells, B O

    1995-01-20

    Over the last several years there have been great improvements in the energy resolution and detection efficiency of angle-resolved photoemission spectroscopy. These improvements have made it possible to discover a number of fascinating features in the electronic structure of the high transition temperature (T(c)) superconductors: apparently bandlike Fermi surfaces, flat-band saddle points, and nested Fermi surface sections. Recent work suggests that these features, previously thought explainable only by one-electron band theory, may be better understood with a many-body approach. Furthermore, other properties of the high-T(c) superconductors, which are difficult to understand with band theory, are well described using a many-body picture. Angle-resolved photoemission spectroscopy has also been used to investigate the nature of the superconducting pairing state, revealing an anisotropic gap consistent with a d-wave order parameter and fueling the current debate over s-wave versus d-wave superconductivity.

  18. Synthesis and Crystal Chemistry of HIGH-Tc Oxide Superconductors

    NASA Astrophysics Data System (ADS)

    Cava, R. J.

    The following sections are included: * INTRODUCTION * THE "123" FAMILY * PHASE EQUILIBRIA IN THE Y-Ba-Cu-O SYSTEM * TRANSITION METAL SUBSTITUTIONS IN CUPRATE SUPERCONDUCTORS * THE T, T', AND T* PHASES * La2-xSrxCaCu2O6+δ * THE INFINITE LAYER PHASE * Pb2Sr2LnCu3O8 * BiO AND TlO BASED COPPER OXIDES * OTHER INTERMEDIARY LAYERS * CONCLUSIONS * REFERENCES

  19. Flux flow and flux dynamics in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Bennett, L. H.; Turchinskaya, M.; Swartzendruber, L. J.; Roitburd, A.; Lundy, D.; Ritter, J.; Kaiser, D. L.

    1991-01-01

    Because high temperature superconductors, including BYCO and BSSCO, are type 2 superconductors with relatively low H(sub c 1) values and high H(sub c 2) values, they will be in a critical state for many of their applications. In the critical state, with the applied field between H(sub c 1) and H(sub c 2), flux lines have penetrated the material and can form a flux lattice and can be pinned by structural defects, chemical inhomogeneities, and impurities. A detailed knowledge of how flux penetrates the material and its behavior under the influence of applied fields and current flow, and the effect of material processing on these properties, is required in order to apply, and to improve the properties of these superconductors. When the applied field is changed rapidly, the time dependence of flux change can be divided into three regions, an initial region which occurs very rapidly, a second region in which the magnetization has a 1n(t) behavior, and a saturation region at very long times. A critical field is defined for depinning, H(sub c,p) as that field at which the hysteresis loop changes from irreversible to reversible. As a function of temperature, it is found that H(sub c,p) is well described by a power law with an exponent between 1.5 and 2.5. The behavior of H(sub c,p) for various materials and its relationship to flux flow and flux dynamics are discussed.

  20. Observations on the thermopower of the high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Yu, R. C.; Naughton, M. J.; Yan, X.; Chaikin, P. M.; Holtzberg, F.; Greene, R. L.; Stuart, J.; Davies, P.

    1988-05-01

    Measurements of the thermopower of the high-temperature superconductor ceramics in the normal state have generally shown a positive, almost temperature-independent Seebeck coefficient, which has been interpreted by several authors in terms of the correlated hopping of the carriers as would be found in the strong Coulomb interaction limit of the Hubbard model. In this case the thermopower has a contribution from spin entropy which can be quenched by a large magnetic field. On the contrary we measure a field-independent thermopower to 30 T. Moreover, in single crystals we find that the thermopower in the Cu-O planes is negative, while the perpendicular thermopower is positive.

  1. MEVVA ion-implantation of high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Martin, J. W.; Cohen, D. D.; Russell, G. J.; Dytlewski, N.; Evans, P. J.

    1995-12-01

    Metallised vapour vacuum arc (MEVVA) ion-implantation has been used to implant transition metal ions into high quality superconductor materials. Analysis of the samples was by the relatively new technique of heavy ion elastic recoil time-of-flight spectroscopy (ERTOFS), employing a 77 MeV 127I 10+ beam. The HIERTOFS technique is ideally suited to samples of this nature, providing individual depth profiles for each element within the matrix. The results were found to be implant-ion species dependent, with ions such as Ni and Co having differing effects to that of Fe. This paper will report on the use of ERTOFS as a method to obtain individual implant and substrate profiles from the ion-beam modified materials.

  2. Activation of high- Tc superconductors with neutron irradiation

    NASA Astrophysics Data System (ADS)

    Nakano, Makito; Ogikubo, Kouji; Terai, Takayuki; Yamawaki, Michio; Hoshiya, Taiji

    2002-10-01

    Activation due to nuclear transmutation is a very important factor for feasibility evaluation on the improvement of superconducting property by neutron irradiation. In this paper, the activation of Bi 2Sr 2CaCu 2O 8+ x (Bi-2212) superconductor was evaluated by the activation analysis and calculation using ORIGEN-JR computer code. The activation analysis was carried out to determine the composition and impurity concentrations of the specimen. Then, based on the data about impurities, the contribution of the impurities and the decay of radioactivity after irradiation were calculated. Main elements for activation were Sr as a component of Bi-2212, and Co, Zn and Fe as impurities. Activation caused by the impurities occupied 40% 1 year after irradiation. When thermal neutron flux was reduced by 80% using a Cd filter, the total activation was reduced to about 30%.

  3. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-10-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enable definition of superconducting and nonsuperconducting regions in the same epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel monolithic devices. Recent experiments are discussed which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronics devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors are presented.

  4. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-10-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis on the laser-writing method, which enables definition of superconducting and nonsuperconducting regions in the same epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3optical modulator is introduced. The second, more futuristic, approach is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments are discussed which reveal intriguing optical properties of HTS films and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors, are presented.

  5. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-09-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enables definition of superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments are discussed, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors will be presented.

  6. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-08-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially electronic, optical, and electro-optical properties. They also operate int he 30 - 80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high-quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach- Zehnder-type YBa2Cu3O7-y-on LiNbO3 optical modulator is introduced. The second, more futuristic, approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments are discussed which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high- frequency modulators, ultrafast-pulse generators, and sensitive photodetectors, are presented.

  7. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-09-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications are given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method. These techniques make it possible to define superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches are presented for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid-nitrogen temperatures. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y- on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTs phases to fabricate novel, monolithic devices. We discuss recent experiments, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors are presented.

  8. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-08-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro- optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optical. A review of the substrate materials and deposition techniques suitable for fabrication of high-quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enables the definition of superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid-nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro- optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices are discussed. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors will be presented.

  9. Applications of high-Tc superconductors in optoelectronics

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman

    1991-08-01

    The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro- optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high-quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enables the definition of superconducting and nonsuperconducting regions in the same, epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid-nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro- optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3/$O(subscript 7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel, monolithic devices. Recent experiments, which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronic devices are discussed. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors will be presented.

  10. AC losses in conductors based on high {Tc} superconductors

    SciTech Connect

    SUENAGA,M.

    2000-03-17

    In electrical power devices, ac losses from a superconductor is a primary factor which determines their usefulness as commercial power equipment. For this reason, extensive studies have been carried out on the losses of Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}/Ag, [Bi(2223)/Ag], tapes. These studies were mostly limited to a single isolated tape. However, a conductor in a power device is surrounded by other conductors and the precise magnetic field distribution around it is very different from that for a single conductor carrying currents or in ac fields. Since the precise field distribution in and around a superconductor is critical in determining the losses, it is very important to measure and to understand the losses in Bi(2223)/Ag tapes which are surrounded by other tapes as in a power device. Taking this fact into consideration, recently the authors have studied ac losses in stacks of Bi(2223)/Ag tapes in parallel and perpendicular applied fields and shown that they can calculate the losses in these cases utilizing the critical state model if a number of appropriate factors about properties of the tape are taken into a consideration. However, in a power device such as a transformer, magnetic fields near the ends of a solenoid vary from parallel to perpendicular with the tape face. Thus, it is important to learn the behavior of the losses in the stacks of Bi(2223)/Ag tapes with respect to the variations in the angle between the applied field direction and the tape face. In order to accomplish this, they measured the angular dependence of the losses in the stacks which were made from two different Bi(2223)/Ag tapes. Here they report this result and discuss under what conditions they can calculate the losses with a reasonable accuracy. The angular dependence of the losses in ac applied fields were measured using a series of stacked Bi(2223)/Ag tapes having the angles with the direction of applied fields of 0, 7.5, 15, 30, 45, 60, and 90 degrees. The measured

  11. Electronic structure Fermi liquid theory of high Tc superconductors: Comparison of predictions with experiments

    NASA Technical Reports Server (NTRS)

    Yu, Jaejun; Freeman, A. J.

    1991-01-01

    Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations.

  12. Preparation and formation mechanism of cube textured Ag substrate for coated high- Tc superconductor

    NASA Astrophysics Data System (ADS)

    Liu, Danmin; Zhou, Meiling; Hu, Yancao; Zuo, Tieyong

    2000-07-01

    A strong cube, {100}<100>, textured silver tape for coated high- Tc superconductor was obtained. The hot-rolling textures and annealed textures of silver were studied systematically. Cube texture can be obtained by hot-rolling. In the process of rolling, twin formation must be avoided in order to increase the strength of the {211}<111>orientation. The crystals in {211}<111>orientation transforms into cube orientation by dynamic recrystallization and subsequent annealing.

  13. Scanning instrumentation for measuring magnetic field trapping in high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Sisk, R. C.; Helton, A. J.

    1993-01-01

    Computerized scanning instrumentation measures and displays trapped magnetic fields across the surface of high Tc superconductors at 77 K. Data are acquired in the form of a raster scan image utilizing stepping motor stages for positioning and a cryogenic Hall probe for magnetic field readout. Flat areas up to 45 mm in diameter are scanned with 0.5-mm resolution and displayed as false color images.

  14. Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-Tc Superconductor

    SciTech Connect

    Chen, Y.

    2010-05-03

    We report the discovery of a self-doped multi-layer high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi surface(FS) sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a T{sub c} of 60K, possessing simultaneously both electron- and hole-doped FS sheets. Intriguingly, the FS sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic ({pi}/a, {pi}/a) scattering.

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

    PubMed

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

    2003-04-17

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

  16. Nonsuperconducting Micron Size Particle as Effective Pinning Centre for Enhanced Jc in High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Roul, B. K.

    2008-10-01

    Understanding the real mechanism responsible for achieving high transport critical current density (Jc) in the high temperature (high-Tc) cuprate superconductors has been one of the primary goal. The only promising way is to tailor the high-Tc cuprate material during preparation stage incorporating suitable non-superconducting particles within superconducting matrix, which are known to serve as effective pining centers. Incorporation of non-superconducting particle like silver with dimension down to micron/submicron size in the superconducting matrix is very stable and form a homogenous solid solution matrix, which has got the better stability on aging and found to be effective in enhancing flux pining in high-Tc superconducting system. In this paper, studies have been made to investigate and review the effect of non-superconducting micron size Ag particle in to the matrix of RE-Ba-Cu-O (RE = Sm, Gd & Y) 123 high-Tc ceramic superconducting system. XRD, SEM, magnetization, magnetotransport and microwave induce DC voltage measurements were carried out to study the effect of Ag into 123-superconducting system. It is observed that controlled addition of Ag into Sm-Ba-Cu-O (SBCO), Gd-Ba-Cu-O (GBCO) and Y-Ba-Cu-O (YBCO) ceramic superconductor do not react with the decomposed phases but remains in the metallic form. This brings about a lowering of the normal-state resistivity. The increase of magnetic critical current density (Jmc), transport critical current density (Jtc), and, hence pinning force density (Fp) with Ag addition into above three systems suggest the creation of an SNS-type proximity junction at the intergranular region and stronger Josephson current paths between the superconducting intergrains. This is attributed to the physical densification and consequent reduction of the total number of weak links by Ag addition into the above mentioned ceramic superconducting system.

  17. Resonance in Optimally Electron-Doped Superconductor Nd1.85Ce0.15CuO4−?

    SciTech Connect

    Zhao, Jun; Dai, Pengcheng; Li, Shiliang; Freeman, Paul G.; Onose, Y,.; Tokura, Y.

    2007-01-01

    We use inelastic neutron scattering to probe magnetic excitations of an optimally electron-doped superconductor Nd1.85Ce0.15CuO4− above and below its superconducting transition temperature Tc = 25 K. In addition to gradually opening a spin pseudo gap at the antiferromagnetic ordering wavevector Q = (1/2, 1/2, 0), the effect of superconductivity is to form a resonance centered also at Q = (1/2, 1/2, 0) but at energies above the spin pseudo gap. The intensity of the resonance develops like a superconducting order parameter, similar to those for hole-doped superconductors and electron-doped Pr0.88LaCe0.12CuO4. The resonance is therefore a general phenomenon of cuprate superconductors, and must be fundamental to the mechanism of high-Tc superconductivity.

  18. Electrical properties of Y-Ba-Na-Cu-O high Tc superconductors thin films

    NASA Astrophysics Data System (ADS)

    Verdyan, A.; Lapsker, I.; Azoulay, J.; Sackler, Raymond; Sackler, Beverly

    1993-04-01

    Y-Ba-Na-Cu-O high Tc superconductors thin films deposited on MgO substrate by resistive evaporation technique were found to have improved electrical properties as compared to pure Y-Ba-Cu-O thin films similarly prepared. A simple conventional inexpensive vacuum system housing a single resistively tungsten heated source was used for the deposition. Pulverized mixture of Y, BaF 2, NaF and Cu in the appropriate atomic proportion was evaporated onto the substrates whose temperature was held constant at 400°C during the evaporation. In situ heat treatment has been carried out at 700°C under oxygen partial pressure of 7 pa. The films thus obtained were found to have the normal superconductors orthorhombic phase at room temperature without any further ex situ heat treatment. The films were characterized and analyzed by x-ray diffraction auger electron spectroscopy and four point dc electrical measurements.

  19. Quantum topological transition in hyperbolic metamaterials based on high Tc superconductors.

    PubMed

    Smolyaninov, Igor I

    2014-07-30

    Hyperbolic metamaterials are known to exhibit a transition in the topology of the photon iso-frequency surface from a closed ellipsoid to an open hyperboloid, resulting in a considerable increase of the photonic density of states. This topological transition may also be described as a change of metric signature of the effective optical space. Here we demonstrate that high Tc superconductors exhibit hyperbolic metamaterial behavior in the far infrared and THz frequency ranges. In the THz range the hyperbolic behavior occurs only in the normal state, while no propagating photon modes exist in the superconducting state. Thus, a quantum topological transition may be observed for THz photons at zero temperature as a function of the external magnetic field, in which the effective Minkowski spacetime arises in the mixed state of the superconductor at some critical value of the external magnetic field. Nucleation of effective Minkowski spacetime occurs via the formation of quantized Abrikosov vortices.

  20. The effect of processing parameters during heat treatment of bulk high- Tc superconductors

    SciTech Connect

    Cha, Y.S.; Dorris, S.E.; Hull, J.R.; Poeppel, R.B.

    1991-04-01

    Plastic extrusion is a promising method for producing the long lengths of high-{Tc} superconductor that will be necessary to meet many potential applications. A crucial phase of the extrusion method is removal of organic constituents. Incomplete removal can leave residual carbon at grain boundaries, which can adversely affect the superconducting properties, whereas excessively rapid removal of the organics can cause the extruded superconductor to disintegrate completely. In this paper, we analyze the effects of the following aspects of organics removal, as they apply to the firing of extruded YBa{sub 2}Cu{sub 3}O{sub x} coils: (1) total pressure in the furnace, (2) oxygen flow, (3) heat conduction, and (4) diffusion of volatile components during removal of organics.

  1. The effect of processing parameters during heat treatment of bulk high-{Tc} superconductors

    SciTech Connect

    Cha, Y.S.; Dorris, S.E.; Hull, J.R.; Poeppel, R.B.

    1991-04-01

    Plastic extrusion is a promising method for producing the long lengths of high-{Tc} superconductor that will be necessary to meet many potential applications. A crucial phase of the extrusion method is removal of organic constituents. Incomplete removal can leave residual carbon at grain boundaries, which can adversely affect the superconducting properties, whereas excessively rapid removal of the organics can cause the extruded superconductor to disintegrate completely. In this paper, we analyze the effects of the following aspects of organics removal, as they apply to the firing of extruded YBa{sub 2}Cu{sub 3}O{sub x} coils: (1) total pressure in the furnace, (2) oxygen flow, (3) heat conduction, and (4) diffusion of volatile components during removal of organics.

  2. Remanent magnetization of ceramic and single-crystal high-Tc superconductors in tilted magnetic fields

    NASA Astrophysics Data System (ADS)

    Bugoslavsky, Yu. V.; Minakov, A. A.; Vasyurin, S. I.

    1996-02-01

    Dependence of the remanent magnetization (Mr) anisotropy on the structure and shape of the superconductor and on the magnetizing procedure was studied for a number of high-Tc superconductor ceramics and single crystals. The experiments were done by means of a vibrating-sample magnetometer with a rotatable sample holder. It was found that the main contribution to the anisotropic behavior of Mr is due to the surface screening currents, and therefore the anisotropy is subject to variation when sample shape is changed. The question is resolved, why the effective demagnetization factors for decoupled ceramic samples are different from those calculated in the inscribed-ellipsoid approximation. Influence of inhomogeneous grain magnetization and global bulk currents on the angular dependencies of Mr in ceramic samples is investigated. The evolution of remanence in YBCO single crystals with an increase of the magnetizing field is described within an extended Bean model.

  3. Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-TcSuperconductor

    SciTech Connect

    Chen, Yulin; Iyo, Akira; Yang, Wanli; Zhou, Xingjiang; Lu,Donghui; Eisaki, Hiroshi; Devereaux, Thomas P.; Hussain, Zahid; Shen, Z.-X.

    2006-06-14

    We report the discovery of a self-doped multilayer high Tcsuperconductor Ba2Ca3Cu4O8F2 (F0234) which contains distinctly differentsuperconducting gap magnitudes along its two Fermi-surface sheets. Whileformal valence counting would imply this material to be an undopedinsulator, it is a self-doped superconductor with a Tc of 60 K,possessing simultaneously both electron- and hole-doped Fermi-surfacesheets. Intriguingly, the Fermi-surface sheet characterized by the muchlarger gap is the electron-doped one, which has a shape disfavoring twoelectronic features considered to be important for the pairing mechanism:the van Hove singularity and the antiferromagnetic (pi/a, pi/a)scattering.

  4. X-Ray Diffraction Line Broadening: Modeling and Applications to High-Tc Superconductors

    PubMed Central

    Balzar, Davor

    1993-01-01

    A method to analyze powder-diffraction line broadening is proposed and applied to some novel high-Tc superconductors. Assuming that both size-broadened and strain-broadened profiles of the pure-specimen profile are described with a Voigt function, it is shown that the analysis of Fourier coefficients leads to the Warren-Averbach method of separation of size and strain contributions. The analysis of size coefficients shows that the “hook” effect occurs when the Cauchy content of the size-broadened profile is underestimated. The ratio of volume-weighted and surface-weighted domain sizes can change from ~1.31 for the minimum allowed Cauchy content to 2 when the size-broadened profile is given solely by a Cauchy function. If the distortion co-efficient is approximated by a harmonic term, mean-square strains decrease linearly with the increase of the averaging distance. The local strain is finite only in the case of pure-Gauss strain broadening because strains are then independent of averaging distance. Errors of root-mean-square strains as well as domain sizes were evaluated. The method was applied to two cubic structures with average volume-weighted domain sizes up to 3600 Å, as well as to tetragonal and orthorhombic (La-Sr)2CuO4, which exhibit weak line broadenings and highly overlapping reflections. Comparison with the integral-breadth methods is given. Reliability of the method is discussed in the case of a cluster of the overlapping peaks. The analysis of La2CuO4 and La1.85M0.15CuO4(M = Ca, Ba, Sr) high-Tc superconductors showed that microstrains and incoherently diffracting domain sizes are highly anisotropic. In the superconductors, stacking-fault probability increases with increasing Tc; microstrain decreases. In La2CuO4, different broadening of (h00) and (0k0) reflections is not caused by stacking faults; it might arise from lower crystallographic symmetiy. The analysis of Bi-Cu-O superconductors showed much higher strains in the [001] direction than in

  5. Theory of quantum oscillations in the vortex-liquid state of high-Tc superconductors.

    PubMed

    Banerjee, Sumilan; Zhang, Shizhong; Randeria, Mohit

    2013-01-01

    The observation of quantum oscillations in underdoped cuprates has generated intense debate about the nature of the field-induced resistive state and its implications for the 'normal state' of high-Tc superconductors. Quantum oscillations suggest an underlying Fermi liquid at high magnetic fields H and low temperatures, in contrast with the pseudogap seen in zero-field, high-temperature spectroscopic experiments. Recent specific heat measurements show quantum oscillations in addition to a large field-dependent suppression of the electronic density of states. Here we present a theoretical analysis that reconciles these seemingly contradictory observations. We model the resistive state as a vortex liquid with short-range d-wave pairing correlations. We show that this state exhibits quantum oscillations, with a period determined by a Fermi surface reconstructed by a competing order parameter, in addition to a large suppression of the density of states that goes like √H at low fields.

  6. Quasiparticle mass enhancement approaching optimal doping in a high-Tc superconductor

    DOE PAGES

    Ramshaw, B. J.; Sebastian, S. E.; McDonald, R. D.; ...

    2015-03-26

    In the quest for superconductors with higher transition temperatures (Tc), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. In recent experiments it is suggested that the existence of the requisite broken-symmetry phase in the high-Tc cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. Here, we used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O6+δ over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effectivemore » mass toward optimal doping. Finally, this mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of pcrit ≈ 0.18.« less

  7. On infrared and terahertz imaging of surface plasmons in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Stinson, H. T.; Fei, Z.; Rodin, A. S.; McLeod, A. S.; Fogler, M. M.; Basov, D. N.

    2013-03-01

    Recent scattering-mode scanning near-field optical microscopy (s-SNOM) experiments have imaged surface plasmons in graphene at infrared frequencies.[1] The scanning probe launches surface plasmons and detects their standing-wave interference pattern upon reflection from the sample edge. The surface plasmon dispersion relation directly relates the standing wave fringe separation and amplitude decay to the optical constants of the sample. We have modeled surface plasmon s-SNOM imaging for high-Tc superconductor (HTSC) thin films. Our results indicate that surface plasmons can be imaged in HTSCs at frequencies near or below the superconducting gap. This would allow for a direct measurement of HTSC optical constants below the gap. For known HTSCs such as YBCO, this is in the far-IR or terahertz range. Our simulations show that this method can also distinguish between superconducting and normal states at the nanoscale.

  8. Magneto-optical imaging and current distributions in high-{Tc} superconductors

    SciTech Connect

    Polyanskii, A. |; Pashitski, A.; Gurevich, A.; Parrell, J.A.; Larbalestier, D.C.; Polak, M. |; Foltyn, S.R.; Arendt, P.N. |

    1997-06-01

    Recent studies on the magneto-optical (MO) imaging of the magnetic flux and current distributions in polycrystalline high-{Tc} superconductors are summarized. The authors studied a wide spectrum of high-{Tc} materials, from single grain boundaries in YBCO bicrystals, to polycrystalline YBCO thick films deposited on an IBAD-buffer layer grown on a polycrystalline Hastelloy substrate, to Bi-2223 tapes. In all cases they found that structural defects (e.g., high-angle grain boundaries, second phase precipitates, microcrack networks, etc.) significantly limit the current-carrying capability. These defects make the magnetic flux distribution highly inhomogeneous, in turn producing granular and percolative current flow. By inverting the Biot-Savart law for thin film and slab geometries, they were able to reconstruct the local current flow patterns around defects and thus identify the current-carrying percolative paths and map the distribution of local critical currents J{sub c}(r). Such studies show that, even in high-J{sub c} materials, the local J{sub c}(r) can vary by a factor 2--10 due to defects. Since the maximum local J{sub c}(r) values can significantly exceed the numbers obtained by transport measurements, it is clear that there are still significant opportunities for raising the J{sub c} of polycrystalline HTS conductors.

  9. Pinning force scaling analysis of Fe-based high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka, Michael R.; Muralidhar, Miryala

    2016-10-01

    Pinning force data, Fp, of a variety of Fe-based high-Tc superconductors (11-, 111-, 122- and 1111-type) were analyzed by means of a scaling approach based on own experimental data and an extensive collection of literature data. The literature data were mostly replotted, but also converted from critical current measurements together with data for the irreversibility line when available from the same authors. Using the scaling approaches of Dew-Hughes [J. Appl. Phys. 44, 1360 (1973)] and Kramer [Philos. Mag. 30, 293 (1974)], we determined the scaling behavior and the best fits to the theory. The data of most experiments analyzed show a good scaling behavior at high temperatures when plotting the normalized pinning force Fp/Fp,max versus the irreversibility field, Hirr. The resulting peak positions, h0, were found at ≈ 0.3 for the 11-type materials, at ≈ 0.48 for the 111-type materials, between 0.32 and 0.5 for the 1111-type materials and between 0.25 and 0.71 for the 122-type materials. Compared to the typical results of Bi2Sr2CaCu2O8+δ (h0 ≈ 0.22) and YBa2Cu3O7-δ (h0 ≈ 0.33), most of the 122 and 1111 samples investigated show peak values higher than 0.4, which is similar to the data obtained on the light-rare earth 123-type HTSC like NdBa2Cu3Oy. This high peak position ensures a good performance of the materials in high applied magnetic fields and is, therefore, a very promising result concerning the possible applications of the Fe-based high-Tc superconductors.

  10. Hidden Fermi liquid: Self-consistent theory for the normal state of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Casey, Philip A.

    The anomalous "strange metal" properties of the normal, non-superconducting state of the high-Tc cuprate superconductors have been extensively studied for over two decades. The resistivity is robustly T-linear at high temperatures, while at low T it appears to maintain linearity near optimal doping and is T2 at higher doping. The inverse Hall angle is strictly T2 and hence has a distinct scattering lifetime from the resistivity. The transport scattering lifetime is highly anisotropic as directly measured by angle-dependent magnetoresistance (ADMR) and indirectly in more traditional transport experiments. The IR conductivity exhibits a non-integer power-law in frequency, which we take as a defining characteristic of the "strange metal". A phenomenological theory of the transport and spectroscopic properties at a self-consistent and predictive level has been much sought after, yet elusive. Hidden Fermi liquid theory (HFL) explicitly accounts for the effects of Gutzwiller projection in the t-J Hamiltonian, widely believed to contain the essential physics of the high-Tc superconductors. We show this theory to be the first self-consistent description for the normal state of the cuprates based on transparent, fundamental assumptions. Our well-defined formalism also serves as a guide for further experimental confirmation. Chapter 1 reviews the "strange metal" properties and the relevant aspects of competing models. Chapter 2 presents the theoretical foundations of the formalism. Chapters 3 and 4 derive expressions for the entire normal state relating many of the properties, for example: angle-resolved photoemission, IR conductivity, resistivity, Hall angle, and by generalizing the formalism to include the Fermi surface topology---ADMR. Self-consistency is demonstrated with experimental comparisons, including the most recent laser-ARPES and ADMR. Chapter 5 discusses entropy transport, as in the thermal conductivity, thermal Hall conductivity, and consequent metrics of non

  11. Lattice dynamics of high-Tc superconductors: Optical modes of the thallium-based compounds

    NASA Astrophysics Data System (ADS)

    Kulkarni, A. D.; de Wette, F. W.; Prade, J.; Schröder, U.; Kress, W.

    1990-04-01

    We present a lattice-dynamical calculation of the Raman- and infrared-active modes of the following six thallium-based high-Tc superconductors: Tl2Ba2CuO6, Tl2CaBa2Cu2O8, and Tl2Ca2Ba2Cu3O10 (body-centered-tetragonal structures) and TlCaBa2Cu2O7, TlCa2Ba2Cu3O9, and TlCa3Ba2Cu4O11 (simple-tetragonal structures). Our calculations are based on a shell model that incorporates short-range overlap potentials, long-range Coulomb potentials, and ionic polarizabilities. We also require that the shell models for different high-Tc superconducting compounds be mutually compatible, namely that the short-range potentials for given ion pairs in equivalent environments be transferable from one compound to the other. The model presented here does in fact utilize a common set of short-range potentials that apply to the entire series of thallium-based superconductors as well as to YBa2Cu3O7 and Bi2CaSr2Cu2O8, studied earlier. The model reproduces the available experimental infrared and Raman data of all these compounds quite well and is thus supported by a broad database, albeit only of optical modes. We expect that our model, which is based on realistic interaction potentials, reproduces eigenvalues and eigenvectors to the same approximation. Thus we conclude from the satisfactory agreement between calculated and measured eigenfrequencies that the calculated eigenvectors provide a realistic description of the displacement patterns of the optical modes.

  12. Momentum and Doping Dependence of Spin Excitations in Electron-Doped Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Jing, Pengfei; Zhao, Huaisong; Kuang, Lülin; Lan, Yu; Feng, Shiping

    2017-01-01

    Superconductivity in copper oxides emerges on doping holes or electrons into their Mott-insulating parent compounds. The spin excitations are thought to be the mediating glue for the pairing in superconductivity. Here the momentum and doping dependence of the dynamical spin response in the electron-doped cuprate superconductors is studied based on the kinetic-energy-driven superconducting mechanism. It is shown that the dispersion of the low-energy spin excitations changes strongly upon electron doping; however, the hour-glass-shaped dispersion of the low-energy spin excitations appeared in the hole-doped case is absent on the electron-doped side due to the electron-hole asymmetry. In particular, the commensurate resonance appears in the superconducting state with the resonance energy that correlates with the dome-shaped doping dependence of the superconducting gap. Moreover, the spectral weight and dispersion of the high-energy spin excitations in the superconducting state are comparable with those in the corresponding normal state, indicating that the high-energy spin excitations do not play an important part in the pair formation.

  13. Diamagnetie Shielding and Meissner Effect in the High Tc Superconductor SrxLa2-xCuO4-y

    NASA Astrophysics Data System (ADS)

    Tokumoto, Madoka; Ihara, Hideo; Murata, Keizo; Hirabayashi, Masayuki; Terada, Norio; Senzaki, Kiyoshi; Kimura, Yoichi

    1987-04-01

    Static magnetization measurements of the high Tc superconductor SrxLa2-xCuO4-y, with the layered perovskite K2NiF4 structure and a 43 K resistive onset, are reported. Diamagnetic susceptivility was observed below 37 K indicating a bulk superconductivity. The magnetization measurement revealed a characteristic nature of type-II superconductor with Hc1(0)≈500 Oe and Hc2(0)>100 kOe.

  14. Ultrasonic study on Bi-based high-Tc superconductors with preferred orientations

    NASA Astrophysics Data System (ADS)

    Dong, Jian; Deng, Tingzhang; Li, Fengying; Yao, Yushu

    1990-07-01

    Ultrasonic experimental studies on Bi-based ceramic superconductors are reported. The specimens used in our experiments were hot pressed after sintering in air; therefore, a preferred orientation of the granules was obtained. The frequencies of ultrasound were about 10 MHz, both for longitudinal and for transverse waves. It has been found that anomalies in the attenuation coefficient and sound velocity occur near 220 K, in the range between 10 and 50 K above Tc, and at Tc, respectively. The investigation shows that the pretransition in the range between 10 and 50 K above Tc leads to a tendency of softness and instability in crystal lattice, and the superconducting transition is present on the background of a rapid decrease in attenuation with the decrease in temperature. It is believed that a strong superconducting fluctuation exists above Tc. The deformation-potential model for acoustic-phonon-electron interaction, which is the basis of BCS theory, may be unsuitable for the high-Tc superconductors. A model of superconductivity due to optical-phonon-electron coupling is suggested.

  15. Short electrical pulse generation using light-induced switching in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Balevicius, Saulius

    2001-03-01

    This report demonstrates that optically triggered switches based on high Tc superconductor thin films can be used for the generation of sub-nanosecond rise time high-power pulses. Presented in this article are the experimental investigations of the light-induced switching dynamics in YBCO thin films biased by high-current nanosecond duration pulses. This research indicates that a high-power superconducting opto-electronic opening switch can operate in several regimes. The following transitions between the various states of the film are realized: superconducting to normal (S-N), super-conducting to mixed (S-M), low resistance mixed to high resistance mixed (MLR-MHR) and mixed to normal (M-N). When the superconductor is biased with a high current, the value of the light intensity needed for triggering the switch decreases by several times. The explanation of the main light-induced switching characteristics and their behavior is based on a model, which takes into account the simultaneous action of the light and the bias current on the superconducting film. The report also includes a discussion f the ultra-fast film damaging phenomenon which appears as a result of the dissipation of intense power during switching. Discussed is also how this process limits the highest amplitude of the generated pulse. The possible application of high-power superconducting opto-electronic switches for the creation of jitter free radar is also discussed.

  16. Experimental test of spin-charge separation in a high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Kirtley, J. R.; Tsuei, C. C.; Raffy, H.; Li, Z. Z.; Kogan, V. G.; Clem, J. R.; Moler, K. A.

    2001-03-01

    We have performed tests of spin-charge separation in the cuprate superconductors following suggestions by Senthil and Fisher (T. Senthil and M.P.A. Fisher, cond-mat 0008082) and Sachdev (S. Sachdev, cond-mat 009456). Our experiments were performed on photolithographically patterned thin film rings of the high-Tc cuprate superconductor Bi_2Sr_2CaCu_2O_8+δ which have been annealed in argon to reduce the doping, and therefore the critical temperature, well below the optimum value. The fluxoid states of the rings were controlled and imaged by rapidly varying the sample temperature and externally applied magnetic field in a variable sample temperature scanning SQUID microscope(J.R. Kirtley et al.), Appl. Phys. Lett. 74, 4011 (1999). To date we have seen no evidence for either persistence of vorticity upon thermal cycling through T_c, as predicted by Senthil and Fisher, or for h/e vortices, as predicted by Sachdev. Measurements of telegraph noise between states with different fluxoid numbers provide a measure of the speed of the dynamics of the conventional vortices in these rings.

  17. Tunneling studies of pseudogap in high-Tc superconductor Bi2212

    NASA Astrophysics Data System (ADS)

    Gupta, Anjan Kumar

    2001-11-01

    The BCS theory predicts an energy gap in superconductors below their critical temperature Tc. This gap has been observed in conventional as well as high-Tc cuprate superconductors. However, in underdoped cuprates an energy gap has been found to exist even above Tc from several experiments. In this dissertation a study of this normal state gap, called the pseudogap, is presented using ab-plane tunneling spectroscopy of a high-Tc superconductor Bi2Sr2CaCu2O8+delta (Bi2212) at different dopings delta. Temperature and magnetic field dependent ab-plane tunneling spectra of Bi2212 crystals were studied using a home built low temperature scanning tunneling microscope (STM). Single crystals of Bi2212 were grown using self flux method, which were than underdoped by annealing in vacuum or in Argon atmosphere at 500--700°C. Resistivity, magnetic susceptibility and X-ray measurements were used for characterization. The Tc of Bi2212 decreases with underdoping while the superconducting energy gap, 2Delta, increases. The energy gap, near the maximum gap direction, at 42K is found to be 30 mV for slightly overdoped (Tc = 85K) and 38 mV for the underdoped (Tc = 70K) crystals giving a 2Delta/ kTc value of 8.2 and 12.6 for the two compounds, respectively. An energy gap is found to exist above T c for underdoped Bi2212 while it gets very weak for the overdoped compound. A dip-hump feature at energies ˜2Delta-3Delta is also seen for both the compounds. The tunneling spectra are analyzed with an interpretation that the pseudogap and the superconducting gaps coexist at low temperatures and that the superconducting gap disappears at Tc. The conservation of states rule is violated but it is recovered if the low temperature spectra are normalized with those above Tc. This normalization also removes the dip-hump and other background features. Such coexistence of two gaps can rule out a scenario that the pre-formed Cooper pairs are responsible for the pseudogap. A new low temperature STM

  18. Cavity phenomena in mesas of cuprate high- Tc superconductors under voltage bias

    NASA Astrophysics Data System (ADS)

    Hu, Xiao; Lin, Shizeng

    2009-08-01

    Modeling a single crystal of cuprate high- Tc superconductor, such as Bi2Sr2CaCu2O8+δ , as a stack of intrinsic Josephson junctions, we formulate explicitly the cavity phenomenon of plasma oscillations and electromagnetic (EM) waves in mesas of cylindrical and annular shapes. The phase differences of the junctions are governed by the inductively coupled sine-Gordon equations, with the Neumann-type boundary condition for sample thickness much smaller than the EM wavelength, which renders the superconductor single crystal a cavity. Biasing a dc voltage in the c direction, a state with ±π kinks in the superconductivity phase difference piled up alternatively along the c axis is stabilized. The ±π phase kinks provide interlock between superconductivity phases in adjacent junctions, taking the advantage of huge inductive couplings inherent in the cuprate superconductors, which establishes the coherence across the whole system of more than ˜600 junctions. They also permit a strong coupling between the lateral cavity mode of the transverse Josephson plasma and the c -axis bias, and enhance the plasma oscillation significantly at the cavity modes which radiates EM waves in the terahertz band when the lateral size of mesa is set to tens of micrometers. It is discussed that the cavity mode realized in a very recent experiment using a cylindrical mesa can be explained by the present theory. In order to overcome the heating effect, we propose to use annular geometry. The dependence of frequency on the radius ratio is analyzed, which reveals that the shape tailor is quite promising for improving the present technique of terahertz excitation. The annular geometry may be developed as a waveguide resonator, mimicking the fiber lasers for visible lights.

  19. Topological nature and the multiple Dirac cones hidden in Bismuth high-Tc superconductors

    PubMed Central

    Li, Gang; Yan, Binghai; Thomale, Ronny; Hanke, Werner

    2015-01-01

    Recent theoretical studies employing density-functional theory have predicted BaBiO3 (when doped with electrons) and YBiO3 to become a topological insulator (TI) with a large topological gap (~0.7 eV). This, together with the natural stability against surface oxidation, makes the Bismuth-Oxide family of special interest for possible applications in quantum information and spintronics. The central question, we study here, is whether the hole-doped Bismuth Oxides, i.e. Ba1-xKxBiO3 and BaPb1-xBixO3, which are “high-Tc” bulk superconducting near 30 K, additionally display in the further vicinity of their Fermi energy EF a topological gap with a Dirac-type of topological surface state. Our electronic structure calculations predict the K-doped family to emerge as a TI, with a topological gap above EF. Thus, these compounds can become superconductors with hole-doping and potential TIs with additional electron doping. Furthermore, we predict the Bismuth-Oxide family to contain an additional Dirac cone below EF for further hole doping, which manifests these systems to be candidates for both electron- and hole-doped topological insulators. PMID:26014056

  20. Phase diagram and isotopic effect in high-Tc pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Chen, Xianhui

    2010-03-01

    We will talk about the discovery of superconductivity with Tc higher than 40 K in Fe-based superconductors SmFeAsO1-xF. Tc higher than McMillan limit of 39 K definitely proves pnictide superconductors high-Tc superconductivity^1,2. In this talk, we present the transport properties: resistivity, Hall coefficient and transport properties under high magnetic field. These results suggest a quantum phase transition around x=0.14 in SmFeAsO1-xFx system. A electronic phase diagram is proposed, and coexistence of superconductivity and spin-density-wave is observed in Sm-1111 and Ba-122 system. We discuss the effect of isotopic effect on TC and TSDW in SmFeAsO1-xFx and Ba1-xKxFe2As2 systems. Our results show that oxygen isotope effect on TC and TSDW is very little, while the iron isotope exponent is about 0.35. Surprisingly, the iron isotope exchange shows the same effect on SDW transition as on superconductivity. Our results indicate that electron-phonon interaction plays some role in the superconducting mechanism, but simple electron-phonon coupling mechanism seems to be rather unlikely because a strong magnon-phonon coupling is included^3. 1. Chen, X. H. et al. Nature 453, 761-762 (2008). 2. Liu, R. H. et al. Phys. Rev. Lett. 101, 087001 (2008). 3. R. H. Liu et al., Nature 459, 64-67(2009).

  1. Nanoscale Structures and Pseudogap in Under-doped High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Saarela, M.; Kusmartsev, F. V.

    We show that superconductor-insulator transitions in oxides and FeAs-based high Tc superconducting multilayers may arise due to a charge density wave instability induced by charged impurities and the over-screening of the long-ranged part of the Coulomb interaction, which is enhanced due to decreasing carrier density [1]. When the carrier density is low enough, impurities begin to trap particles and form bound states of clusters of charge carriers, which we call Coulomb bubbles. These bubbles are embedded inside the superconductor and form nuclei of the new insulating state. The growth of a bubble is terminated by the Coulomb force and each of them has a quantized charge and a fluctuating phase. When clusters first appear, they are covered by superfluid liquid due to the proximity effect and invisible. However, when the carrier density decreases the size of bubbles increases and the superconducting proximity inside them vanishes. The insulating state arises via a percolation of these insulating islands, which form a giant percolating cluster that prevents the flow of the electrical supercurrent through the system. We also show the formation of two groups of charge carriers in these compounds associated with free and localized states. The localized component arises due to the Coulomb bubbles. Our results are consistent with the two-component picture for cuprates deducted earlier by Gorkov and Teitelbaum [2] from the analysis of the Hall effect data and ARPES spectra. The Coulomb clusters induce nanoscale superstructures observed in scanning tunneling microscope (STM) experiments [3] and are responsible for the pseudogap [4].

  2. Singularity in the positive Hall coeffcient near pre-onset temperatures in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Vezzoli, G. C.; Chen, M. F.; Craver, F.; Moon, B. M.; Safari, A.; Burke, T.; Stanley, W.

    1990-10-01

    Hall measurements using continuous extremely slow cooling and reheating rates as well as employing eqiulibrium point-by-point conventional techniques reveals a clear anomally in RH at pre-onset temperatures near Tc in polycrystalline samples Y1Ba2Cu3O7 and Bi2Sr2Ca2Cu3O10. The anomaly has the appearance of a singularity of Dirac-delta function which parallels earlier work on La1-xSrxCuO4. Recent single crystal work on the Bi-containing high-Tc superconductor is in accord with a clearcut anomaly. The singularity is tentatively interpreted to be associated (upon cooling) with initially the removal of positive holes from the hopping conduction system of the normal state such as from the increased concentration of bound virtual excitons due to increased exciton and hole lifetimes at low temperature. Subsequently the formation of Cooper pairs by mediation from these centers (bound-holes) and/or bound excitons) may cause an ionization of these bound virtual excitons thereby re-introducing holes and electrons into the conduction system at Tc.

  3. Synthesis of high-Tc superconductors at Uppsala University: ceramics and crystal growth

    NASA Astrophysics Data System (ADS)

    Lundström, Torsten; Lönnberg, Bertil; Tergenius, Lars-Erik

    1991-07-01

    Synthetic and process studies of the new high-Tc super-conductors are carried out using the methods of powder technology. The equipment for these studies at the Institute of Chemistry, University of Uppsala is described. The laboratory is equipped with jaw crusher, various mills, powder mixer, spray dryer and several sintering furnaces. The laboratory has excellent facilities for powder characterization, such as a semi-automatic image analyzer, a system for X-ray line broadening analysis, BET apparatus, sample divider and a sieving machine. Single-crystal growth experiments are also reported. Single crystals of YBa2Cu3O7 and Bi2Sr2CaCu2O8 were grown by the off-stoichiometric method. The largest crystals of YBa2Cu3O7 were obtained with the soaking temperature of 980°C and a cooling rate of 2°C h-1. A soaking temperature of 925°C and a cooling rate of 40°C h-1 produced the largest Bi2Sr2CaCu2O8 single crystals. A single crystal examination showed that the structure of Bi2Sr2CaCu2O8 is incommensurate along the b axis. The lattice parameters were a = 5.40 Å, b = 25.25 Å, c = 30.62 Å.

  4. Unconventional charge order in a co-doped high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Pelc, D.; Vučković, M.; Grafe, H.-J.; Baek, S.-H.; Požek, M.

    2016-09-01

    Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8-xEu0.2SrxCuO4. We use three complementary experiments--nuclear quadrupole resonance, nonlinear conductivity and specific heat--to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order.

  5. Some consequences of the breakdown of Migdal's theorem in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ummarino, G. A.; Gonnelli, R. S.

    1999-05-01

    In order to reproduce the experimental Tc and tunneling data of high- Tc superconductors in the framework of the Eliashberg theory for strong electron-boson interaction, it is necessary to use large values of the coupling constant. In this work, we investigate whether this fact is a possible consequence of the breakdown of Migdal's theorem that certainly occurs in the cuprates due to their very low value of Fermi energy as compared to the characteristic phonon energy. In order to numerically quantify the consequences of the violation of the Migdal's approximation, we use the theoretical approach developed by Pietronero et al. [L. Pietronero, S. Strässler, C. Grimaldi, Phys. Rev. B 52, 10516 (1995)] and Grimaldi et al. [C. Grimaldi, L. Pietronero, S. Strässler, Phys. Rev. B 52, 10530 (1995)] on experimental data taken from the literature. The effects on the electron-phonon coupling constant λ, on the critical temperature Tc and on the superconducting gap Δ are calculated also by means of a direct solution of the standard Eliashberg equations and discussed in different kinds of superconducting materials both with low and high critical temperature.

  6. NMR in pulsed high-field magnets and application to high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Stork, H.; Bontemps, P.; Rikken, G. L. J. A.

    2013-09-01

    This article deals with the implementation of Nuclear Magnetic Resonance (NMR) experiments in pulsed magnetic fields at the pulsed-field facility of the Laboratoire National des Champs Magnétiques Intenses and its application to the high-TC superconductor YBa2Cu3O6.51. The experimental setup is described in detail, including a low-temperature probe head adapted for pulsed fields. An entire paragraph is dedicated to the discussion of NMR in pulsed field and the introduction of an advanced deconvolution technique making use of the induction voltage in an additional pick-up coil. The 63Cu/65Cu NMR experiments on an YBa2Cu3O6.51 single crystal were performed at 2.5 K during a field pulse of 46.8-T-amplitude. In the recorded spectrum the 63Cu center line and high-frequency satellites as well as the 65Cu center line are identified and are compared with results in literature.

  7. Inverse correlation between quasiparticle mass and Tc in a cuprate high-Tc superconductor

    PubMed Central

    Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E.; Proust, Cyril; Carrington, Antony

    2016-01-01

    Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature Tc is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-Tc superconductivity. We have tested the robustness of this correlation between m* and Tc by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as Tc increases under pressure. This inverse correlation between m* and Tc suggests that quantum fluctuations of the charge order enhance m* but do not enhance Tc. PMID:27034989

  8. Unconventional charge order in a co-doped high-Tc superconductor

    PubMed Central

    Pelc, D.; Vučković, M.; Grafe, H. -J.; Baek, S. -H.; Požek, M.

    2016-01-01

    Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8−xEu0.2SrxCuO4. We use three complementary experiments—nuclear quadrupole resonance, nonlinear conductivity and specific heat—to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order. PMID:27605152

  9. Dielectric response of electron-doped ionic superconductor LixZrNCl

    NASA Astrophysics Data System (ADS)

    Botana, Antia S.; Pickett, Warren E.

    2014-09-01

    When electron doped, the layered transition metal nitrides TNCl (T =group IVB transition metal ion) become impressive superconductors with critical temperature Tc=15-26 K. Here we take the most studied member ZrNCl as a representative and calculate the dielectric response ɛ (ω) versus frequency and concentration of doped electronic carriers. The static dielectric constant ɛ∞=5 is reproduced extremely well. We establish that the differences between rigid band modeling and virtual crystal treatment are small, and compare also with actual lithium doping using supercells. We obtain the variations upon changing the doping level of the reflectivity and energy loss function as well, many of which are found not to be correlated with the observed (non)variation of Tc(x). The main plasmon peaks appear where the electron gas model suggests, in the range 1.2-2.0 eV for x varying from 0.16 to 0.50.

  10. High Tc superconductors - Electronic structure; Proceedings of the International Symposium, Rome, Italy, Oct. 5-7, 1988

    NASA Astrophysics Data System (ADS)

    Bianconi, Antonio; Marcelli, Augusto

    Recent theoretical and experimental investigations of the electronic structure of high-Tc superconductors are discussed in reviews and reports. Sections are devoted to theoretical models, optical properties, magnetic interactions, materials, photoemission, and X-ray spectroscopy. Topics addressed include the roles of apex oxygen atoms in doped holes and low-energy excitations, the energy gap and two-component absorption, vibrational modes in the CuO2 planes of YBa2Cu3O(7-delta), neutron-scattering studies of magnetic excitations in La(2-x)Sr(x)CuO4, interface formation between metals and high-Tc superconductors, and the temperature dependence of the Cu-O structure in EuBa2Cu3O(7-delta).

  11. Electronic structure of electron doped BaAs2Fe2 superconductors revealed by Angle Resolved Photoemission

    NASA Astrophysics Data System (ADS)

    Vilmercati, P.; Vobornik, I.; Unnikrishnan, M.; Fedorov, A.; Goldoni, A.; Panaccione, G.; Safa-Sefat, A.; Jin, R.; McGuire, M. A.; Sales, B. C.; Singh, D. J.; Mandrus, D.; Mannella, N.

    2009-03-01

    The electronic structure in the normal state of Co-doped BaAs2Fe2 superconductors has been measured by Angle Resolved photoemission (ARPES). Co doping on the Fe site results in electron doping [A. S. Sefat et al., Phys. Rev. Lett. 101, 117004 (2008)]. The data qualitatively reveal that Co-doping results in raising the chemical potential, as expected with electron doping. The Fermi surface topology and the possible relevance to the mechanism of spin fluctuation will also be discussed.

  12. Dependence of critical current density on microstructure and processing of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Goyal, A.; Specht, E. D.; Wang, Z. L.; Kroeger, D. M.; Sutliff, J. A.; Tkaczyk, J. E.; Deluca, J. A.; Masur, L.; Riley, G. N.

    1994-11-01

    Microstructural origins for reduced weak-link behavior in high-Jc melt-processed YBCO, spray pyrolyzed thick films of Tl-1223, metallic precursor Y-124 polycrystalline powder-in-tube (PIT) wires and PIT Bi-2212/2223 are discussed. Since the materials studied are the highest Jc, polycrystalline, high-Tc superconductors fabricated worldwide, the results provide important guidelines for further improvements in superconducting properties, thereby enabling practical applications of these materials. It is found that strongly linked current flow within domains of melt-processed 123 occurs effectively through a single crystal path. In c-axis oriented, polycrystalline Tl-1223 thick films, local in-plane texture has been found to play a crucial role in the reduced weak-link behavior. Formation of “colonies” of grains with a common c-axis and modest in-plane misorientation was observed. Furthermore, a colony boundary in general has a varying misorientation along the boundary. Large regions comprised primarily of low angle boundaries were observed. Percolative transport through a network of such small angle boundaries appears to provide the nonweak-linked current path. Although powder-in-tube BSCCO 2212 and 2223 also appear to have a “colony” microstructure, there are some important differences. Colonies in BSCCO consist of stacks of grains with similar c-axis orientation in contrast to colonies in Tl-1223 films where few grains are stacked on top of one another. Furthermore, most grains within a colony in BSCCO have the same lateral dimensions as that of the colony, resulting largely largely in “twist” boundaries. Further microstructural characterization of high-Jc PIT 2212 and 2223 is currently underway. In the case of Y-124 wires, weak macroscopic in-plane texture is found. Additional measurements are underway to determine if a sharper, local in-plane texture also exists. It is found that in three of the four types of superconductors studied, reduced weak

  13. 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

  14. Rigid levitation, flux pinning, thermal depinning and fluctuation in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Brandt, E. H.

    1991-01-01

    Here, the author shows that the strong velocity-independent frictional force on a levitating superconductor and on any type-II superconductor moving in a homogeneous magnetic field is caused by pinning and depinning of the magnetic flux lines in its interior. Levitation may thus be used to investigate the pinning properties of a superconductor, and friction in a superconductor bearing may be minimized by choosing appropriate materials and geometries.

  15. Impurity effect in electron-doped high-T c superconductors

    NASA Astrophysics Data System (ADS)

    Shen, Xiao-Ling; Zhou, Tao

    2016-12-01

    The quasiparticle states around a nonmagnetic impurity in electron-doped high-T c superconductors are studied systematically based on the Bogoliubov-de Gennes equations. In the antiferromagnetic state, one in-gap impurity resonance state is revealed. As the impurity scattering potential increases, the resonance peak shifts to the gap edge and finally disappears for a strong impurity. The antiferromagnetic order and superconducting order coexist when the doping density increases. In this coexisting state, the in-gap resonance peaks are rather robust and appear in pairs that are lying symmetric with the Fermi energy. The peak positions and intensities strongly depend on the impurity potentials and the next-nearest-neighbour hopping constants. For a rather strong impurity, the resonance peaks shift to near the gap edge. When further increasing the doping density, the system is in the pure superconducting state. The resonance peaks still appear in pairs, with the peak intensities being weaker compared to those in the coexisting state. The two resonance peaks may occasionally merge into one zero-energy peak for both the coexisting state and the pure superconducting state. The spin-resolved LDOS are also investigated and may be used to detect possible antiferromagnetic order.

  16. Preparation of the High-Tc Phase of Bi-Sr-Ca-Cu-O Superconductor

    NASA Astrophysics Data System (ADS)

    Endo, Utako; Koyama, Satoshi; Kawai, Tomoji

    1988-08-01

    Co-decomposition of mixed nitrates of Bi, Pb, Sr, Ca and Cu around 830°C under low oxygen pressure led to the formation of a high-Tc superconducting phase of Bi(Pb)-Sr-Ca-Cu-O with Tc(zero) at 107.5 K. A sample prepared by a conventional solid state reaction method under low oxygen pressure also showed the superconducting transition at 107.5 K. X-ray powder diffraction and magnetic susceptibility measurements on these samples revealed the high-Tc phase without 80 K or semiconducting phase. The reaction under low oxygen pressure has an effect to lower the temperature with broad ranges to render the high-Tc phase of the Bi-Sr-Ca-Cu-O.

  17. Edge ferromagnetism from Majorana flat bands: application to split tunneling-conductance peaks in high-Tc cuprate superconductors.

    PubMed

    Potter, Andrew C; Lee, Patrick A

    2014-03-21

    In mean-field descriptions of nodal d-wave superconductors, generic edges exhibit dispersionless Majorana fermion bands at zero energy. These states give rise to an extensive ground-state degeneracy, and are protected by time-reversal symmetry. We argue that the infinite density of states of these flat bands make them inherently unstable to interactions, and show that repulsive interactions lead to edge ferromagnetism which splits the flat bands. This edge ferromagnetism offers an explanation for the observation of the splitting of zero-bias peaks in edge tunneling in high-Tc cuprate superconductors. We argue that this mechanism for splitting is more likely than previously proposed scenarios and describe its experimental consequences.

