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Sample records for electron-doped high-tc superconductors

  1. Superconducting anisotropy in the electron-doped high-Tc superconductors Pr2-xCexCuO4-y.

    PubMed

    Wu, Guoqing; Greene, R L; Reyes, A P; Kuhns, P L; Moulton, W G; Wu, Bing; Wu, Feng; Clark, W G

    2014-10-01

    We report superconducting anisotropy measurements in the electron-doped high-Tc superconductors (HTSCs) Pr(2-x)Ce(x)C(u)O(4-y) (PCCO, x = 0.15 and 0.17) with an applied magnetic field (H0) up to 28 T. Our results show that the upper critical field [H(c2)(T)] of PCCO is highly anisotropic and as the temperature T → 0, the value of it at H0 ∥ c [H(c2,∥c)(0)] is far less than the Pauli limit. The low temperature anisotropic character of PCCO is found to be rather similar to that of hole-doped cuprate HTSCs, but apparently larger than that of typical Fe-based superconductors. This study also proves a new sensitive probe of detecting rich properties of unconventional superconductors with the use of the resonant frequency of an NMR probe circuit. PMID:25219526

  2. Superconducting anisotropy in the electron-doped high-Tc superconductors Pr2-xCexCuO4-y

    NASA Astrophysics Data System (ADS)

    Wu, Guoqing; Greene, R. L.; Reyes, A. P.; Kuhns, P. L.; Moulton, W. G.; Wu, Bing; Wu, Feng; Clark, W. G.

    2014-10-01

    We report superconducting anisotropy measurements in the electron-doped high-Tc superconductors (HTSCs) Pr2-xCexCuO4-y (PCCO, x = 0.15 and 0.17) with an applied magnetic field (H0) up to 28 T. Our results show that the upper critical field [Hc2(T)] of PCCO is highly anisotropic and as the temperature T → 0, the value of it at H0 ∥ c [Hc2,∥c(0)] is far less than the Pauli limit. The low temperature anisotropic character of PCCO is found to be rather similar to that of hole-doped cuprate HTSCs, but apparently larger than that of typical Fe-based superconductors. This study also proves a new sensitive probe of detecting rich properties of unconventional superconductors with the use of the resonant frequency of an NMR probe circuit.

  3. 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.

  4. Scanning tunneling microscopy studies of an electron-doped high-Tc superconductor, praseodymium lanthanum cerium copper oxide

    NASA Astrophysics Data System (ADS)

    Kunwar, Shankar

    It has been more than two decades since the first high temperature superconductor was discovered. In this time there has been tremendous progress in understanding these materials both theoretically and experimentally. Some important questions however remain to be answered; one of them is the temperature dependence of the superconducting gap which is in turn tied to question of the origin of the pseudogap and its connection with superconductivity. In this thesis, we present detailed Scanning Tunneling Microscopy (STM) spectroscopic studies of an electron doped superconductor, Pr0.88LaCe 0.12CuO4-delta (PLCCO). The electron doped compounds form an interesting venue for STM studies for many reasons. In the hole-doped materials, especially in the underdoped side of the phase diagram, there is mounting evidence of a second gap that survives to high temperatures (high temperature pseudogap) that may have a different origin from superconductivity. This complicates studies of the temperature dependence of the superconducting gap in these materials. In PLCCO however, there is little evidence for a high temperature pseudogap potentially allowing us to address the question of the temperature evolution of the superconducting gap without the complication of a second gap. Secondly, the low Tc of the optimally doped materials makes it easily accessible to temperature dependent STM studies. Finally, while hole-doped materials have been extensively studied by scanning tunneling microscopy (STM), there have been no detailed STM spectroscopic studies on the electron doped compounds. In the first part of the thesis, we investigate the effect of temperature on the superconducting gap of optimally doped PLCCO with Tc = 24K. STM spectroscopy data is analyzed to obtain the gap as a function of temperature from 5K to 35K. The gap is parameterized with a d-wave form and the STM spectra are fit at each temperature to extract the gap value. A plot of this gap value as a function of

  5. Measurements of the anisotropic irreversibility field in the electron-doped high-Tc superconductor Pr2-xCexCuO4-y

    NASA Astrophysics Data System (ADS)

    Wu, Guoqing; Clark, W. G.; Brown, S. E.; Greene, R. L.; Balci, H.; Reyes, A. P.; Kuhns, P.; Moulton, W. G.

    2008-03-01

    We report measurements of the irreversibility field (Hirf) in single crystals of the electron-doped high-Tc superconductor (HTSC) Pr2-xCexCuO4-y (x = 0.15 and 0.17) with an applied magnetic field (B0) up to 28 T, using the method of the shift in a nuclear magnetic resonance (NMR) probe circuit resonance frequency (f) caused by the susceptibility of the sample. It is observed that Hirf is highly anisotropic, and that as the temperature T -> 0 the upper critical field [Hc2, c(T -> 0)] at B0 c is far less than the Pauli limit and very different from that at B0 c. A phase diagram that involves the vortex solid and/or vortex liquid states depending on the alignment of B0 relative to the lattice c-axis is proposed, and the obtained anisotropic Hc2 character along with the evaluated zero T coherence length [ξab(c)(T -> 0)] and penetration depth [λab(c)( T -> 0)] at B0 ab(c) is compared with that of hole-doped HTSCs. This work is supported at UCLA by NSF Grants DMR-0334869 (WGC) and 0520552 (SEB), at U. Maryland by 0352735 (RLG), and NHMFL by 0084173 and the State of Florida.

  6. 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.

  7. Shock compaction of high- Tc superconductors

    SciTech Connect

    Weir, S.T.; Nellis, W.J.; McCandless, P.C.; Brocious, W.F. ); Seaman, C.L.; Early, E.A.; Maple, M.B. . Dept. of Physics); Kramer, M.J. ); Syono, Y.; Kikuchi, M. )

    1990-09-01

    We present the results of shock compaction experiments on high-{Tc} superconductors and describe the way in which shock consolidation addresses critical problems concerning the fabrication of high J{sub c} bulk superconductors. In particular, shock compaction experiments on YBa{sub 2}Cu{sub 3}O{sub 7} show that shock-induced defects can greatly increase intragranular critical current densities. The fabrication of crystallographically aligned Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} samples by shock-compaction is also described. These experiments demonstrate the potential of the shock consolidation method as a means for fabricating bulk high-{Tc} superconductors having high critical current densities.

  8. Peak Effect in High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Ling, Xinsheng

    1996-03-01

    Like many low-Tc superconductors, high-quality YBCO single crystals are found(X.S. Ling and J.I. Budnick, in Magnetic Susceptibility of Superconductors and Other Spin Systems), edited by R.A. Hein, T.L. Francavilla, and D.H. Liebenberg (Plenum Press, New York, 1991), p.377. to exhibit a striking peak effect. In a magnetic field, the temperature dependence of the critical current has a pronounced peak below T_c(H). Pippard(A.B. Pippard, Phil. Mag. 19), 217 (1969)., and subsequently Larkin and Ovchinnikov(A.I. Larkin and Yu.N. Ovchinnikov, J. Low Temp. Phys. 34), 409 (1979)., attributed the onset of the peak effect to a softening of the vortex lattice. In this talk, the experimental discovery^1 of the peak effect in high-Tc superconductors will be described, followed by a brief historical perspective of the understanding of this phenomenon and a discussion of a new model(X.S. Ling, C. Tang, S. Bhattacharya, and P.M. Chaikin, cond-mat/9504109, (NEC Preprint 1995).) for the peak effect. In this model, the peak effect is an interesting manifestation of the vortex-lattice melting in the presence of weak random pinning potentials. The rise of critical current with increasing temperature is a signature of the ``melting'' of the Larkin domains. This work is done in collaboration with Joe Budnick, Chao Tang, Shobo Bhattacharya, Paul Chaikin, and Boyd Veal.

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

    PubMed Central

    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

    2014-01-01

    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. PMID:24625746

  10. 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

  11. HIGH-Tc Superconductivity in Electron-Doped Layer Structured Nitrides

    NASA Astrophysics Data System (ADS)

    Yamanaka, Shoji

    2000-08-01

    A new series of superconductors based on layer structured nitrides has been developed. The general compositions of the nitrides are MNX (M = Zr, Hf; X = Cl, Br, I). The beta-type polymorph consists of MN double layers sandwiched between close-packed halogen layers, which are characterized as semiconductors with a band gap of 3-4 eV. Electrons can be doped to the nitride layers by intercalation of alkali metals between the layers. Upon the intercalation, the compounds become superconductors with the transition temperatures (Tcs) as high as 13 and 25.5 K for beta-ZrNCl and beta-HfNCl systems, respectively. The Tc of the electron doped beta-HfNCl is higher than that observed in any intermetallic compound and suggests that layered nitrides may exhibit Tcs comparable to those observed in layer structured complex copper oxide superconductors. The layer structured nitrides can be variously modified by the amounts of doping, the types of alkali metals, and the interlayer separation, which can be controlled by co-intercalation of organic molecules with alkali metals. This article dicusses topics including the synthesis and structure of the transition metal nitride halides, intercalation, superconductivity, and band structures.

  12. Laser surface interactions of high-(Tc) superconductors

    NASA Astrophysics Data System (ADS)

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

    1990-01-01

    During the past two years, one of the most exciting research fields in science has been the study of the newly discovered high-(Tc) metal oxide superconductors. Although many theoretical models were proposed, there has been no general agreement on any theory to explain these materials. One of the peculiar features of these high-(Tc) materials is the noninteger number of oxygen atoms. The oxygen content is extremely critical to the superconductive properties. Our results from mass spectroscopy of laser desorbed species indicate that significant quantities of oxygen molecules are trapped in the bulk of these superconductors. It appears that these trapped oxygen molecules may play key roles in superconductive properties.

  13. 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.

  14. Oxygen diffusion in high- Tc superconductors

    SciTech Connect

    Rothman, S.J.; Routbort, J.L.

    1992-07-01

    The cuprate superconductors are fascinating not only because of their technical promise, but also because of their structures, especially the anisotropy of the crystal lattice. There are some structural similarities among these compounds, but also significant differences. Measurements of the oxygen tracer diffusion coefficients have been carried out as a function of temperature, oxygen partial pressure, crystal orientation, and doping in the La-Sr-Cu-0, Y-Ba-Cu-0, and Bi-Sr-Ca-Cu-0 systems. These measurements have revealed a variety of defect mechanisms operating in these compounds; the exact nature of the mechanism depends on the details of the structure.

  15. Oxygen diffusion in high-{Tc} superconductors

    SciTech Connect

    Rothman, S.J.; Routbort, J.L.

    1992-07-01

    The cuprate superconductors are fascinating not only because of their technical promise, but also because of their structures, especially the anisotropy of the crystal lattice. There are some structural similarities among these compounds, but also significant differences. Measurements of the oxygen tracer diffusion coefficients have been carried out as a function of temperature, oxygen partial pressure, crystal orientation, and doping in the La-Sr-Cu-0, Y-Ba-Cu-0, and Bi-Sr-Ca-Cu-0 systems. These measurements have revealed a variety of defect mechanisms operating in these compounds; the exact nature of the mechanism depends on the details of the structure.

  16. High-Tc superconductor coplanar waveguide filter

    NASA Technical Reports Server (NTRS)

    Chew, Wilbert; Bajuk, Louis J.; Cooley, Thomas W.; Foote, Marc C.; Hunt, Brian D.; Rascoe, Daniel L.; Riley, A. L.

    1991-01-01

    Coplanar waveguide (CPW) low-pass filters made of YBa2Cu3O(7-delta) (YBCO) on LaAlO3 substrates, with dimensions suited for integrated circuits, were fabricated and packaged. A complete filter gives a true idea of the advantages and difficulties in replacing thin-film metal with a high-temperature superconductor in a practical circuit. Measured insertion losses in liquid nitrogen were superior to the loss of a similar thin-film copper filter throughout the 0- to 9.5-GHz passband. These results demonstrate the performance of fully patterned YBCO in a practical CPW structure after sealing in a hermetic package.

  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. Proximity Effect at Graphene - High Tc Superconductor Junctions

    NASA Astrophysics Data System (ADS)

    Wang, Da; Shih, En-Min; Arefe, Ghidewon; Kim, Youngduck; Edelberg, Drew; Andrade, Erick; Wang, Dennis; Hone, James; Dean, Cory; Pasupathy, Abhay; Department of Physics, Columbia University, New York, NY 10027, USA Collaboration

    The proximity effect is a well-known mesoscopic phenomenon where Cooper pairs from a superconductor (S) enter into a normal metal (N) that is well coupled to it. Since graphene was discovered a decade ago, the proximity effect at superconductor-graphene junctions has been extensively studied and interesting phenomena such as specular Andreev reflection and ballistic transport at graphene Josephson junctions have been observed. However, superconductors used in these experiments to date are of conventional low Tc, such as aluminum(Tc=1.2K), NbSe2(Tc=7K), and MoRe(Tc=8K). Understanding how the proximity effect works between high-Tc superconductors (pnictides and cuprates) and the Dirac Fermions of graphene remains largely unexplored. The chief technical challenge here is to create high-quality junctions between high-Tc superconductors and graphene. In this work, we will introduce a home-made setup that allows us to exfoliate, transfer and encapsulate superconductor-graphene junctions in a well controlled inert atmosphere. Transport measurements of the proximity effect at graphene-iron pnictide(FeSe, FeTeSe) and graphene-cuprate(BSCCO) junctions will be described.

  19. Are the high Tc superconductors d-wave?

    NASA Astrophysics Data System (ADS)

    Kallin, Catherine; Berlinsky, A. John

    1994-12-01

    Although it has been widely accepted for several years that the normal state of high Tc superconductors is anomalous, only recently has there been growing evidence for the anomalous nature of the superconducting state. A number of recent experiments show clear evidence for the existence of low-lying excitations in the superconducting state. Moreover, the observation by Bonn, Hardy and coworkers of a linear temperature dependence in the microwave surface resistance and penetration depth of YBCO at low temperatures suggests d-wave pairing with line nodes. The evidence for and against unconventional superconductivity in the high Tc oxides is reviewed. Specific topics discussed include the different behaviours observed for the penetration depth in thin films and in single crystals, what is known about the absolute value of the penetration depth, the role of disorder and inelastic scattering, the relative merits of strong vs. weak correlation theories of d-wave superconductivity in the high Tc oxides, and most important, what have we actually learned about the penetration depth of high Tc superconductors from μSR?

  20. Microstructures and critical currents in high-{Tc} superconductors

    SciTech Connect

    Suenaga, Masaki

    1998-11-01

    Microstructural defects are the primary determining factors for the values of critical-current densities in a high {Tc} superconductor after the electronic anisotropy along the a-b plane and the c-direction. A review is made to assess firstly what would be the maximum achievable critical-current density in YBa{sub 2}Cu{sub 3}O{sub 7} if nearly ideal pinning sites were introduced and secondly what types of pinning defects are currently introduced or exist in YBa{sub 2}Cu{sub 3}O{sub 7} and how effective are these in pinning vortices.

  1. Pairing theory of high Tc and low Tc superconductors

    NASA Astrophysics Data System (ADS)

    Sang, Boo Nam

    1994-09-01

    New solutions for Tc, the order parameter, and the density of states are obtained, based on the fact that pairs are formed within the pairing interaction range, TD (Debye), via the BCS pairing theory (not the BCS results). They are valiid for all ify = {T D}/{πT c}, and are applicable to low Tc (LTC) and high Tc (HTS) superconductors. The order parameter variation with y is shown to account for all features of HTS. A new density of states via the zero order parameter outside the pairing interaction range is found to account for low energy states observed in HTS. For large y (LTS), the BCS results are reproduced.

  2. Organic conductor/high-Tc superconductor bilayer structures

    NASA Astrophysics Data System (ADS)

    Clevenger, Marvin B.; Jones, Christopher E.; Haupt, Steven G.; Zhao, Jianai; McDevitt, John T.

    1996-07-01

    Electrochemical techniques are exploited to fabricate conductive polymer/high Tc superconductor bilayer structures. SCanning electron microscopy and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa2Cu3O7-(delta ) films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperatures (Tc) and critical currents (Jc) of the underlying superconductor film are suppressed. Reversible modulation of the values of the transition temperatures of up to 50K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, both Tc and Jc are found to return to values close to those acquired for the underivatized YBa2Cu3O7-(delta ) film. Moreover, measurements as a function of temperature of the polymer/superconductor interface resistance show dramatic decrease in this value at Tc. ALso, estimates of superconducting coherence lengths within the organic conductor samples suggest superconducting properties over macroscopically large distances within the organic materials can be expected. Collectively these results are consistent with the first observation of a conductive polymer proximity effect.

  3. Organic conductor/high-{Tc} superconductor bilayer structures

    SciTech Connect

    Clevenger, M.B.; Jones, C.E.; Haupt, S.G.; Zhao, J.; McDevitt, J.T.

    1996-12-31

    Electrochemical techniques are exploited to fabricate conducive polymer/high-{Tc} superconductor bilayer structures. Scanning electron microscopy and electrochemical techniques are utilized to characterize the electrodeposition of polypyrrole layers grown onto YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperature ({Tc}) and critical currents (J{sub c}) of the underlying superconductor films are suppressed. Reversible modulation of the values of the transition temperatures of up to 50 K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, both {Tc} and J{sub c} are found to return to values close to those acquired for the underivatized YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films. Moreover, measurements as a function of temperature of the polymer/superconductor interface resistance show dramatic decrease in this value at {Tc}. Also, estimates of superconducting coherence lengths within the organic conductor samples suggest superconducting properties over macroscopically large distances within the organic materials can be expected. Collectively these results are consistent with the first observation of a conductive polymer proximity effect.

  4. Modeling of tunneling spectroscopy in high-TC superconductors

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.; Namiranian, A.; Najafi, A.

    2001-01-01

    The tunneling density of states of high-Tc superconductors is calculated taking into account the tight-binding band structure, group velocity, and tunneling directionality for s-wave and d-wave gap symmetry. The characteristic density of states has asymmetry of the quasiparticle peaks, flat s-wave and cusplike d-wave subgap behavior, and an asymmetric background. It is assumed that the underlying asymmetry of the conductance peaks is primarily due to the features of the quasiparticle energy spectrum and that the d-wave symmetry enhances the degree of asymmetry of the peaks. Increasing the lifetime broadening factor changes the degree of asymmetry of the tunneling conductance peaks and leads to confluence of the quasiparticle and van Hove singularity peaks.

  5. 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

  6. 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

  7. 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.

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

    PubMed

    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. 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. PMID:26014056

  9. Submillimeter residual losses in high-{Tc} superconductors

    SciTech Connect

    Miller, D.

    1993-09-01

    Bolometry was used obtain accurate submillimeter residual loss data for epitaxial films of YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO), Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10}, Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub 8} (TCBCO), and Ba{sub 0.6}K{sub 0.4}BiO{sub 3} (BKBO). We were able to fit the absorptivity measured for Nb films to an Eliashberg strong coupling calculation; excellent agreement resulted between parameters from best fits and measured Residual Resistivity Ratio. Microwave surface resistance measurements made on the same YBCO and TCBCO films are in excellent agreement with submillimeter measurements. Absorptivities for all YBCO films studied are qualitatively similar, increasing smoothly with frequency, with no gap-like features below the well known absorption edge at 450 cm{sup {minus}1}. Losses in YBCO films were fit to a weakly coupled grain model for the a-b plane conductivity. Strong phonon structure was observed in TCBCO films between 60 and 700 cm{sup {minus}1} (2 THz and 23 THz); these losses could not be fitted to the simple weakly coupled grain model, in contrast to the case for other high-{Tc} superconductors where phonon structure observed in ceramics are is absent in epitaxial oriented films and crystals because of electronic screening due to high conductivity of a-b planes. Absorptivity data for the BKBO films all show a strong absorption onset near the BCS tunneling gap of 3.5 k{sub B}{Tc}. Comparison with strong coupling Eliashberg predictions and of a Kramers-Kronig analysis indicate that the absorption onset is consistent with a superconducting energy gap. Effects of magnetic field on residual losses in YBCO films show a resonant absorption feature in vicinity of predicted

  10. Laser surface interaction of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    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.

  11. 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.

  12. Modelling of hysteresis of high-[Tc] superconductors

    SciTech Connect

    Vajda, I.; Mohacsi, L. . Dept. of Electrical Machines and Drives); Szalay, A. ); Lukacs, J. ); Projesz, T. . Dept. of General Physics)

    1998-12-20

    For the numerical calculation of the magnetic field and forces between HTSC materials and permanent magnets an algorithm and a two-dimensional finite difference computer code has been developed. The superconductor has been treated with its nonlinear and anisotropic dc magnetization curve. The magnetization curves are used as input characteristics for the field calculations. The basic ideas of the physical modelling are discussed.

  13. 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.

  14. Levitation effects involving high Tc thallium based superconductors

    NASA Astrophysics Data System (ADS)

    Harter, William G.; Hermann, A. M.; Sheng, Z. Z.

    1988-09-01

    The thallium based superconductor Tl2Ca2Ba2Cu3O(10 + y) has been shown to exhibit very stable and unusual levitation equilibria in various arrangements involving this material and permanent magnets. Attractive and repulsive forces are evident in experiments in which samples are levitated above and below magnets. Photographs of these experiments and approximate quantitative discussions of the results are given.

  15. Bi-Sr-Ca-Cu-O high TC superconductors (abstract)

    NASA Astrophysics Data System (ADS)

    Sherwood, R. C.; Tiefel, T. H.; Jin, S.; Davis, M. E.; Kammlott, G. W.; Fastnacht, R. A.

    1988-11-01

    A recent paper by Maeda et al.1 reported the discovery of a new 120 K superconductor based on a rare-earth-free ceramic material in the bismuth-strontium-calcium-copper-oxide system. We have confirmed the existence of the 120-K phase in the oxide system. The resistivity-temperature curve showed a fairly well-defined double-dip shape with the first dip starting at ˜120 K and the second at ˜95 K. The transition temperature, TC(R=0), was 84 K. This material appears to contain two superconducting phases with different TC's. A pellet made from this superconductor levitates well at 77 K (liquid-nitrogen temperature) above a neodynium-iron-boron magnet with a surface magnetic field of ˜3000 Oe, thus indicating a nontrivial critical field in this material. The critical current density and its magnetic field dependence will be reported. The magnetic and mechanical behavior of the new superconductor will also be discussed.

  16. Simulations of high-Tc superconductors using the DCA+ algorithm

    NASA Astrophysics Data System (ADS)

    Staar, Peter

    2015-03-01

    For over three decades, the high Tc-cuprates have been a gigantic challenge for condensed matter theory. Even the simplest representation of these materials, i.e. the single band Hubbard model, is hard to solve quantitatively and its phase-diagram is therefore elusive. In this talk, we present the recent algorithmic and implementation advances to the Dynamical Cluster Approximation (DCA). The algorithmic advances allow us to determine self-consistently a continuous self-energy in momentum space, which in turn reduces the cluster-shape dependency of the superconducting transition temperature and thus accelerates the convergence of the latter versus cluster-size. Furthermore, the introduction of the smooth self-energy suppresses artificial correlations and thus reduces the fermionic sign-problem, allowing us to simulate larger clusters at much lower temperatures. By combining these algorithmic improvements with a very efficient GPU accelerated QMC-solver, we are now able to determine the superconducting transition temperature accurately and show that the Cooper-pairs have indeed a d-wave structure, as was predicted by Zhang and Rice.

  17. Transport anomalies and quantum criticality in electron-doped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Yu, Heshan; He, Ge; Hu, Wei; Yuan, Jie; Zhu, Beiyi; Jin, Kui

    2016-06-01

    Superconductivity research is like running a marathon. Three decades after the discovery of high-Tc cuprates, there have been mass data generated from transport measurements, which bring fruitful information. In this review, we give a brief summary of the intriguing phenomena reported in electron-doped cuprates from the aspect of electrical transport as well as the complementary thermal transport. We attempt to sort out common features of the electron-doped family, e.g. the strange metal, negative magnetoresistance, multiple sign reversals of Hall in mixed state, abnormal Nernst signal, complex quantum criticality. Most of them have been challenging the existing theories, nevertheless, a unified diagram certainly helps to approach the nature of electron-doped cuprates.

  18. Strength and flexibility of bulk high-{Tc} superconductors

    SciTech Connect

    Goretta, K.C.; Jiang, M.; Kupperman, D.S.; Lanagan, M.T.; Singh, J.P.; Vasanthamohan, N.; Hinks, D.G.; Mitchell, J.F.; Richardson, J.W. Jr.

    1996-08-01

    Strength, fracture toughness, and elastic modulus data have been gathered for bulk high-temperature superconductors, commercial 99.9% Ag, and a 1.2 at.% Mg/Ag alloy. These data have been used to calculate fracture strains for bulk conductors. The calculations indicate that the superconducting cores of clad tapes should begin to fracture at strains below 0.2%. In addition, residual strains in Ag-clad (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} tapes have been measured by neutron diffraction. An explanation is offered for why many tapes appear to be able to tolerate large strains before exhibiting a reduction in current transport.

  19. Flux-motion related ac losses in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Chen, Q. Y.

    1993-03-01

    The ac losses of high-temperature superconductors in the flux-depinned mixed-state have been treated using the classical magnetic diffusion equation in conjunction with various models of flux-motion. With the imaginary part representing the ac losses, the field- and frequency-dependent ac susceptibilities were investigated. The imaginary component was found to obey a scaling rule with a characteristic frequency, estimated to be about 10 exp 5-10 exp 9 Hz, that depended on the sample size and normal state resistivity. This frequency range agrees with earlier experimental results, which could not be accounted for previously based upon the notion of thermally activated hopping of vortices. The frequency scaling behaviors using flux-creep and flux-flow models are presented.

  20. Melt processing of bulk high Tc superconductors and their application

    NASA Astrophysics Data System (ADS)

    Murakami, M.; Oyama, T.; Fujimoto, H.; Gotoh, S.; Yamaguchi, K.

    1991-03-01

    The authors report a melt-powder-melt-growth (MPMG) process which results in high Jc for bulk Y-Ba-Cu-O superconductors. The Y-Ba-Cu-O pellets or powders are melt quenched. The quenched plates are crushed into powder and mixed well. The powder is then compacted into desired shapes, remelted, and slowly cooled in a thermal gradient. When the starting composition is changed from the 1:2:3 stoichiometry toward the Y2BaCuO5(211) rich region, the 211 inclusions can be dispersed in the YBa2Cu3O(x) matrix, which contributes to increases in both flux pinning force and fracture toughness. A Jc value exceeding 3 x 108 A/sq m has been achieved at 77 K and 1 T. Another attractive feature of the MPMG process is that other components such as fine Ag powders can be added during solid-state mixing. Fine dispersion of Ag particles can effectively reduce the amount of cracking. MPMG-processed Y-Ba-Cu-O with Ag doping can levitate a mass of 3-kg at 1-mm height using a repulsive force against a 0.4-T magnet. A noncontacting rotation device such as a magnetic bearing can be made utilizing bulk high-Jc materials. A superconducting permanent magnet is also a promising candidate for future application. MPMG-processed Y-Ba-Cu-O can generate 0.25 T at 77 K.

  1. High- Tc superconductor characteristics control by ion implantation

    NASA Astrophysics Data System (ADS)

    Matsui, S.; Matsutera, H.; Yoshitake, T.; Fujita, J.; Satoh, T.

    1989-03-01

    Transition temperature ( Tc) control and annealing effects of YBa 2Cu 3O x and Bi 2Sr 1.4 Ca 1.8Cu 2.2O y superconductor thin films implanted by 200 keV Ne + have been investigated. YBa 2Cu 3 O xTc end points for 0, 1 × 10 14, 1 × 10 15 and 1 × 10 16 ions/cm 2 doses are 75, 71, 62 and 16 K, respectively. On the other hand, Bi 2Sr 1.4Ca 1.8Cu 2.2O y, Tc end points for 0, 1 × 10 12 and 1 × 10 13 ions/cm 2 doses are 78, 76 and 54 K, respectively, c lattice constant increases were observed for the implanted films. It is confirmed that the superconducting characteristics for films, are recovered by anneaing in O 2 atomosphere. Moreover, microcrystal growth caused by annealing the implanted YBa 2Cu 3O x film was observed on the surface.

  2. Infrared Hall effect in the electron-doped high- Tc cuprate Pr2-xCexCuO4

    NASA Astrophysics Data System (ADS)

    Zimmers, A.; Shi, L.; Schmadel, D. C.; Fisher, W. M.; Greene, R. L.; Drew, H. D.; Houseknecht, M.; Acbas, G.; Kim, M.-H.; Yang, M.-H.; Cerne, J.; Lin, J.; Millis, A.

    2007-08-01

    The electron-doped cuprate Pr2-xCexCuO4 is investigated using infrared magneto-optical measurements. The optical Hall conductivity σxy(ω) shows a strong doping, frequency, and temperature dependence consistent with the presence of a temperature- and doping-dependent coherent backscattering amplitude which doubles the electronic unit cell and produces a spin density wave state. At low temperatures, the data suggest that the coherent backscattering vanishes at a quantum critical point inside the superconducting dome and is associated with the commensurate antiferromagnetic order observed by other workers. Using a spectral weight analysis, we have further investigated the Fermi-liquid-like behavior of the overdoped sample. The observed Hall-conductance spectral weight is about ten times less than that predicted by band theory, raising the fundamental question of the effect of Mott and antiferromagnetic correlations on the Hall conductance of strongly correlated materials.

  3. 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.

  4. Development and study of high-Tc superconductor conductive polymer assemblies

    NASA Astrophysics Data System (ADS)

    Schougaard, Steen Brian

    2002-01-01

    This dissertation presents the development and study of organic polymeric conductor/High-Tc superconductor bilayers, for exploration of the superconductor proximity effect. A major obstacle to this research is the instability of the High-Tc superconductor towards H2O and CO2 as it is necessary to create hybrid structures where the two conductors have intimate contact. For this reason, a study of the corrosion characteristics of the RBa2Cu3O 7 (R=Y, Eu, Nd) series was undertaken. In this study, R=Nd was shown to have enhanced corrosion resistance. In an effort to develop chemical processing methods that allow for the production of intimate contact between the cuprate superconductor and the conductive polymer systems, a study of alkyl amine adsorbed onto the surface of the superconductor is presented. In the electrochemical part of the study, alkyl amine ferrocene adsorbed onto the surface revealed that the amines are strongly adhered to the superconductor while still allowing electrons to pass from the superconductor to the ferrocene moiety. The self-assembled monolayer (SAM) structure of CF3(CF2)3(CH2) 11NH2 atop the superconductor was elucidated by employing several techniques, including atomic scale atomic force microscopy (AFM). A novel multistep bilayer sample preparation protocol is presented involving thin film fabrication by pulsed laser deposition (PLD), patterning by shadow mask ablation, sample thinning by scanning probe and electropolymerization of the polymer. Scanning probe thinning yields a smooth superconductor surface, a known superconductor thickness, and if a blocking layer is employed prior to thinning, the localization of polymer growth. Studies of the response of a bilayer structure of Y0.6Ca 0.4Ba1.6La0.4 Cu3O7/poly pyrrole to polymer redox cycling showed a semi-reversible suppression of transition temperature qualitatively consistent with a combination of corrosion and superconductor proximity effect. Quantitative analysis in the framework of

  5. 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.

  6. 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.

  7. 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. PMID:25001512

  8. Resistivity at low temperatures in electron-doped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Finkelman, S.; Sachs, M.; Droulers, G.; Butch, N. P.; Paglione, J.; Bach, P.; Greene, R. L.; Dagan, Y.

    2010-09-01

    We measured the magnetoresistance as a function of temperature down to 20 mK and magnetic field for a set of underdoped Pr1.88Ce0.12CuO4-δ thin films with controlled oxygen content. This allows us to access the edge of the superconducting dome on the underdoped side. The sheet resistance increases with increasing oxygen content whereas the superconducting transition temperature is steadily decreasing down to zero. Upon applying various magnetic fields to suppress superconductivity we found that the sheet resistance increases when the temperature is lowered. It saturates at very low temperatures. These results, along with the magnetoresistance, cannot be described in the context of zero-temperature two-dimensional superconductor-to-insulator transition nor as a simple Kondo effect due to scattering off spins in the copper-oxide planes. We conjecture that due to the proximity to an antiferromagnetic phase magnetic droplets are induced. This results in negative magnetoresistance and in an upturn in the resistivity.

  9. Hole superconductivity in the electron-doped superconductor Pr2-xCexCuO4

    NASA Astrophysics Data System (ADS)

    Dagan, Y.; Greene, R. L.

    2007-07-01

    We measure the resistivity and Hall angle of the electron-doped superconductor Pr2-xCexCuO4 as a function of doping and temperature. The resistivity ρxx at temperatures 100Kelectron doped cuprates holes are responsible for the superconductivity.

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

    DOE PAGES

    Ramshaw, B. J.; Sebastian, S. E.; McDonald, R. D.; Day, J.; Tan, B. S.; Zhu, Z.; Betts, J. B.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; et al

    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

  11. 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.

  12. 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

  13. Spectroscopic evidence for a pseudogap in the normal state of underdoped high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ding, H.; Yokoya, T.; Campuzano, J. C.; Takahashi, T.; Randeria, M.; Norman, M. R.; Mochiku, T.; Kadowaki, K.; Giapintzakis, J.

    1996-07-01

    IT is well known that BCS mean-field theory is remarkably successful in describing conventional superconductors. A central concept of BCS theory is the energy gap in the electronic excitation spectrum below the superconducting transition temperature, Tc. The gap also serves as the order parameter: quite generally, long-range phase coherence and a non-zero gap go hand-in-hand1. But in underdoped high-Tc superconductors there is considerable evidence that a pseudogap (a suppression of spectral weight) is already formed in the normal state above Tc-first, from studies of the spin excitation spectrum2-5,24, which measure a 'spin gap', and later from a variety of other probes6-10. Here we present a study of underdoped Bi2Sr2CaCu2O8+δ (Bi2212) using angle-resolved photoemission spectroscopy (ARPES), which directly measures the momentum-resolved electron excitation spectrum of the CuO2 planes. We find that a pseudogap with d-wave symmetry opens up in the normal state below a temperature T* > Tc, and develops into the d-wave superconducting gap once phase coherence is established below Tc.

  14. Application of electron backscatter diffraction to bulk high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka-Veneva, A.; Koblischka, M. R.; Simon, P.; Mücklich, F.; Murakami, M.

    2002-05-01

    We have successfully obtained electron backscatter diffraction (EBSD) Kikuchi patterns on various bulk high-Tc superconductors (polycrystalline KClO3-doped and undoped YBa2Cu3O7-δ (YBCO), single crystalline YBCO and NdBa2Cu3O7-y) and on YBCO and NdBCO thin films. We have established a sample polishing procedure to obtain intense Kikuchi patterns without an additional carbon coating of the ceramic superconductors. We present Kikuchi patterns, pole figures and orientation maps of the samples. On the polycrystalline KClO3-doped YBCO samples we find two major orientations (001) and (100) normal to the sample surface, while the undoped sample does not exhibit any orientation maxima, which is ascribed to the effect of a liquid phase due to the KClO3-additive during the preparation process. Furthermore, we discuss the future possibilities for the application of the EBSD technique for growing larger, bulk melt-textured samples for applications.

  15. 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

  16. 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.

  17. 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.

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

    PubMed

    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.

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

    PubMed

    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

  20. 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

  1. Influence of coupling parameter on current-voltage characteristics of intrinsic Josephson junctions in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.; Mahfouzi, F.

    2006-02-01

    We study the current-voltage characteristics of intrinsic Josephson junctions in high-Tc superconductors by numerical calculations and in framework of capacitively coupled Josephson junctions model we obtain the total number of branches. The influence of the coupling parameter α on the current-voltage characteristics at fixed parameter β (β2 = 1/βc, where βc is McCumber parameter) and the influence of α on β-dependence of the current-voltage characteristics are investigated. We obtain the α-dependence of the branch's slopes and branch's endpoints. The presented results show new features of the coupling effect on the scheme of hysteresis jumps in current-voltage characteristics of intrinsic Josephson junctions in high-Tc superconductors.

  2. Possible solution of the grain-boundary problem for applications of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Hammerl, G.; Herrnberger, A.; Schmehl, A.; Weber, A.; Wiedenmann, K.; Schneider, C. W.; Mannhart, J.

    2002-10-01

    It is shown that the critical current density of high-Tc wires can be greatly enhanced by using a three-fold approach, which consists of grain alignment, doping, and optimization of the grain architecture. According to model calculations, current densities of 4 x106 A/cm2 can be achieved for an average grain alignment of 10deg at 77 K. Based on this approach, a road to competitive high-Tc cables is proposed.

  3. 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.

  4. 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.

  5. A new type of superconducting journal bearing using high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Komori, M.; Kitamura, T.

    The characteristics between a set of alternating-polarity ring magnets and a superconductor are studied. The magnets have strong repulsion and attraction forces with the superconductor owing to the pinning effect. Using these characteristics a prototype of a superconducting journal bearing with a magnet shaft supported by a cylindrical housing has been developed. The superconductors (type-II superconductors) and a magnet shaft as the rotor of alternating-polarity ring magnets of the same size. The magnet shaft can be levitated in the center of the housing without contact. Levitation and drag forces of the superconducting journal bearing are investigated. The levitation force shows circular hysteresis loops depending on the displacement because of the flux pinning effect. Owing to the simple and useful structure of the superconducting journal bearing it is applicable to practical devices in the industrial field.

  6. 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.

  7. 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.

  8. 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).

  9. A microscopic two-band model for the electron-hole asymmetry in high-Tc superconductors and reentering behavior

    NASA Astrophysics Data System (ADS)

    Bru, J.-B.; Pedra, W. de Siqueira; Dömel, A.-S.

    2011-07-01

    To our knowledge there is no rigorously analyzed microscopic model explaining the electron-hole asymmetry of the critical temperature seen in high-Tc cuprate superconductors - at least no model not breaking artificially this symmetry. We present here a microscopic two-band model based on the structure of energetic levels of holes in CuO2 conducting layers of cuprates. In particular, our Hamiltonian does not contain ad hoc terms implying - explicitly - different masses for electrons and holes. We prove that two energetically near-lying interacting bands can explain the electron-hole asymmetry. Indeed, we rigorously analyze the phase diagram of the model and show that the critical temperatures for fermion densities below half-filling can manifest a very different behavior as compared to the case of densities above half-filling. This fact results from the inter-band interaction and intra-band Coulomb repulsion in interplay with thermal fluctuations between two energetic levels. So, if the energy difference between bands is too big (as compared to the energy scale defined by the critical temperatures of superconductivity) then the asymmetry disappears. Moreover, the critical temperature turns out to be a non-monotonic function of the fermion density and the phase diagram of our model shows "superconducting domes" as in high-Tc cuprate superconductors. This explains why the maximal critical temperature is attained at donor densities away from the maximal one. Outside the superconducting phase and for fermion densities near half-filling the thermodynamics governed by our Hamiltonian corresponds, as in real high-Tc materials, to a Mott-insulating phase. The nature of the inter-band interaction can be electrostatic (screened Coulomb interaction), magnetic (for instance, some Heisenberg-type one-site spin-spin interaction), or a mixture of both. If the inter-band interaction is predominately magnetic then - additionally to the electron-hole asymmetry - we observe a

  10. 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).

  11. Oliver E. Buckley Condensed Matter Prize Talk: High-resolution Photoemission Studies of the High Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Johnson, Peter

    2011-03-01

    In the last decade, high resolution angle-resolved photoelectron spectroscopy has evolved into one of the most powerful probes of the electronic structure of condensed matter systems. This development reflects new technological advances coupled to the enormous research effort devoted to the study of strongly correlated systems, particularly the high Tc cuprate superconductors. Two decades after their initial discovery the latter still present some of the biggest challenges for materials science. In this talk we review some of the developments in new instrumentation and analysis techniques in photoemission and include discussion of both self-energy effects and Fermi surface studies. In the latter case, the discussion will focus on the pseudogap phase of the underdoped cuprates with particular reference to an observed particle-hole asymmetry and the possibility of hole pockets. Work at Brookhaven is supported by the U.S. Department of Energy.

  12. Fabrication and properties of high- Tc tapes and coils made from silver-clad Bi-2223 superconductors

    SciTech Connect

    Haldar, P.; Hoehn, J.G. Jr.; Rice, J.A. ); Motowidlo, L.R. ); Balachandran, U.; Youngdahl, C.A. ); Tkaczyk, J.E.; Bednarczyk, P.J. . Corporate Research and Development Center)

    1992-08-01

    Long lengths of flexible silver-clad Bi-2223 high-{Tc} superconductors have been fabricated by the powder-in-tube. technique. By improving process conditions dc transport measurements at liquid helium (4.2K) and hydrogen (20K) temperatures yield J{sub c}'s greater than 10{sup 5} A/cm{sup 2} at zero field and exceed 3 {times} 10{sup 4} A/cm{sup 2} at liquid nitrogen (77K) temperature in short tape samples. Detailed microstructural analysis and J{sub c} measurements with applied fields up to 20 T are reported. Coils have been fabricated from 1 meter lengths of conductor with J{sub c}'s at 77K approaching 10{sup 4} A/cm{sup 2}. Measurements on small pancake coils made from 10 meter tapes are also reported.

  13. Fabrication and properties of high-{Tc} tapes and coils made from silver-clad Bi-2223 superconductors

    SciTech Connect

    Haldar, P.; Hoehn, J.G. Jr.; Rice, J.A.; Motowidlo, L.R.; Tkaczyk, J.E.; Bednarczyk, P.J.

    1992-08-01

    Long lengths of flexible silver-clad Bi-2223 high-{Tc} superconductors have been fabricated by the powder-in-tube. technique. By improving process conditions dc transport measurements at liquid helium (4.2K) and hydrogen (20K) temperatures yield J{sub c}`s greater than 10{sup 5} A/cm{sup 2} at zero field and exceed 3 {times} 10{sup 4} A/cm{sup 2} at liquid nitrogen (77K) temperature in short tape samples. Detailed microstructural analysis and J{sub c} measurements with applied fields up to 20 T are reported. Coils have been fabricated from 1 meter lengths of conductor with J{sub c}`s at 77K approaching 10{sup 4} A/cm{sup 2}. Measurements on small pancake coils made from 10 meter tapes are also reported.

  14. General Rule of Negative Effective Ueff System & Materials Design of High-Tc Superconductors by ab initio Calculations

    NASA Astrophysics Data System (ADS)

    Katayama-Yoshida, Hiroshi; Nakanishi, Akitaka; Uede, Hiroki; Takawashi, Yuki; Fukushima, Tetsuya; Sato, Kazunori

    2014-03-01

    Based upon ab initio electronic structure calculation, I will discuss the general rule of negative effective U system by (1) exchange-correlation-induced negative effective U caused by the stability of the exchange-correlation energy in Hund's rule with high-spin ground states of d5 configuration, and (2) charge-excitation-induced negative effective U caused by the stability of chemical bond in the closed-shell of s2, p6, and d10 configurations. I will show the calculated results of negative effective U systems such as hole-doped CuAlO2 and CuFeS2. Based on the total energy calculations of antiferromagnetic and ferromagnetic states, I will discuss the magnetic phase diagram and superconductivity upon hole doping. I also discuss the computational materials design method of high-Tc superconductors by ab initio calculation to go beyond LDA and multi-scale simulations.

  15. 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.

  16. Flux Trapping Properties of Bulk HIGH-TC Superconductors in Static Field-Cooling Magnetization

    NASA Astrophysics Data System (ADS)

    Deng, Z.; Tsuzuki, K.; Miki, M.; Felder, B.; Hara, S.; Izumi, M.

    2013-06-01

    The trapping process and saturation effect of trapped magnetic flux of bulk high-temperature superconductors by static field-cooling magnetization (FCM) are reported in the paper. With a cryogenic Bell Hall sensor attached on the center of the bulk surface, the synchronous magnetic signals were recorded during the whole magnetization process. It enables us to know the flux trapping behavior since the removal of the excitation field, as well as the subsequent flux relaxation phenomenon and the flux dissipation in the quench process of the bulk sample. With the help of flux mapping techniques, the relationship between the trapped flux and the applied field was further investigated; the saturation effect of trapped flux was discussed by comparing the peak trapped field and total magnetic flux of the bulk sample. These studies are useful to understand the basic flux trapping properties of bulk superconductors.

  17. Anisotropy Effect on Levitation Performance of Bulk High-Tc Superconductors Above a Permanent Magnet Guideway

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Liao, Xinglin; Jing, Hailian; Lin, Qunxu; Ma, Guangtong; Yen, Fei; Wang, Suyu; Wang, Jiasu

    The anisotropy properties of bulk high-temperature superconductors (HTSCs) are taken into consideration for the application of high-temperature superconducting (HTS) Maglev systems, which are especially based on the different flux-trapping capabilities as well as critical current density, Jc, values between the growth section boundary (GSB) and the growth sections (GS) in bulk superconductors. By adjusting the angle between the GSB of bulk HTSCs and the strongest magnetic field position of a permanent magnet guideway (PMG), the levitation force and its relaxation processes are compared at different field-cooling conditions. Experimental results show that the levitation capability and the suppression of levitation force decay can be enhanced by optimizing the GS/GSB alignment of every bulk HTSC above the PMG. Meanwhile, our conclusions may provide references to other HTS maglev systems with small levitation gaps, i.e., superconducting magnetic bearings.

  18. On field effect studies and superconductor-insulator transition in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Dubuis, G.; Bollinger, A. T.; Pavuna, D.; Božović, I.

    2013-07-01

    We summarize previous field effect studies in high- T c cuprates and then discuss our method to smoothly tune the carrier concentration of a cuprate film over a wide range using an applied electric field. We synthesized epitaxial one-unit-cell thick films of La2- x Sr x CuO4 and from them fabricated electric double layer transistor devices utilizing various gate electrolytes. We were able to vary the carrier density by about 0.08 carriers per Cu atom, with the resulting change in T c of 30 K. The superconductor-insulator transition occurred at the critical resistance very close to the quantum resistance for pairs, R Q = h/(2 e)2 = 6.5 kΩ. This is suggestive of a quantum phase transition, possibly driven by quantum phase fluctuations, between a "Bose insulator" and a high- T c superconductor state.

  19. Field induced microwave absorption in melt textured and sintered high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Patanjali, P. V.; Sudhakar Reddy, E.; Kadam, R. M.; Bai, V. Seshu; Sastry, M. D.; Rajasekharan, T.

    1999-10-01

    Low and high field dependent microwave absorption is studied in various sintered and melt textured HTSs. The low field loss is found to originate from weak links and the high field loss is due to thermally assisted flux flow. Melt textured superconductors are found to be best suited for low field device applications due to the drastic reduction in low field induced loss when compared to sintered samples. Melt textured superconductors with 211 inclusions are found to show reduced high field losses due to pinning of field at the secondary defects created by 211 particulates. Various parameters of the critical state such as Jc and the pinning force constant, Kx, are determined from the microwave absorption study.

  20. Nodal Liquid Theory of the Pseudo-Gap Phase of High-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Balents, Leon; Fisher, Matthew P. A.; Nayak, Chetan

    We introduce and study the nodal liquid, a novel zero-temperature quantum phase obtained by quantum-disordering a d-wave superconductor. It has numerous remarkable properties which lead us to suggest it as an explanation of the pseudo-gap state in underdoped high-temperature superconductors. In the absence of impurities, these include power-law magnetic order, a T-linear spin susceptibility, nontrivial thermal conductivity, and two- and one-particle charge gaps, the latter evidenced, e.g. in transport and electron photoemission (which exhibits pronounced fourfold anisotropy inherited from the d-wave quasiparticles). We use a (2+1)-dimensional duality transformation to derive an effective field theory for this phase. The theory is comprised of gapless neutral Dirac particles living at the former d-wave nodes, weakly coupled to the fluctuating gauge field of a dual Ginzburg-Landau theory. The nodal liquid interpolates naturally between the d-wave superconductor and the insulating antiferromagnet, and our effective field theory is powerful enough to permit a detailed analysis of a panoply of interesting phenomena, including charge ordering, antiferromagnetism, and d-wave superconductivity. We also discuss the zero-temperature quantum phase transitions which separate the nodal liquid from various ordered phases.

  1. Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Campi, G.; Bianconi, A.; Poccia, N.; Bianconi, G.; Barba, L.; Arrighetti, G.; Innocenti, D.; Karpinski, J.; Zhigadlo, N. D.; Kazakov, S. M.; Burghammer, M.; Zimmermann, M. V.; Sprung, M.; Ricci, A.

    2015-09-01

    It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave `puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26, 27, 28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity.

  2. Inhomogeneity of charge-density-wave order and quenched disorder in a high-Tc superconductor.

    PubMed

    Campi, G; Bianconi, A; Poccia, N; Bianconi, G; Barba, L; Arrighetti, G; Innocenti, D; Karpinski, J; Zhigadlo, N D; Kazakov, S M; Burghammer, M; Zimmermann, M v; Sprung, M; Ricci, A

    2015-09-17

    It has recently been established that the high-transition-temperature (high-Tc) superconducting state coexists with short-range charge-density-wave order and quenched disorder arising from dopants and strain. This complex, multiscale phase separation invites the development of theories of high-temperature superconductivity that include complexity. The nature of the spatial interplay between charge and dopant order that provides a basis for nanoscale phase separation remains a key open question, because experiments have yet to probe the unknown spatial distribution at both the nanoscale and mesoscale (between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both short-range charge-density-wave 'puddles' (domains with only a few wavelengths) and quenched disorder in HgBa2CuO4 + y, the single-layer cuprate with the highest Tc, 95 kelvin (refs 26-28). We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of self-organization near a critical point. However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usually assumed random, uncorrelated distribution. The interstitial-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, because higher doping does not favour the stripy charge-density-wave puddles, leading to a complex emergent geometry of the spatial landscape for superconductivity. PMID:26381983

  3. Terahertz applications of integrated circuits based on intrinsic Josephson junctions in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Wang, Huabing; Wu, Peiheng; Yamashita, Tsutomu

    2001-10-01

    Using a newly developed double-side fabrication method, an IJJ stack plus a bow-tie antenna and chokes were integrated in a slice 200 nm thick and singled out from inside a bulk Bi2Sr2CaCu2O8+x (BSCCO) single crystal. The junctions in the fabricated stack were very uniform, and the number of junctions involved was rather controllable. In addition to this method, which can be used to fabricate integrated circuits based on intrinsic Josephson junctions in high temperature (Tc) superconductors, also reported will be terahertz responses of IJJs, and the possible applications in quantum voltage standard, spectroscopy, and so on.

  4. On the force relaxation in the magnetic levitation system with a high-Tc superconductor

    NASA Astrophysics Data System (ADS)

    Smolyak, B. M.; Zakharov, M. S.

    2014-05-01

    The effect of magnetic flux creep on the lift force in a magnet/superconductor system was studied. It was shown experimentally that in the case of real levitation (when a levitating object bears only on a magnetic field) the suspension height and consequently the lift force did not change over a long period of time. When the levitating object is fixed for some time (i.e. a rigid constraint is imposed on it), the levitation height decreases after removal of the external constraint. It is assumed that free oscillations of the levitating object slow down the flux creep process, which is activated when these oscillations are suppressed.

  5. 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.

  6. 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.

  7. 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.

  8. Transport evidence of a magnetic quantum phase transition in electron-doped high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Yu, W.; Higgins, J. S.; Bach, P.; Greene, R. L.

    2007-07-01

    We present magnetotransport evidence for antiferromagnetism in films of the electron-doped cuprates Pr2-xCexCuO4 . Our results show clear signature of static or quasistatic antiferromagnetism up to optimal doping x=0.15 , with a quantum phase transition close to x=0.16 , and a coexistence of antiferromagnetism and superconductivity for 0.12⩽x⩽0.15 .

  9. Formation of the low-field peak in magnetization loops of high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Koblischka, M. R.; Půst, L.; Jirsa, M.; Johansen, T. H.

    1999-07-01

    The positions of the central (low-field) peak in the magnetization hysteresis loops (MHLs) are analyzed in various high- Tc superconducting samples comprising several RBa 2Cu 3O 7- δ (RBCO; R=rare earths) single crystals of different thicknesses, a laser-ablated YBa 2Cu 3O 7- δ (YBCO) thin film, Ag-sheathed (Pb,Bi) 2Sr 2Ba 2Cu 3O 10+ δ (Bi-2223) mono- and multifilamentary tapes, and a model sample designed to reproduce a layer of grains [M.R. Koblischka et al., Appl. Phys. Lett. 70 (1997) 514]. The single crystals and the thin film show the peak at zero-field or at negative applied fields on the descending field branch according to the critical state models, the Bi-2223 tapes are found to exhibit the peak anomalously in positive applied fields. In order to better understand the magnetization processes leading to the formation of the central peak in the MHLs, the local field distributions in applied fields close to zero were studied using magneto-optic (MO) flux visualization on the same samples. These flux patterns show how the vortices are rearranged when sweeping through zero-field. A large demagnetizing effect (“perpendicular geometry”) facilitates the penetration of vortices of opposite polarity, especially along structural defects, thus, forcing the central peak towards zero or even to very small positive fields. To explain the anomalous behaviour found in Bi-2223 tapes, effects of granularity have to be considered additionally. Further, we discuss the interaction of the central peak with other “peak effects” observed in MHLs.

  10. High-Tc superconductor/linear low density polyethylene (LLDPE) composite materials for diamagnetic applications

    NASA Astrophysics Data System (ADS)

    Bhadrakumari, S.; Predeep, P.

    2006-08-01

    A series of composite samples of YBa2Cu3O7-x and linear low density polyethylene (Y-123/LLDPE) with volume percentage ranging from 0 to 75% was prepared. The crystallinity of the composites was studied using x-ray diffraction (XRD) patterns. It is found that the percentage of crystallinity in the composite samples increases with increasing volume of the LLDPE. A four-phase system for the composite materials may be inferred from a combination of XRD and density data. Repulsive force measurements showed that the diamagnetic properties were preserved in the composites and the samples exhibited appreciable magnetic levitation forces and this force increases with increasing volume fraction of the superconductor filler.

  11. Study of dendritic avalanches by current noise measurements in High Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Celasco, Edvige; Eggenhöffner, Roberto; Tolotto, Graziano; Celasco, Marcello

    2005-08-01

    Spectral noise power measurements are reported in a bulk YBa2Cu3O7-δ superconductor at 4.2 K to investigate the flux vortex avalanche processes originated from thermomagnetic instabilities in an applied magnetic field up to 600 mT and in feeding current close to the critical value. 1/fγ behavior is shown at frequencies below 10 Hz, γ values range from 0.7 to 1.7. A sharp peak is observed in applied field and from these results we have obtained a cutoff frequency around 20 Hz for Lorentzian shape knee from which we estimate a mean number of 500 vortices and a mean velocity of about 20 cm/s for the average avalanche.

  12. Flux Creep and Giant Flux Creep in High Tc Hg,Pb-based Superconductors

    NASA Astrophysics Data System (ADS)

    Kirven, Douglas; Owens, Frank; Iqbal, Z.; Bleiweiss, M.; Lungu, A.; Datta, T.