  18. Comparative study on the fastest effective fault limitation for stabilized and stabilizer-free high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Kar, Soumen; Rao, V. V.

    2017-10-01

    The fastest effective fault limitation is one of the selection criterion of high Tc superconductors (HTS) for resistive type fault current limiter (R-SFCLs) application. In the present work, we have given a comparative DC & AC performance study on HTS tapes with and without stabilizer. At first, we have investigated the temperature dependent DC resistivity of the SS stabilized Bi2223 based conductor, Cu (50 μm substrate) and SS (75 μm substrate) stabilized YBCO based coated conductors (CCs) and compared with the stabilizer free YBCO based CC (50 μm and 100 μm substrate). We have studied the DC transport properties (E-I) of the stabilized and stabilizer-free tapes to obtain flux-flow resistance before reaching normal state, critical current and 'n' factor at 1 μV/cm criterion. Further, the 1st peak limitation, response time and resistance attained during fault limitation have been compared for AC over-current pulses of 1.5 kA for 100 ms duration. The aforesaid measurements helped us to select a suitable high Tc superconductor for fastest effective fault limitation to be used in R-SFCL application.

  19. A Twisted Ladder: Relating the Fe Superconductors to the High Tc Cuprates

    SciTech Connect

    Berg, E.

    2010-05-26

    We construct a 2-leg ladder model of an Fe-pnictide superconductor and discuss its properties and relationship with the familiar 2-leg cuprate model. Our results suggest that the underlying pairing mechanism for the Fe-pnictide superconductors is similar to that for the cuprates.

  20. Sintering of bulk high- Tc superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. ); Nash, A.S. )

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  1. Sintering of bulk high-{Tc} superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B.; Nash, A.S.

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  2. Bearing design for flywheel energy storage using high-TC superconductors

    DOEpatents

    Hull, John R.; Mulcahy, Thomas M.

    2000-01-01

    A high temperature superconductor material bearing system (38) This system (38) includes a rotor (50) having a ring permanent magnet (60), a plurality of permanent magnets (16, 20 and 70) for interacting to generate levitation forces for the system (38). This group of magnets are a push/pull bearing (75). A high temperature superconductor structure (30) interacts with the ting permanent magnet (60) to provide stabilizing forces for the system (38).

  3. Processing and properties of high Tc oxide/silver matrix composite superconductors

    NASA Technical Reports Server (NTRS)

    Curreri, P. A.; Peters, P. N.; Leong, P. T.; Chou, H.; Wu, M. K.

    1989-01-01

    This paper describes the processing conditions for the formation of strong flux pinning high-Tc (REE)1Ba2Cu3O7/AgO (RE-123/AgO) composites with the RE-123:AgO ratio of 3:1 and presents the magnetization and critical field data on these composites. The results obtained indicate that proper processing conditions are critical to the formation of strong flux pinning RE-123/AgO composites. Resistance measurements in a magnetic field show that the upper critical field in Y-123/AgO is about three times larger than that of the Y-123 compound.

  4. Processing and properties of high Tc oxide/silver matrix composite superconductors

    NASA Technical Reports Server (NTRS)

    Curreri, P. A.; Peters, P. N.; Leong, P. T.; Chou, H.; Wu, M. K.

    1989-01-01

    This paper describes the processing conditions for the formation of strong flux pinning high-Tc (REE)1Ba2Cu3O7/AgO (RE-123/AgO) composites with the RE-123:AgO ratio of 3:1 and presents the magnetization and critical field data on these composites. The results obtained indicate that proper processing conditions are critical to the formation of strong flux pinning RE-123/AgO composites. Resistance measurements in a magnetic field show that the upper critical field in Y-123/AgO is about three times larger than that of the Y-123 compound.

  5. Finding new superconductors: the spin-fluctuation gateway to high Tc and possible room temperature superconductivity.

    PubMed

    Pines, David

    2013-10-24

    We propose an experiment-based strategy for finding new high transition temperature superconductors that is based on the well-established spin fluctuation magnetic gateway to superconductivity in which the attractive quasiparticle interaction needed for superconductivity comes from their coupling to dynamical spin fluctuations originating in the proximity of the material to an antiferromagnetic state. We show how lessons learned by combining the results of almost three decades of intensive experimental and theoretical study of the cuprates with those found in the decade-long study of a strikingly similar family of unconventional heavy electron superconductors, the 115 materials, can prove helpful in carrying out that search. We conclude that, since Tc in these materials scales approximately with the strength of the interaction, J, between the nearest neighbor local moments in their parent antiferromagnetic state, there may not be a magnetic ceiling that would prevent one from discovering a room temperature superconductor.

  6. Magneto-optical studies of magnetization processes in high-Tc superconductors structure.

    SciTech Connect

    Vlasko-Vlasox, V. K.

    1998-12-02

    Magneto-optical imaging is a powerful tool for nondestructive quality control and scientific research through visualization of magnetic fields around any magnetic flux or current carrying sample. It allows real time observations of domain structures and their transformations in magnetics, static and dynamic field patterns due to inhomogeneous currents in electric circuits and superconductors, and reveals distortions of the fields due to defects. In addition to qualitative pictures showing different details in the intensities of the magneto-optical images, one can obtain quantitative maps of field distributions and retrieve values of the underlying currents or magnetization variations. In this review we discuss the advantages of magneto-optics for studies of superconductors, show its place among other techniques, and report recent results in magneto-optical investigations of high temperature superconductors (HTS).

  7. Superfluid and normal-fluid densities in the high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Tanner, D. B.; Gao, F.; Kamarás, K.; Liu, H. L.; Quijada, M. A.; Romero, D. B.; Yoon, Y.-D.; Zibold, A.; Berger, H.; Margaritondo, G.; Forró, L.; Kelly, R. J.; Onellion, M.; Cao, G.; Crow, J. E.; O, Beom-Hoan; Market, J. T.; Rice, J. P.; Ginsberg, D. M.; Wolf, Th.

    In clean metallic superconductors, 100% of the mobile carriers participate in the condensate, so that the London penetration depth (which measures the electromagnetic screening by the superconductor) indicates charge densities comparable to those inferred from the free-carrier plasma frequency. In the cuprates, this is not the case, even though penetration depth measurements have shown a good correlation between superfluid density and superconducting transition temperature in the underdoped-to-optimally-doped part of the phase diagram. Optical measurements, which permit independent determination of the total doping-induced spectral weight and the superfluid density, show that in optimally doped materials only about 20% of the doping-induced spectral weight joins the superfluid. The rest remains in finite-frequency, midinfrared absorption. In underdoped materials, the superfluid fraction is even smaller. This result implies extremely strong coupling for these superconductors.

  8. A New Piece in the High Tc Superconductivity Puzzle: Fe based Superconductors

    NASA Astrophysics Data System (ADS)

    Moreo, Adriana

    2011-10-01

    An overview of the historic and current developments in superconductivity will be be presented. The phenomenon of superconductivity was discovered almost 100 hundred years ago and it is still one of the hottest research topics providing fascinating puzzles and challenges to both theoreticians and experimentalists. There was a lag of almost 50 years between the experimental discovery of (low Tc) superconductivity and the development of the BCS theory which explained the phenomenon in terms of pairs of electrons held together by the interaction with the phonons in the material. The quest to discover superconducting materials with higher Tc's continued quietly for many years until huge progress occurred in the 1980' when Tc's higher than 77K were observed in copper-oxide based materials. The study of these new materials generated tremendous advances in both experimental and theoretical methods and much is now known about their properties; but the mechanism, i.e., the ``glue,'' that binds the electrons together is still unknown; it appears that phonons are unable to do the job and there is controversy on whether the magnetism present in these materials helps or hurts. Very recently, in 2008, high Tc was discovered in a new family of iron based materials. While they are similar to the cuprates in some ways, i.e., magnetism is present, there are many differences as well. This discovery provides a new chance to unveil the high-Tc mystery and the condensed matter community is intensely working on the subject.

  9. Magnetoresistance in High-Tc Superconductors: The Role of Vertex Corrections

    NASA Astrophysics Data System (ADS)

    Kontani, Hiroshi

    2001-07-01

    In high-Tc cuprates, the orbital magnetoresistance in plane (Δρ/ρ) is anomalously enhanced at lower tempemeratures compared with conventional Fermi liquids, and thus Kohler's rule is strongly violated. Moreover, it should be noted that an intimate relation between Δρ/ρ and the Hall coefficient (RH), Δρ/ρ∝(RH/ρ)2, holds well experimentally, and is called the “modified Kohler's rule”. In this letter, we study this long-standing problem in terms of the nearly antiferromagnetic (AF) Fermi liquid. We analyze the exact expression for Δρ/ρ by including the vertex corrections (VC's) to keep the conservation laws, and find the approximate relation Δρ/ρ∝ξAF4 ρ-2 ·H2 (ξAF being the AF correlation length) in the presence of AF fluctuations. The factor ξAF4, which comes from the VC's for the current, gives the additional temperature dependence. By taking account of the relation RH ∝ξAF2 [Kontani et al.: Phys. Rev. B 59 (1999) 14723], we can naturally explain the modified Kohler's rule. In conclusion, based on the Fermi liquid theory, the famous seemingly non-Fermi liquid behaviors of RH and Δρ/ρ in high-Tc cuprates are naturally understood on an equal footing.

  10. Momentum-Resolved Electronic Structure of the High-Tc Superconductor Parent Compound BaBiO3

    NASA Astrophysics Data System (ADS)

    Plumb, N. C.; Gawryluk, D. J.; Wang, Y.; Ristić, Z.; Park, J.; Lv, B. Q.; Wang, Z.; Matt, C. E.; Xu, N.; Shang, T.; Conder, K.; Mesot, J.; Johnston, S.; Shi, M.; Radović, M.

    2016-07-01

    We investigate the band structure of BaBiO3 , an insulating parent compound of doped high-Tc superconductors, using in situ angle-resolved photoemission spectroscopy on thin films. The data compare favorably overall with density functional theory calculations within the local density approximation, demonstrating that electron correlations are weak. The bands exhibit Brillouin zone folding consistent with known BiO6 breathing distortions. Though the distortions are often thought to coincide with Bi3 +/Bi5 + charge ordering, core level spectra show that bismuth is monovalent. We further demonstrate that the bands closest to the Fermi level are primarily oxygen derived, while the bismuth 6 s states mostly contribute to dispersive bands at deeper binding energy. The results support a model of Bi-O charge transfer in which hole pairs are localized on combinations of the O 2 p orbitals.

  11. Fermi-liquid-based theory for the in-plane magnetic anisotropy in untwinned high-Tc superconductors.

    PubMed

    Eremin, I; Manske, D

    2005-02-18

    Using a generalized RPA-type theory we calculate the in-plane anisotropy of the magnetic excitations in hole-doped high-Tc superconductors. Extending our earlier Fermi-liquid-based studies on the resonance peak by inclusion of orthorhombicity we still find two-dimensional spin excitations, however, being strongly anisotropic. This reflects the underlying anisotropy of the hopping matrix elements and of the resultant superconducting gap function. We compare our calculations with new experimental data on fully untwinned YBa2Cu3O6.85 and find good agreement. Our results are in contrast to earlier interpretations on the in-plane anisotropy in terms of stripes [H. Mook, Nature (London) 404, 729 (2000)], but reveal a conventional solution to this important problem.

  12. Heat treatment of wires on the basis of the high Tc superconductor YBa2Cu3Ox

    NASA Astrophysics Data System (ADS)

    Müller, P.; Schubert, M.; Rodig, Ch.; Fuchs, G.; Fischer, K.

    1989-08-01

    Ag-sheathed powder-in-tube wires on the basis of the high Tc superconductor YBa2Cu3Ox are produced by a drawing process. After cold working, the wires are not superconducting. By heat treatment at temperatures >900 °C, lattice defects are healed and the contact between the grains is improved. After this heat treatment the wires are slowly cooled in an O2 atmosphere in order to adjust the optimum O2 stoichiometry. The annealing temperature has a strong influence on the attainable critical current density. By annealing a wire with 420 ppm carbon content at 950 °C, jc values of 5020 A/cm2 at 4.2 K and 1130 A/cm2 at 77 K were achieved. Drastically reduced critical current densities in wires with high carbon content demonstrate the importance of a low carbon content for achieving high critical current densities in YBa2Cu3Ox .

  13. Genuine Phase Diagram of Homogeneously Doped CuO2 Plane in High-Tc Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Mukuda, Hidekazu; Yamaguchi, Yuhei; Shimizu, Sunao; Kitaoka, Yoshio; Shirage, Parasharam; Iyo, Akira

    2008-12-01

    We report a genuine phase diagram for a disorder-free CuO2 plane based on the precise evaluation of the local hole density (Nh) by site-selective Cu-NMR studies on five-layered high-Tc cuprates. It has been unraveled that (1) the antiferromagnetic metallic state (AFMM) is robust up to Nh≈ 0.17, (2) the uniformly mixed phase of superconductivity (SC) and AFMM is realized at Nh≤ 0.17, (3) the tetracritical point for the AFMM/(AFMM+SC)/SC/PM (paramagnetism) phases may be present at Nh≈ 0.15 and T≈ 75 K, (4) Tc is maximum close to a quantum critical point (QCP) at which the AFM order collapses, suggesting the intimate relationship between the high-Tc SC and the AFM order. The results presented here strongly suggest that the AFM interaction plays the vital role as the glue for the Cooper pairs, which will lead us to a genuine understanding of why the Tc of cuprate superconductors is so high.

  14. Nature of the effective interaction in electron-doped cuprate superconductors: A sign-problem-free quantum Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Li, Zi-Xiang; Wang, Fa; Yao, Hong; Lee, Dung-Hai

    2017-06-01

    Understanding the mechanism of Cooper pairing amounts to determining the effective interaction that operates at low energies. Efforts to achieve such a goal for superconducting materials, especially strongly correlated ones, from both bottom-up and top-down approaches, have been plagued by having to use uncontrolled approximations. Here, we perform large-scale, numerically exact, sign-problem-free zero-temperature quantum Monte Carlo simulations on an effective theory based on "hot spots" plus fluctuating collective modes. Because hot spots are clearly identified by angle-resolved photoemission spectroscopy for electron-doped cuprates, we focus our attention on such materials. Our goal is to determine the minimum effective action that can describe the observed superconductivity and charge-density wave. The results suggest that antiferromagnetic fluctuation alone is not sufficient—the effective action needs to be amended with nematic fluctuations. We believe that our results address the pairing mechanism of high-Tc superconductivity in electron-doped cuprates, and they shed light on the pairing mechanism of hole-doped cuprates.

  15. p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor

    NASA Astrophysics Data System (ADS)

    di Bernardo, A.; Millo, O.; Barbone, M.; Alpern, H.; Kalcheim, Y.; Sassi, U.; Ott, A. K.; de Fazio, D.; Yoon, D.; Amado, M.; Ferrari, A. C.; Linder, J.; Robinson, J. W. A.

    2017-01-01

    Electron pairing in the vast majority of superconductors follows the Bardeen-Cooper-Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.

  16. p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor

    PubMed Central

    Di Bernardo, A.; Millo, O.; Barbone, M.; Alpern, H.; Kalcheim, Y.; Sassi, U.; Ott, A. K.; De Fazio, D.; Yoon, D.; Amado, M.; Ferrari, A. C.; Linder, J.; Robinson, J. W. A.

    2017-01-01

    Electron pairing in the vast majority of superconductors follows the Bardeen–Cooper–Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K. PMID:28102222

  17. p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor.

    PubMed

    Di Bernardo, A; Millo, O; Barbone, M; Alpern, H; Kalcheim, Y; Sassi, U; Ott, A K; De Fazio, D; Yoon, D; Amado, M; Ferrari, A C; Linder, J; Robinson, J W A

    2017-01-19

    Electron pairing in the vast majority of superconductors follows the Bardeen-Cooper-Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.

  18. Phase diagram of high- Tc superconductor: Cu-NMR studies on multi-layered cuprates

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Abe, M.; Shimizu, S.; Kitaoka, Y.; Iyo, A.; Kodama, Y.; Tanaka, Y.; Tokiwa, K.; Watanabe, T.

    2008-04-01

    A new phase diagram is presented for an ideally flat CuO2 plane through the Cu-NMR studies on five-layered cuprates MBa2Ca4Cu5Oy(M-1245) (M=Hg,Tl,Cu), which includes an antiferromagnetic (AFM) metal phase and a uniform mixing phase of AFM metal and high- Tc superconductivity (HTSC) in an under-doped region. It has been found that a disorder causes a quantum-phase transition from an AFM metal to an insulating state in an under-doped regime in the Cu-1245 where a disorder is introduced via an oxygen-reduced process. This finding reinforces that an AFM metallic phase exists between the AFM insulating phase and the SC phase for the ideally flat CuO2 plane provided that a disorder is absent.

  19. 43Ca NMR Study of Bismuth-Based High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Trokiner, A.; Le Noc, L.; Yakubovskii, A.; Mykhalyov, K. N.; Verkhovskii, S. V.

    1994-02-01

    As a first step of a study of the electronic properties of CuO2 planes by probing calcium nuclei in the bismuth-based high-Tc materials we report here the structural assignment of Ca NMR lines measured in 43Ca-enriched samples of n = 2 ((Bi,Pb)2Sr2CaCu2O8+x) and n = 3 ((Bi,Pb)2Sr2-Ca2Cu3O10+x) bismuth compounds. Powdered samples were investigated as well as oriented pow­ ders, achieved by uniaxial alignment of the grains in a 7T magnetic field. For the main calcium site (Ca between two CuO2 planes), we could determine the quadrupolar as well as the shift tensors. The results indicate that, in the same way as yttrium nuclei in YBaCuO, calcium nuclei are sensitive to the magnetic susceptibility of the metallic CuO2 planes.

  20. Manipulation of magnetic carriers for drug delivery using pulsed-current high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Cha, Yung; Chen, Lihua; Askew, Thomas; Veal, Boyd; Hull, John

    2007-04-01

    An innovative method of manipulating magnetic carriers is proposed, and its feasibility for drug delivery and therapy is demonstrated experimentally. The proposed method employs pulsed-field solenoid coils with high-critical- temperature ( Tc) superconductor inserts. Pulsed current is used to magnetize and de-magnetize the superconductor insert. The proposed method was demonstrated to be able to (1) move magnetic particles, ranging in size from a few millimeters to 10 μm, with strong enough forces over a substantial distance, (2) hold the particles at a designated position as long as needed, and (3) reverse the processes and retrieve the particles. We further demonstrated that magnetic particles can be manipulated in a stationary environment, in water flow, and in simulated blood (water/glycerol mixture) flow.

  1. Monte Carlo Study of the Magnetic Flux Lattice Fluctuations in High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Beny, Cedric

    By allowing to measure the magnetic field distribution inside a material, muon spin rotation experiments have the potential to provide valuable information about microscopic properties of high-temperature superconductors. Nevertheless, information about the intrinsic superconducting properties of the material is masked by random thermal and static fluctuations of the magnetic field which penetrates the material in the form of vortices of quantized magnetic flux. A good understanding of the fluctuations of those vortices is needed for the correct determination of intrinsic properties, notably the coherence length [xi], and the field penetration depth [lambda]. We develop a simulation based on the Metropolis algorithm in order to understand the effect, on the magnetic field distribution, of disorder- and thermally-induced fluctuations of the vortex lattice inside a layered superconductor. Our model correctly predicts the melting temperatures of the YBa2Cu3O6. 95 (YBCO) superconductor but largely underestimates the observed entropy jump. Also we failed to simulate the high field disordered phase, possibly because of a finite size limitation. In addition, we found our model unable to describe the first-order transition observed in the highly anisotropic Bi2Sr2CaCu2O8+y. Our model predicts that for YBCO, the effect of thermal fluctuations on the field distribution is indistinguishable from a change in [xi]. It also confirms the usual assumption that the effect of static fluctuations at low temperature can be efficiently modeled by convolution of the field distribution with a Gaussian function. However the extraction of [xi] at low fields requires a very high resolution of the field distribution because of the low vortex density.

  2. Microwave (EPR) measurements of the penetration depth measurements of high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Dalal, N. S.; Rakvin, B.; Mahl, T. A.; Bhalla, A. S.; Sheng, Z. Z.

    1991-01-01

    The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T sub c superconductors. The method uses the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T sub c is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, neutron scattering, and magnetic susceptibility.

  3. Huge metastability in high-Tc superconductors induced by parallel magnetic field

    NASA Astrophysics Data System (ADS)

    Dias, R. G.; Silva, J. A.

    2003-03-01

    We present a study of the temperature-magnetic-field phase diagram of homogeneous and inhomogeneous superconductivity in the case of a quasi-two-dimensional superconductor with an extended saddle point in the energy dispersion under a parallel magnetic field. At low temperature, a huge metastability region appears, limited above by a steep superheating critical field Hsh and below by a strongly reentrant supercooling field Hsc. We show that the Pauli limit Hp for the upper critical magnetic field is strongly enhanced due to the presence of the Van Hove singularity in the density of states. The formation of a nonuniform superconducting state is predicted to be very unlikely.

  4. Giant flux creep through the surface barriers and the irreversibility line in high-{Tc} superconductors

    SciTech Connect

    Burlachkov, L.; Geshkenbein, V.B. ||; Koshelev, A.E. |; Larkin, A.I. |; Vinokur, V.M.

    1994-05-01

    Magnetic flux relaxation over the surface barrier in high temperature superconductors are investigated Vortex dynamics controlled by the penetration both of pancake vortices and vortex lines are discussed. The penetration field H{sub p} for pancakes decay is exponentially with temperature. The size of the magnetization loop is determined by the decay of H{sub p} during the process of relaxation, but its shape remains unchanged. The irreversibility line associated with the pancake penetration is given by H{sub irr} {proportional_to} exp(- 2T/T{sub o}), and may lie both above and below the melting line.

  5. Positron annihilation studies of the electronic structure and fermiology of the high-{Tc} superconductors

    SciTech Connect

    Smedskjaer, L.C.; Bansil, A.

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T{sub c} superconductors, with focus on the YBa{sub 2}Cu{sub 3}O{sub 7} system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  6. Positron annihilation studies of the electronic structure and fermiology of the high-[Tc] superconductors

    SciTech Connect

    Smedskjaer, L.C. ); Bansil, A. . Dept. of Physics)

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T[sub c] superconductors, with focus on the YBa[sub 2]Cu[sub 3]O[sub 7] system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  7. Implications of charge ordering in high Tc cuprate superconductors in far-infrared spectroscopy.

    PubMed

    Kim, Y H; Hor, P H

    2013-09-04

    We addressed the issue of the absence of far-infrared signatures pertaining to charge ordering in the published far-infrared reflectivity data of La2-xSrxCuO4 single crystals while other experimental probes reveal that charge ordering is a hallmark of superconducting cuprates. Through direct comparison of the far-infrared data reported by various groups side by side and also with the Raman scattering data, we found that the inconsistencies stem from the failure in capturing delicate spectral features embedded in the close-to-perfect ab-plane far-infrared reflectivity of La2-xSrxCuO4 single crystals by misidentifying the reflectivity as the Drude-like metallic reflectivity. The analysis of the close-to-true reflectivity data reveals that only a small fraction (<3%) of the total doping-induced charge carriers (electrons) are itinerant on the electron lattice made up with the rest of the electrons (>97%) at all doping levels up to 16%. We conclude that the far-infrared reflectivity study is far from being ready to construct a coherent picture of the ubiquitous charge ordering phenomenon and its relationship with the high Tc superconductivity.

  8. Strong periodic flux pinning in oxygen-ion-irradiated high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Villegas, Javier; Swiecicki, I.; Briatico, J.; Bernard, R.; Crassous, A.; Wolf, T.; Bergeal, N.; Lesueur, J.; Ulysse, C.; Faini, G.; Hallet, X.; Piraux, L.

    2012-02-01

    We used oxygen ion irradiation to transfer into high-TC superconducting thin films the nanoscale pattern of different types of masks (alumina [1] and [2] PMMA templates with ordered arrays of holes). This causes a nanoscale spatial modulation of superconductivity, and strongly affects the magneto-transport in the mixed-state. By tuning the irradiation dose and the array parameters, it is possible to engineer vortex energy landscapes sufficiently strong to govern flux dynamics. This is evidenced by a periodic series of strong magneto-resistance oscillations, the well-known fingerprint of periodic flux pinning. Interestingly, this irradiation technique allows tuning the geometry and the strength of the pinning potential wells at the nanoscale. This allows the observation of unusually strong matching effects at relatively high fields (up to several kOe). We show that the amplitude of the magneto-resistance oscillations is intimately connected with vortex channeling effects. [1] J.E. Villegas et al. Nanotechnology 22 075302 (2011). [2] I. Swiecicki et al. submitted

  9. Phonon characteristics of high {Tc} superconductors from neutron Doppler broadening measurements

    SciTech Connect

    Trela, W.J.; Kwei, G.H.; Lynn, J.E.; Meggers, K.

    1994-12-01

    Statistical information on the phonon frequency spectrum of materials can be measured by neutron transmission techniques if they contain nuclei with low energy resonances, narrow enough to be Doppler-broadened, in their neutron cross sections. The authors have carried out some measurements using this technique for materials of the lanthanum barium cuprate class, La{sub 2{minus}x}Ba{sub x}CuO{sub 4}. Two samples with slightly different concentrations of oxygen, one being superconductive, the other not, were examined. Pure lanthanum cuprate was also measured. Lanthanum, barium and copper all have relatively low energy narrow resonances. Thus it should be possible to detect differences in the phonons carried by different kinds of atom in the lattice. Neutron cross section measurements have been made with high energy resolution and statistical precision on the 59m flight path of LANSCE, the pulsed spallation neutron source at Los Alamos National Laboratory. Measurements on all three materials were made over a range of temperatures from 15K to 300K, with small steps through the critical temperature region near 27K. No significant changes in the mean phonon energy of the lanthanum atoms were observed near the critical temperature of the super-conducting material. It appears however that the mean phonon energy of lanthanum in the superconductor is considerably higher than that in the non-superconductors. The samples used in this series of experiments were too thin in barium and copper to determine anything significant about their phonon spectra.

  10. Emerging Diluted Ferromagnetism in High-Tc Superconductors Driven by Point Defect Clusters.

    PubMed

    Gazquez, Jaume; Guzman, Roger; Mishra, Rohan; Bartolomé, Elena; Salafranca, Juan; Magén, Cesar; Varela, Maria; Coll, Mariona; Palau, Anna; Valvidares, S Manuel; Gargiani, Pierluigi; Pellegrin, Eric; Herrero-Martin, Javier; Pennycook, Stephen J; Pantelides, Sokrates T; Puig, Teresa; Obradors, Xavier

    2016-06-01

    Defects in ceramic materials are generally seen as detrimental to their functionality and applicability. Yet, in some complex oxides, defects present an opportunity to enhance some of their properties or even lead to the discovery of exciting physics, particularly in the presence of strong correlations. A paradigmatic case is the high-temperature superconductor YBa2Cu3O7-δ (Y123), in which nanoscale defects play an important role as they can immobilize quantized magnetic flux vortices. Here previously unforeseen point defects buried in Y123 thin films that lead to the formation of ferromagnetic clusters embedded within the superconductor are unveiled. Aberration-corrected scanning transmission microscopy has been used for exploring, on a single unit-cell level, the structure and chemistry resulting from these complex point defects, along with density functional theory calculations, for providing new insights about their nature including an unexpected defect-driven ferromagnetism, and X-ray magnetic circular dichroism for bearing evidence of Cu magnetic moments that align ferromagnetically even below the superconducting critical temperature to form a dilute system of magnetic clusters associated with the point defects.

  11. Tunneling characteristics and low-frequency noise of high-Tc superconductor/noble-metal junctions

    NASA Astrophysics Data System (ADS)

    Xu, Yizi; Ekin, J. W.

    2004-03-01

    We report extensive measurements of transport characteristics and low-frequency resistance noise of c-axis yttrium-barium-copper-oxide (YBCO)/Au junctions. The dominant conduction mechanism is tunneling at low temperatures. The conductance characteristic is asymmetric, and the conductance minimum occurs at a nonzero voltage. These features can be qualitatively explained by modeling the YBCO/Au interface with a Schottky barrier. The model shows that the YBCO surface behaves like a p-type degenerate semiconductor, with a Fermi degeneracy of about 0.1 eV. The barrier height is approximately 1.0 eV. We present evidence that interface states and disorder play an important role in determining the conductance characteristics. Low-frequency noise measurements of these junctions reveal that junction noise is dominated by resistance fluctuations with a 1/f-like power spectrum over a wide range of temperature and bias voltage. For temperatures between 4.2 and 77 K, the junction noise can be parameterized in terms of a normalized resistance fluctuation: δR/R≃6.3×10-4/√(f), in units of Hz-1/2, where f is the center frequency of the measurement bandwidth. At f=10 Hz, for example, it is 2×10-4 Hz-1/2. This noise figure should prove to be useful for engineering design of high-Tc electronics. A more detailed analysis shows that at low temperatures the noise spectrum is characterized by random telegraph signals withe a Lorentzian power spectrum, which can have a distribution of corner frequencies that mimics a 1/f dependence. The random telegraph signals provide evidence for the existence of localized states.

  12. Analysis of Magnetic Critical Fields in Iron-Based SmFeAsO0.85 HIGH-Tc Superconductor

    NASA Astrophysics Data System (ADS)

    Ahmad, Dawood; Song, Tae Kwon; Park, In Suk; Kim, G. C.; Ren, Zhi-An; Kim, Y. C.

    The magnetic properties of the newly discovered iron-oxypnictide SmFeAsO0.85 high-Tc superconductor with a Tc of around 55 K were investigated. Bulk SmFeAsO0.85 was prepared by a method for high-pressure synthesis. The lower critical field Hc1 was estimated from the magnetization at low fields; Hc1(0) was measured to be 212 Oe. A linear temperature dependence instead of saturation at low temperatures in Hc1(T) revealed unconventional superconductivity with a nodal gap structure in our SmFeAsO0.85 superconductor. The results showed that the well-known secondary peak in the temperature dependence of the critical current density Jc is absent in the SmFeAsO0.85 high-Tc superconductor. The irreversibility line Birr was fitted well by the power law dependence (1 - T/Tc)n with n ~ 1.5. This is indicative of the flux creep phenomena in the SmFeAsO0.85 high-Tc superconductor. In addition, within the range of measurement temperatures in this study, no crossover was observed in the temperature dependence of the irreversibility line Birr which may be due to low anisotropy in our SmFeAsO0.85 superconductor.

  13. AC Inductive Measurement of Intergrain and Intragrain Currents in High-Tc Oxide Superconductors

    NASA Astrophysics Data System (ADS)

    Ni, Baorong; Munakata, Toshiyuki; Matsushita, Teruo; Iwakuma, Masataka; Funaki, Kazuo; Takeo, Masakatsu; Yamafuji, Kaoru

    1988-09-01

    Bulk intergrain current and closed intragrain current in sintered Y-Ba-Cu-O superconductors were measured at 77 K by using an ac inductive method. These currents can be separated because of the large difference in penetrating rates of the magnetic flux into specimens with respect to the ac field amplitude. The obtained intergrain current density agreed approximately with critical current density measured resistively. The closed intragrain current density amounted to 4.3× 108 A/m2 at B{=}0.5 T and decreased gradually with increasing magnetic field. The present results show that the ac inductive measurement is one of the available nondestructive methods to characterize sintered oxide specimens.

  14. Double criticality in the magnetic field driven transition of a high-TC superconductor

    NASA Astrophysics Data System (ADS)

    Leridon, Brigitte; Vanacken, Johan; Moshchalkov, V. V.; Vignolle, Baptiste; Porwal, Rajni; Budhani, R. C.

    2015-03-01

    The magnetic-field driven transition of a set of high critical temperature La2 - x Srx CuO4 superconducting thin films has been investigated using high pulsed magnetic fields. For the underdoped samples, the existence of two distinct critical regions in the superconductor/insulator transition has been evidenced for the first time. The first quantum critical region is observed at intermediate magnetic fields (~= 19 T)and temperatures and gives way at lower temperature to a quantum critical point at about twice critical magnetic field and resistance per square. The critical exponents inferred from scaling behaviour are markedly different for the two regions. We attribute this behaviour to the existence of a clean/dirty crossover due to the presence of electronic inhomogeneities. This work has been supported by a SESAME grant from Region Ile-de-France. Part of the experiments at KULeuven have been founded by EuroMagNET II under the EU Contract Number 228043.

  15. Grain orientation in high Tc superconductors by molten salt powder synthesis

    NASA Technical Reports Server (NTRS)

    Gopalakrishnan, Sudhakar; Schulze, Walter A.

    1991-01-01

    The molten salt or the flux method is used to fabricate a grain oriented YBa2Cu3O(7-x) (123) superconductor. Here we suggest a two-stage approach in using the 'green phase', Y2BaCuO5 (211), as seed crystals in the formation of YBa2Cu3O(7-x). The process uses Y2BaCuO5 formed by molten salt synthesis. The Y2BaCuO5 phase was observed to be stable in water and in most of the salt systems. Salt processing can form a small quantity of anisotropic particles of Y2BaCuO5. This material can form the 123 phase when tape cast and sintered in the presence of the required levels of Ba and Cu.

  16. Theory of the vortex matter transformations in high-Tc superconductor YBCO.

    PubMed

    Li, Dingping; Rosenstein, Baruch

    2003-04-25

    Flux line lattice in type II superconductors undergoes a transition into a "disordered" phase such as vortex liquid or vortex glass, due to thermal fluctuations and random quenched disorder. We quantitatively describe the competition between the thermal fluctuations and the disorder using the Ginzburg-Landau approach. The following T-H phase diagram of YBCO emerges. There are just two distinct thermodynamical phases, the homogeneous and the crystalline one, separated by a single first order transition line. The line, however, makes a wiggle near the experimentally claimed critical point at 12 T. The "critical point" is reinterpreted as a (noncritical) Kauzmann point in which the latent heat vanishes and the line is parallel to the T axis. The magnetization, the entropy, and the specific heat discontinuities at melting compare well with experiments.

  17. The search for circular dichroism in high-Tc superconductors (abstract)

    NASA Astrophysics Data System (ADS)

    Lyons, K. B.; Kwo, J.; Dillon, J. F., Jr.; Espinosa, G. P.; McGlashan-Powell, M.; Ramirez, A. P.; Schneemeyer, L. F.

    1991-04-01

    Stimulated by recent predictions of broken time reversal symmetry in cuprate superconductors, we have carried out a study of the polar Kerr ellipticity (the ellipticity of normally reflected light with the incident beam linearly polarized) for various cuprate materials, both superconducting and nonsuperconducting. The technique used employs a rotating half-wave retardation plate in order to discriminate against linear polarization effects. The results reveal a signature of a nonzero polar Kerr ellipticity which appears on cooling near 200 K in a variety of superconducting materials, and which is not observed in the corresponding insulating compounds. In this talk, in addition to summarizing these results, we plan to discuss the measurement technique itself in some detail. Measurements on both thin films and bulk samples will be discussed, together with a variety of tests on unrelated materials, which serve to eliminate various possible experimental artifacts.

  18. Electron energy spectrum and magnetic interactions in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Turshevski, S. A.; Liechtenstein, A. I.; Antropov, V. P.; Gubanov, V. A.

    1991-01-01

    The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T(sub N1) and T(sub N2). The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T(sub N2) reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T(sub N1) and T(sub N2) which depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg Hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J(sub ij) parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

  19. High- Tc superconductors with antiferromagnetic order: limitations on spin-fluctuation pairing mechanism

    NASA Astrophysics Data System (ADS)

    Kulić, Miodrag L.; Kulić, Igor M.

    2003-08-01

    The antagonistic interplay of antiferromagnetism (AF) and superconductivity (SC), recently discovered in high-temperature superconductors, is studied in the framework of a microscopic theory. We explain the surprisingly large increase of the magnetic Bragg peak intensity IQ at Q∼( π, π) in the magnetic field H≪ Hc2 at low temperatures 0< T≪ Tc, TAF in La 2- xSr xCuO 4. Good agreement with experimental results is found. The theory predicts large anisotropy of the relative intensity RQ( H)=( IQ( H)- IQ(0))/ IQ(0), i.e. R Q( H∥c -axis)≫R Q( H⊥c -axis) . The quantum ( T=0) phase diagram at H=0 is constructed. The theory also predicts: (i) that the magnetic field can induce the AF order in the SC state; (ii) that the spin-fluctuation (SF) effective coupling constant g<0.1 eV is small, which gives small SC critical temperature Tc (≪40 K)--thus questioning the SF mechanism of pairing in HTS oxides.

  20. Exponential dependence of the vortex pinning potential on current density in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Yan, H.; Abdelhadi, M. M.; Jung, J. A.; Willemsen, B. A.; Kihlstrom, K. E.

    2005-08-01

    We investigated the dependence of the vortex pinning potential on current density Ueff(J) in Tl2Ba2CaCu2Oy , Tl2Ba2Ca2Cu3Oy , and YBa2Cu3Oy thin films and single crystals, measured by us and other research groups. In all these cases Ueff(J) was calculated from the magnetic relaxation data using Maley’s procedure [Phys. Rev. B 42, 2639 (1990)]. We explored the exponential dependence of Ueff(J) , first introduced by Thompson [Phys. Rev. B 44, 456 (1991).] to explain long-term nonlogarithmic magnetic relaxations in high-temperature superconductors (HTSC), as an alternative to power-law and logarithmic forms of Ueff(J) . The results revealed that for J larger than approximately 0.4Jc , the energy barrier can be expressed in the following form: Ueff(J)=aIco(1-T/T*)3/2exp(-bJ/Jco) , where the constant b is the same for all samples investigated. This result is independent of the anisotropy (the interplanar coupling). The experimental results were analyzed taking into account the spatial dependence of the pinning potential, proposed by Qin [J. Appl. Phys. 77, 2618 (1995)]. We suggested that the exponential form of Ueff(J) could represent vortex pinning and motion in the a-b planes due to a nanoscopic variation of the order parameter, in agreement with the growing experimental evidence for the presence of nanostructures, stripes (filaments) in HTSC.

  1. Stabilization of high Tc phase in bismuth cuprate superconductor by lead doping

    NASA Technical Reports Server (NTRS)

    Gupta, Ram. P.; Pachauri, J. P.; Khokle, W. S.; Nagpal, K. C.; Date, S. K.

    1991-01-01

    It has been widely ascertained that doping of lead in Bi-Sr-Ca-Cu-O systems promotes the growth of high T sub c (110 K) phase, improves critical current density, and lowers processing temperature. A systematic study was undertaken to determine optimum lead content and processing conditions to achieve these properties. A large number of samples with cationic compositions of Bi(2-x)Pb(x)Sr2Ca2Cu3 (x = 0.2 to 2.0) were prepared by conventional solid state reaction technique. Samples of all compositions were annealed together at a temperature and characterized through resistance temperature (R-T) measurements and x ray diffraction to determine the zero resistance temperature, T sub c(0) and to identify presence of phases, respectively. The annealing temperature was varied between 790 and 880 C to optimize processing parameters. Results are given. In brief, an optimum process is reported along with composition of leaded bismuth cuprate superconductor which yields nearly a high T sub c single phase with highly stable superconducting properties.

  2. Resolution of two apparent paradoxes concerning quantum oscillations in underdoped high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Jia, Xun; Goswami, Pallab; Chakravarty, Sudip

    2009-10-01

    Recent quantum-oscillation experiments in underdoped high-temperature superconductors seem to imply two paradoxes. The first paradox concerns the apparent nonexistence of the signature of the electron pockets in angle-resolved photoemission spectroscopy (ARPES). The second paradox is a clear signature of a small electron pocket in quantum-oscillation experiments, but no evidence as yet of the corresponding hole pockets of approximately double the frequency of the electron pocket. This hole pockets should be present if the Fermi-surface reconstruction is due to a commensurate density wave, assuming that Luttinger sum rule relating the area of the pockets and the total number of charge carriers holds. Here we provide possible resolutions of these apparent paradoxes from the commensurate d -density wave theory. To address the first paradox we have computed the ARPES spectral function subject to correlated disorder, natural to a class of experiments relevant to the materials studied in quantum oscillations. The intensity of the spectral function is significantly reduced for the electron pockets for an intermediate range of disorder correlation length, and typically less than half the hole pocket is visible, mimicking Fermi arcs. Next we show from an exact transfer-matrix calculation of the Shubnikov-de Haas oscillation that the usual disorder affects the electron pocket more significantly than the hole pocket. However, when, in addition, the scattering from vortices in the mixed state is included, it wipes out the frequency corresponding to the hole pocket. Thus, if we are correct, it will be necessary to do measurements at higher magnetic fields and even higher-quality samples to recover the hole-pocket frequency.

  3. MAGLEV: The double benefits of high-Tc superconductors and its development as an aerospace technology

    NASA Astrophysics Data System (ADS)

    Johnson, L. R.; Giese, R. F.

    1988-04-01

    The potential for magnetically levitated (MAGLEV) vehicles is discussed as a means of both inter-city travel and a technology option to relieve the growing problem of air traffic congestion. A brief summary is presented of the two primary MAGLEV concepts: (1) the attractive-force, electromagnetic system (EMS) and (2) the repulsive-force, electrodynamic system (EDS), and continues with a discussion of the advantages, potential for reduced costs and higher reliability, that the newly-discovered, high-temperature superconductors offer for EDS MAGLEV vehicles. A summary of the current status of worldwide MAGLEV research is presented, followed by a discussion of the resurgence of US interest in MAGLEV. An analysis of air-traffic congestion suggests that MAGLEV can substitute for short-to-medium distance air travel. By promoting MAGLEV as an airline technology, airlines can retain their familiar hub-and-spoke systems with MAGLEVs an integral part of the spoke portion. A preliminary analysis suggests that MAGLEV capital costs are likely to be comparable to those of interstate highways, and use of MAGLEVs can delay the need for new airport construction. For each short-to-medium flight diverted to MAGLEV, an airline can substitute a longer flight. The short-haul flights use an inordinate amount of fuel, which is a major component of airline operating costs. MAGLEV energy consumption would be significantly less and would not have the emissions associated with petroleum fuel. Finally, passengers should benefit from MAGLEV technology: travel options will be extended, delays will be reduced, and costs for inter-city travel will be reduced.

  4. Ultrafast momentum-dependent quasiparticle dynamics in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Bovensiepen, Uwe

    2013-03-01

    Femtosecond time- and angle-resolved photoelectron spectroscopy trARPES facilitates insight into electronic relaxation and electronic structure of non-equilibrium states of matter. Hot electrons and holes relax in metals on ultrafast time scales due to the screened Coulomb interaction. In superconductors the relaxation rates of quasiparticles at energies close to the superconducting gap edge are reduced because of the loss of quasiparticle states near EF. Since in the superconducting state the relaxation of optically excited carriers proceeds partly by Cooper pair reformation, the study of the quasiparticle dynamics bears the potential to analyze the interaction responsible for Cooper pair formation. Results of trARPES will be discussed for optimally doped Bi2Sr2CaCu2O8+δ in the superconducting state and on EuFe2As2 in the antiferromagnetic state. In the cuprate system we find a predominant excitation of quasiparticles at momenta near the antinode. We show furthermore, that at excitation densities of several 10 μJ/cm2 quasiparticle relaxation is dominated by Cooper pair reformation, which again proceeds near the antinode. In the Fe-pnictide material we monitor a difference in the relaxation rate for electrons and holes near the Fermi momentum, which disappears above the Neel temperature. We conclude that this anisotropic relaxation of electrons and holes is a consequence of the optical modification of the antiferromagnetic order. Analysis of energy transfer from electrons to phonons allows to determine the momentum averaged electron-phonon coupling constant λ. We find values below 0.25 for Bi2Sr2CaCu2O8+δ and below 0.15 for EuFe2As2. We acknowledge funding through the Deutsche Forschungsgemeinschaft through BO 1823/2, SPP 1458 and the Alexander von Humboldt foundation.

  5. Synthesis and characterization of high-Tc superconductors in the Tl-Ca-Ba-Cu-O system

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Farrell, D. E.

    1989-01-01

    Both Tl2Ca2Ba2Cu3O10 and TlCa3BaCu3O8.5 are investigated for superconductivity as a function of the sintering temperature, time, atmosphere, and quench rate in an effort to synthesize the high-Tc superconducting phase in the thallium system. The samples are characterized by electrical resistivity measurements, X-ray diffraction, and scanning electron microscopy. Samples of starting composition Tl2Ca2Ba2Cu3O10 fired in air at 860-900 C and rapidly quenched show a Tc of 96-107 K. In contrast, specimens of starting composition TlCa3BaCu3O8.5 when baked at 900 C and slowly cooled in oxygen superconduct at 116 K and above and consist of Tl2Ca2Ba2Cu3O(10+x) as the dominant phase. The results also show that, in contrast to the case of YBa2Cu3O(7-x), doping with a small concentration of fluorine sharpens the resistive transition and produces a large Tc increase in thallium-based superconductors.

  6. Compensated electron and hole pockets in an underdoped high- Tc superconductor

    NASA Astrophysics Data System (ADS)

    Sebastian, Suchitra E.; Harrison, N.; Goddard, P. A.; Altarawneh, M. M.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Andersen, O. K.; Lonzarich, G. G.

    2010-06-01

    We report quantum oscillations in the underdoped high-temperature superconductor YBa2Cu3O6+x over a wide range in magnetic field 28≤μ0H≤85T corresponding to ≈12 oscillations, enabling the Fermi surface topology to be mapped to high resolution. As earlier reported by Sebastian [Nature (London) 454, 200 (2008)10.1038/nature07095], we find a Fermi surface comprising multiple pockets, as revealed by the additional distinct quantum oscillation frequencies and harmonics reported in this work. We find the originally reported broad low-frequency Fourier peak at ≈535T to be clearly resolved into three separate peaks at ≈460 , ≈532 , and ≈602T , in reasonable agreement with the reported frequencies of Audouard [Phys. Rev. Lett. 103, 157003 (2009)10.1103/PhysRevLett.103.157003]. However, our increased resolution and angle-resolved measurements identify these frequencies to originate from two similarly sized pockets with greatly contrasting degrees of interlayer corrugation. The spectrally dominant frequency originates from a pocket (denoted α ) that is almost ideally two-dimensional in form (exhibiting negligible interlayer corrugation). In contrast, the newly resolved weaker adjacent spectral features originate from a deeply corrugated pocket (denoted γ ). On comparison with band structure, the d -wave symmetry of the interlayer dispersion locates the minimally corrugated α pocket at the “nodal” point knodal=(π/2,π/2) , and the significantly corrugated γ pocket at the “antinodal” point kantinodal=(π,0) within the Brillouin zone. The differently corrugated pockets at different locations indicate creation by translational symmetry breaking—a spin-density wave has been suggested from the suppression of Zeeman splitting for the spectrally dominant pocket. In a broken-translational symmetry scenario, symmetry points to the nodal (α) pocket corresponding to holes, with the weaker antinodal (γ) pocket corresponding to electrons—likely responsible

  7. Phonon suppression of the coherence peak in nuclear spin relaxation rate in strong coupling superconductor TIMo 6Se 7.5. Comparison with high- Tc superconductor

    NASA Astrophysics Data System (ADS)

    Yoshio, Kitaoka; Shigeki, Ohsugi; Kunisuke, Asayama; Tsukio, Ohtani

    1992-03-01

    The phonon suppression effect on the coherence peak just below Tc in the nuclear spin relaxation rate {1}/{T 1} has been investigated by 205Tl NMR of a Chevrel phase superconductor TlMO 6Se 7.5 with Tc = 12.2 K. The lack of a coherence peak of 205( {1}/{T 1) } is demonstrated in a strong coupling superconductor TlMo 6Se 7.5 while the exponential decrease of {1}/{T 1} is confirmed over four orders of magnitude below 0.8 Tc (10 K) with 2 Δ=4.5 kBTc. As argued by Allen and Rainer, the strong electron-phonon decay channels open to excitation cause the unexpectedly strong damping of the quasi-particles in all dynamical properties, being the origin of the depression of the coherence peak. From a comparison with an s-wave model in which the quasi-particle damping is taken into account, it is reinforced that the unusual relaxation behavior observed in high- Tc cuprates, i.e. a power-lawT-dependence with no coherence peak below Tc cannot be accounted for by the conventional theory of the superconductivity and/or the model based on “s-wave” paring.

  8. High-Tc Superconductivity and Raman Scattering Study of the phonon properties of electron doped (transition metal, rare-earth) - Oxygen-Free CaFeAsF and compared with RFeAsO system

    NASA Astrophysics Data System (ADS)

    Sasmal, Kalyan; Hadjiev, Viktor; Chu, C. W.(Paul)

    Quaternary CaFeAsF has ZrCuSiAs-type structure,(RO)δ+ layer in RFeAsO replaced by (CaF)δ+ layer,with tetragonal (P4/nmm)-orthorhombic (Cmma) phase transition at 134K,while magnetic order,SDW sets in at 114K. Partial replacement of Fe with Co/Ni is direct electron doping to (FeAs)δ+ layer.Tc ~15K in CaFe0.9Ni0.1AsF.Substitution of rare earth metal for alkaline earth metal suppresses anomaly in resistivity & induces superconductivity.Tc ~52K in Ca0.5Pr0.5FeAsF.Characterized by resistivity, susceptibility,XRD & EDX-SEM.Upper critical field estimated from magneto resistance.Bulk superconductivity proved by DC magnetization. Hall coefficient RH revealed hole-like charge carriers in parent compound CaFeAsF, while electron-type (RH in normal state is -Ve) for Ca0.5Pr0.5FeAsF.Evolution of Raman active phonons of Ca1-xPrxFeAsF measured with polarized Raman spectroscopy at room temperature from absurfaces of impurity-free microcrystals.Spectra exhibit sharp phonon lines on very weak electronic scattering background.Frequency and symmetry of Raman phonons involving out-of-plane atomic vibrations are found at 162.5 cm-1 (A1 g, Pr), 201 cm-1 (A1 g, As), 215.5 cm-1 (B1 g, Fe), 265 cm-1 (Eg, Fe) and 334 cm-1 (B1 g, F) for Ca0.5Pr0.5FeAsF.Observations are compared with RFeAsO unconventional superconductors also possibly related to magnetic fluctuations

  9. Crystal growth of high- TC superconductors Pr 2 - xCe xCuO 4 + δ with substitutions of Ni and Co for Cu

    NASA Astrophysics Data System (ADS)

    Brinkmann, Matthias; Rex, Thomas; Bach, Heinrich; Westerholt, Kurt

    1996-06-01

    We report the crystal growth of the electron-doped high- TC superconducting Pr 2 - xCe xCuO 4 + δ by a modified CuO self-flux flow method. We found that for the crystal growth process at different Ce concentrations the maximum growth temperature is the most important parameter and report about optimized crystal growth procedures for the Ce-concentration range x = 0-0.18. Using this flux growth method only Ni and Co atoms can be substituted for Cu in the Pr 2 - xCe x(Cu 1 - yM y)O 4 + δ crystals, the other substitutional elements that we have tested (M = Fe, Zn, Ga, and Sn) do not dissolve in the T' phase. We introduce a new reduction treatment for single crystalline samples which ensures a homogeneous and variable oxygen stoichiometry over the whole crystal.

  10. Superconducting gap structure in the electron doped BiS2-based superconductor

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, A.; Adroja, D. T.; Hillier, A. D.; Jha, R.; Awana, V. P. S.; Strydom, A. M.

    2017-07-01

    The influence of electron doping on semimetallic SrFBiS2 has been investigated by means of resistivity, zero and transverse  -  field (ZF/TF) muon spin relaxation/rotation (μSR) experiments. SrFBiS2 is semimetallic in its normal state and small amounts of La doping results in bulk superconductivity at 2.8 K, at ambient pressure. The temperature dependence of the superfluid density as determined by TF-μSR can be best modelled by an isotropic s  -  wave type superconducting gap. We have estimated the magnetic penetration depth {λL}(0)=1087 nm, superconducting carrier density {{n}s}=3.7× {{10}26} carriers m-3 and effective-mass enhancement m *  =  1.558 m e. Additionally, there is no clear sign of the occurrence of spontaneous internal magnetic fields below {{T}\\mathbf{c}} , which implies that the superconducting state in this material can not be categorized by the broken time-reversal symmetry which is in agreement with the previous theoretical prediction.

  11. Low temperature specific heat anomaly in electron doped R2-xCexCuO4 superconductors

    NASA Astrophysics Data System (ADS)

    Mohapatra, S. P.; Rout, G. C.

    2014-04-01

    The electron doped rare earth copper oxide superconductors R2-xCexCuO4 exhibit anomalous heavy fermion behavior at low temperature with large Sommerfeld specific heat coefficient which is different from the conventional heavy fermion systems. The system is described by a model Hamiltonian consisting of staggered magnetic field in the two sub-lattices of the copper sites in presence of hybridization between the localized 4f electrons of Nd atom and the conduction electrons as well as the f-electron kinetic energy term. The Hamiltonian is solved by Zubarev's Green's function technique and the sub-lattice magnetization is calculated and solved self-consistently. The entropy and specific heat are calculated from the free energy of the system. The temperature dependent entropy and specific heat are numerically evaluated by successive differentiations of sub-lattice magnetization and temperature dependent entropy. It is observed that when the position of the f-level of Nd atom is of the order of hybridization strength, the sub-lattice magnetization is destroyed drastically at lower temperatures. As a result, the specific heat exhibits a large enhancement at low temperatures suggesting the enhancement of the electron density of states and the effective mass of the itinerant electrons exhibiting the heavy fermion character. Similarly, the specific heat shows anomalously sharp jump near the Néel temperature.

  12. A 63Cu-NMR study on four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2

    NASA Astrophysics Data System (ADS)

    Shimizu, S.; Mukuda, H.; Kitaoka, Y.; Kito, H.; Kodama, Y.; Shirage, P. M.; Iyo, A.

    2010-01-01

    We report on superconducting and magnetic characteristics in four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2 with apical fluorine through 63Cu-NMR measurements. The temperature dependence of the Knight shift shows that the substitution of oxygen for fluorine at the apical site increases carrier density (Nh) and Tc from 55 up to 102 K. The 63Cu-NMR spectra suggest that antiferromagnetic (AFM) order takes place in underdoped CuO2 layers; especially, the AFM order coexists with superconductivity in a single CuO2 plane at y=1.0.

  13. Large-moment antiferromagnetic order in overdoped high-Tc superconductor (154)SmFeAsO1-x D x.

    PubMed

    Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C; Otomo, Toshiya; Hosono, Hideo

    2017-05-30

    In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of (154)SmFeAsO1-x D x , and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

  14. Magnetic fluctuations in n-type high-Tc superconductors reveal breakdown of fermiology:Experiments and Fermi-liquid/RPA calculations

    SciTech Connect

    Krueger, S.D.