    1996-03-01

    Dynamic behavior of the trapped flux in fields of up to 17.5 T was studied in a set of Hg-Pb based superconductors with a Tc in excess of 130 K. Depending on the experimental conditions, both creep and giant flux creep dynamics were observed. Results were analyzed using to standard models such as Anderson-Kim and giant-flux creep models (GFC). The plots of relaxation rate of remnant magnetization versus temperature show a peak below Tc. These results were compared with other Cu-O compounds. A distribution of activation energies was found from the magnetization rate. The activation energy distribution shows a peak around 50 K. The peak determines the temperature where the flux flow rate is a maximum. A universal relation of the resistive behavior was also found as a function of temperature and field. The zero-field/field-cooled results gave a reversibility curve that also obeyed a universal power relation.

  13. 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.

  14. 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.

  15. Emission of terahertz electromagnetic waves by vortex flow in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Tachiki, Masashi; Iizuka, Mikio; Minami, Kazuo; Tejima, Shogo; Nakamura, Hisashi

    2006-05-01

    Continuous terahertz electromagnetic waves have new applications in scientific and industrial fields such as medicine and information technology. Cuprate high-temperature superconductors have a layer structure, and form a naturally multi-connected Josephson junction system called intrinsic Josephson junction (IJJ). In IJJ, there appears a new excitation called the Josephson plasma. Its frequency is in the region of terahertz inside the superconducting energy gap. The excited plasma wave is converted into an electromagnetic wave at sample surfaces. Therefore the IJJ has a great potential to generate terahertz continuous wave. Here we report the results of simulations to find the optimum condition for obtaining the strongest emission power of the terahertz waves. The simulations were carried out using our theory. Since the simulation uses very large-sized coupled nonlinear equations therefore difficult to compute, we used the fastest supercomputer named as Earth Simulator. We found that the quite intense continuous terahertz coherent wave is emitted from a small sample with high-energy efficiency.

  16. Coupled bipolarons and optical phonons as a model for high-Tc superconductors

    NASA Technical Reports Server (NTRS)

    Kasperczyk, J.

    1991-01-01

    The coherence length of the new high-temperature superconductors reaches a small value which is comparable to the dimensions of the unit cell of the compound. This means that a pair consists of two holes occupying the same site or two adjacent sites. Such a situation is described by a model of the local-pairs (bipolarons). The origin of local-pairs may come not only from strong enough electron or hole-phonon interaction but also from other interactions. Independent of the specific nature of such local-pairs, they can undergo a Bose-like condensation to the superconducting state at a critical temperature which is usually much lower than the temperature of the pair formation. An interplay of ferroelectric and superconducting properties is considered within the model of hole-like local-pairs interacting with optical phonons. Therefore, researchers extend the usual local-pair Hamiltonian by including a direct interaction between the local-pairs and the optical phonons. These optical phonons are known to play an important role in the ferroelectric transition and they transform into an additional pseudo-acoustic branch at the ferroelectric critical temperature. (This is associated with nonzero electric polarization due to the existence of two separate lattices composed of negative and positive ions, respectively.)

  17. Development of commercially viable high-{Tc} Bi-2223 superconductor tapes

    SciTech Connect

    Balachandran, U.; Youngdahl, C.A.; Haldar, P.; Motowidlo, L.R.

    1993-02-01

    Long lengths of flexible Ag-clad Bi-2223 Superconductors have been fabricated by the powder-in-tube technique using prereacted, poly-phase, Pb-doped Bi-Sr-Ca-Cu-O powders. At liquid helium (4.2 K) temperature, improved process conditions yielded transport critical current density (J{sub c}) values greater than 10{sup 5} A/cm{sup 2} at zero field; at liquid nitrogen (77K) temperature, the J{sub c} values of short tape samples exceeded 4 {times} 10{sup 4} A/cm{sub 2}. Rolled tapes are cut into lengths up to 2 - meters long and are used in parallel to fabricate small superconducting pancake coils by the ``wind-and-react`` technique. The cots are characterized at 77K and 4.2 K. The J{sub c} of the coils are up to 80% of the short, rolled sample result at 77 K. The coils exhibited these results even after being cooled and warmed several times between ambient, 77 K and 4.2 K, indicating their stability following thermal cycling.

  18. Development of commercially viable high-[Tc] Bi-2223 superconductor tapes

    SciTech Connect

    Balachandran, U.; Youngdahl, C.A. . Materials and Components Technology Div.); Haldar, P. ); Motowidlo, L.R. )

    1993-02-01

    Long lengths of flexible Ag-clad Bi-2223 Superconductors have been fabricated by the powder-in-tube technique using prereacted, poly-phase, Pb-doped Bi-Sr-Ca-Cu-O powders. At liquid helium (4.2 K) temperature, improved process conditions yielded transport critical current density (J[sub c]) values greater than 10[sup 5] A/cm[sup 2] at zero field; at liquid nitrogen (77K) temperature, the J[sub c] values of short tape samples exceeded 4 [times] 10[sup 4] A/cm[sub 2]. Rolled tapes are cut into lengths up to 2 - meters long and are used in parallel to fabricate small superconducting pancake coils by the wind-and-react'' technique. The cots are characterized at 77K and 4.2 K. The J[sub c] of the coils are up to 80% of the short, rolled sample result at 77 K. The coils exhibited these results even after being cooled and warmed several times between ambient, 77 K and 4.2 K, indicating their stability following thermal cycling.

  19. 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.

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

    SciTech Connect

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

    1988-01-01

    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 declay the need for new airport and 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.

  1. 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.

  2. 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.

  3. Quantum quenching an O(N) non linear sigma model (NLSM) and oscillation experiments of high Tc underdoped cuprate superconductor

    NASA Astrophysics Data System (ADS)

    Hung, Ling Yan

    2014-03-01

    Recent X-ray scattering experiments have provided strong evidence of the coexistence of a charge density wave order (CDW) and superconductivity (SC) in underdoped crystals of the prototypical high-Tc cuprate superconductor, YBa2Cu3O6+x. Sachdev et al have proposed a O(6) NLSM as an effective description of the competing orders, which finds excellent quantitative fit with the X-ray data. On the other hand, Hinton et al report coherent oscillations associated with CDW in these cuprates, whose phenomenology above and below Tc find qualitative match with the picture of the competing orders. Motivated by these recent results, we study the dynamical evolution of the O(6) NLSM model upon a quantum quench - a sudden disturbance of some parameters of the model to mimic the effect of the laser pulse in the oscillation experiment. As a first brush, we simplify the problem by taking the large-N limit of the O(6) NLSM. We observe a general exponentially decaying oscillations, which experiences phase shift as temperature is varied, at an extent determined by the specific choice of the parameter that is quenched. We also discuss the variation of the oscillation frequency and amplitude as various parameters are varied. The author is supported by the Croucher Foundation (Hong Kong)

  4. Fermi Surfaces of Iron-Pnictide High-Tc Superconductors from the Limit of Local Magnetic Moments

    NASA Astrophysics Data System (ADS)

    Araujo, Miguel; Sacramento, Pedro; Rodriguez, Jose

    2012-02-01

    We study a 2-orbital t-J model for an isolated square lattice of iron atoms, which stack up to form an iron-pnictide high-Tc superconductor. The two orbitals in question are the degenerate d±= 3d(x±iy)z ones, which maximize the Hund's Rule coupling. First-neighbor and second-neighbor hopping (t) and Heisenberg exchange (J) are included. A Schwinger-boson-slave-fermion mean-field analysis yields a hidden half metal state in which holes hop through a d+d- spin background without much hopping across orbitals. This state is characterized by an inner and an outer Fermi surface pocket centered at the γ point. The Fermi surface pockets resemble those predicted by band structure calculations that include all five 3d orbitals. By sweeping the Hund's coupling, we also identify a quantum-critical point (QCP) where zero-energy spin-wave excitations exist at the momenta associated with commensurate spin-density-wave (cSDW) order. These low-energy spin-waves result in nested Fermi-surface pockets centered at cSDW momenta. Exact diagonalization of one hole in the 2-orbital t-J model over a 4x4 square lattice yields low-energy spectra that are consistent with the nested Fermi surfaces that are predicted to exist at the QCP.

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

    NASA Astrophysics Data System (ADS)

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

    1989-05-01

    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.

  7. Band structure of the heavily-electron-doped FeAs-based Ba(Fe,Co)2As2 superconductor suppresses antiferromagnetic correlations.

    PubMed

    Sudayama, T; Wakisaka, Y; Takubo, K; Morinaga, R; Sato, T J; Arita, M; Namatame, H; Taniguchi, M; Mizokawa, T

    2010-04-30

    In the heavily-electron-doped regime of the Ba(Fe,Co)2As2 superconductor, three hole bands at the zone center are observed and two of them reach the Fermi level. The larger hole pocket at the zone center is apparently nested with the smaller electron pocket around the zone corner. However, the (pi,0) Fermi surface reconstruction reported for the hole-doped case is absent in the heavily-electron-doped case. This observation shows that the apparent Fermi surface nesting alone is not enough to enhance the antiferromagnetic correlation as well as the superconducting transition temperature.

  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. Material Specific Rational Design of A1B2C3O7 High-Tc Superconductors without Copper [A, B, C = Cations

    NASA Astrophysics Data System (ADS)

    Isikaku-Ironkwe, O'paul; Schaffer, Michael J.

    Soon after the discovery of YBa2Cu3O7 with Tc = 93K, a similar structured system with Ag replacing Cu was discovered with a Tc = 50K. Also, the discovery of Ba0 . 6 K0 . 4 BiO3 with Tc = 30K indicated that Cu was not indispensable for high temperature superconductivity (HTSC). Latter, the discoveries of the Pnictide and Chalcogenide high-Tc superconductors confirmed those earlier experimental indications. Using our recently developed Material Specific Characterization Dataset (MSCD) model for analysis and design of superconductors, we have computed many designs that satisfy the MSCD characteristics of YBa2Cu3O7 as a design model. Our design recognizes the valence state characteristics that make YBa2Cu3O6 a semiconductor, while YBa2Cu3O7is a superconductor. Here we present ten material specific rational design examples of potential A1B2C3O7 HTSCs without Cu, using the YBa2Cu3O7 design model. This MSCD design model opens the possibility for search and discovery of high-Tc oxide superconductor systems without copper.

  10. Determination of the phase diagram of the electron doped superconductor Ba(Fe1-xCox)2As2

    SciTech Connect

    Chu, Jiun-Haw; Analytis, James G.; Kucharczyk, Chris; Fisher, Ian R.; /Stanford U., Geballe Lab.

    2010-02-15

    Systematic measurements of the resistivity, heat capacity, susceptibility and Hall coefficient are presented for single crystal samples of the electron-doped superconductor Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2}. These data delineate an x-T phase diagram in which the single magnetic/structural phase transition that is observed for undoped BaFe{sub 2}As{sub 2} at 134 K apparently splits into two distinct phase transitions, both of which are rapidly suppressed with increasing Co concentration. Superconductivity emerges for Co concentrations above x {approx}0.025, and appears to coexist with the broken symmetry state for an appreciable range of doping, up to x {approx} 0.06. The optimal superconducting transition temperature appears to coincide with the Co concentration at which the magnetic/structural phase transitions are totally suppressed, at least within the resolution provided by the finite step size between crystals prepared with different doping levels. Superconductivity is observed for a further range of Co concentrations, before being completely suppressed for x {approx} 0.018 and above. The form of this x-T phase diagram is suggestive of an association between superconductivity and a quantum critical point arising from suppression of the magnetic and/or structural phase transitions.

  11. Doping dependent charge correlation in electron-doped cuprates

    NASA Astrophysics Data System (ADS)

    da Silva Neto, Eduardo; Boschini, F.; Zonno, M.; Sawatzky, G. A.; Damascelli, A.; Minola, M.; Bluschke, M.; Le Tacon, M.; Keimer, B.; Wu, B.; Li, Y.; Yu, G.; Greven, M.; Higgins, J.; Jiang, Y.; Greene, R. L.; Sutarto, R.; He, F.; Schierle, E.; Weschke, E.

    We use resonant x-ray scattering to measure the charge order in electron-doped high-Tc superconductors and its relationship to antiferromagnetism and superconductivity. First, we establish the presence of charge order in a second family of electron-doped cuprates, LCCO thin films, with similar characteristics to previous observations in NCCO. Second, doping and temperature dependent measurements of NCCO single crystals show that charge order is present in the x = 0.059 to 0.166 doping range, and its doping-dependent wavevector is consistent with the separation between the hot spots on the Fermi surface. For NCCO samples near optimal doping (x = 0.14) the charge order remains constant through the superconducting transition temperature and we find that magnetic fields up to 6 T have a negligible effect on its intensity. The implications of our data to the connections of charge order to antiferromagnetism and superconductivity will be discussed.

  12. Local tunneling spectroscopy of the electron-doped cuprate superconductor Sm1.85Ce0.15CuO4

    NASA Astrophysics Data System (ADS)

    Zimmers, A.; Noat, Y.; Cren, T.; Sacks, W.; Roditchev, D.; Liang, B.; Greene, R. L.

    2007-10-01

    We present local tunneling spectroscopy in the optimally electron-doped cuprate Sm2-xCexCuO4 , x=0.15 . A clear signature of the superconducting gap is observed with an amplitude ranging from place to place and from sample to sample ( Δ˜3.5 6meV) . Another spectroscopic feature is simultaneously observed at high energy with an amplitude ranging from ±60 to ±80meV . Its energy scale and temperature evolution are found to be compatible with previous photoemission and optical experiments. If interpreted as the signature of antiferromagnetic order in the samples, these results could suggest the coexistence on the local scale of antiferromagnetism and superconductivity on the electron-doped side of cuprate superconductors.

  13. 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.

  14. 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.

  15. Single superconducting energy scale in the electron-doped cuprate superconductor Pr2-xCexCuO4-δ

    NASA Astrophysics Data System (ADS)

    Diamant, I.; Greene, R. L.; Dagan, Y.

    2009-07-01

    The tunneling spectra of the electron-doped cuprate Pr2-xCexCuO4-δ as a function of doping and temperature are reported. We find that the superconducting gap, Δ , shows a BCS-type temperature dependence even for extremely low carrier concentrations. Moreover, Δ follows the doping dependence of Tc , in strong contrast with tunneling studies of the hole-doped cuprates. From our results we conclude that there is a single superconducting energy scale in the electron-doped cuprates.

  16. Processing and properties of long-lengths of Ag-clad BSCCO superconductors and high-{Tc} magnets

    SciTech Connect

    Balachandran, U.; Iyer, A.N.; Jammy, R.; Haldar, P.; Hoehn, J.G. Jr.; Suenaga, M.

    1994-10-01

    Long lengths of Ag-clad mono and multicore BSCCO tapes were fabricated by the powder-in-tube technique. The critical current density (J{sub c}) of 125-m-long monocore tapes was {approx}12,000 A/cm{sup 2} (critical current, I{sub c} 20 A) at 77 K. A 230-m-long 37-filament tape carried an I{sub c} of 14 A (corresponding to a J{sub c} of {approx}10,000 A/cm{sup 2}). Pancake-shaped coils were formed from long-length conductors by the wind-and-react approach. High-T{sub c} magnets were then assembled by stacking the pancake coils and connecting them in series. The magnets were tested as a function of applied magnetic fields at 4.2, 27, 64, and 77 K. A magnet containing 480 m of high-{Tc} tape generated a record-high field of 2.6 T at 4.2 K. Another magnet assembled with {approx}770 m of tape generated a field of {approx}1 T at 4.2 K and {approx}0.6 T at 27 K, both in an applied background field of {approx}20 T. Strain tolerance of high-{Tc} tapes was evaluated by measuring J{sub c} retention as a function of applied strain in an 0.5 T applied field at 77 K.

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

    DOE PAGES

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

  18. High Tc superconductors for plasmonics and metamaterials fabrication: A preliminary normal state optical characterisation of Nd123 and Gd1212

    NASA Astrophysics Data System (ADS)

    Gombos, M.; Romano, S.; Rendina, I.; Carapella, G.; Ciancio, R.; Mocella, V.

    2013-08-01

    The application of metamaterials and plasmonic structures in the visible and near infrared are strongly limited by the dissipative losses due to the low conductivity of the most used metals in this frequency range. High temperature superconductors are plasmonic materials at nonzero temperature that can provide a possible alternative approach to overcome this limit. Moreover, they can have zero or even negative dielectric constant, and a bipolar behavior. All these characteristics are attractive for plasmonic applications, and encourage further studies aimed at a more detailed knowledge of the parameters characterizing high temperature superconductors as possible optical materials. In this paper, Fourier Transform Infrared Spectroscopy analysis and ellipsometric measurements in the visible and infrared spectral regions on NdBa2Cu3O7-δ (Nd123) and ruthenocuprate superconductor GdSr2RuCu2O8-δ (Gd1212) are reported. As a matter of fact, Nd123 presents the highest transition temperature (Tc = 96 K) and the most interesting magnetic response properties among YBCO-like cuprate superconductors, whereas the coexistence in the same cell of superconductivity and magnetic order below Tc in Gd1212 can be an interesting feature for next metamaterial-like applications. The obtained results confirm the promising features of the considered materials.

  19. 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.; Kreshchuk, Michael; Lee, Yong Kiat; Reijnders, Anjan A.; Jain, Achint; Xu, Zhijun; Liu, T. S.; Gu, G. D.; et al

    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

  20. p -orbital density wave with d symmetry in high-Tc cuprate superconductors predicted by renormalization-group + constrained RPA theory

    NASA Astrophysics Data System (ADS)

    Tsuchiizu, Masahisa; Yamakawa, Youichi; Kontani, Hiroshi

    2016-04-01

    The discovery of the charge-density-wave formation in the high-Tc cuprate superconductors has activated intensive theoretical studies for the pseudogap states. However, the microscopic origin of the charge-density-wave state has been unknown so far since the many-body effects beyond the mean-field-level approximations, called the vertex corrections, are essential. Toward solving this problem, we employ the recently developed functional renormalization group method, by which we can calculate the higher-order vertex corrections in a systematic and unbiased way with high numerical accuracy. We discover the critical development of the p -orbital-density-wave (p -ODW) instability in the strong-spin-fluctuation region. The obtained p -ODW state possesses the key characteristics of the charge-ordering pattern in Bi- and Y-based superconductors, such as the wave vector parallel to the nearest Cu-Cu direction, and the d -symmetry form factor with the antiphase correlation between px and py orbitals in the same unit cell. In addition, from the observation of the beautiful scaling relation between the spin susceptibility and the p -ODW susceptibility, we conclude that the main driving force of the density wave is the Aslamazov-Larkin vertex correction that becomes very singular near the magnetic quantum-critical point.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. Nd, Ce(fπ)-O(pπ) Hybridization in Nd2-xCexCuO4 and Dynamic Jahn-Teller Pairing in HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Johnson, K. H.; Clougherty, D. P.; McHenry, M. E.

    Hybridization of Nd(fπ) and Ce(fπ) orbitals with composite O(pπ)-O(pπ) bonding/ Cu(dπ*)-O(pπ) antibonding orbitals at the Fermi energy (EF) is shown to promote high-Tc superconductivity in Nd2-xCexCuO4. Dynamic Jahn-Teller coupling of these hybrid molecular orbitals to the lattice leads to Cooper pairing as it does in other high-Tc superconductors, such as La2-xSrxCuO4, where O(pπ) character at EF is dominant.

  6. Two-Fermi-Surface Superconducting State and a Nodal d-Wave Energy Gap of the Electron-Doped Sm1.85Ce0.15CuO4-δ Cuprate Superconductor

    NASA Astrophysics Data System (ADS)

    Santander-Syro, A. F.; Ikeda, M.; Yoshida, T.; Fujimori, A.; Ishizaka, K.; Okawa, M.; Shin, S.; Greene, R. L.; Bontemps, N.

    2011-05-01

    We report on laser-excited angle-resolved photoemission spectroscopy in the electron-doped cuprate Sm1.85Ce0.15CuO4-δ. The data show the existence of a nodal hole-pocket Fermi surface both in the normal and superconducting states. We prove that its origin is long-range antiferromagnetism by an analysis of the coherence factors in the main and folded bands. This coexistence of long-range antiferrmagnetism and superconductivity implies that electron-doped cuprates are two-Fermi-surface superconductors. The measured superconducting gap in the nodal hole pocket is compatible with a d-wave symmetry.

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

    NASA Astrophysics Data System (ADS)

    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.

    2016-02-01

    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, Pr1.3-xLa0.7CexCuO4 (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.

  8. 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

    2016-01-01

    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.

  9. Synthesis and Structural/microstructural Characteristics of Zn-DOPED Tl-BASED HIGH-Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Yadav, B. S.; Verma, G. D.; Phase, D. M.; Lalla, N. P.; Das, B.

    Bulk superconducting samples of type Tl2Ba2Can-1Cun-xZnxO8 (where n = 2, 3 and x = 0, 0.1, 0.25, 0.50) were prepared by standard ceramic method. The gross structural characteristics/phase identification of the as synthesized samples were carried out by powder X-ray diffraction technique. The microstructural characteristics of these samples were explored by scanning electron microscopic and transmission electron microscopic techniques. The chemical compositions of these samples were determined by energy dispersive analysis of X-rays technique. The powder X-ray diffraction patterns indicate that the lattice parameter "c" vary and "a" showed no regular variation but the gross structure of Tl-2212 and Tl-2223 remain tetragonal with Zn substitution upto 0.50. The transition temperature (Tc) measured by standard four-probe method decreases as x increases from 0 to 0.50. The transport critical density (Jc) values were also measured by standard four-probe method as potential difference of 1 μV/cm appears across the sample by increasing current. The electron microscopic explorations exhibit various structural features (stacking faults and uniform distribution of ZnO nanoparticles) which improve the physical properties (e.g., transport critical current density "Jc") of these superconductors. The observed enhancement in transport critical current densities (Jc) of at least one order of magnitude (from 102 to 103 A/cm2) is due to the uniform distribution of ZnO nanoparticles which act as flux pinning centres.

  10. Emergent nesting of the Fermi surface from local-moment description of iron-pnictide high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Rodriguez, Jose P.; Araujo, Miguel A. N.; Sacramento, Pedro D.

    2014-07-01

    We uncover the low-energy spectrum of a t-J model for electrons on a square lattice of spin-1 iron atoms with 3dxz and 3dyz orbital character by applying Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of one hole roaming over a 4 × 4 × 2 lattice. Hopping matrix elements are set to produce hole bands centered at zero two-dimensional (2D) momentum in the free-electron limit. Holes can propagate coherently in the t-J model below a threshold Hund coupling when long-range antiferromagnetic order across the d + = 3d(x + iy)z and d - = 3d(x - iy)z orbitals is established by magnetic frustration that is off-diagonal in the orbital indices. This leads to two hole-pocket Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate spin-density wave (cSDW) that exists above the threshold Hund coupling results in emergent Fermi surface pockets about cSDW momenta at a quantum critical point (QCP). This motivates the introduction of a new Gutzwiller wavefunction for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta indicates that the dispersion of the nested band of one-particle states that emerges is electron-type. Increasing Hund coupling past the QCP can push the hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy level, in agreement with recent determinations of the electronic structure of mono-layer iron-selenide superconductors.

  11. Rare Earth Ion Effects on the Pseudo-Gap in Electron-Doped Superconductors And Possible Nodeless D-Wave Gap

    SciTech Connect

    Park, S.R.; Leem, C.S.; Roh, Y.S.; Choi, K.J.; Kim, J.H.; Kim, B.J.; Koh, H.; Eisaki, H.; Lu, D.H.; Shen, Z.-X.; Armitage, N.P.; Kim, C.

    2009-05-21

    We report angle resolved photoemission (ARPES) studies on electron-doped cuprate superconductor Sm{sub 2-x}Ce{sub x}CuO{sub 4} (x = 0.14 and 0.18). A wide energy range scan shows clear 'waterfall' effect at an energy scale close to 500 meV which is consistent with the value found in Nd{sub 2-x}Ce{sub x}CuO{sub 4} (NCCO) but larger than that from hole-doped superconductors. High resolution results from both dopings show pseudo-gap effects that were observed in NCCO. However, the effects are found to be stronger than that observed in optimally doped NCCO. The overall electronic structure is well understood within a simple model in which a {radical}2 x {radical}2 static order is assumed. Both ARPES and optical measurements give the coupling strengths to the Q = ({pi}/2,{pi}/2) (due to the {radical}2 x {radical}2 order) to be about 0.1 eV, compatible with each other. The effect is strong enough to push the band near the nodal region below the Fermi energy, resulting in possible nodeless d-wave superconductivity where zero energy quasi-particle excitation is inhibited.

  12. Mapping the Electronic Structure of Each Ingredient Oxide Layer of High-Tc Cuprate Superconductor Bi2 Sr2 CaCu2 O8 +δ

    NASA Astrophysics Data System (ADS)

    Lv, Yan-Feng; Wang, Wen-Lin; Peng, Jun-Ping; Ding, Hao; Wang, Yang; Wang, Lili; He, Ke; Ji, Shuai-Hua; Zhong, Ruidan; Schneeloch, John; Gu, Gen-Da; Song, Can-Li; Ma, Xu-Cun; Xue, Qi-Kun

    2015-12-01

    Understanding the mechanism of high transition temperature (Tc) superconductivity in cuprates has been hindered by the apparent complexity of their multilayered crystal structure. Using a cryogenic scanning tunneling microscopy (STM), we report on layer-by-layer probing of the electronic structures of all ingredient planes (BiO, SrO, CuO2 ) of Bi2 Sr2 CaCu2 O8 +δ superconductor prepared by argon-ion bombardment and annealing technique. We show that the well-known pseudogap (PG) feature observed by STM is inherently a property of the BiO planes and thus irrelevant directly to Cooper pairing. The SrO planes exhibit an unexpected van Hove singularity near the Fermi level, while the CuO2 planes are exclusively characterized by a smaller gap inside the PG. The small gap becomes invisible near Tc, which we identify as the superconducting gap. The above results constitute severe constraints on any microscopic model for high Tc superconductivity in cuprates.

  13. Primary Phase Field of the Pb-Doped 2223 High-Tc Superconductor in the (Bi, Pb)-Sr-Ca-Cu-O System

    PubMed Central

    Wong-Ng, W.; Cook, L. P.; Kearsley, A.; Greenwood, W.

    1999-01-01

    Both liquidus and subsolidus phase equilibrium data are of central importance for applications of high temperature superconductors in the (Bi, Pb)-Sr-Ca-Cu-O system, including material synthesis, melt processing and single crystal growth. The subsolidus equilibria of the 110 K high-Tc Pb-doped 2223 ([Bi, Pb], Sr, Ca, Cu) phase and the location of the primary phase field (crystallization field) have been determined in this study. For the quantitative determination of liquidus data, a wicking technique was developed to capture the melt for quantitative microchemical analysis. A total of 29 five-phase volumes that include the 2223 phase as a component was obtained. The initial melt compositions of these volumes range from a mole fraction of 7.3 % to 28.0 % for Bi, 11.3 % to 27.8 % for Sr, 1.2 % to 19.4 % for Pb, 9.8 % to 30.8 % for Ca, and 17.1 % to 47.0 % for Cu. Based on these data, the crystallization field for the 2223 phase was constructed using the convex hull technique. A section of this “volume” was obtained by holding two components of the composition at the median value, allowing projection on the other three axes to show the extent of the field.

  14. Progress and perspectives on electron-doped cuprates

    NASA Astrophysics Data System (ADS)

    Armitage, N. P.; Fournier, P.; Greene, R. L.

    2010-07-01

    Although the vast majority of high- Tc cuprate superconductors are hole-doped, a small family of electron-doped compounds exists. Underinvestigated until recently, there has been tremendous recent progress in their characterization. A consistent view is being reached on a number of formerly contentious issues, such as their order-parameter symmetry, phase diagram, and normal-state electronic structure. Many other aspects have been revealed exhibiting both their similarities and differences with the hole-doped compounds. This review summarizes the current experimental status of these materials. This information is synthesized into a consistent view on a number of topics important to both this material class and the overall cuprate phenomenology including the phase diagram, the superconducting order-parameter symmetry, electron-phonon coupling, phase separation, the nature of the normal state, the role of competing orders, the spin-density wave mean-field description of the normal state, and pseudogap effects.

  15. Conditions for observing Shapiro steps in a Bi2Sr2CaCu2O8+δ high- Tc superconductor intrinsic Josephson junction: Numerical calculations

    NASA Astrophysics Data System (ADS)

    Kitamura, Michihide; Irie, Akinobu; Oya, Gin-Ichiro

    2007-08-01

    Conditions to observe Shapiro steps clearly and stably are studied for an intrinsic Josephson junction (IJJ) in Bi2Sr2CaCu2O8+δ high- Tc superconductors. The current equation normalized by the critical current Ic(T) is solved fully numerically. In the calculations, the quasiparticle tunneling current is evaluated by using the normalized I-V characteristics obtained within the d -wave symmetry superconducting gap, while the Cooper-pair (CP) one is calculated on the basis of the general way in which the coherent and incoherent CP tunneling currents can be correctly calculated within the d -wave treatment and the current due to thermal noises is also simulated by using normal random numbers. It is found that the product SRshunt of the junction cross section S and the shunt resistance Rshunt , and the critical current density Jc are important junction parameters, and moreover, that the current equation of the IJJ with no shunt resistance depends on only a universal curve μ(i0) as a function of the normalized external dc current i0 . Furthermore, the effects of the noise, the normalized CP tunneling currents, the SRshunt product, the normalized amplitude ir of external ac modulation, and the Jc on observing the Shapiro steps are studied. When the IJJ is operated under the condition that the shunt resistance is added and the external ac modulation frequency fr is higher than the plasma frequency fp , it is found that (1) clear and stable Shapiro steps with good responses are obtained within the wide range of ir , (2) the response does not so largely depend on the value of SRshunt , and (3) the response for the high Jc junction is much better than that for the low one.

  16. EDITORIAL: PLASMA 2006: The 5th International Conference on the Intrinsic Josephson Effect and Plasma Oscillations in High-TC Superconductors

    NASA Astrophysics Data System (ADS)

    Warburton, Paul; Yurgens, August

    2007-02-01

    The 5th International Conference on the Intrinsic Josephson Effect and Plasma Oscillations in High-TC Superconductors (known as `PLASMA' for short) took place in London from July 17th to 19th 2006. The meeting was organised jointly by the Superconductivity Group of the Institute of Physics and the European Science Foundation network `Arrays of Quantum Dots and Josephson Junctions' (AQDJJ). It was sponsored by the UK Engineering and Physical Sciences Research Council, AQDJJ, the Japan Society for the Promotion of Physics and the National Institute of Materials Science (NIMS). The meeting was chaired by Paul Warburton of University College London who wishes to put on record his thanks to the conference sponsors for their generosity, without which the conference could not have taken place. Since the previous PLASMA conference in Tsukuba in 2004 the most significant advance in intrinsic Josephson junction (IJJ) research has arguably been the observation of macroscopic quantum tunnelling in IJJs. At the time of the conference this had been observed by both the RIEC/NIMS/AIST collaboration in Japan and by Paul M\\"uller's group in Erlangen. We therefore felt that the conference presented an ideal and timely opportunity for the IJJ community to learn from the more established community of researchers on macroscopic quantum phenomena in low-TC superconductors---and indeed vice versa. As a result a number of leading researchers from the field of low-TC Josephson qubit devices gave several illuminating presentations. Other sessions included those on Josephson vortex dynamics in layered systems and terahertz oscillations in IJJs, in addition to a lively poster session on the first evening. The conference was rounded off by an excellent summary of the highlights of the meeting given by Professor Hu-Jong Lee. The conference organisers would like to thank all those who made the meeting possible and contributed to its smooth running. In addition to the international organising

  17. Pseudogap behavior in the emery model for the electron-doped superconductor Nd2 - x Ce x CuO4: Multiband LDA + DMFT + Σk approach

    NASA Astrophysics Data System (ADS)

    Kuchinskii, E. Z.; Nekrasov, I. A.; Pavlov, N. S.

    2013-08-01

    We propose a generalization of the LDA + DMFT + Σ k approach to the multiband case, in which correlated and uncorrelated states are present in the model simultaneously. Using the multiband version of the LDA + DMFT + Σ k approach, we calculate the density of states and spectral functions for the Emery model in a wide energy interval around the Fermi level. We also obtain the Fermi surfaces for the electron-doped high-temperature superconductor Nd2 - x Ce x CuO4 in the pseudogap phase. The self-energy part Σ k introduced additionally to take into account pseudogap fluctuations describes the nonlocal interaction of correlated electrons with collective Heisenberg short-range spin fluctuations. To solve the effective impurity model, the numerical renorm-group (NRG) method is used for the DMFT equations. Good qualitative agreement of the Fermi surfaces calculated using the LDA + DMFT + Σ k approach and experimental angle-resolved photoemission spectroscopic data is attained. The stability of the dielectric solution with charge transfer in the Emery model with correction for double counting is analyzed in the Appendix.

  18. High-pressure effects on single crystals of electron-doped Pr2-xCexCuO4

    NASA Astrophysics Data System (ADS)

    Rotundu, C. R.; Struzhkin, V. V.; Somayazulu, M. S.; Sinogeikin, S.; Hemley, Russell J.; Greene, R. L.

    2013-01-01

    We present high-pressure diamond-anvil cell synchrotron x-ray, resistivity, and ac-susceptibility measurements on the electron-doped cuprate Pr2-xCexCuO4 to much higher pressures than previously reported. At 2.72 GPa between 88 and 98% of the superconducting T' phase of the optimally doped Pr1.85Ce0.15CuO4 transforms into the insulating phase T. With application of pressure, the T phase becomes more insulating, so we present here an example of electron doping in the T structure. The results have implications for the search for ambipolar high-Tc cuprate superconductors. The Tc of the remaining 2-12% T' phase is suppressed continuously from 22 to 18.5 K at about 14 GPa. Remarkably, the Tc of the overdoped Pr1.83Ce0.17CuO4 remains practically unchanged even at 32 GPa.

  19. Fracture behavior of an inclined crack interacting with a circular inclusion in a high-TC superconductor under an electromagnetic force

    NASA Astrophysics Data System (ADS)

    Xue, Feng; Zhang, Zhaoxia; Gou, Xiaofan

    2015-11-01

    A simple model is proposed to investigate the interaction problem for a circular nonsuperconducting inclusion embedded in a high-TC superconducting matrix which contains an inclined crack, oriented at an arbitrary angle from the direction of the critical currents. The electromagnetic behavior is described by the critical state, the original Bean model. The perturbation brought upon by the circular inclusion and the crack on the critical current density is assumed to be negligible and not considered in this model. The distribution dislocation technology is applied to formulate the current problem. The stress intensity factors (SIFs) are obtained by solving the formulated singular integral equations. The effects of the crack angle, the elastic modulus, the inclusion-crack distance and the inclusion-crack size on the stress intensity factors are discussed in detail.

  20. Resistivity tensor correlations in the mixed state of electron-doped superconductor Nd2-xCexCuO4+δ

    NASA Astrophysics Data System (ADS)

    Charikova, T. B.; Shelushinina, N. G.; Harus, G. I.; Petukhov, D. S.; Petukhova, O. E.; Ivanov, A. A.

    2016-06-01

    The magnetic-field dependencies of the longitudinal and Hall resistance of the electron-doped compounds Nd2-xCexCuO4+δ in underdoped region with x = 0.14 and with varying degrees of disorder (δ) were investigated. It was established experimentally that the correlation between the longitudinal electrical resistivity and the Hall resistivity can be analyzed on the basis of scaling relationships: ρxy(B) ∼ [ρxx(B)]β. For the totality of the investigated single-crystal films of Nd2-xCexCuO4+δ/SrTiO3 the values of β from 0.8 to 1.55 is found. The observed feature in the electron-doped two-dimensional systems can be associated both with a displaying of anisotropic s - wave or d - wave pairing symmetry and with a pinning due to an essential degree of disorder in the samples under study.

  1. High T(c) electron doped Ca10(Pt3As8)(Fe2As2)5 and Ca10(Pt4As8)(Fe2As2)5 superconductors with skutterudite intermediary layers.

    PubMed

    Ni, Ni; Allred, Jared M; Chan, Benny C; Cava, Robert Joseph

    2011-11-01

    It has been argued that the very high transition temperatures of the highest T(c) cuprate superconductors are facilitated by enhanced CuO(2) plane coupling through heavy metal oxide intermediary layers. Whether enhanced coupling through intermediary layers can also influence T(c) in the new high T(c) iron arsenide superconductors has never been tested due the lack of appropriate systems for study. Here we report the crystal structures and properties of two iron arsenide superconductors, Ca(10)(Pt(3)As(8))(Fe(2)As(2))(5) (the "10-3-8 phase") and Ca(10)(Pt(4)As(8))(Fe(2)As(2))(5) (the "10-4-8 phase"). Based on -Ca-(Pt(n)As(8))-Ca-Fe(2)As(2)- layer stacking, these are very similar compounds for which the most important differences lie in the structural and electronic characteristics of the intermediary platinum arsenide layers. Electron doping through partial substitution of Pt for Fe in the FeAs layers leads to T(c) of 11 K in the 10-3-8 phase and 26 K in the 10-4-8 phase. The often-cited empirical rule in the arsenide superconductor literature relating T(c) to As-Fe-As bond angles does not explain the observed differences in T(c) of the two phases; rather, comparison suggests the presence of stronger FeAs interlayer coupling in the 10-4-8 phase arising from the two-channel interlayer interactions and the metallic nature of its intermediary Pt(4)As(8) layer. The interlayer coupling is thus revealed as important in enhancing T(c) in the iron pnictide superconductors.

  2. Unusual isotope effects on the pseudogap in high-Tc cuprate superconductors as support for the BCS-like pairing theory of large polarons above Tc

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Baimatov, P. J.; Djumanov, Sh. S.

    2015-06-01

    The BCS-like pairing theory is extended to the intermediate coupling regime and to the cases of exotic cuprate superconductors with large and small Fermi surfaces, so as to describe the pairing correlations above Tc , the opening of a pseudogap (PG) at a mean-field temperature T∗ >Tc and the unusual isotope effects on the PG in these materials within the large polaron model and two different BCS-like approaches. We argue that unconventional electron-phonon interactions are responsible for the polaron formation and the separation between temperatures T∗ (the onset of precursor Cooper pairing) and Tc (the onset of the superconducting transition) in exotic cuprate superconductors. Using the extended BCS-like approaches, we calculate the PG formation temperature T∗ , isotope shifts ΔT∗ , oxygen and copper isotope exponents and show that isotope effects on the PG basically depend on strengths of Coulomb and electron-phonon interactions, doping levels and dielectric constants of the cuprates. The new BCS-like pairing theory of polaronic carriers predicts the existence of small and sizable positive oxygen isotope effect and very large negative oxygen and copper isotope effects on the PG in the cuprates with large Fermi surfaces. The calculated results for T∗ , isotope shifts and exponents are compared with experimental data on various cuprate superconductors. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also predict the existence of small and sizable negative isotope effects on T∗ in deeply underdoped cuprates with small Fermi surfaces. Further, we find that the isotope effects on T∗ (=Tc) in heavily overdoped cuprates just like in some metals are relatively small positive or become even negative.

  3. Model of the electronic structure of electron-doped iron-based superconductors: evidence for enhanced spin fluctuations by diagonal electron hopping.

    PubMed

    Suzuki, Katsuhiro; Usui, Hidetomo; Iimura, Soshi; Sato, Yoshiyasu; Matsuishi, Satoru; Hosono, Hideo; Kuroki, Kazuhiko

    2014-07-11

    We present a theoretical understanding of the superconducting phase diagram of the electron-doped iron pnictides. We show that, besides the Fermi surface nesting, a peculiar motion of electrons, where the next nearest neighbor (diagonal) hoppings between iron sites dominate over the nearest neighbor ones, plays an important role in the enhancement of the spin fluctuation and thus superconductivity. In the highest T(c) materials, the crossover between the Fermi surface nesting and this "prioritized diagonal motion" regime occurs smoothly with doping, while in relatively low T(c) materials, the two regimes are separated and therefore results in a double dome T(c) phase diagram. PMID:25062222

  4. 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.

  5. Energy Gaps in the Failed High-Tc Superconductor La_1.875Ba_0.125Cu_O4

    SciTech Connect

    Tanaka, K.

    2011-08-19

    A central issue on 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, while 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 (ARPES) 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-wave 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 which involves a possible precursor pairing energy scale around the node and another of different but unknown origin near the antinode.

  6. Energy Gaps in the Failed High-Tc Superconductor La_1.875Ba_0.125CuO_4

    SciTech Connect

    He, R.

    2010-05-04

    A central issue on 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, while 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 (ARPES) 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-wave 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 which involves a possible precursor pairing energy scale around the node and another of different but unknown origin near the antinode.

  7. 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].

  8. 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.

  9. 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.

  10. 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

  11. 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 .

  12. Nuclear magnetic resonance: Its role as a microscopic probe of the electronic and magnetic properties of High-{Tc} superconductors and related materials

    SciTech Connect

    Suh, Byoung Jin

    1995-12-27

    NMR experiments are reported for Sr{sub 2}CuO{sub 2}Cl{sub 2}, HgBa{sub 2}CuO{sub 4+d}, YNi{sub 2}B{sub 2}C and YBa{sub 2}Cu{sub 3}O{sub 7}. NMR studies typify three different aspects of microscopic properties of HTSC. In non-superconducting antiferromagnetic (AF) prototype Sr{sub 2}CuO{sub 2}Cl{sub 2}, we used NMR to investigate Cu{sup 2+} correlated spin dynamics and AF phase transition in CuO2 layers. In the superconductors, we used NMR both to investigate the electronic properties of the Fermi-liquid in normal and superconducting states and to investigate flux lattice and flux-line dynamics in the superconducting state in presence of magnetic field. A summary of each study is given: {sup 35}Cl NMR was measured in Sr{sub 2}CuO{sub 2}Cl{sub 2} single crystals with T{sub N}=257K. {sub 35}Cl NMR relaxation rates showed crossover of Cu{sup 2+} spin dynamics from Heisenberg to XY-like correlation at 290 K well above T{sub N}. A field-dependent T{sub N} for H{perpendicular}c was observed and explained by a field-induced Ising-like anisotropy in ab plane. {sup 199}Hg NMR was measured in HgBa{sub 2}CuO{sub 4+d}. Properties of the Fermi-liquid are characterized by a single-spin fluid picture and opening of a spin pseudo-gap at q=0 above {Tc}. Below {Tc}, spin component of Knight shift decreases rapidly in agreement with prediction for d-wave pairing scheme. {sup 11}B and {sup 89}Y NMR/magnetization were measured in YNi{sub 2}B{sub 2}C. Temperature dependence of {sup 11}B Knight shift and of the NSLR gave a normal state which agrees with the Korringa relation, indicating that the AF fluctuations on the Ni sublattice are negligible. Opening of the superconducting gap obeys BCS. A NMR approach to investigate vortex thermal motion in HTSC is presented, based on contribution of thermal flux-lines motion to both T{sub 2}{sup {minus}1} and T{sub 1}{sup {minus}1}. Effects are demonstrated in YBa{sub 2}Cu{sub 3}O{sub 7} and HgBa{sub 2}CuO{sub 4+d}.

  13. 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

  14. Enhancement of pairing interaction and magnetic fluctuations toward a band insulator in an electron-doped Li(x)ZrNCl Superconductor.

    PubMed

    Kasahara, Yuichi; Kishiume, Tsukasa; Takano, Takumi; Kobayashi, Katsuki; Matsuoka, Eiichi; Onodera, Hideya; Kuroki, Kazuhiko; Taguchi, Yasujiro; Iwasa, Yoshihiro

    2009-08-14

    The doping dependence of specific heat and magnetic susceptibility has been investigated for Li(x)ZrNCl superconductors derived from a band insulator. As the carrier concentration is decreased, the anisotropy of superconducting gap changes from highly anisotropic to almost isotropic. It was also found that, upon reducing carrier density, the superconducting coupling strength and the magnetic susceptibility are concomitantly enhanced in parallel with T(c), while the density of states at the Fermi level is kept almost constant. Theoretical calculations taking into account the on-site Coulomb interaction reproduced the experimental results, suggesting a possible pairing mediated by magnetic fluctuations, even in the doped band insulators. PMID:19792678

  15. Anisotropic flux pinning in high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Koleśnik, S.; Igalson, J.; Skośkiewicz, T.; Szymczak, R.; Baran, M.; Pytel, K.; Pytel, B.

    1995-02-01

    In this paper we present a comparison of the results of FC magnetization measurements on several PbSr(Y,Ca)CuO crystals representing various levels of flux pinning. The pinning centers in our crystals have been set up during the crystal growth process or introduced by neutron irradiation. Some possible explanations of the observed effects, including surface barrier, flux-center distribution and sample-shape effects, are discussed.

  16. Nonlinear Hall effect and Shubnikov-de Haas quantum oscillations in thin films of the electron doped superconductor Pr2 CuO4

    NASA Astrophysics Data System (ADS)

    Breznay, Nicholas; Nair, Nityan; Analytis, James; Zhu, Zengwei; Modic, Kimberly; McDonald, Ross

    2015-03-01

    Recent quantum oscillation studies in cuprate superconductors have allowed for considerable progress in understanding their Fermi surface topography. However, important questions remain about the influence of quantum criticality and competing orders, as well as the universality of these results; in particular quantum oscillation studies to date have been largely confined to a limited range of hole-doped bulk crystal systems. We have observed a field nonlinear Hall effect in superconducting thin films of the cuprate Pr2CuO4, and studied the temperature and magnetic field dependence of this behavior. The Hall effect data are consistent with a simple two-band transport model in this material, and we will interpret them in light of recently observed Shubnikov-de Haas quantum oscillations in these films.

  17. Quantum criticality in the electron doped cuprates

    NASA Astrophysics Data System (ADS)

    Dagan, Y.; Greene, R. L.

    2007-09-01

    We report transport measurements at low temperatures on the electron doped superconductor Pr 2- xCe xCuO 4- δ. Above a certain doping level we observe an abrupt change in the doping dependence of the Hall coefficient along with a significant change in the temperature dependence of the resistivity. At this doping the spin scattering channel in the magnetoresistance vanishes and the temperature dependence of the Hall angle changes. This suggests a quantum phase transition as a function of doping. This transition is most probably due to vanishing of an antiferromagnetic order persisting into the superconducting dome.

  18. Technical issues of a high-Tc superconducting bulk magnet

    NASA Astrophysics Data System (ADS)

    Fujimoto, Hiroyuki

    2000-06-01

    Superconducting magnets made of high-Tc superconductors are promising for industrial applications. It is well known that REBa2Cu3O7-x superconductors prepared by melt processes have a high critical current density, Jc, at 77 K and high magnetic fields. The materials are very promising for high magnetic field applications as a superconducting permanent/bulk magnet with liquid-nitrogen refrigeration. Light rare-earth (LRE) BaCuO bulks, compared with REBaCuO bulks, exhibit a larger Jc in high magnetic fields and a much improved irreversibility field, Hirr, at 77 K. In this study, we discuss technical issues of a high-Tc superconducting bulk magnet, namely the aspects of the melt processing for bulk superconductors, their characteristic superconducting properties and mechanical properties, and trapped field properties of a superconducting bulk magnet. One of the possible applications is a superconducting bulk magnet for the magnetically levitated (Maglev) train in the future.

  19. Transition from three-dimensional anisotropic spin excitations to two-dimensional spin excitations by electron doping the FeAs-based BaFe1.96Ni0.04As2 superconductor.

    PubMed

    Harriger, Leland W; Schneidewind, Astrid; Li, Shiliang; Zhao, Jun; Li, Zhengcai; Lu, Wei; Dong, Xiaoli; Zhou, Fang; Zhao, Zhongxian; Hu, Jiangping; Dai, Pengcheng

    2009-08-21

    We use neutron scattering to study the effect of electron doping on the structural or magnetic order in BaFe2As2. In the undoped state, BaFe2As2 exhibits simultaneous structural and magnetic phase transitions below 143 K. Upon electron doping to form BaFe1.96Ni0.04As2, the system first displays the lattice distortion near approximately 97 K, and then orders antiferromagnetically at 91 K before developing weak superconductivity below approximately 15 K. The effect of electron doping is to reduce the c-axis exchange coupling in BaFe2As2 and induce quasi-two-dimensional (2D) spin excitations. These results suggest that the transition from 3D spin waves to quasi-2D spin excitations by electron doping is important for the separated structural and magnetic phase transitions in iron arsenides.

  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. 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.

  2. High Tc thin film and device development

    SciTech Connect

    Betts, K.; Burbank, M.B.; Cragg, A.; Fife, A.A.; Kubik, P.R.; Lee, S.; Chaklader, A.C.D.; Roemer, G.; Heinrich, B.; Chrzanowski, J.

    1989-03-01

    Thin films of the high Tc superconductor YBa/sub 2/Cu/sub 3/O/sub y/ have been deposited on various substrates by diode and magnetron sputtering using bulk sintered targets. These films have been analyzed by a variety of methods - SEM, X-rays, Electron Beam Microprobe, Mass Spectrometry and Raman Spectroscopy. The stoichiometries of the films have been measured as a function of the radial position from the centre of the sputtered beam at a fixed target-substrate distance. Patterning of the films has been carried out to form planar structures such as strip lines, microbridges and RF SQUIDs. DC current-voltage characteristics of the microbridges were measured as a function of temperature. RF SQUID behaviour has been observed for single loop devices and their properties established at 4.2 K and higher temperatures. Flux locked noise spectra with a 1/f noise power response were recorded in the frequency range 0.01 to approx.100 Hz. RF SQUID signals have been observed for temperatures up to 55 K.

  3. Direct observation of intrinsic Josephson junction characteristics in electron-doped Sm2-xCexCuO4-δ

    NASA Astrophysics Data System (ADS)

    Kawakami, Tsuyoshi; Suzuki, Minoru

    2007-10-01

    We have investigated the current-voltage (CV) characteristics of the intrinsic Josephson junctions (IJJs) in the electron-doped high- Tc superconductor Sm2-xCexCuO4-δ by using a small mesa structure fabricated on a single crystal surface. It is found that multiple resistive branches, i.e., typical IJJ characteristics, are observed in the CV characteristics when the junction area of a mesa is 10μm2 or less. It is also found that a typical Josephson critical current density Jc is 7.5kA/cm2 at 4.2K for Tc=20.7K . The Josephson penetration depth is experimentally estimated to be 1.0-1.6μm from the size dependence of Jc . Both Jc and Tc are found to decrease with the carrier doping level, as is found for hole-doped Bi2Sr2CaCu2O8+δ in the heavily overdoped region. These results are discussed in relation to the current locking in terms of the coupled Josephson junction stack model.

  4. 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

  5. Applications using high-Tc superconducting terahertz emitters.

    PubMed

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

    2016-03-17

    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.

  6. 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.

  7. High- Tc superconductivity: new issues from photoemission data

    NASA Astrophysics Data System (ADS)

    Margaritondo, G.; Grioni, M.; Vobornik, I.; Pavuna, D.

    2001-11-01

    Recent high-resolution photoemission results on high- Tc superconductors and other low-dimensional systems solve some critical issues but also open new fundamental questions. A recent breakthrough enabled us to clarify the interplay of conflicting periodicities in photoemission data, thus legitimizing the photoemission analysis of crystals with super-periodicities. On the other hand, results on the role of doping and of intentional disorder in Bi 2Sr 2CaCu 2O 8+ x single crystals raise questions about the origin of the pseudogap.

  8. 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}.

  9. 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.

  10. Predicted Mechanical Behavior of High-Tc Superconducting Ceramic Films

    NASA Astrophysics Data System (ADS)

    Suhir, Ephraim

    1990-03-01

    In potential applications, the recently discovered high transition temperature (high-Tc) ceramic superconductors (Bednorz and Muller, 1986, Wu et al., 1987, Cava et al., 1987) may experience large mechanical stresses and strains. These can be imposed by magnet fabrication, high magnetic fields, and, in the case of superconducting films, also by thermal contraction mismatch with the substrate material (see, for instance, Baynham, 1988, Severin and de With, 1988). Although mechanical strength of a superconductor may appear to be not as important a property, as, say, high superconducting transition temperature, high upper critical magnetic field or high critical current density, it may play a decisive role, when a superconducting material is used for practical purposes. Since ceramics are brittle materials, and break quite easily when stretched, bent or hit, use of ceramics as practical superconductors requires that they possess high ultimate stress and strain, sufficient fracture toughness and good shock resistance. It is also important that the actual stresses and strains arising in superconducting ceramics at low temperatures can be predicted and, if possible, minimized.

  11. Defect-Induced Changes in the Spectral Properties of HIGH-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Vobornik, I.; Berger, H.; Rullier-Albenque, F.; Margaritondo, G.; Pavuna, D.; Grioni, L. Forroand M.

    Superconductivity in high-Tc cuprates is particularly sensitive to disorder due to the unconventional d-wave pairing symmetry. We investigated effects of disorder on the spectral properties of Bi2Sr2CaCu2O8+x high-Tc superconductor. We found that already small defect densities suppress the characteristic spectral signature of the superconducting state. The spectral line shape clearly reflects new excitations within the gap, as expected for defect-induced pair breaking. At the lowest defect concentrations the normal state remains unaffected, while increased disorder leads to suppression of the normal quasiparticle peaks.

  12. High Tc superconductivity; Thin films and applications; Proceedings of the Meeting, San Diego, CA, Mar. 20, 21, 1990

    NASA Astrophysics Data System (ADS)

    Chi, Cheng-Chung; van Dover, R. Bruce

    Various papers on high-Tc superconductivity in thin films and applications are presented. Individual topics addressed include: preparation of high-Tc YBa2Cu3O(7-x) thin films, study of epitaxial YBa2Cu3O(x) films, electrochemical deposition of high-Tc superconducting thin films, relative surface stoichiometry of high-Tc materials by total reflection X-ray fluorescence, preparation and properties YBa2Cu3O(7-x) thin-film SQUIDs, Si-coupled superconducting FETs using microfabrication technologies, enhanced critical currents by high-pressure impregnation of 1-2-3 systems with normal conductors. Also discussed are: YBaCuO thin films used as electrical switch or current limiter, optically triggered switching of superconducting YBa2Cu3O7 thin films, high-Tc superconducting thin films as optical radiation detectors, MBE as a path to novel high-Tc superconductors, ion-beam codeposition of HTSC films on SrTiO3 and ITO/Si, plasma luminescence spectroscopy for sputtering growth of high-Tc superconductors, barium diffusion in metalloorganic solution deposited barrier layers and Y1Ba2Cu3O(7-x) films.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Magnetic measurement of RF-induced flux lattice annealing (RIFLA) in the electron-doped superconductor Pr1.85Ce0.15CuO4-y.

    NASA Astrophysics Data System (ADS)

    Clark, W. G.; Gaidos, G.; Wu, G.; Brown, S. E.; Greene, R. L.; Balci, H.