    2010-03-02

    By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr{sub 0.88}LaCe{sub 0.12}CuO{sub 4} with theoretical calculations, we demonstrate that the conventional fermiology approach cannot possibly account for the magnetic fluctuations in these materials. In particular, we perform tunneling experiments on the very same sample for which a dynamical magnetic resonance has been reported recently and use photoemission data by others on a similar sample to characterize the fermionic quasiparticle excitations in great detail. We subsequently use this information to calculate the magnetic response within the conventional fermiology framework as applied in a large body of work for the hole-doped superconductors to find a profound disagreement between the theoretical expectations and the measurements: this approach predicts a steplike feature rather than a sharp resonance peak, it underestimates the intensity of the resonance by an order of magnitude, it suggests an unreasonable temperature dependence of the resonance, and most severely, it predicts that most of the spectral weight resides in incommensurate wings which are a key feature of the hole-doped cuprates but have never been observed in the electron-doped counterparts. Our findings strongly suggest that the magnetic fluctuations reflect the quantum-mechanical competition between antiferromagnetic and superconducting orders.

  15. Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-xDx

    NASA Astrophysics Data System (ADS)

    Iimura, Soshi; Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C.; Otomo, Toshiya; Hosono, Hideo

    2017-05-01

    In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1-xDx, and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.

  16. Large-moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1−xDx

    PubMed Central

    Okanishi, Hiroshi; Matsuishi, Satoru; Hiraka, Haruhiro; Honda, Takashi; Ikeda, Kazutaka; Hansen, Thomas C.; Otomo, Toshiya; Hosono, Hideo

    2017-01-01

    In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE is heavy rare earth (RE) element). Although hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high-concentration electron doping and carrying out neutron experiments. Here, we present a systematic neutron powder diffraction study of 154SmFeAsO1−xDx, and the discovery of a long-range antiferromagnetic ordering with x ≥ 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 μB/Fe, which is the largest in all nondoped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest-neighbor hopping parameter becomes zero. The unique phase diagram, i.e., highest-Tc superconducting phase adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity. PMID:28507123

  17. The Generalized Joint Density of States and Its Application to Exploring the Pairing Symmetry of High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Dan-Bo; Han, Qiang; Wang, Zi-Dan

    2013-05-01

    We introduce a generalized joint density of states (GJDOS), which incorporates the coherent factors into the JDOS, to study quasiparticle interference (QPI) in superconductors. The intimate relation between the Fourier-transformed local density of states and GJDOS is revealed: they correspond respectively to the real and imaginary parts of a generalized impurity-response function, and particularly share the same angular factors and singular boundaries, as seen from our approximate analytic results for d-wave superconductors. Remarkably, our numerical GJDOS analysis agrees well with the QPI patten of d-wave cuprates and s±-wave iron-based superconductors. Moreover, we illustrate that the present GJDOS scenario can uncover the sign features of the superconducting gap and thus can be used to explore the pairing symmetry of the A1-xFe2—ySe2 (A=K, Cs, etc) superconductors.

  18. Quasiparticle tunneling spectroscopy of high {Tc} cuprates

    SciTech Connect

    Zasadzinski, J.; Ozyuzer, L.; Yusof, Z.; Chen, J.; Gray, K.E.; Mogilevsky, R.; Hinks, D.G.; Cobb, J.L.; Markert, J.T.

    1996-04-01

    Superconductor-insulator-normal metal (SIN) and superconductor-insulator-superconductor (SIS) tunnel junctions provide important information on pairing state symmetry and mechanism. Measurements of such junctions on high {Tc} superconductors (HTS) are reported using mechanical point contacts, which generally display the optimum characteristics that can be obtained from HTS native-surface tunnel barriers. New tunneling data on the infinite-layer cuprate, Sr{sub 1{minus}x}Nd{sub x}CuO{sub 2} are reported which show a remarkable similarity to another electron-doped cuprate, Nd{sub 1.85}Ce{sub 0.85}CuO{sub 4}. In particular, there is a strong, asymmetric linear background conductance that is indicative of inelastic tunneling from a continuum of states. A discussion is given of the anomalous dip feature found in the tunneling and photoemission data on BSCCO 2212. It is shown that a similar feature is found in many cuprate junctions and that this dip scales with the gap energy over a wide range. New data on the single-layer, tetragonal cuprate, Tl{sub 2}Ba{sub 2}CuO{sub 6} (Tl2201) are presented and discussed in light of recent published results on the similar compound HgBa{sub 2}CuO{sub 4} (Hg1201). The HG1201 data display a low, flat sub-gap tunneling conductance which is consistent with a BCS density of states whereas the T12201 data display a cusp-like feature at zero bias which is more consistent with d{sub x}2-{sub y}2 symmetry.

  19. Images of interlayer vortices and c -axis penetration depth of high- Tc YBa2Cu3O7-y superconductor

    NASA Astrophysics Data System (ADS)

    Iguchi, Ienari; Takeda, Tomohiro; Uchiyama, Tetsuji; Sugimoto, Akira; Hatano, Takeshi

    2006-06-01

    The measurements on the magnetic image of interlayer vortices are performed for the high- Tc YBa2Cu3O7-y(110) thin film using a high sensitive scanning SQUID microscopy. Clear images of aligned giant interlayer vortices are observable. For the majority of vortices, using the London model, the c -axis penetration depth is estimated to be about 20μm at 3K . The temperature dependence of λc is obtained from the observed vortex images at different temperatures, whose behavior is in good agreement with those of the microwave cavity measurement.

  20. NMR characterization of sulphur substitution effects in the KxFe2-ySe2-zSz high-Tc superconductor

    DOE PAGES

    Torchetti, D. A.; Imai, T.; Lei, H. C.; ...

    2012-04-17

    We present a⁷⁷ Se NMR study of the effect of S substitution in the high-Tc superconductor KxFe2-ySe2-zSz in a temperature range up to 250 K. We examine two S concentrations, with z=0.8 (Tc~ 26 K) and z=1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the KxFe₂Se₂ sample due to local disorder in the Se environment. Our Knight shift ⁷⁷K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itself decreases with increased S concentration. In addition, S substitution progressively suppresses low-frequency spin fluctuations. None ofmore » the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near Tc in 1/T₁T, as seen in FeSe.« less

  1. Sol-gel processing of precursor for high- Tc superconductors: influence of rhenium on the synthesis of Ba 2Ca 2Cu 3O x

    NASA Astrophysics Data System (ADS)

    Sin, A.; Odier, P.; Núñez-Regueiro, M.

    2000-03-01

    A sol-gel method for processing precursors of mercury-cuprates is described. It uses the gelification of a solution by acrylamide polymerisation and may be applied to concentrated solutions if a proper stabilisation of the cations is ensured. The method is described here for Ba 2Ca 2Cu 3O x and Re 0.25Ba 2Ca 2Cu 3O x but may serve to other precursors. Barium carbonate contamination is avoided in a large extent and Re-addition even helps by its efficient combination at low temperature with barium species. The precursor, with Re, might be handled without complicated precautions. Superconductors have been prepared in this way with an excellent homogeneity and high Tc.

  2. Examination of the peak in dICO/dlnt in weak-linked high Tc superconductors caused by trapped flux

    NASA Astrophysics Data System (ADS)

    Rezeq, Moh'd.; LeBlanc, M. A. R.

    2007-04-01

    Altshuler et al discovered that dICO/dlnt, the rate of increase of the critical current IC with time in polycrystalline high TC samples, traced a peak when measured versus HM, the amplitude of the sweep of the flux trapping magnetic field. We show that the sharp peak in dICO/dlnt which their model generates arises from a special feature of the formulae they use to describe IC versus HM. Pursuing an extension of these formulae, and exploiting a Brandt-Indenbom formula for the return field of the magnetized grains, we (i) reproduce observations of Altshuler et al, Batista-Leyva et al and a family of curves of dICO/dlnt reported by Cobas et al, and (ii) estimate the return fields. We also explore the peak structure of dICO/dlnt versus HM generated by using two well known empirical expressions for IC(H), and the Brandt-Indenbom formula.

  3. Lorentz microscopy observation of vortices in high-Tc superconductors using a 1-MV field emission transmission electron microscope.

    PubMed

    Harada, Ken

    2013-06-01

    Lorentz microscopy has opened the door to observing a single quantized magnetic flux line (i.e. a vortex) and its dynamic behavior inside a superconductor in real time. It resulted from the efforts of Dr Akira Tonomura and his collaborators, who developed a field emission electron microscope and advanced the technologies used for visualizing vortices (e.g. a low-temperature specimen stage and a magnetic-field application system). They used a 1-MV field emission transmission electron microscope with an electron beam that can penetrate thick specimens of high-temperature superconductors (Bi2Sr2CaCu2O8+δ and YB2C3O7-δ) to reveal the flux-line features inside materials and their interactions with defects. This memorial paper reviews the results of research in the area of vortex matter physics.

  4. Evidence for a new excitation at the interface between a high-Tc superconductor and a topological insulator

    DOE PAGES

    Zareapour, Parisa; Hayat, Alex; Zhao, Shu Yang F.; ...

    2014-12-09

    In this research, high-temperature superconductors exhibit a wide variety of novel excitations. If contacted with a topological insulator, the lifting of spin rotation symmetry in the surface states can lead to the emergence of unconventional superconductivity and novel particles. In pursuit of this possibility, we fabricated high critical-temperature (Tc ~ 85 K) superconductor/topological insulator (Bi₂Sr₂CaCu₂O₈₊δ/Bi₂Te₂Se) junctions. Below 75 K, a zero-bias conductance peak (ZBCP) emerges in the differential conductance spectra of this junction. The magnitude of the ZBCP is suppressed at the same rate for magnetic fields applied parallel or perpendicular to the junction. Furthermore, it can still be observedmore » and does not split up to at least 8.5 T. The temperature and magnetic field dependence of the excitation we observe appears to fall outside the known paradigms for a ZBCP.« less

  5. International Workshop on Ion Beam Modification and Processing of High Tc- Superconductors: Physics and Devices: Program and Abstracts

    DTIC Science & Technology

    1989-04-12

    handled by standard rate theory. A stochastic treatment of the problem, based on a Fokker Planck approximation of the relevant master equation is summarized...talk, I will attempt to summarize the key differences between the oxide superconductors and niobium alloys that have caused this delay in...commercialization. These differences range from crystal structure and anisotropy, to the sensitivity of Tc to chemical doping, to the effects of damage and

  6. Thallium 2223 high Tc superconductor in a silver matrix and its magnetic shielding, hermal cycle and time aging properties

    SciTech Connect

    Fei, X.; He, W.S.; Havenhill, A.

    1994-12-31

    Superconducting Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (Tl2223) was ground to powder. Mixture with silver powder (0--80% weight) and press to desired shape. After proper annealing, one can get good silver-content Tl2223 bulk superconductor. It is time-stable and has good superconducting property as same as pure Tl2223. It also has better mechanical property and far better thermal cycle property than pure Tl2223.

  7. Crystallography, chemistry and structural disorder in the new high-Tc Bi-Ca-Sr-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Veblen, D. R.; Heaney, P. J.; Angel, R. J.; Finger, L. W.; Hazen, R. M.

    1988-01-01

    Diffraction experiments are reported which indicate that the new Bi-Ca-Sr-Cu-O layer-structure superconductor possesses a primitive orthorhombic unit cell with probable space group Pnnn. The material exhibits severe structural disorder which is primarily related to stacking within the layers. The apparent orthorhombic structure is an average resulting from orthorhombic material mixed with monoclinic domains in two twinned orientations. Two distinct types of structural disorder that are common in materials synthesized to date are also described. This disorder complicates the crystallographic analysis and suggests that X-ray and neutron diffraction methods may yield only an average structure.

  8. Temperature dependence of thermal and electrical conductivity of Bi-based high- Tc (2 2 2 3) superconductor

    NASA Astrophysics Data System (ADS)

    Gul, I. H.; Anis-ur-Rehman, M.; Maqsood, A.

    2006-12-01

    Superconducting samples with nominal composition Bi 1.6Pb 0.4Sr 2Ca 2Cu 3O δ were prepared by the conventional solid-state reaction technique. The samples have been characterized by X-ray diffraction, dc electrical resistivity, ac magnetic susceptibility and thermal conductivity. The X-ray diffraction studies were done at room temperature and the lattice constants of the material were determined by indexing all the peaks. All the above measurements show that, there exists two phases i.e. high- Tc (2 2 2 3) and low- Tc (2 2 1 2). The information obtained from dc electrical resistivity data agrees with ac magnetic susceptibility measurements. The onset temperature Tc (onset) and zero resistivity temperature Tc ( R = 0) of the samples remains within the temperature 120 ± 1 K and 103 ± 1 K. Thermal conductivity has been measured with a transient plane source (TPS) technique in the temperature range 77-300 K. The estimation of the electrical resistivity change due to scattering by phonons and impurities has been discussed. An increase in thermal conductivity is observed above and below Tc ( R = 0). The electron-phonon scattering time, phonon-limited mobility and the size of the electron-phonon constant are also calculated. Wiedemann-Franz law is applied to gain prediction about the magnitude of electronic and phonon contribution to the total thermal conductivity of the samples. It is observed that heat is mainly conducted by the phonons in this system.

  9. A multi-component Fermi surface in the vortex state of an underdoped high-Tc superconductor.

    PubMed

    Sebastian, Suchitra E; Harrison, N; Palm, E; Murphy, T P; Mielke, C H; Liang, Ruixing; Bonn, D A; Hardy, W N; Lonzarich, G G

    2008-07-10

    To understand the origin of superconductivity, it is crucial to ascertain the nature and origin of the primary carriers available to participate in pairing. Recent quantum oscillation experiments on high-transition-temperature (high-T(c)) copper oxide superconductors have revealed the existence of a Fermi surface akin to that in normal metals, comprising fermionic carriers that undergo orbital quantization. The unexpectedly small size of the observed carrier pocket, however, leaves open a variety of possibilities for the existence or form of any underlying magnetic order, and its relation to d-wave superconductivity. Here we report experiments on quantum oscillations in the magnetization (the de Haas-van Alphen effect) in superconducting YBa(2)Cu(3)O(6.51) that reveal more than one carrier pocket. In particular, we find evidence for the existence of a much larger pocket of heavier mass carriers playing a thermodynamically dominant role in this hole-doped superconductor. Importantly, characteristics of the multiple pockets within this more complete Fermi surface impose constraints on the wavevector of any underlying order and the location of the carriers in momentum space. These constraints enable us to construct a possible density-wave model with spiral or related modulated magnetic order, consistent with experimental observations.

  10. Signatures of the electronic nature of pairing in high-Tc superconductors obtained by non-equilibrium boson spectroscopy

    PubMed Central

    Krasnov, Vladimir M.; Katterwe, Sven-Olof; Rydh, Andreas

    2013-01-01

    Understanding the pairing mechanism that gives rise to high-temperature superconductivity is one of the longest-standing problems of condensed-matter physics. Almost three decades after its discovery, even the question of whether or not phonons are involved remains a point of contention to some. Here we describe a technique for determining the spectra of bosons generated during the formation of Cooper pairs on recombination of hot electrons as they tunnel between the layers of a cuprate superconductor. The results obtained indicate that the bosons that mediate pairing decay over micrometre-scale distances and picosecond timescales, implying that they propagate at a speed of around 106 m s−1. This value is more than two orders of magnitude greater than the phonon propagation speed but close to Fermi velocity for electrons, suggesting that the pairing mechanism is mediated by unconventional repulsive electron–electron, rather than attractive electron–phonon, interactions. PMID:24336159

  11. Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Emery, V. J.; Moodenbaugh, A. R.; Suenaga, M.; Johnston, D. C.

    1988-01-01

    The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

  12. Systematic variation of magnetic-field penetration depth in high-Tc superconductors studied by muon-spin relaxation

    NASA Technical Reports Server (NTRS)

    Uemura, Y. J.; Emery, V. J.; Moodenbaugh, A. R.; Suenaga, M.; Johnston, D. C.

    1988-01-01

    The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 SrO.15 CuO4 in transverse external magnetic fields 1 is approximately 4 kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

  13. Modelling the interactions between magnets and granular high-Tc superconductor material with a finite-element method

    NASA Astrophysics Data System (ADS)

    Hofmann, C.; Ries, G.

    2001-01-01

    A computational model for the interaction of magnets with HTS material of arbitrary grain size and critical current density is presented. The two-dimensional solution technique is based on a finite-element method and the superconductor is assumed to obey a power-law voltage-current characteristic. The currents inside the grains are generated by the periodic movement of a magnet stack consisting of permanent magnets and iron shims which gives an exciting field with a strong gradient. The considered application of this is a so-called high magnetic gradient bearing. The motivation for this work was to investigate the dependence of the levitation force and loss on the grain size and the intragrain jc.

  14. Resonance in the electron-doped high-transition-temperature superconductor Pr0.88LaCe0.12CuO4-delta.

    PubMed

    Wilson, Stephen D; Dai, Pengcheng; Li, Shiliang; Chi, Songxue; Kang, H J; Lynn, J W

    2006-07-06

    In conventional superconductors, the interaction that pairs the electrons to form the superconducting state is mediated by lattice vibrations (phonons). In high-transition-temperature (high-T(c)) copper oxides, it is generally believed that magnetic excitations might play a fundamental role in the superconducting mechanism because superconductivity occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds. Indeed, a sharp magnetic excitation termed 'resonance' has been observed by neutron scattering in a number of hole-doped materials. The resonance is intimately related to superconductivity, and its interaction with charged quasi-particles observed by photoemission, optical conductivity, and tunnelling suggests that it might play a part similar to that of phonons in conventional superconductors. The relevance of the resonance to high-T(c) superconductivity, however, has been in doubt because so far it has been found only in hole-doped materials. Here we report the discovery of the resonance in electron-doped superconducting Pr0.88LaCe0.12CuO4-delta (T(c) = 24 K). We find that the resonance energy (E(r)) is proportional to T(c) via E(r) approximately 5.8k(B)T(c) for all high-T(c) superconductors irrespective of electron- or hole-doping. Our results demonstrate that the resonance is a fundamental property of the superconducting copper oxides and therefore must be essential in the mechanism of superconductivity.

  15. Neutron-Spin Resonance in the Optimally Electron-Doped Superconductor Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4-{delta}}

    SciTech Connect

    Zhao Jun; Li Shiliang; Dai Pengcheng; Freeman, Paul G.; Onose, Y.; Tokura, Y.

    2007-07-06

    We use inelastic neutron scattering to probe magnetic excitations of an optimally electron-doped superconductor Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4-{delta}} above and below its superconducting transition temperature T{sub c}=25 K. In addition to gradually opening a spin pseudogap at the antiferromagnetic ordering wave vector Q=(1/2,1/2,0), the effect of superconductivity is to form a resonance centered also at Q=(1/2,1/2,0) but at energies above the spin pseudogap. The intensity of the resonance develops like a superconducting order parameter, similar to those for hole-doped superconductors and electron-doped Pr{sub 0.88}LaCe{sub 0.12}CuO{sub 4}. The resonance is therefore a general phenomenon of cuprate superconductors, and must be fundamental to the mechanism of high-T{sub c} superconductivity.

  16. Hidden Fermi-liquid Charge Transport in the Antiferromagnetic Phase of the Electron-Doped Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Li, Yangmu; Tabis, W.; Yu, G.; Barišić, N.; Greven, M.

    2016-11-01

    Systematic analysis of the planar resistivity, Hall effect, and cotangent of the Hall angle for the electron-doped cuprates reveals underlying Fermi-liquid behavior even deep in the antiferromagnetic part of the phase diagram. The transport scattering rate exhibits a quadratic temperature dependence, and is nearly independent of doping and compound and carrier type (electrons versus holes), and hence is universal. Our analysis moreover indicates that the material-specific resistivity upturn at low temperatures and low doping has the same origin in both electron- and hole-doped cuprates.

  17. Time-resolved neutron diffraction investigation of the effect of hydrogen on the high- Tc superconductor YBa 2Cu 3O 7-δ

    NASA Astrophysics Data System (ADS)

    Balagurov, A. M.; Mironova, G. M.; Rudnickij, L. A.; Galkin, V. Ju.

    1990-12-01

    The results of a time-resolved neutron diffraction investigation of the interaction of hydrogen flow with the high- Tc superconductor YBa 2Cu 3O 7-δ are presented. The experiment was carried out on the TOF diffractometer DN-2 at the reactor IBR-2 in Dubna. Hydrogenation was performed on small pieces of 1-2-3 ceramics which were enclosed inside a quartz tube. The sample was heated up to 350°C at a constant rate of 5°C/min. Diffraction patterns were collected every 3 min within the dhkl-interval of 1-20 Å. Up to 220°C the refinement yielded the well-known orthorhombic phase of the 1-2-3 structure without any remarkable reduction of the ( b- a)/( a+ b) ratio. Below this temperature the only change in the specimen was a gradual increase of the incoherent background which occured even at room temperature. Once the temperature of 220°C was reached, sample degradation took place as evidence by precipitation of metallic copper, a drastic increase of background and widening of the diffraction peaks. Simultaneously, the occupancy of O(4)+ O(5) sites fell to 0.6. No evidence was found for the formation of a solid solution of hydrogen in 1-2-3 structure.

  18. The critical current density, irreversibility line, and flux pinning properties of Ba2CaCu2O4(O,F)2 high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Shirage, P. M.; Tanaka, Y.; Iyo, A.

    2010-05-01

    The high-Tc superconductor of Ba2CaCu2O4(O,F)2 (F-0212) is an appealing material for application as it has a simple crystal structure with a highest Tc of 108 K. We have derived the intragrain critical current density (Jc), irreversibility field (Birr), flux pinning properties, etc., for the polycrystalline samples from under doping (Tc=82 K) to slightly-over doping (Tc=106 K) from the dc magnetization hysteresis loops. The Jc and Birr properties were found to improve rapidly as the doping state changes from under doping to slightly-over doping. Here we show that property of the spacing is crucial to enhance Birr as well as its thickness. An anisotropy factor for under doped Ba2CaCu2O4F2 was reckoned to 118 from a three-dimensional-two-dimensional crossover field of about 0.28 T. The double logarithmic plot of irreversibility field versus [1-(T /Tc)] analysis hints that the flux line melting model is adopted. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and reduced magnetic field bmax=0.2 agree with surface pinning mechanism with closely spaced pins.

  19. Critical current densities and irreversibility fields of new high- Tc Ba 2CaCu 2O 4(O,F) 2 superconductor

    NASA Astrophysics Data System (ADS)

    Shirage, P. M.; Shivagan, D. D.; Crisan, A.; Tanaka, Y.; Kodama, Y.; Kito, H.; Iyo, A.

    2008-04-01

    Ba2CaCu2O4(O2-yFy) (F-0212), a new high-Tc superconductor (HTSC) including fluorine at an apical site, is an attractive material for application because it shows a highest Tc of 108 K and has thin spacing between conduction layers that is favorable for high critical current density (Jc) and irreversibility field (Birr). The polycrystalline samples of F-0212 were synthesized under high pressure. A doping state was controlled from under doping (Tc = 82 K) to slightly-over doping (Tc = 106 K) via optimally-doping (Tc = 108 K). From the DC magnetization hysteresis loops, we determined the intragrain Jc and Birr using Bean's critical state model. The Jc and Birr properties of F-0212 were found to improve rapidly as the doping state changes from under doping to slightly-over doping to via optimally doping state. The irreversibility lines for the optimally- and slightly-over doped F-0212 are higher than optimally-doped Bi-2212. However, they are much lower than that of Cu-1212 (Y-123) though the spacing of F-0212 is thinner than that of Cu-1212. This indicates that property of the spacing is important to enhance Birr as well as its thickness. An anisotropy factor for under doped F-0212 was estimated to 118 from a 3D-2D crossover field of about 0.28 T.

  20. Suppression of the antiferromagnetic pseudogap in the electron-doped high-temperature superconductor by protect annealing.

    PubMed

    Horio, M; Adachi, T; Mori, Y; Takahashi, A; Yoshida, T; Suzuki, H; Ambolode, L C C; Okazaki, K; Ono, K; Kumigashira, H; Anzai, H; Arita, M; Namatame, H; Taniguchi, M; Ootsuki, D; Sawada, K; Takahashi, M; Mizokawa, T; Koike, Y; Fujimori, A

    2016-02-04

    In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr(1.3-x)La0.7Ce(x)CuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime.

  1. Topological phase transition from nodal to nodeless d-wave superconductivity in electron-doped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhu, Guo-Yi; Zhang, Guang-Ming

    2017-03-01

    Unlike the hole-doped cuprates, both nodal and nodeless superconductivity (SC) are observed in the electron-doped cuprates. To understand these two types of SC states, we propose a unified theory by considering the two-dimensional t\\text-J model in proximity to an antiferromagnetic (AF) long-range ordering state. Within the slave-boson mean-field approximation, the d-wave pairing symmetry is still the most energetically favorable even in the presence of the external AF field. In the nodal phase, it is found that the nodes carry vorticity and are protected by the adjoint symmetry of time-reversal and one unit lattice translation. Robust edge modes are obtained, suggesting the nodal d-wave SC being a topological weak-pairing phase. As decreasing the doping concentration or increasing the AF field, the nodes with opposite vorticity annihilate and the nodeless strong-pairing phase emerges. The topological phase transition is characterized by a critical point with anisotropic Bogoliubov quasiparticles, and a universal understanding is thus established for all electron-doped cuprates.

  2. Interaction between localized and conduction-electron spins in the high-Tc superconductor Gd:EuBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Shaltiel, D.; Noble, C.; Pilbrow, J.; Hutton, D.; Walker, E.

    1996-05-01

    This work studies the spin-spin interaction between the conduction electrons and localized spins in high-Tc superconductors. We report the ESR at 9.74 GHz of low concentration of Gd substituting the Eu in single crystals of EuBa2Cu3O6+x (x~=0.85). At low temperatures just above Tc, the Gd ESR spectra in the c axis direction is almost resolved. With increasing temperature, exchange effects narrow most of the spectrum into a line close to g=2.00 except the 7/2⇆5/2 transition, which remains partially resolved. This transition has a Dysonian line shape and shows a Korringa behavior. The narrowing of the spectra and the Korringa behavior indicate an exchange coupling between the conduction electrons and the Gd spin systems, and can be analyzed by the Barnes-Plefka theory. From the linewidth broadening of the 7/2⇆5/2 transition and the Barnes-Plefka theory we obtain a Korringa constant ΔHK/T=0.5 G/K. From this value we calculated the exchange interaction JSs between the Gd spins, S, and the conduction electrons, s, using reported values for conduction electron susceptibility. We obtain JSs=0.5+/-0.1×10-3 eV, a value that is two or three orders of magnitude smaller than those observed in metals. It explains the small effect of magnetic ions on the Tc in the RBa2Cu3O6+x compounds. (R = rare earth). From the angular dependent spectra of Gd:EuBa2Cu3O6+x we obtain zero field terms of b02=-1800 MHz, b04=-180 MHz, and b44=+600 MHz. These values are not significantly different from those obtained for Gd in YBa2Cu3O6+x.

  3. Electronic transport measurements in the electron-doped high-temperature superconductor Praseodymium(2-x) Cerium(x) Copper (II) oxide(4+-delta)

    NASA Astrophysics Data System (ADS)

    Bach, Paul Leonard

    2011-12-01

    This thesis is composed of four major parts centered around the electron-doped superconductor Pr2-xCexCuO4+/-delta: angular magnetoresistance studies of antiferromagnetism, doping effects of oxygenation, Tc enhancement by the creation of superlattices, and comparison of high-temperature resistivity with the pnictides. The first part focuses on transport measurements of the magnetism in Pr2-xCexCuO4+/-delta and La 2-xCexCuO4+/-delta. It was found that the thermal evolution of the angular dependence of magnetoresistance in Pr 2-xCexCuO4+/-delta can be used to determine the Neel temperature in that material. This angular magnetoresistance technique was also applied to La2-xCexCuO4+/-delta ; evidence for antiferromagnetism in this system was observed as well. This section additionally develops angular magnetoresistance as a useful probe in other cuprate projects here described. The second part investigates over-oxygenated and irradiated Pr2-x CexCuO4+/-delta, in under- and optimal dopings. Resistivity, Hall effect, and angular magnetoresistance measurements show oxygen both doping and disordering the system, in agreement with over-doped films. The evolution of both the Hall effect and angular magnetoresistance shows that over-oxygenation results in significant changes in the number of charge carriers, regardless of the increase in scattering incurred. Additionally, this study indicates that annealing primarily removes apical oxygen, rather than other proposed behaviors. The third part studies multi-layer films of Pr2-xCex CuO4+/-delta and La2-xCexCuO 4+/-delta. These superlattices exhibit a significant Tc enhancement over component layers' T cs. Interface effects are excluded as a source of this Tc increase based upon critical current measurments. The Tc enhancement is found to be due to charge redistribution. Based on Hall and angular magnetoresistance measurements, the result of this redistribution is slightly net-under-doped films. The fourth part uses Pr2-xCexCuO4

  4. A limit on spin-charge separation in high-Tc superconductors from the absence of a vortex-memory effect.

    PubMed

    Bonn, D A; Wynn, J C; Gardner, B W; Lin, Y J; Liang, R; Hardy, W N; Kirtley, J R; Moler, K A

    There is a long-standing debate about whether spin-charge separation is the root cause of the peculiar normal-state properties and high superconducting transition temperatures of the high-Tc materials. In the proposed state of matter, the elementary excitations are not electron-like, as in conventional metals, but rather the electron 'fractionalizes' to give excitations that are chargeless spin-1/2 fermions (spinons) and charge +e bosons (chargons). Although spin-charge separation has been well established in one dimension, the theoretical situation for two dimensions is controversial and experimental evidence for it in the high-Tc materials is indirect. A model with sharp experimental tests for a particular type of separation in two dimensions has recently been proposed. Here we report the results of those experimental tests, placing a conservative upper limit of 190 K on the energy of the proposed topological defects known as visons. There is still debate about the extent to which this experiment can settle the issue of spin-charge separation in the high-Tc copper oxides, because some forms of the separation are able to avoid the need for visons. But at least one class of theories that all predict a vortex-memory effect now are unlikely models for the copper oxides.

  5. Superconductivity without a hole pocket in electron-doped FeSe: Analysis beyond the Migdal-Eliashberg formalism

    NASA Astrophysics Data System (ADS)

    Yamakawa, Youichi; Kontani, Hiroshi

    2017-07-01

    High-Tc pairing mechanism absent of hole pockets in heavily electron-doped FeSe is one of the key unsolved problems in Fe-based superconductors. Here, this problem is attacked by focusing on the higher-order many-body effects neglected in conventional Migdal-Eliashberg formalism. We uncover two significant many-body effects for high-Tc superconductivity. (i) Due to the "vertex correction", the dressed multiorbital Coulomb interaction acquires prominent orbital dependence for low-energy electrons. The dressed Coulomb interaction not only induces the orbital fluctuations, but also magnifies the electron-boson coupling constant. Therefore, moderate orbital fluctuations give strong attractive pairing interaction. (ii) The "multi-fluctuation-exchange pairing process" causes large interpocket attractive force, which is as important as the usual single-fluctuation-exchange process. Due to these two significant effects dropped in the Migdal-Eliashberg formalism, the anisotropic s++-wave state in heavily electron-doped FeSe is satisfactorily explained. The proposed "inter-electron-pocket pairing mechanism" will enlarge Tc in other Fe-based superconductors.

  6. Phase-sensitive evidence for dx2-y2-pairing symmetry in the parent-structure high-Tc cuprate superconductor Sr1-xLaxCuO2

    NASA Astrophysics Data System (ADS)

    Tomaschko, Jochen; Scharinger, Sebastian; Leca, Victor; Nagel, Joachim; Kemmler, Matthias; Selistrovski, Teresa; Koelle, Dieter; Kleiner, Reinhold

    2012-09-01

    We report on a phase sensitive study of the superconducting order parameter of the infinite layer cuprate Sr1-xLaxCuO2 (SLCO), with x≈0.15. For the study a SLCO thin film was grown epitaxially on a tetracrystal substrate and patterned into direct-current superconducting quantum interference devices (dc SQUIDs). The geometry was designed to be frustrated for dx2-y2-wave pairing, that is, the SQUID ring comprising the tetracrystal point contains one 0 Josephson junction and one π Josephson junction, if the order parameter has dx2-y2-wave symmetry. Our results show that SLCO indeed is a dx2-y2-wave superconductor. This symmetry thus seems to be inherent to cuprate superconductivity. Subdominant order parameter components can be ruled out at least on a 5% level and may not be a necessary ingredient of high-Tc superconductivity.

  7. Antiferromagnetic Phase Transition in Four-Layered High-Tc Superconductors Ba2Ca3Cu4O8(FyO1-y)2 with Tc=55--102 K: 63Cu- and 19F-NMR Studies

    NASA Astrophysics Data System (ADS)

    Shimizu, Sunao; Mukuda, Hidekazu; Kitaoka, Yoshio; Kito, Hijiri; Kodama, Yasuharu; Shirage, Parasharam M.; Iyo, Akira

    2009-06-01

    We report on the magnetic characteristics of four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2 with apical fluorine through 63Cu- and 19F-NMR measurements. The substitution of oxygen for fluorine at the apical site increases carrier density (Nh) and Tc from 55 up to 102 K. The NMR measurements reveal that antiferromagnetic order, which can uniformly coexist with superconductivity, exists up to Nh ≃ 0.15, which is somewhat smaller than Nh ≃ 0.17, the quantum critical point (QCP) for five-layered compounds. The fact that the QCP for the four-layered compounds moves to a region of lower carrier density than for five-layered ones ensures that a decrease in the number of CuO2 layers makes an interlayer magnetic coupling weaker.

  8. A zero-field Cu-NMR study on antiferromagnetic ordered state in four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2

    NASA Astrophysics Data System (ADS)

    Shimizu, S.; Mukuda, H.; Kitaoka, Y.; Kito, H.; Kodama, Y.; Shirage, P. M.; Iyo, A.

    2010-12-01

    We report on superconducting and magnetic characteristics in four-layered high-Tc superconductors Ba2Ca3Cu4O8(FyO1-y)2 with apical fluorine through zero-field Cu-NMR measurements. The zero-field NMR spectra shows that the internal magnetic field, induced by antiferromagnetic (AFM) ordered moments, decreases with increasing the local carrier density (Nh). The AFM phase expands up to Nh˜0.15, which is the magnetic critical point where the AFM order collapses. Moreover, for y=1.0, the AFM order is observed at all CuO2 layers, although superconducting transition takes place at Tc=55K. This result suggests that the AFM order uniformly coexists with superconductivity in a single CuO2 plane in an underdoped region.

  9. Preparation and physical properties of polycrystalline (Bi{sub 1{minus}x}Pb{sub x}){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} high {Tc} superconductors

    SciTech Connect

    Awan, M.S.; Maqsood, M.; Mirza, S.A.; Yousaf, M.; Maqsood, A.

    1995-02-01

    (Bi{sub 1{minus}x}Pb{sub x}){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (x = 0.3) high critical transition temperature ({Tc}) superconductors are synthesized by the solid-state reaction method in polycrystalline form. X-ray diffraction (XRD) studies, direct current (dc) electrical resistivity measurements, scanning electron microscopic (SEM) studies, critical current density measurements and zero-field alternating current (ac) susceptibility measurements are performed to investigate the physical changes, structural changes, and magnetic behavior of the superconducting samples. X-ray diffraction studies show that a high {Tc} phase exists with orthorhombic symmetry in the specimen. According to the XRD data, the lattice parameters of the high {Tc} phase were determined as a = 0.537(1) nm, b = 0.539(1) nm, and c = 3.70(1) nm. The compound exhibits a superconducting transition at 106 {plus_minus} 1 K for zero resistance. The ac susceptibility measurements in zero field confirm the dc electrical resistivity results; hence both support the XRD results. The particle size and structural changes as a function of the cold-pressing and aging effect are also reported.

  10. Temperature dependence of the upper critical field of high- Tc superconductors from isothermal magnetization data: influence of a temperature dependent Ginzburg-Landau parameter

    NASA Astrophysics Data System (ADS)

    Landau, I. L.; Ott, H. R.

    2003-11-01

    We show that the scaling procedure, recently proposed for the evaluation of the temperature variation of the normalized upper critical field of type-II superconductors, may easily be modified in order to take into account a possible temperature dependence of the Ginzburg-Landau parameter κ. As an example we consider κ( T) as it follows from the microscopic theory of superconductivity.

  11. Genuine phase diagram of high-Tc superconductors based on site-selective Cu-NMR studies on five-layered cuprates

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Yamaguchi, Y.; Shimizu, S.; Kitaoka, Y.; Shirage, P. M.; Iyo, A.

    2009-03-01

    We report a genuine phase diagram for a disorder-free CuO2 plane based on the evaluation of the local hole density (Nh) by site-selective Cu-NMR studies on five-layered cuprates. It has been unraveled that (1) the antiferromagnetic (AFM) metallic state is robust up to Nh approx 0.17, (2) the uniformly mixed phase of SC and AFM metal (AFMM) is realized at Nh <= 0.17, (3) the tetracritical point for the AFMM/(AFMM+SC)/SC/PM(Paramagnetism) phases may be present at Nh approx 0.15 and T approx 75 K, (4) Tc is maximum just outside a quantum critical point (QCP) at which the AFM order collapses, suggesting the intimate relationship between the high-Tc SC and the AFM order. Our finding experimentally suggests that the AFM interaction plays the vital role as the glue for the Cooper pairs.

  12. Strong correlations and the search for high-Tc superconductivity in chromium pnictides and chalcogenides

    NASA Astrophysics Data System (ADS)

    Pizarro, J. M.; Calderón, M. J.; Liu, J.; Muñoz, M. C.; Bascones, E.

    2017-02-01

    Undoped iron superconductors accommodate n =6 electrons in five d orbitals. Experimental and theoretical evidence shows that the strength of correlations increases with hole doping, as the electronic filling approaches half filling with n =5 electrons. This evidence delineates a scenario in which the parent compound of iron superconductors is the half-filled system, in analogy to cuprate superconductors. In cuprates the superconductivity can be induced upon electron or hole doping. In this work we propose to search for high-Tc superconductivity and strong correlations in chromium pnictides and chalcogenides with n <5 electrons. By means of ab initio slave-spin and multiorbital random-phase-approximation calculations we analyze the strength of the correlations and the superconducting and magnetic instabilities in these systems with the main focus on LaCrAsO. We find that electron-doped LaCrAsO is a strongly correlated system with competing magnetic interactions, with (π ,π ) antiferromagnetism and nodal d -wave pairing being the most plausible magnetic and superconducting instabilities, respectively.

  13. High-Tc superconductivity and antiferromagnetism on self-doped high-Tc cuprate Ba2Ca3Cu4O8F2

    NASA Astrophysics Data System (ADS)

    Shimizu, Sunao; Mukuda, Hidekazu; Kitaoka, Yoshio; Iyo, Akira; Kodama, Yasuharu; Kito, Hijiri; Tokiwa, Kazuyasu; Watanabe, Tsuneo

    2007-03-01

    We report on the antiferromagnetism and high-Tc superconductivity in a F-substituted four-layered cuprate, composed of two outer and inner CuO2 planes in a unit cell, Ba2Ca3Cu4O8F2. Although a formal Cu valence is expected to be just +2.0 in the nominal composition, this is not a half-filled Mott insulator but a superconductor with Tc = 55K. Recently, it has been suggested that the origin of the superconductivity in this compound is self-doping by ARPES measurement [1] and band calculation [2], which means either outer or inner CuO2 planes are hole-doped, and the others are electron-doped. From F-NMR study, we have confirmed magnetic order with TN = 100K, concluding the uniform mixing of superconductivity and magnetic order in a single CuO2 plane. In addition, we have compared a three-layered compound Ba2Ca2Cu3O6F2, which is also superconductor with Tc = 76K. We will introduce the unique magntic and superconducting phenomena in F-substituted cuprates from microscopic points of view. [1]Y. Chen, et al., cond-mat/0611291 (2006) [2] W. Xie, et al., cond-mat/0607198 (2006)

  14. Magnetic field effect on the static antiferromagnetism of the electron-doped superconductor Pr1-xLaCexCuO4 (x=0.11 and 0.15).

    PubMed

    Fujita, M; Matsuda, M; Katano, S; Yamada, K

    2004-10-01

    Effects of magnetic fields (applied along the c axis) on static spin correlation were studied for the electron-doped superconductors Pr1-xLaCexCuO4 with x=0.11 (T(c)=25 K) and x=0.15 (T(c)=16 K) by neutron-scattering measurements. In the x=0.11 sample, which is located near the antiferromagnetic (AF) and superconducting phase boundary, a commensurate magnetic order develops below around T(c) at zero field. Upon applying a magnetic field up to 9 T both the magnetic intensity and the onset temperature of the order increase with the maximum field effect at approximately 5 T. In contrast, in the overdoped x=0.15 sample any static AF order is neither observed at zero field nor induced by the field up to 8.5 T. Difference and similarity of the field effect between the hole- and electron-doped high-T(c) cuprates are discussed.

  15. Temperature dependence of the hole density in high-TC superconductors Bi2-yPbySr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Ghafari, A.; Janowitz, C.; Ariffin, A. K.; Dwelk, H.; Krapf, A.; Manzke, R.

    2013-02-01

    One of the most puzzling anomalies of high-TC cuprates is the strong temperature dependence of the Hall coefficient (RH) and the hole density (nH). Gor’kov and Teitel’baum (GT) proposed by using experimental data of La2-xSrxCuO4 (LSCO) a two fluid model. The number of holes per Cu atom nH, changes with temperature according to nH(T,x) = n0(x) + n1(x)exp(-Δ(x)/T) [1]. To clarify the temperature dependence of nH we have determined nH from X-ray absorption spectra (XAS) at the CuL3 edge for nearly optimum and slightly underdoped Bi2-yPbySr2CaCu2O8+δ single crystals yielding directly the absolute value of nH in the CuO2 planes and also its change with temperature nH(T). It shows pronounced structures between 10 K and 300 K. The temperature dependence puts constraints to the applicability of previously developed models: (i) the two-band model without any explicit temperature dependence and (ii) the formula of GT, because the latter is not able to fit our data over the whole temperature range from 10 K to 300 K. Instead the thermal behavior of nH proposes a function with at least three terms, i.e. a third term added to the formula of GT is of exponential form ∼T3/2.

  16. Hysteretic Vortex-Matching Effects in High-Tc Superconductors with Nanoscale Periodic Pinning Landscapes Fabricated by He Ion-Beam Projection

    NASA Astrophysics Data System (ADS)

    Zechner, G.; Jausner, F.; Haag, L. T.; Lang, W.; Dosmailov, M.; Bodea, M. A.; Pedarnig, J. D.

    2017-07-01

    Square arrays of submicrometer columnar defects in thin YBa2 Cu3 O7 -δ (YBCO) films with spacings down to 300 nm are fabricated by a He ion-beam projection technique. Pronounced peaks in the critical current and corresponding minima in the resistance demonstrate the commensurate arrangement of flux quanta with the artificial pinning landscape, despite the strong intrinsic pinning in epitaxial YBCO films. While these vortex-matching signatures are exactly at the predicted values in field-cooled experiments, they are displaced in zero-field-cooled, magnetic-field-ramped experiments, conserving the equidistance of the matching peaks and minima. These observations reveal an unconventional critical state in a cuprate superconductor with an artificial, periodic pinning array. The long-term stability of such out-of-equilibrium vortex arrangements paves the way for electronic applications employing fluxons.

  17. Effect of particle size and particle size distribution on physical characteristics, morphology and crystal strucutre of explosively compacted high-Tc superconductors

    SciTech Connect

    Kotsis, I.; Enisz, M.; Oravetz, D.

    1994-12-31

    A superconductor, of composition Y(Ba,K,Na){sub 2}Cu{sub 3}O{sub x}/F{sub y} and a composite, of composition Y(Ba,K,Na){sub 2}Cu{sub 3}O{sub x}/F{sub y}+Ag, with changing K, Na and F content, but a constant silver content (Ag=10 mass per cent) was prepared using a single heat treatment. The resulting material was ground in a corundum lined mill, separated to particle size fractions of 0-40 {mu}m, 0-63 {mu}m and 63-900 {mu}m and explosively compacted, using an explosive pressure of 10{sup 4} MPa and a subsequent heat treatment. Best results were obtained with the 63-900 {mu}m fraction of composition Y(Ba{sub 1,95}K{sub 0,01})Cu{sub 3}O{sub x}F{sub 0,05}/Ag: porosity <0.01 cm{sup 3}/g and current density 2800 A/cm{sup 2} at 77 K.

  18. High Tc superconductors: The scaling of Tc with the number of bound holes associated with charge transfer neutralizing the multivalence cations

    NASA Technical Reports Server (NTRS)

    Vezzoli, G. C.; Chen, M. F.; Craver, F.

    1991-01-01

    It is observed that for the known high-T(sub c) Cu-, Tl-, and Bi-based superconductors, T(sub c) scales consistently with the number of bound holes per unit cell which arise from charge transfer excitations of frequency approximately = 3 x 10(exp 13) that neutralized the multivalence cations into diamagnetic states. The resulting holes are established on the oxygens. Extrapolation of this empirical fit in the up-temperature direction suggests a T(sub c) of about 220-230 K at a value of 25 holes/unit cell (approximately the maximum that can be materials-engineered into a high-T(sub c) K2MnF4 or triple Perovskite structure). In the down-temperature direction, the extrapolation gives a T(sub c) in the vicinity of 235 K for the Y-Ba-Cu-O system as well as the known maximum temperature of 23 K for low-T(sub c) materials shown by Nb3Ge. The approach is also consistent with the experimental findings that only multivalence ions which are diamagnetic in their atomic state (Cu, Tl, Bi, Pb, and Sb) associate with high-T(sub c) compounds.

  19. Energy Gaps in the Failed High-Tc Superconductor La1.875Ba0.125CuO4

    SciTech Connect

    Not Available

    2011-08-11

    A central issue in high-T{sub c} superconductivity is the nature of the normal-state gap (pseudogap) in the underdoped regime and its relationship with superconductivity. Despite persistent efforts, theoretical ideas for the pseudogap evolve around fluctuating superconductivity, competing order, and spectral weight suppression due to many-body effects. Recently, although some experiments in the superconducting state indicate a distinction between the superconducting gap and pseudogap, others in the normal state, either by extrapolation from high-temperature data or directly from La{sub 1.875)Ba{sub 0.125}CuO{sub 4} (LBCO-1/8) at low temperature, suggest the ground-state pseudogap is a single gap of d-wave form. Here, we report angle-resolved photoemission data from LBCO-1/8, collected with improved experimental conditions, that reveal the ground-state pseudogap has a pronounced deviation from the simple d-wave form. It contains two distinct components: a d-waev component within an extended region around the node and the other abruptly enhanced close to the antinode, pointing to a dual nature of the pseudogap in this failed high-T{sub c} superconductor that involves a possible precursor-pairing energy scale around the node and another of different but unknown origin near the antinode.

  20. A review of electron-phonon coupling seen in the high-Tc superconductors by angle-resolved photoemission studies (ARPES)

    NASA Astrophysics Data System (ADS)

    Cuk, T.; Lu, D. H.; Zhou, X. J.; Shen, Z.-X.; Devereaux, T. P.; Nagaosa, N.

    2005-01-01

    This issue of pss (b) - basic solid state physics contains a collection of Review Articles on the rather controversially discussed topic of Electron-Phonon Interaction in High-Temperature Superconductors, guest-edited by Miodrag Kuli, Johann Wolfgang Goethe-Universität Frankfurt/Main, Germany, with a Preface written by V. L. Ginzburg and E. G. Maksimov [1].The cover picture, taken from the review [2] by T. Cuk et al., shows plots of the electron-phonon coupling vertex, g2(k, k), where k, k are the initial and final electron momentum for electrons scattered by the bond-buckling phonon B1g (the out-of-phase vibration of the in-plane oxygen) in a tight-binding model of the copper-oxygen plane. The momentum dependence of this vertex, along with the d-wave superconducting gap and the van Hove singularity at the anti-node, accounts for the momentum dependence of the collective mode coupling seen in angle-resolved photoemission data on Bi2212.The present issue also sees the start of our rapid research letters, the fastest peer-reviewed publication medium in solid state physics. For more information see www.pss-rapid.com and the Editorial by the Editor-in-Chief Martin Stutzmann on page 7 [3].

  1. NMR Characterization of Sulphur Substitution Effects in the KxFe2−ySe2−zSz High-Tc Superconductor

    SciTech Connect

    Petrovic C.; Torchetti, D.A.; Imai, T.; Lei, H.C.

    2012-04-17

    We present a {sup 77}Se NMR study of the effect of S substitution in the high-T{sub c} superconductor K{sub x}Fe{sub 2-y}Se{sub 2-z}S{sub z} in a temperature range up to 250 K. We examine two S concentrations, with z = 0.8 (T{sub c} {approx} 26 K) and z = 1.6 (nonsuperconducting). The samples containing sulphur exhibit broader NMR line shapes than the K{sub x}Fe{sub 2}Se{sub 2} sample due to local disorder in the Se environment. Our Knight shift {sup 77}K data indicate that in all samples, uniform spin susceptibility decreases with temperature, and that the magnitude of the Knight shift itself decreases with increased S concentration. In addition, S substitution progressively suppresses low-frequency spin fluctuations. None of the samples exhibit an enhancement of low-frequency antiferromagnetic spin fluctuations near T{sub c} in 1/T{sub 1}T, as seen in FeSe.

  2. Imaging studies of hole-electron asymmetry observed in a lightly-doped high-Tc superconductor Ca2-xNaxCuO2Cl2

    NASA Astrophysics Data System (ADS)

    Kohsaka, Yuhki; Hanaguri, Tetsuo; Azuma, Masaki; Takagi, Hidenori; Davis, Seamus

    2005-03-01

    We have reported spectroscopic imaging on the electronic state intervening between the Mott insulator and the d-wave superconductor [1]. The electronic state with |E|<100 meV shows complex spatial modulations with 4a0x4a0 (a0: in-plane lattice constant) correlations. Moreover, the tunneling spectra show characteristic hole-electron asymmetry, which is thought to be related to the approach of the Mott insulator [2]. Here we report on new studies of imaging the 'Mottness' through mapping the asymmetry in tunneling spectra associated with high energies |E|>100 meV. Spectroscopic mapping of the asymmetry reveals strong 4a0x4a0 periodic modulation up to several hundreds meV. However the 4a0/3x4a0/3 component, which appears in the Fourier transform of the checkerboard pattern observed at |E|<100 meV, is negligle. This spatial modulation of the 'Mottness' may indicate that hole density is modulated with the 4a0x4a0 periodicity. This would imply that the 4a0/3x4a0/3 periodicity observed at lower energies may arise from umklapp scattering due to the hole density modulation. [1] T. Hanaguri et al., Nature 430, 1001 (2004). [2] P. W. Anderson and N. P. Ong, cond-mat/0405518.

  3. 77Se NMR Investigation of the KxFe2−ySe2 high-Tc Superconductor (Tc = 33 K)

    SciTech Connect

    Petrovic, C.; Torchetti, D.A. Fu, M.; Christensen, D.C.; Nelson, K.J.; Imai, T.; Lei, H.C.

    2011-03-18

    We report comprehensive {sup 77}Se NMR measurements on a single crystalline sample of the recently discovered FeSe-based high-temperature superconductor K{sub x}Fe{sub 2-y}Se{sub 2} (T{sub c} = 33 K) in a broad temperature range up to 290 K. Despite deviations from the stoichiometric KFe{sub 2}Se{sub 2} composition, we observed {sup 77}Se NMR line shapes as narrow as 4.5 kHz under a magnetic field applied along the crystal c axis, and found no evidence for co-existence of magnetic order with superconductivity. On the other hand, the {sup 77}Se NMR line shape splits into two peaks with equal intensities at all temperatures when we apply the magnetic field along the ab plane. This suggests that K vacancies may have a superstructure and that the local symmetry of the Se sites is lower than the tetragonal fourfold symmetry of the average structure. This effect might be a prerequisite for stabilizing the s{sub {+-}} symmetry of superconductivity in the absence of the hole bands at the Brillouin zone center. From the increase of NMR linewidth below T{sub c} induced by the Abrikosov lattice of superconducting vortices, we estimate the in-plane penetration depth {lambda}{sub ab} {approx} 290 nm and the carrier concentration n{sub e} {approx} 1 x 10{sup +21} cm{sup -3}. Our Knight shift {sup 77}K data indicate that the uniform spin susceptibility decreases progressively with temperature, in analogy with the case of FeSe (T{sub c} {approx} 9 K) as well as other FeAs high-T{sub c} systems. The strong suppression of {sup 77}K observed immediately below T{sub c} for all crystal orientations is consistent with a singlet pairing of Cooper pairs. We do not however observe the Hebel-Slichter coherence peak of the nuclear spin-lattice relaxation rate 1/T1 immediately below T{sub c}, expected for conventional BCS s-wave superconductors. In contrast with the case of FeSe, we do not observe evidence for an enhancement of low-frequency antiferromagnetic spin fluctuations near T{sub c

  4. Nernst effect in the electron-doped cuprate superconductor Pr2-xCexCuO4: Superconducting fluctuations, upper critical field Hc2, and the origin of the Tc dome

    NASA Astrophysics Data System (ADS)

    Tafti, F. F.; Laliberté, F.; Dion, M.; Gaudet, J.; Fournier, P.; Taillefer, Louis

    2014-07-01

    The Nernst effect was measured in the electron-doped cuprate superconductor Pr2-xCexCuO4 (PCCO) at four concentrations, from underdoped (x =0.13) to overdoped (x=0.17), for a wide range of temperatures above the critical temperature Tc. A magnetic field H up to 15 T was used to reliably access the normal-state quasiparticle contribution to the Nernst signal Nqp, which is subtracted from the total signal N, to obtain the superconducting contribution Nsc. As a function of H, Nsc peaks at a field H whose temperature dependence obeys Hc2ln(T /Tc), as it does in a conventional superconductor such as NbxSi1-x. The doping dependence of the characteristic field scale Hc2, shown to be closely related to the upper critical field Hc2, tracks the domelike dependence of Tc, showing that superconductivity is weakened below the quantum critical point where the Fermi surface is reconstructed, presumably by the onset of antiferromagnetic order. Our data at all dopings are quantitatively consistent with the theory of Gaussian superconducting fluctuations, eliminating the need to invoke unusual vortexlike excitations above Tc, and ruling out phase fluctuations as the mechanism for the fall of Tc with underdoping. We compare the properties of PCCO with those of hole-doped cuprates and conclude that the domes of Tc and Hc2 versus doping in the latter materials are also controlled predominantly by phase competition rather than phase fluctuations.

  5. High-{Tc} rf SQUID magnetometers

    SciTech Connect

    Mueck, M.

    1994-12-31

    The discovery of high temperature superconductors has revived the interest in rf SQUIDS, which, in the case of conventional superconductors had been surpassed in performance by the dc SQUID. Several advantages are offered by the rf SQUID, like the requirement for only a single weak link and a low 1/f noise. With high bias frequencies (> 100 MHz) it is possible to obtain flux noise values comparable to dc SQUIDS. At present, HTS rf SQUIDs offer a field sensitivity of less than 100 fT/{radical}Hz ({at} 1 Hz). This is already sufficient for a number of serious applications. This paper reviews recent developments towards practical rf SQUIDs made of high-{Tc} superconductors.

  6. EPR, magnetization, and resistivity studies in doped (4-f or 3-d ions) and undoped RBa2Cu3Oy high TC superconductors (R=Y,Pr,Nd,Eu,Gd,Ho,Er, or Yb) (abstract)

    NASA Astrophysics Data System (ADS)

    Vier, D. C.; Smyth, J. F.; Salling, C. T.; Schultz, S.; Dalichaouch, Y.; Lee, B. W.; Yang, K. N.; Torikachvili, M.; Maple, M. B.; Oseroff, S. B.; Fisk, Z.; Thompson, J. D.; Smith, J. L.; Zirngiebl, E.

    1988-04-01

    We have measured electron paramagnetic resonance (EPR), resistivity, and dc susceptibility from 2 to 300 K for the oxide high Tc superconductors (R)Ba2Cu3Oy (R=Y,Pr,Nd,Eu,Gd,Ho,Er,Tm, or Yb). Selected systems were doped with 3-d ions (Cr,Mn,Fe,Ni,Co, or Zn) or 4-f ions (Gd or Er) which presumably substitute for the Cu or R site, respectively. In the systems studied we have observed an EPR line at low temperatures (T<40 K), which exhibits an increase in intensity and decrease in field for resonance as the temperature is lowered. The ESR linewidth is also temperature dependent and exhibits a minimum at about 15 K. An additional EPR line that can be associated with a Gd3+, Mn2+ or Er3+ ion was observed for those samples where these ions were present as dilute impurities. In some of the samples another EPR signal is observed with properties that depend on sample preparation conditions. The behavior and origin of all lines will be discussed. The variation of Tc with concentration of the added impurities over the range (1%-15%) will also be presented, and compared with previous studies in other superconducting systems.

  7. Role of the upper branch of the hour-glass magnetic spectrum in the formation of the main kink in the electronic dispersion of high-Tc cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Geffroy, Dominique; Chaloupka, Jiří; Dahm, Thomas; Munzar, Dominik

    2016-04-01

    We investigate the electronic dispersion of the high-Tc cuprate superconductors using the fully self-consistent version of the phenomenological model, where charge planar quasiparticles are coupled to spin fluctuations. The inputs we use, the underlying (bare) band structure and the spin susceptibility χ , are extracted from fits of angle-resolved photoemission and inelastic neutron scattering data of underdoped YBa2Cu3O6.6 by T. Dahm and coworkers [Nat. Phys. 5, 217 (2009), 10.1038/nphys1180]. Our main results are as follows: (i) We have confirmed the finding by Dahm and coworkers that the main nodal kink is, for the present values of the input parameters, determined by the upper branch of the hourglass of χ . We demonstrate that the properties of the kink depend qualitatively on the strength of the charge-spin coupling. (ii) The effect of the resonance mode of χ on the electronic dispersion strongly depends on its kurtosis in the quasimomentum space. A low (high) kurtosis implies a negligible (considerable) effect of the mode on the dispersion in the near-nodal region. (iii) The energy of the kink decreases as a function of the angle θ between the Fermi surface cut and the nodal direction, in qualitative agreement with recent experimental observations. We clarify the trend and make a specific prediction concerning the angular dependence of the kink energy in underdoped YBa2Cu3O6.6 .

  8. Gauge Model of High-Tc Superconductivity

    NASA Astrophysics Data System (ADS)

    Kui Ng, Sze

    2012-12-01

    A simple gauge model of superconductivity is presented. The seagull vertex term of this gauge model gives an attractive potential between electrons for the forming of Cooper pairs of superconductivity. This gauge model gives a unified description of superconductivity and magnetism including antiferromagnetism, pseudogap phenomenon, stripes phenomenon, paramagnetic Meissner effect, Type I and Type II supeconductivity and high-Tc superconductivity. The doping mechanism of superconductivity is found. It is shown that the critical temperature Tc is related to the ionization energies of elements and can be computed by a formula of Tc. For the high-Tc superconductors such as La2-xSrxCuO4, Y Ba2Cu3O7, and MgB2, the computational results of Tc agree with the experimental results.

  9. Fabrication Of High-Tc Superconducting Integrated Circuits

    NASA Technical Reports Server (NTRS)

    Bhasin, Kul B.; Warner, Joseph D.

    1992-01-01

    Microwave ring resonator fabricated to demonstrate process for fabrication of passive integrated circuits containing high-transition-temperature superconductors. Superconductors increase efficiencies of communication systems, particularly microwave communication systems, by reducing ohmic losses and dispersion of signals. Used to reduce sizes and masses and increase aiming accuracies and tracking speeds of millimeter-wavelength, electronically steerable antennas. High-Tc superconductors preferable for such applications because they operate at higher temperatures than low-Tc superconductors do, therefore, refrigeration systems needed to maintain superconductivity designed smaller and lighter and to consume less power.

  10. Energy dependence of the electron-boson coupling strength in the electron-doped cuprate superconductor Pr1.85Ce0.15CuO4 -δ

    NASA Astrophysics Data System (ADS)

    Beck, M.; Klammer, M.; Rousseau, I.; Obergfell, M.; Leiderer, P.; Helm, M.; Kabanov, V. V.; Diamant, I.; Rabinowicz, A.; Dagan, Y.; Demsar, J.

    2017-02-01

    The quest for a pairing boson in cuprate high-temperature superconductors is one of the outstanding tasks of solid-state physics. Numerous time-resolved studies of pair breaking, related to pairing by time-reversal symmetry, have been performed using femtosecond optical pulses. By considering energy relaxation pathways between charge, spin, and lattice degrees of freedom, evidence for both phonon and antiferromagnetic fluctuation-mediated pairing has been obtained. Here we present a study of the superconducting-state depletion process in an electron-doped cuprate Pr1.85Ce0.15CuO4 -δ , where the superconducting gap is smaller than the energy of relevant bosonic excitations. When pumping with above-gap terahertz pulses, we find that the absorbed energy density required to deplete superconductivity, Adep, matches the thermodynamic condensation energy. On the contrary, by near-infrared pumping, Adep is an order of magnitude higher, as in the case of hole-doped, large-gap cuprates. These results imply that only a small subset of bosons, which are generated during the relaxation of optically excited carriers, contributes to pairing. This observation implies that, contrary to the common assumptions, electron-boson coupling in cuprates is strongly energy dependent.

  11. Phase diagrams for high Tc superconductors

    SciTech Connect

    Whitler, J.D.; Roth, R.S. NIST, Gaithersburg, MD )

    1991-01-01

    The phase diagrams of ternary and quaternary systems containing superconducting phases are presented, as are the phase diagrams of the associated binary systems. The diagrams are divided into two large groups: (1) alkaline earth-rare earth-copper-oxygen diagrams, and (2) alkaline earth-bismuth/lead-copper-oxygen diagrams. The first group includes BaO-REO-CuO systems followed by SrO-REO-CuO or Nd2O3-CeO-CuO systems. The second group includes systems related to the AE-Bi2O3-CuO and AE-PbO-CuO systems. The phase diagrams are accompanied by notes relating procedures used in the studies, results obtained, and comparisons with the results in the literature for the same system.

  12. EM Properties of High Tc Superconductors

    DTIC Science & Technology

    1992-06-01

    those calculated by Kes and van den Berg’ 9 for pinning 12A. M. CamDbell and J. Evetts, Adv. Phys. 21. 199 (1972). by twin boundaries . Our...consstet wih dnsey poulaed pnni 9~nter. ao ’J. Clem, in Proceedings of the International Conf’erence on pinning due to twin boundaries is Unlikely to be the

  13. STM tunneling spectroscopy on high Tc superconductors

    SciTech Connect

    Hasegawa, T.; Nantoh, M.; Ogino, M.

    1995-08-01

    STM tunneling spectroscopy has been performed on the bulk single crystals of BiSrCaCuO (BSCCO) and the epitaxial thin films of YBaCuO (YBCO) at cryogenic temperatures. The STM images and tunneling spectra observed on the (001) surfaces can be classified into three cases; (1) Atomic image is visible. However, the tunneling spectrum shows semiconducting or smeared superconducting gap structures, depending on the tip-sample distance. (2) Clear atomic image can be obtained. But, the tunneling spectrum shows flat bottom region with quite low zero bias conductance. (3) Tunneling spectra demonstrate gapless behavior, independent of the tip-sample separation. These observations support the quasi-2D electronic picture in which s-wave like 2D superconducting layers are coupled with each other through the Josephson effect.

  14. Heavy electron doping induced antiferromagnetic phase as the parent for the iron oxypnictide superconductor LaFeAs O1 -xHx

    NASA Astrophysics Data System (ADS)

    Iimura, Soshi; Matsuishi, Satoru; Hosono, Hideo

    2016-07-01

    We perform transport measurements and band structure calculations of electron-doped LaFeAs O1 -xHx over a wide range of x from 0.01 to 0.66. The T2 and √ T dependency of the resistivity are observed at x ˜0.17 and 0.41, respectively. The sign change of RH without opening of the spin-density-wave gap for 0.45 ≤x ≤0.58 and T

  15. Quantum spin correlations through the superconducting-to-normal phase transition in electron-doped superconducting Pr0.88LaCe0.12CuO4-δ

    PubMed Central

    Wilson, Stephen D.; Li, Shiliang; Zhao, Jun; Mu, Gang; Wen, Hai-Hu; Lynn, Jeffrey W.; Freeman, Paul G.; Regnault, Louis-Pierre; Habicht, Klaus; Dai, Pengcheng

    2007-01-01

    The quantum spin fluctuations of the S = 1/2 Cu ions are important in determining the physical properties of high-transition-temperature (high Tc) copper oxide superconductors, but their possible role in the electron pairing of superconductivity remains an open question. The principal feature of the spin fluctuations in optimally doped high-Tc superconductors is a well defined magnetic resonance whose energy (ER) tracks Tc (as the composition is varied) and whose intensity develops like an order parameter in the superconducting state. We show that the suppression of superconductivity and its associated condensation energy by a magnetic field in the electron-doped high-Tc superconductor Pr0.88LaCe0.12CuO4-δ (Tc = 24 K), is accompanied by the complete suppression of the resonance and the concomitant emergence of static antiferromagnetic order. Our results demonstrate that the resonance is intimately related to the superconducting condensation energy, and thus suggest that it plays a role in the electron pairing and superconductivity. PMID:17884981

  16. Gate-tuned superconductor-insulator transition in (Li,Fe)OHFeSe

    NASA Astrophysics Data System (ADS)

    Lei, B.; Xiang, Z. J.; Lu, X. F.; Wang, N. Z.; Chang, J. R.; Shang, C.; Zhang, A. M.; Zhang, Q. M.; Luo, X. G.; Wu, T.; Sun, Z.; Chen, X. H.

    2016-02-01

    The antiferromagnetic (AFM) insulator-superconductor transition has always been a center of interest in the underlying physics of unconventional superconductors. However, in the family of iron-based high-Tc superconductors, no intrinsic superconductor-insulator transition has been confirmed so far. Here, we report a first-order transition from superconductor to AFM insulator with a strong charge doping induced by ionic gating in the thin flakes of single crystal (Li,Fe)OHFeSe. The superconducting transition temperature (Tc) is continuously enhanced with electron doping by ionic gating up to a maximum Tc of 43 K, and a striking superconductor-insulator transition occurs just at the verge of optimal doping with highest Tc. A phase diagram of temperature-gating voltage with the superconductor-insulator transition is mapped out, indicating that the superconductor-insulator transition is a common feature for unconventional superconductivity. These results help to uncover the underlying physics of iron-based superconductivity as well as the universal mechanism of high-Tc superconductivity. Our finding also suggests that the gate-controlled strong charge doping makes it possible to explore novel states of matter in a way beyond traditional methods.

  17. Phase diagram of the electron-doped La2-xCexCuO4 cuprate superconductor from Andreev bound states at grain boundary junctions.

    PubMed

    Wagenknecht, M; Koelle, D; Kleiner, R; Graser, S; Schopohl, N; Chesca, B; Tsukada, A; Goennenwein, S T B; Gross, R

    2008-06-06

    We use quasiparticle tunneling across La2-xCexCuO4 grain boundary junctions to probe the superconducting state and its disappearance with increasing temperature and magnetic field. A zero bias conductance peak due to zero energy surface Andreev bound states is a clear signature of the phase coherence of the superconducting state. Hence, such a peak must disappear at or below the upper critical field Bc2(T). For La2-xCexCuO4 this approach sets a lower bound for Bc2(0) approximately 25 T which is substantially higher than reported previously. The method of probing the superconducting state via Andreev bound states should also be applicable to other cuprate superconductors.

  18. Analysis and characterization of high- Tc superconducting planar transmission lines for microwave circuit components

    SciTech Connect

    Kong Keonshik.

    1991-01-01

    A loss modeling of high {Tc} superconducting planar transmission lines is presented in this dissertation. Transmission structures such as microstrip lines, coplanar waveguides and conductor backed coplanar waveguides are investigated for implementation of a high-{Tc} superconductor. Also, short pulse propagation in the superconducting coplanar stripline is characterized. The motivation for this work is to provide an analytical basis for the effective application of a high {Tc} superconductor to planar transmission lines for microwave components. First, a loss characterization of the various high {Tc} superconducting microstrip line structures is presented in which either the strip or the ground plane is a high {Tc} superconductor. In the analysis, the internal impedances in the strip and the ground plane are separately calculated, and the total internal impedance is obtained by the superposition of the internal impedances. Next, the characteristic of a superconducting coplanar waveguide is investigated and compared with a superconducting microstrip line.

  19. High-Tc SQUID biomagnetometers

    NASA Astrophysics Data System (ADS)

    Faley, M. I.; Dammers, J.; Maslennikov, Y. V.; Schneiderman, J. F.; Winkler, D.; Koshelets, V. P.; Shah, N. J.; Dunin-Borkowski, R. E.

    2017-08-01

    In this paper, we review the preparation technology, integration in measurement systems and tests of high-Tc superconducting quantum interference devices (SQUIDs) intended for biomagnetic applications. A focus is on developments specific to Forschungszentrum Jülich GmbH, Chalmers University of Technology, MedTech West, and the University of Gothenburg, while placing these results in the perspective of those achieved elsewhere. Sensor fabrication, including the deposition and structuring of epitaxial oxide heterostructures, materials for substrates, epitaxial bilayer buffers, bicrystal and step-edge Josephson junctions, and multilayer flux transformers are detailed. The properties of the epitaxial multilayer high-Tc direct current SQUID sensors, including their integration in measurement systems with special electronics and liquid nitrogen cryostats, are presented in the context of biomagnetic recording. Applications that include magnetic nanoparticle based molecular diagnostics, magnetocardiography, and magnetoencephalography are presented as showcases of high-Tc biomagnetic systems. We conclude by outlining future challenges.

  20. High Tc superconducting materials and devices

    NASA Technical Reports Server (NTRS)

    Haertling, Gene H.

    1990-01-01

    The high Tc Y1Ba2Cu3O(7-x) ceramic materials, initially developed in 1987, are now being extensively investigated for a variety of engineering applications. The superconductor applications which are presently identified as of most interest to NASA-LaRC are low-noise, low thermal conductivity grounding links; large-area linear Meissner-effect bearings; and sensitive, low-noise sensors and leads. Devices designed for these applications require the development of a number of processing and fabrication technologies. Included among the technologies most specific to the present needs are tapecasting, melt texturing, magnetic field grain alignment, superconductor/polymer composite fabrication, thin film MOD (metal-organic decomposition) processing, screen printing of thick films, and photolithography of thin films. The overall objective of the program was to establish a high Tc superconductivity laboratory capability at NASA-LaRC and demonstrate this capability by fabricating superconducting 123 material via bulk and thin film processes. Specific objectives include: order equipment and set up laboratory; prepare 1 kg batches of 123 material via oxide raw material; construct tapecaster and tapecaster 123 material; fabricate 123 grounding link; fabricate 123 composite for Meissner linear bearing; develop 123 thin film processes (nitrates, acetates); establish Tc and Jc measurement capability; and set up a commercial use of space program in superconductivity at LaRC. In general, most of the objectives of the program were met. Finally, efforts to implement a commercial use of space program in superconductivity at LaRC were completed and at least two industrial companies have indicated their interest in participating.

  1. High Tc superconducting materials and devices

    NASA Astrophysics Data System (ADS)

    Haertling, Gene H.

    1990-09-01

    The high Tc Y1Ba2Cu3O(7-x) ceramic materials, initially developed in 1987, are now being extensively investigated for a variety of engineering applications. The superconductor applications which are presently identified as of most interest to NASA-LaRC are low-noise, low thermal conductivity grounding links; large-area linear Meissner-effect bearings; and sensitive, low-noise sensors and leads. Devices designed for these applications require the development of a number of processing and fabrication technologies. Included among the technologies most specific to the present needs are tapecasting, melt texturing, magnetic field grain alignment, superconductor/polymer composite fabrication, thin film MOD (metal-organic decomposition) processing, screen printing of thick films, and photolithography of thin films. The overall objective of the program was to establish a high Tc superconductivity laboratory capability at NASA-LaRC and demonstrate this capability by fabricating superconducting 123 material via bulk and thin film processes. Specific objectives include: order equipment and set up laboratory; prepare 1 kg batches of 123 material via oxide raw material; construct tapecaster and tapecaster 123 material; fabricate 123 grounding link; fabricate 123 composite for Meissner linear bearing; develop 123 thin film processes (nitrates, acetates); establish Tc and Jc measurement capability; and set up a commercial use of space program in superconductivity at LaRC. In general, most of the objectives of the program were met. Finally, efforts to implement a commercial use of space program in superconductivity at LaRC were completed and at least two industrial companies have indicated their interest in participating.

  2. Graphoepitaxial high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Faley, M. I.; Meertens, D.; Poppe, U.; Dunin-Borkowski, R. E.

    2014-05-01

    The fabrication process and physical properties of graphoepitaxially engineered high-Tc direct current superconducting quantum interferometer devices (DC SQUIDs) are studied. Double buffer layers, each comprising a graphoepitaxial seed layer of YBa2Cu3O7-x and an epitaxial blocking layer of SrTiO3, were deposited over textured step edges on (001) surfaces of MgO substrates. Scanning electron microscopy and high-resolution transmission electron microscopy were used to investigate the microstructural properties of DC SQUIDs with graphoepitaxial Josephson junctions. Both direct coupled and inductively coupled high-Tc DC SQUIDs with graphoepitaxial step edge junctions and flux transformers were studied.

  3. Enhanced charge excitations in electron-doped cuprates by resonant inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Tohyama, Takami; Tsutsui, Kenji; Mori, Michiyasu; Sota, Shigetoshi; Yunoki, Seiji

    2015-07-01

    Resonant inelastic x-ray scattering (RIXS) tuned for the Cu L edge is a possible tool to detect charge excitations in cuprate superconductors. We theoretically investigate the possibility for observing a collective charge excitation by the RIXS. The RIXS process via the intermediate state inevitably makes the spectral weight of charge excitation stronger in electron doping than in hole doping. Electron-hole asymmetry also appears in the dynamical charge structure factor, showing a new enhanced small-momentum low-energy mode in electron doping. These facts indicate a possibility of detecting the new charge mode by RIXS in electron-doped systems.

  4. Research on high Tc superconducting compounds

    NASA Technical Reports Server (NTRS)

    Oliver, Frederick W. (Principal Investigator)

    1996-01-01

    Mossbauer research using the 21.54 kev resonance radiation of Eu-151 on the high temperature superconductors Bi(2)Ca(0.5)Eu(0.5)Sr(2)CU2O(x), and EuBa(2)CU(3)O(7-x) is performed. For the Bismuth compound the Mossbauer measurements gave a weak signal at room temperature but improved at lower temperatures. Experimental data indicated that europium is located at only one crystallographic site. Isomer shift measurements were .69 + 0.02 mm/s with respect to EuF(3). The linewidth at room temperature was found to be 2.54 mm/s. This value falls within the values observed by other researchers on Eu based 1,2,3 high-Tc compounds. Our results also show the Eu to be trivalent with no trace of divalent europium present. Superconducting europium based 1,2,3 compounds were prepared and measurements completed. Our results show the Eu to be trivalent with no trace of divalent europium present. These compounds had an average isomer shift of .73 mm/s +/- O.02 for all samples made. One of these was irradiated with 3.5 X 10(exp 16) neutrons and a comparison made of the Mossbauer parameters for the irradiated and non-irradiated samples. Experimental results showed no difference between linewidths but a measurable effect was seen for the isomer shift.

  5. Mechanical resonance characteristics of a high-{Tc} superconducting levitation system

    SciTech Connect

    Sugiura, Toshihiko; Fujimori, Hideki

    1996-05-01

    This research deals with dynamic response of a permanent magnet freely levitated above an excited high-{Tc} superconductor. Evaluation of dynamic characteristics is required in mechanical design of high-{Tc} superconducting levitation systems. Their dynamics is coupled with Type-II superconducting phenomena. By a numerical approach based on some macroscopic models they evaluate mechanical resonance characteristics of a superconducting levitation system. Numerical results show some nonlinear properties and effect of the flux flow in Type-II superconductor, which are observed in experiments or predicted by analyses.

  6. Layer-engineering of high-Tc superconductors: (Cu,Mo)Sr2(Ce,Y)4Cu2O13+delta with a quadruple-fluorite-layer block between CuO2 planes.

    PubMed

    Grigoraviciute, Inga; Yamauchi, Hisao; Karppinen, Maarit

    2007-03-07

    Among high-Tc superconductive copper oxides, there have been known phases that contain fluorite-structured layers as an additional "blocking block" between adjacent CuO2 planes. Here, we report that even a phase with the CuO2 planes separated by a 12-A thick quadruple-fluorite-layer block can be synthesized in a single phase and strongly oxygenated form to exhibit superconductivity with a Tc value as high as 55 K. The new phase is the fourth member of the (Cu,Mo)Sr2(Ce,Y)sCu2O(5+2s+delta) or (Cu,Mo)-12s2 homologous series. Comparison with the previously known s = 1, 2, and 3 members of the series reveals the amazing conclusion that Tc remains essentially unaffected upon inserting additional fluorite-structured layers between the two CuO2 planes as long as the hole-doping level of the planes is kept constant.

  7. Structural and superconducting properties of co-doped YBa2-xLaxCu3-xMxOz and La-free YBa2Cu3-xMxOz (M = Al, Zn) high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Hao, S. J.; Jin, W. T.; Guo, C. Q.; Zhang, H.

    2012-05-01

    Two co-doped high-Tc superconducting systems, YBa2-xLaxCu3-xAlxOz and YBa2-xLaxCu3-xZnxOz (0 ⩽ x ⩽ 0.3), both of which have not been reported up to the present, were synthesized. The structural and superconducting properties have been investigated by X-ray diffraction (XRD) and DC magnetization measurement. Comparing the properties of these co-doped systems with single-doped systems YBa2Cu3-xAlxOz and YBa2Cu3-xZnxOz, it shows that in the Al-single-doped YBCO system, the depression of the critical temperature (Tc) with doping is stronger than that in (La, Al)-co-doped system, however, in the Zn-single-doped system, the Tc descends slower than that in (La, Zn)-co-doped system. This is possibly due to the opposite change of the distance between the Ba site and the CuO2 plane induced by the La doping. Besides, the La doping has another effect of improving the solid solubility compared with the Al- or Zn-single-doped system.

  8. Applications using high-Tc superconducting terahertz emitters

    NASA Astrophysics Data System (ADS)

    Nakade, Kurama; Kashiwagi, Takanari; Saiwai, Yoshihiko; Minami, Hidetoshi; Yamamoto, Takashi; Klemm, Richard A.; Kadowaki, Kazuo

    2016-03-01

    Using recently-developed THz emitters constructed from single crystals of the high-Tc superconductor Bi2Sr2CaCu2O8+δ, we performed three prototype tests of the devices to demonstrate their unique characteristic properties for various practical applications. The first is a compact and simple transmission type of THz imaging system using a Stirling cryocooler. The second is a high-resolution Michelson interferometer used as a phase-sensitive reflection-type imaging system. The third is a system with precise temperature control to measure the liquid absorption coefficient. The detailed characteristics of these systems are discussed.

  9. Applications using high-Tc superconducting terahertz emitters

    PubMed Central

    Nakade, Kurama; Kashiwagi, Takanari; Saiwai, Yoshihiko; Minami, Hidetoshi; Yamamoto, Takashi; Klemm, Richard A.; Kadowaki, Kazuo

    2016-01-01

    Using recently-developed THz emitters constructed from single crystals of the high-Tc superconductor Bi2Sr2CaCu2O8+δ, we performed three prototype tests of the devices to demonstrate their unique characteristic properties for various practical applications. The first is a compact and simple transmission type of THz imaging system using a Stirling cryocooler. The second is a high-resolution Michelson interferometer used as a phase-sensitive reflection-type imaging system. The third is a system with precise temperature control to measure the liquid absorption coefficient. The detailed characteristics of these systems are discussed. PMID:26983905

  10. Experimental evidence for importance of Hund's exchange interaction for incoherence of charge carriers in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Fink, J.; Rienks, E. D. L.; Thirupathaiah, S.; Nayak, J.; van Roekeghem, A.; Biermann, S.; Wolf, T.; Adelmann, P.; Jeevan, H. S.; Gegenwart, P.; Wurmehl, S.; Felser, C.; Büchner, B.

    2017-04-01

    Angle-resolved photoemission spectroscopy is used to study the scattering rates of charge carriers from the hole pockets near Γ in the iron-based high-Tc hole-doped superconductors KxBa1 -xFe2As2 , x =0.4 , and KxEu1 -xFe2As2 , x =0.55 , and the electron-doped compound Ba (Fe1-xCox) 2As2 , x =0.075 . The scattering rate for any given band is found to depend linearly on the energy, indicating a non-Fermi-liquid regime. The scattering rates in the hole-doped compound are considerably higher than those in the electron-doped compounds. In the hole-doped systems the scattering rate of the charge carriers of the inner hole pocket is about three times higher than the binding energy, indicating that the spectral weight is heavily incoherent. The strength of the scattering rates and the difference between electron- and hole-doped compounds signals the importance of Hund's exchange coupling for correlation effects in these iron-based high-Tc superconductors. The experimental results are in qualitative agreement with theoretical calculations in the framework of combined density functional dynamical mean-field theory.

  11. High-{Tc} superconducting superlattices

    SciTech Connect

    Wood, R.F.

    1993-06-01

    Superlattices composed of YBa{sub 2}CU{sub 3}O{sub 7} and PrBa{sub 2}Cu{sub 3}O{sub 7} have been studied extensively experimentally and several theoretical attempts to correlate the resistivity as a function of temperature with the superlattice structure have appeared in the literature. The theoretical interest in such structures comes about primarily because of insight into dimensionality effects, interlayer coupling, and interlayer charge redistribution in high-T {sub c}, superconductors. On the experimental side, there are possibilities for device applications that are just now beginning to be explored. After an overview of the experimental work and a discussion of charge transfer calculations, a description of how the experimental data can be explained using a model that incorporates Kosterlitz-Thouless (vortex-antivortex unbinding) and Azlamazov-Larkin (fluctuation-enhanced conductivity) theories in the resistive transition region and charge-transfer effects, variable-range hopping, etc. in the normal state. Difficulty in disentangling charge transfer and dimensionality effects in determining the nominal transition temperature is pointed out and other mechanisms that influence the width of the resistive transition are considered.

  12. Modulation effect of interlayer spacing on the superconductivity of electron-doped FeSe-based intercalates.

    PubMed

    Hayashi, Fumitaka; Lei, Hechang; Guo, Jiangang; Hosono, Hideo

    2015-04-06

    FeSe-based intercalates are regarded as promising candidates for high-critical temperature (Tc) superconductors. Here we present new Na- and Sr-intercalated FeSe superconductors with embedded linear diamines (H2N)CnH2n(NH2) (abbreviated as DA; n = 0, 2, 3, or 6) prepared using a low-temperature ammonothermal method to investigate the effect of interlayer spacing on the superconductivity of electron-doped FeSes. The embedded DA formed a monolayer or bilayer in the interlayer of FeSe. The interlayer spacing between nearest FeSe layers could be tuned from 0.87 to 1.14 nm without significant change in the Na/Sr content or the ratio of Fe to Se. Importantly, bilayer phases Na/ethylenediamine- and Sr/hydrazine-FeSe show improved structural stability compared to that of Na/NH3-FeSe. The series of Na- and Sr-intercalated FeSe samples exhibited nearly the same high Tc values of 41-46 and 34-38 K, respectively, irrespective of rather different interlayer spacing d. The peculiar insensitivity for both series can be ascribed to the negligible dispersions of bands along the c axis; i.e., Fermi surfaces are nearly two-dimensional when d is larger than a certain threshold value (dsat) of ∼0.9 nm. The Fermi surface shape is already optimal for Tc, and a larger d will not enhance Tc further. On the other hand, the difference in Tc between two series may be explained by the higher carrier doping level in Na/DA-FeSes compared to that in Sr/DA-FeSes, resulting in the increased density of states at the Fermi level and superconducting pairing strength.

  13. Role of hydrogen in the electronic properties of CaFeAsH-based superconductors

    NASA Astrophysics Data System (ADS)

    Huang, Y. N.; Liu, D. Y.; Zou, L. J.; Pickett, W. E.

    2016-05-01

    The electronic and magnetic properties of the hydride superconductor CaFeAsH, which superconducts up to 47 K when electron doped with La, and the isovalent alloy system CaFeAsH1 -xFx are investigated using density functional based methods. The Q ⃗=(π ,π ,0 ) peak of the nesting function ξ (q ⃗) is found to be extremely strong and sharp, and the additional structure in ξ (q ⃗) associated with the near-circular Fermi surfaces (FSs) that may impact low energy excitations is quantified. The unusual band introduced by H, which shows strong dispersion perpendicular to the FeAs layers, is shown to be connected to a peculiar van Hove singularity just below the Fermi level. This band provides a three-dimensional electron ellipsoid Fermi surface not present in other Fe-based superconducting materials nor in CaFeAsF. Electron doping by 25% La or Co has a minor effect on this ellipsoid Fermi surface, but suppresses FS nesting strongly, consistent with the viewpoint that eliminating strong nesting and the associated magnetic order allows high Tc superconductivity to emerge. Various aspects of the isovalent alloy system CaFeAsH1 -xFx and means of electron doping are discussed in terms of influence of incipient bands.

  14. Optical and Hall conductivities of a thermally disordered two-dimensional spin-density wave : two-particle response in the pseudogap regime of electron-doped high-T{sub c} superconductors.

    SciTech Connect

    Lin, J.; Millis, A. J.

    2011-03-18

    We calculate the frequency-dependent longitudinal ({sigma}{sub xx}) and Hall ({sigma}{sub xy}) conductivities for two-dimensional metals with thermally disordered antiferromagnetism using a generalization of a theoretical model, involving a one-loop quasistatic fluctuation approximation, which was previously used to calculate the electron self-energy. The conductivities are calculated from the Kubo formula, with current vertex function treated in a conserving approximation satisfying the Ward identity. In order to obtain a finite dc limit, we introduce phenomenologically impurity scattering, characterized by a relaxation time {tau}. {sigma}{sub xx}({Omega}) satisfies the f-sum rule. For the infinitely peaked spin-correlation function, {chi}(q){proportional_to}{delta}(q-Q), we recover the expressions for the conductivities in the mean-field theory of the ordered state. When the spin-correlation length {zeta} is large but finite, both {sigma}{sub xx} and {sigma}{sub xy} show behaviors characteristic of the state with long-range order. The calculation runs into difficulty for {Omega} {approx}< 1/{tau}. The difficulties are traced to an inaccurate treatment of the very-low-energy density of states within the one-loop quasistatic approximation for the self-energy. The results for {sigma}{sub xx}({Omega}) and {sigma}{sub xy}({Omega}) are qualitatively consistent with data on electron-doped cuprates when {Omega} > 1/{tau}.

  15. Five Possible Reasons why HIGH-Tc Superconductivity is Stalled

    NASA Astrophysics Data System (ADS)

    Grether, M.; de Llano, M.

    Five commonly held premises considered questionable assumptions in the microscopic theory of superconductivity are discussed as possible reasons why the search appears to be stalled for a theoretical framework, admittedly ambitious, capable of predicting materials with critical temperatures Tc higher than the 1993 record of 164K in HgTlBaCaCuO (under pressure). We focus the dilemma as a whole in terms of a generalized Bose-Einstein condensation (GBEC) interpretation that includes and further extends BCS theory, as well as substantially enhancing its predicted Tcs within the electron-phonon mechanism producing pairing. The new GBEC model is an extension of the Friedberg-T.D. Lee 1989 boson-fermion BEC theory of high-Tc superconductors in that it includes hole pairs as well as electron pairs.

  16. Five Possible Reasons why HIGH-Tc Superconductivity is Stalled

    NASA Astrophysics Data System (ADS)

    Grether, M.; de Llano, M.

    2007-09-01

    Five commonly held premises considered questionable assumptions in the microscopic theory of superconductivity are discussed as possible reasons why the search appears to be stalled for a theoretical framework, admittedly ambitious, capable of predicting materials with critical temperatures Tc higher than the 1993 record of 164K in HgTlBaCaCuO (under pressure). We focus the dilemma as a whole in terms of a generalized Bose-Einstein condensation (GBEC) interpretation that includes and further extends BCS theory, as well as substantially enhancing its predicted Tcs within the electron-phonon mechanism producing pairing. The new GBEC model is an extension of the Friedberg-T.D. Lee 1989 boson-fermion BEC theory of high-Tc superconductors in that it includes hole pairs as well as electron pairs.

  17. Effects of non-magnetic doping on high- Tc cuprates

    NASA Astrophysics Data System (ADS)

    Ming-wen, Xiao; Zheng-zhong, Li; Da-ning, Shi

    1992-11-01

    The Anderson lattice model (ALM) is adopted to study the substitution effects of non-magnetic impurities at Cu-sites on the properties of high- Tc superconductors by the slave-boson technique. We found that they can weaken the effective strength of Cu O hybridization and lower the characteristic temperature Tk of the normal state. The ability of these effects to depress superconductivity is proved to be important and not negligible. Non-magnetic impurities turn out to be pair-breaking and responsible for the quick decreasing of Tc because of the energy dependence of the superconducting order parameter in ALM. Particularly, the linear relationship between Tc and doping concentration in the dilute case is obtained analytically, which is in good agreement with experiment.

  18. Bec Model of HIGH-Tc Superconductivity in Layered Cuprates

    NASA Astrophysics Data System (ADS)

    Lomnitz, M.; Villarreal, C.; de Llano, M.

    2013-11-01

    High-Tc superconductivity in layered cuprates is described in a BCS-BEC formalism with linearly-dispersive s- and d-wave Cooper pairs moving in quasi-2D finite-width layers around the CuO2 planes. This yields a closed formula for Tc involving the layer width, the Debye frequency, the pairing energy and the in-plane penetration depth. The new formula has no free parameters and reasonably reproduces empirical values of superconducting Tcs for 11 different layered superconductors over a wide doping regime including YBCO itself as well as other compounds like LSCO, BSCCO and TBCCO. In agreement with the London formalism, the formula also yields a fair description of the Tc dependence of the lower critical magnetic field in highly underdoped YBCO.

  19. Theory of High-TC Superconductivity: Accurate Predictions of TC

    NASA Astrophysics Data System (ADS)

    Harshman, Dale; Fiory, Anthony

    2012-02-01

    The superconducting transition temperatures of high-TC compounds based on copper, iron, ruthenium and certain organic molecules is discovered to be dependent on bond lengths, ionic valences, and Coulomb coupling between electronic bands in adjacent, spatially separated layers [1]. Optimal transition temperature, denoted as TC0, is given by the universal expression kBTC0 = e^2λ/lζ; l is the spacing between interacting charges within the layers, ζ is the distance between interacting layers and λ is a universal constant, equal to about twice the reduced electron Compton wavelength (suggesting that Compton scattering plays a role in pairing). Non-optimum compounds in which sample degradation is evident typically exhibit TC < TC0. For the 31+ optimum compounds tested, the theoretical and experimental TC0 agree statistically to within ± 1.4 K. The elemental high-TC building block comprises two adjacent and spatially separated charge layers; the factor e^2/ζ arises from Coulomb forces between them. The theoretical charge structure representing a room-temperature superconductor is also presented. * 1. doi:10.1088/0953-8984/23/29/295701

  20. Superconducting bolometers: high-Tc and low-Tc

    NASA Astrophysics Data System (ADS)

    Richards, Paul L.

    1991-07-01

    A description is given of recent work at Berkeley on superconducting detectors and mixers for infrared and millimeter wavelengths. The first report is a review article which summarizes the status of development of superconducting components for infrared and millimeter wave receivers. Next, a report is given on measurements and theoretical modeling of the absorptivity (surface resistance) of high quality epitaxial films of the high-Tc superconductor YBCO from 750 GHz to 21 THz. The next report describes measurements of the thermal boundary resistance between YBCO films and various substrates. This resistance is much larger than expected from the acoustic impedance mismatch model and gives a thermal time constant in the nanosecond range for typical YBCO films. Reports are also included on the design and experimental performance of two different types of high-Tc bolometric detectors. One is a conventional bolometer with a gold-black absorber. The other is an antenna coupled microbolometer. The properties of a low-Tc microbolometer are also described. The last reports describe accurate measurements and also theoretical modeling of an SIS quasi-particle waveguide mixer for W-band which uses very high quality Ta junctions. The best mixer noise is only 1.3 times the quantum limit. Both the mixer gain and the noise are in quantitative agreement with the quantum theory.

  1. Vortex dynamics and correlated disorder in high-{Tc} superconductors

    SciTech Connect

    Vinokur, V.M.

    1993-08-01

    We develop a theory for the vortex motion in the presence of correlated disorder in the form of the twin boundaries and columnar defects. Mapping vortex trajectories onto boson world lines enables us to establish the duality of the vortex transport in the systems with correlated disorder and hopping conductivity of charged particles in 2D systems. A glassy-like dynamics of the vortex lines with zero linear-resistivity and strongly nonlinear current-voltage behavior as V {proportional_to} exp[{minus} const/J{sup {mu}}] in a Bose glass state is predicted.

  2. Program to Study AC Loss in High-Tc Superconductors

    DTIC Science & Technology

    2007-11-02

    larger), which is assumed here. Then since one can always write (27) t ■" »trwuport + »nwgiwtlMtlon v ’ the intragrain current is all...as in (25), since the direction of the intragrain current depends on the local electric field inside a grain. The only transport-like current comes...that of the intragrain circulating current or that of percolation loops are important, the high-Te case is quite different from the low-T« case

  3. Dipolar clusters and ferroelectricity in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Kusmartsev, F. V.; Saarela, M.

    2015-08-01

    In this paper, we show that doping of hole charge carriers induces formation of resonance plaquettes (RPs) having electric dipolar moments and fluctuating stripes in cuprates. A single RP is created by many-body interactions between the dopant ion or a charge fluctuation outside and holes inside the CuO plane. In such a process, Coulomb interacting holes in the CuO plane are self-organized into four-particles resonance valence bond plaquettes bound with dopants or polarons located in the spacer layer between CuO planes. Such RPs have ordered and disordered phases. They are ordered into charge density waves (CDW) or stripes only at certain conditions. The lowest energy of the ordered phase corresponds to a local antiferroelectric ordering. The RPs mobility is very low at low temperatures and they are bound into dipole-dipole pairs. Electromagnetic radiation interacts strongly with RPs electric dipoles and when the sample is subjected to it, the mobility changes significantly. This leads to a fractal growth of dipolar RP clusters. The existence of electric dipoles and CDW reveal a series of new phenomena such as ferroelectricity, strong light and microwave absorption and the field induced superconductivity.

  4. Magnetism and electron pairing in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Tsang, T.

    1990-01-01

    Correlated wave functions are used for YBa2Cu3O(7-y) where epsilon(d)-epsilon(p) is about 0 for Cu3d- and 02p-electrons. The electrons are delocalized (metallic) for y less than 0.5 with weak and temperature-independent paramagnetism. In contrast, the systems are conventional antiferromagnetic insulators for y greater than 0.6 with a narrow y between 0.5 and 0.6 transition region. These results are in agreement with magnetic and neutron diffraction data.

  5. Chemical Compatibility of High-Tc Superconductors with Other Materials

    DTIC Science & Technology

    1988-07-22

    the metallic and semiconducting elements in the periodic table . To generate this table, compilations of thermochemical data were consulted (2,3), and...will not reduce CuO: Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, and Hg. These are grouped with a bold border in the periodic table of Fig. 1. No solid oxidC of...Figure 1. Periodic table of the elements showing the heat of formation (in kcallgrarn-atom) of the most stable solid oxide of each element The more

  6. Development of high-Tc superconductor wires for magnet applications

    NASA Astrophysics Data System (ADS)

    Tenbrink, J.; Heine, K.; Krauth, H.; Wilhelm, M.

    1991-03-01

    Bi-2212/Ag 1-mm round untextured wires have been produced with critical current densities of 1200 A/sq cm at 77 K, 0 T and up to about 2.0 x 10 to the 4th A/sq cm at 4.2 K in magnetic fields beyond 20 T. In order to achieve this, a two-step annealing procedure is necessary with a partial melting of the wire core, the melt having a composition near Bi2(Sr,Ca)2Cu1O(6+x). On cooling, the Bi2(Sr,Ca)2Cu1O(6+x) phase appears at 880 C, as revealed by in situ XRD (X-ray diffraction) measurements. Long-term annealing at 840 C leads to the transformation of this phase into the Bi2Sr2Ca1Cu2O(8+x) phase. The alkaline earth cuprate (Sr,Ca)14Cu24O=40 and CuO occur as major extraneous phases. Helically shaped samples yield a lower jc between 3 x 103 and maximum 1.0 x 10 to the 4th A/sq cm at 4.2 K, 10 T. Cracks due to thermal expansion mismatch with the sample holder and remaining inhomogeneities along the wire are responsible for these lower values. From I-V curves measured at 4.2 K, n-values were determined to be 20 to 25 in the interesting very-high-field region beyond 20 T. Bi-2223/Ag highly textured thin tapes yield an appreciably higher jc of 2.6 x 10 to the 4th A/sq cm at 77 K, 0 T. Temperature-dependent measurements of jc as a function of magnetic field B yielded onset of significant flux creep above 20 K, limiting the range of application in magnet technology to the temperature range up to 20 K unless an additional more effective pinning mechanism is introduced.

  7. Bismuth cuprate high-Tc superconductors using cationic substitution

    NASA Astrophysics Data System (ADS)

    Tarascon, J.-M.; Barboux, P.; Hull, G. W.; Ramesh, R.; Greene, L. H.; Giroud, M.; Hegde, M. S.; McKinnon, W. R.

    1989-03-01

    The Bi4Sr4Ca2-xRxCu4BOy materials (R is a rare-earth element) were studied to determine their structural and physical properties. For most of the rare-earth elements, a complete solid solution exists up to x=2. Below x=0.5,Tc is not affected and for each added rare-earth element we find that about 0.5 oxygen atom is added to the structure. However, the structural modulation observed along the b axis for the undoped material persists and remains of the same amplitude for the rare-earth-doped samples. When more than one R(x>=1) is substituted, Tc is depressed and the compound becomes semiconducting beyond x=1.5. The depression in the Tc from 85 K (x=0) to less than 4.2 K (x=1.5) correlates to a decrease in the formal valence of copper and is independent whether the rare-earth element is magnetic or nonmagnetic. No evidence for magnetic ordering over the range of temperature 1.7-400 K has been observed in all the substituted compounds. The substitution for Cu by 3d metals or for Sr by rare-earth elements fails for the 85-K Bi phase but succeeds for the 10-K Bi phase. Consequently, the following series Bi2Sr2Cu1-xMxOy (M=Fe, Co) and Bi2RCaCuOy (R=La, Pr, Nd, Sm) were made for study. These substitutions result in an uptake of oxygen (0.5 for each substituted element). But the materials become semiconducting even though the formal valence of Cu remains greater than 2. An antiferromagnetic transition at 140 K has been found for the Co sample for which Co is found to be in the +3 state.

  8. Magnetism and electron pairing in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Tsang, T.

    1990-01-01

    Correlated wave functions are used for YBa2Cu3O(7-y) where epsilon(d)-epsilon(p) is about 0 for Cu3d- and 02p-electrons. The electrons are delocalized (metallic) for y less than 0.5 with weak and temperature-independent paramagnetism. In contrast, the systems are conventional antiferromagnetic insulators for y greater than 0.6 with a narrow y between 0.5 and 0.6 transition region. These results are in agreement with magnetic and neutron diffraction data.

  9. Studying the kinetics of magnetization in high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Turchinskaya, Marina

    1993-01-01

    The first microscopic maps of magnetic induction in YBa2Cu3O(7-x) crystals which directly show the dependence of flux flow on twin density and polytwin block and twin boundary orientation are reported. These maps were obtained by means of a recently-improved magneto-optical imaging technique. Pinning was lowest in untwinned regions and increased with increasing twin density. An isotropy in twin boundary pinning, defined as the ratio of the magnetic induction gradient across twin boundaries to that along twin boundaries, was 10 at 17 K; this ratio increased with increasing temperature. In polycrystals, twin boundaries also had a strongly anisotropic effect on flux flow into a grain from a grain boundary.

  10. Environmental considerations for application of high Tc superconductors in space

    NASA Technical Reports Server (NTRS)

    Carlberg, I. A.; Kelliher, W. C.; Wise, S. A.; Hooker, M. W.; Buckley, J. D.

    1993-01-01

    The impact of the environmental factors on the performance of the superconductive devices during spaceflight missions is reviewed. Specific factors typical of spaceflight are addressed to evaluate superconductive devices for space-based applications including preflight storage, radiation, vibration, and thermal cycling.

  11. Studying the kinetics of magnetization in high Tc superconductors

    NASA Technical Reports Server (NTRS)

    1993-01-01

    We report the first microscopic maps of magnetic induction in YBa2Cu3O(7-x) crystals which directly show the dependence of flux flow on twin density, polytwin block, and twin boundary orientation. These maps were obtained by means of a recently-improved magneto-optical imaging technique. Pinning was lowest in untwinned regions and increasing with increasing twin density. Anisotropy in twin boundary pinning, defined as the ratio of the magnetic induction gradient across twin boundaries to that along twin boundaries, was 10 at 17 K; this ratio increased with increasing temperature. In polycrystals, twin boundaries also had a strongly anisotropic effect on flux flow into a grain from a grain boundary.

  12. Magnetic and thermal properties of high Tc superconductors

    SciTech Connect

    Lee, Wonchoon.

    1990-09-21

    Measurements of the normal state magnetic susceptibility {chi}(T) of YBa{sub 2}Cu{sub 3}O{sub 7}, Bi{sub 1.8}Pb{sub 0.2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}, and Bi{sub 2{minus}x}Pb{sub x}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+{delta}} (x = 0.2 and 0.25) were carried out. All {chi}(T) data show negative curvature below {approximately}2{Tc}. The data for YBa{sub 2}Cu{sub 3}O{sub 7} are in excellent agreement with a new calculation of the superconducting fluctuation diamagnetism. From the analysis, we infer s-wave pairing and microscopic parameters are obtained. For {chi}(T) of YBa{sub 2}Cu{sub 3}O{sub 7}, part of the negative curvature is inferred to arise from the normal state background. We find a strong temperature dependent anisotropy {delta}{chi} {equivalent to} {chi}{sub c} {minus} {chi}{sub ab} and estimate the normal state spin contributions to {chi}(T). The heat capacity C(T) of YBa{sub 2}Cu{sub 3}O{sub 7} is reported for 0.4 K < T < 400 K in zero and 70 kG magnetic fields. In addition to the feature associated with the onset of the superconductivity at {Tc}, two anomalies in C(T) were observed near 74 K and 330 K, with another possible anomaly near 102 K; the temperatures at which they occur correlate with anomalies in {chi}(T) and ultransonic measurements. The occurrence of the anomaly at {approx equal} 330 K is found to be sample-dependent. The influences of a magnetic field and the thermal and/or magnetic field treatment history dependence of a pellet sample on C(T), the entropy and the influence of superconducting fluctuations on C(T) near {Tc}, and the possible source of the observed intrinsic nonzero {gamma}(0) at low T are discussed.

  13. High Tc YBCO superconductor deposited on biaxially textured Ni substrate

    DOEpatents

    Budai, John D.; Christen, David K.; Goyal, Amit; He, Qing; Kroeger, Donald M.; Lee, Dominic F.; List, III, Frederick A.; Norton, David P.; Paranthaman, Mariappan; Sales, Brian C.; Specht, Eliot D.

    1999-01-01

    A superconducting article includes a biaxially-textured Ni substrate, and epitaxial buffer layers of Pd (optional), CeO.sub.2 and YSZ, and a top layer of in-plane aligned, c-axis oriented YBCO having a critical current density (J.sub.c) in the range of at least 100,000 A/cm.sup.2 at 77 K.

  14. Vortex movement and magnetization of high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Roytburd, A. L.; Turchinskaya, M. J.

    1991-01-01

    The basic characteristics of the thermoactivated vortex mobility in Y1Ba2Cu3O7 are determined by measurement of the kinetics of magnetization in two time regimes. The analysis of the kinetics of the approach of the equilibrium results in the activation energy, while the measurement of the log-creep rate allows determination of the activated moment. It is shown that the movement of vortices can be regarded as the diffusion process.

  15. Model of electron pairs in electron-doped cuprates

    NASA Astrophysics Data System (ADS)

    Singh, R. J.; Khan, Shakeel

    2016-07-01

    In the order parameter of hole-doped cuprate superconductors in the pseudogap phase, two holes enter the order parameter from opposite sides and pass through various CuO2 cells jumping from one O2- to the other under the influence of magnetic field offered by the Cu2+ ions in that CuO2 cell and thus forming hole pairs. In the pseudogap phase of electron-doped cuprates, two electrons enter the order parameter at Cu2+ sites from opposite ends and pass from one Cu2+ site to the diagonally opposite Cu2+ site. Following this type of path, they are subjected to high magnetic fields from various Cu2+ ions in that cell. They do not travel from one Cu2+ site to the other along straight path but by helical path. As they pass through the diagonal, they face high to low to very high magnetic field. Therefore, frequency of helical motion and pitch goes on changing with the magnetic field. Just before reaching the Cu2+ ions at the exit points of all the cells, the pitch of the helical motion is enormously decreased and thus charge density at these sites is increased. So the velocity of electrons along the diagonal path is decreased. Consequently, transition temperature of electron-doped cuprates becomes less than that of hole-doped cuprates. Symmetry of the order parameter of the electron-doped cuprates has been found to be of 3dx2-y2 + iS type. It has been inferred that internal magnetic field inside the order parameter reconstructs the Fermi surface, which is requisite for superconductivity to take place. Electron pairs formed in the pseudogap phase are the precursors of superconducting order parameter when cooled below Tc.

  16. High-Tc Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

    NASA Astrophysics Data System (ADS)

    Sun, J. P.; Ye, G. Z.; Shahi, P.; Yan, J.-Q.; Matsuura, K.; Kontani, H.; Zhang, G. M.; Zhou, Q.; Sales, B. C.; Shibauchi, T.; Uwatoko, Y.; Singh, D. J.; Cheng, J.-G.

    2017-04-01

    The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (Tc ). However, the absence of hole pockets near the Fermi level of the iron-selenide (FeSe) derived high-Tc superconductors raises a fundamental question of whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in the high-Tc phase induced by pressure in bulk FeSe from magnetotransport measurements and first-principles calculations. With increasing pressure, the low-Tc superconducting phase transforms into the high-Tc phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstrating dominant hole carriers in contrast to other FeSe-derived high-Tc systems. Moreover, the Hall coefficient is enlarged and the magnetoresistance exhibits anomalous scaling behaviors, evidencing strongly enhanced interband spin fluctuations in the high-Tc phase. These results in FeSe highlight similarities with high-Tc phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.

  17. NEUTRON SCATTERING STUDY OF THE HIGH-Tc SUPERCONDUCTING SYSTEM YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Rossat-Mignod, J.; Regnault, L. P.; Bourges, P.; Burlet, P.; Vettier, C.; Henry, J. Y.

    The following sections are included: * Introduction * The neutron scattering technique * Phase diagrams of high-Tc superconductors * The undoped AF-doped * The doped AF-state * The weakly-doped metallic state * The heavily-doped metallic state * The overdoped metallic state * Discussion and concluding remarks * Acknowledgements * References

  18. High-Tc SQUID magnetocardiography imaging system.

    PubMed

    Yang, H C; Hung, S Y; Wu, C H; Chen, J C; Hsu, S J; Liao, S H; Horng, H E

    2004-11-30

    We set up a high-Tc SQUID system for magnetocardiography (MCG) in a moderately magnetically shielded room. The electronically balanced gradiometer consists of superconducting quantum interference device (SQUID) magnetometer. One reference SQUID was mounted above the sensing SQUID while the sensing SQUID is seated at the bottom of the cryostat. The baseline of the gradiometer is varied from 5 cm to 7 cm. The output of the MCG signal was filtered with the band pass filter (0.5 - 40 Hz) and the power-line filter. The MCG system was used to detect the magnetic signal of the human heart. Equivalent current sources were used to study the inverse problem.

  19. Epitaxial thick film high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Faley, M. I.; Mi, S. B.; Jia, C. L.; Poppe, U.; Urban, K.; Fagaly, R. L.

    2008-02-01

    Low-noise operation of superconducting quantum interference devices (SQUIDs) in magnetic fields requires high critical current and strong pinning of vortices in the superconducting electrodes and in the flux transformer. Crack-free epitaxial high-Tc dc-SQUID structures with a total thickness ?5 μm and a surface roughness determined by 30 nm high growth spirals were prepared with YBa2Cu3O7-x (YBCO) films on MgO substrates buffered by a SrTiO3/BaZrO3-bilayer. HRTEM demonstrated a high quality epitaxial growth of the films. The YBCO films and SQUID structures deposited on the buffered MgO substrates had a superconducting transition temperature Tc exceeding 91 K and critical current densities Jc > 3 MA/cm2 at 77 K up to a thickness ~5 μm. The application of thicker superconducting and insulator films helped us to increase the critical current and dynamic range of the multilayer high-Tc flux transformer and improve the insulation between the superconducting layers. An optimization of SQUID inductance allowed us to fabricate 8 mm SQUID magnetometers with SQUID voltage swings of ~60 μV and a field resolution of ~30 fT/√Hz at 77 K.

  20. High- Tc Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

    DOE PAGES

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

    2017-04-07

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

  1. Voltage-biased high-{Tc} superconducting infrared bolometers with strong electrothermal feedback

    SciTech Connect

    Lee, A.T.; Gildemeister, J.M.; Lee, Shih-Fu; Richards, P.L.