    2007-03-01

    A strained flux lattice (FL) in a superconductor (SC) can be annealed to a lower free energy by the RF-field used to generate an NMR spin-echo signal [W.G. Clark et al., J. Phys. IV Proceedings 9, Pr10-49-52 (1999)]. Here, we report the change in the rf magnetic susceptibility (χ) in the SC phase of a single crystal of Pr1.85Ce0.15CuO4-y with a strained FL by successive RIFLA pulses. The distorted FL is prepared by rotating the sample through a small angle in a magnetic field well below the SC transition temperature, leaving the FL pinned in a non-equilibrium configuration. RIFLA pulses then reduce χ, which is measured by the change in the inductance of a coil surrounding the sample using an NMR probe and spectrometer. The interpretation is that shaking the FL by the RF pulses progressively anneals it to a lower free energy configuration, which has a smaller χ. These measurements provide a very sensitive measure of the RIFLA effect. Work at UCLA was supported by NSF Grants DMR-0334869 (WGC) and DMR-0520552 (SEB).

  2. High- Tc thin-film magnetometer

    SciTech Connect

    Miklich, A.H.; Wellstood, F.C.; Kingston, J.J.; Clarke, J. ); Colclough, M.S. ); Cardona, A.H.; Bourne, L.C.; Olson, W.L.; Eddy, M.M. )

    1990-09-01

    We have constructed and tested high-{Tc} magnetometers by coupling a high-{Tc} thin-film Superconducting QUantum Interference Device (SQUID) to two different high-{Tc} thin-film flux transformers. The SQUID was made from Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub 8+y} films grown on MgO, with junctions consisting of native grain boundaries. The flux transformers were made from YBa{sub 2}Cu{sub 3}O{sub 7-x}, and each had 10-turn input coils and a single-turn pickup loop. The first transformer, which was patterned with a combination of shadow masks and photolithography, yielded a magnetic field gain of about {minus}7.5, functioned up to 79 K, and gave a magnetic field sensitivity B{sub N} (10 Hz) {approx} 3.1 pT Hz{sup {minus}1/2}at 38 K. The second transformer, which was patterned entirely by photolithography, yielded a gain of about {minus}8.7, functioned up to 25 K, and had a sensitivity B{sub N} (10 Hz) {approx} 3.5 pT Hz{sup {minus}1/2} at 4.2 K. In both cases, the limiting noise arose in the SQUID. 10 refs., 5 figs., 1 tab.

  3. Direct observation of a Fermi liquid-like normal state in an iron-pnictide superconductor.

    PubMed

    Tytarenko, Alona; Huang, Yingkai; de Visser, Anne; Johnston, Steve; van Heumen, Erik

    2015-01-01

    There are two prerequisites for understanding high-temperature (high-Tc) superconductivity: identifying the pairing interaction and obtaining a correct description of the normal state from which superconductivity emerges. The nature of the normal state of iron-pnictide superconductors, and the role played by correlations arising from partially screened interactions, are still under debate. Here we show that the normal state of carefully annealed electron-doped BaFe(2-x)Co(x)As2 at low temperatures has all the hallmark properties of a local Fermi liquid, with a more incoherent state emerging at elevated temperatures, an identification made possible using bulk-sensitive optical spectroscopy with high frequency and temperature resolution. The frequency dependent scattering rate extracted from the optical conductivity deviates from the expected scaling M2 (ω, T) ∝ (ħω)(2) + (pπkBT)(2) with p ≈ 1.47 rather than p = 2, indicative of the presence of residual elastic resonant scattering. Excellent agreement between the experimental results and theoretical modeling allows us to extract the characteristic Fermi liquid scale T0 ≈ 1700 K. Our results show that the electron-doped iron-pnictides should be regarded as weakly correlated Fermi liquids with a weak mass enhancement resulting from residual electron-electron scattering from thermally excited quasi-particles. PMID:26201499

  4. Local fields in high- Tc materials

    NASA Astrophysics Data System (ADS)

    Tarrio, C.; Benitez, E. L.; Schnatterly, S. E.

    1992-04-01

    Most high-temperature superconductors exhibit two-dimensional conductance; therefore the conduction electrons are localized in the third dimension, and experience the local electric field rather than the macroscopic applied field in that direction. We report model calculations which indicate that the local field leads to enhanced electron-phonon coupling in these materials which may play a role in determining the high transition temperatures.

  5. First-principles studies for understanding diverse high- Tc

    NASA Astrophysics Data System (ADS)

    Cheng, Hai-Ping

    2011-03-01

    In this talk, I survey results and insights gained from first-principles calculations on materials that exhibit superconducting behavior at temperatures higher than those characteristic of conventional BCS superconductors. These range from highly correlated cuprate Mott insulators as represented by the bismuth-strontium-calcium-copper-oxides (BSCCOs) to border-line itinerant-Mott systems such as the recently discovered 1111 and 122 pnictides. ultimate goal of our studies is to correlate Tc with specific material composition using detailed first-principles calculations in conjunction with many-body physics techniques via the critical step of constructing real-materials model Hamiltonians. By manipulating impurity doping, which plays a crucial role in the phase diagrams of high Tc materials, we hope to find guidance for designing candidate systems with Tc higher than ones currently known. BSCCO material, density functional calculations using a good generalized-gradient approximation (GGA) yield structural information that is correlated to the experimentally observed (STM) super-modulation and impurity peak in the high energy regime (~ 1 eV), even though the Kohn-Sham bands from such functionals fail to have a band gap. For FeAs-based high-Tc systems, DFT band-structure calculations provide a very good starting point for constructing model Hamiltonians for studies of spin fluctuation and electron pairing mechanisms. Fermi sheets that have been constructed using Wannier transformed Kohn-Sham states have provided critical information for understanding this family of superconducting materials. Analysis of the details of magnetic ordering, density of states, and 2D vs. 3D features in both the 1111 and 122 materials have been valuable in understanding sometimes perplexing experimental findings. Effects of Co impurities have been studied and fully analyzed as well., I will discuss persistent challenges related to calculations on the structure of the non-magnetic state Ba 1

  6. 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'.

  7. 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'. PMID:27501971

  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. Superconductor as movie star

    SciTech Connect

    Pool, R.

    1993-12-03

    Japanese researchers have succeeded in producing a movie of changes in the magnetic flux lattice of a high-Tc superconductor as it is warmed. They used a technique called electron holography, in which electrons are passed through a superconductor, and flux lines are visualized as interference patterns induced by the electrons as they undergo a phase change as they pass to one side or another of the flux lines. The technique will have application in designing superconductors so that they do not lose their superconductivity when exposed to magnetic fields.

  10. Predicting Unconventional High-Temperature Superconductors in Trigonal Bipyramidal Coordinations

    NASA Astrophysics Data System (ADS)

    Hu, Jiangping; Le, Congcong; Wu, Xianxin

    2015-10-01

    Cuprates and iron-based superconductors are two classes of unconventional high-Tc superconductors based on 3 d transition elements. Recently, two principles, the correspondence principle and the magnetic selective pairing rule, have emerged to unify their high-Tc superconducting mechanisms. These principles strongly regulate electronic structures that can host high-Tc superconductivity. Guided by these principles, here, we propose high-Tc superconducting candidates that are formed by cation-anion trigonal bipyramidal complexes with a d7 filling configuration on the cation ions. Their superconducting states are expected to be dominated by the dx y±i dx2-y2 pairing symmetry.

  11. Dirty Superconductivity in the Electron-Doped Cuprate Pr2-xCexCuO4-δ: Tunneling Study

    NASA Astrophysics Data System (ADS)

    Dagan, Y.; Beck, R.; Greene, R. L.

    2007-10-01

    We report a tunneling study between Pr2-xCexCuO4-δ and lead as a function of doping, temperature, and magnetic field. The temperature dependence of the gap follows the BCS prediction. Our data fit a nonmonotonic d-wave order parameter for the whole doping range studied. From our data we are able to conclude that the electron-doped cuprate Pr2-xCexCuO4-δ is a weak-coupling BCS dirty superconductor.

  12. 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

  13. 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.

  14. Doping and temperature dependence of the superconducting energy gap in the electron-doped cuprate Pr2-xCexCuO4-δ

    NASA Astrophysics Data System (ADS)

    Diamant, I.; Greene, R. L.; Dagan, Y.

    2010-12-01

    In hole-doped cuprate superconductors at low carrier concentrations two energy scales are identified: the superconducting energy gap and the pseudogap. The relation between these energy scales is still a puzzle. In these compounds a measurement of the energy gap is not necessarily a probe of the order parameter. In the electron-doped cuprates the pseudogap does not obscure the superconducting state. Consequently, the superconducting gap can be studied directly in a tunneling experiment. Here we show that by studying superconductor/insulator/superconductor planar tunnel junctions we are able to map the behavior of the gap amplitude for the entire (doping-temperature) phase diagram of the electron-doped cuprate superconductor Pr2-xCexCuO4-δ. The superconducting gap, Δ, shows a BCS-like temperature dependence even for extremely low carrier concentrations. Moreover, Δ follows the doping dependence of Tc. We can therefore conclude that there is a single superconducting energy scale in the electron-doped cuprates.

  15. 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 .

  16. 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

  17. 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

    2016-01-01

    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

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

    DOE PAGES

    Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C. -T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; et al

    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

  19. 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.

  20. 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

    2016-01-01

    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.

  1. Imaging of local temperature distributions in mesas of high-Tc superconducting terahertz sources

    NASA Astrophysics Data System (ADS)

    Tsujimoto, M.; Kambara, H.; Maeda, Y.; Yoshioka, Y.; Nakagawa, Y.; Kakeya, I.

    2014-12-01

    Stacks of intrinsic Josephson junctions in high-Tc superconductors are a promising source of intense, continuous, and monochromatic terahertz waves. In this paer, we establish a fluorescence-based temperature imaging system to directly image the surface temperature on a Bi2Sr2CaCu2O8+δ mesa sample. Intense terahertz emissions are observed in both high- and low-bias regimes, where the mesa voltage satisfies the cavity resonance condition. In the high- bias regime, the temperature distributions are shown to be inhomogeneous with a considerable temperature rise. In contrast, in the low-bias regime, the distributions are rather uniform and the local temperature is close to the bath temperature over the entire sample.

  2. Preparation and transport properties of high-Tc superconducting thick films

    NASA Astrophysics Data System (ADS)

    Aponte, J. M.; Octavio, M.

    1989-08-01

    We have prepared thick films of high Tc superconductors on a variety of substrates: SrTiO3, BeO, Zr(Ca)O2, alumina, and sapphire. The powder of the YBa2Cu3O7-δ compound is mixed with an organic solvent and painted on the substrates. The films are then dried and fired. We have studied the effect of the substrate and of the firing temperature on the superconducting properties of the films. We found an optimum firing temperature of 990 °C. The films prepared are superconducting with Tc (R=0) as high as 82 K. We discuss the shape of the resistance-versus-temperature curves as well as the temperature dependence of the critical currents of these films.

  3. Dynamic Jahn-Teller Coupling, Anharmonic Oxygen Vibrations and HIGH-Tc Superconductivity in Oxides

    NASA Astrophysics Data System (ADS)

    Johnson, K. H.; Clougherty, D. P.; McHenry, M. E.

    A universal dynamic Jahn-Teller (DJT) mechanism for superconductivity and its applications to CuO and BaBiO3 high-Tc oxides are reviewed. Dynamical interconversion between the shallow "double-well" potentials of degenerate delocalized oxygen-oxygen "pπ-bonds" at the Fermi energy (EF) induces anharmonic oxygen vibrations, lattice-electron coupling, and Cooper pairing. This mechanism yields high Tc's and small-to-vanishing isotope shifts for cuprates, where O(pπ)-O(pπ) bond overlap at EF is promoted by Cu(dπ*)-O(pπ) hybridization. It yields lower Tc's and larger isotope shifts for BaBiO3's, where O(pπ)-O(pπ) overlap is small. For vanishing bond overlap at EF, DJT coupling reduces to harmonic phonon coupling in BCS theory. Simple formulae for calculating Tc and isotope shifts for any superconductor from the "real-space" chemical bonding at EF are presented, yielding (Tc)max ≈ 230 K.

  4. Levitation performance of the magnetized bulk high- Tc superconducting magnet with different trapped fields

    NASA Astrophysics Data System (ADS)

    Liu, W.; Wang, J. S.; Liao, X. L.; Zheng, S. J.; Ma, G. T.; Zheng, J.; Wang, S. Y.

    2011-03-01

    To a high- Tc superconducting (HTS) maglev system which needs large levitation force density, the magnetized bulk high- Tc superconductor (HTSC) magnet is a good candidate because it can supply additional repulsive or attractive force above a permanent magnet guideway (PMG). Because the induced supercurrent within a magnetized bulk HTSC is the key parameter for the levitation performance, and it is sensitive to the magnetizing process and field, so the magnetized bulk HTSC magnets with different magnetizing processes had various levitation performances, not only the force magnitude, but also its force relaxation characteristics. Furthermore, the distribution and configuration of the induced supercurrent are also important factor to decide the levitation performance, especially the force relaxation characteristics. This article experimentally investigates the influences of different magnetizing processes and trapped fields on the levitation performance of a magnetized bulk HTSC magnet with smaller size than the magnetic inter-pole distance of PMG, and the obtained results are qualitatively analyzed by the Critical State Model. The test results and analyses of this article are useful for the suitable choice and optimal design of magnetized bulk HTSC magnets.

  5. Operation of high- Tc SFQ devices at near liquid nitrogen temperature

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Kang, J. H.; Lee, J. M.; Hahn, T. S.; Choi, S. S.; Park, S. J.

    1997-02-01

    As the operating temperature of the SFQ logic circuits gets higher by using high- Tc superconductors, the effect of noise on switching a Josephson junction to the voltage state becomes more important. In this paper, we report our work on high- Tc SFQ RS flip-flop which was made with YBCO thin film deposited on a SrTiO 3 bi-crystal. The circuit operated correctly at 71 K over the 200 computer-generated clock cycles without making errors, where a reset or a set operation was made over one clock cycle. Good agreement between the measured data and the calculation based on the thermal activation theory was obtained. The effective noise temperature used to fit the data was much higher than the physical temperature. This could be due to the instrument noise. Improvement in the measurement set-up might reduce the effective noise temperature. Also our measurement results indicate that the elevation of the operating temperature near the liquid nitrogen temperature may not affect the margin of the circuit.

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

    PubMed

    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

    2016-08-01

    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-x Ce x CuO4 and Nd2-x Ce x CuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2-x Ce x CuO4 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

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

    PubMed

    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

    2016-08-01

    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-x Ce x CuO4 and Nd2-x Ce x CuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2-x Ce x CuO4 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.

  8. Analysis of mid-infrared optical conductivity in electron-doped cuprates

    NASA Astrophysics Data System (ADS)

    Varshney, Dinesh; Patel, G. S.; Singh, R. K.

    2003-05-01

    Observed frequency dependent optical conductivity sigma(omega) of electron-doped cuprate Nd1.85Ce0.15CuO4-delta (delta approx 0.02, Tc approx 25 K) superconductors has been theoretically analysed. Starting from an effective two-dimensional (2D) interaction potential for superlattice of electron-doped cuprates treated as a layered electron gas, the spectral function is developed. Calculations of sigma(omega) have been made within the two component scheme: one is the coherent Drude carriers responsible for superconductivity and the other is incoherent motion of carriers from one site to the other that leads to a pairing between Drude carriers. The approach accounts for the anomalies observed (frequency dependence of optical conductivity) in the optical measurements for the normal state. Estimating the effective mass from specific heat measurement and varepsiloninfty from band structure calculations for the low-energy charge density waves, the model has only one free parameter, the relaxation rate. The frequency dependent relaxation rates are expressed in terms of memory functions, and the coherent Drude carriers from the effective interaction potential lead to a sharp peak at zero frequency and a long tail at higher frequencies, i.e. in the infrared region, while the hopping of carriers from one site to the other (incoherent motion of doped carriers) yields a peak value in the optical conductivity centred at mid-infrared region. We find that both the Drude and hopping carriers in the superlattice of electron-doped cuprates will contribute to the optical process of conduction in the CuO2 planes and show similar results on optical conductivity in the mid-infrared as well as infrared frequency regions as those revealed from experiments.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. The specific heat of the electron-doped La-1038 compound (Ca0.85La0.15)10(FeAs)10(Pt3As8).

    PubMed

    Kim, J S; Stürzer, T; Johrendt, D; Stewart, G R

    2013-04-01

    The specific heat of polycrystalline (Ca0.85La0.15)10(FeAs)10(Pt3As8), an electron-doped iron-based superconductor (T(c)(onset) = 34.6 K) with Ca/La ions and Pt3As8 separating the FeAs layers, was measured between 0.4 and 48 K.This compound has been recently reported to represent an electron-doped variant of the non-superconducting 10-3-8 phase, featuring a superconducting transition in the range of that of the 10-4-8 phase. This family of compounds is unique among the iron pnictide superconductors discovered to date due to the second metal pnictide layer, Pt3As8, present in the structure competing with the familiar FeAs layer for the electron from the Ca/La. This superconductor is further unusual in that it has a rather low crystalline symmetry (triclinic) for such a high superconducting transition temperature. The specific heat γ is found to be approximately 26 mJ/(Ca/La mol)K(2), comparable to 122 iron-based superconductors electron-doped on the Fe sites and a factor of two smaller than 122 compounds hole-doped on the cation site, e.g., Ba(1-x)K(x)Fe2As2. The present work also investigates the discontinuity in the specific heat at T(c), ΔC, to compare with the global trend, established by Bud'ko, Ni and Canfield (BNC), of ΔC/T(c) versus T(c) found for essentially all iron-based superconductors. The result is a value lower than the BNC trend by a factor of ten, consistent with a severely broadened superconducting transition.

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

    PubMed

    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

  15. 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.

  16. 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

  17. The phase diagram of electron-doped La2-xCexCuO4-δ

    NASA Astrophysics Data System (ADS)

    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.

    2015-01-01

    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 La2-xCexCuO4-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.

  18. Infrared detection with high-{Tc} bolometers and response of Nb tunnel junctions to picosecond voltage pulses

    SciTech Connect

    Verghese, S.

    1993-05-01

    Oxide superconductors with high critical temperature {Tc} make sensitive thermometers for several types of infrared bolometers. The authors built composite bolometers with YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} thermometers on sapphire substrates which have higher sensitivity than competing thermal detectors which operate at temperatures above 77 K. A 1 x 1 mm bolometer with gold black serving as the radiation absorber has useful sensitivity for wavelengths 20--100 {mu}m. A 3 x 3 mm bolometer with a bismuth film as the absorber operates from 20--100 {mu}m. High-{Tc} bolometers which are fabricated with micromachining techniques on membranes of Si or Si{sub 3}N{sub 4} have potential application to large-format arrays which are used for infrared imaging. A nonisothermal high-{Tc} bolometer can be fabricated on a membrane of yttria-stabilized zirconia (YSZ) which is in thermal contact with the heat sink along the perimeter of the membrane. A thermal analysis indicates that the YSZ membrane bolometer can have improved sensitivity compared to the sapphire bolometer for spectrometer applications. The quasiparticle tunneling current in a superconductor-insulator-superconductor (SIS) junction is highly nonlinear in the applied voltage. The authors have made the first measurement of the linear response of the quasiparticle current in a Nb/AlO{sub x}/Nb junction over a broad bandwidth from 75--200 GHz. Nonlinear measurements made with these pulses may provide information about the quasiparticle lifetime. Preliminary data from such measurements are presented.

  19. 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

  20. From quantum oscillations to charge order in high-Tc copper oxides in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Vignolle, Baptiste; Vignolles, David; Julien, Marc-Henri; Proust, Cyril

    2013-01-01

    This article constitutes an update made of numerous elements from an article by Vignolle et al. [C. R. Phys. 12 (2011) 446] published in the issue of C. R. Physique dedicated to superconductivity. By including this article to the present issue on physics in high magnetic field, we have aimed, in agreement with the editorial board of the review, offering a complete issue and also reporting on the last developments in the study of superconductors in high field. We review how experiments in very high magnetic fields over the last five years have given a new twist to the understanding of the normal state of hole-doped cuprate superconductors. The discovery of quantum oscillations in underdoped YBa2Cu3Oy and overdoped Tl2Ba2CuO6 + δ has proven the existence of a Fermi surface across the whole phase diagram, which had been a controversial issue for more than twenty years. However, the striking difference in oscillation frequency for the two compounds has revealed a very different Fermi surface topology. The observation of negative Hall and Seebeck coefficients in the underdoped materials has shown that the large hole-like Fermi surface of overdoped materials undergoes a reconstruction in the high field and low temperature limits for which quantum oscillation can be observed. This has been interpreted as evidence for a translational symmetry breaking due to some form of electronic (spin, charge, or orbital current) order. The angular dependence of the quantum oscillations has constrained the source of the Fermi-surface reconstruction to something other than a spin-density wave with moments perpendicular to the field. Finally, nuclear magnetic resonance studies have revealed that it is actually charge order, without spin order, which is induced in the copper oxide planes as soon as superconductivity is sufficiently weakened by the magnetic field. The results suggest that there is a generic competition between superconductivity and a charge-density-wave instability in high

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Underlying mechanisms of pseudogap phenomena and Bose-liquid superconductivity in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Karimboev, E. X.; Djumanov, Sh. S.

    2016-06-01

    We show that the high-Tc cuprates are non-BCS superconductors exhibiting distinct pseudogap (PG) behaviors (related to real and momentum space excitations) and other anomalies above Tc, novel Bose-liquid superconductivity below Tc, and also a λ-like superconducting (SC) transition at Tc similar to the λ transition in liquid 4He. In these materials, the relevant charge carriers are polarons which are bound into bosonic Cooper pairs above Tc followed by condensing into a Bose superfluid at Tc. We found that the polaronic effects and related PG weaken with increasing of the doping level and disappear in the overdoped region, where the crossover from Bose-liquid to Fermi-liquid (BCS-type) superconductivity occurs at the quantum critical point. We identify the real phase diagrams of the cuprates, the PG and vortex-like states above Tc, the novel SC state and two distinct SC phases below Tc like two superfluid phases of 3He, and explain the rich cuprate phenomenology from lightly doped to overdoped region.

  7. 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.

  8. 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.

  9. Tunable topological states in electron-doped HTT-Pt

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Wang, Zhenhai; Zhao, Mingwen; Liu, Feng

    2016-04-01

    Modulating topologically nontrivial states in trivial materials is of both scientific and technological interest. Using first-principles calculations, we propose a demonstration of electron-doping- (or gate-voltage-) induced multiple quantum states; namely, quantum spin Hall (QSH) and quantum anomalous Hall (QAH) states, in a single material of the organometallic framework (HTT-Pt) synthesized from triphenylene hexathiol molecules (HTT) and PtC l2 . At a low doping level, the trivial HTT-Pt converts to a QSH insulator protected by time-reversal symmetry (TRS). When the electronic doping concentration is further increased, TRS will be broken, making the HTT-Pt a QAH insulator. The band gaps of these topologically nontrivial states can be as large as 42.5 meV, suggesting robustness at high temperatures. The possibility of switching between the QSH and QAH states offers an intriguing platform for a different device paradigm by interfacing between QSH and QAH states.

  10. 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.

  11. Polytypoids in high Tc thallium based superconducting materials

    SciTech Connect

    Singh, A.K. ); Imam, M.A.; Sadananda, K.; Qadri, S.B.; Skelton, E.F.; Osofsky, M.S.; Le Tourneau, V.; Gubser, D.U. )

    1990-08-01

    Several high {Tc} compounds containing Tl (thallium) were prepared starting from different initial compositions. Superconducting properties and the structure were determined for each sample. Electron diffraction and transmission electron microscopy showed the existence of polytypic high {ital T}{sub {ital c}} compounds with the same {ital a}- and {ital b}-axes but different {ital c}-axis values. The {ital c}-axis appears to increase approximately in integral multiples of 0.15 nm with varying composition could be associated with the insertion of Cu-Ca or Cu-Tl layers in each unit cell. Several random stacking faults were also noted which give rise to diffuse streaking in the electron diffraction pattern.

  12. 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.

  13. 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.

  14. 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.

  15. Terahertz wave emission from intrinsic Josephson junctions in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Ozyuzer, L.; Simsek, Y.; Koseoglu, H.; Turkoglu, F.; Kurter, C.; Welp, U.; Koshelev, A. E.; Gray, K. E.; Kwok, W. K.; Yamamoto, T.; Kadowaki, K.; Koval, Y.; Wang, H. B.; Müller, P.

    2009-11-01

    Recently, we experimentally demonstrated that rectangular mesa structures of intrinsic Josephson junctions (IJJ) in Bi2Sr2CaCu2O8+d (Bi2212) can be used as a compact solid-state generator of continuous, coherent and polarized terahertz (THz) radiation. In the present work, we will exhibit tall mesas (over 600 junctions) which were fabricated using UV lithography, e-beam lithography with photoresist and e-beam lithography with a Ti selective etching technique. We will present measurements of the c-axis resistance as a function of temperature and of current-voltage characteristics of THz emitting mesas with lateral sizes ranging from 30 × 300 to 100 × 300 µm2. Furthermore, we will discuss the dependence of the characteristics of the mesa structures on the oxygen doping level of the Bi2212 crystals. We will also experimentally show that the voltage-frequency relation of the ac Josephson effect has to match the cavity resonance for successful emission.

  16. First principles investigation of electronic structures and hyperfine properties of semiconductors and high-[Tc] superconductors

    SciTech Connect

    Sulaiman, S.B.

    1992-01-01

    The first principles Unrestricted Hartree-Fock Cluster procedure has been applied to investigate the electronic structures and associated hyperfine properties of several categories for solid systems. The first category is concerned with the location and nuclear quadrupole interactions (NQI) of fluorine impurity centers in crystalline silicon (c-Si). The Time Differential Perturbed Angular Distribution experiments show that when excited nuclear static fluorine ([sup 19]F*) is implanted into c-Si, two [sup 19]F* centers are formed characterized by two unique axially symmetric electric field gradients (efg). Models have been examined to determine the stable [sup 19]F* sites in the bulk c-Si. The two models, IB and AB, are also able to explain the experimental [sup 19]F* NQI data in crystalline germanium where two centers with axially symmetric efg are observed. The experimental trends of [sup 19]F* NQI are well reproduced by the investigation using the IB and AB models. The second category of the systems investigated deals with the NQI and magnetic hyperfine interaction of [sup 63]Cu in La[sub 2]CuO[sub 4] and YBa[sub 2]Cu[sub 3]O[sub 6] as well as the NQI of [sup 139]La and [sup 135]Ba in the former and the latter compounds respectively. In the third category, the author investigates the possible stable sites of the Muon Spin Rotation ([mu]SR) probe atom, positive muon ([mu][sup +]) in La[sub 2]CuO[sub 4], and the hyperfine field (H[sub hyp]) at [mu][sup +] site in the antiferromagnetic phase of the system. The most stable [mu][sup +] site is at (0.121a, 0.0, 0.110c) of the tetragonal La[sub 2]CuO[sub 4] unit cell. The value of H[sub hyp] at this site is in reasonable order of magnitude with the observed one.

  17. 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.

  18. 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.

  19. Lilienfeld Prize Recipient: Numerical Computations and the Physics of the High Tc Superconductors

    NASA Astrophysics Data System (ADS)

    Scalapino, Douglas J.

    1998-04-01

    Numerical calculations provided early evidence for d_x^2-y^2 pairing in various models believed to embody the basic physics characteristic of the high transition temperature superconducting cuperates. Here we will review this focusing on what these studies tells us about the mechanism which is responsible for high temperature superconductivity.

  20. Low-frequency noise in high-{Tc} superconductor Josephson junctions, SQUIDs, and magnetometers

    SciTech Connect

    Miklich, A.H.

    1994-05-01

    Design and performance of high-T{sub c} dc superconducting quantum interference devices (SQUEDs), junctions that comprise them, and magnetometers made from them are described, with attention to sources of 1/f noise. Biepitaxial junctions are found to have large levels of critical current fluctuations which make them unsuitable for low-noise SQUIDS; this suggests a poorly connected interface at the grain boundary junction. SQUIDs from bicrystal junctions have levels of critical current noise controllable using bias current reversal techniques which leave the noise white down to frequencies of a few Hz. A SQUID with an energy resolution of 1.5{times}10{sup {minus}30} J Hz{sup {minus}1} at 1 Hz is reported. Magnetometers in which a (9 mm){sup 2} pickup loop is directly coupled to a SQUID body have achieved field resolutions of 93 fT Hz{sup {minus}1/2} down to frequencies below I Hz, improving to 39 fT Hz{sup {minus}1/2} at 1 Hz with the addition of a 50mm-diameter single-turn flux transformer. Poor coupling to pickup loop makes it difficult to satisfy competing goals of high field resolution and small detector size necessary for multichannel biomagnetic imaging. Improved coupling is demonstrated by the use of multiturn-input-coil flux transformers, and a resolution of 35 fT Hz{sup {minus}1/2} in the white noise region is reported with a (10 mm){sup 2} pickup loop. However, additional 1/f noise from processed multilayer structures in the transformer limits the resolution at 1 Hz to 114 fT Hz{sup {minus}1/2}. High-T{sub c} SQUIDs exhibit additional 1/f noise when cooled in a nonzero static magnetic field because of additional flux vortices trapped in the film, with the noise power at 1 Hz typically increasing by a factor of 10--20 in a field of 0.05mT (0.5 G). Finally, a SQUID-based voltmeter with a resolution of 9.2 pV.Hz{sup {minus}1/2} at 10 Hz (24 pV Hz{sup {minus}1/2} at 1 Hz) is described.

  1. Future prospects of high Tc superconductors-coated conductors and their applications

    NASA Astrophysics Data System (ADS)

    Shiohara, Yuh; Yoshizumi, Masateru; Takagi, Yuji; Izumi, Teruo

    2013-01-01

    The research and development of high-temperature superconducting wires, especially yttrium-based coated conductors (CCs), and their energy applications have been expected to reduce CO2 emissions. This article reviews recent progress in this area, mainly focusing on the results obtained by national projects in Japan. The Ic (critical current) × L (wire length) value of CCs has been improved to reach 466,752 A m (572 A/cm-W, 816 m), which exceeds that of Bi-system wires. CCs have also been improved in terms of in-field performance and AC loss reduction to meet market requirements. Power applications such as superconducting magnetic energy storage (SMES) systems, power cables and transformers have been developed using CCs in the current project. Because of fundamental research on high-capacity power cables, a low AC loss of 0.8 W/m-ph at 3 kA and 73.7 K was achieved. System design and fundamental research were performed on a 2GJ-class SMES system and a 20 MVA-class transformer. Based on the technologies developed by the end of the current project (FY2012), the innovation process of those applications will reach the implementation stage, where the long-term reliability tests will be performed. The process is expected to reach the penetration and propagation stage around 2020.

  2. All-high-Tc superconductor rapid-single-flux-quantum circuit operating at ˜30 K

    NASA Astrophysics Data System (ADS)

    Shokhor, S.; Nadgorny, B.; Gurvitch, M.; Semenov, V.; Polyakov, Yu.; Likharev, K.; Hou, S. Y.; Phillips, Julia M.

    1995-11-01

    We have implemented a simple circuit of the rapid single-flux-quantum (RSFQ) logic family using a single-layer YBa2Cu3O7-x thin-film structure with 14 in-plane Josephson junctions formed by direct electron beam writing. The circuit includes two dc/SFQ converters, two Josephson transmission lines, a complete RS SFQ flip-flop, and an SFQ/dc converter (readout SQUID). Low-frequency testing has shown that the dc-current-biased circuit operates correctly and reliably at T˜30 K, a few degrees below the effective critical temperature of the junctions. Prospects for a further increase of the operation temperature and implementation of more complex RSFQ circuits are discussed in brief.

  3. 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.

  4. Effect of superconducting fluctuations on the NMR relaxation rate of high-Tc superconductors

    SciTech Connect

    Appel, J. ); Fay, D.; Kautz, C. )

    1994-06-01

    The effect of superconducting order parameter fluctuations on the nuclear-spin relaxation rate, 1/T[sub 1], is studied for clean two-dimensional systems by calculating the three Maki-Thomson-type diagrams which represent the lowest-order fluctuation contributions to the transverse susceptibility. For Gaussian fluctuations and for temperatures near the mean field transition temperature, T[sub c0], we employ a weak-coupling theory in which the pair-fluctuation propagator can also include pair-breaking effects. We also go beyond the Gaussian theory and take into account the interactions between Cooper-pair fluctuations corresponding to the fourth-order Ginzburg Landau fluctuation terms. We compare our results with previous results in the dirty limit and in 3D. We obtain a pronounced peak in 1/T[sub 1] at Tc and briefly discuss possible reasons why this peak is not observed. 6 refs., 4 figs., 1 tab.

  5. 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.

  6. 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.

  7. Current-voltage characteristics near the glass-liquid transition in high- Tc superconductors

    NASA Astrophysics Data System (ADS)

    Yamafuji, K.; Kiss, T.

    1997-02-01

    Theoretical expressions for the induced DC electric field, E, are derived as a function of the applied current density, J, near the glass-liquid transition temperature of T= TGL as E(J) = Ẽ(J)[1 + ( {δE(J)}/{Ẽ(J) })] , where Ẽ(J) is the scalable part and {δE(j)}/{Ẽ(j) } is the unscalable part given by a power series of | TGL - T| nv( z + 2 - D) wi Then the condition of {δE}/{Ẽ}≪1 gives a measure of the width of the critical regime, in which E = E( J) is well scalable. The general scaling characteristics of E= Ẽ(J) are the same as those predicted by Fisher and coworkers based on the conventional theories of phase transitions with the scaling hypothesis, while the present theory provides a concrete expression for Ẽ(J) . Furthermore, the expressions for the scaled master curves of the AC impedance are derived. The reason, why the observed E vs. J characteristics are scalable over wider ranges of the temperature and flux density than the critical regime, is also discussed.

  8. Plasmon excitations in layered high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Greco, Andrés; Yamase, Hiroyuki; Bejas, Matías

    2016-08-01

    Motivated by the recent resonant inelastic x-ray scattering (RIXS) experiment for the electron-doped cuprates Nd2 -xCexCuO4 with x ≈0.15 , we compute the density-density correlation function in the t -J model on a square lattice by including interlayer hopping and the long-range Coulomb interaction. We find that collective charge excitations are realized not inside the particle-hole continuum, but above the continuum as plasmons. The plasmon mode has a rather flat dispersion near the in-plane momentum q∥=(0 ,0 ) with a typical excitation energy of the order of the intralayer hopping t when the out-of-plane momentum qz is zero. However, when qz becomes finite, the plasmon dispersion changes drastically near q∥=(0 ,0 ) , leading to a strong dispersive feature with an excitation gap scaled by the interlayer hopping tz. We discuss the mode recently observed by RIXS near q∥=(0 ,0 ) in terms of the plasmon mode with a finite qz.

  9. Local tunneling spectroscopy and infrared spectroscopy of the electron-doped cuprate Sm2-xCexCuO4

    NASA Astrophysics Data System (ADS)

    Zimmers, A.; Noat, Y.; Cren, T.; Sacks, W.; Roditchev, D.; Liang, B.; Greene, R. L.; Lobo, R. P. S. M.; Bontemps, N.

    2008-03-01

    We present infrared and local tunneling spectroscopy of the electron-doped cuprate Sm2-xCexCuO4. In STM, at optimal doping x=0.15, a clear signature of the superconducting gap is observed with an amplitude ranging from place to place and from sample to sample (δ˜ 3.5-6meV). Another spectroscopic feature is simultaneously observed at high energy above ±50meV. Its energy scale and temperature evolution is found to be compatible with previous photoemission and optical experiments. If interpreted as the signature of antiferromagnetic order in the samples, these results could suggest the coexistence on the local scale of antiferromagnetism and superconductivity on the electron-doped side of cuprate superconductors. Using optical spectroscopy, we analyzed the effects of the normal state gap opening (the higher energy gap seen in STM) and phonon structure as a function of temperature and doping from the underdoped to the metallic composition.

  10. 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.

  11. 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

  12. First 13 Years of HIGH-Tc:. Brief Review and Open Questions

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor

    Exactly 13 years ago, in April 1986, appeared the famous paper1 by Bednorz and Müller, that announced a striking discovery of high-Tc superconductivity in cuprates. Some 40'000 papers later, we are still struggling to understand the high-Tc superconductivity. Here I summarize 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.

  13. 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.

  14. 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.

  15. High-[Tc] superconducting magnets based on thick film arrangements

    SciTech Connect

    Kirschner, I.; Zsolt, G.; Karman, T.; Porjesz, T. . Dept. for Low Temperature Physics); Leppaevuori, S.; Uusimaeki, A. . Microelectronics Lab.); Lukacs, P. )

    1993-11-01

    On the basis of the authors' earlier idea on magnetic feeding, high-[Tc] superconducting magnets can be built consisting of Y-Ba-Cu-O or Bi(Pb)-Sr-Ca-Cu-O thick films. Critical current densities of the samples prepared by an oxalate route are between 7,000 and 23,000 A/cm[sup 2] at helium temperatures depending on the details of the preparation. The self-magnetic field of the individual layer rings are 0.5--1.7 mT which can produce field strength of the magnets of 55 178 mT, corresponding to the experimental critical currents. If the specimens of oxide-nitrate reactions can provide critical current densities of 5,000--15,000 A/cm[sup 2] at nitrogen temperatures they lead to the number of ampere-turns of 550--22,500 A/cm and magnetic field intensity of 69 mT--2.82 T. Since the applicable techniques of the film preparation are very flexible concerning the shape and size of the products, magnetic field profiles of different character can be obtained for various purposes.

  16. High-{Tc} DC SQUID and flux transformer development

    SciTech Connect

    Fife, A.A.; Angus, V.; Betts, K.

    1994-12-31

    A description is presented of the fabrication and properties of high {Tc} DC SQUIDS and flux transformers fabricated by dry processing of pulsed laser ablated YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO) thin films. SQUIDs have been fabricated with either bicrystal substrate or step edge junctions. For all devices fabricated thus far, measurements indicate a similar character to the flux noise spectra with a significant 1/f noise component below 100--500 Hz. The transfer function and energy sensitivities as a function of SQUID inductances in the range 60--200 pH have been measured for bicrystal DC SQUIDs and compared with estimates. Various techniques have been employed to improve the magnetic field sensitivity of the uncoupled DC SQUID toward more practical levels including the use of large area washers, single layer magnetometers and 3-level flux transformers fabricated from trilayers of YBCO/SrTiO{sub 3}/YBCO. The properties of open input coils are presented as well as the performance of closed loop transformers coupled via flip chip geometry to the SQUID washer. A white magnetic noise level of {approx} 130 fT rms/{radical}Hz above 200 Hz has been reached with a flux transformer with a 15 turn input coil and pick-up loop area of 13 mm{sup 2}.

  17. 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.

  18. High-Tc Superconducting Thin- and Thick-Film-Based Coated Conductors for Energy Applications

    SciTech Connect

    Cantoni, Claudia; Goyal, Amit

    2010-01-01

    Although the first epitaxial films of YBCO with high Tc were grown nearly 20 years ago, the understanding and control of the nanostructures responsible for the dissipation-free electrical current transport in high temperature superconductors (HTS) is quite recent. In the last six to seven years, major advances have occurred in the fundamental investigation of low angle grain boundaries, flux-pinning phenomena, growth mode, and atomic-level defect structures of HTS epitaxial films. As a consequence, it has been possible to map and even engineer to some extent the performance of HTS coatings in large regions of the operating H, T, J phase space. With such progress, the future of high temperature superconducting wires looks increasingly promising despite the tremendous challenges offered by these brittle and anisotropic materials. Nevertheless, further performance improvements are necessary for the superconducting technology to become cost-competitive against copper wires and ultimately succeed in revolutionizing the transmission of electricity. This can be achieved by further diminishing the gap between theoretical and experimental values of the critical current density Jc, and/or increasing the thickness of the superconductive layer as much as possible without degrading performance. In addition, further progress in controlling extrinsic and/or intrinsic nano-sized defects within the films is necessary to significantly reduce the anisotropic response of HTS and obtain a nearly constant dependence of the critical current on the magnetic field orientation, which is considered crucial for power applications. This chapter is a review of the challenges still present in the area of superconducting film processing for HTS wires and the approaches currently employed to address them.

  19. 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.

  20. 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.

  1. Correlated electronic structures and the phase diagram of hydrocarbon-based superconductors

    NASA Astrophysics Data System (ADS)

    Kim, Minjae; Choi, Hong Chul; Shim, Ji Hoon; Min, B. I.

    2013-11-01

    We have investigated correlated electronic structures and the phase diagram of electron-doped hydrocarbon molecular solids, based on the dynamical mean-field theory. We have found that the ground state of hydrocarbon-based superconductors such as electron-doped picene and coronene is a multi-band Fermi liquid, while that of non-superconducting electron-doped pentacene is a single-band Fermi liquid in the proximity of the metal-insulator transition. The size of the molecular orbital energy level splitting plays a key role in producing the superconductivity of electron-doped hydrocarbon solids. The multi-band nature of hydrocarbon solids would boost the superconductivity through the enhanced density of states at the Fermi level.

  2. 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.

  3. Electronic doping and trap reduction of quantum dots

    NASA Astrophysics Data System (ADS)

    Thorsen, Amanda Leigh

    Both undoped and doped semiconductor quantum dots (QDs) offer unique opportunities for studying the fundamental physics of quantum confinement. Obtaining a thorough understanding of their physical properties is necessary for development of efficient and robust materials for use in a wide range of applications such as optoelectronics (optical switches, light emitting diodes (LEDs), photovoltaics, and lasers), biosensing, and nanoelectronics. This thesis involves studies that look specifically at the effects of electronic doping and trap reduction in undoped and Mn2+ -doped QDs. Investigation of the effect of electron-Mn2+ exchange interactions on Mn 2+ luminescence in Mn2+:CdS nanocrystal films through an electrochemical method reveals effective Auger de-excitation of photoexcited Mn2+. The doped QDs demonstrate increased sensitivity to Auger de-excitation versus undoped QDs due to the long lifetime of the Mn2+ excited state. Photochemical electronic doping of colloidal CdSe nanocrystals is achieved for the first time through the use of a borohydride hole quencher, Li[Et3BH], and the high spectroscopic quality of the resulting n-type nanocrystals allows for advanced characterization by absorption and photoluminescence. Additionally, chemical titrations of the n-type nanocrystals confirm electron accumulation and suggest significant electron trapping for some of the nanocrystals. Spectroelectrochemical measurements on undoped and Mn2+-doped ZnSe QDs target charge injection into traps within the semiconductor bandgap. In both the undoped and doped QDs, transfer of electrons into the nanocrystal film is directly correlated with enhanced photoluminescence quantum yield and dubbed "electrobrightening." This method of brightening through trap passivation is extended to colloidal systems through the use of outer-sphere reductants and ultimately improves the ensemble photoluminescence quantum yield of Mn2+ -doped ZnSe QDs from 14% to 80%.

  4. Properties of HIGH-Tc Cuprates: Some Recent Results and Open Questions

    NASA Astrophysics Data System (ADS)

    Vobornik, Ivana; Pavuna, Davor

    Thirteen years ago, late in 1986, several groups confirmed striking claims of the famous paper by Bednorz and M[Z Phys. B 64 (1986) 189] that announced the discovery of high-Tc superconductivity in cuprates. Some 60,000 papers later, we are still struggling to understand the high-Tc oxide superconductivity. Here we present some of the most relevant recent experiments and discuss some open questions across rather complex electronic phase diagram; we also note an important role of un-intentional and intentional disorder in these layered, high-Tc oxides.

  5. μSR Studies on Magnetism in High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Koike, Yoji; Adachi, Tadashi

    2016-09-01

    Since the discovery of high-Tc superconductivity in cuprates, muon spin relaxation (μSR) measurements have greatly contributed to the understanding of high-Tc superconductivity. In this paper, μSR studies on the magnetism in high-Tc cuprates obtained these past three decades are reviewed. Antiferromagnetic long-range order, 1/8 anomaly, stripes of Cu spins and holes, impurity-induced magnetism, magnetic-field-induced magnetism, pseudogap, ferromagnetism in the heavily overdoped regime, and undoped superconductivity in T'-type cuprates are discussed. Moreover, the fundamentals of μSR measurements for the study of magnetism are described for μSR beginners.

  6. 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

  7. Microwave surface resistance of high Tc superconducting films

    NASA Astrophysics Data System (ADS)

    Apte, Prakash R.; Pinto, R.; Kumar, Dhananjay; Vijayaraghavan, R.

    1995-09-01

    The surface resistance, Rs, at microwave frequencies has been an important qualification parameter for high temperature superconductor (HTS) thin films. HTS thin films with low Rs have been realized on many substrates, and many groups have realized Rs values in the range 300 - 400 (mu) (Omega) at 10 GHz at 77 K with YBa2Cu3O7-(delta ) (YBCO) films on <100> LaAlO3 substrates. Both microstrip resonator and parallel plate resonator techniques are being used to measure Rs values of HTS thin films. It has been observed that the value of Rs at given frequency and temperature critically depends upon the epitaxial quality and granularity of the films. For example, YBCO films grown on <100> MgO have been found to be granular and weak link limited with a significant microwave power dependence of Rs. On the other hand, YBCO films insitu grown on <100> LaAlO3 have shown better epitaxy with low Rs. This is obviously due to the much better lattice match of YBCO with <100> LaAlO3 if the targets used for laser deposition are doped with Ag. Extensive work carried out in our laboratory has shown that a Ag-doping level of around 5 wt.% in YBCO is the optimum which results in YBCO films of much improved quality. We have realized Ag-doped YBCO films with Jc values of 6 - 8 X 106 Acm-2 at 77 K and a low Rs value of 210 (mu) (Omega) at 10 GHz at 77 K on <100> LaAlO3. Both these values are the best realized on LaAlO3 to date. What is equally important is the fact that with Ag-doping the reproducibility of the epitaxial quality of the films improves significantly. This has been found to be due to the enhanced oxygenation of films during growth and the surfactant effect of Ag. Experiments have shown that even the optimum temperature for insitu growth in reduced considerably by Ag-doping. It must be mentioned, however, that the only negative aspect of Ag-doping is the higher microwave residual surface resistance, Rres, observed in these films at (very) low temperatures. This is obviously due

  8. Normal state incoherent pseudogap in FeSe superconductor

    NASA Astrophysics Data System (ADS)

    Craco, Luis; Laad, Mukul S.

    2016-05-01

    The normal state of Iron chalcogenide superconductors show a range of unconventional features. Bad-metallic resistivity and proximity to insulating state manifest themselves in spectral and transport responses. In particular, obervation of low-energy pseudogap feature in the normal state raises the issue of the nature of processes underpinning its emergence as well as its relation to unconventional superconductivity. Here, using the LDA+DMFT method, we show how correlation-induced orbital-selective pseudogap-like physics underpin these incoherent features in stoichimetric and electron-doped FeSe superconductor. We discuss the pseudogap regime microscopically, along with implications for the superconductive instability.

  9. Dynamical Mean-Field Theory Study of Correlated Electronic Structures and the Phase Diagram of Hydrocarbon Superconductors

    NASA Astrophysics Data System (ADS)

    Kim, Minjae; Choi, Hong Chul; Shim, Ji Hoon; Min, B. I.

    2014-03-01

    We have studied correlated electronic structures and the phase diagram of electron-doped hydrocarbon molecular solids, based on the dynamical mean-field theory. We have determined the phase diagram of hydrocarbon molecular solids as functions of doping and energy parameters including the Coulomb correlation, the Hund coupling, and the molecular-orbital (MO) energy level splitting. We have found that the hydrocarbon superconductors (electron-doped picene and coronene) belong to the multi-band Fermi liquid state, while non-superconducting electron-doped pentacene belongs to the single-band state in the proximity of the metal-insulator transition. The size of the MO energy level splitting plays an important role in deriving the superconductivity of electron-doped hydrocarbon solids. The multi-band nature of hydrocarbon solids from the small MO energy level splitting boosts the superconductivity through the enhanced density of states at the Fermi level.

  10. Evolution of Coherence and Superconductivity in Electron-Doped Cuprates

    NASA Astrophysics Data System (ADS)

    Blumberg, G.; Qazilbash, M. M.; Dennis, B. S.; Greene, R. L.

    2006-09-01

    The superconducting (SC) phase diagram of the electron-doped cuprates has been explored by Raman spectroscopy as a function of doping x, temperature T, and magnetic field H. The data is consistent with nonmonotonic SC order parameter (OP) of the d-wave form. The persistence of SC coherence peaks in the B2g channel for all dopings implies that superconductivity is mainly governed by interactions in the vicinity of (±π/2a, ±π/2a31) regions of the Brillouin zone. Effective upper critical field lines Hc2*(T,x) at which the superfluid stiffness vanishes and Hc22Δ(T,x) at which the SC amplitude is suppressed by field have been determined. The difference between the two quantities suggests the presence of phase fluctuations that increase for x < 0.15. It is found that the field suppresses the magnitude of the SC gap linearly at an anomalously large rate. Hc22Δ value that is about 10 T for optimally doped samples decreases below a Tesla for overdoped cuprates.

  11. 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.

  12. High-temperature processing of cuprate oxide superconductors

    NASA Technical Reports Server (NTRS)

    Wu, M. K.; Ashburn, J. R.; Higgins, C. A.; Fellows, C. W.; Loo, B. H.; Burns, D. H.; Ibrahim, A.; Rolin, T. D.; Peters, P. N.; Sisk, R. C.

    1988-01-01

    Superconducting Y1Ba2Cu3O7 ('123') films were fabricated on the Y2BaCuO5 ('211') phase substrate. The superconducting characteristics of these films, in terms of superconducting transition temperature (Tc) and width, are better than those using other oxide compounds as substrates. In addition, using high-temperature processing, the bulk 211 phase was converted into the 123 phase. A new high Tc copper oxide material with non-rare-earth elements (Bi-Sr-Cu-O) was prepared using similar high-temperature processing. High-temperature processing presents an alternative synthetic route in the search of new high Tc superconductors.

  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. 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.

  15. 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.

  16. Ac losses for the self field of an ac transport current with a dc transport current offset in high {Tc} superconducting magnet coils for MagLev application

    SciTech Connect

    Koosh, V.F.

    1993-10-01

    Although much research has been conducted concerning the losses of high-{Tc} superconductors, very little has concentrated on the self-field losses in an actual magnet arrangement. The coils studied in this work were designed for use as actual magnets in an industrial application. Self field loss measurements were made upon tape-wound 2223 superconducting helix coils. The self-field losses were produced by an AC transport current with a DC transport current offset. Losses were taken for single, double and triple tape windings, giving essentially monofilament, dual, and three filament cases. The losses measured here were varied over a range of AC current values for several different DC values, and over a range of frequencies. The currents were all AC sinusoids with a DC offset. All measurements were made at T = 77K.

  17. 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.

  18. James C. McGroddy Prize Lecutre: Iron-Based Superconductors: Discovery and Progress

    NASA Astrophysics Data System (ADS)

    Hosono, Hideo

    2015-03-01

    The largest breakthrough in the history is the discovery of high Tc Cuprates by G.Bednorz and A.Muller in 1986 and the maximum Tc exceeded 77K, boiling temperature of liquid nitrogen in 1987. However, no new superconductors with high Tc had been reported since then except MgB2 (Tc =39K) discovered by J.Akimitsu in 2001.We found LaFePO superconductor with Tc =3K in 2006 and LaFeAsO1-xFx with Tc =26K (42K at under high pressure of 5GPa) in early 2008. The latter discovery rekindled the extensive superconductivity research globally, and more than 10,000 papers have been published to now. This excitement originates from disprovement of a widely accepted belief that iron with a large magnetic moment is harmful for emergence of superconductivity and relatively high Tc. Extensive research on iron-based superconductors pushed up the maximal Tc to 56K, which is next to high Tc cuprates and has led to the discovery of more than 50 new iron-based superconducting materials to date. Seen are so many advances in elucidation of superconducting properties and pairing mechanism. In this talk, I introduce a tale to the discovery and show the current status by reviewing progresses in materials, properties, mechanism and the application covering the recent hot topics. Emphases are placed on the unique characteristics arising from multi-orbital nature which totally differs from high Tc cuprates.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. The Nernst effect in layered superconductors under a magnetic field

    NASA Astrophysics Data System (ADS)

    Tinh, Bui Duc; Thu, Le Minh; Hoc, Nguyen Quang

    2016-08-01

    We calculated the Nernst signal eN, describing the Nernst effect in type-II superconductor in the vortex-liquid regime, by using the time-dependent Ginzburg-Landau (TDGL) equation with thermal noise. The nonlinear interaction term in the TDGL equation is treated within self-consistent Gaussian approximation. The expression of the Nernst signal eN including all the Landau levels is presented in explicit form which is applicable essentially to the whole phase. Our results are compared with the recent experimental data on high-Tc superconductor.

  6. High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O(8+x) down to half-unit-cell thickness by protection with graphene.

    PubMed

    Jiang, Da; Hu, Tao; You, Lixing; Li, Qiao; Li, Ang; Wang, Haomin; Mu, Gang; Chen, Zhiying; Zhang, Haoran; Yu, Guanghui; Zhu, Jie; Sun, Qiujuan; Lin, Chengtian; Xiao, Hong; Xie, Xiaoming; Jiang, Mianheng

    2014-01-01

    High-Tc superconductors confined to two dimension exhibit novel physical phenomena, such as superconductor-insulator transition. In the Bi2Sr2CaCu2O(8+x) (Bi2212) model system, despite extensive studies, the intrinsic superconducting properties at the thinness limit have been difficult to determine. Here, we report a method to fabricate high quality single-crystal Bi2212 films down to half-unit-cell thickness in the form of graphene/Bi2212 van der Waals heterostructure, in which sharp superconducting transitions are observed. The heterostructure also exhibits a nonlinear current-voltage characteristic due to the Dirac nature of the graphene band structure. More interestingly, although the critical temperature remains essentially the same with reduced thickness of Bi2212, the slope of the normal state T-linear resistivity varies by a factor of 4-5, and the sheet resistance increases by three orders of magnitude, indicating a surprising decoupling of the normal state resistance and superconductivity. The developed technique is versatile, applicable to investigate other two-dimensional (2D) superconducting materials. PMID:25483591

  7. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGES

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; et al

    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.

  8. High-temperature resistivity in the iron pnictides and the electron-doped cuprates

    NASA Astrophysics Data System (ADS)

    Bach, P. L.; Saha, S. R.; Kirshenbaum, K.; Paglione, J.; Greene, R. L.

    2011-06-01

    We measured the high-temperature (up to 800 K) resistivity of several dopings of SrFe2-x(Ni,Co)xAs2 (Sr-122) and compared the results with similar measurements on electron-doped cuprates. We find that the Sr-122 pnictide resistivity saturates above 500 K at around 400-700 μΩcm, consistent with the Mott-Ioffe-Regel (MIR) limit and in contrast with the MIR-violating behavior of the hole-doped cuprates and our measurements on electron-doped cuprates. This supports the view that electronic correlations in the ferropnictides may be weaker than in the cuprates.

  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. 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.

  11. 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.

  12. 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.