    1996-08-01

    In the current generation of high-{Tc} bolometers the thermal conductance is often chosen for a short time-constant rather than for optimal sensitivity. We describe a novel bolometer bias and readout scheme that promises to relax this constraint. Voltage bias of the superconductor results in strong negative electrothermal feedback that greatly reduces the time-constant of the bolometer. We estimate that a decrease of more than one order of magnitude in time-constant should be possible with existing high-Tc thermometers. We give theoretical estimates of the performance gain with voltage bias for several bolometers that have been reported in the literature. We find cases where the sensitivity can be greatly improved (by changing the thermal conductance) while holding the time constant fixed and others where the bolometer can be made much faster while maintaining the sensitivity.

  2. Superfluid inhomogeneity and microwave absorption in a model for thin high- Tc superconducting films

    NASA Astrophysics Data System (ADS)

    Barabash, Sergey V.; Stroud, David

    2003-10-01

    We investigate the microwave absorption arising from inhomogeneity in the superfluid density of thin high- Tc superconducting films. Such inhomogeneities may arise from a wide variety of sources, including quenched random disorder and static charge density waves such as stripes. We show that both mechanisms will inevitably produce additional absorption at finite frequencies. We present simple model calculations for this extra absorption, and discuss applications to other transport properties in high- Tc materials. Finally, we discuss the connection of these predictions to recent measurements by Corson et al. (Nature (London) 398 (1999) 221) of absorption by the high-temperature superconductor Bi 2Sr 2CaCu 2O 8+δ in the THz frequency regime.

  3. Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy.

    PubMed

    Wen, C H P; Xu, H C; Chen, C; Huang, Z C; Lou, X; Pu, Y J; Song, Q; Xie, B P; Abdel-Hafiez, Mahmoud; Chareev, D A; Vasiliev, A N; Peng, R; Feng, D L

    2016-03-08

    FeSe layer-based superconductors exhibit exotic and distinctive properties. The undoped FeSe shows nematicity and superconductivity, while the heavily electron-doped KxFe2-ySe2 and single-layer FeSe/SrTiO3 possess high superconducting transition temperatures that pose theoretical challenges. However, a comprehensive study on the doping dependence of an FeSe layer-based superconductor is still lacking due to the lack of a clean means of doping control. Through angle-resolved photoemission spectroscopy studies on K-dosed thick FeSe films and FeSe0.93S0.07 bulk crystals, here we reveal the internal connections between these two types of FeSe-based superconductors, and obtain superconductivity below ∼ 46 K in an FeSe layer under electron doping without interfacial effects. Moreover, we discover an exotic phase diagram of FeSe with electron doping, including a nematic phase, a superconducting dome, a correlation-driven insulating phase and a metallic phase. Such an anomalous phase diagram unveils the remarkable complexity, and highlights the importance of correlations in FeSe layer-based superconductors.

  4. Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy

    PubMed Central

    Wen, C. H. P.; Xu, H. C.; Chen, C.; Huang, Z. C.; Lou, X.; Pu, Y. J.; Song, Q.; Xie, B. P.; Abdel-Hafiez, Mahmoud; Chareev, D. A.; Vasiliev, A. N.; Peng, R.; Feng, D. L.

    2016-01-01

    FeSe layer-based superconductors exhibit exotic and distinctive properties. The undoped FeSe shows nematicity and superconductivity, while the heavily electron-doped KxFe2−ySe2 and single-layer FeSe/SrTiO3 possess high superconducting transition temperatures that pose theoretical challenges. However, a comprehensive study on the doping dependence of an FeSe layer-based superconductor is still lacking due to the lack of a clean means of doping control. Through angle-resolved photoemission spectroscopy studies on K-dosed thick FeSe films and FeSe0.93S0.07 bulk crystals, here we reveal the internal connections between these two types of FeSe-based superconductors, and obtain superconductivity below ∼46 K in an FeSe layer under electron doping without interfacial effects. Moreover, we discover an exotic phase diagram of FeSe with electron doping, including a nematic phase, a superconducting dome, a correlation-driven insulating phase and a metallic phase. Such an anomalous phase diagram unveils the remarkable complexity, and highlights the importance of correlations in FeSe layer-based superconductors. PMID:26952215

  5. Unconventional high-Tc superconductivity in fullerides.

    PubMed

    Takabayashi, Yasuhiro; Prassides, Kosmas

    2016-09-13

    A3C60 molecular superconductors share a common electronic phase diagram with unconventional high-temperature superconductors such as the cuprates: superconductivity emerges from an antiferromagnetic strongly correlated Mott-insulating state upon tuning a parameter such as pressure (bandwidth control) accompanied by a dome-shaped dependence of the critical temperature, Tc However, unlike atom-based superconductors, the parent state from which superconductivity emerges solely by changing an electronic parameter-the overlap between the outer wave functions of the constituent molecules-is controlled by the C60 (3-) molecular electronic structure via the on-molecule Jahn-Teller effect influence of molecular geometry and spin state. Destruction of the parent Mott-Jahn-Teller state through chemical or physical pressurization yields an unconventional Jahn-Teller metal, where quasi-localized and itinerant electron behaviours coexist. Localized features gradually disappear with lattice contraction and conventional Fermi liquid behaviour is recovered. The nature of the underlying (correlated versus weak-coupling Bardeen-Cooper-Schrieffer theory) s-wave superconducting states mirrors the unconventional/conventional metal dichotomy: the highest superconducting critical temperature occurs at the crossover between Jahn-Teller and Fermi liquid metal when the Jahn-Teller distortion melts.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  6. Stationary Josephson current as a tool to detect charge density waves in high-Tc oxides

    NASA Astrophysics Data System (ADS)

    Gabovich, Alexander M.; Voitenko, Alexander I.; Li, Mai Suan; Szymczak, Henryk

    2015-09-01

    Nonmonotonic and even sign-changing dependences on the temperature and the doping level were predicted for the stationary Josephson tunnel current Ic between superconductors with d-wave order parameter symmetry and partial gapping by charge density waves (CDWs). The junction electrodes were considered in the framework of the two-dimensional electron spectrum appropriate to high-Tc cuprates. The non-trivial behavior can be observed for certain relative electrode orientations. Hence, Ic -measurements in wide ranges of doping and temperature may serve as an indicator of CDW existence.

  7. Magnetization and flux pinning in high-Tc cuprates: Irradiated and oxygen deficient materials

    NASA Astrophysics Data System (ADS)

    Thompson, J. R.; Sun, Yang Ren; Ossandon, J. G.; Christen, D. K.; Kerchner, H. R.; Sales, B. C.; Chakoumakos, B. C.; Civale, L.; Marwick, A. C.; Holtzberg, F.

    1992-11-01

    Recent studies of the intragrain current density J and vortex pinning in high Tc superconductors are surveyed. Materials include Y1Ba2Cu3O(7-delta) and Bi2Sr2Ca1Cu2O8 single crystals and aligned polycrystals. To probe the flux pinning, the strength, number, and morphology of defects were modified. Varying the oxygen content (7-delta) in YBa2Cu3O(7-delta) or irradiating the materials with ions, having either light or heavy masses, gives systematic changes in the character of the all-important defects.

  8. Searching for the Genes of Unconventional High Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Hu, Jiangping

    In the past, both curates and iron-based superconductors were discovered accidentally. Lacking of successful predictions on new high Tc materials is one of major obstacles to reach a consensus on the high Tc mechanism. In this talk, we discuss two emergent principles, which are called as the correspondence principle and the selective magnetic pairing rule, to unify the understanding of both cuprates and iron-based superconductors. These two principles provide an unified explanation why the d-wave pairing symmetry and the s-wave pairing symmetry are robust respectively in cuprates and iron-based superconductors. In the meanwhile, the above two principles explain the rareness of unconventional high Tc superconductivity, identify necessary electronic environments required for high Tc superconductivity and finally serve as direct guiding rules to search new high Tc materials. We predict that the third family of unconventional high Tc superconductors exist in the compounds which carry two dimensional hexagonal lattices formed by cation-anion trigonal bipyramidal complexes with a d filling configuration on the cation ions. Their superconducting states are expected to be dominated by the d+id pairing symmetry and their maximum Tc should be higher than those of iron-based superconductors. Verifying the prediction can convincingly establish the high Tc superconducting mechanism and pave a way to design new high Tc superconductors

  9. High-Tc SQUID Magnetometers for Industrial Applications

    NASA Astrophysics Data System (ADS)

    Diiorio, Mark; Yang, Kai-Yueh; Yoshizumi, Shozo; Haupt, Steven; Haran, Don; Koch, Roger; Lathrop, Dan; Trammel, Hoke

    1998-03-01

    We have developed high-Tc SQUID magnetometers for use in a variety of industrial applications. Relatively inexpensive direct-coupled magnetometers have been developed for low-frequency applications including fetal-magnetocardiography. A manufacturable process has been developed to reproducibly fabricate high-resistance (up to 6 Ω) SNS step-edge junctions with YBa_2Cu_3O_7-x as the superconductor and Ag-Au alloy as the normal metal. Magnetic field sensitivities at 77K of 22 ft/Hz^1/2 at 1 KHz and 32 ft/Hz^1/2 at 1 Hz have been achieved in a well-shielded laboratory environment. Current effort is focused on operation in an unshielded environment using flux dams(Milliken et al. Appl. Phys. Lett. 71 1857 (1997)) in conjunction with narrow superconducting pickup coils placed in parallel. An integrated magnetometer process has also been optimized for use in high-frequency applications. The integrated megnetometer utilizes two layers of YBa_2Cu_3O_7-x and one layer of deposited SrTiO_3, all on the same 24 mm x 5 mm substrate. The applications under development include the detection of the explosive material in non-metallic land mines using nuclear quadrupole resonance as well as the non-destructive evaluation of non-metallic composites using nuclear magnetic resonance. For operation in the MHz regime, these applications demand a high quality insulator layer and a robust SQUID that can withstand high current transients.

  10. A study of high {Tc} superconducting ceramic/metal alloy composites

    SciTech Connect

    Stevens, M.G.; Du, J.; Lee, R.M; Unsworth, J.; Hely, J.; Hodges, J.

    1995-09-01

    High-{Tc} superconducting ceramic YBa{sub 2}Cu{sub 3}O{sub 7{minus}x}/metal alloy composites were fabricated. The metal matrix was a low melting point alloy of bismuth, lead, tin, cadmium and indium. The structure, DC electrical resistivity, AC magnetic susceptibility, levitation and mechanical strength of the composites were investigated. The influence of filler content on these properties was also studied. The composites behaved as a typical metal with the resistivity increasing with temperature increase and, further, did not undergo the characteristic superconducting transition to zero resistance that is obtained with the ceramic superconductor. On the other hand, the diamagnetic properties of the superconducting ceramic were preserved in the composites. The values of diamagnetic susceptibility and levitation force increase with the volume fraction of the superconducting material. The flexural strength of the composites is improved significantly in comparison with the ceramic superconductor.

  11. Elementary excitations in hole- and electron-doped cuprates: kink and resonance peak

    NASA Astrophysics Data System (ADS)

    Manske, Dirk; Eremin, Ilya; Bennemann, Karl

    2004-03-01

    Elementary excitations in high-Tc cuprates are of central interest in order to learn more about the electronic correlations and the pairing mechanism for superconductivity. In this talk we focus on recent experimental and theoretical work on the kink feature and resonance peak and their possible interpretations due to phonons and spin fluctuations (1-3). Although the phase diagram of hole- and electron-doped cuprates reveal some similarities (4), both effects seem to be present only in hole-doped cuprates, but not in electron-doped ones. The kink feature and resonance peak are also related to tunneling experiments and measurements of the optical conductivity and shed important light on the essential ingredients a theory for Cooper-pairing in the cuprates must contain (5). (1) A. Lanzara et al., Nature 412, 510 (2001) (2) Ph. Bourges et al., Science 288, 1234 (2000) (3) D. Manske et al., PRB 63, 054517 (2001); D. Manske et al., PRL 87, 177005 (2001) (4) D. Manske et al., PRB 64, 144520 (2001); D. Manske et al., PRB 63, 13922 (2000) (5) D. Manske et al., PRB 67, 134520 (2003)

  12. Electron doping a kagome spin liquid

    SciTech Connect

    Kelly, Z. A.; Gallagher, M. J.; McQueen, T. M.

    2016-10-13

    Herbertsmithite, ZnCu3(OH)6Cl2, is a two-dimensional kagome lattice realization of a spin liquid, with evidence for fractionalized excitations and a gapped ground state. Such a quantum spin liquid has been proposed to underlie high-temperature superconductivity and is predicted to produce a wealth of new states, including a Dirac metal at 1/3 electron doping. Here, we report the topochemical synthesis of electron-doped ZnLixCu3(OH)6Cl2 from x=0 to x=1.8 (3/5 per Cu2+). Contrary to expectations, no metallicity or superconductivity is induced. Instead, we find a systematic suppression of magnetic behavior across the phase diagram. Lastly, our results demonstrate that significant theoretical work is needed to understand and predict the role of doping in magnetically frustrated narrow band insulators, particularly the interplay between local structural disorder and tendency toward electron localization, and pave the way for future studies of doped spin liquids.

  13. Electron Doping a Kagome Spin Liquid

    NASA Astrophysics Data System (ADS)

    Kelly, Z. A.; Gallagher, M. J.; McQueen, T. M.

    2016-10-01

    Herbertsmithite, ZnCu3 (OH )6Cl2 , is a two-dimensional kagome lattice realization of a spin liquid, with evidence for fractionalized excitations and a gapped ground state. Such a quantum spin liquid has been proposed to underlie high-temperature superconductivity and is predicted to produce a wealth of new states, including a Dirac metal at 1 /3 electron doping. Here, we report the topochemical synthesis of electron-doped ZnLix Cu3 (OH )6Cl2 from x =0 to x =1.8 (3 /5 per Cu2 + ). Contrary to expectations, no metallicity or superconductivity is induced. Instead, we find a systematic suppression of magnetic behavior across the phase diagram. Our results demonstrate that significant theoretical work is needed to understand and predict the role of doping in magnetically frustrated narrow band insulators, particularly the interplay between local structural disorder and tendency toward electron localization, and pave the way for future studies of doped spin liquids.

  14. Electron doping a kagome spin liquid

    DOE PAGES

    Kelly, Z. A.; Gallagher, M. J.; McQueen, T. M.

    2016-10-13

    Herbertsmithite, ZnCu3(OH)6Cl2, is a two-dimensional kagome lattice realization of a spin liquid, with evidence for fractionalized excitations and a gapped ground state. Such a quantum spin liquid has been proposed to underlie high-temperature superconductivity and is predicted to produce a wealth of new states, including a Dirac metal at 1/3 electron doping. Here, we report the topochemical synthesis of electron-doped ZnLixCu3(OH)6Cl2 from x=0 to x=1.8 (3/5 per Cu2+). Contrary to expectations, no metallicity or superconductivity is induced. Instead, we find a systematic suppression of magnetic behavior across the phase diagram. Lastly, our results demonstrate that significant theoretical work is neededmore » to understand and predict the role of doping in magnetically frustrated narrow band insulators, particularly the interplay between local structural disorder and tendency toward electron localization, and pave the way for future studies of doped spin liquids.« less

  15. Fabrication of sensitive high Tc bolometers

    NASA Technical Reports Server (NTRS)

    Nahum, Michael; Verghese, S.; Hu, Qing; Richards, Paul L.; Char, K.; Newman, N.; Sachtjen, Scott A.

    1990-01-01

    The rapid change of resistance with temperature of high quality films of high T sub c superconductors can be used to make resistance thermometers with very low temperature noise. Measurements on c-axis yttrium barium copper oxide (YBCO) films have given a spectral intensity of temperature noise less than 4 times 10(exp -8) K/Hz(exp 1/2) at 10 Hz. Consequently, the opportunity exists to make useful bolometric infrared detectors that operate near 90 K which can be cooled with liquid nitrogen. The fabrication and measurement of two bolometer architectures are discussed. The first is a conventional bolometer which consists of a 3000 A thick YBCO film deposited in situ by laser ablation on top of a 500 A thick SrTiO3 thickness and diced into 1x1 mm(exp 2) bolometer chips. Gold black smoke was used as the radiation absorber. The voltage noise was less than the amplifier noise when the film was current biased. Optical measurements gave an NEP of 5 times 10(exp -11) W/Hz(exp 1/2) at 10 Hz. The second architecture is that of an antenna-coupled microbolometer which consists of a small (5x10 cubic microns) YBCO film deposited directly on a bulk substrate with a low thermal conductance (YSZ) and an impedance matched planar lithographed spiral or log-periodic antenna. This structure is produced by standard photolithographic techniques. Measurements gave an electrical NEP of 4.7 times 10(exp -12) W/Hz(exp 1/2) at 10 kHz. Measurements of the optical efficiency are in progress. The measured performance of both bolometers will be compared to other detectors operating at or above liquid nitrogen temperatures so as to identify potential applications.

  16. High- Tc superconductivity due to coexisting wide and narrow bands: A fluctuation exchange study of the Hubbard ladder as a test case

    NASA Astrophysics Data System (ADS)

    Kuroki, Kazuhiko; Higashida, Takafumi; Arita, Ryotaro

    2005-12-01

    We propose that when the Fermi level lies within a wide band and also lies close to but not within a coexisting narrow band, high- Tc superconductivity may take place due to the large number of interband pair scattering channels and the small renormalization of the quasiparticles. We show using the fluctuation exchange method that this mechanism works for the Hubbard model on a ladder lattice with diagonal hoppings. From this viewpoint, we give a possible explanation for the low Tc for the actual hole-doped ladder compound, and further predict a higher Tc for the case of electron doping.

  17. High-Tc superconducting quantum interference device recordings of spontaneous brain activity: Towards high-Tc magnetoencephalography

    NASA Astrophysics Data System (ADS)

    Öisjöen, F.; Schneiderman, J. F.; Figueras, G. A.; Chukharkin, M. L.; Kalabukhov, A.; Hedström, A.; Elam, M.; Winkler, D.

    2012-03-01

    We have performed single- and two-channel high transition temperature (high-Tc) superconducting quantum interference device (SQUID) magnetoencephalography (MEG) recordings of spontaneous brain activity in two healthy human subjects. We demonstrate modulation of two well-known brain rhythms: the occipital alpha rhythm and the mu rhythm found in the motor cortex. We further show that despite higher noise-levels compared to their low-Tc counterparts, high-Tc SQUIDs can be used to detect and record physiologically relevant brain rhythms with comparable signal-to-noise ratios. These results indicate the utility of high-Tc technology in MEG recordings of a broader range of brain activity.

  18. Detection of the Cracks using High-Tc SQUID

    NASA Astrophysics Data System (ADS)

    Fujii, Tatsuhiko; Hyun-Sung, Tae; Takamatsu, Tsuyoshi; Sakuta, Ken; Itozaki, Hideo

    Eddy current non-distractive evaluation (NDE) is very useful technique for detection of cracks. We use the high-Tc SQUID in this system. First, we respect the result of this measurement by the finite element method. We can detect of the signal from the hole by NDE system with high-Tc SQUID. This result is reasonable to compare with the result of simulation. Finaly, we can detect of the hidden defect under 5mm depth from the sample surface.

  19. Possible new edge barriers in polycrystalline superconductors

    NASA Astrophysics Data System (ADS)

    Belevtsov, L. V.

    2002-09-01

    We present a theoretical prediction of the new edge barriers for Abrikosov vortex penetration into polycrystalline superconductors. The traditional Bean-Livingston surface barrier is governed by the strength of the external field. Edge barriers in polycrystalline superconductors are also governed by the external field as well as by the anisotropy ratio, grain-coupling strength and grain size. We support our theory with concrete calculation of the critical current density in both high-Tc oxide and MgB2 superconductors.

  20. A stoichiometry criterion for high T c superconductors

    NASA Astrophysics Data System (ADS)

    Veljković, V.; Lalović, D.

    1989-12-01

    We consider high Tc superconducting materials from point of view of the famous Matthias empirical rules for superconductivity. We point out that for all recently discovered high Tc superconductors the average number of electrons outside of the closed shells per atom is close to 7. We offer a possible explanation of this fact and point to its practical implications.

  1. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    DOE PAGES

    Gray, B. A.; Middey, S.; Conti, G.; ...

    2016-09-15

    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leadingmore » to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.« less

  2. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.

    PubMed

    Gray, B A; Middey, S; Conti, G; Gray, A X; Kuo, C-T; Kaiser, A M; Ueda, S; Kobayashi, K; Meyers, D; Kareev, M; Tung, I C; Liu, Jian; Fadley, C S; Chakhalian, J; Freeland, J W

    2016-09-15

    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

  3. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    DOE PAGES

    Gray, B. A.; Middey, S.; Conti, G.; ...

    2016-09-15

    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leadingmore » to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.« less

  4. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C.-T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; Tung, I. C.; Liu, Jian; Fadley, C. S.; Chakhalian, J.; Freeland, J. W.

    2016-09-01

    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

  5. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    PubMed Central

    Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C.-T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; Tung, I. C.; Liu, Jian; Fadley, C. S.; Chakhalian, J.; Freeland, J. W.

    2016-01-01

    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates. PMID:27627855

  6. The self-energies and bosonic spectrum of high Tc cuprate from laser-based ARPES

    NASA Astrophysics Data System (ADS)

    Bok, Jin Mo; Bae, Jong Ju; Choi, Han-Yong; Yu, Li; Zhou, X. J.; Varma, Chandra M.

    While phonon mediated conventional superconductors are revealed by comparing tunneling and neutron scattering experiment, high Tc cuprate which has d-wave symmetry is still in debate. Laser-based AREPS can provide both momentum and energy dependence of spectral function that enables self-energy extraction using one particle Green's function. It is well known that anisotropy of electronic structure and d-wave superconducting gap on ARPES experiments. We analyzed high resolution APRES data of under and overdoped Bi2212 and extracted both normal and pairing self-energy. Here we report the extracted normal and pairing self-energy in supercondcuting state. Also we obtained bosonic spectrum from both self-energies by performing maximum entropy method. Implications of these results for understanding the superconductivity mechanism will be discussed.

  7. Investigation of high-Tc superconducting tunnel junction after laser radiation processing

    NASA Astrophysics Data System (ADS)

    Broslavez, U. U.; Fomitchev, A. A.; Yakshin, Mikhail A.

    1995-03-01

    We investigate dynamic resistance (dV/dI) of high-Tc superconducting thin films and tunnel junction after laser radiation processing. The films of YBaCuO were prepared by laser and magnetron ablation on Al2O3 substrates. The tunnel junctions were made by fine silver wires attached to the processing surfaces. The resistance (dV/dI) was determined by a four-probe measurement. The YAG laser operating in Q-switched mode was used to interact with superconductors. The anomaly is observed in the current-voltage curve of the junction after radiation interaction. We observe hysteresis in the shape of V(I) curve. These effects are not observed without laser radiation interaction and in this case the behavior of tunnel junction is described for the standard BCS theory.

  8. Development of a Compact Moving-Sample Magnetometer Using High-Tc Superconducting Quantum Interference Device

    NASA Astrophysics Data System (ADS)

    Mawardi Saari, Mohd; Sakai, Kenji; Kiwa, Toshihiko; Tsukamoto, Akira; Adachi, Seiji; Tanabe, Keiichi; Kandori, Akihiko; Tsukada, Keiji

    2012-04-01

    We developed a compact moving-sample magnetometer that uses a high-temperature superconductor-superconducting quantum interference device (high-Tc SQUID) to directly measure the flux coupled to a normal detection coil from a sample's magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-Tc SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1×10-7 emu.

  9. Development of a Compact Moving-Sample Magnetometer Using High-Tc Superconducting Quantum Interference Device

    NASA Astrophysics Data System (ADS)

    Saari, Mohd Mawardi; Sakai, Kenji; Kiwa, Toshihiko; Tsukamoto, Akira; Adachi, Seiji; Tanabe, Keiichi; Kandori, Akihiko; Tsukada, Keiji

    2012-04-01

    We developed a compact moving-sample magnetometer that uses a high-temperature superconductor--superconducting quantum interference device (high-Tc SQUID) to directly measure the flux coupled to a normal detection coil from a sample's magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-Tc SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1× 10-7 emu.

  10. Vibration reduction using autoparametric resonance in a high-Tc superconducting levitation system

    NASA Astrophysics Data System (ADS)

    Yamasaki, Hiroshi; Takazakura, Toyoki; Sakaguchi, Ryunosuke; Sugiura, Toshihiko

    2014-05-01

    High-Tc superconducting levitation systems have very small damping and enable stable levitation without control. Therefore, they can be applied to various kinds of application. However, there are some problems that small damping produces large vibration and nonlinearity of magnetic force can generate complicated phenomena. Accordingly, analysis of these phenomena and reduction of vibration occurring in the system are important. In this study, we examined reduction of vibration without using any absorbers, but utilizing autoparametric resonance caused by nonlinear coupling between vertical oscillation and horizontal oscillation. We conducted numerical analysis and experiments in order to investigate motions of a rigid bar levitated by the electromagnetic force from high-Tc superconductors. As a result, if the ratio of the natural frequency of vertical oscillation and that of horizontal oscillation is two to one, the vertical oscillation decreases while the horizontal oscillation is excited. Thus, it was confirmed that the amplitude of a primary resonance can be reduced by occurrence of autoparametric resonance without using any absorbers.

  11. Electron scattering from interacting tunneling units: A model for high-Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Simanovsky, Sergey B.; Klein, Michael W.

    1996-09-01

    We consider the existence of high-Tc superconductivity and the symmetry of the gap function when electrons are scattered from tunneling units that interact via an elastic strainlike potential. We examine the consequences of conduction electron scattering for the specific case of tunneling units found in experiments on the high-Tc superconductors YBa2Cu3O6+x, Bi2CaSr2Cu2O8, Tl2CaBa2Cu2O8, Tl2Ca2Ba2Cu3O10, and Tl2CaBa2CuO6. Our calculations give (i) a strongly anisotropic scattering of the conduction electrons, (ii) a strongly anisotropic superconducting gap in k space, (iii) an isotope effect different from that associated with phonon scattering in the BCS theory, (iv) a high transition temperature, and (v) a gap function with nodes and a combination of an s-wave and a dx2-y2-wave symmetry. The dx2-y2 symmetry arises from the directionally dependent scattering of electrons by the tunneling units which have a well-defined orientation with respect to the crystal axis.

  12. Evidence for a quantum phase transition in electron-doped Pr2-xCexCuO4-δ from thermopower measurements

    NASA Astrophysics Data System (ADS)

    Li, Pengcheng; Behnia, K.; Greene, R. L.

    2007-01-01

    The evidence for a quantum phase transition under the superconducting dome in the high- Tc cuprates has been controversial. We report low-temperature normal state thermopower (S) measurements in electron-doped Pr2-xCexCuO4-δ as a function of doping ( x from 0.11 to 0.19). We find that at 2K both S and S/T increase dramatically from x=0.11 to 0.16 and then saturate in the overdoped region. This behavior has a remarkable similarity to previous Hall effect results in Pr2-xCexCuO4-δ . Our results are further evidence for an antiferromagnetic to paramagnetic quantum phase transition in electron-doped cuprates near x=0.16 .

  13. An Economical Magnetocardiogram System Based on High-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Li, Zhuo; Zhu, Xue-Min; Zhang, Li-Hua; Huang, Xu-Guang; Ren, Yu-Feng; Chen, Geng-Hua; Yang, Qian-Sheng; Feng, Ji

    2006-08-01

    An economical magnetocardiogram (MCG) system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-Tc superconducting quantum interference device (SQUID) magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements.

  14. High Tc superconducting bolometric and nonbolometric infrared (IR) detectors

    NASA Technical Reports Server (NTRS)

    Lakeou, Samuel

    1994-01-01

    The original workplan for the first year of the project includes the following: establishment of a pilot superconductivity application laboratory at UDC to support the research component of the project; research on the source of electrical noise in High Tc superconducting films in order to optimize the film microstructure and lower the NEP; and lay the foundation of an academic support for exposing UDC students to the theory and application of High Tc superconductivity. Attached to this status report are abstracts and the course description for Introduction to Applications of Superconductivity.

  15. Doping-dependent charge order correlations in electron-doped cuprates

    PubMed Central

    da Silva Neto, Eduardo H.; Yu, Biqiong; Minola, Matteo; Sutarto, Ronny; Schierle, Enrico; Boschini, Fabio; Zonno, Marta; Bluschke, Martin; Higgins, Joshua; Li, Yangmu; Yu, Guichuan; Weschke, Eugen; He, Feizhou; Le Tacon, Mathieu; Greene, Richard L.; Greven, Martin; Sawatzky, George A.; Keimer, Bernhard; Damascelli, Andrea

    2016-01-01

    Understanding the interplay between charge order (CO) and other phenomena (for example, pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. We use resonant x-ray scattering to measure the CO correlations in electron-doped cuprates (La2−xCexCuO4 and Nd2−xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2−xCexCuO4 show that CO is present in the x = 0.059 to 0.166 range and that its doping-dependent wave vector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166 but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wave vector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall, these findings indicate that, although verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates. PMID:27536726

  16. Computed tomography image using sub-terahertz waves generated from a high-Tc superconducting intrinsic Josephson junction oscillator

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Nakade, K.; Saiwai, Y.; Minami, H.; Kitamura, T.; Watanabe, C.; Ishida, K.; Sekimoto, S.; Asanuma, K.; Yasui, T.; Shibano, Y.; Tsujimoto, M.; Yamamoto, T.; Marković, B.; Mirković, J.; Klemm, R. A.; Kadowaki, K.

    2014-02-01

    A computed tomography (CT) imaging system using monochromatic sub-terahertz coherent electromagnetic waves generated from a device constructed from the intrinsic Josephson junctions in a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+δ was developed and tested on three samples: Standing metallic rods supported by styrofoam, a dried plant (heart pea) containing seeds, and a plastic doll inside an egg shell. The images obtained strongly suggest that this CT imaging system may be useful for a variety of practical applications.

  17. High-Tc superconducting quantum interference devices: Status and perspectives

    NASA Astrophysics Data System (ADS)

    Yang, Hong-Chang; Chen, Ji-Chen; Chen, Kuen-Lin; Wu, Chiu-Hsien; Horng, Herng-Er; Yang, S. Y.

    2008-07-01

    In this paper, an overview of the current status of high-Tc superconducting quantum interference devices (SQUIDs), from device engineering to biomagnetic applications, is given. The authors offer a description of the current status of SQUID sensors, challenges encountered, and the solution of fabricating SQUID sensors with low flux noises. The current challenge that we face is to fabricate high-Tc SQUIDs that are not only more reproducible than the current technology but also capable of providing a high IcRn product and fabricating SQUID with high yield. Improvement of flux noises and fabrication yield in the integrated multichoices directly coupled SQUID magnetometer or gradiometer with series SQUID array are presented. High-Tc SQUID magnetometers exhibiting magnetic field sensitivity of ˜30-50fT/Hz1/2 or better at 100Hz was demonstrated by incorporating serial SQUID into the pickup loop of the magnetometers. New technologies currently being developed and applications for high-Tc SQUIDs are addressed.

  18. Ultrafast Broadband Photodetectors for High-Tc Superconductive Optoelectronics

    DTIC Science & Technology

    1997-01-01

    TITLE AND SUBTITLE Ultrafast Broadband Photodetectors for High-Tc Supercondcutive Optoelectronics 6. AUTHOR(S) Dr. Roman Sobolewski (PI) Dr...The rapid suppression of the Maki-Thompson process for the oxygen-deficient YBCO films, indicated an unconventional symmetry of the superconducting

  19. High Tc SQUID Detector for Magnetic Metallic Particles in Products

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Akai, Tomonori; Hatsukade, Yoshimi; Suzuki, Shuichi

    High-Tc superconducting quantum interference device (SQUID) is an ultra-sensitive magnetic sensor. After the discovery of the high-Tc superconducting materials, the performance of the high-Tc SQUID has been improved and stabilized. One strong candidate for application is a detection system of magnetic foreign matters in industrial products. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. If this happens, the manufacturer of the product suffers a great loss recalling products. The outer dimension of metallic particles less than 100 micron cannot be detected using X-ray imaging, which is commonly used for the inspection. Therefore a highly sensitive system for small foreign matters is required. We developed detection systems based on high-Tc SQUID for industrial products. We could successfully detect small iron particles of less than 50 micron on a belt conveyer. These detection levels were hard to be achieved using conventional X-ray detection or other methods.

  20. Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure

    NASA Astrophysics Data System (ADS)

    Liu, Hanyu; Naumov, Ivan I.; Hoffmann, Roald; Ashcroft, N. W.; Hemley, Russell J.

    2017-07-01

    A systematic structure search in the La-H and Y-H systems under pressure reveals some hydrogen-rich structures with intriguing electronic properties. For example, LaH10 is found to adopt a sodalite-like face-centered cubic (fcc) structure, stable above 200 GPa, and LaH8 a C2/m space group structure. Phonon calculations indicate both are dynamically stable; electron phonon calculations coupled to Bardeen-Cooper-Schrieffer (BCS) arguments indicate they might be high-Tc superconductors. In particular, the superconducting transition temperature Tc calculated for LaH10 is 274-286 K at 210 GPa. Similar calculations for the Y-H system predict stability of the sodalite-like fcc YH10 and a Tc above room temperature, reaching 305-326 K at 250 GPa. The study suggests that dense hydrides consisting of these and related hydrogen polyhedral networks may represent new classes of potential very high-temperature superconductors.

  1. The unusually high Tc in rare-earth-doped single crystalline CaFe2As2

    NASA Astrophysics Data System (ADS)

    Wei, Fengyan; Lv, Bing; Deng, Liangzi; Meen, James K.; Xue, Yu-Yi; Chu, Ching-Wu

    2014-08-01

    In rare-earth-doped single crystalline CaFe2As2, the mysterious small volume fraction which superconducts up to 49 K, much higher than the bulk Tc ~ 30 s K, has prompted a long search for a hidden variable that could enhance the Tc by more than 30% in iron-based superconductors of the same structure. Here we report a chemical, structural and magnetic study of CaFe2As2 systematically doped with La, Ce, Pr and Nd. Coincident with the high Tc phase, we find extreme magnetic anisotropy, accompanied by an unexpected doping-independent Tc and equally unexpected superparamagnetic clusters associated with As vacancies. These observations lead us to conjecture that the tantalizing Tc enhancement may be associated with naturally occurring chemical interfaces and may thus provide a new paradigm in the search for superconductors with higher Tc.

  2. Bio-application of high-Tc SQUID magnetic sensor

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Aspanut, Zarina; Kurita, Hirofumi; Toriyabe, Chika; Hatuskade, Yoshimi; Katsura, Shinji

    2006-05-01

    We propose medical applications using ultra-small magnetic particles and a SQUID magnetic sensor. A high-Tc SQUID system for biological molecules (DNA) detection is one of that. This system is based on a hybridization process. Two strands in a DNA molecule are held together by hydrogen bonds between base pairs like a ladder. The two strands are referred to as being complementary to each other. One strand (sample DNA) was labeled with Fe 3O 4 ultra-small magnetic particles and the other (probe DNA) was anchored on a glass slide. Then they were hybridized each other on the slide. After washing the excess sample DNA, the hybridized DNA was evaluated in the presence of excitation AC field by high-Tc SQUID. The signal was initially proportional to the concentration of the sample DNA and then saturated. It means that the hybridization occurred successfully between the sample DNA and the probe DNA.

  3. Progress in Neutron Scattering Studies of Spin Excitations in High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Fujita, Masaki; Hiraka, Haruhiro; Matsuda, Masaaki; Matsuura, Masato; Tranquada, John M.; Wakimoto, Shuichi; Xu, Guangyong; Yamada, Kazuyoshi

    2012-01-01

    Neutron scattering experiments continue to improve our knowledge of spin fluctuations in layered cuprates, excitations that are symptomatic of the electronic correlations underlying high-temperature superconductivity. Time-of-flight spectrometers, together with new and varied single crystal samples, have provided a more complete characterization of the magnetic energy spectrum and its variation with carrier concentration. While the spin excitations appear anomalous in comparison with simple model systems, there is clear consistency among a variety of cuprate families. Focusing initially on hole-doped systems, we review the nature of the magnetic spectrum, and variations in magnetic spectral weight with doping. We consider connections with the phenomena of charge and spin stripe order, and the potential generality of such correlations as suggested by studies of magnetic-field and impurity induced order. We contrast the behavior of the hole-doped systems with the trends found in the electron-doped superconductors. Returning to hole-doped cuprates, studies of translation-symmetry-preserving magnetic order are discussed, along with efforts to explore new systems. We conclude with a discussion of future challenges.

  4. High-temperature superconductors; Proceedings of the Symposium, Boston, MA, Nov. 30-Dec. 4, 1987

    NASA Astrophysics Data System (ADS)

    Brodsky, Merwyn B.; Dynes, Robert C.; Kitazawa, Koichi; Tuller, Harry L.

    Papers are presented on neutron diffraction studies of high-Tc superconductors, the preparation of bulk and thick films of YBa2Cu3O(7-y) using a solution technique, the effects of oxygen stoichiometry and oxygen ordering on superconductivity in Y1Ba2Cu3O(9-x), and the n-p transition in YBa2Cu3O(6.5+x). Also considered are high-Tc superconducting oxide films produced from solution precursors, the deposition, fabrication, and characteristics of high critical temperature devices, and the application of gel technology in the preparation of high-Tc perovskite superconductors. Other topics include high-Tc superconducting films from metalloorganic precursors, a photoemission study of the electronic structure of copper oxide superconductors, oxygen stoichiometry in La-Ba-Cu-O perovskites, and the advantages of barium peroxide in the powder synthesis of perovskite superconductors.

  5. Direct theoretical evidence for weaker correlations in electron-doped and Hg-based hole-doped cuprates

    NASA Astrophysics Data System (ADS)

    Jang, Seung Woo; Sakakibara, Hirofumi; Kino, Hiori; Kotani, Takao; Kuroki, Kazuhiko; Han, Myung Joon

    2016-09-01

    Many important questions for high-Tc cuprates are closely related to the insulating nature of parent compounds. While there has been intensive discussion on this issue, all arguments rely strongly on, or are closely related to, the correlation strength of the materials. Clear understanding has been seriously hampered by the absence of a direct measure of this interaction, traditionally denoted by U. Here, we report a first-principles estimation of U for several different types of cuprates. The U values clearly increase as a function of the inverse bond distance between apical oxygen and copper. Our results show that the electron-doped cuprates are less correlated than their hole-doped counterparts, which supports the Slater picture rather than the Mott picture. Further, the U values significantly vary even among the hole-doped families. The correlation strengths of the Hg-cuprates are noticeably weaker than that of La2CuO4. Our results suggest that the strong correlation enough to induce Mott gap may not be a prerequisite for the high-Tc superconductivity.

  6. Direct theoretical evidence for weaker correlations in electron-doped and Hg-based hole-doped cuprates

    PubMed Central

    Jang, Seung Woo; Sakakibara, Hirofumi; Kino, Hiori; Kotani, Takao; Kuroki, Kazuhiko; Han, Myung Joon

    2016-01-01

    Many important questions for high-Tc cuprates are closely related to the insulating nature of parent compounds. While there has been intensive discussion on this issue, all arguments rely strongly on, or are closely related to, the correlation strength of the materials. Clear understanding has been seriously hampered by the absence of a direct measure of this interaction, traditionally denoted by U. Here, we report a first-principles estimation of U for several different types of cuprates. The U values clearly increase as a function of the inverse bond distance between apical oxygen and copper. Our results show that the electron-doped cuprates are less correlated than their hole-doped counterparts, which supports the Slater picture rather than the Mott picture. Further, the U values significantly vary even among the hole-doped families. The correlation strengths of the Hg-cuprates are noticeably weaker than that of La2CuO4. Our results suggest that the strong correlation enough to induce Mott gap may not be a prerequisite for the high-Tc superconductivity. PMID:27633802

  7. Detecting defect in cast iron using high- TC SQUID

    NASA Astrophysics Data System (ADS)

    He, D. F.; Yoshizawa, M.; Oyama, Y.; Nakamura, M.

    2004-10-01

    For eddy-current NDE, due to the big permeability of ferromagnetic material, low testing frequency is needed to detect defects in it. SQUID has advantages in low frequency eddy current NDE. But the large magnetic field produced by ferromagnetic material often exceeds the dynamic range of general SQUID system. We developed a mobile high- TC SQUID system, with which, the dc and low-frequency magnetic field could be compensated well. Using our mobile SQUID system, the magnetic field produced by the cast iron could be compensated well and the defect in it could be successfully detected.

  8. Scanning high-Tc SQUID imaging system for magnetocardiography

    NASA Astrophysics Data System (ADS)

    Yang, Hong-Chang; Wu, Tsung-Yeh; Horng, Herng-Er; Wu, Chau-Chung; Yang, S. Y.; Liao, Shu-Hsien; Wu, Chiu-Hsien; Jeng, J. T.; Chen, J. C.; Chen, Kuen-Lin; Chen, M. J.

    2006-05-01

    A scanning magnetocardiography (MCG) system constructed from SQUID sensors offers potential to basic or clinical research in biomagnetism. In this work, we study a first order scanning electronic high-Tc (HTS) SQUID MCG system for biomagnetic signals. The scanning MCG system was equipped with an x-y translation bed powered by step motors. Using noise cancellation and μ-metal shielding, we reduced the noise level substantially. The established scanning HTS MCG system was used to study the magnetophysiology of hypercholesterolaemic (HC) rabbits. The MCG data of HC rabbits were analysed. The MCG contour map of HC rabbits provides experimental models for the interpretation of human cardiac patterns.

  9. How to optimize high-Tc superconductive cuprates

    NASA Astrophysics Data System (ADS)

    Raveau, B.; Michel, C.; Hervieu, M.; Groult, D.; Maignan, A.; Provost, J.

    1992-06-01

    Several examples are used here to illustrate the way that modifying the structure of high-Tc superconductive cuprates (HTSCs) allows their superconducting properties to be significantly improved. It is shown that energetic heavy ions can be used as projectiles to modify and tailor superconducting properties. In particular, the creation of columnar defects with dimensions of Xi(ab) or more can act as efficient pinning centers for flux lines and can be used to extend the operating field range of HTSCs to substantially higher fields near Tc's. The crucial role of radiation-induced defects in controlling the magnetic hysteresis shape and therefore the critical current density is demonstrated.

  10. On the coherent quasiparticle weight in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Zheng, Yong; Zhang, Xiaowei; Zhou, Wulei; Liu, Xiaochun; Zhao, Hua

    2017-09-01

    The anomalous temperature dependence of the coherent quasiparticle weight below the superconducting transition temperature Tc in high-Tc cuprates, as has been extensively revealed by angle-resolved photoemission measurements, has been addressed theoretically. We find that this puzzling phenomenon universally appears along the whole Fermi surface, from the nodal to antinodal regions, in momentum space, and can be well comprehended in a mean-field slave-boson picture. The ordinary deduction that the coherent quasiparticle peak is a superconducting one, just from such temperature dependence of the coherent quasiparticle weight below Tc, is found to be questionable, and it could correspond to a competing order, especially in the antinodal region.

  11. EDITORIAL: Focus on Iron-Based Superconductors FOCUS ON IRON-BASED SUPERCONDUCTORS

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

    Superconductivity is the most dramatic and clear cut phenomenon in condensed matter physics. Realization of room temperature superconductors, which would lead to the revolution of our society, is an ultimate goal for researchers. The discovery of high Tc cuprate superconductors in 1986 by Bednorz and Müller triggered intensive research worldwide and the maximum critical temperature has been raised above 100 K. Scientific research on this break-through material clarified a new route to high Tc materials, carrier doping to a Mott insulator with anti-ferromagnetic ordering. High superconductivity occurs in the neighborhood of Mott-insulators and Fermi-metals. Such a view, which was completely new, now stands as a guiding principle for exploring new high Tc materials. Many theoretical approaches to the mechanism for cuprate superconductors have been carried out to understand this unexpected material and to predict new high Tc materials. In 2006 a new superconductor based on iron, LaFeOP, was discovered by a group at Tokyo Institute of Technology, Japan. Iron, as a ferromagnet, was believed to be the last element for the realization of superconductivity because of the way ferromagnetism competes against Cooper pair formation. Unexpectedly, however, the critical temperature remained at 4-6 K irrespective of hole/electron-doping. A large increase in the Tc to 26 K was then found in LaFe[O1-xFx]As by the same group (and was published on 23 February 2008, in the Journal of the American Chemical Society). The Tc of this material was further raised to 43 K under a pressure of 2 GPa and scientists in China then achieved a Tc of 56 K at ambient pressure by replacing La with other rare earth ions with smaller radius—a critical temperature that is second only to the high Tc cuprates. This fast progress has revitalized research within superconductivity and in 2008 there were more than seven international symposia specifically on Fe(Ni)-based superconductors. Through the rapid

  12. Superconductivity and its mechanism in an ab initio model for electron-doped LaFeAsO

    NASA Astrophysics Data System (ADS)

    Misawa, Takahiro; Imada, Masatoshi

    2014-12-01

    Two families of high-temperature superconductors whose critical temperatures are higher than 50 K are known. One are the copper oxides and the other are the iron-based superconductors. Comparisons of mechanisms between these two in terms of common ground as well as distinctions will greatly help in searching for higher Tc superconductors. However, studies on mechanisms for the iron family based on first principles calculations are few. Here we first show that superconductivity emerges in the state-of-the-art numerical calculations for an ab initio multi-orbital model of an electron-doped iron-based superconductor LaFeAsO, in accordance with experimental observations. Then the mechanism of the superconductivity is identified as enhanced uniform density fluctuations by one-to-one correspondence with the instability towards inhomogeneity driven by first-order antiferromagnetic and nematic transitions. Despite many differences, certain common features with the copper oxides are also discovered in terms of the underlying orbital-selective Mottness found in the iron family.

  13. Superconductivity and its mechanism in an ab initio model for electron-doped LaFeAsO.

    PubMed

    Misawa, Takahiro; Imada, Masatoshi

    2014-12-22

    Two families of high-temperature superconductors whose critical temperatures are higher than 50 K are known. One are the copper oxides and the other are the iron-based superconductors. Comparisons of mechanisms between these two in terms of common ground as well as distinctions will greatly help in searching for higher T(c) superconductors. However, studies on mechanisms for the iron family based on first principles calculations are few. Here we first show that superconductivity emerges in the state-of-the-art numerical calculations for an ab initio multi-orbital model of an electron-doped iron-based superconductor LaFeAsO, in accordance with experimental observations. Then the mechanism of the superconductivity is identified as enhanced uniform density fluctuations by one-to-one correspondence with the instability towards inhomogeneity driven by first-order antiferromagnetic and nematic transitions. Despite many differences, certain common features with the copper oxides are also discovered in terms of the underlying orbital-selective Mottness found in the iron family.

  14. Pressure and high-Tc superconductivity in sulfur hydrides

    PubMed Central

    Gor’kov, Lev P.; Kresin, Vladimir Z.

    2016-01-01

    The paper discusses fundamentals of record-TC superconductivity discovered under high pressure in sulfur hydride. The rapid increase of TC with pressure in the vicinity of Pcr ≈ 123GPa is interpreted as the fingerprint of a first-order structural transition. Based on the cubic symmetry of the high-TC phase, it is argued that the lower-TC phase has a different periodicity, possibly related to an instability with a commensurate structural vector. In addition to the acoustic branches, the phonon spectrum of H3S contains hydrogen modes with much higher frequencies. Because of the complex spectrum, usual methods of calculating TC are here inapplicable. A modified approach is formulated and shown to provide realistic values for TC and to determine the relative contributions of optical and acoustic branches. The isotope effect (change of TC upon Deuterium for Hydrogen substitution) originates from high frequency phonons and differs in the two phases. The decrease of TC following its maximum in the high-TC phase is a sign of intermixing with pairing at hole-like pockets which arise in the energy spectrum of the cubic phase at the structural transition. On-pockets pairing leads to the appearance of a second gap and is remarkable for its non-adiabatic regime: hydrogen mode frequencies are comparable to the Fermi energy. PMID:27167334

  15. Pressure and high-Tc superconductivity in sulfur hydrides

    NASA Astrophysics Data System (ADS)

    Gor'Kov, Lev P.; Kresin, Vladimir Z.

    2016-05-01

    The paper discusses fundamentals of record-TC superconductivity discovered under high pressure in sulfur hydride. The rapid increase of TC with pressure in the vicinity of Pcr ≈ 123GPa is interpreted as the fingerprint of a first-order structural transition. Based on the cubic symmetry of the high-TC phase, it is argued that the lower-TC phase has a different periodicity, possibly related to an instability with a commensurate structural vector. In addition to the acoustic branches, the phonon spectrum of H3S contains hydrogen modes with much higher frequencies. Because of the complex spectrum, usual methods of calculating TC are here inapplicable. A modified approach is formulated and shown to provide realistic values for TC and to determine the relative contributions of optical and acoustic branches. The isotope effect (change of TC upon Deuterium for Hydrogen substitution) originates from high frequency phonons and differs in the two phases. The decrease of TC following its maximum in the high-TC phase is a sign of intermixing with pairing at hole-like pockets which arise in the energy spectrum of the cubic phase at the structural transition. On-pockets pairing leads to the appearance of a second gap and is remarkable for its non-adiabatic regime: hydrogen mode frequencies are comparable to the Fermi energy.

  16. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    SciTech Connect

    Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C. -T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; Tung, I. C.; Liu, Jian; Fadley, C. S.; Chakhalian, J.; Freeland, J. W.

    2016-09-15

    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

  17. Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures

    SciTech Connect

    Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C. -T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; Tung, I. C.; Liu, Jian; Fadley, C. S.; Chakhalian, J.; Freeland, J. W.

    2016-09-15

    The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

  18. Spectroscopy of metal "superatom" nanoclusters and high-Tc superconducting pairing

    NASA Astrophysics Data System (ADS)

    Halder, Avik; Kresin, Vitaly V.

    2015-12-01

    A unique property of metal nanoclusters is the "superatom" shell structure of their delocalized electrons. The electronic shell levels are highly degenerate and therefore represent sharp peaks in the density of states. This can enable exceptionally strong electron pairing in certain clusters composed of tens to hundreds of atoms. In a finite system, such as a free nanocluster or a nucleus, pairing is observed most clearly via its effect on the energy spectrum of the constituent fermions. Accordingly, we performed a photoionization spectroscopy study of size-resolved aluminum nanoclusters and observed a rapid rise in the near-threshold density of states of several clusters (A l37 ,44 ,66 ,68 ) with decreasing temperature. The characteristics of this behavior are consistent with compression of the density of states by a pairing transition into a high-temperature superconducting state with Tc≳100 K. This value exceeds that of bulk aluminum by two orders of magnitude. These results highlight the potential of novel pairing effects in size-quantized systems and the possibility to attain even higher critical temperatures by optimizing the particles' size and composition. As a new class of high-temperature superconductors, such metal nanocluster particles are promising building blocks for high-Tc materials, devices, and networks.

  19. High-Tc superconducting quantum interference filters (SQIFs) made by ion irradiation

    NASA Astrophysics Data System (ADS)

    Ouanani, S.; Kermorvant, J.; Ulysse, C.; Malnou, M.; Lemaître, Y.; Marcilhac, B.; Feuillet-Palma, C.; Bergeal, N.; Crété, D.; Lesueur, J.

    2016-09-01

    Superconducting quantum interference filters (SQIFs) are arrays of superconducting loops of different sizes including Josephson junctions (JJ). For a random distribution of sizes, they present a non-periodic response to an applied magnetic field, with a large transfer function and a magnetic field sensitivity potentially improved with respect to that of a single SQUID. Such properties make SQIFs interesting devices to detect the magnetic component of electromagnetic waves at microwave frequencies. We have used the highly scalable technique of ion irradiation to make SQUIDs and SQIFs based on commercial YBa2Cu3O7 films, and studied their properties. Both display optimal performance as a function of temperature and bias current, that can be understood in the frame of numerical simulations that we developed. The role of asymmetries and dispersion in JJ characteristics (routinely found in high Tc superconductors technologies) is also studied. We have found that none of them impede the existence of a SQIF effect but both play a role on the emergence of the optimal point. We finally present results on SQIF made with 2000 SQUIDs in series, showing a transfer function {{d}}V/{{d}}B∼ 1000V/T.

  20. A universal order underlying the pseudogap regime of the underdoped high Tc cuprates

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    2014-03-01

    A major achievement in condensed matter physics in the last quarter century has been a step towards the understanding of the unconventional d-wave superconducting state in the copper-oxide materials. Surprisingly, the normal state out of which the superconducting state emerges remains a mystery at low charge carrier densities, i.e., in the underdoped regime. This regime is of particular interest because it is characterised by an unusual momentum dependent energy pseudogap in the excitation spectrum that has defied explanation and is key to a full understanding of the unconventional d-wave superconducting state. I will present new quantum oscillation experimental results within the pseudogap regime of the high Tc superconductors YBa2Cu3O6+x and YBa2Cu4O8 which now extend up to the optimally-doped regime. These data reveal the evolution of the Fermi surface approaching the putative quantum critical point under the superconducting dome. A comprehensive angle-resolved study of the Fermi surface enables us to unambiguously identify a specific form of order that accounts for the observed quantum oscillations as well as other spectroscopic, transport and thermodynamic probes within the pseudogap regime. The author would like to thank B. Ramshaw, S. Sebastian, F. Balakirev, C. Mielke, M. Altarawneh, P. Goddard, S. Sabok, B. Babrowski, D. Bonn, W. Hardy, R. Liang and G. Lonzarich. This work was supported by the DOE BES ``Science of 100 tesla'' project and by the NSF and Florida State.

  1. The Discovery of High-Tc Superconductivity and the Countdown to the Rally

    NASA Astrophysics Data System (ADS)

    Bednorz, J. Georg

    2007-03-01

    The guiding ideas on our road towards high-Tc superconductivity and the early work at the IBM Zurich Research Laboratory are briefly addressed. I will shed some light onto the environment and the decisive circumstances that in January 1986 led to the breakthrough with the discovery of superconductivity in the cuprates. The pre-``Woodstock'' period, which lasted less than a year, covers the time in which the Zurich team tested different La2CuO4-based compounds, confirmed the Meissner effect, and studied flux trapping in these new materials. It was also the time in which the news of the discovery started to spread and in which we experienced mixed reactions ranging from silent skepticism to polite (cautious) congratulations. This changed dramatically into excitement with the confirmation of the Zurich results by the Tokyo (S. Tanaka) and the Houston ( C.W. Chu) group, and cumulated in the take-off of the new field at the famous ``Woodstock Meeting of Physics'' after the discovery of the 90 K superconductor.