  13. Electrochemical insertion of lithium into the Bi2Sr2CaCu2O8+ y high- Tc superconductor

    NASA Astrophysics Data System (ADS)

    Fleischer, Niles A.; Manassen, Joost; Coppens, Philip; Lee, Peter; Gao, Yan; Greenbaum, Steven G.

    1992-01-01

    The insertion compound LixBi2Sr2CaCu2O8+ y (for lithium contents up to the studied level of x=2) was prepared by electro-chemical insertion of lithium into Bi2Sr2CaCu2O8+ y pellets at room temperature in galvanic cells using 1.4 M LiAsF 6 in 2Me-THF as electrolyte. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists but the superconducting fraction appears to be lower in the reacted samples. XRD data show that insertion of Li ions is accompanied by interlayer expansion between BiO planes and a small increase in the a and b cell lattice parameters. 7Li NMR measurements indicate a substantial donation of electrons to the 2212 host lattice. The changes in the a and b lattice parameters and the effect on superconductivity is consistent with some of the donated electrons entering the CuO planes and reducing holes in these layers.

  14. In situ observation of oxygen deficiency occurring during electron irradiation in high Tc superconductor YBa2Cu3Oy.

    PubMed

    Akase, Z; Tomokiyo, Y; Watanabe, M

    2001-07-01

    The decreasing process of oxygen in YBa2Cu3Oy is investigated through high resolution electron microscopy (HREM) and convergent beam electron diffraction (CBED). Measurements of the axial length in HREM images show that oxygen content y decreases faster near a twin boundary than at the inner part of a twin lamella. The transformation from an orthorhombic to a tetragonal phase starts at a twin boundary and the transformed region propagates to an inner region of lamella. Lattice strains are observed near boundaries between transformed and non-transformed regions. The transformation is almost complete within 30 s during observation of HREM images at 400 kV and at room temperature. A value of y was quantitatively measured by analysing observed intensities of energy-filtered CBED patterns with the dynamical theory. The value of y decreases from 6.9 to 6.5 when 200 kV electrons are irradiated for 160 s in a microscope at 108 K. More precise analysis of the intensities provides information on charge distribution along the c-axis as well as local oxygen content at a spatial resolution of several nanometres. PMID:11454148

  15. Apparatus for nonresonant rf power absorption studies in high Tc superconductors and CMR materials using rf oscillators

    NASA Astrophysics Data System (ADS)

    Sarangi, S.; Bhat, S. V.

    2005-02-01

    The design, fabication, and performance of an apparatus for measurement of nonresonant rf power absorption (NRRA) in superconducting and CMR samples are described. The system consists of an effective self-resonant LC tank circuit driven by a NOT gate (Logic gate). The samples under investigation are placed in the core of an inductive coil and nonresonant power absorption is determined from the measured shift in total current supplies to the whole oscillator circuit. A customized low temperature insert is used to integrate the experiment with a commercial oxford cryostat and temperature controller. The system makes use of a sensitive digital multimeter (Keithley 2002 model) and is capable of measuring NRRA in superconducting and colossal magnetoresistance samples of volume as small as 1×10-3cm3 with a signal to noise ratio of 10. Further increase in the sensitivity of the experimental setup can be obtained by summing the results of repeated measurements obtained in the same temperature interval. The system has been tested for an IC 74LS04 oscillator at frequencies between 1MHz and 25MHz in the temperature range from 4.2Kto400K and in magnetic field from 0to1.4T. The system performance is evaluated by measuring the NRRA in YBa2Cu3O7 (YBCO) superconducting sample and La0.7Sr0.3MnO3 (LSMO) colossal magnetoresistive (CMR) manganite samples at different rf frequencies. During a measurement all operation are controlled automatically by computer from a menu-driven software system, with user input required only on initiation of measurement sequence.

  16. “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

  17. 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.

  18. 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.

  19. Magneto-Optical Response of Electron Doped Cuprates Pr2-xCexCuO4

    NASA Astrophysics Data System (ADS)

    Margankunte, Naveen; Zimmers, Alexandra; Tanner, D. B.; Greene, R. L.; Wang, Y. J.

    2006-09-01

    We report mid-infrared transmission measurements of electron doped Pr2-xCexCuO4 (PCCO) thin films for a wide range of dopings, in the large energy pseudogap regime both as a function of temperature and magnetic field. While the temperature dependent measurements show clear signatures of pseudogap, there is no magnetic field induced effect.

  20. Iron-Based Superconductors as topological matter

    NASA Astrophysics Data System (ADS)

    Hu, Jiangping

    We show the existence of non-trivial topological properties in Iron-based superconductors. Several examples are provided, including (1) the single layer FeSe grown on SrTiO3 substrate, in which an topological insulator phase exists due to the band inversion at M point; (2) CaFeAs2, a staggered intercalation compound that integrates both quantum spin hall and superconductivity in which the nontrivial topology stems from the chain-like As layers away from FeAs layers; (3) the Fe(Te,Se) thin films in which the nontrivial Z2 topological invariance originates from the parity exchange at Γ point that is controlled by the Te(Se) height; (4 nontrivial topology that is driven by the nematic order in FeSe. These results lay ground for integrating high Tc superconductivity with topological properties to realize new emergent phenomena, such as majorana particles, in iron-based high temperature superconductors

  1. Topological properties in Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    Hu, Jiangping; Hao, Ningning; Wu, X. X.

    2015-03-01

    We show the existence of non-trivial topological properties in Iron-based superconductors. Several examples are provided, including (1) the single layer FeSe grown on SrTiO3 substrate, in which an topological insulator phase exists due to the band inversion at M point; (2) CaFeAs2, a staggered intercalation compound that integrates both quantum spin hall and superconductivity in which the nontrivial topology stems from the chain-like As layers away from FeAs layers; (3) the Fe(Te,Se) thin films in which the nontrivial Z2 topological invariance originates from the parity exchange at ? point that is controlled by the Te(Se) height. These results lay ground for integrating high Tc superconductivity with topological properties to realize new emergent phenomena, such as majorana particles, in iron-based high temperature superconductors. The work is supported by NSFC and the Ministry of Science and Technology of China.

  2. High-Tc/high-coupling relaxed PZT-based single crystal thin films

    NASA Astrophysics Data System (ADS)

    Wasa, K.; Matsushima, T.; Adachi, H.; Matsunaga, T.; Yanagitani, T.; Yamamoto, T.

    2015-03-01

    Pb(Zr,Ti)O3 (PZT)-based ferroelectric ceramics exhibit high piezoelectricity, however, their Curie temperature (Tc) values are not so high, i.e., Tc < 400 °C. PZT-based piezoelectric thin films with higher Tc would be beneficial for improved micro actuators, sensors, memories, and piezoelectric micro-electro mechanical systems. In-plane biaxial strained PZT thin films in a laminated composite structure are known to exhibit enhanced Tc; however, the thickness of PZT-based thin films is limited to below a critical thickness typically <50 nm. The Tc of relaxed PZT-based thin films with thicknesses greater than the critical thickness is the same as bulk Tc. However, a sort of relaxed PZT-based single-crystal thin films exhibit extraordinary high Tc, Tc = ˜600 °C. In addition, the films show extremely low dielectric constant, ɛ/ɛo ˜ 100 with high coupling factor, kt ˜ 0.7, and large remnant polarization, Pr ˜ 100 μC/cm2. These exotic properties would result from the single-domain/single-crystal structure. The enhanced Tc is possibly caused by the highly stable interface between the PZT-based thin films and substrates. Their ferroelectric performances are beyond those of conventional PZT. The high-Tc/high-coupling performances are demonstrated, and the possible mechanisms of the high Tc behavior in relaxed PZT-based single-crystal thin films are discussed.

  3. 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.

  4. Critical Activation Parameters for LaFeAsO-BASED Superconductors

    NASA Astrophysics Data System (ADS)

    Chu, Zotin Kwang-Hua

    The occurrence of high-Tc superconductivity in the iron pnictides shares a similar amorphous characteristic with that of high-Tc superconducting cuprates. Here we show that nearly frictionless (electric-field-driven) transport of condensed electrons in amorphous superconductors could happen after using the Eyring's transition-rate approach which has been successfully adopted to study the critical transport of other superconductors as well as supersolid helium in very low temperature environment. The critical temperatures related to the nearly frictionless transport of electrons were found to be directly relevant to the superconducting temperature of high-temperature superconductors (like La[O1-xFx]FeAs (x = 0.11-0.12)) after selecting specific activation energies and activation volumes.

  5. 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.

  6. 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.

  7. 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.

  8. Inelastic electron scattering in the high-Tc compound YBa2Cu3O7-x

    NASA Astrophysics Data System (ADS)

    Tarrio, C.; Schnatterly, S. E.

    1988-07-01

    We have carried out inelastic electron scattering transmission measurements on the high-Tc compound YBa2Cu3O7-x in the energy range 1-100 eV. We have directly observed the free-electron plasma peak at 1.1 eV in addition to the bound electron plasmon at 25.5 eV. The interband threshold is at 2.1 eV, above which the material behaves as a typical oxide insulator.

  9. Laser Plasma Vapour Deposition Of Photoconducting And High Tc Superconducting Films

    NASA Astrophysics Data System (ADS)

    Popescu, Mihai A.; Apostol, Ileana; Mihailescu, Ion N.; Botila, T.; Pentia, E.; Ciurea, M. L.; Dinescu, M.; Jaklovsky, J.; Aldica, Gheorghe V.; Miu, L.; Rusu, C.; Hening, Al. A.; Mihai, S.; Constantin, C.; Stoica, Mihaela; Pausescu, P.; Cruceanu, Eugen; Pompe, Wolfgang; Wuensch, R.; Richter, Asta; Scheibe, H. J.

    1989-05-01

    Device quality PbS photoconducting films were obtained by laser plasma vapour deposition on special glass substrates at room temperature and their structure was investigated by X-ray diffraction. High Tc superconducting films of composition Dy0.2Y0.8Ba2Cu3O~7 and YBa2Cu3O~7 were deposited on sapphire substrate. It was shown for laser deposited YBa2Cu3O~7 that a buffer layer of the same composition predeposited by rf sputtering allows for getting high quality superconducting films.

  10. Tunneling Spectral Dip Feature in High Tc Cuprates: Experiment and Analysis

    NASA Astrophysics Data System (ADS)

    Zasadzinski, John; Coffey, Liam; Kurter, Cihan; Gray, Ken

    2009-03-01

    A fully self-consistent Eliashberg analysis is presented to analyze the spectral dip feature observed in tunnel junctions on Bi2212. Methods include SIS break junctions, intrinsic Josephson junctions in mesas and SIN junctions from STM. This analysis is presented for a variety of doping levels and the resulting electron-boson spectral function and self-energy is compared with other spectroscopic probes. Evidence of spectral dip features in other high Tc cuprates is presented including Tl2212 to demonstrate the universality of the spectral dip and its relation to the mechanism of pairing.

  11. 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.

  12. Anisotropic softening of magnetic excitations in lightly electron-doped Sr2IrO4

    DOE PAGES

    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.; et al

    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

  13. 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.

  14. Lateral restoring force on a magnet levitated above a superconductor

    NASA Astrophysics Data System (ADS)

    Davis, L. C.

    1990-03-01

    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.

  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. 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.

  17. Levitation force from high-Tc superconducting thin-film disks

    NASA Astrophysics Data System (ADS)

    Riise, Anjali B.; Johansen, T. H.; Bratsberg, H.; Koblischka, M. R.; Shen, Y. Q.

    1999-10-01

    Experimental studies and theoretical modeling of the levitation force between a permanent magnet and superconducting thin film are reported. Measurements of the force Fz and magnetic stiffness κz=\\|δFz/δz\\| as functions of the magnet-superconductor separation z, show several features contrasting all previous levitation force data for bulk superconductors. In particular, the Fz(z) curves measured for decreasing and increasing separation form hysteresis loops of nearly symmetrical shape, also displaying a peak in the repulsive force branch. Recent theories for flux penetration in thin type-II superconductors in transverse magnetic fields are invoked to explain the results, which were obtained using a cylindrical Nd-Fe-B magnet and a YBa2Cu3O7-δ circular disk made by laser ablation. We derive explicit formulas for both Fz and κz, reproducing quantitatively all the features seen experimentally.

  18. 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

  19. 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.

  20. Quantum oscillation signatures of spin-orbit interactions controlling the residual nodal bilayer-splitting in underdoped high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Harrison, Neil; Shekhter, Arkady

    2015-03-01

    We investigate the origin of the small residual nodal bilayer-splitting in the underdoped high-Tc superconductor YBa2Cu3O6+x using the results of recently published angle-resolved quantum oscillation data [Sebastian et al., Nature 511, 61 (2014)]. A crucial clue to the origin of the residual bilayer-splitting is found to be provided by the anomalously small Zeeman-splitting of some of the observed cyclotron orbits. We show that such an anomalously Zeeman-splitting (or small effective g-factor) for a subset of orbits can be explained by spin-orbit interactions, which become significant in the nodal regions as a result of the vanishing bilayer coupling. The primary effect of spin-orbit interactions is to cause quasiparticles traversing the nodal region of the Brillouin zone to undergo a spin flip. We suggest that the Rashba-like spin-orbit interactions, naturally present in bilayer systems, have the right symmetry and magnitude to give rise to a network of coupled orbits consistent with experimental observations in underdoped YBa2Cu3O6+x. This work is supported by the DOEm BES proposal LANLF100, while the magnet lab is supported by the NSF and Florida State.

  1. 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.

  2. 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. PMID:25879999

  3. 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.; Kondo, Takeshi; Fernandes, R. M.; Mun, E. D.; Hodovanets, H.; Thaler, A. N.; Schmalian, J.; Bud’ko, S. L.; et al

    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

  4. Fabrication of single electron tunneling devices using layered structures of high- Tc superconducting materials

    NASA Astrophysics Data System (ADS)

    Kim, S.-J.; Yamashita, T.

    2006-10-01

    We have fabricated the submicron structures using high-Tc superconducting materials of Bi2Sr2CuO6+δ (Bi-2201). The stacks of layered structures are made by focused-ion-beam (FIB) etching methods. The fabricated 3D three terminal devices consist of source, drain and gate electrodes on the same chip. A gate electrode is capacitively coupled to a central island between two ultra-small tunnel junctions with in plane area S = 0.25 μm2 in series. Two stacks including an island structure show a Coulomb blockade region of 15 mV at zero gate potential. The effects are not smeared out by thermal fluctuations until temperatures greater than 150 K are reached.

  5. High Tc superconducting magnetic multivibrators for fluxgate magnetic-field sensors

    SciTech Connect

    Mohri, K.; Uchiyama, T.; Ozeki, A. . Faculty of Engineering)

    1989-09-01

    Sensitive and quick-response nonlinear inductance characteristics are found for high Tc superconducting (YBa/sub 2/Cu/sub 3/O/sub 7-chi/) disk cores at 77K in which soft magnetic BH hysteresis loops are observed. Various quick response magnetic devices such as modulators, amplifiers and sensors are built using these cores. The magnetizing frequency can be set to more than 20 MHz, which is difficult for conventional ferromagnetic bulk materials such as Permalloy amorphous alloys and ferrite. New quick-response fluxgate type magnetic-field sensors are made using ac and dc voltage sources. The former is used for second-harmonic type sensors, while the latter is for voltage-output multivibrator type sensors. Stable and quick-response sensor characteristics were obtained for two-core type multivibrators.

  6. 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.

  7. Kinetic inductance effects in high-Tc microstrip circuits at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Byrne, D. P.; Kwor, R.; Kalkur, T. S.

    1990-10-01

    This paper describes the fabrication of high-Tc superconducting thin films of BiCaSrCuO and the patterning of these films into integrated microstrip transmission line resonators designed to exhibit the effects of kinetic inductance. Emphasis is given to techniques to fabricate very thin, low-loss dielectric layers on BiCaSrCuO. Microwave S-parameter measurements on these resonators are reported along with functional dependence of tranmission line phase velocity and the characteristic impedance with temperature and microwave power density, especially at temperatures just below Tc. The results are used to infer high-frequency penetration depths and surface resistivities in BiCaSrCuO.

  8. Microstrip ring resonator technique for measuring microwave attenuation in high-Tc superconducting thin films

    NASA Astrophysics Data System (ADS)

    Takemoto, June H.; Oshita, Floyd K.; Fetterman, Harold R.; Kobrin, Paul; Sovero, Emilio

    1989-10-01

    Microwave attenuation of high-Tc superconducting (HTS) films sputtered on MgO and ZrO2 were measured using a microstrip ring resonator circuit. The results for Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O resonators were compared to those for gold-plated resonators of identical design. The losses of superconducting and gold-plated films were determined from unloaded Q-factor measurements. The attenuation of Y-Ba-Cu-O film on an MgO substrate is approximately 31 percent lower than that of gold films at 6.6 GHz and 33 percent lower at 19.2 GHz for temperatures below 50 K. The approach of using microstrips to characterize microwave losses shows the usefulness of HTS films in integrated circuit technology.

  9. Hilbert Spectral Analysis of THz Radiation Sources by High-Tc Josephson Detectors

    NASA Astrophysics Data System (ADS)

    Divin, Yuriy; Lyatti, Matvey; Poppe, Ulrich

    A Hilbert spectrum analyzer was developed and characterized with monochromatic radiation sources at the frequency range from 30 GHz to 1 THz. The analyzer was based on a high-Tc frequency-selective Josephson detector and cooled to temperatures of 60-80K by a Stirling cryocooler. The instrumental function of the spectrum analyzer was shown to be of Lorentz type and within accuracy up to 0.1% without any harmonic and subharmonic contributions. Spectral characterization of THz sources, based on frequency multiplication of input microwave radiation by Schottky diodes, was demonstrated for input frequencies from 10 to 20 GHz with a total scanning time as low as 50 ms per scan. The developed Hilbert spectrum analyzer might be considered as a compact and high-speed substitute of conventional Fourier spectrometers, which are used for characterization of THz radiation sources in combination with liquid-helium-cooled silicon bolometers.

  10. On detection of the Fermi edge in in situ grown thin films of high- Tc oxides

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Ariosa, D.; Saleh, S. A.; Rast, S.; Margaritondo, G.; Onellion, M.; Pavuna, D.

    2001-11-01

    We discuss our systematic series of experiments on the photoelectric detection of the Fermi edge using a cylindrical mirror analyser on films of high- Tc oxides, grown in situ by pulsed laser ablation. The Fermi edge (comparable to the edge of the reference Ag) is very easily observed even in the two-phase BSCCO-2212 film that exhibits onsets of superconducting transitions, at 85 and 45 K. In contrast, the Fermi edge is weaker and more difficult to observe even in the state-of-the-art, highly epitaxial, monophase YBa 2Cu 3O 7- y (YBCO) and NdBa 2Cu 3O 7- y (NBCO-123) films (both with Tc=92 K). So far we could not detect the Fermi edge in the films of the double-`chain' YBCO-124.

  11. Twenty years of talking past each other: The theory of high Tc

    NASA Astrophysics Data System (ADS)

    Anderson, Philip W.

    2007-09-01

    In 1988, the outline of an essentially correct theory of the high Tc cuprates was published by two groups, Zhang et al. in Zurich and Kotliar et al. in the US, based on earlier suggestions. The rather startling experimental predictions: that the gap would be real d-wave with nodes; that the gap would greatly increase with underdoping; that Tc would exhibit a dome terminating linearly around x = 30%; were so bizarre that these papers gathered little attention from others, including myself and at least 8 other Nobel prize-winners, and as they came to be substantiated one by one nobody much noticed that fact until the method was revived a dozen years later by Paramekanti et al. and Sorella et al. I will discuss some recent achievements and generalizations of these methods.

  12. Electrical characteristics of high- Tc superconducting mini-model cable under mechanical stresses in liquid nitrogen

    NASA Astrophysics Data System (ADS)

    Kim, H. J.; Kwag, D. S.; Kim, Y. S.; Kim, S. H.

    2005-01-01

    To develop 22.9 kV class high- Tc superconducting (HTS) cable in Korea, we have been studying electrical insulation properties of dielectric paper, such as breakdown voltage, partial discharge, which is one of the HTS cable structure elements. However, the research on the mechanical stress of dielectric paper compared to breakdown properties of dielectric paper is insufficient. A cracking and variation of the electrical insulation due to mechanical stresses during cooling and bending of HTS cables in cryogenic temperature is a serious problem. Thus, we investigated tensile stress and breakdown stress of dielectric paper under mechanical stress. Moreover, we manufactured mini-model cables investigated breakdown stress under bending stress to design a cable drum for conveyance. In the AC, impulse and partial discharge properties, all test results showed a similar tendency, and the suitable bending radius ratio R/ r was decided to be more than 25.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. Practical superconductor development for electrical power applications. Annual report for FY 1995

    SciTech Connect

    Balachandran, U.

    1995-10-01

    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 in the (Bi,Pb)-Sr-Ca-Cu, (Tl,Pb,Bi,V)-(Ba,Sr)-Ca-Cu, and Y-Ba-Cu oxide systems. The topics that are discussed are synthesis and heat treatment of high-{Tc} superconductors, formation of monolithic and composite conductors, characterization of structures and superconducting and mechanical properties, and fabrication and testing of prototype components. Collaboration with industry and academia is documented.

  18. 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.

  19. Present status of the theory of the high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Anderson, P. W.

    2006-04-01

    The Gutzwiller-projected mean-field theory, also called plain vanilla or renormalized mean-field theory, is explained, and its successes and possible extensions in describing the phenomenology of the cuprate superconductors are discussed. Throughout, we emphasize that while this is a Hartree-Fock-based BCS theory, it embodies fundamental differences from conventional perturbative many-body theory which may be characterized by calling it a theory of the doped Mott insulator.

  20. EDITORIAL: Focus on Superconductors with Exotic Symmetries FOCUS ON SUPERCONDUCTORS WITH EXOTIC SYMMETRIES

    NASA Astrophysics Data System (ADS)

    Rice, T. Maurice; Sigrist, Manfred; Maeno, Yoshiteru

    2009-05-01

    Superconductors can usefully be divided into two classes, those that are well described by the classic Bardeen-Cooper-Schrieffer (BCS) theory and its extensions and those which require a different microscopic description. The BCS theory of superconductivity solved the long standing mystery of this spectacular phenomenon and described all superconductors that were known when it was formulated in the 1950s. The key ingredient is an attractive interaction generated by the exchange of phonons between electrons which overcomes a Coulomb repulsion weakened by screening, to give a net attractive force on the low energy scale. In this case the simplest s-wave pairing always maximises the energy gain. There were speculations a little later that other types of electron pairing could be possible, but it took a quarter of a century until the first signs of superconductors with different and exotic pairing appeared. In the intervening thirty years many superconductors with exotic pairing have been and continue to be discovered and the study of their superconductivity has grown into a major subfield of condensed matter physics today. The importance of these exotic superconductors with unconventional symmetry is that their pairing is of electronic origin. As a result they are freed from the restrictions of low transition temperatures that go along with the phonon driven conventional superconductors. However in two of the main classes of the exotic superconductors, namely heavy fermion and organic superconductors, the intrinsic energy scales are very small leading to low temperature scales. The third class contains the small number of superconducting transition metal compounds with exotic pairing symmetry. The most studied of these are the high-Tc cuprates, the newly discovered iron pnictides and strontium ruthenate which is closely related to superfluid 3He. Although the basic electronic structure of these materials is well understood, the origin of the pairing is more complex

  1. Pairing Mechanism for the High-TC Superconductivity: Symmetries and Thermodynamic Properties

    PubMed Central

    Szczęśniak, Radosław

    2012-01-01

    The pairing mechanism for the high- superconductors based on the electron-phonon (EPH) and electron-electron-phonon (EEPH) interactions has been presented. On the fold mean-field level, it has been proven, that the obtained s-wave model supplements the predictions based on the BCS van Hove scenario. In particular: (i) For strong EEPH coupling and the energy gap () is very weak temperature dependent; up to the critical temperature extends into the anomalous normal state to the Nernst temperature. (ii) The model explains well the experimental dependence of the ratio on doping for the reported superconductors in the terms of the few fundamental parameters. In the presented paper, the properties of the d-wave superconducting state in the two-dimensional system have been also studied. The obtained results, like for s-wave, have shown the energy gap amplitude crossover from the BCS to non-BCS behavior, as the value of the EEPH potential increases. However, for the energy gap amplitude extends into the anomalous normal state to the pseudogap temperature. Finally, it has been presented that the anisotropic model explains the dependence of the ratio on doping for the considered superconductors. PMID:22529891

  2. Electronic structure, irreversibility line and magnetoresistance of Cu0.3Bi2Se3 superconductor

    DOE PAGES

    Hemian, Yi; Gu, Genda; Chen, Chao -Yu; Sun, Xuan; Xie, Zhuo -Jin; Feng, Ya; Liang, Ai -Ji; Peng, Ying -Ying; He, Shao -Long; Zhao, Lin; et al

    2015-06-01

    CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ~4000 Oe formore » the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.« less

  3. Magnetic frustration in the three-band Anderson lattice model for high-temperature superconductors

    SciTech Connect

    Ihle, D.; Kasner, M. )

    1990-09-01

    The three-band Anderson lattice model for the CuO{sub 2} planes in high-{Tc} superconductors is established. Treating this model by perturbation theory, the effective spin interactions are derived. The antiferromagnetic superexchange integrals are calculated as functions of the direct oxygen transfer and the hole concentration. It is found that frustration in the superexchange occurs, even in the undoped case, which increases with oxygen trnasfer and decreases with hole concentration.

  4. The fluctuation Hall conductivity and the Hall angle in type-II superconductor under magnetic field

    NASA Astrophysics Data System (ADS)

    Tinh, Bui Duc; Hoc, Nguyen Quang; Thu, Le Minh

    2016-02-01

    The fluctuation Hall conductivity and the Hall angle, describing the Hall effect, are calculated for arbitrary value of the imaginary part of the relaxation time in the frame of the time-dependent Ginzburg-Landau theory in type II-superconductor with thermal noise describing strong thermal fluctuations. The self-consistent Gaussian approximation is used to treat the nonlinear interaction term in dynamics. We obtain analytical expressions for the fluctuation Hall conductivity and the Hall angle summing all Landau levels without need to cutoff higher Landau levels to treat arbitrary magnetic field. The results are compared with experimental data on high-Tc superconductor.

  5. An Ultra-Thin Molecular Superconductor Made from Charge Transfer Complexes

    NASA Astrophysics Data System (ADS)

    Clark, Kendal; Hassenien, A.; Khan, S.; Braun, K.-F.; Tanaka, H.; Hla, S.-W.

    2010-03-01

    A class of charge transfer molecular systems having a D2A arrangement (D = donor, A = accepter) exhibit superconductivity in the bulk and are often termed ``unusual superconductors'' based on the different nature of their superconducting states as compared to convention BCS superconductors. In this study we have formed an ultra-thin (BETS)2-GaCl4 molecular superconductor consisting of a single sheet of layered molecules composed of individual GaCl4 sandwiched between the chains of a double domino stacked BETS on a Ag(111) surface. Amazingly, the superconducting gap can still be detected in such an ultra-thin molecular layer, and the shape of the gap reveals a d-wave pairing symmetry. Moreover, real space STM spectroscopic images provide direct evidence of the superconducting site as the BETS chains. In stark contrast to the high Tc superconductors, the spectroscopic maps clearly display nanoscale electronic order indicating robust superconducting properties at this extreme spatial limit..

  6. Vortex Dynamics and the Hall-Anomaly in (HTC)-Superconductors

    NASA Astrophysics Data System (ADS)

    van Otterlo, A.; Geshkenbein, V.; Blatter, G.; Feigelman, M.