  2. Separation of charge-order and magnetic QCPs in heavy fermions and high Tc cuprates

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    2010-03-01

    The Fermi surface topology of high temperature superconductors inferred from magnetic quantum oscillation measurements provides clues for the origin of unconventional pairing thus previously not accessed by other spectroscopy techniques. While the overdoped regime of the high Tc phase diagram has a large Fermi surface consistent with bandstructure calculations, the underdoped regime of YBa2Cu2O6+x is found to be composed of small pockets. There is considerable debate as to whether the small observed ``pocket'' is hole-like or electron-like- whether the Fermi surface is best described by a t-J model or a conventional band folding picture- whether or not a Fermi liquid description applies- or- whether bilayer coupling splits the degeneracy of the observed pockets. We (myself and collaborators) have now collected an extensive body of experimental data that brings this debate to rest, but raises new questions about the nature of itinerant magnetism in underdoped high Tc cuprates. Quantum oscillation measurements are performed on multiple samples in magnetic fields extending to 85 T, temperatures between 30 mK (dilution fridge in dc fields to 45 T) and 18 K, over a range of hole dopings and with samples rotated in-situ about multiple axes with respect to the magnetic field. We perform a topographical map of the Fermi surface, enabling the in-plane shape of one of the pockets to be determined- imposing stringent constraints on the origin of the Fermi surface. While quantum oscillations measurements are consistent with a topological Fermi surface change associated with magnetism near optimal doping, they also point to a secondary instability deep within the underdoped regime beneath a high Tc superconducting sub-dome. An steep upturn in the quasiparticle effective mass is observed on underdoping, suggestive of a quantum critical point near x= 0.46 separating the metallic regime (composed of small pockets) from a more underdoped insulating charge-ordered regime (earlier

  3. Practical superconductor development for electrical power applications

    SciTech Connect

    Goretta, K.C.

    1991-10-01

    Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes technical progress of research and development efforts aimed at producing superconducting components based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and Tl-Ba-Ca-Cu oxides systems. Topics discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, and fabrication and properties of thin films. Collaborations with industry and academia are also documented. 10 figs.

  4. Practical superconductor development for electrical power applications

    SciTech Connect

    Goretta, K.C.

    1992-10-01

    Development of useful high-critical-temperature (high-[Tc]) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components that are based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and (TI,Pb)-(Ba,Sr)-Ca-Cu oxide systems. Topics discussed are synthesis and heat treatment of high-[Tc] superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, fabrication and properties of thin films, and development of prototype components. Collaborations with industry and academia are documented.

  5. Buffer layers for high-Tc thin films on sapphire

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

    1992-01-01

    Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

  6. Deformation processing of high-Tc superconducting oxides

    NASA Astrophysics Data System (ADS)

    Rajan, K.; German, R. M.; Knorr, D. B.; Maccrone, R. K.; Misiolek, W.; Wright, R. N.

    1989-04-01

    Plastic deformation and texture development in polycrystalline YBa2Cu3O7- δ has been studied to expedite the process development of high-critical-temperature (high-Tc) superconducting wires and tapes. It is anticipated that deformation texture will be a major processing consideration in terms of maximizing critical current density, assessing conductor-fabrication options in light of critical current density, and developing such mechanical properties as strength, toughness and thermal fatigue. The intrinsic texture development in YBa2Cu3O7- δ deformation processing should be highly beneficial, insofar as the c axes of the crystals tend to become oriented along the compression axis. This means that conducting tapes and wires formed by rolling, extrusion and drawing can develop textures with the c axis in the transverse or radial direction, thus maximizing the flow of current along the length of the conductor.

  7. NMR/MRI with hyperpolarized gas and high Tc SQUID

    DOEpatents

    Schlenga, Klaus; de Souza, Ricardo E.; Wong-Foy, Annjoe; Clarke, John; Pines, Alexander

    2000-01-01

    A method and apparatus for the detection of nuclear magnetic resonance (NMR) signals and production of magnetic resonance imaging (MRI) from samples combines the use of hyperpolarized inert gases to enhance the NMR signals from target nuclei in a sample and a high critical temperature (Tc) superconducting quantum interference device (SQUID) to detect the NMR signals. The system operates in static magnetic fields of 3 mT or less (down to 0.1 mT), and at temperatures from liquid nitrogen (77K) to room temperature. Sample size is limited only by the size of the magnetic field coils and not by the detector. The detector is a high Tc SQUID magnetometer designed so that the SQUID detector can be very close to the sample, which can be at room temperature.

  8. Buffer layers for high-Tc thin films on sapphire

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

    1992-01-01

    Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

  9. Compensated electron and hole pickets in an underdoped high Tc superconductor

    SciTech Connect

    Harrison, Neil; Altarawneh, Moaz M; Mielke, Charles H; Sebastian, Suchitra E; Goddard, P A; Liang, Ruixing; Bonn, D A; Hardy, W N; Andersen, O K; Lonzarich, G G

    2010-01-01

    Important to the question of high temperature superconductivity is whether bound fermionic pairs with zero or finite momentum - exhibiting bosonic physics - are involved. Here we use angle-dependent magnetic quantum oscillation measurements in underdoped YBa{sub 2}Cu{sub 3}O{sub 6+x} to reveal two significantly differently corrugated small sections of Fermi surface, identifying them as comprising opposite carriers located at different locations of the Brillouin zone. The surprising finding that these disproportionately heavy small pockets are equal in size indicates they are prone to a finite momentum excitonic insulator instability. We discuss the possibility that reducing the doping drives YBa{sub 2}Cu{sub 3}O{sub 6+x} closer to an instability of this nature, its ultimate realization occuring at the metal-insulator quantum critical point, accompanied by a potential enhancement of superconducting transition temperatures.

  10. Phase transitions to dipolar clusters and charge density waves in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Saarela, M.; Kusmartsev, F. V.

    2017-02-01

    We show that doping of hole charge carriers leads to formation of electric dipolar clusters in cuprates. They are created by many-body interactions between the dopant ion outside and holes inside the CuO planes. Because of the two-fold degeneracy holes in the CuO plane cluster into four-particles resonance valence bond plaquettes bound with dopant ions. Such dipoles may order into charge-density waves (CDW) or stripes or form a disordered state depending on doping and temperature. The lowest energy of the ordered system corresponds to a local anti-ferroelectric ordering. The mobility of individual disordered dipoles is very low at low temperatures and they prefer first to bind into dipole-dipole pairs. Electromagnetic radiation interacts strongly with electric dipoles and when the sample is subjected to it the mobility changes significantly. This leads to a fractal growth of dipolar clusters. The existence of electric dipoles and CDW induce two phase transitions with increasing temperature, melting of the ordered state and disappearance of the dipolar state. Ferroelectricity at low doping is a natural consequence of such dipole moments. We develop a theory based on two-level systems and dipole-dipole interaction to explain the behavior of the polarization as a function of temperature and electric field.

  11. Magnetic properties of fluorinated Pb-doped Hg-1223 high Tc superconductors

    SciTech Connect

    Hamdan, N.M.; Sastry, P.V.P.S.S.; Schwartz, J.

    2001-09-23

    Fluorination of Pb-doped HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (Hg-1223) system was investigated. Structural and magnetic measurements reveal that fluorine addition promotes the phase formation, optimize the charge carrier concentration, and enhance flux pinning. We report an increase in both the transition temperature and the critical current density through controlled fluorine incorporation. Even a possible change in the pinning mechanism in this technologically important system is suggested.

  12. Absolute measurements of the high-frequency magnetic dynamics in high-{Tc} superconductors

    SciTech Connect

    Hayden, S.M.; Aeppli, G.; Dai, P.; Mook, H.A.; Perring, T.G.; Cheong, S.W.; Fisk, Z.; Dogan, F.; Mason, T.E.

    1997-08-07

    The authors review recent measurements of the high-frequency dynamic magnetic susceptibility in the high-T{sub c} superconducting systems La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub 6+x}. Experiments were performed using the chopper spectrometers HET and MARI at the ISIS spallation source. The authors have placed their measurements on an absolute intensity scale, this allows systematic trends to be seen and comparisons with theory to be made. They find that the insulating S = 1/2 antiferromagnetic parent compounds show a dramatic renormalization in the spin wave intensity. The effect of doping on the response is to cause broadenings in wave vector and large redistributions of spectral weight in frequency.

  13. Thin-film-formation study of high-Tc superconductors by resistive evaporation

    NASA Astrophysics Data System (ADS)

    Azoulay, Jacob

    1991-10-01

    Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O thin films were prepared with use of a conventional vacuum system for the evaporation of the constituents. This method produces stoichiometric films upon complete evaporation of the constituents. No thickness monitor or any other control system is required. In this study, substrates were kept at room temperature during the evaporation process. The bismuth-based thin films are shown to lose bismuth during heat treatment unless the Cu constituent is evaporated last and fully oxidized at 400 °C subsequently. Y-Ba-Cu-O films prepared by using a pulverized mixture of Y, BaF2, and Cu constituents show an improved quality over films obtained from YF3, BaF2, and Cu starting materials. This improvement is attributed to fluorine reduction in the starting-material mixture.

  14. Investigation of inter- and intragrain critical currents in high Tc ceramic superconductors

    NASA Astrophysics Data System (ADS)

    Kuepfer, H.; Apfelstedt, I.; Fluekiger, R.; Keller, C.; Meier-Hirmer, R.

    1988-10-01

    Polycrystalline sintered bulk samples of REBa2Cu3O7 with RE = Y, Gd were studied by ac susceptibility and an inductive measurement technique which allows the separation of intergrain (transport) from intragrain critical current density. Field and temperature dependence of the intergrain current are compared with theoretical predictions for a weakly coupled grain structure. Up to fields 0.3 T the weak link character of the intergrain current predominates. At higher fields it changes and points to a percolation current via superconducting grain boundaries. A quantitative correlation between intragrain current and twin spacing is hidden, probably by oxygen deficiency in the grain interior. No variation of the intragrain critical current density with temperature is observed up to 85 K in a textured specimen.

  15. Reactive nanophase oxide additions to melt-processed high-{Tc} superconductors

    SciTech Connect

    Goretta, K.C.; Brandel, B.P.; Lanagan, M.T.; Hu, J.; Miller, D.J.; Sengupta, S.; Parker, J.C.; Ali, M.N.; Chen, Nan

    1994-10-01

    Nanophase TiO{sub 2} and Al{sub 2}O{sub 3} powders were synthesized by a vapor-phase process and mechanically mixed with stoichiometric YBa{sub 2}Cu{sub 3}O{sub x} and TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} powders in 20 mole % concentrations. Pellets produced from powders with and without nanophase oxides were heated in air or O{sub 2} above the peritectic melt temperature and slow-cooled. At 4.2 K, the intragranular critical current density (J{sub c}) increased dramatically with the oxide additions. At 35--50 K, effects of the oxide additions were positive, but less pronounced. At 77 K, the additions decreased J{sub c}, probably because of inducing a depresion of the transition temperature.

  16. Synthesis of One-dimensional Nano-sized Defects in High Tc Superconductor

    DTIC Science & Technology

    2006-07-31

    AAO template (pore size ~ 20-100 nm, pore density ~ 1010 – 1011 /cm2 ), (3) filling and produce RE-Ba-Cu-O 211 particles by sol gel + spin coating process...template is used as a mask for the wet (or dry) etching process, (4) filling and produce RE-Ba-Cu-O 211 particles by sol gel + spin coating process, (5...moderate etching rate of Y-Ba-Cu-O and with insignificant etching rate of AAO. Two steps spin - coating process(1 st step500 rpm5 s, 2 nd step1500rpm

  17. Design and performance of a high-Tc superconductor coplanar waveguide filter

    NASA Technical Reports Server (NTRS)

    Chew, Wilbert; Riley, A. L.; Rascoe, Daniel L.; Hunt, Brian D.; Foote, Marc C.; Cooley, Thomas W.; Bajuk, Louis J.

    1991-01-01

    The design of a coplanar waveguide low-pass filter made of YBa2Cu3O(7-delta) (YBCO) on an LaAlO3 substrate is described. Measurements were incorporated into simple models for microwave CAD analysis to develop a final design. The patterned and packaged coplanar waveguide low-pass filter of YBCO, with dimensions suited for integrated circuits, exhibited measured insertion losses when cooled in liquid nitrogen superior to those of a similarly cooled thin-film copper filter throughout the 0 to 9.5 GHz passband. Coplanar waveguide models for use with thin-film normal metal (with thickness either greater or less than the skin depth) and YBCO are discussed and used to compare the losses of the measured YBCO and copper circuits.

  18. Development of a thermal-hydraulics experimental system for high Tc superconductors cooled by liquid hydrogen

    NASA Astrophysics Data System (ADS)

    Tatsumoto, H.; Shirai, Y.; Shiotsu, M.; Hata, K.; Kobayashi, H.; Naruo, Y.; Inatani, Y.; Kato, T.; Futakawa, M.; Kinoshita, K.

    2010-06-01

    A thermal-hydraulics experimental system of liquid hydrogen was developed in order to investigate the forced flow heat transfer characteristics in the various cooling channels for wide ranges of subcoolings, flow velocities, and pressures up to supercritical. A main tank is connected to a sub tank through a hydrogen transfer line with a control valve. A channel heater is located at one end of the transfer line in the main tank. Forced flow through the channel is produced by adjusting the pressure difference between the tanks and the valve opening. The mass flow rate is measured from the weight change of the main tank. For the explosion protection, electrical equipments are covered with a nitrogen gas blanket layer and a remote control system was established. The first cryogenic performance tests confirmed that the experimental system had satisfied with the required performances. The forced convection heat transfer characteristics was successfully measured at the pressure of 0.7 MPa for various flow velocities.

  19. Experimental evidence for flux-lattice melting. [in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.

    1991-01-01

    A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of YBa2Cu3O(7-delta). The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range H = 0.1-2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.

  20. Theory of Enhanced Interlayer Tunneling in Optically Driven High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Okamoto, Jun-ichi; Cavalleri, Andrea; Mathey, Ludwig

    2016-11-01

    Motivated by recent pump-probe experiments indicating enhanced coherent c -axis transport in underdoped YBCO, we study Josephson junctions periodically driven by optical pulses. We propose a mechanism for this observation by demonstrating that a parametrically driven Josephson junction shows an enhanced imaginary part of the low-frequency conductivity when the driving frequency is above the plasma frequency, implying an effectively enhanced Josephson coupling. We generalize this analysis to a bilayer system of Josephson junctions modeling YBCO. Again, the Josephson coupling is enhanced when the pump frequency is blue detuned to either of the two plasma frequencies of the material. We show that the emergent driven state is a genuine, nonequilibrium superconducting state, in which equilibrium relations between the Josephson coupling, current fluctuations, and the critical current no longer hold.

  1. Experimental evidence for flux-lattice melting. [in high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.

    1991-01-01

    A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of YBa2Cu3O(7-delta). The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range H = 0.1-2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.

  2. Qdr-Based Approach to Microwave Characterization of HIGH-TC Superconductors

    NASA Astrophysics Data System (ADS)

    Cherpak, N. T.; Izhyk, E. V.; Kirichenko, A. Ya.; Velichko, A. V.

    2000-09-01

    A technique for HTS microwave characterization based on using quasioptical dielectric resonator (QDR) is proposed. Experimental set-up with 8mm waveband QDR has been developed. The setup operates as an integral one performing several functions. It enables measuring not only the temperature dependences of the microwave surface resistance, radiofrequency response of HTS to microwave irradiation, but also the nonlinear surface resistance. Authors discuss the scope for progress of the QDR-based technique and its new abilities.

  3. Disentangling the Electronic and Phononic Glue in a High-Tc Superconductor

    NASA Astrophysics Data System (ADS)

    Dal Conte, S.; Giannetti, C.; Coslovich, G.; Cilento, F.; Bossini, D.; Abebaw, T.; Banfi, F.; Ferrini, G.; Eisaki, H.; Greven, M.; Damascelli, A.; van der Marel, D.; Parmigiani, F.

    2012-03-01

    Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamental step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (Ω)-dependent bosonic function, Π(Ω). We performed optical spectroscopy on Bi2Sr2Ca0.92Y0.08Cu2O8+δ crystals with simultaneous time and frequency resolution; this technique allowed us to disentangle the electronic and phononic contributions by their different temporal evolution. The spectral distribution of the electronic excitations and the strength of their interaction with fermionic quasiparticles fully account for the high critical temperature of the superconducting phase transition.

  4. Disentangling the electronic and phononic glue in a high-Tc superconductor.

    PubMed

    Dal Conte, S; Giannetti, C; Coslovich, G; Cilento, F; Bossini, D; Abebaw, T; Banfi, F; Ferrini, G; Eisaki, H; Greven, M; Damascelli, A; van der Marel, D; Parmigiani, F

    2012-03-30

    Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamental step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (Ω)-dependent bosonic function, Π(Ω). We performed optical spectroscopy on Bi(2)Sr(2)Ca(0.92)Y(0.08)Cu(2)O(8+δ) crystals with simultaneous time and frequency resolution; this technique allowed us to disentangle the electronic and phononic contributions by their different temporal evolution. The spectral distribution of the electronic excitations and the strength of their interaction with fermionic quasiparticles fully account for the high critical temperature of the superconducting phase transition.

  5. Cluster Calculation of CuO2 in High-Tc Superconductors

    DTIC Science & Technology

    1991-01-01

    Rev. B38. 4 (1988) and V. J. Emery and G. I e fer. Phvs. Rev. 638, (1988). 6. J. M. Tranquada . S. M. Heald. A. R. Moodenbaugh, G. Liang and J. Croft...Nature 37.,2 (1989). 7. J. M. Tranquada . S. M. Heald and A. R. Moodenbaugh, Phys. Rev. B36. 5263(1987). 8. J1. A. Tranquada , S. M. Heald and A. R

  6. Dynamical Layer Decoupling in a Stripe-Ordered High-Tc Superconductor

    NASA Astrophysics Data System (ADS)

    Fradkin, Eduardo; Berg, Erez; Kim, Eun-Ah; Kivelson, Steve; Oganesyan, Vadim; Tranquada, John; Zhang, Shoucheng

    2008-03-01

    In the stripe-ordered state of a strongly correlated two-dimensional electronic system, under a set of special circumstances, the superconducting condensate, like the magnetic order, can occur at a nonzero wave vector corresponding to a spatial period double that of the charge order. In this case, the Josephson coupling between near neighbor planes, especially in a crystal with the special structure of La2-xBaxCuO4, vanishes identically. We propose that this is the underlying cause of the dynamical decoupling of the layers recently observed in transport measurements at x =1/8. [1] E. Berg et al, PRL 99, 127003 (2007)

  7. Dynamical Layer Decoupling in a Stripe-Ordered High-Tc Superconductor

    NASA Astrophysics Data System (ADS)

    Berg, E.; Fradkin, E.; Kim, E.-A.; Kivelson, S. A.; Oganesyan, V.; Tranquada, J. M.; Zhang, S. C.

    2007-09-01

    In the stripe-ordered state of a strongly correlated two-dimensional electronic system, under a set of special circumstances, the superconducting condensate, like the magnetic order, can occur at a nonzero wave vector corresponding to a spatial period double that of the charge order. In this case, the Josephson coupling between near neighbor planes, especially in a crystal with the special structure of La2-xBaxCuO4, vanishes identically. We propose that this is the underlying cause of the dynamical decoupling of the layers recently observed in transport measurements at x=1/8.

  8. The t J model for the oxide high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ogata, Masao; Fukuyama, Hidetoshi

    2008-03-01

    A theoretical review is given on high temperature superconductivity in copper oxides (cuprates) by focusing on the hole doping cases based on the view that it is realized in carrier doped Mott insulators, as noted by Anderson in the initial stage. From the detailed knowledge of electronic states deduced from experiments that showed the undoped parent case is Mott insulators (charge transfer type insulators, to be precise) and that the hole doping is mainly on oxygen sites, the t-J model, as derived by Zhang and Rice, is shown to be a canonical model for hole doped cuprates and values of various parameters of the model have been assessed. Results of many different numerical methods so far obtained for this t-J model, especially the variational Monte Carlo method, have clearly indicated the stability of the \\rmd_{x^2-y^2} -wave superconductivity at absolute zero for the parameter region of actual experimental interest and the particular doping dependences of the condensation energy of superconductivity reflecting particular features of doped Mott insulators. For finite temperatures, on the other hand, the field theoretical slave-boson approximation based on the spin (spinons) and charge (holons) separations and the gauge fields as a glue combining them predicts qualitatively particular features of the existence of characteristic crossover temperatures of the spin singlet of the resonating valence bond (RVB) state, TRVB and the onset of Bose condensation of holons, TB, triggering coherent motion of electrons as convoluted particles of spinons and holons. The considerations based on the gauge field indicate that the onset temperature of superconductivity, Tc, is the lower one of these two, i.e. either TB (overdoped cases) or TRVB (underdoped cases), respectively. These characteristic features of the 'phase diagram' at finite temperatures are in overall agreement with various experimental observations, especially with the existence of spin-gap or pseudo-gap phases. In more detailed examinations of the underdoped region, the antiferromagnetic long-range order and superconductivity show a very intricate relationship at low temperatures depending on the system; they coexist as clarified in the inner layer of Hg-1245 but spin glass states intervene between them in La2-xSrxCuO4 (LSCO). It is argued that these differences can be attributed to the different degrees of disorder. Actually, theories based on the t-J model have also predicted the coexistence of antiferromagnetism and superconductivity in the ground state of clean systems. On the other hand, interesting experimental findings of large Nernst effect and 'Fermi arc' in LSCO and impurity effects in YBCO have prompted the necessity of theoretical investigations of electronic states of lightly doped Mott insulators in the presence of strong disorder.

  9. What Can Ultracold Fermi Gases Teach Us About High Tc Superconductors and Vice Versa?

    SciTech Connect

    Levin, Kathryn

    2007-01-10

    Studies of superfluidity in ultracold trapped Fermi gases are attracting physicists from a wide range of sub-disciplines including nuclear, condensed matter and particle physics. The excitement in the field is due, in large part, to the remarkable tuneability of these Fermi gases. One can tune the attractive interaction strength continuously from weak to strong (thereby effecting a transition from a BCS to Bose Einstein condensed (BEC) superfluid). One can introduce polarization into the gases at will, which may lead to long-sought-after, but not yet confirmed, exotic superfluid phases. In this talk we discuss the relevance of the cold Fermi gases to other physics subdisciplines. We then summarize how BCS-BEC crossover in the ultracold gases connects with a particularly important topic in condensed matter: high temperature superconductivity. We emphasize some striking similarities relating to the very unusual normal or 'pseudogap' phase of each of the two systems. In the process we give a summary of some of the latest exciting experimental developments in the two fields.

  10. Dynamics of Bragg glass in high-Tc superconductors near depinning transition

    NASA Astrophysics Data System (ADS)

    Luo, Meng-Bo; Hu, Xiao

    2010-12-01

    The dynamics of vortices near depinning transition is studied in terms of a three-dimensional flux-line model with point-like pinning centers. The zero-temperature critical depinning force F is determined with two methods consistently. We find two universal exponents β≈0.64 and δ≈2.3 which characterize the critical behaviors of depinning transition of Bragg glass (BrG). The dynamical modes of flux lines near F are also discussed.

  11. Theoretical analysis of NMR experiments in normal and superconducting states of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Mack, Frank; Kulić, Miodrag L.; Mehring, Michael

    1998-01-01

    The Knight shift and T1- and T2-rates of YBa 2Cu 3O 6+ x in the normal and superconducting state are modeled by calculating the magnetic susceptibility in the bi-layer Hubbard model within various approximations. An optimal set of parameters (OSP) is found in the RPA approximation which fits experiments on YBCO for optimal and nearly optimal doping. The analysis of the self-consistent FLEX approximation for the particle self-energy and susceptibility shows that the latter is renormalized quantitatively but not qualitatively. The differences in the oxygen and copper T1-rates are explained by using the OSP parameters and assuming the finite hyperfine coupling C‧ between 17O and next-nearest neighboring Cu spins. The numerical analysis of T1-1 and T2-1 and the ratio 63T1 ab-1/ 63T1 c-1 in the superconducting state supports strongly the idea of d-wave pairing in YBa 2Cu 3O 7 with much stronger intraplane rather than interplane pairing. It is also shown that the simple RPA or FLEX approximations are inadequate in explaining NMR data in underdoped YBCO systems, where antiferromagnetic fluctuations are very pronounced.

  12. The Crystallographic Study of Pr Substituted Eu-123 High Tc Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Huse, V. R.; Mote, V. D.; Hasan, K. I.; Dole, B. N.; Shah, S. S.

    2011-07-01

    We have investigated Eu1-xPrxBa2Cu3O7-δ high purity samples with compositions x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 by well known ceramic route. The XRD study of all samples is carried out. The XRD study of the samples prepared by ceramic route show EuPr-123 system has an orthorhombic pervoskite structure. The lattice parameters, oxygen content, volume of unit cell, orthorhombicity, X-ray density, bulk density and porosity were evaluated using XRD data. It is found that the lattice parameters, volume of unit cell and porosity increase while oxygen content orthorhombicity, X-ray density and bulk density decrease as doping percentage of Pr increases. We report such qualitative results of Pr substituted Eu-123 in this paper quantitatively.

  13. A technique to measure the thermal diffusivity of high Tc superconductors

    NASA Technical Reports Server (NTRS)

    Powers, Charles E.

    1991-01-01

    High T(sub c) superconducting electrical current leads and ground straps will be used in cryogenic coolers in future NASA Goddard Space Flight Center missions. These superconducting samples are long, thin leads with a typical diameter of two millimeters. A longitudinal method is developed to measure the thermal diffusivity of candidate materials for this application. This technique uses a peltier junction to supply an oscillatory heat wave into one end of a sample and will use low mass thermocouples to follow the heat wave along the sample. The thermal diffusivity is calculated using both the exponential decay of the heat wave and the phase shift to the wave. Measurements are performed in a cryostat between 10 K and room temperature.

  14. Moderately shielded high-Tc SQUID system for rat MCG

    NASA Astrophysics Data System (ADS)

    Bechstein, S.; Kim, I.-S.; Drung, D.; Novikov, I.; Schurig, Th

    2010-06-01

    Recently, we have developed a 5-channel high-Tc SQUID system with one signal channel intended for rat magnetocardiography (MCG) in moderately shielded or "quiet" real environment. This system is an adapted version of a human MCG system which has been improved with respect to user-friendliness and stability. A dewar with a cold-warm distance of 7 mm and a refill cycle time of up to one week is utilized. The implemented high-Tc SQUIDs are single-layer devices with grain boundary junctions fabricated at KRISS with laser ablation on 10 mm × 10 mm STO substrates. In order to cancel environmental magnetic noise, three of the five SQUIDs are arranged to build an axial software first-order or second-order gradiometer with a base line of 35 mm. The other two SQUIDs are used for balancing. To overcome previous system instabilities, we have implemented an Earth field compensation for each SQUID. For this, the SQUIDs were mounted in capsules containing integrated field compensation coils. The three Earth field components are measured with an additional triaxial fluxgate, and compensated at the SQUID locations using the low-noise current source of the SQUID readout electronics. This way, the SQUIDs can be cooled and operated in a low residual field that improves system stability and reduces low-frequency SQUID noise. It is even possible to slowly move the dewar in the Earth field (dynamic field compensation). Different noise cancellation procedures were optimized and compared employing a periodic signal source.

  15. Characterization of bulk superconductors through EBSD methods

    NASA Astrophysics Data System (ADS)

    Koblischka, M. R.; Koblischka-Veneva, A.

    2003-10-01

    The application of electron backscatter diffraction (EBSD) technique to bulk high- Tc superconductors is presented and reviewed. Due to the ceramic nature and the complex crystallographic unit cells of the perovskite-type high- Tc superconductors, the EBSD analysis is not yet as common as it deserves. We have successfully performed EBSD analysis on a variety of high- Tc compounds and samples including polycrystalline YBCO (pure and doped by alkali metals), melt-textured YBCO, thin and thick films of YBCO; the “green phase” Y 2BaCuO 5, thin film and melt-textured NdBa 2Cu 3O x and Bi-2212 single crystals and tapes. It is shown that the surface preparation of the samples is crucial due to the small information depth (up to 100 nm) of the EBSD technique. High quality Kikuchi patterns are the requirement in order to enable the automated EBSD mapping, which yields phase distributions, individual grain orientations and the misorientation angle distribution. The results can be presented in form of mappings, as charts, and as pole figures. These informations are required for a better understanding of the growth mechanism(s) of bulk high- Tc superconductors intended for applications.

  16. Update on copper oxide superconductors

    SciTech Connect

    Cava, R.J.

    1995-05-01

    The early high-{Tc} superconductors Ba{sub 2}YCu{sub 3}O{sub 7} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} remain the most studied for their potential application. The number and variety of new copper oxide superconductors discovered since 1986 is remarkable. Although physicists like to take credit for the superconductivity revolution, it is really a revolution in new materials. New materials of continually increasing complexity have driven the field forward since its beginning. It is no accident that the chemically simplest copper oxide superconductors were discovered first. Higher {Tc} values have been caused by the rapid growth in general knowledge in the material community of the empirical factors necessary for the occurrence of high-{Tc} superconductivity. The growth is based on improving chemical understanding of previous discoveries. The chemical understanding and complexity of cuprate superconductors continue to increase. The appearance in 1993 of mercury-based materials has further raised {Tc} values.

  17. Electron-doping of graphene-based devices by hydrazine

    SciTech Connect

    Feng, Tingting; Xie, Dan; Wang, Dongxia; Wen, Lang; Wu, Mengqiang

    2014-12-14

    A facile and effective technique to tune the electronic properties of graphene is essential to facilitate the flexibility of graphene-based device performances. Here, the use of hydrazine as a solution-processable and effective n-type dopant for graphene is described. By dropping hydrazine solutions at different concentrations on a graphene surface, the Dirac point of graphene can be remarkably tuned. The transport behavior of graphene can be changed from p-type to n-type accordingly, demonstrating the controllable and adjustable doping effect of the hydrazine solutions. Accompanying the Dirac point shift is an enhanced hysteretic behavior of the graphene conductance, indicating an increasing trap state density induced by the hydrazine adsorbates. The electron-doping of graphene by the hydrazine solutions can be additionally confirmed with graphene/p-type silicon heterojunctions. The decrease of the junction current after the hydrazine treatment demonstrates an increase of the junction barrier between graphene and silicon, which is essentially due to the electron-doping of graphene and the resultant upshift of the Fermi level. Finally, partially doped graphene is realized and its electrical property is studied to demonstrate the potential of the hydrazine solutions to selectively electron-doping graphene for future electronic applications.

  18. Study of Cu-wound Flux transformer for High-Tc SQUID Ultra-Low Field MRI

    NASA Astrophysics Data System (ADS)

    Tanaka, S.; Murata, H.; Imamura, K.; Hatsukade, Y.

    2014-05-01

    We constructed a ultra-low field (ULF) nuclear magnetic resonance (NMR) / magnetic resonance imaging (MRI) system employing a high-temperature superconductor (High Tc) SQUID with a separated Cu-wound flux transformer. The pickup coil consisted of two single solenoid coils and each coil was differentially connected each other. The flux transformer consisted of a pickup coil at room temperature and an input coil, which was put in liquid nitrogen and was magnetically coupled with a high-Tc SQUID. The ratio of the transformer was considered and optimized. A water phantom of 10 mL was located in the one side of pickup coil. In the system, we applied polarizing field Bp perpendicular to the measurement field Bm before measurements. Bp was 0.8 T and permanent magnet was used. By using this system, free induction decay (FID) signals of 2H were measured at Bm of 30 μT to evaluate the system. The longitudinal relaxation times T1 of water were also estimated by changing the polarizing time of Bp.

  19. Magnetic forces in high-Tc superconducting bearings

    NASA Technical Reports Server (NTRS)

    Moon, F. C.

    1991-01-01

    In September 1987, researchers at Cornell levitated a small rotor on superconducting bearings at 10,000 rpm. In April 1989, a speed of 120,000 rpm was achieved in a passive bearing with no active control. The bearing material used was YBa2Cu307. There is no evidence that the rotation speed has any significant effect on the lift force. Magnetic force measurements between a permanent rare-earth magnet and high T(sub c) superconducting material versus vertical and lateral displacements were made. A large hysteresis loop results for large displacements, while minor loops result for small displacements. These minor loops seem to give a slope proportional to the magnetic stiffness, and are probably indicative of flux pinning forces. Experiments of rotary speed versus time show a linear decay in a vacuum. Measurements of magnetic dipole over a high-T(sub c) superconducting disc of YBCO show that the lateral vibrations of levitated rotors were measured which indicates that transverse flux motion in the superconductor will create dissipation. As a result of these force measurements, an optimum shape for the superconductor bearing pads which gives good lateral and axial stability was designed. Recent force measurements on melt-quench processed superconductors indicate a substantial increase in levitation force and magnetic stiffness over free sintered materials. As a result, application of high-T(sub c) superconducting bearings are beginning to show great promise at this time.

  20. Early High Tc Activity in Japan: The Franco Rasetti Lecture

    NASA Astrophysics Data System (ADS)

    Tanaka, Shoji

    2007-03-01

    From 1960 to 1980, R&D of superconductivity in Japan was carried out mainly to improve A15 superconducting wires and magnets. Improvement of wires were made mainly in the National Institute for Metals, and improvements of superconducting magnets were made in the Japan Atomic Energy Research Institute for future nuclear fusion reactors, the National Railway Laboratory for future maglev trains and also in the Electo-Technical Laboratory for MHD generators. I began the research of BPBO in 1975 and at that time the research of oxide superconductors was limited only to my laboratory in the University of Tokyo. During the study of this new superconductor, we learned quite a lot on how to make ceramic samples, how to measure electrical conductivity and magnetic susceptibility at low temperatures. In 1982, Prof. S. Nakajima organized a rather small group for investigating ``New Superconducting Phenomena,'' and I became a member of the group. In 1985, Nakajima expanded the research group to include more than 5 experimentalists and 5 theoreticians. The title of the research was ``New Superconducting Materials'' and the funds came from the Ministry of Education of Japan. In late October, 1986, we followed the first paper of Bednorz and Muller, and immediately found the material includes high temperature superconductor and reported it to the group meeting held in early November. In early December, we confirmed La2-xBaxCuO4 is the real high temperature superconductor, the critical temperature is 28K. I sent a copy of our paper to Prof. Beasley of California and asked to inform this fact to his colleagues. Asahi Shimbun, the biggest newspaper in Japan announced this in its science section, and then many people knew the high temperature superconductor had been discovered. Then many physicists and chemists rushed to this field very quickly and many kinds of materials were synthesized. In the Government, the Ministry of Education, the Ministry of International Trade and Industry

  1. Torque magnetometry in unconventional superconductors

    NASA Astrophysics Data System (ADS)

    Li, Lu

    This thesis describes torque magnetometry studies on unconventional superconductors. Torque magnetometry measures the anisotropic magnetization of samples by recording their torque signals in a tilted magnetic field. Applied to superconductors, this method provides a reliable way to measure the field dependence of magnetization with high resolution under extreme conditions: DC magnetic fields from zero to 45.2 T, and temperature from 300 mK to 300K. The results can be used to determine many important parameters, such as the upper critical field H c2, the superconducting condensation energy, the onset temperature of diamagnetic signals, and so on. We carried out the torque magnetometry measurements on unconventional superconductors---high Tc superconductors and the p-wave superconductor Sr2RuO4---and uncovered new features that do not exist in conventional BCS superconductors. In high Tc superconductors, our torque magnetometry studies focus on the properties of the vortex liquid state. First, by comparing the observed magnetization curves with the Nernst effect results in Bi 2Sr2CaCu2O8+delta, we confirm that the unusually large Nernst effect signals originate from the surviving vortex liquid state above Tc. Second, the M-H curves near the critical temperature Tc suggest that the nature of the transition is the Kosterlitz-Thouless transition. Near Tc, the magnetization response at low field is strongly nonlinear, and the T dependence of the magnetic susceptibility in the low-field limit approaches the predicted curve from the Kosterlitz-Thouless transition. Third, the measurements in intense magnetic field up to 45 T reveal the unusual, weak T-dependence of Hc2. These observations strongly support the existence of the vortex liquid state above Tc. The superconducting state is destroyed by the phase fluctuation of the pair condensate, while the pair condensate keeps its amplitude above T c. Further studies in single-layered high Tc superconductors reveal more

  2. Ferrite-superconductor devices for advanced microwave applications

    SciTech Connect

    Dionne, G.F.; Oates, D.E.; Temme, D.H.; Weiss, J.A.

    1996-07-01

    Microwave devices comprising magnetized ferrite in contact with superconductor circuits designed to eliminate magnetic field penetration of the superconductor have demonstrated phase shift without significant conduction losses. The device structures are adaptable to low- or high-{Tc} superconductors. A nonoptimized design of a ferrite phase shifter that employs niobium or YBCO meanderlines has produced over 1,000 degrees of differential phase shift with a figure of merit exceeding 1,000 degrees/dB at X band. By combining superconductor meanderline sections with alternating T junctions on a ferrite substrate in a configuration with three-fold symmetry, a low-loss three-port switching circulator has been demonstrated.

  3. First 13 years of high-{Tc}: Brief review and open questions

    SciTech Connect

    Pavuna, D.

    1999-12-20

    Exactly 13 years ago, in April 1986, appeared the famous paper by Bednorz and Mueller, that announced a striking discovery of high-{Tc} superconductivity in cuprates. Some 40,000 papers later, scientists are still struggling to understand the high-{Tc} superconductivity. Here the author summarizes some of the most relevant recent results and open questions by discussing the observed phenomena in a rather complex electronic phase diagram of high-{Tc} oxides.

  4. Development of Elements of a High Tc Superconducting Cable

    DTIC Science & Technology

    1989-03-31

    0 0O DTIC N ELECTE MA 61989D N00014-88-C-000681 DEVELOPMENT OF ELEMENTS OF A HIGH T SUPERCONDUCTING CABLE C Dr. Kenneth W. Lay 518-387-6147 FAX 518... superconducting coating on a supporting fiber. The composite will also include a barrier layer between the fiber and the superconductor and a protective layer...is the development of textured polycrystalline YBa 2Cu3Oy (Y-123) with improved critical current carrying capacity. Phase II is the development of

  5. High-Tc SQUID gradiometer system for immunoassays

    NASA Astrophysics Data System (ADS)

    Öisjöen, F.; Magnelind, P.; Kalabukhov, A.; Winkler, D.

    2008-03-01

    A high-Tc dc SQUID (superconducting quantum interference device) gradiometer was developed for magnetic immunoassays where magnetic nanoparticles are used as markers to detect biological reactions. The gradiometer was fabricated on a 5 × 10 mm2 SrTiO3 bicrystal substrate and has a gradiometer resolution of 2.1 pT cm-1 Hz-1/2. A magnetic signal was detected from a sample of 1 µl of Fe3O4 nanoparticles in a 40 mg ml-1 solution kept in a microcavity fabricated on Si wafers with Si3N4 membranes using MEMS (micro-electro-mechanical-systems) technology. It was found that volumes as small as 0.3 nl in principle would be detectable with our present device. This corresponds to a total number of particles of 2.2 × 107. The estimated average dipole moment per particle is 4.8 × 10-22 A m2. We are aiming at reading out immunoassays by detecting the Brownian relaxation of magnetic nanoparticles, and we also intend to integrate MEMS technology into our system.

  6. Terahertz imaging system using high-Tc superconducting oscillation devices

    NASA Astrophysics Data System (ADS)

    Tsujimoto, M.; Minami, H.; Delfanazari, K.; Sawamura, M.; Nakayama, R.; Kitamura, T.; Yamamoto, T.; Kashiwagi, T.; Hattori, T.; Kadowaki, K.

    2012-06-01

    Microwatt power oscillation devices at sub-terahertz frequency region between 0.3 and 1.0 terahertz (THz) were fabricated from high-Tc superconducting single crystalline Bi2Sr2CaCu2O8+δ and used as a source of the transmission terahertz imaging system. As test examples, terahertz images of coins and a razor blade placed inside the brownish paper envelopes with the spatial resolution of 1 mm are presented. The signal-to-noise ratio exceeds 130 in these images. Using a simple wedge-shaped interferometer and analysing the interference fringe pattern, the wavelength of the terahertz wave is calibrated within 0.1% accuracy. This interferometer also provides a simple method to measure the absorption coefficient of the liquid sample. Two test measurements for distilled water and ethanol are demonstrated and their absorption coefficients are obtained with 99.2% accuracy. This suggests that our terahertz imaging system can be applied to many practical applications, such as biological and biomedical imaging, environmental monitoring, microanalysis of impurities, structure and dynamical analyses of large molecules and ions in solution.

  7. Dynamic resistance of a high-Tc superconducting flux pump

    NASA Astrophysics Data System (ADS)

    Jiang, Zhenan; Hamilton, K.; Amemiya, Naoyuki; Badcock, R. A.; Bumby, C. W.

    2014-09-01

    Superconducting flux pumps enable large currents to be injected into a superconducting circuit, without the requirement for thermally conducting current leads which bridge between the cryogenic environment and room temperature. In this work, we have built and studied a mechanically rotating flux pump which employs a coated conductor high-Tc superconducting (HTS) stator. This flux pump has been used to excite an HTS double pancake coil at 77 K. Operation of the flux pump causes the current within the superconducting circuit to increase over time, before saturating at a limiting value. Interestingly, the superconducting flux pump is found to possess an effective internal resistance, Reff, which varies linearly with frequency, and is two orders of magnitude larger than the measured series resistance of the soldered contacts within the circuit. This internal resistance sets a limit for the maximum achievable output current from the flux pump, which is independent of the operating frequency. We attribute this effect to dynamic resistance within the superconducting stator wire which is caused by the interaction between the DC transport current and the imposed alternating magnetic field. We provide an analytical expression describing the output characteristics of our rotating flux pump in the high frequency limit, and demonstrate that it describes the time-dependent behavior of our experimental circuit. Dynamic resistance is highlighted as a generic issue that must be considered when optimizing the design of an HTS flux pump.

  8. A novel propulsion method for high- Tc superconducting maglev vehicle

    NASA Astrophysics Data System (ADS)

    Ma, Guangtong; Wang, Jiasu; Wang, Suyu; Liu, Minxian; Jing, Hua; Lu, Yiyun; Lin, Qunxu

    2008-01-01

    High-Tc superconducting (HTS) maglev is considered as a perfect transportation type because of its unique inherent stability. A direct current (DC) linear motor using the permanent magnet guideway (PMG) as the stator and the on-board coil as the rotor instead of the present inductive or synchronous alternate current (AC) linear motor which has an economic disadvantage due to the necessity to lay primary coil along the guideway is proposed in this paper. In order to modulate the magnetic field under the PMG, an inverse E shape ferromagnetic device (IESFD) core is designed. The possible winding method for the on-board coil is listed, and the analytical result shows that a considerable net ampere force and thus the propulsion force can be generated by this special structure. The influence of the concentrated effect of the IESFD on the maglev performance of HTS bulk is studied by a numerical program, and the results show that the levitation force with the IESFD is 90% of that without. It is also indicated that the load capability and lateral performance of the maglev vehicle combined this propulsion method can be improved thanks to the attractive effect between the IESFD and PMG. The cost of the HTS maglev vehicle will be remarkably reduced and then shorten the distance to practical application with this propulsion method.

  9. Analysis of microstrip lines with alternative implementation of conductors and superconductors

    NASA Astrophysics Data System (ADS)

    Kong, K.-S.; Lee, H.-Y.; Itoh, T.; Chorey, C. M.; Bhasin, K. B.

    1990-09-01

    An analysis of microstrip line structures in which either the strip or the ground plane or both are made of a high Tc superconductor is presented. The effect of implementation of a superconductor to the strip and the ground plane is explained with the calculation of a conductor loss of the structure by the Phenomenological Loss Equivalence Method (PEM). The theoretical values are compared with the experimental results from a ring resonator which is made of a gold ground plane and a high Tc superconductor, YBa2Cu3O(7-x), strip.

  10. Analysis of microstrip lines with alternative implementation of conductors and superconductors

    NASA Technical Reports Server (NTRS)

    Kong, K.-S.; Lee, H.-Y.; Itoh, T.; Chorey, C. M.; Bhasin, K. B.

    1990-01-01

    An analysis of microstrip line structures in which either the strip or the ground plane or both are made of a high Tc superconductor is presented. The effect of implementation of a superconductor to the strip and the ground plane is explained with the calculation of a conductor loss of the structure by the Phenomenological Loss Equivalence Method (PEM). The theoretical values are compared with the experimental results from a ring resonator which is made of a gold ground plane and a high Tc superconductor, YBa2Cu3O(7-x), strip.

  11. X-ray photoemission study of the infinite-layer cuprate superconductor Sr(0.9) La (0.1) CuO(2)

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Jung, C. U.; Kim, J. Y.; Kim, M. S.; Lee, S. Y.; Lee, S. I.

    2001-01-01

    The electron-doped infinite-layer superconductor Sr(0.9)La(0.1) CuO(2) is studied with x-ray photoemission spectroscopy (XPS). A nonaqueous chemical etchant is shown to effectively remove contaminants and to yield surfaces from which signals intrinsic to the superconductor dominate.

  12. X-ray photoemission study of the infinite-layer cuprate superconductor Sr(0.9) La (0.1) CuO(2)

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Jung, C. U.; Kim, J. Y.; Kim, M. S.; Lee, S. Y.; Lee, S. I.

    2001-01-01

    The electron-doped infinite-layer superconductor Sr(0.9)La(0.1) CuO(2) is studied with x-ray photoemission spectroscopy (XPS). A nonaqueous chemical etchant is shown to effectively remove contaminants and to yield surfaces from which signals intrinsic to the superconductor dominate.

  13. Fermi surface splittings in multilayered high-Tc cuprates with charge imbalance

    NASA Astrophysics Data System (ADS)

    Mori, M.; Tohyama, T.; Maekawa, S.

    2006-03-01

    Cuprate superconductors have layered structure of CuO2 planes, which makes conducting blocks separated by an charge- reservoir block. Multilayered high-Tc cuprates, e.g., Ba2Ca3Cu4O8(O1-yFy)2 and HgBa2Ca4Cu5Oy, have two kinds of CuO2 planes in a unit cell; the outer-pyramidal-coordinated-planes (OP's) and the inner- square-coordinated-planes (IP's). The carrier density in the OP is generally different from that in the IP. We call such an inhomogeneous charge-distribution charge imbalance'. We study doping dependence of interlayer hoppings, t, in such a charge-imbalance system in the Gutzwiller approximation. When the double occupancy is forbidden in the CuO2 plane, an effective amplitude of t is shown to be proportional to the square root of the product of doping rates in adjacent two planes. Therefore, the charge imbalance in more than three-layered cuprates results in two different values of t^eff, i.e., t^eff1t√δIP δIP between IP's, and t^eff2t√δIP δOP between IP and OP, where δIP (δOP) is the doping rates in IP (OP). Fermi surfaces are calculated in the four-layered t-t'- t''-J model by the mean-field theory. The order parameters, the renormalization factor of t, and the site- potential making the charge imbalance between IP and OP are self-consistently determined for several doping rates. We show the interlayer splitting of the Fermi surfaces, which may be observed in the angle resolved photoemission spectroscopy measurement. *cond-mat/0511249.

  14. Characteristics of an electromagnetic levitation system using a bulk superconductor

    SciTech Connect

    Senba, A.; Kitahara, H.; Ohsaki, H.; Masada, E.

    1996-09-01

    It is beneficial to apply a high-Tc bulk superconductor as a large flux source to an electromagnetic levitation system, which needs large amounts of levitation force. The authors made an attractive-type electromagnetic levitation system using a hybrid magnet that mainly consisted of bulk superconductor and control coils to confirm the principle of the levitation, and obtained characteristics of its system by both experiment and numerical analysis with magnetic circuit calculation. This is applicable to maglev transportation systems.

  15. High-Tc and low-Tc dc SQUID electronics

    NASA Astrophysics Data System (ADS)

    Drung, Dietmar

    2003-12-01

    Superconducting quantum interference devices (SQUIDs) are commonly operated in a flux-locked loop (FLL). The SQUID electronics amplifies the small SQUID signal to an acceptable level without adding noise, and it linearizes the transfer function of the SQUID in order to provide sufficient dynamic range. In this paper, the fundamentals of SQUID readout are reviewed including a discussion of preamplifier noise. The basic FLL concepts, direct readout and flux modulation readout, are discussed both with dc bias and bias reversal. Alternative readout concepts such as additional positive feedback (APF), two-stage SQUIDs, SQUID series arrays, relaxation oscillation SQUIDs and digital SQUIDs are briefly described. The FLL dynamics are discussed on the basis of a simple model with finite loop delay. It is shown that with optimized SQUID electronics a system bandwidth of ap18 MHz and a corresponding slew rate of ap8 PHgr0 µs-1 are possible. A novel FLL scheme involving a Smith predictor is presented which allows one to increase the FLL bandwidth to about 100 MHz. The theoretical predictions are experimentally checked using a high-speed SQUID electronics prototype with a small-signal bandwidth of 300 MHz. Methods for increasing the dynamic range of SQUID systems are described: flux-quanta counting and dynamic field compensation (DFC). With DFC, the residual magnetic field at the SQUID can be kept close to zero even if the device is moved in the Earth's field. Therefore, the noise level of a high-Tc magnetometer measured inside a magnetically shielded room (60 fT Hz-1/2 with a 1/f corner at 2 Hz) remained unchanged after moving the device in the magnetic field outside the room (60 µT dc plus 0.8 µT peak-to-peak power line interference).

  16. Enhanced superconductivity in surface-electron-doped iron pnictide Ba(Fe1.94Co0.06)2As2.

    PubMed

    Kyung, W S; Huh, S S; Koh, Y Y; Choi, K-Y; Nakajima, M; Eisaki, H; Denlinger, J D; Mo, S-K; Kim, C; Kim, Y K

    2016-12-01

    The superconducting transition temperature (TC) in a FeSe monolayer on SrTiO3 is enhanced up to 100 K (refs ,,,). High TC is also found in bulk iron chalcogenides with similar electronic structure to that of monolayer FeSe, which suggests that higher TC may be achieved through electron doping, pushing the Fermi surface (FS) topology towards leaving only electron pockets. Such an observation, however, has been limited to chalcogenides, and is in contrast to the iron pnictides, for which the maximum TC is achieved with both hole and electron pockets forming considerable FS nesting instability. Here, we report angle-resolved photoemission characterization revealing a monotonic increase of TC from 24 to 41.5 K upon surface doping on optimally doped Ba(Fe1-xCox)2As2. The doping changes the overall FS topology towards that of chalcogenides through a rigid downward band shift. Our findings suggest that higher electron doping and concomitant changes in FS topology are favourable conditions for the superconductivity, not only for iron chalcogenides, but also for iron pnictides.

  17. Enhanced superconductivity in surface-electron-doped iron pnictide Ba(Fe1.94Co0.06)2As2

    NASA Astrophysics Data System (ADS)

    Kyung, W. S.; Huh, S. S.; Koh, Y. Y.; Choi, K.-Y.; Nakajima, M.; Eisaki, H.; Denlinger, J. D.; Mo, S.-K.; Kim, C.; Kim, Y. K.

    2016-12-01

    The superconducting transition temperature (TC) in a FeSe monolayer on SrTiO3 is enhanced up to 100 K (refs ,,,). High TC is also found in bulk iron chalcogenides with similar electronic structure to that of monolayer FeSe, which suggests that higher TC may be achieved through electron doping, pushing the Fermi surface (FS) topology towards leaving only electron pockets. Such an observation, however, has been limited to chalcogenides, and is in contrast to the iron pnictides, for which the maximum TC is achieved with both hole and electron pockets forming considerable FS nesting instability. Here, we report angle-resolved photoemission characterization revealing a monotonic increase of TC from 24 to 41.5 K upon surface doping on optimally doped Ba(Fe1-xCox)2As2. The doping changes the overall FS topology towards that of chalcogenides through a rigid downward band shift. Our findings suggest that higher electron doping and concomitant changes in FS topology are favourable conditions for the superconductivity, not only for iron chalcogenides, but also for iron pnictides.

  18. Epitaxial stabilization of ultra thin films of electron doped manganites

    SciTech Connect

    Middey, S. Kareev, M.; Meyers, D.; Liu, X.; Cao, Y.; Tripathi, S.; Chakhalian, J.; Yazici, D.; Maple, M. B.; Ryan, P. J.; Freeland, J. W.

    2014-05-19

    Ultra-thin films of the electron doped manganite La{sub 0.8}Ce{sub 0.2}MnO{sub 3} were grown in a layer-by-layer growth mode on SrTiO{sub 3} (001) substrates by pulsed laser interval deposition. High structural quality and surface morphology were confirmed by a combination of synchrotron based x-ray diffraction and atomic force microscopy. Resonant X-ray absorption spectroscopy measurements confirm the presence of Ce{sup 4+} and Mn{sup 2+} ions. In addition, the electron doping signature was corroborated by Hall effect measurements. All grown films show a ferromagnetic ground state as revealed by both dc magnetization and x-ray magnetic circular dichroism measurements and remain insulating contrary to earlier reports of a metal-insulator transition. Our results hint at the possibility of electron-hole asymmetry in the colossal magnetoresistive manganite phase diagram akin to the high-T{sub c} cuprates.

  19. Anomalous electron doping independent two-dimensional superconductivity

    NASA Astrophysics Data System (ADS)

    Zhou, Wei; Xing, Xiangzhuo; Zhao, Haijun; Feng, Jiajia; Pan, Yongqiang; Zhou, Nan; Zhang, Yufeng; Qian, Bin; Shi, Zhixiang

    2017-07-01

    Transition metal (Co and Ni) co-doping effects are investigated on an underdoped Ca0.94La0.06Fe2As2 compound. It is discovered that electron doping from substituting Fe with transition metal (TM = Co, Ni) can trigger high-{T}{{c}} superconductivity around 35 K, which emerges abruptly before the total suppression of the innate spin-density-wave/anti-ferromagnetism (SDW/AFM) state. Remarkably, the critical temperature for the high-{T}{{c}} superconductivity remains constant against a wide range of TM doping levels. And the net electron doping density dependence of the superconducting {T}{{c}} based on the rigid band model can be nicely scaled into a single curve for Co and Ni substitutions, in stark contrast to the case of Ba(Fe1-x TM x )2As2. This carrier density independent superconductivity and the unusual scaling behavior are presumably resulted from the interface superconductivity based on the similarity with the interface superconductivity in a La2-x Sr x CuO4-La2CuO4 bilayer. Evidence of the two-dimensional character of the superfluid by angle-resolved magneto-resistance measurements can further strengthen the interface nature of the high-{T}{{c}} superconductivity.

  20. Selective Mottness as a key to iron superconductors: weak and strong correlations

    NASA Astrophysics Data System (ADS)

    de Medici, Luca

    2014-03-01

    I will discuss the strength of electronic correlations in the normal phase of Fe-superconductors and trace a comparison with cuprates. The phase diagram of the high-Tc cuprates is dominated by the Mott insulating phase of the parent compounds. Approaching it from large doping, a standard Fermi-liquid is seen to gradually turn into a bad non-Fermi liquid metal in which quasiparticles have heavily differentiated coherence depending on momentum, a process which culminates in the pseudogap regime, in which the antinodal region in momentum space acquires a gap before the material reaches a fully gapped Mott state. I will show that experiments for electron- and hole-doped BaFe2As2 support an analogous scenario. The doping evolution is dominated by the influence of a Mott insulator that would be realized for half-filled conduction bands, while the stoichiometric compound does not play a special role. Weakly and strongly correlated conduction electrons coexist in much of the phase diagram, a differentiation that increases with hole-doping. We identify the reason for this ``selective Mottness'' in a simple emergent mechanism, an ``orbital decoupling,'' triggered by the strong Hund's coupling. When this mechanism is active charge excitations in the different orbitals are decoupled and each orbital behaves as a single band Hubbard model, where the correlation degree almost only depends on how doped is each orbital from half-filling. This scenario reconciles contrasting evidences on the electronic correlation strength, implies a strong asymmetry between hole- and electron-doping and establishes a deep connection with the cuprates. L. de' Medici, G. Giovannetti and M. Capone, ArXiv:1212.3966 Work supported by CNRS - ESPCI ParisTech, France

  1. High-Tc superconducting materials for electric power applications.

    PubMed

    Larbalestier, D; Gurevich, A; Feldmann, D M; Polyanskii, A

    2001-11-15

    Large-scale superconducting electric devices for power industry depend critically on wires with high critical current densities at temperatures where cryogenic losses are tolerable. This restricts choice to two high-temperature cuprate superconductors, (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Ox, and possibly to MgB2, recently discovered to superconduct at 39 K. Crystal structure and material anisotropy place fundamental restrictions on their properties, especially in polycrystalline form. So far, power applications have followed a largely empirical, twin-track approach of conductor development and construction of prototype devices. The feasibility of superconducting power cables, magnetic energy-storage devices, transformers, fault current limiters and motors, largely using (Bi,Pb)2Sr2Ca2Cu3Ox conductor, is proven. Widespread applications now depend significantly on cost-effective resolution of fundamental materials and fabrication issues, which control the production of low-cost, high-performance conductors of these remarkable compounds.

  2. The phase diagram of electron-doped La(2-x)Ce(x)CuO(4-δ).

    PubMed

    Saadaoui, H; Salman, Z; Luetkens, H; Prokscha, T; Suter, A; MacFarlane, W A; Jiang, Y; Jin, K; Greene, R L; Morenzoni, E; Kiefl, R F

    2015-01-21

    Superconductivity is a striking example of a quantum phenomenon in which electrons move coherently over macroscopic distances without scattering. The high-temperature superconducting oxides (cuprates) are the most studied class of superconductors, composed of two-dimensional CuO2 planes separated by other layers that control the electron concentration in the planes. A key unresolved issue in cuprates is the relationship between superconductivity and magnetism. Here we report a sharp phase boundary of static three-dimensional magnetic order in the electron-doped superconductor La(2-x)Ce(x)CuO(4-δ), where small changes in doping or depth from the surface switch the material from superconducting to magnetic. Using low-energy spin-polarized muons, we find that static magnetism disappears close to where superconductivity begins and well below the doping level at which dramatic changes in the transport properties are reported. These results indicate a higher degree of symmetry between the electron and hole-doped cuprates than previously thought.

  3. Theory of high-TC superconductivity: transition temperature

    NASA Astrophysics Data System (ADS)

    Harshman, Dale R.; Fiory, Anthony T.; Dow, John D.

    2010-12-01

    After reading over our published manuscript, we noticed that the discussion concerning the determination of σ for the ruthenate Ba2YRu0.9Cu0.1O6 in section 2.3.1 (3rd paragraph) is somewhat terse. Herein we provide an expanded analysis which better explains our estimate of γ (and thus σ) for this compound. All numbers, figures and conclusions remain unaltered. The ruthenate compounds A2YRu1-xCuxO6 (with A = Ba or Sr; x = 0.05-0.15) are double-perovskites containing no cuprate planes and with ν = μ = 1 [1] (reference [82] in the paper). The determination of γ follows from equation (2.5b), wherein rule 1b introduces the factor 1/2. In the lower limit, one expects a minimum of ~2 charges per Cu dopant, which are shared between two charge reservoirs of each layer type (AO and 1/2 (YRu1-xCuxO4)), producing a net factor of unity. Thus, for Ba2YRu0.9Cu0.1O6 (with TC0 ~ 30-40 K), we estimate γ = (1/2)(1) = 1/2, yielding σ = 0.05 as stated by equation (2.5c) in the paper. While one may expect an average effective charge state for Ru near +5, and that of Cu to be between +2 and +3 (post anneal) [2], the lower-limit estimation provided, which places the corresponding data point in figure 2 to the left of the line, appears sufficient to include the ruthenates with the other high-TC compounds found to follow equation (2.6) so far. Owing to the uncertainty in the experimental values for TC0, as well as the Ru and Cu valence states, however, this compound was excluded in the data analyses presented. Future research will attempt a more accurate determination of the charge per doped Cu, and thus σ. We would also like to point out a typographical correction in the definition of the corresponding ruthenate type II reservoir in the last column of table 1, which should read 1/2 (YRu0.9Cu0.1O4). An unrelated item is found in the fourth line of section 2.3.3, where Tb(O0.80F0.20)FeAs should read Tb(O0.80-yF0.20)FeAs. Additionally, reference [132] is now known and has the form

  4. Self-limited kinetics of electron doping in correlated oxides

    SciTech Connect

    Chen, Jikun Zhou, You; Jiang, Jun; Shi, Jian; Ramanathan, Shriram; Middey, Srimanta; Chakhalian, Jak; Chen, Nuofu; Chen, Lidong; Shi, Xun; Döbeli, Max

    2015-07-20

    Electron doping by hydrogenation can reversibly modify the electrical properties of complex oxides. We show that in order to realize large, fast, and reversible response to hydrogen, it is important to consider both the electron configuration on the transition metal 3d orbitals, as well as the thermodynamic stability in nickelates. Specifically, large doping-induced resistivity modulations ranging several orders of magnitude change are only observed for rare earth nickelates with small ionic radii on the A-site, in which case both electron correlation effects and the meta-stability of Ni{sup 3+} are important considerations. Charge doping via metastable incorporation of ionic dopants is of relevance to correlated oxide-based devices where advancing approaches to modify the ground state electronic properties is an important problem.

  5. Self-limited kinetics of electron doping in correlated oxides

    NASA Astrophysics Data System (ADS)

    Chen, Jikun; Zhou, You; Middey, Srimanta; Jiang, Jun; Chen, Nuofu; Chen, Lidong; Shi, Xun; Döbeli, Max; Shi, Jian; Chakhalian, Jak; Ramanathan, Shriram

    2015-07-01

    Electron doping by hydrogenation can reversibly modify the electrical properties of complex oxides. We show that in order to realize large, fast, and reversible response to hydrogen, it is important to consider both the electron configuration on the transition metal 3d orbitals, as well as the thermodynamic stability in nickelates. Specifically, large doping-induced resistivity modulations ranging several orders of magnitude change are only observed for rare earth nickelates with small ionic radii on the A-site, in which case both electron correlation effects and the meta-stability of Ni3+ are important considerations. Charge doping via metastable incorporation of ionic dopants is of relevance to correlated oxide-based devices where advancing approaches to modify the ground state electronic properties is an important problem.

  6. 14N nuclear quadrupole resonance of p-nitrotoluene using a high-Tc rf SQUID

    NASA Astrophysics Data System (ADS)

    He, D. F.; Tachiki, M.; Itozaki, H.

    2007-03-01

    Using a high-Tc radio-frequency superconducting quantum interference device (rf SQUID), we successfully detected nuclear quadrupole resonance (NQR) at about 887 kHz for 14N in p-nitrotoluene (PNT). A normal metal transformer made of copper wire was used to improve the sensitivity of the high-Tc rf SQUID and pulse-controlled rf switches and cross diodes were inserted in the transformer to reduce the influence of the strong excitation field. The preliminary results for NQR detection using the high-Tc SQUID had a similar signal-to-noise ratio to that of using a low noise preamplifier.

  7. Spin and charge excitations in artificial hole- and electron-doped infinite layer cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Dellea, G.; Minola, M.; Galdi, A.; Di Castro, D.; Aruta, C.; Brookes, N. B.; Jia, C. J.; Mazzoli, C.; Moretti Sala, M.; Moritz, B.; Orgiani, P.; Schlom, D. G.; Tebano, A.; Balestrino, G.; Braicovich, L.; Devereaux, T. P.; Maritato, L.; Ghiringhelli, G.

    2017-09-01

    The asymmetry between electron and hole doping in high critical-temperature superconducting (HTS) cuprates is key information for the understanding of Cooper pair formation mechanisms. Despite intensive studies on different cuprates, a comprehensive description of related magnetic and charge excitations is still fragmentary. In the present work, artificial cuprates were used to cover the entire phase diagram within the same HTS family. In particular, Cu L3-edge resonant inelastic x-ray scattering (RIXS) measurements were performed on artificial n - and p -type infinite layer (IL) epitaxial films. Beside several similarities, RIXS spectra show noticeable differences in the evolution, with doping level, of magnetic and charge intensity and damping. Compatible trends can be found in spectra measured on bulk cuprates, as well as in theoretical calculations of the spin dynamical structure factor S (q ,ω ) . The findings give a deeper insight into the evolution of collective excitations across the cuprate phase diagram, and on underlying general features, only connected to the doping type. Moreover, they pave the way to the exploration of general properties of HTS physics over a broad range of conditions, by means of artificial compounds not constrained by the thermodynamic limitations governing the chemical stability of bulk materials.

  8. High-temperature processing of oxide superconductors and superconducting oxide-silver oxide composite

    NASA Technical Reports Server (NTRS)

    Wu, M. K.; Loo, B. H.; Peters, P. N.; Huang, C. Y.

    1988-01-01

    High temperature processing was found to partially convert the green 211 phase oxide to 123 phase. High Tc superconductivity was observed in Bi-Sr-Cu-O and Y-Sr-Cu-O systems prepared using the same heat treatment process. High temperature processing presents an alternative synthetic route in the search for new high Tc superconductors. An unusual magnetic suspension with enhancement in critical current density was observed in the 123 and AgO composite.

  9. Antiferromagnetic order and spin dynamics in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Dai, Pengcheng

    2015-07-01

    High-transition temperature (high-Tc) superconductivity in the iron pnictides or chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxide superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-Tc superconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this paper, an overview is presented of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin-excitation spectra as a function of electron and hole doping and isoelectronic substitution. Spin dynamical properties of iron-based superconductors are compared with those of copper oxide and heavy fermion superconductors and the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity are discussed.

  10. Superconductor developments

    SciTech Connect

    Larbalestier, D.

    1989-04-05

    I will cover the technology of the new oxide supeconductors and how they might relate to the existing superconductors. Fermilab and the high energy physics community in general have had much to do with the development of the ''old'' superconductors. Bednorz and M/umlt u/ller must be credited with the idea of setting out on the search for the new superconductors.

  11. Hall Resistivity Correlations in Disordered Electron-Doped {Nd}_{2-x} {Ce}_x {CuO}_{4+delta } Nd 2 - x Ce x CuO 4 + δ Films

    NASA Astrophysics Data System (ADS)

    Charikova, T.; Shelushinina, N.; Harus, G.; Petukhov, D.; Petukhova, O.; Ivanov, A.

    2017-06-01

    The resistivity tensor correlations ρ _{xy}(B)˜ [ρ _{xx}(B)]^β for the mixed state magnetic field dependencies of the resistivity tensor of electron-doped {Nd}_{2-x}{Ce}_x{CuO}_{4+δ }/SrTiO_3 single-crystal films near the antiferromagnetic-superconducting phase transition and with varying degree of disorder (δ ) were studied. The decrease of β from 1.2 ± 0.2 at x = 0.14 to 0.6 ± 0.1 at x = 0.15 points out on the evidence of the change from the anisotropic s-wave to the d-wave pairing symmetry in the external magnetic field at the transition from underdoped to optimally doped region. Peculiarities of the power law dependence of the vortex motion in the mixed state can be connected with some features of the non-stoichiometric disorder in layered electron-doped superconductors.

  12. Shielded high-TC BSCCO tapes or wires for high field applications

    DOEpatents

    Balachandran, Uthamalingam; Lelovic, Milan; Eror, Nicholas G.

    2001-01-01

    A composite superconductor having an interior component of multiple filaments of superconducting Bi-2223 sheathed in a Ag or Ag alloy material, and a RE, TI or Hg based superconductor surrounding the interior component.

  13. Shielded high-Tc bscco tapes or wires for high field applications

    DOEpatents

    Balachandran, Uthamalingam; Lelovic, Milan; Eror, Nicholas G.

    2002-01-01

    A composite superconductor having an interior component of multiple filaments of superconducting Bi-2223 sheathed in a Ag or Ag alloy material, and a RE, TI or Hg based superconductor surrounding the interior component.

  14. Organic superconductors.

    PubMed

    Saito, Gunzi; Yoshida, Yukihiro

    2011-06-01

    The present status of organic superconductors of charge-transfer (CT) type based on donor molecules is reviewed. Along with the superconducting phases of such materials and also of oxide superconductors, reside spin-ordered phases such as spin-density wave (SDW) and antiferromagnetic (AF) phases. We briefly describe the recent development of superconductors having a superconducting phase next to a spin-disorder state (quantum spin liquid state). In addition to the CT type superconductors, there are a few single-component superconductors under high pressure.

  15. Magnetic properties of a high Tc superconductivity related system Y1 - xPrxBa2Fe3O8

    NASA Astrophysics Data System (ADS)

    Yuen, T.; Seyedahmadian, M.; Salomon, R. E.; Myer, G. H.; Cao, G.

    1996-04-01

    We studied Pr substitution for Y in a 123 high Tc superconductor related system, Y1-xPrxBa2Fe3O8 using of x-ray diffraction, magnetization, and 57Fe transmission Mössbauer spectroscopy. The Fe sublattices are magnetically ordered through the whole system. The Pr substitution, however, suppressed the Fe ordering temperature. The low temperature susceptibility across the system increases with increased Pr concentration x, and an additional antiferromagnetic ordering at 24 K is observed for x=1, indicating a possible Pr ordering. The averaged magnetic hyperfine field at Fe sites measured at 15 K is also reduced as x increases. The dramatic effect of Pr substitution for Y in this system, which is not observed in studies of Y substitution by other rare-earth elements, is interpreted as the effect of the hybridization between the Pr 4-f electrons and the electrons in the Fe(2)O2 layers, similar to the Pr hybridization in Y1-xPrxBa2Cu3O7-y system.

  16. Measurement of repulsive force of high Tc materials due to Meissner effect and its two dimensional distribution

    NASA Astrophysics Data System (ADS)

    Ishigaki, H.; Itoh, M.; Hida, A.; Endo, H.; Oya, T.

    1991-03-01

    As a basic study for magnetic bearings using high-Tc superconductors, evaluations of the materials were conducted. These evaluations included measurements of the repulsive force and lateral restoring force of various kinds of YBCO pellets. Pure air, which was supplied in the process of fabrication, and the presence of Ag in YBCO showed evidence of the effects of increasing the repulsive force. The lateral restoring force which was observed in the lateral displacement of a levitated permanent magnet over YBCO pellets was also affected by pure air and the presence of Ag. A new measuring instrument for magnetic fields was developed by using a highly sensitive force sensor. Because this instrument has the capability of measuring the repulsive force due to the Meissner effect, it was used for evaluating the two-dimensional distribution of superconducting properties. Results show that the pellets had nonuniform superconducting properties. The two-dimensional distribution of residual flux density on the pellets which had been cooled in a magnetic field (field cooling) was also observed by means of the instrument. The mechanism for generating lateral force is discussed in relation to the distribution.

  17. Effect of phase fluctuations on INS and NMR experiments in the pseudogap regime of the high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Westfahl, Harry; Morr, Dirk K.

    2000-03-01

    In this talk we present a theoretical scenario for inelastic neutron (INS) and nuclear magnetic resonance (NMR) experiments in the pseudogap region of the underdoped high-Tc superconductors. Within the spin-fermion model we study the effect of phase fluctuations in the superconducting d-wave order parameter on the spin susceptibility, probed in INS and NMR experiments. We show that the spin susceptibility is determined by the average square Doppler shift, W(T), which results from the coupling between the quasiparticle momentum and the thermally excited supercurrents. Our scenario provides an explanation for the temperature dependence of the resonance peak and of the ^63Cu spin lattice relaxation rate, 1/T_1, in the region where the phase fluctuations are present. Moreover, we show that 1/T1 is a direct probe of W(T). Our results for W(T) are in good qualitative agreement with those obtained in scanning tunneling spectroscopy (Ch. Remer et al., Phys. Rev. Lett. 80), 149 (1998) and high frequency ac transport(J. Corson et al., Nature 398), 221 (1999)

  18. Superconductors and Complex Transition Metal Oxides for Tunable THz Plasmonic Metamaterials

    SciTech Connect

    Singh, Ranjan; Xiong, Jie; Azad, Md A.; Yang, Hao; Trugman, Stuart A.; Jia, Quanxi; Taylor, Antoinette; Chen, Houtong

    2012-07-13

    The outline of this presentation are: (1) Motivation - Non-tunability of metal metamaterials; (2) Superconductors for temperature tunable metamaterials; (3) Ultrafast optical switching in superconductor metamaterials; (4) Controlling the conductivity with infrared pump beam; (5) Complex metal oxides as active substrates - Strontium Titanate; and (6) Conclusion. Conclusions are: (1) High Tc superconductors good for tunable and ultrafast metamaterials; (2) Large frequency and amplitude tunability in ultrathin superconductor films; (3) Such tunable properties cannot be accessed using metals; (4) Complex metal oxides can be used as active substrates - large tunability; (5) Complex oxides fail to address the issue of radiation losses in THz metamaterials.

  19. Vibration suppression of a disk-shaped superconductor with PD control

    NASA Astrophysics Data System (ADS)

    Komori, M.; Ide, T.; Fukata, S.; Matsushita, T.

    In order to investigate superconducting magnetic bearings (SMBs) using repulsion forces between superconductors and electromagnets, an experimental setup for a thrust SMB able to move in one direction has been made. The experimental setup is composed of a high Tc superconductor, permanent magnets, electromagnets and a Hall sensor. The superconductor used in this paper is supported by the permanent magnets in the radial direction. The vibration of the superconductor is suppressed by an analog PD (proportional and derivative) controller. From the experiments, it is found that suppressing the vibration is well performed by the PD controller. Also, it is found that the controller needs more resistance against disturbance caused by the pinning effect.

  20. Transport and Raman signatures of electron-doped SmNiO3 thin films

    NASA Astrophysics Data System (ADS)

    Ramadoss, Koushik; Mandal, Nirajan; Zhou, You; Chen, Yong; Ramanathan, Shriram

    We report low temperature transport and Raman spectroscopy measurements of electron-doped SmNiO3 (SNO) thin films. It has been shown that pristine SNO films can be doped with electrons using hydrogen. Our transport measurements indicate a Coulomb interaction dominated variable range hopping (VRH) for electron-doped samples whereas the pristine films show a Mott type VRH mechanism at low temperatures. The electron-doped samples display a strong localization which can be correlated with the high spin state of Ni2+ ions. The spatial Raman map shows a remarkable shift of about 167 cm-1 with electron doping thus serving as a spectroscopic tool to investigate hydrogen in our films. Birck Nanotechnology Center, Purdue University.

  1. Electron Doping of the Parent Cuprate La2CuO4 without Cation Substitution

    NASA Astrophysics Data System (ADS)

    Wei, Haofei I.; Adamo, Carolina; Nowadnick, Elizabeth A.; Lochocki, Edward B.; Chatterjee, Shouvik; Ruf, Jacob P.; Beasley, Malcolm R.; Schlom, Darrell G.; Shen, Kyle M.

    2016-09-01

    In the cuprates, carrier doping of the Mott insulating parent state is necessary to realize superconductivity as well as a number of other exotic states involving charge or spin density waves. Cation substitution is the primary method for doping carriers into these compounds, and is the only known method for electron doping in these materials. Here, we report electron doping without cation substitution in epitaxially stabilized thin films of La2CuO4 grown via molecular-beam epitaxy. We use angle-resolved photoemission spectroscopy to directly measure their electronic structure and conclusively determine that these compounds are electron doped with a carrier concentration of 0.09 ±0.02 e-/Cu . We propose that intrinsic defects, most likely oxygen vacancies, are the sources of doped electrons in these materials. Our results suggest a new approach to electron doping in the cuprates, one which could lead to a more detailed experimental understanding of their properties.

  2. Proof-of-principle of a novel method for sputter-deposition of high Tc supeconducting films via a computer-controlled mass analyzed ion beam

    NASA Astrophysics Data System (ADS)

    Auciello, Orlando; Krauss, Alan R.

    1988-02-01

    A novel concept is demonstrated for ion beam sputter-induced deposition of high Tc superconductor films. The concept involves the use of a well-focused ion beam which can be sequentially directed via a set of x-y electrostatic deflection plates onto three or more different elemental or compound targets which are constituents of the desired composite film. The deflection plates are driven by two ±1000 volt bipolar programmable power supplies which are controlled by a DEC LSI 11/73 computer. A custom program drives two D/A converters to provide the ±10 volt analog signal which is used to drive the power supplies in such a way that the ion beam is positioned on selected spots on the different targets. By programming the dwell time for each targe according to the known sputtering yield and desired layer thickness for each material, it is possible to deposit composite films from a well-controlled sub-monolayer up to thicknesses determined only by the available deposition time. Initial results on the deposition of Y-Ba-Cu-O films are presented to demonstrate the concept, which in principle can also be applied to the deposition of high Tc superconducting films by electron- and laser-induced evaporation of elemental or oxide targets.

  3. Organic Superconductors

    SciTech Connect

    Charles Mielke

    2009-02-27

    Intense magnetic fields are an essential tool for understanding layered superconductors. Fundamental electronic properties of organic superconductors are revealed in intense (60 tesla) magnetic fields. Properties such as the topology of the Fermi surface and the nature of the superconducting order parameter are revealed. With modest maximum critical temperatures~13K the charge transfer salt organic superconductors prove to be incredibly valuable materials as their electronically clean nature and layered (highly anisotropic) structures yield insights to the high temperature superconductors. Observation of de Haas-van Alphen and Shubnikov-de Haas quantum oscillatory phenomena, magnetic field induced superconductivity and re-entrant superconductivity are some of the physical phenomena observed in the charge transfer organic superconductors. In this talk, I will discuss the nature of organic superconductors and give an overview of the generation of intense magnetic fields; from the 60 tesla millisecond duration to the extreme 1000 tesla microsecond pulsed magnetic fields.

  4. Extreme anisotropy and anomalous transport properties of heavily electron doped Lix(NH3)yFe2Se2 single crystals

    NASA Astrophysics Data System (ADS)

    Sun, Shanshan; Wang, Shaohua; Yu, Rong; Lei, Hechang

    2017-08-01

    We report the growth of heavily electron doped Li-NH3 intercalated FeSe single crystals that are free of material complexities and allow access to the intrinsic superconducting properties. Lix(NH3)yFe2Se2 single crystals show extremely large electronic anisotropy in both normal and superconducting states. They also exhibit anomalous transport properties in the normal state, which are believed to possibly be related to the anisotropy of relaxation time and/or temperature-dependent electron carrier concentration. Taking into account the great chemical flexibility of intercalants in the system, our findings provide a platform to understanding the origin of superconductivity in FeSe-related superconductors.

  5. A close look at antiferromagnetic phase boundary in multidimensional phase diagram of electron-doped copper oxide

    NASA Astrophysics Data System (ADS)

    Yu, Heshan; He, Ge; Lin, Ziquan; Yuan, Jie; Zhu, Beiyi; Yang, Yi-Feng; Xiang, Tao; Kusmartsev, Feo. V.; Li, Liang; Wang, Junfeng; Jin, Kui

    In copper-oxide superconductors, spin fluctuations play a predominant role in electron pairing with electron dopants yet composite orders veil the nature of superconductivity for hole-doped family. However, in electron-doped ones the ending point of AFM is still in controversy for different probes or its sensitivity to oxygen content. Here, by carefully tuning the oxygen content, a systematic study of Hall signal and magnetoresistivity up to 58 Tesla on optimally doped La2-xCexCuO4+/-δ (x = 0.10) thin films identifies two characteristic temperatures at 62.5 K (error is 7.5 K) and 25 K (error is 5 K). The former is quite robust whereas the latter becomes flexible with increasing magnetic field, thereby linked to two- and three-dimensional AFM, evident from the multidimensional phase diagram as a function of oxygen as well as Ce dopants. Consequently, the observation of extended AFM phase in contrast to μSR probe corroborates an elevated critical doping in field, providing an unambiguous picture to understand the interactions between AFM and superconductivity.

  6. Avoided valence transition in a plutonium superconductor.

    PubMed

    Ramshaw, B J; Shekhter, Arkady; McDonald, Ross D; Betts, Jon B; Mitchell, J N; Tobash, P H; Mielke, C H; Bauer, E D; Migliori, Albert

    2015-03-17

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5--the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)--and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability--therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5.

  7. Avoided valence transition in a plutonium superconductor

    PubMed Central

    Ramshaw, B. J.; Shekhter, Arkady; McDonald, Ross D.; Betts, Jon B.; Mitchell, J. N.; Tobash, P. H.; Mielke, C. H.; Bauer, E. D.; Migliori, Albert

    2015-01-01

    The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5—the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)—and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability—therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5. PMID:25737548

  8. Anomalous optical conductivity in the normal state of high Tc oxides

    NASA Astrophysics Data System (ADS)

    Moriya, Toru; Takahashi, Yoshinori

    1991-03-01

    The optical resistivity due to antiferromagnetic spin fluctuations in two-dimensional metals, as a possible model for high Tc oxides, is calculated within the Born approximation and the self-consistent renormalization (SCR) theory for the spin fluctuations. The result is shown to explain the observed anomalous behavior of optical conductivity in YBa2Cu3O7 above Tc quantitatively.

  9. Note: A hand-held high-Tc superconducting quantum interference device operating without shielding.

    PubMed

    He, D F

    2011-02-01

    By improving the compensation circuit, a hand-held high-Tc rf superconducting quantum interference devices (SQUID) system was developed. It could operate well when moving in unshielded environment. To check the operation, it was used to do eddy-current testing by hand moving the SQUID, and the artificial defect under 6 mm aluminum plate could be successfully detected in shielded environment.

  10. Simple and reliable method for determination of oxygen content in high- Tc copper oxides

    NASA Astrophysics Data System (ADS)

    Maeno, Yoshiteru; Teraoka, Hideki; Matsukuma, Kuniko; Yoshida, Koji; Sugiyama, Kimihiko; Nakamura, Fumihiko; Fujita, Toshizo

    1991-12-01

    We present the details of a simple and reliable iodine-titration method suited for high- Tc copper oxides, in which the use of a solution of ammonium acetate and acetic acid as a buffer agent substantially improves the operation. The results applied to La 2- xM xCuO 4- δ (M = Ba, Sr and Ca) are presented.

  11. Nernst effect in high temperature superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Yayu

    This thesis presents a study of the Nernst effect in high temperature superconductors. The vortex Nernst measurements have been carried out on various high Tc cuprates to high magnetic fields. These results provide vital information about the properties and relations of the pseudogap phase and superconducting phase in high Tc superconductors. Our first finding is the existence of vortex-like excitations at temperatures much higher than Tc0, the zero filed transition temperature, in the underdoped cuprates. This result suggests that in the putative normal state of cuprates, although bulk Meissner effect is absent and resistivity looks normal, the amplitude of the Cooper pairing is still sizable. The transition at Tc0 is driven by the loss of long range phase coherence rather than the disappearance of superconducting condensate. The high field Nernst effect offers a reliable way to determine the upper critical field Hc2 of high Tc cuprates and many unusual properties are uncovered. For cuprates with relatively large hole density (x > 0.15), we found that H c2 is almost temperature independent for T < Tc0. This is in strong contrast to the Hc2 - T relation of conventional superconductors. Moreover, using a scaling analysis, we have demonstrated that H c2 increases with decreasing hole density x in this doping range, implying a stronger pairing potential at lower doping. In the severely underdoped regime (x < 0.12), some new features become apparent and they imply that the vortex Nernst signal is comprised of two distinct contributions. The first is from coherent regions with long range phase coherence and relatively low upper critical field, more like the superconducting phase; the second is from phase incoherent regions with much larger field scales, indicative of the pseudogap phase. As temperature rises, the superconducting phase gives weight to the pseudogap phase. Moreover, the upper critical field Hc2 of the superconducting phase scales with the onset

  12. Practical superconductor development for electrical power applications. Quarterly report for the period ending June 30, 2000

    SciTech Connect

    2000-07-21

    This is a multiyear experimental research program focused on improving relevant material properties of high-{Tc} superconductors (HTSs) and on development of fabrication methods that can be transferred to industry for production of commercial conductors. The development of teaming relationships through agreements with industrial partners is a key element of the Argonne (ANL) program.

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

    NASA Technical Reports Server (NTRS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1994-01-01

    Experimental work on this project over the last four years has resulted in establishing processing and characterization techniques for producing both the Bi-based and Tl-based superconductors in their high temperature (2223) forms. In the bulk, dry pressed form, maximum critical temperatures (Tc) of 108.2 K and 117.8 K, respectively, were measured. Results have further shown that the Bi and Tl-based superconducting materials in bulk form are noticeably different from the Y-based 123 material in that superconductivity is considerably harder to achieve, maintain, and reproduce. This is due primarily to the difficulty in obtaining the higher Tc phase in pure form since it commonly co-exists with other undesirable, lower Tc phases. In particular, it has been found that long processing times for calcining and firing (20 - 200 hrs.) and close control of temperatures which are very near the melting point are required in order to obtain higher proportions of the desirable, high Tc (2223) phase. Thus far, the BSCCO bulk materials has been prepared in uniaxially pressed, hot pressed, and tapecast form. The uniaxially pressed material has been synthesized by the mixed oxide, coprecipitation, and melt quenching processes. The tapecast and hot pressed materials have been prepared via the mixed oxide process. In addition, thick films of BSCCO (2223 phase) have been prepared by screen printing on to yttria and magnesia stabilized zirconia with only moderate success; i.e., superconductivity was achieved in these thick films, but the highest Tc obtained in these films was 89.0 K. The Tc's of the bulk hot pressed, tapecast, and screen printed thick film materials were found to be 108.2, 102.4, and 89.0 K, respectively.

  14. Melting of the Abrikosov flux lattice in anisotropic superconductors

    NASA Technical Reports Server (NTRS)

    Beck, R. G.; Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.; Kogan, V. G.

    1992-01-01

    It has been proposed that the Abrikosov flux lattice in high-Tc superconductors is melted over a significant fraction of the phase diagram. A thermodynamic argument is provided which establishes that the angular dependence of the melting temperature is controlled by the superconducting mass anisotropy. Using a low-frequency torsional-oscillator technique, this relationship has been tested in untwinned single-crystal YBa2Cu3O(7-delta). The results offer decisive support for the melting proposal.

  15. Model for large arrays of Josephson junctions with unconventional superconductors

    NASA Astrophysics Data System (ADS)

    Khveshchenko, D. V.; Crooks, R.

    2011-10-01

    We study large arrays of mesoscopic junctions made out of gapless unconventional superconductors where the tunneling processes of both particle-hole and Cooper pairs give rise to a strongly retarded effective action which, contrary to the standard case, cannot be readily characterized in terms of a local Josephson energy. This action can be relevant, for example, to grain boundary and c-axis junctions in layered high-Tc superconductors. By using a particular functional representation, we describe emergent collective phenomena in this system, ascertain its phase diagram, and compute electrical conductivity.

  16. Low-loss, high-speed, high-{Tc} superconducting bearings

    DOEpatents

    Hull, J.R.; Mulcahy, T.M.; Uherka, K.L.

    1997-06-24

    A flywheel energy storage device is disclosed including an iron structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet. The stationary permanent magnet levitates the iron structure while the superconductor structure can stabilize the rotating iron structure. 15 figs.

  17. Low-loss, high-speed, high-{Tc} superconducting bearings

    DOEpatents

    Hull, J.R.; Mulcahy, T.M.; Uherka, K.L.

    1996-07-30

    A flywheel energy storage device is disclosed including an iron structure disposed for rotation adjacent a stationary superconductor material structure and a stationary permanent magnet. The stationary permanent magnet levitates the iron structure while the superconductor structure can stabilize and levitate the rotating iron structure. 15 figs.

  18. Quantum interference in an interfacial superconductor.

    PubMed

    Goswami, Srijit; Mulazimoglu, Emre; Monteiro, Ana M R V L; Wölbing, Roman; Koelle, Dieter; Kleiner, Reinhold; Blanter, Ya M; Vandersypen, Lieven M K; Caviglia, Andrea D

    2016-10-01

    The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (Tc; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-Tc superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

  19. Quantum interference in an interfacial superconductor

    NASA Astrophysics Data System (ADS)

    Goswami, Srijit; Mulazimoglu, Emre; Monteiro, Ana M. R. V. L.; Wölbing, Roman; Koelle, Dieter; Kleiner, Reinhold; Blanter, Ya. M.; Vandersypen, Lieven M. K.; Caviglia, Andrea D.

    2016-10-01

    The two-dimensional superconductor that forms at the interface between the complex oxides lanthanum aluminate (LAO) and strontium titanate (STO) has several intriguing properties that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (Tc; ref. 7), revealing a dome-shaped phase diagram reminiscent of high-Tc superconductors. So far, experiments with oxide interfaces have measured quantities that probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable the in situ creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understanding the nature of superconductivity at oxide interfaces.

  20. Phase engineering of monolayer transition-metal dichalcogenide through coupled electron doping and lattice deformation

    SciTech Connect

    Ouyang, Bin; Lan, Guoqiang; Song, Jun; Guo, Yinsheng; Mi, Zetian

    2015-11-09

    First-principles calculations were performed to investigate the phase stability and transition within four monolayer transition-metal dichalcogenide (TMD) systems, i.e., MX{sub 2} (M = Mo or W and X = S or Se) under coupled electron doping and lattice deformation. With the lattice distortion and electron doping density treated as state variables, the energy surfaces of different phases were computed, and the diagrams of energetically preferred phases were constructed. These diagrams assess the competition between different phases and predict conditions of phase transitions for the TMDs considered. The interplay between lattice deformation and electron doping was identified as originating from the deformation induced band shifting and band bending. Based on our findings, a potential design strategy combining an efficient electrolytic gating and a lattice straining to achieve controllable phase engineering in TMD monolayers was demonstrated.

  1. Sign reversal of magnetoresistance in a perovskite nickelate by electron doping

    NASA Astrophysics Data System (ADS)

    Ramadoss, Koushik; Mandal, Nirajan; Dai, Xia; Wan, Zhong; Zhou, You; Rokhinson, Leonid; Chen, Yong P.; Hu, Jiangpin; Ramanathan, Shriram

    2016-12-01

    We present low temperature resistivity and magnetotransport measurements conducted on pristine and electron doped SmNiO3 (SNO). The low temperature transport in both pristine and electron-doped SNO shows a Mott variable range hopping with a substantial decrease in localization length of carriers by one order in the case of doped samples. Undoped SNO films show a negative magnetoresistance (MR) at all temperatures characterized by spin fluctuations with the evolution of a positive cusp at low temperatures. In striking contrast, upon electron doping of the films via hydrogenation, we observe a crossover to a linear nonsaturating positive MR ˜0.2 % at 50 K. The results signify the role of localization phenomena in tuning the magnetotransport response in doped nickelates. Ionic doping is therefore a promising approach to tune magnetotransport in correlated perovskites.

  2. Tunneling study based on the circuit theory in d-wave superconductors

    NASA Astrophysics Data System (ADS)

    Shigeta, Iduru; Asano, Yasuhiro; Tanaka, Yukio; Ichikawa, Fusao; Kashiwaya, Satoshi

    2006-01-01

    We propose a new interpretation about zero-bias conductance peak (ZBCP) behaviours in high-Tc superconductors. The ZBCP has been frequently observed in many tunneling spectroscopic experiments for unconventional superconductors. The ZBCP mechanism was well understood by the Andreev bound states theory for unconventional superconductors. On the other hand, the circuit theory has been recently developed from conventional superconductors to unconventional superconductors. The ZBCP often appears in this theory as well. Therefore, we have analyzed experimental spectra with the ZBCP of Bi2Sr2CaCu2O8+δ planar tunnel junctions by using both theories for d-wave paring symmetry. The experimental spectra are consistent with those of recent studies on the circuit theory for d-wave superconductors.

  3. Correlation between fabrication factor and superconducting properties of the Tl-and-Bi-based high-Tc superconductor

    NASA Technical Reports Server (NTRS)

    Maki, Naoki; Okada, Michiya; Doi, Toshiya J.; Kanai, Tsuneyuki; Sato, Junichi; Higashiyama, Kazutoshi

    1995-01-01

    Large critical current densities (J(sub c)) were obtained in c axis oriented Tl-1 223/Ag composite tapes fabricated by spraying methods without a vacuum. Transport measurements at 77K under a zero field indicated a J(sub c) of 9 x 10(exp 4) A/sq cm and 7 x 10(exp 3) A/sq cm at 1T for the tapes fabricated by spray pyrolysis. The novel GPM method was also applied for Bi-2212/Ag PIT composite wire, and found to be very effective for improving the distribution of voids, which caused from the melt-solidifying process. The GPM showed a marked effect for obtaining homogeneous long wire. A 1 T class coil was successfully fabricated with monocore wire.

  4. Role of twins in peak effect phenomenon observed at microwave frequencies in high Tc superconductor thin films

    NASA Astrophysics Data System (ADS)

    Banerjee, Tamalika; Bagwe, V. C.; John, J.; Pai, S. P.; Ganesh Kumara, K.; Pinto, R.

    2004-05-01

    Measurements of microwave surface resistance, Rs, at subcritical currents as a function of temperature with varying dc magnetic field upto 0.8 T have shown peak effect (PE) in epitaxial DyBa 2Cu 3O 7- δ (DBCO) and YBa 2Cu 3O 7- δ (YBCO) thin films grown by pulsed laser deposition on <1 0 0> LaAlO 3 substrates. Microwave measurements were performed on microstrip resonators as test vehicles. Occurrence of a peak in Rs in dc magnetic field is governed by the nature and concentration of defects. Evidence shows that thinner films with a higher ratio of areal density of extended defects, ne (such as twin boundaries), to the areal density of point defects, np, show PE at the measurement frequencies 4.88 and 9.55 GHz; whereas, thicker films (⩾3000 Å) with a smaller ne/ np ratio do not show PE. 2500 Å thick YBCO film shows a double peak structure at 9.55 GHz, thereby suggesting two sets of twin boundaries in this film having different κp values. Measurements carried out on low-twinned LaAlO 3 substrates show that 2400 Å thick DBCO film does not exhibit the PE phenomenon at 4.88 GHz upto to an applied field of 0.8 T; this indicates that twins propagated from the LaAlO 3 substrates are responsible for the occurrence of PE at microwave frequencies. Oxygen ion irradiation (90 MeV, 3 × 10 13 ions/cm 2) of 2500 Å DBCO film has been found to shift the peak to lower temperature at 4.88 GHz, but significantly suppress the peak at 9.55 GHz. Depinning frequency, ωp vs. T plot obtained for the 2400 Å DBCO film shows a peak due to the peak in its Rs vs. T plots.

  5. Interaction of Abrikosov vortex with grain boundaries near Hc1. I. Potential barriers in polycrystalline high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Belevtsov, L. V.

    2005-02-01

    The effects of the interaction of an Abrikosov vortex with grain boundaries is investigated in the framework of a model in which the vortex, grain, and grain boundaries are treated on a unified basis. An exact solution is found for the vortex-laminar model. New types of potential barriers for the entry of a vortex into a superconducting polycrystalline are predicted. Like the traditional Bean-Livingston barrier, the value of the "edge" barrier in these materials depends on the value of the external field, but it also depends on the normalized grain size, the intensity of the coupling between grains, the anisotropy, and the degree of "specularity" (smoothness) of the material in the case of ultrafine-grained superconducting materials.

  6. Fabrication, properties, and microstructures of high (Tc) tapes and coils made from Ag-clad Bi-2223 superconductor

    NASA Astrophysics Data System (ADS)

    Balachandran, U.; Iyer, A. N.; Youngdahl, C. A.; Motowidlo, L. R.; Hoehn, J. G.; Haldar, P.

    1993-07-01

    Bi-2223 precursor powders were prepared via a solid-state reaction using carbonates and oxides of Bi, Pb, Sr, Ca, and Cu. Results indicate that an in-situ reaction between constituent phases with the formation of a transient liquid that is consumed during final heat treatment, is essential to obtain increased density with greater connectivity between the 2223 grains. Relative amounts of the constituent phases were adjusted in the powder by varying the calcination conditions, and the powder was then used to fabricate Ag-clad tapes by a powder-in-tube technique. By improving process conditions, transport critical current density (J(sub c)) values greater than 4 (times) 10(exp 4) A/cm(sup 2) at 77 K and 2 (times) 10(exp 5) A/cm(sup 2) at 4.2 and 27 K have been obtained in short tape samples. Long tapes were cut into lengths upto 10 m long and used in parallel to fabricate small superconducting pancake coils. The coils were characterized at 77, 27 and 4.2 K and results are discussed.

  7. “Nodal Gap” induced by the incommensurate diagonal spin density modulation in underdoped high- Tc superconductors

    DOE PAGES

    Zhou, Tao; Gao, Yi; Zhu, Jian -Xin

    2015-03-07

    Recenmore » tly it was revealed that the whole Fermi surface is fully gapped for several families of underdoped cuprates. The existence of the finite energy gap along the d-wave nodal lines (nodal gap) contrasts the common understanding of the d-wave pairing symmetry, which challenges the present theories for the high-Tcsuperconductors. Here we propose that the incommensurate diagonal spin-density-wave order can account for the above experimental observation. The Fermi surface and the local density of states are also studied. Our results are in good agreement with many important experiments in high-Tcsuperconductors.« less

  8. The superconducting gap ratio, isotope-shift exponent and pressure coefficient of Tc for high- Tc systems

    NASA Astrophysics Data System (ADS)

    Das, A. N.; Sarkar, Sujit

    1996-02-01

    The superconducting gap ratio, isotope-shift exponent and the pressure co-efficient of the superconducting transition temperature are studied within different models proposed for high- Tc cuprate oxide systems. A comparison with the experimental results of high- Tc oxide systems is made.

  9. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    SciTech Connect

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; Markiewicz, R. S.; Bansil, A.; Wilson, S. D.; He, Rui -Hua

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  10. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGES

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; ...

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  11. Superconductor Composite

    DOEpatents

    Dorris, Stephen E.; Burlone, Dominick A.; Morgan; Carol W.

    1999-02-02

    A superconducting conductor fabricated from a plurality of wires, e.g., fine silver wires, coated with a superconducting powder. A process of applying superconducting powders to such wires, to the resulting coated wires and superconductors produced therefrom.

  12. A high-Tc flip-chip SQUID gradiometer for mobile underwater magnetic sensing

    NASA Astrophysics Data System (ADS)

    Keenan, S. T.; Young, J. A.; Foley, C. P.; Du, J.

    2010-02-01

    We report on the development of a magnetic gradient tensor sensor based on high- Tc SQUIDs for marine surveying applications. The proposed system uses six planar gradiometers incorporated into a hexagonal pyramid structure where the combined output will provide a measure of the gradient tensor. This report focuses on the development and characterization of long baseline high- Tc SQUID gradiometers for this purpose. We compare the performance of two separate fabricated gradiometer designs. These devices both consist of a large 40 mm × 20 mm gradiometric pickup loop antenna flip-chip coupled to a small readout SQUID gradiometer. We have thus far demonstrated an unshielded gradient sensitivity of ~29 fT cm-1 Hz-1/2 at 1 kHz and ~170 fT cm-1 Hz-1/2 at 10 Hz through optimizing the coupling inductances of our device.

  13. N-14 NQR using a high-Tc rf SQUID with a normal metal transformer

    NASA Astrophysics Data System (ADS)

    He, D. F.; Tachiki, M.; Itozaki, H.

    2008-01-01

    We have improved our high-Tc SQUID-based N-14 nuclear quadrupole resonance (NQR) detection system. By using a reed relay SIL5-1A72-71L (MEDER electronic) in the normal metal transformer, the isolation to the excitation field was much improved. The high-Tc rf SQUID could operate stably when the rf excitation field was over 20 mT. By optimizing the input coil of the transformer, better sensitivity of 0.5 fT Hz-1/2 was obtained at the resonant frequency of the tuned normal metal transformer. A spin-locking spin-echo (SLSE) multi-pulse sequence was also used in the system to detect the weak NQR signals produced by samples with longer spin-spin relaxation time T2, such as trinitrotoluene (TNT).

  14. Metallic Contaminant Detection System for Industrial Products by High TC SQUID Magnetic Sensor

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Fujita, Hiroyoshi; Hatsukade, Yoshimi; Otani, Takeyoshi; Suzuki, Shuichi

    High-Tc superconducting quantum interference device (SQUID) system for detection of magnetic foreign matter in industrial products was developed. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products, such as lithium ion batteries. The outer dimension of metallic particles less than 100 microns cannot be detected by conventional X-ray imaging. Therefore, we developed a detection system based on high-Tc SQUID microscopes with a high-performance magnetic shield. Using SQUID microscopes with a 0.5 mm-thick vacuum window was proposed. This design enables the SQUID to approach an object to be measured as close as 1 mm and enhances the sensitivity. A new magnetic shield with sleeves was carefully designed and built. As a result, we could successfully measure a small iron particle with 100 μm. This detection level was hard to achieve by conventional X-ray detection methods.

  15. Multi-Channel High-Tc SQUID Detection System for Metallic Contaminants

    NASA Astrophysics Data System (ADS)

    Kitamura, Yoshihiro; Hatsukade, Yoshimi; Tanaka, Saburo; Ohtani, Takeyoshi; Suzuki, Shuichi

    Finding ultra-small metallic contaminants is a big issue for manufacturers of lithium-ion batteries nowadays. Therefore, we have developed high-Tc SQUID systems for detection of such fine magnetic metallic contaminants. In this paper, we constructed an eight channel high-Tc SQUID gradiometer system for inspection of a sheet electrode of a lithium ion battery with width of about 70 mm. By this system, a small iron ball of about 30 μm in diameter was successfully detected. It is shown that this system has a detectable range of 70 mm in width. These results suggest that the system is a promising tool for the detection of the contaminants in lithium ion batteries.

  16. Search for high-Tc conventional superconductivity at megabar pressures in the lithium-sulfur system

    NASA Astrophysics Data System (ADS)

    Kokail, Christian; Heil, Christoph; Boeri, Lilia

    2016-08-01

    Motivated by the recent report of superconductivity above 200 K in ultra-dense hydrogen sulfide, we search for high-TC conventional superconductivity in the phase diagram of the binary Li-S system, using ab initio methods for crystal structure prediction and linear response calculations for the electron-phonon coupling. We find that at pressures higher than 20 GPa, several new compositions, besides the known Li2S , are stabilized; many exhibit electride-like interstitial charge localization observed in other alkali-metal compounds. Of all predicted phases, only an fcc phase of Li3S , metastable before 640 GPa, exhibits a sizable TC, in contrast to what is observed in sulfur and phosphorus hydrides, where several stoichiometries lead to high TC. We attribute this difference to 2 s -2 p hybridization and avoided core overlap, and predict similar behavior for other alkali-metal compounds.

  17. Superconductor consolidation

    SciTech Connect

    Staudhammer, K.P.

    1988-01-01

    A program to develop explosively shock consolidated monoliths of YBa/sub 2/Cu/sub 3/O/sub 7/minus/x/ ceramic superconductors has been ongoing at Los Alamos National Laboratory since last year. Shock consolidation can produce a near 100% theoretical density, bulk superconductor that does not require a post anneal in oxygen. Shock compaction is also an excellent means of creating a good electrical contact weld between the ceramic superconductor and a metal such as copper. Elimination of the post anneal and low temperature shock welding of the cladding metal are unique advantages stemming from the shock compaction processing. Successful shock compaction processing will enable production of a wide variety of complex ceramic-superconductor forms tailored for specific defense application requirements. Shock compaction can be developed into industrial manufacturing processes. DuPont now makes diamond powder this way. Shock compacted superconductor billets can be used in applications where a solid superconductor form is required (e.g., magnetic bearings, bus bar for a niobium-tin FEL SMES, motor rotors, etc.), or they can be post processed by extrusion and other swaging processes to produce textured wires and tapes for electrical current carrying applications. 11 refs., 1 fig.

  18. Superconductor consolidation

    NASA Astrophysics Data System (ADS)

    Staudhammer, K. P.

    A program to develop explosively shock consolidated monoliths of YBa2Cu3O(sub 7-x) ceramic superconductors has been ongoing at Los Alamos National Laboratory since last year. Shock consolidation can produce a near 100 percent theoretical density, bulk superconductor that does not require a post anneal in oxygen. Shock compaction is also an excellent means of creating a good electrical contact weld between the ceramic superconductor and a metal such as copper. Elimination of the post anneal and low temperature shock welding of the cladding metal are unique advantages stemming from the shock compaction processing. Successful shock compaction processing will enable production of a wide variety of complex ceramic superconductor forms tailored for specific defense application requirements. Shock compaction can be developed into industrial manufacturing processes. Shock compacted superconductor billets can be used in applications where a solid superconductor form is required (e.g., magnetic bearings, bus bar for a niobium-tin FEL SMES, motor rotors, etc.) or they can be post processed by extrusion and other swaging processes to produce textured wires and tapes for electrical current carrying applications.

  19. A novel quadruple excitation in high-Tc SQUID-based non-destructive evaluation

    NASA Astrophysics Data System (ADS)

    Kong, X. Y.; Ren, Y. F.; Li, J. W.; Yu, H. W.; Chen, G. H.; Yang, Q. S.

    2006-02-01

    A high-Tc SQUID-based non-destructive evaluation (NDE) system has been set up in our laboratory. The SQUID was made on a 24° bicystal SrTiO3 substrate. A novel quadruple excitation coil was proposed for the first time and applied in the artificial holes in the aluminium multilayer structure in a noisy unshielded environment. The experimental data shows that it has good balance and is very effective at detecting small hole defects.

  20. Nonlinear Harmonic Responses of Live Cells Using High-Tc Superconducting Quantum Interference Devices

    NASA Astrophysics Data System (ADS)

    Miller, J. H.; Nawarathna, D.; Sanabria, H.; Vajrala, V.; Claycomb, J. R.

    2006-09-01

    We report on a novel application of high-Tc SQUIDs, in which harmonics produced by live cells in response to a sinusoidal electric field are measured. The use of SQUIDs to probe induced currents without contacts reduces spurious harmonics generated at electrode interfaces, and enables one to noninvasively probe metabolic activity manifested by changes in conformational states of protein complexes in the plasma membrane and internal organelles. The method can also potentially be developed for clinical applications.

  1. Truncated Hilbert space approach to models of high-{Tc} superconductivity

    SciTech Connect

    Riera, J.

    1995-07-01

    In this talk the author introduces a method of diagonalization in a systematically expanded Hilbert space. The author shows some applications of this procedure to several models of relevance to high-Tc superconductivity like the t-J, the t-J{sub z} and Hubbard models. Finally, the author discusses the relation of this method of diagonalization in a reduced Hilbert space with perturbation theory and with variational methods.

  2. Unconventional Disorder Effects in Correlated Superconductors

    NASA Astrophysics Data System (ADS)

    Gastiasoro, Maria N.; Bernardini, Fabio; Andersen, Brian M.

    2016-12-01

    We study the effects of disorder on unconventional superconductors in the presence of correlations, and explore a novel correlated disorder paradigm dominated by strong deviations from standard Abrikosov-Gor'kov theory due to generation of local bound states and cooperative impurity behavior driven by Coulomb interactions. Specifically we explain under which circumstances magnetic disorder acts as a strong poison destroying high-Tc superconductivity at the sub-1% level, and when nonmagnetic disorder, counterintuitively, hardly affects the unconventional superconducting state while concomitantly inducing an inhomogeneous full-volume magnetic phase. Recent experimental studies of Fe-based superconductors have discovered that such unusual disorder behavior seems to be indeed present in those systems.

  3. Voltage-current and voltage-flux characteristics of asymmetric high TC DC SQUIDs

    NASA Astrophysics Data System (ADS)

    Novikov, I. L.; Greenberg, Ya. S.; Schultze, V.; Ijsselsteijn, R.; Meyer, H.-G.

    2009-01-01

    We report measurements of transfer functions and flux shifts of 20 on-chip high TC DC SQUIDs half of which were made purposely geometrically asymmetric. All of these SQUIDs were fabricated using standard high TC thin-film technology and they were single layer ones, having 140 nm thickness of YBa 2Cu 3O 7- x film deposited by laser ablation onto MgO bicrystal substrates with 24° misorientation angle. For every SQUID the parameters of its intrinsic asymmetry, i.e., the density of critical current and resistivity of every junction, were measured directly and independently. We showed that the main reason for the on-chip spreading of SQUIDs’ voltage-current and voltage-flux characteristics was the intrinsic asymmetry. We found that for SQUIDs with a relative large inductance ( L > 120 pH) both the voltage modulation and the transfer function were not very sensitive to the junctions asymmetry, whereas SQUIDs with smaller inductance ( L ≃ 65-75 pH) were more sensitive. The results obtained in the paper are important for the implementation in the sensitive instruments based on high TC SQUID arrays and gratings.

  4. Noncubic layered structure of Ba1-xKxBiO3 superconductor

    NASA Astrophysics Data System (ADS)

    Klinkova, L. A.; Uchida, M.; Matsui, Y.; Nikolaichik, V. I.; Barkovskii, N. V.

    2003-04-01

    Bismuthate superconductor Ba1-xKxBiO3 (x=0.27-0.49, Tc=25-32 K) grown by an electrolysis technique was studied by electron diffraction and high-resolution electron microscopy. The crystalline structure thereof has been found to be noncubic, noncentrosymmetric and of the layered nature, with the lattice parameters a≈ap, c≈2ap (ap is a simple cubic perovskite cell parameter) containing an ordered arrangement of barium and potassium. The evidence for the layered nature of the bismuthate superconductor removes the principal crystallographic contradiction between bismuthate and cuprate high-Tc superconductors.

  5. Recent Advances in Layered Metal Chalcogenides as Superconductors and Thermoelectric Materials: Fe-Based and Bi-Based Chalcogenides.

    PubMed

    Mizuguchi, Yoshikazu

    2016-04-01

    Recent advances in layered (Fe-based and Bi-based) chalcogenides as superconductors or functional materials are reviewed. The Fe-chalcogenide (FeCh) family are the simplest Fe-based high-Tc superconductors. The superconductivity in the FeCh family is sensitive to external or chemical pressure, and high Tc is attained when the local structure (anion height) is optimized. The Bi-chalcogenide (BiCh2) family are a new group of layered superconductors with a wide variety of stacking structures. Their physical properties are also sensitive to external or chemical pressure. Recently, we revealed that the emergence of superconductivity and the Tc in this family correlate with the in-plane chemical pressure. Since the flexibility of crystal structure and electronic states are an advantage of the BiCh2 family for designing functionalities, I briefly review recent developments in this family as not only superconductors but also other functional materials.

  6. Practical superconductor development for electrical power applications. Annual report for FY 1992

    SciTech Connect

    Goretta, K.C.

    1992-10-01

    Development of useful high-critical-temperature (high-{Tc}) superconductors requires synthesis of superconducting compounds; fabrication of wires, tapes, and films from these compounds; production of composite structures that incorporate stabilizers or insulators; and design and testing of efficient components. This report describes the technical progress of research and development efforts aimed at producing superconducting components that are based on the Y-Ba-Cu, Bi-Sr-Ca-Cu, Bi-Pb-Sr-Ca-Cu, and (TI,Pb)-(Ba,Sr)-Ca-Cu oxide systems. Topics discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite wires and tapes, superconductor/metal connectors, characterization of structures and superconducting and mechanical properties, fabrication and properties of thin films, and development of prototype components. Collaborations with industry and academia are documented.

  7. 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.

  8. Electronic transport in unconventional superconductors

    SciTech Connect

    Graf, M.J.

    1998-12-31

    The author investigates the electron transport coefficients in unconventional superconductors at low temperatures, where charge and heat transport are dominated by electron scattering from random lattice defects. He discusses the features of the pairing symmetry, Fermi surface, and excitation spectrum which are reflected in the low temperature heat transport. For temperatures {kappa}{sub B}T {approx_lt} {gamma} {much_lt} {Delta}{sub 0}, where {gamma} is the bandwidth of impurity induced Andreev states, certain eigenvalues become universal, i.e., independent of the impurity concentration and phase shift. Deep in the superconducting phase ({kappa}{sub B}T {approx_lt} {gamma}) the Wiedemann-Franz law, with Sommerfeld`s value of the Lorenz number, is recovered. He compares the results for theoretical models of unconventional superconductivity in high-{Tc} and heavy fermion superconductors with experiment. The findings show that impurities are a sensitive probe of the low-energy excitation spectrum, and that the zero-temperature limit of the transport coefficients provides an important test of the order parameter symmetry.

  9. Quantum tunneling of vortices in the Tl2CaBa2Cu2O8 superconductor

    NASA Astrophysics Data System (ADS)

    Tejada, J.; Chudnovsky, E. M.; García, A.

    1993-05-01

    Magnetic-relaxation measurements of a Tl-based high-Tc superconductor show temperature-independent flux creep below 6 K. The effect is analyzed in terms of the overdamped quantum diffusion of two-dimensional vortices. Good agreement between theory and experiment is found.

  10. A New Mechanism for High-Tc:. Electron Scattering from Interacting Tunneling Units

    NASA Astrophysics Data System (ADS)

    Klein, Michael W.; Simanovsky, Sergey B.

    A theoretical model for high-Tc superconductivity is presented based on electron pairing due to their interaction with two-level or multi-level tunneling units (TU's) present in high-Tc materials. TU's were found experimentally in YBa2Cu3O7-δ, Bi2CaSr2Cu2O8, Tl2CaBa2Cu2O8 and in Tl2CaBa2CuO6. The TU's have specific directions of orientation with respect to the crystal axis and hence cause a strongly anisotropic scattering of the conduction electrons and a strongly anisotropic gap function Δ(k) with wave vector k. For the weak coupling case we obtain, (i) an analytically derived Δ(k) which has a linear combination of s-wave and dx2-y2-wave symmetry with nodes in Δ(k), (ii) a high-Tc determined by the elastic interaction potential between the TU's, (iii) an isotope effect consistent with experiment, (iv) a large uniaxial pressure p dependence of Tc for YBa2Cu3O7-δ close to optimal oxygen doping and (dTc/dpa) ≈ -(dTc/dpb) where Pa and Pb are the pressures in the a and b directions, (v) a quantitative agreement with experiment for dTc/dPi (i = a, b) when we use the elastic constant. The recently observed d ± s wave pairing in twinned YBa2Cu3O7-δ, with a reversal of the sign of s-wave component across the twin boundary, is also in agreement with our model.

  11. Development of a High-Tc SQUID-Based System for Neurophysiology Studies In-Vitro

    NASA Astrophysics Data System (ADS)

    Magnelind, Per; Tarte, Ed; Winkler, Dag; Hanse, Eric

    2006-06-01

    In this paper we report on the development of a system based on a high-Tc SQUID (HTS) sensor for measurements of the neuromagnetic field generated by neurons inside tissue slices. SQUIDs have successfully been measured inside the system. The system white noise level is lower than 7 pT/Hz{1/2}, which is only slightly higher than previously reported 4.5 pT/Hz{1/2} for the same kind of SQUID measured inside a superconducting shield.

  12. Magnetic microscopy based on high-Tc SQUIDs for room temperature samples

    NASA Astrophysics Data System (ADS)

    Wang, H. W.; Kong, X. Y.; Ren, Y. F.; Yu, H. W.; Ding, H. S.; Zhao, S. P.; Chen, G. H.; Zhang, L. H.; Zhou, Y. L.; Yang, Q. S.

    2003-11-01

    The SQUID microscope is the most suitable instrument for imaging magnetic fields above sample surfaces if one is mainly interested in field sensitivity. In this paper, both the magnetic moment sensitivity and spatial resolution of the SQUID microscope are analysed with a simple point moment model. The result shows that the ratio of SQUID sensor size to sensor-sample distance effectively influences the sensitivity and spatial resolution. In comparison with some experimental results of magnetic images for room temperature samples from our high-Tc SQUID microscope in an unshielded environment, a brief discussion for further improvement is presented.

  13. Noise properties of high-Tc superconducting flux transformers fabricated using chemical-mechanical polishing

    NASA Astrophysics Data System (ADS)

    Chukharkin, M.; Kalabukhov, A.; Schneiderman, J. F.; Öisjöen, F.; Snigirev, O.; Lai, Z.; Winkler, D.

    2012-07-01

    Reproducible high-temperature superconducting multilayer flux transformers were fabricated using chemical mechanical polishing. The measured magnetic field noise of the flip-chip magnetometer based on one such flux transformer with a 9 × 9 mm2 pickup loop coupled to a bicrystal dc SQUID was 15 fT/Hz1/2 above 2 kHz. We present an investigation of excess 1/f noise observed at low frequencies and its relationship with the microstructure of the interlayer connections within the flux transformer. The developed high-Tc SQUID magnetometers may be advantageous in ultra-low field magnetic resonance imaging and, with improved low frequency noise, magnetoencephalography applications.

  14. Nexus between quantum criticality and the chemical potential pinning in high- Tc cuprates

    NASA Astrophysics Data System (ADS)

    Kopeć, T. K.

    2005-08-01

    For strongly correlated electrons the relation between total number of charge carriers ne and the chemical potential μ reveals for large Coulomb energy the apparently paradoxical pinning of μ within the Mott gap, as observed in high- Tc cuprates. By unraveling consequences of the nontrivial topology of the charge gauge U(1) group and the associated ground state degeneracy we found a close kinship between the pinning of μ and the zero-temperature divergence of the charge compressibility κ˜∂ne/∂μ , which marks a novel quantum criticality governed by topological charges rather than Landau principle of the symmetry breaking.

  15. Lateral restoring force on a magnet levitated above a superconductor

    NASA Technical Reports Server (NTRS)

    Davis, L. C.

    1990-01-01

    The lateral restoring force on a magnet levitated above a superconductor is calculated as a function of displacement from its original position at rest using Bean's critical-state model to describe flux pinning. The force is linear for small displacements and saturates at large displacements. In the absence of edge effects the force always attracts the magnet to its original position. Thus it is a restoring force that contributes to the stability of the levitated magnet. In the case of a thick superconductor slab, the origin of the force is a magnetic dipole layer consisting of positive and negative supercurrents induced on the trailing side of the magnet. The qualitative behavior is consistent with experiments reported to date. Effects due to the finite thickness of the superconductor slab and the granular nature of high-Tc materials are also considered.

  16. Superconductor cable

    DOEpatents

    Allais, Arnaud; Schmidt, Frank; Marzahn, Erik

    2010-05-04

    A superconductor cable is described, having a superconductive flexible cable core (1) , which is laid in a cryostat (2, 3, 4), in which the cable core (1) runs in the cryostat (2, 3, 4) in the form of a wave or helix at room temperature.

  17. Organic superconductors

    NASA Astrophysics Data System (ADS)

    Jérome, D.

    1994-10-01

    The discovery of organic superconductors in 1980 was an happy conclusion of a search for high T c superconductors (although T c was modestly in the Kelvin range). The first generation of organic superconductors belonged to a large family of quasi-one-dimensional conducting cation radical salts. Most of them exhibit a wide range of new phenomena, including the competition between ground states, the influence of a magnetic field on the non ordered phase of a quasi-one-dimensional electron gas and the onset of spin density wave phases at high magnetic field with quantized Hall effect. The extensive study of the (TM) 2X series has shown that electron interactions are repulsive and of the order of the electron bandwidth. However, the nature of the ground states relies essentially on the balance between charge localisation boosted by the Umklapp scattering and the interchain hopping intergal. Second and third generation organic superconductors are two and three dimensional molecular conductors respectively with maximum T c of 12K (ET) 2X and 33 K (fullerides).

  18. Magnetic levitation force measurement on high [Tc] superconducting ceramic/polymer composites

    SciTech Connect

    Unsworth, J.; Du, Jia; Crosby, B.J. ); Macfarlane, J.C. )

    1993-01-01

    An experimental study of magnetic levitation force for 0--3 and 3--3 superconducting ceramic/polymer composites is presented. A simple, inexpensive force versus distance measurement technique is described. The measurements of force against distance or magnetic field show strong hysteretic behavior, which is similar to the sintered superconductor ceramics and is consistent with the hysteresis in magnetization of superconductor. The volume fraction dependence and sample thickness dependence of the levitation forces are also studied for 0--3 composites. Results suggest that the new composite materials are most suitable for levitation applications.

  19. Metallic contaminant detection system using multi-channel high Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Kitamura, Yoshihiro; Hatsukade, Yoshimi; Ohtani, Takeyoshi; Suzuki, Shuichi

    2012-10-01

    We have developed the magnetic metallic contaminant detectors using multiple high Tc SQUID gradiometers for industrial products. Finding ultra-small metallic contaminants is a big issue for manufacturers producing commercial products. The quality of industrial products such as lithium ion batteries can deteriorate by the inclusion of tiny metallic contaminants. When the contamination does occur, the manufacturer of the product suffers a great loss to recall the tainted products. Metallic particles with outer dimension less than 50 μm cannot be detected by a conventional X-ray imaging. Therefore a high sensitive detection system for small foreign matters is required. However, in most of the cases, the matrix of an active material coated sheet electrode is magnetized and the magnetic signal from the matrix is large enough to mask the signal from contaminants. Thus we have developed a detection system based on a SQUID gradiometer and a horizontal magnetization to date. For practical use, we should increase the detection width of the system by employing multiple sensors. We successfully realized an eight-channel high-Tc SQUID gradiometer system for inspection of sheet electrodes of a lithium ion battery with width of at least 60 to 70 mm. Eight planar SQUID gradiometers were mounted with a separation of 9.0 mm. As a result, small iron particles of less than 50 μm were successfully measured. This result suggests that the system is a promising tool for the detection of contaminants in a lithium ion battery.

  20. Anisotropic softening of magnetic excitations in lightly electron-doped Sr2IrO4

    DOE PAGES

    Liu, X.; Dean, M. P. M.; Meng, Z. Y.; ...

    2016-06-10

    The magnetic excitations in electron doped (Sr1-xLax)2IrO4 with x = 0:03 were measured using resonant inelastic X-ray scattering at the Ir L3-edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the anti-nodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron doped (Sr1-xLax)2IrO4 with close analogies to the hole doped cuprates, further motivating the searchmore » for high temperature superconductivity in this system.« less

  1. Disordered dimer state in electron-doped Sr3Ir2O7

    NASA Astrophysics Data System (ADS)

    Hogan, Tom; Dally, Rebecca; Upton, Mary; Clancy, J. P.; Finkelstein, Kenneth; Kim, Young-June; Graf, M. J.; Wilson, Stephen D.

    2016-09-01

    Spin excitations are explored in the electron-doped spin-orbit Mott insulator (Sr1-xLax) 3Ir2O7 . As this bilayer square lattice system is doped into the metallic regime, long-range antiferromagnetism vanishes, yet a spectrum of gapped spin excitation remains. Excitation lifetimes are strongly damped with increasing carrier concentration, and the energy-integrated spectral weight becomes nearly momentum independent as static spin order is suppressed. Local magnetic moments, absent in the parent system, grow in metallic samples and approach values consistent with one J =1/2 impurity per electron doped. Our combined data suggest that the magnetic spectra of metallic (Sr1-xLax) 3Ir2O7 are best described by excitations out of a disordered dimer state.

  2. Anisotropic softening of magnetic excitations in lightly electron-doped Sr2IrO4

    SciTech Connect

    Liu, X.; Dean, M. P. M.; Meng, Z. Y.; Upton, M. H.; Qi, T.; Gog, T.; Cao, Y.; Lin, J. Q.; Meyers, D.; Ding, H.; Cao, G.; Hill, J. P.

    2016-06-10

    The magnetic excitations in electron doped (Sr1-xLax)2IrO4 with x = 0:03 were measured using resonant inelastic X-ray scattering at the Ir L3-edge. Although much broadened, well defined dispersive magnetic excitations were observed. Comparing with the magnetic dispersion from the undoped compound, the evolution of the magnetic excitations upon doping is highly anisotropic. Along the anti-nodal direction, the dispersion is almost intact. On the other hand, the magnetic excitations along the nodal direction show significant softening. These results establish the presence of strong magnetic correlations in electron doped (Sr1-xLax)2IrO4 with close analogies to the hole doped cuprates, further motivating the search for high temperature superconductivity in this system.

  3. Electron doping through lithium intercalation to interstitial channels in tetrahedrally bonded SiC

    SciTech Connect

    Sakai, Yuki; Oshiyama, Atsushi

    2015-11-07

    We report on first-principles calculations that clarify the effect of lithium atom intercalation into zinc blende 3C-silicon carbide (3C-SiC) on electronic and structural properties. Lithium atoms inside 3C-SiC are found to donate electrons to 3C-SiC that is an indication of a new way of electron doping through the intercalation. The electrons doped into the conduction band interact with lithium cations and reduce the band spacing between the original valence and conduction bands. We have also found that a silicon monovacancy in 3C-SiC promotes the lithium intercalation, showing that the vacancy generation makes SiC as a possible anode material for lithium-ion battery.

  4. SHMUTZ & PROTON-DIAMANT H + Irradiated/Written-Hyper/Super-conductivity(HC/SC) Precognizance/Early Experiments Connections: Wet-Graphite Room-Tc & Actualized MgB2 High-Tc: Connection to Mechanical Bulk-Moduli/Hardness: Diamond Hydrocarbon-Filaments, Disorder, Nano-Powders:C,Bi,TiB2,TiC

    NASA Astrophysics Data System (ADS)

    Wunderman, Irwin; Siegel, Edward Carl-Ludwig; Lewis, Thomas; Young, Frederic; Smith, Adolph; Dresschhoff-Zeller, Gieselle

    2013-03-01

    SHMUTZ: ``wet-graphite''Scheike-....[Adv.Mtls.(7/16/12)]hyper/super-SCHMUTZ-conductor(S!!!) = ``wet''(?)-``graphite''(?) = ``graphene''(?) = water(?) = hydrogen(?) =ultra-heavy proton-bands(???) = ...(???) claimed room/high-Tc/high-Jc superconductOR ``p''-``wave''/ BAND(!!!) superconductIVITY and actualized/ instantiated MgB2 high-Tc superconductors and their BCS- superconductivity: Tc Siegel[ICMAO(77);JMMM 7,190(78)] connection to SiegelJ.Nonxline-Sol.40,453(80)] disorder/amorphous-superconductivity in nano-powders mechanical bulk/shear(?)-moduli/hardness: proton-irradiated diamond, powders TiB2, TiC,{Siegel[Semis. & Insuls.5:39,47, 62 (79)])-...``VS''/concommitance with Siegel[Phys.Stat.Sol.(a)11,45(72)]-Dempsey [Phil.Mag. 8,86,285(63)]-Overhauser-(Little!!!)-Seitz-Smith-Zeller-Dreschoff-Antonoff-Young-...proton-``irradiated''/ implanted/ thermalized-in-(optimal: BOTH heat-capacity/heat-sink & insulator/maximal dielectric-constant) diamond: ``VS'' ``hambergite-borate-mineral transformable to Overhauser optimal-high-Tc-LiBD2 in Overhauser-(NW-periodic-table)-Land: CO2/CH4-ETERNAL-sequestration by-product: WATER!!!: physics lessons from

  5. Electron-Phonon Interaction in Oxide Superconductors - Proceedings of the First Cinvestav Superconductivity Symposium

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koichi; Hashimoto, Takasu

    1991-12-01

    The Table of Contents for the book is as follows: * List of Invited Speakers * Preface * PHONONS * Lattice Vibrations of the Cuprate Superconductors * INFRARED * Evidence of Strong Electron-Phonon Interaction from the Infrared Spectra of YBa2Cu3O7 * Electron-Phonon Interaction and Infrared Spectra of High Temperature Superconductors * TUNNELING * Tunneling Studies of Bismuthate and Cuprate Superconductors * Phonon Mechanism of the High Tc Superconductivity Based on the Tunneling Structure * LATTICE INSTABILITIES * Lattice Instabilities in High Temperature Superconductors: The X Point Tilt Energy Surface for La2-xBaxCuO4 * Structural Instability and Strong Coupling in Oxide Superconductors * ISOTOPE EFFECT * On the Isotope Effect * Electron-Phonon Coupling, Oxygen Isotope Effect and Superconductivity in Ba1-xKxBio3 * BCJ AND ELIASHBERG THEORY * Weak Coupling Theory of the High Tc Superconductors Based on the Electron-Phonon Interaction * Phonon Self-Energy Effects in Migdal-Eliashberg Theory * OTHER TOPICS * Electron-Phonon Interaction and Superconductivity in BaxK1-xBio3 * The Effect of Strong Coulomb Correlations on Electron-Phonon Interactions in the Copper Oxides: Implications for Transport * EXPERIMENT (OTHER TOPICS) * Zinc Substitution Effects on the Superconducting Properties of Nd1.85Ce0.15CuO4-δ * SUMMARY * Manifestations of the e-ph Interaction: A Summary * Author Index

  6. Controlled thermodynamics for tunable electron doping of graphene on Ir(111)

    NASA Astrophysics Data System (ADS)

    Struzzi, C.; Praveen, C. S.; Scardamaglia, M.; Verbitskiy, N. I.; Fedorov, A. V.; Weinl, M.; Schreck, M.; Grüneis, A.; Piccinin, S.; Fabris, S.; Petaccia, L.

    2016-08-01

    The electronic properties and surface structures of K-doped graphene supported on Ir(111) are characterized as a function of temperature and coverage by combining low-energy electron diffraction, angle-resolved photoemission spectroscopy, and density functional theory (DFT) calculations. Deposition of K on graphene at room temperature (RT) yields a stable (√ 3 ×√ 3 ) R30° surface structure having an intrinsic electron doping that shifts the graphene Dirac point by ED=1.30 eV below the Fermi level. Keeping the graphene substrate at 80 K during deposition generates instead a (2 ×2 ) phase, which is stable until full monolayer coverage. Further deposition of K followed by RT annealing develops a double-layer K-doped graphene that effectively doubles the K coverage and the related charge transfer, as well as maximizing the doping level (ED=1.61 eV ). The measured electron doping and the surface reconstructions are rationalized by DFT calculations. These indicate a large thermodynamic driving force for K intercalation below the graphene layer. The electron doping and Dirac point shifts calculated for the different structures are in agreement with the experimental measurements. In particular, the K4 s bands are shown to be sensitive to both the K intercalation and periodicity and are therefore suggested as a fingerprint for the location and ordering of the K dopants.

  7. Persistence of polar distortion with electron doping in lone-pair driven ferroelectrics

    NASA Astrophysics Data System (ADS)

    He, Xu; Jin, Kui-juan

    2016-12-01

    Free electrons can screen out long-range Coulomb interaction and destroy the polar distortion in some ferroelectric materials, whereas the coexistence of polar distortion and metallicity were found in several non-central-symmetric metals (NCSMs). Therefore, the mechanisms and designing of NCSMs have attracted great interest. In this work, by first-principles calculation, we found the polar distortion in the lone-pair driven ferroelectric material PbTiO3 cannot only persist but also increase with electron doping. We further analyzed the mechanisms of the persisting of the polar distortion. We found that the Ti site polar instability is suppressed, but the Pb site polar instability is intact with the electron doping. The Pb-site instability is due to the lone-pair mechanism which can be viewed as a pseudo-Jahn-Teller effect, a mix of the ground state and the excited state by ion displacement from the central symmetric position. The lone-pair mechanism is not strongly affected by the electron doping because neither the ground state nor the excited state involved is at the Fermi energy. The enhancement of the polar distortion is related to the increasing of the Ti ion size by doping. These results show that the long-pair stereoactive ions can be used for designing NCSMs.

  8. High-Tc Nodeless s±-wave Superconductivity in (Y,La)FeAsO1-y with Tc=50K:As75-NMR Study

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Furukawa, S.; Kinouchi, H.; Yashima, M.; Kitaoka, Y.; Shirage, P. M.; Eisaki, H.; Iyo, A.

    2012-10-01

    We report on an As75-NMR study on the Fe-pnictide high-Tc superconductor Y0.95La0.05FeAsO1-y (Y0.95La0.051111) with Tc=50K that includes no magnetic rare-earth elements. The measurement of the nuclear-spin lattice-relaxation rate (751/T1) has revealed that the nodeless bulk superconductivity takes place at Tc=50K while antiferromagnetic spin fluctuations develop moderately in the normal state. These features are consistently described by the multiple fully gapped s±-wave model based on the Fermi-surface nesting. Incorporating the theory based on band calculations, we propose that the reason that Tc=50K in Y0.95La0.051111 is larger than Tc=28K in La1111 is that the Fermi-surface multiplicity is maximized, and hence the Fermi-surface nesting condition is better than that in La1111.

  9. Electronic structure and superconductivity of FeSe-related superconductors.

    PubMed

    Liu, Xu; Zhao, Lin; He, Shaolong; He, Junfeng; Liu, Defa; Mou, Daixiang; Shen, Bing; Hu, Yong; Huang, Jianwei; Zhou, X J

    2015-05-13

    FeSe superconductors and their related systems have attracted much attention in the study of iron-based superconductors owing to their simple crystal structure and peculiar electronic and physical properties. The bulk FeSe superconductor has a superconducting transition temperature (Tc) of ~8 K and it can be dramatically enhanced to 37 K at high pressure. On the other hand, its cousin system, FeTe, possesses a unique antiferromagnetic ground state but is non-superconducting. Substitution of Se with Te in the FeSe superconductor results in an enhancement of Tc up to 14.5 K and superconductivity can persist over a large composition range in the Fe(Se,Te) system. Intercalation of the FeSe superconductor leads to the discovery of the AxFe2-ySe2 (A = K, Cs and Tl) system that exhibits a Tc higher than 30 K and a unique electronic structure of the superconducting phase. A recent report of possible high temperature superconductivity in single-layer FeSe/SrTiO3 films with a Tc above 65 K has generated much excitement in the community. This pioneering work opens a door for interface superconductivity to explore for high Tc superconductors. The distinct electronic structure and superconducting gap, layer-dependent behavior and insulator-superconductor transition of the FeSe/SrTiO3 films provide critical information in understanding the superconductivity mechanism of iron-based superconductors. In this paper, we present a brief review of the investigation of the electronic structure and superconductivity of the FeSe superconductor and related systems, with a particular focus on the FeSe films.

  10. Conditions for superconductivity in the electron-doped copper-oxide system, (Nd{sub 1-x}Ce{sub x}){sub 2}CuO{sub 4+{delta}}

    SciTech Connect

    Tanaka, Y.; Motohashi, T.; Karppinen, M. Yamauchi, H.

    2008-02-15

    We report systematic studies on the relations among the Ce{sup IV}-for-Nd{sup III} substitution level (x), oxygen-partial pressure (P{sub O{sub 2}}), oxygen content (4+{delta}), lattice parameters (a, c) and superconductivity characteristics (T{sub c}, volume fraction) in the (Nd{sub 1-x}Ce{sub x}){sub 2}Cu{sub 1-y}O{sub 4+{delta}} system which includes electron-doped superconductors. Independent of the Ce-doping level x, samples synthesized in air are found oxygen deficient, i.e. {delta}<0. Nevertheless, reductive annealing is needed to induce superconductivity in the air-synthesized samples. At the same time, the amount of oxygen removed upon the annealing is found very small (e.g. 0.004 oxygen atoms per formula unit at x=0.075), and consequently the effect of the annealing on the valence of copper (and thereby also on the electron doping level) is insignificant. Rather, the main function of the reductive annealing is likely to repair the Cu vacancies believed to exist in tiny concentrations (y) in the air-synthesized samples. - Graphical abstract: Superconductivity in the electron-doped (Nd{sub 1-x}Ce{sub x}){sub 2}Cu{sub 1-y}O{sub 4+{delta}} system is sensitively controlled not only by the Ce{sup IV}-for-Nd{sup III} substitution level (x) but also by the the Cu-vacancy concentration (y) and the oxygen content ({delta}) determined by oxygen-partial pressure used for the post-annealing.

  11. Temperature dependence of the upper critical field of type-II superconductors from isothermal magnetization data: Application to high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Landau, I. L.; Ott, H. R.

    2002-10-01

    Using the Ginzburg-Landau theory in very general terms, we develop a simple scaling procedure which allows to establish the temperature dependence of the upper critical field Hc2 and the value of the superconducting critical temperature Tc of type-II superconductors from measurements of the reversible isothermal magnetization. An analysis of existing experimental data shows that the normalized dependencies of Hc2 on T/Tc are practically identical for all families of high-Tc superconductors at all temperatures for which the magnetization data are available.

  12. Superconductor cable

    DOEpatents

    Smith, Jr., Darrell F.; Lake, Bill L.; Ballinger, Ronald G.

    1988-01-01

    A superconducting cable comprising an in-situ-formed type II superconductor, e.g. Nb.sub.3 Sn, in association with a stabilizing conductor both in heat transfer relationship with at least one passage adapted to carry liquified gaseous refrigerant. The conductor and said at least one passage are enclosed by a sheath comprising an alloy consisting essentially of about 49% nickel, about 4% chromium, about 3% niobium, about 1.4% titanium, about 1% aluminum, balance essentially iron.

  13. Chiral superconductors.

    PubMed

    Kallin, Catherine; Berlinsky, John

    2016-05-01

    Chiral superconductivity is a striking quantum phenomenon in which an unconventional superconductor spontaneously develops an angular momentum and lowers its free energy by eliminating nodes in the gap. It is a topologically non-trivial state and, as such, exhibits distinctive topological modes at surfaces and defects. In this paper we discuss the current theory and experimental results on chiral superconductors, focusing on two of the best-studied systems, Sr2RuO4, which is thought to be a chiral triplet p-wave superconductor, and UPt3, which has two low-temperature superconducting phases (in zero magnetic field), the lower of which is believed to be chiral triplet f-wave. Other systems that may exhibit chiral superconductivity are also discussed. Key signatures of chiral superconductivity are surface currents and chiral Majorana modes, Majorana states in vortex cores, and the possibility of half-flux quantum vortices in the case of triplet pairing. Experimental evidence for chiral superconductivity from μSR, NMR, strain, polar Kerr effect and Josephson tunneling experiments are discussed.

  14. Experimental Studies of the Isotope Effect in High Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Franck, Jürgen P.

    The following sections are included: * INTRODUCTION * BACKGROUND * DEFINITIONS * CONNECTION WITH THEORY * OUTLINE * EXPERIMENTAL METHODS * SAMPLE PREPARATION * DETERMINATION OF ISOTOPIC SHIFTS * THE OXYGEN ISOTOPE EFFECT IN HIGH Tc CUPRATES * YBa2Cu3O7 AND RELATED SYSTEMS * Completely Isotope Exchanged * Partially and Selectively Isotope Exchanged * SUBSTITUTED YBa2Cu3O7 AND RELATED SYSTEMS * YBa2Cu4O8 * La2-xMxCuO4 (M = Sr, Ba) AND RELATED SYSTEMS * Bi-Sr-Ca-Cu OXIDES * (Nd1-xCex)2CuO4 * Tℓ BASED SYSTEMS * PARTIAL ISOTOPE EFFECTS FOR ELEMENTS OTHER THAN OXYGEN IN HIGH Tc CUPRATES * THE COPPER ISOTOPE EFFECT * ISOTOPE EFFECT FOR ELEMENTS OTHER THAN OXYGEN OR COPPER * THE OXYGEN ISOTOPE EFFECT IN RELATED SUPERCONDUCTORS * Ba-Pb-Bi OXIDE AND Ba-K-Bi OXIDE * FULLERENES * DISCUSSION * SUMMARY OF EXPERIMENTAL RESULTS * THEORETICAL CONSIDERATIONS * CONCLUSION * ACKNOWLEDGEMENTS * REFERENCES

  15. New type of second-order high- Tc SQUID planar gradiometer

    NASA Astrophysics Data System (ADS)

    Lang, P. L.; Zheng, D. N.; Zhang, M. J.; Chen, K.; Qi, H. H.; Zhao, Z. X.

    2004-09-01

    We have proposed a novel type of high- Tc superconducting quantum interference device (SQUID) planar gradiometer that could measure the mixed partial derivative of magnetic fields ∂2Bz/ ∂x ∂y . The device consists of two parts, one is the signal pickup antenna formed by four square pickup loops, and another one is a SQUID directly coupled to the common line which separates the antenna loops. The four pickup loops were arranged to a two-dimensional array. The loops in the diagonal direction are connected in series. The total current in the common line in this configuration is directly proportional to the mixed partial derivative of the magnetic field. We have made a device of such design on a STO bicrystal substrate and tested the device in gradient field.

  16. Detection of magnetic nanoparticles utilizing cooled normal pickup coil and high Tc SQUID

    NASA Astrophysics Data System (ADS)

    Enpuku, K.; Nabekura, S.; Tsuji, Y.; Okada, S.; Matsuo, M.; Tsukamoto, A.; Mizoguchi, T.; Kandori, A.

    2009-10-01

    Magnetic nanoparticles coupled with medicine or reagents have been studied for the application to in vivo medical diagnosis and drug delivery. For these applications, we have been developing a measurement system to detect the position and amount of the magnetic nanoparticles accumulated inside the body by using a cooled Copper pickup coil and high Tc SQUID. The susceptibility measurement method with an excitation filed is used to detect the magnetic nanoparticles. Experimental results, such as contour map of the signal field and the distance-dependence of the detected signal, are shown. At present, we could detect 50 μg of Fe 3O 4 particles that are located below the pickup coil at the distance of 30 mm.

  17. High-Tc planar SQUID gradiometer for eddy current non-destructive evaluation

    NASA Astrophysics Data System (ADS)

    Zhang, Ming-Jian; Lang, Pei-Lin; Peng, Zhi-Hui; Chen, Ying-Fei; Chen, Ke; Zheng, Dong-Ning

    2006-08-01

    This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10-4Φ0/(Hz)1/2. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation (NDE) experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.

  18. Measurement of metallic contaminants in food with a high-Tc SQUID

    NASA Astrophysics Data System (ADS)

    Tanaka, Saburo; Natsume, Miyuki; Uchida, Masashi; Hotta, Naoki; Matsuda, Takemasa; Spanut, Zarina A.; Hatsukade, Yoshimi

    2004-04-01

    We have proposed and demonstrated a high-Tc SQUID system for detecting metallic contaminants in foodstuffs. There is a demand for the development of systems for detecting not only magnetic materials but also non-magnetic materials such as Cu and aluminium in foodstuffs to ensure food safety. The system consists of a SQUID magnetometer, an excitation coil and a permanent magnet. For a non-magnetic sample, an AC magnetic field is applied during detection to induce an eddy current in the sample. For a magnetizable sample, a strong magnetic field is applied to the sample prior to the detection attempt. We were able to detect a stainless steel ball with a diameter of 0.1 mm and a Cu ball less than 1 mm in diameter, for example.

  19. Development of a rat biomagnetic measurement system using a high-TC SQUID magnetometer

    NASA Astrophysics Data System (ADS)

    Kim, In-Seon; Lee, Chul-Ho; Lee, Yong-Ho

    2010-08-01

    We have developed a rat magnetocardiograph (MCG) system employing a high-TC SQUID magnetometer and a tabletop magnetic shield. We obtained clear MCG signals from a healthy Wistar Kyoto rat with a relatively high peak amplitude of 50 pT by virtue of the small gap cryostat developed in this study. Well defined P-, QRS- and T-waves were observed on the MCG of the healthy rat. In the case of a spontaneously hypertensive rat measurement, the MCG showed quite a disturbed wave pattern thought to be caused by the hypertensive heart abnormality. The results suggest that the rat biomagnetic measurement system has a strong potential for monitoring the progress of the heart disease model.

  20. The fine magnetic image of a high TC SQUID probe microscope

    NASA Astrophysics Data System (ADS)

    Hayashi, Tadayuki; Itozaki, Hideo

    2005-01-01

    We have developed a high TC SQUID probe microscope. A high permeability probe was used as a flux guide to improve its spatial resolution. The SQUID head with the flux guide makes it possible to measure samples with high spatial resolution in air at room temperature. The end of the flux guide and the SQUID were in vacuum with a 0.1 mm separation. The tip of the flux guide was in air. The rod diameter and length of the flux guide were 0.6 and 7 mm, respectively. The sharp tip of the flux guide required for high spatial resolution was prepared by microelectropolishing. Its tip radius was less than 1 µm. The static magnetic field pattern of magnetized toner particles was detected by this system and we obtained a high-resolution magnetic image with a spatial resolution of several microns.

  1. Research on high-Tc SQUID based non-destructive evaluation

    NASA Astrophysics Data System (ADS)

    Wang, Hui-Wu; Kong, Xiang-Yan; Ren, Yu-Feng; Yu, Hong-Wei; Ding, Hong-Sheng; Zhao, Shi-Ping; Chen, Geng-Hua; Zhou, Yue-Liang; Zhang, Li-Hua; He, Yu-Sheng; Yang, Qian-Sheng

    2004-01-01

    A non-destructive evaluation system based on high-Tc dc-SQUID (superconducting quantum interference device) incorporating a gradient field excitation has been built. By using this system a 1mm-diameter hole at a depth of 2mm inside an aluminium plate at room temperature can be easily detected and imaged in an unshielded environment. The relation between the spatial resolution, or the smallest detectable flaw size and experimental parameters is briefly analysed in terms of a simple metal ring model. The result shows that the spatial resolution depends strongly on the sensor-sample separation as well as on some other parameters, such as signal-to-noise ratio of excitation, excitation frequency and material conductivity.

  2. Fundamental operation of single-flux-quantum circuits using coplanar-type high-Tc SQUIDs

    NASA Astrophysics Data System (ADS)

    Fuke, Hiroyuki; Saitoh, Kazuo; Utagawa, Tadashi; Enomoto, Youichi

    1996-11-01

    We have fabricated coplanar type dc SQUIDs using NdBa2Cu3Oy superconducting thin films and operated fundamental single-flux-quantum (SFQ) circuits. The Josephson junctions were made by the narrow-focused ion beam irradiation technique. For a 145 μm wide and 10 μm long logic SQUID having a critical current of 105 μA and an inductive parameter (βL) of 28, a store and a restore of the flux quantum have been demonstrated at temperatures of 4.2-30 K. These operations were performed with an input pulsewidth of 5 ns (5 ns was the shortest input pulse width available from our function generating equipment). These results show experimentally the possibility of high speed operation in all high-Tc superconducting digital circuits.

  3. Analysis of a high Tc superconducting levitation system with vibration isolation control

    SciTech Connect

    Nagaya, Kosuke

    1996-03-01

    This paper presents a method for controlling vibrations of a levitated high Tc superconducting body subjected to base disturbances. To have the control forces, an actuator consisting of a permanent magnet with an electromagnet was presented. The analytical solution for calculating levitation forces due to the permanent magnet and the control currents in the electromagnet was obtained. The levitation forces obtained coincide with the previously published results. The equation of motion of the levitated body subjected to base disturbances under the control was presented. Nonlinear vibrations of the body were first discussed; then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was investigated. Numerical calculations were carried out for the levitation forces, with respect to the levitated body subjected to harmonic or pulse base excitations. It was clarified that the present method is valid for controlling nonlinear systems like the magnetic levitated superconducting body.

  4. Inductance measurements in multilevel high Tc step-edge grain boundary SQUIDS

    NASA Astrophysics Data System (ADS)

    Forrester, M. G.; Davidson, A.; Talvacchio, J.; Gavaler, J. R.; Przybysz, J. X.

    1994-10-01

    Multilevel high Tc SQUIDs, suitable for digital circuit applications, have been fabricated and tested. The devices employ a YBa2Cu3O7-δ (YBCO) ground plane, an epitaxial SrTiO3 insulator, and a YBCO microstrip layer. Junctions are formed by the step-edge grain boundary process, with a ground plane contact for the ``low'' side of each junction, using only isotropic sputtering and milling techniques. Control current is directly injected in a microstrip segment of the SQUID loop, allowing us to measure the microstrip inductance, and thus to infer the magnetic penetration depth of the YBCO. The SQUIDs are operational above 77 K, at which temperature we infer a penetration depth of 350 nm. The temperature dependence of the penetration depth is found to be in reasonable agreement with the Gorter-Casimir form close to Tc.

  5. Fabrication of Monolithic Sapphire Membranes for High Tc Bolometer Array Development

    NASA Technical Reports Server (NTRS)

    Pugel, D. E.; Lakew, B.; Aslam, S.; Wang, L.

    2003-01-01

    This paper examines the effectiveness of Pt/Cr thin film masks for the architecture of monolithic membrane structures in r-plane sapphire. The development of a pinhole-free Pt/Cr composite mask that is resistant to hot H2SO4:H3PO4 etchant, will lead to the fabrication of smooth sapphire membranes whose surfaces are well-suited for the growth of low-noise high Tc films. In particular, the relationship of thermal annealing conditions on the Pt/Cr composite mask system to: (1) changes in the surface morphology and elemental concentration of the Pt/Cr thin film layers and (2) etch pit formation on the sapphire surface will be presented.

  6. Scattering rates and specific heat jumps in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Storey, James

    Inspired by recent ARPES and tunneling studies on high-Tc cuprates, we examine the effect of a pair-breaking term in the self-energy on the shape of the electronic specific heat jump. It is found that the observed specific heat jump can be described in terms of a superconducting gap, that persists above the observed Tc, in the presence of a strongly temperature dependent pair-breaking scattering rate. An increase in the scattering rate is found to explain the non-BCS-like suppression of the specific heat jump with magnetic field. A discussion of these results in the context of other properties such as the superfluid density and Raman spectra will also be presented. Supported by the Marsden Fund Council from Government funding, administered by the Royal Society of New Zealand.

  7. Relaxation of the transport critical current in high-Tc polycrystals

    NASA Astrophysics Data System (ADS)

    Altshuler, E.; Cobas, R.; Batista-Leyva, A. J.; Noda, C.; Flores, L. E.; Martínez, C.; Orlando, M. T. D.

    1999-08-01

    We perform a systematic study of the time evolution of the transport critical current in polycrystalline samples of the high temperature superconducting system (Hg1-xRex)Ba2Ca2Cu3O8+δ and YBa2Cu3O7-δ after application and removal of an external magnetic field Hm. Within our time, temperature, and remanent field windows, the transport critical current increases logarithmically in time. The relaxation rates in the range 80-115 K decrease with increasing temperature at a fixed Hm, while temperature-dependent maxima are observed in the relaxation rate versus Hm plots. These experimental results are reproduced by a phenomenological model applicable to any high-Tc polycrystals. In the model, the time increase of the transport current is determined by the effective field at the intergrain junctions, which relaxes in time due to the flux creep of the intragrain magnetization.

  8. Metal-insulator quantum critical point beneath the high Tc superconducting dome

    PubMed Central

    Sebastian, Suchitra E.; Harrison, N.; Altarawneh, M. M.; Mielke, C. H.; Liang, Ruixing; Bonn, D. A.; Lonzarich, G. G.; Hardy, W. N.

    2010-01-01

    An enduring question in correlated systems concerns whether superconductivity is favored at a quantum critical point (QCP) characterized by a divergent quasiparticle effective mass. Despite such a scenario being widely postulated in high Tc cuprates and invoked to explain non-Fermi liquid transport signatures, experimental evidence is lacking for a critical divergence under the superconducting dome. We use ultrastrong magnetic fields to measure quantum oscillations in underdoped YBa2Cu3O6+x, revealing a dramatic doping-dependent upturn in quasiparticle effective mass at a critical metal-insulator transition beneath the superconducting dome. Given the location of this QCP under a plateau in Tc in addition to a postulated QCP at optimal doping, we discuss the intriguing possibility of two intersecting superconducting subdomes, each centered at a critical Fermi surface instability. PMID:20304800

  9. Uniform mixing of antiferromagnetism and high-temperature superconductivity in electron-doped layers of four-layered Ba(2)Ca(3)Cu(4)O(8)F(2): a new phenomenon in an electron underdoped regime.

    PubMed

    Shimizu, S; Mukuda, H; Kitaoka, Y; Iyo, A; Tanaka, Y; Kodama, Y; Tokiwa, K; Watanabe, T

    2007-06-22

    We report (63,65)Cu- and (19)F-NMR studies on a four-layered high-temperature superconductor Ba(2)Ca(3)Cu(4)O(8)F(2)((0234F(2.0)) with apical fluorine (F(-1)), an undoped 55 K superconductor with a nominal Cu(2+) valence on average. We reveal that this compound exhibits the antiferromagnetism (AFM) with a Néel temperature T(N)=100 K despite being a T(c)=55 K superconductor. Through a comparison with a related trilayered cuprate Ba(2)Ca(3)Cu(4)O(8)F(2)(0233F(2.0)), it is demonstrated that electrons are transferred from the inner plane (IP) to the outer plane (OP) in 0234F(2.0) and 0223F(2.0), confirming the self-doped high-temperature superconductivity (HTSC) having electron and hole doping in a single compound. Remarkably, uniform mixing of AFM and HTSC takes place in both the electron-doped OPs and the hole-doped IPs in 0234F(2.0).

  10. Uniform Mixing of Antiferromagnetism and High-Temperature Superconductivity in Electron-Doped Layers of Four-Layered Ba2Ca3Cu4O8F2: A New Phenomenon in an Electron Underdoped Regime

    NASA Astrophysics Data System (ADS)

    Shimizu, S.; Mukuda, H.; Kitaoka, Y.; Iyo, A.; Tanaka, Y.; Kodama, Y.; Tokiwa, K.; Watanabe, T.

    2007-06-01

    We report Cu63,65- and F19-NMR studies on a four-layered high-temperature superconductor Ba2Ca3Cu4O8F2((0234F(2.0)) with apical fluorine (F-1), an undoped 55 K superconductor with a nominal Cu2+ valence on average. We reveal that this compound exhibits the antiferromagnetism (AFM) with a Néel temperature TN=100K despite being a Tc=55 K superconductor. Through a comparison with a related trilayered cuprate Ba2Ca2Cu3O6F2(0233F(2.0)), it is demonstrated that electrons are transferred from the inner plane (IP) to the outer plane (OP) in 0234F(2.0) and 0223F(2.0), confirming the self-doped high-temperature superconductivity (HTSC) having electron and hole doping in a single compound. Remarkably, uniform mixing of AFM and HTSC takes place in both the electron-doped OPs and the hole-doped IPs in 0234F(2.0).

  11. Quantum spin correlations through the superconducting-to-normal phase transition in electron-doped superconducting Pr0.88LaCe0.12CuO4-delta.

    PubMed

    Wilson, Stephen D; Li, Shiliang; Zhao, Jun; Mu, Gang; Wen, Hai-Hu; Lynn, Jeffrey W; Freeman, Paul G; Regnault, Louis-Pierre; Habicht, Klaus; Dai, Pengcheng

    2007-09-25

    The quantum spin fluctuations of the S = 1/2 Cu ions are important in determining the physical properties of high-transition-temperature (high T(c)) copper oxide superconductors, but their possible role in the electron pairing of superconductivity remains an open question. The principal feature of the spin fluctuations in optimally doped high-T(c) superconductors is a well defined magnetic resonance whose energy (E(R)) tracks T(c) (as the composition is varied) and whose intensity develops like an order parameter in the superconducting state. We show that the suppression of superconductivity and its associated condensation energy by a magnetic field in the electron-doped high-T(c) superconductor Pr(0.88)LaCe(0.12)CuO(4-delta) (T(c) = 24 K), is accompanied by the complete suppression of the resonance and the concomitant emergence of static antiferromagnetic order. Our results demonstrate that the resonance is intimately related to the superconducting condensation energy, and thus suggest that it plays a role in the electron pairing and superconductivity.

  12. High Energy Spin Excitations in Electron-Doped Superconducting Pr0.88LaCe0.12CuO4-δ with Tc=21 K

    SciTech Connect

    Wilson, Stephen D.; Li, Shiliang; Woo, H.; Dai, Pengcheng; Mook Jr, Herbert A; Frost, C.; Komiya, S.; Ando, Y.

    2006-01-01

    We use high-resolution inelastic neutron scattering to study the low-temperature magnetic excitations of the electron-doping superconductor Pr{sub 0.88}LaCe{sub 0.12}CuO{sub 4-{delta}} (T{sub c} = 21 {+-} 1 K) over a wide energy range (4 meV {le} {le} {omega} {le} 330 meV). The effect of electron doping is to cause a wave vector (Q) broadening in the low-energy ({omega} {le} 80 meV) commensurate spin fluctuations at (0.5, 0.5) and to suppress the intensity of spin-wave-like excitations at high energies ({omega} {ge} 100 meV). This leads to a substantial redistribution in the spectrum of the local dynamical spin susceptibility {chi}{sup -}({omega}), and reveals a new energy scale similar to that of the lightly hole-doped YB{sub 2}Cu{sub 3}O{sub 6.353} (T{sub c} = 18 K).

  13. Design of a Cryogen Free Cryo-flipper using a High Tc YBCO Film

    NASA Astrophysics Data System (ADS)

    Parnell, S. R.; Kaiser, H.; Washington, A. L.; Li, F.; Wang, T.; Baxter, D. V.; Pynn, R.

    It is well-known that the Meissner effect in superconducting materials can be used to provide a well-defined non- adiabatic magnetic field transition that can be utilised to produce an efficient white beam neutron spin flipper. Typically these devices utilise niobium and hence require continuous use of liquid helium in order to maintain the device tem- perature. The use of high Tc materials removes the need for cryogens and has been explored previously and shown to provide efficient flipping of the neutron spin. Improvements in thin high Tc films over the past few years make these materials even more attractive. Here we present a design using a 350-nm-thick YBCO film capped with 100 nm of gold on a 78 x 100 x 0.5 mm sapphire substrate (Theva, Germany). The apparatus is compact (200 mm in length along the neutron beam), consisting of an oxygen-free high-conductivity copper frame, which holds the YBCO film and is mounted to the cold finger of a closed-cycle refrigerator. The part of the vacuum chamber, where the YBCO film is located, is ≈ 50 mm wide, which allows us to minimise the distance from the film to the external magnets. This distance is 26 mm on each side. The details of the guide field design are also discussed. In this design, the maximum neutron beam size that can be used is 40 × 40 mm2 and we can easily switch from a vertical to a horizontal guide field on either side of the YBCO film.

  14. Chromium analogs of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Edelmann, Martin; Sangiovanni, Giorgio; Capone, Massimo; de'Medici, Luca

    2017-05-01

    We theoretically investigate the d4 (Cr2 +) compound BaCr2As2 and show that, despite non-negligible differences in the electronic structure, its many-body physics mirrors that of BaFe2As2 , which has instead a d6 (Fe2 +) configuration. This reflects a symmetry of the electron correlation effects around the half-filled d5 Mott insulating state. Dynamical mean-field calculations correctly reproduce the experimental antiferromagnetic phase and, for realistic values of the interactions, they show a moderate mass enhancement of order ˜2 . This value can be insensitive to, or even be lowered by, an increase of the interaction parameters, as a result of a larger magnetic moment. In the paramagnetic phase however, correlation effects are much stronger, and the influence of the half-filled Mott insulator shows up as a crossover from a weakly correlated to an orbitally differentiated "Hund's metal" phase. This mirrors an analogous phenomenon in d6 iron compounds including a strong enhancement of the compressibility in a zone just inside the frontier between the normal and the Hund's metal. The experimental evidence and our theoretical description place BaCr2As2 at interaction strength slightly below the crossover which implies that negative pressures and/or electron doping (e.g., Cr → Mn, Fe or Ba → Sc, Y, La) might strongly enhance the compressibility, thereby possibly inducing high-Tc superconductivity in this nonsuperconducting compound.

  15. The Search for Higher Temperature Superconductors: Two Case Studies

    NASA Astrophysics Data System (ADS)

    Beasley, Malcolm

    2013-03-01

    The recent confluence of optimism in the prospects for higher temperature superconductivity and the documented need for new higher temperature superconductors (if electric power applications above liquid nitrogen temperatures are to be possible) has simulated several focused programs in the search new and improved high-Tc superconductors. In this talk, we review these motivating factors and present the results of two case studies. The first is the study of the high Tc bismuthate superconductors to understand the mechanism of their superconductivity and the factors governing Tc. We find that the bismuthates are moderately correlated materials with a dynamically enhanced electron-phonon interaction that exhibit dimorphism and a sensitivity of Tc to disorder. The second is the study of Cu/CuO interfaces (for which evidence of trace high temperature superconductivity has been reported) at which we find a new proximity effect in which antiferromagnetism is induced into a metal (Cu) by proximity to a charge transfer insulator (CuO). This work has been a collaborative effort carried out under AFOSR MURI support involving Stanford (Beasley and Fisher), Princeton (Cava) and Rutgers (Kotliar).

  16. Long-range two-dimensional superstructure in the superconducting electron-doped cuprate Pr0.88LaCe0.12CuO4

    SciTech Connect

    Campbell, B. J.; Rosenkranz, S.; Kang, H. J.; Stokes, H. T.; Chupas, P. J.; Komiya, S.; Ando, Y.; Li, Shiliang; Dai, Pengcheng

    2015-07-29

    Utilizing single-crystal synchrotron x-ray scattering, we observe distorted CuO2 planes in the electron- doped superconductor Pr1-xLaCexCuO4+δ , x =0.12. Resolution-limited rods of scattering are indicative of a long-range two-dimensional 2√2 × 2√2 superstructure in the a-b plane, adhering to planar space-group symmetry p4gm, which is subject to stacking disorder perpendicular to the planes. This superstructure is present only in annealed, superconducting samples, but not in the as-grown, nonsuperconducting samples. These long-range distortions of the CuO2 planes, which are generally considered to be detrimental to superconductivity, have avoided detection to date due to the challenges of observing and interpreting subtle diffuse-scattering features.

  17. Electronic Raman Response in Disordered Unconventional Superconductors

    NASA Astrophysics Data System (ADS)

    Devereaux, Thomas

    1998-03-01

    Due to the strong symmetry dependence of the observed Raman spectra in all high Tc compounds, i.e., the characteristic features of light scattering for different incident and scattered polarization orientations, electronic Raman scattering in unconventional superconductors has grown to be of considerable interest in light of identifying the symmetry of the energy gap and ultimately, the mechanism of superconductivity in high temperature superconductors. I review the theory of the effects of impurities on the Raman response of unconventional superconductors with a view towards understanding the role polarization plays in determining the order parameter symmetry in the cuprates.(T. P. Devereaux, Phys. Rev. Lett. 74), 4313 (1995) (T. P. Devereaux and A. P. Kampf, Int. Journ. Mod. Phys. B 11), 2093 (1997) Signatures of the effects of disorder on the low frequency and low temperature behavior of the Raman spectra obtained for different polarizations will be discussed in relation to the magnitude and phase of the energy gap. Extensions of the theory to include anisotropic impurity scattering and inelastic spin fluctuation scattering will be discussed. Good agreement of the theory with the data on optimally- and overdoped-samples will be shown, although discrepancies remain.

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  19. Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe1-xCox)₂As₂

    DOE PAGES

    Liu, Chang; Palczewski, A. D.; Dhaka, R. S.; ...

    2011-07-25

    We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe1-xCox)₂As₂ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions—topological changes of the Fermi surface—occur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. Tc decreases and goes to zero around x~0.15—between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance of the underlying Fermiologymore » in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.« less

  20. Electron Doping by Charge Transfer at LaFeO 3 /Sm 2 CuO 4 Epitaxial Interfaces

    SciTech Connect

    Bruno, Flavio Y.; Schmidt, R; Varela, Maria; Garcia-Barriocanal, Javier; Rivera-Calzada, Alberto; Cuellar, F.; Leon, Carlos; Thakur, P.; Cezar, J. C.; Brookes, N. B.; Garcia-Hernandez, M; Dagotto, Elbio R; Pennycook, Stephen J; Santamaria, J.

    2013-01-01

    The breakdown of the lattice translational invariance symmetry that occurs at complex oxide interfaces may profoundly modify their electronic structure, leading to interfacial states with properties drastically different from those of the superlattice individual components. The appearance of a conducting two dimensional (2D) electron gas at the interface between two insulating oxides and induced magnetism in a non-magnetic material are just two among many fascinating examples. [ 1 8 ] One of the key factors underlying novel properties is the modifi cation of the doping and orbital occupancy near those interfaces, which may result from charge transfer processes. [ 3 , 9 11 ] If materials used in heterostructures have different work functions, a non-equilibrium situation will be created at the interface and charge will be transferred until the chemical potential levels off. [ 12 ] The use of such phenomena to modify doping in heterostructures has been proposed theoretically as a new route to avoid the quenched disorder that inevitably accompanies the chemical doping. At the interface between a Mott insulating parent compound of the high critical temperature superconductor (HTSC) family and a suitable material that would act as the charge donor, electron doped phases could be stabilized which would eventually turn metallic and perhaps superconducting. [ 12 , 13 ] Such charge transfer processes have been observed at interfaces involving copper oxides such as La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7 , [ 14 ] La 2 x Sr x CuO 4 /La 2 CuO 4 [ 15 ] and SrTi 1 x Nb x O 3 / Sm 2 CuO 4 . [ 16 ] While a novel 2D superconducting state was found at the La 2-x Sr x CuO 4 /La 2 CuO 4 interface, [ 17 ] the effect of doping by charge transfer could not be examined in the other two cases due to the detrimental effect on the YBa 2 Cu 3 O 7 superconductivity of the spin polarized electrons from La 0.7 Ca 0.3 MnO 3 in one case and due to the conducting nature of the SrTi 1 x Nb x O 3 in the