    1996-03-01

    One of the most puzzling phenomena in the context of vortex dynamics in superconductors is the sign change in the Hall angle in the mixed phase of both low and high TC superconductors. This Hall-Anomaly cannot be understood within the framework of the conventional theories. We present a new microscopic derivation of the equation of motion for a vortex in a superconductor [Phys. Rev. Lett. 75, 3736 (1995)]. A coherent view on vortex dynamics is obtained, in which both hydrodynamics and the vortex core contribute to the forces acting on a vortex. The competition between these two provides an interpretation of the observed sign change in the Hall angle in superconductors with mean free path l of the order of the coherence length ξ in terms of broken particle-hole symmetry, which is related to details of the microscopic mechanism of superconductivity.

  7. Influence of Electron Doping on Magnetic Order in CeRu2Al10

    NASA Astrophysics Data System (ADS)

    Kobayashi, Riki; Kaneko, Koji; Saito, Kotaro; Mignot, Jean-Michel; André, Gilles; Robert, Julien; Wakimoto, Shuichi; Matsuda, Masaaki; Chi, Songxue; Haga, Yoshinori; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Nishioka, Takashi; Matsumura, Masahiro; Tanida, Hiroshi; Sera, Masafumi

    2014-10-01

    The effect of electron doping by the substitution of Rh for Ru on unconventional magnetic order in CeRu2Al10 was investigated via neutron powder diffraction. In Ce(Ru1-xRhx)2Al10 with x = 0.05, 0.12, and 0.2, reorientation of the ordered moment from the c-axis as in pure CeRu2Al10 to the a-axis takes place in all samples, while the ordering vector q = (0,1,0) remains unchanged within this concentration range. The moment reorientation is accompanied by an increase in its size by a factor of ˜2.4, from μ = 0.43 μB at x = 0 to μ = 1.06, 1.04, and 1.02 μB for x = 0.05, 0.12, and 0.2, respectively. The continuous decrease in the Néel temperature T0(TN), despite an abrupt increase in μ, underlines the strong anisotropy in the exchange interaction in CeRu2Al10 and the fact that this anisotropy is easily suppressed by electron doping.

  8. Spin-state blockade in Te6+-substituted electron-doped LaCoO3

    NASA Astrophysics Data System (ADS)

    Tomiyasu, Keisuke; Koyama, Shun-Ichi; Watahiki, Masanori; Sato, Mika; Nishihara, Kazuki; Onodera, Mitsugi; Iwasa, Kazuaki; Nojima, Tsutomu; Yamasaki, Yuuichi; Nakao, Hironori; Murakami, Youichi

    2015-03-01

    Perovskite-type LaCoO3 (Co3+: d6) is a rare inorganic material with sensitive and characteristic responses among low, intermediate, and high spin states. For example, in insulating nonmagnetic low-spin states below about 20 K, light hole doping (Ni substitution) induces much larger magnetization than expected; over net 10μB/hole (5μB/Ni) for 1μB/hole (1μB/Ni), in which the nearly isolated dopants locally change the surrounding Co low-spin states to magnetic ones and form spin molecules with larger total spin. Further, the former is isotropic, whereas the latter exhibits characteristic anisotropy probably because of Jahn-Teller distortion. In contrast, for electron doping, relatively insensitive spin-state responses were reported, as in LaCo(Ti4+) O3, but are not clarified, and are somewhat controversial. Here, we present macroscopic measurement data of another electron-doped system LaCo(Te6+) O3 and discuss the spin-state responses. This study was financially supported by Grants-in-Aid for Young Scientists (B) (No. 22740209 and 26800174) from the MEXT of Japan.

  9. Oxygen Annealing in the Synthesis of the Electron-Doped Cuprates

    NASA Astrophysics Data System (ADS)

    Higgins, J. S.; Bach, P. L.; Yu, W.; Weaver, B. D.; Greene, R. L.

    2015-03-01

    Post-synthesis oxygen reduction (annealing) in the electron-doped, high-temperature superconducting cuprates is necessary for the establishment of superconductivity. It is not established what effect this reduction has microscopically on the lattice structure. Several mechanisms have been put forth as explanations; they range from disorder minimization1, antiferromagnetic suppression2, and copper migration3. Here we present an electronic transport study on electron-doped cuprate Pr2-xCexCuO4+/-δ (PCCO) thin films in an attempt to better understand the need for this post-synthesis process. Several different cerium doping concentrations of PCCO were grown. Within each doping, a series of films were grown with varying levels of oxygen concentration. As a measure of disorder on the properties of PCCO, several films were irradiated with various doses of 2 MeV protons. Analysis within each series, and among the different dopings, favors disorder minimization through the removal of apical oxygen as the explanation for the necessary post-synthesis annealing process. 1P. K. Mang, et al., Physical Review Letters, 93(2):027002, 2004. 2P. Richard, et al., Physical Review B, 70 (6), 064513, 2004. 3Hye Jung Kang, et al., Nature Materials, 2007. Supported by NSF DMR 1104256.

  10. Influence of Electron Doping on Magnetic Order in CeRu2Al10

    DOE PAGES

    Kobayashi, Riki; Kaneko, Koji; Saito, Kotaro; Mignot, Jean-Michel; André, Gilles; Robert, Julien; Wakimoto, Shuichi; Matsuda, Masaaki; Chi, Songxue; Haga, Yoshinori; et al

    2014-09-17

    The effect of electron doping by the substitution of Rh for Ru on unconventional magnetic order in CeRu2Al10 was investigated via neutron powder diffraction. In Ce(Ru1-xRhx)2Al10 with x = 0.05, 0.12, and 0.2, reorientation of the ordered moment from the c- to the a-axis takes place in all samples, while the ordering vector q=(0 1 0) remains unchanged within this concentration range. The moment reorientation is accompanied by an enhancement in its size by a factor of ~2.4, from μ=0.43 μB at x=0 to μ =1.06, 1.04, and 1.02 μB for x=0.05, 0.12 and 0.2, respectively. The continuous decrease inmore » N´eel temperature T0(TN), despite an abrupt increase in μ , underlines the strong anisotropy in the exchange interaction in CeRu2Al10, and the fact that this anisotropy is easily suppressed by electron doping.« less

  11. Electron doping evolution of the magnetic excitations in NaFe1 xCoxAs

    DOE PAGES

    Carr, Scott V.; Zhang, Chenglin; Song, Yu; Tan, Guotai; Li, Yu; Abernathy, Douglas L.; Stone, Matthew B.; Granroth, Garrett E.; Perring, T. G.; Dai, Pengcheng

    2016-06-13

    We use time-of-flight (TOF) inelastic neutron scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1-xCoxAs with x = 0, 0.0175, 0.0215, 0.05, and 0.11. The effect of electron-doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden and suppress low energy (E 80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high energy (E > 80 meV) spin excitations are weakly Co-doping dependent. Integration of the local spin dynamic susceptibility "(!) of NaFe1-xCoxAs reveals a total fluctuating moment of 3.6 μ2 B/Fe andmore » a small but systematic reduction with electron doping. The presence of a large spin gap in the Cooverdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel Ni-doping evolution of spin excitations in BaFe2-xNixAs2, confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping dependent high-energy spin excitations result from localized moments.« less

  12. A high Tc superconducting terahertz emitter operated from 0.5 to 2.4 THz

    NASA Astrophysics Data System (ADS)

    Kashiwagi, T.; Sakamoto, K.; Kubo, H.; Shibano, Y.; Enomoto, T.; Kitamura, T.; Asanuma, K.; Yasui, T.; Watanabe, C.; Nakade, K.; Saiwai, Y.; Katsuragawa, T.; Tanaka, T.; Yuasa, T.; Tsujimoto, M.; Yoshizaki, R.; Yamamoto, T.; Minami, H.; Klemm, R. A.; Kadowaki, K.

    According to our previous studies, the efficiency of the THz radiation from a high Tc superconducting emitter can be improved greatly when the stand-alone mesa structure of Bi2212 single crystal is used for the emitter1). The principal reason for that lies in the heat removal from the mesa. Recently, we developed a new device structure with high heat exhaust from the stand-alone mesa structures and studied the radiation characteristics from the different shape of mesa structures. The results obtained from a cylindrical stand alone mesa show very wide the radiation frequencies ranging from 0.5 to 2.4 THz. Strong emission power peaks were observed at about 1.0 THz and 1.6 THz2). 1) T. Kitamura et al., Appl. Phys. Lett. 105, 202603 (2014) 2) T. Kashiwagi et al., Appl. Phys. Lett. 107, 082601 (2015) T. K. is supported by Futaba Electronics Memorial Foundation and JSPS KAKENHI Grant No. 15K20897. This work is in part performed in collaboration with Dr. Wai Kwok and his group in Argonne National Lab.

  13. Emergence of Complex States in CMR Manganites and High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Dagotto, Elbio

    2005-03-01

    Recent developments in the context of theory and experiments for manganites and cuprates will be discussed. It will be argued that the presence of nanoscale phase separation is at the heart of the colossal magnetoresistance phenomenon [1]. Simulation results support this view, as well as experimental data. These effects are not limited to manganites, but they may appear in other compounds as well, such as the high-Tc cuprates. New results will be presented in this area, on the phenomenological competition between antiferromagnetism and d-wave superconductivity, suggesting the possibility of ``colossal'' effects in this context [2]. This is compatible with the recent discovery of ``giant proximity effects'' in Cu-oxides [3]. All this suggests that clustered or mixed-phase states could form a new paradigm for the understanding of compounds in condensed matter physics. Work in collaboration with G. Alvarez, M. Mayr, A. Moreo, C. Sen, and I. Sergienko, supported by NSF DMR. [1] A. Moreo et al., Science 283, 2034 (1999); E.D., T. Hotta and A. Moreo, Physics Reports 344,1 (2001); E.D., ``Nanoscale Phase Separation and Colossal Magnetoresistance'', Springer-Verlag, 2002. [2] G. Alvarez et al., cond-mat/0401474, PRB to appear. [3] I. Bozovic et al., Phys. Rev. Lett. 93, 157002 (2004)

  14. Normal-state nodal electronic structure in underdoped high-Tc copper oxides.

    PubMed

    Sebastian, Suchitra E; Harrison, N; Balakirev, F F; Altarawneh, M M; Goddard, P A; Liang, Ruixing; Bonn, D A; Hardy, W N; Lonzarich, G G

    2014-07-01

    An outstanding problem in the field of high-transition-temperature (high-Tc) superconductivity is the identification of the normal state out of which superconductivity emerges in the mysterious underdoped regime. The normal state uncomplicated by thermal fluctuations can be studied using applied magnetic fields that are sufficiently strong to suppress long-range superconductivity at low temperatures. Proposals in which the normal ground state is characterized by small Fermi surface pockets that exist in the absence of symmetry breaking have been superseded by models based on the existence of a superlattice that breaks the translational symmetry of the underlying lattice. Recently, a charge superlattice model that positions a small electron-like Fermi pocket in the vicinity of the nodes (where the superconducting gap is minimum) has been proposed as a replacement for the prevalent superlattice models that position the Fermi pocket in the vicinity of the pseudogap at the antinodes (where the superconducting gap is maximum). Although some ingredients of symmetry breaking have been recently revealed by crystallographic studies, their relevance to the electronic structure remains unresolved. Here we report angle-resolved quantum oscillation measurements in the underdoped copper oxide YBa2Cu3O6 + x. These measurements reveal a normal ground state comprising electron-like Fermi surface pockets located in the vicinity of the nodes, and also point to an underlying superlattice structure of low frequency and long wavelength with features in common with the charge order identified recently by complementary spectroscopic techniques. PMID:24930767

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

    PubMed

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

    2014-01-01

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

  16. Nodal bilayer-splitting controlled by spin-orbit interactions in underdoped high-Tc cuprates

    DOE PAGES

    Harrison, N.; Ramshaw, B. J.; Shekhter, A.

    2015-06-03

    The highest superconducting transition temperatures in the cuprates are achieved in bilayer and trilayer systems, highlighting the importance of interlayer interactions for high Tc. It has been argued that interlayer hybridization vanishes along the nodal directions by way of a specific pattern of orbital overlap. Recent quantum oscillation measurements in bilayer cuprates have provided evidence for a residual bilayer-splitting at the nodes that is sufficiently small to enable magnetic breakdown tunneling at the nodes. Here we show that several key features of the experimental data can be understood in terms of weak spin-orbit interactions naturally present in bilayer systems, whosemore » primary effect is to cause the magnetic breakdown to be accompanied by a spin flip. These features can now be understood to include the equidistant set of three quantum oscillation frequencies, the asymmetry of the quantum oscillation amplitudes in c-axis transport compared to ab-plane transport, and the anomalous magnetic field angle dependence of the amplitude of the side frequencies suggestive of small effective g-factors. We suggest that spin-orbit interactions in bilayer systems can further affect the structure of the nodal quasiparticle spectrum in the superconducting phase. PACS numbers: 71.45.Lr, 71.20.Ps, 71.18.+y« less

  17. Local effects of apical oxygen on superconductivity in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Mori, Michiyasu; Tohyama, Takami; Maekawa, Sadamichi

    2008-03-01

    The superconducting critical temperature (Tc) of high- Tc cuprates widely distributes among various series of crystal structures, even if the doping rate is optimized in the CuO2 planes. In addition, the Tc is enhanced by applying pressure[1]. These material- and pressure dependences have meaningful correlation with an energy difference of oxygen sites in an apical site and in the CuO2 plane (VA)[2]. On the other hand, Slezak et al. has found that locally modulated gap energy has anti-correlation with a distance between a Cu- and an apical O-sites, i.e., the larger distance is related to the smaller gap energy[3]. We study such a local effect of apical oxygen on superconductivity by calculating the Madelung potential. In particular, we focus on a local variation of VA, whose value approximately corresponds to stability of the Zhang- Rice singlet state[2]. It is found that, on neighboring sites of apical sites close to Cu sites, VA are locally enhanced compared to other sites. To estimate the gap energy, we propose a toy model like a BCS mean field Hamiltonian with an additional degree of freedom, which describes a role of apical oxygen. We will discuss an anti-correlation between the gap energy and the position of apical oxygen. [1] N. Tanahashi et al: Jpn. J. Appl. Phys. 28, L762 (1989). [2] Y. Ohta, T. Tohyama, and S. Maekawa: Phys. Rev. B 43, 2968 (1991). [3] J. Slezak, PhD thesis.

  18. Possible enhancements of AFM spin-fluctuations in high-TC cuprates

    NASA Astrophysics Data System (ADS)

    Jarlborg, Thomas

    2009-03-01

    Ab-initio band calculations for high-TC cuprates, together with modelling based of a free electron like band, show a strong interaction between anti-ferromagnetic (AFM) spin waves and periodic lattice distortions as for phonons, even though this type of spin-phonon coupling (SPC) is underestimated in calculations using the local density approximation. The SPC has a direct influence on the properties of the HTC cuprates and it can explain many observations. The strongest effects are seen for modulated waves in the CuO bond direction, and a band gap is formed near the X,Y points, but unusal band dispersion (like ``waterfalls'') might also be induced below the Fermi energy (EF) in the diagonal direction. The band results are used to propose different ways of increasing AFM spin-fluctuations locally, and to have a higher density-of-states (DOS) at EF. Static potential modulations, via periodic distribution of dopants or lattice distortions, can be tuned to increase the DOS. This opens for possibilities to enhance coupling for spin fluctuations (λsf) and superconductivity. The exchange enhancement is in general increased near a surface, which suggests a tendency towards static spin configurations. The sensivity of the band results to corrections of the local density potential are discussed.

  19. Verification of electron doping in single-layer graphene due to H{sub 2} exposure with thermoelectric power

    SciTech Connect

    Hong, Sung Ju; Kang, Hojin; Soler-Delgado, David; Kim, Kyung Ho; Park, Yung Woo E-mail: kbh37@incheon.ac.kr; Park, Min; Lee, Minwoo; Jeong, Dae Hong; Shin, Dong Seok; Kim, Byung Hoon E-mail: kbh37@incheon.ac.kr; Kubatkin, Sergey

    2015-04-06

    We report the electron doping of single-layer graphene (SLG) grown by chemical vapor deposition (CVD) by means of dissociative hydrogen adsorption. The transfer characteristic showed n-type doping behavior similar to that of mechanically exfoliated graphene. Furthermore, we studied the thermoelectric power (TEP) of CVD-grown SLG before and after exposure to high-pressure H{sub 2} molecules. From the TEP results, which indicate the intrinsic electrical properties, we observed that the CVD-grown SLG is n-type doped without degradation of the quality after hydrogen adsorption. Finally, the electron doping was also verified by Raman spectroscopy.

  20. Andreev-Bragg Reflection from an Amperian Superconductor.

    PubMed

    Baireuther, P; Hyart, T; Tarasinski, B; Beenakker, C W J

    2015-08-28

    We show how an electrical measurement can detect the pairing of electrons on the same side of the Fermi surface (Amperian pairing), recently proposed by Patrick Lee for the pseudogap phase of high-Tc cuprate superconductors. Bragg scattering from the pair-density wave introduces odd multiples of 2k(F) momentum shifts when an electron incident from a normal metal is Andreev reflected as a hole. These Andreev-Bragg reflections can be detected in a three-terminal device, containing a ballistic Y junction between normal leads (1, 2) and the superconductor. The cross-conductance dI1/dV2 has the opposite sign for Amperian pairing than it has either in the normal state or for the usual BCS pairing.

  1. Superconductor cable

    DOEpatents

    Allais, Arnaud; Schmidt, Frank (Langenhagen, DE

    2009-12-15

    A superconductor cable includes a superconductive cable core (1) and a cryostat (2) enclosing the same. The cable core (1) has a superconductive conductor (3), an insulation (4) surrounding the same and a shielding (5) surrounding the insulation (4). A layer (3b) of a dielectric or semiconducting material is applied to a central element (3a) formed from a normally conducting material as a strand or tube and a layer (3c) of at least one wire or strip of superconductive material is placed helically on top. The central element (3a) and the layer (3c) are connected to each other in an electrically conducting manner at the ends of the cable core (1).

  2. Anomalous open-circuit voltage from a high-Tc superconducting dynamo

    NASA Astrophysics Data System (ADS)

    Bumby, C. W.; Jiang, Zhenan; Storey, J. G.; Pantoja, A. E.; Badcock, R. A.

    2016-03-01

    We report on the behavior of a high-Tc superconducting (HTS) homopolar dynamo which outputs a DC open-circuit voltage when the stator is in the superconducting state, but behaves as a conventional AC alternator when the stator is in the normal state. We observe that this time-averaged DC voltage arises from a change in the shape of the AC voltage waveform that is obtained from a normal conducting stator. The measured DC voltage is proportional to frequency, and decreases with increasing flux gap between the rotor magnet and the HTS stator wire. We observe that the DC output voltage decreases to zero at large flux gaps, although small differences between the normal-conducting and superconducting waveforms are still observed, which we attribute to screening currents in the HTS stator wire. Importantly, the normalised pulse shape is found to be a function of the rotor position angle only. Based on these observations, we suggest that the origin of this unexpected DC effect can be explained by a model first proposed by Giaever, which considers the impact of time-varying circulating eddy currents within the HTS stator wire. Such circulating currents form a superconducting shunt path which "short-circuits" the high field region directly beneath the rotor magnet, at those points in the cycle when the rotor magnet partially overlaps the superconducting stator wire. This reduces the output voltage from the device during these periods of the rotor cycle, leading to partial rectification of the output voltage waveform and hence the emergence of a time-averaged DC voltage.

  3. Impact of lattice distortion and electron doping on α-MoO3 electronic structure

    PubMed Central

    Huang, Peng-Ru; He, Yao; Cao, Chao; Lu, Zheng-Hong

    2014-01-01

    Band structure of transition metal oxides plays a critical role in many applications such as photo-catalysis, photovoltaics, and electroluminescent devices. In this work we report findings that the band structure of MoO3 can be significantly altered by a distortion in the octahedral coordination structure. We discovered that, in addition to epitaxial type of structural strain, chemical force such as hydrogen inclusion can also cause extended lattice distortion. The lattice distortion in hydrogenated MoO3 led to a significant reduction of the energy gap, overshadowing the Moss-Burstein effect of band filling. Charge doping simulations revealed that filling of conduction band drives the lattice distortion. This suggests that any charge transfer or n-type electron doping could lead to lattice distortion and consequentially a reduction in energy gap. PMID:25410814

  4. Electron doping evolution of the magnetic excitations in NaFe1 -xCoxAs

    NASA Astrophysics Data System (ADS)

    Carr, Scott V.; Zhang, Chenglin; Song, Yu; Tan, Guotai; Li, Yu; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Perring, T. G.; Dai, Pengcheng

    2016-06-01

    We use time-of-flight (TOF) inelastic-neutron-scattering (INS) spectroscopy to investigate the doping dependence of magnetic excitations across the phase diagram of NaFe1 -xCoxAs with x =0 , 0.0175, 0.0215, 0.05, and 0.11 . The effect of electron doping by partially substituting Fe by Co is to form resonances that couple with superconductivity, broaden, and suppress low-energy (E ≤80 meV) spin excitations compared with spin waves in undoped NaFeAs. However, high-energy (E >80 meV) spin excitations are weakly Co-doping-dependent. Integration of the local spin dynamic susceptibility χ''(ω ) of NaFe1 -xCoxAs reveals a total fluctuating moment of 3.6 μB2/Fe and a small but systematic reduction with electron doping. The presence of a large spin gap in Co-overdoped nonsuperconducting NaFe0.89Co0.11As suggests that Fermi surface nesting is responsible for low-energy spin excitations. These results parallel the Ni-doping evolution of spin excitations in BaFe2 -xNixAs2 in spite of the differences in crystal structures and Fermi surface evolution in these two families of iron pnictides, thus confirming the notion that low-energy spin excitations coupling with itinerant electrons are important for superconductivity, while weakly doping-dependent high-energy spin excitations result from localized moments.

  5. Fabrication and testing of long length high-{Tc} composite conductors. Final report

    SciTech Connect

    Fisher, L.M.

    1997-12-31

    Presently some methods of HTS-conductors processing are under study in the authors laboratory. ``Powder-in-tube`` (PIT), ``Jelly-roll``, electrophorethis are among them. PIT process has developed predominantly both in a view of the achieved J{sub c} values Bi-2223 phase was used as a core material for these tapes. Since the main purpose of the task order was to enhance the development of long length high temperature superconductor tapes, the authors have considered reasonable to lay the perfection idea of the PIT process step by step or tape by tape. To realize it they have assumed, keeping stable the basic scheme of PIT process, to vary some technological parameters which are as follows: (1) type of initial powder; (2) sheath material; (3) tape construction (filaments number, cross section e.a.); and (4) processing regimes. This report covers the fabrication process and characteristics of the produced conductors.

  6. Passive magnetic field cancellation device by multiple high-Tc superconducting coils

    NASA Astrophysics Data System (ADS)

    Gu, C.; Zou, S.; Han, Z.; Qu, T.-M.

    2010-04-01

    A passive magnetic field cancellation device (PMFCD) is designed. The PMFCD could automatically cancel the field as an active cancellation system did; however it requires no power sources and feedback systems. The capability of the PMFCD is based on the principle that a closed loop can resist flux variation and keep the flux constant inside. The closed loop in the PMFCD is formed by connecting two pairs of high temperature superconductor Helmholtz coils with different radii in series. More important thing is that the ratio of the radius and the turn number between the coils has to satisfy a number of conditions, with which 100% cancellation can be reached. Theoretical methods to obtain the turn number ratio and radius ratio are the major part of the paper. Numerical simulation was followed, aiming to evaluate field distribution under a cancellation state and correct the theoretical values.

  7. Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

    NASA Astrophysics Data System (ADS)

    Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2015-09-01

    The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (x z ,y z ,x y ) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. In this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations reveal that the fast reduction with doping of the Néel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. This study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped 122 compounds.

  8. Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

    SciTech Connect

    Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2015-09-21

    The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. Moreover, in this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations reveal that the fast reduction with doping of the N eel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Finally, our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. Our study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found

  9. Isotropic in-plane quenched disorder and dilution induce a robust nematic state in electron-doped pnictides

    DOE PAGES

    Liang, Shuhua; Bishop, Christopher B.; Moreo, Adriana; Dagotto, Elbio

    2015-09-21

    The phase diagram of electron-doped pnictides is studied varying the temperature, electronic density, and isotropic in-plane quenched disorder strength and dilution by means of computational techniques applied to a three-orbital (xz,yz,xy) spin-fermion model with lattice degrees of freedom. In experiments, chemical doping introduces disorder but in theoretical studies the relationship between electronic doping and the randomly located dopants, with their associated quenched disorder, is difficult to address. Moreover, in this publication, the use of computational techniques allows us to study independently the effects of electronic doping, regulated by a global chemical potential, and impurity disorder at randomly selected sites. Surprisingly,more » our Monte Carlo simulations reveal that the fast reduction with doping of the N eel TN and the structural TS transition temperatures, and the concomitant stabilization of a robust nematic state, is primarily controlled in our model by the magnetic dilution associated with the in-plane isotropic disorder introduced by Fe substitution. In the doping range studied, changes in the Fermi surface produced by electron doping affect only slightly both critical temperatures. Our results also suggest that the specific material-dependent phase diagrams experimentally observed could be explained as a consequence of the variation in disorder profiles introduced by the different dopants. Finally, our findings are also compatible with neutron scattering and scanning tunneling microscopy, unveiling a patchy network of locally magnetically ordered clusters with anisotropic shapes, even though the quenched disorder is locally isotropic. Our study reveals a remarkable and unexpected degree of complexity in pnictides: the fragile tendency to nematicity intrinsic of translational invariant electronic systems needs to be supplemented by quenched disorder and dilution to stabilize the robust nematic phase experimentally found in electron-doped

  10. Cryocooler cooled HTS current lead for a 35 kJ/7 kW-class high- Tc SMES system

    NASA Astrophysics Data System (ADS)

    Ren, L.; Tang, Y.; Shi, J.; Chen, N.; Li, J.; Cheng, S.

    2008-09-01

    Within 863 program of China, a 35 kJ/7 kW-class high- Tc superconducting magnetic energy storage system (SMES) was completed in Nov. 2005. It operates at 100 A in the cryogenic environment of 20 K and is cooled by conduction cooling. It is essential to minimize heat loss from room temperature and to optimize the ohmic heating of current leads. So, 100 A hybrid type current leads, consisting of conventional copper parts and high- Tc superconducting (HTS) parts, were designed, fabricated and tested. The HTS parts of the leads were made of Bi-2223 cylindrical bulk and the copper parts were winded into just like a sparse solenoid to prolong the path for heat transfer. The current leads were cooled directly by a two-stage cryocooler. And, a series of experiments were carried out. The experimental results show a good according with the simulation, which verify that the hybrid current lead meets the requirements of high- Tc SMES.

  11. Effect of Van Hove singularities on high-Tc superconductivity in H3S

    NASA Astrophysics Data System (ADS)

    Sano, Wataru; Koretsune, Takashi; Tadano, Terumasa; Akashi, Ryosuke; Arita, Ryotaro

    2016-03-01

    One of the interesting open questions for the high-transition-temperature (Tc) superconductivity in sulfur hydrides is why high-pressure phases of H3S have extremely high Tc's. Recently, it has been pointed out that the presence of the Van Hove singularities (VHS) around the Fermi level is crucial. However, while there have been quantitative estimates of Tc based on the Migdal-Eliashberg theory, the energy dependence of the density of states (DOS) has been neglected to simplify the Eliashberg equation. In this study, we go beyond the constant DOS approximation and explicitly consider the electronic structure over 40 eV around the Fermi level. In contrast with the previous conventional calculations, this approach with a sufficiently large number of Matsubara frequencies enables us to calculate Tc without introducing the empirical pseudo Coulomb potential. We show that while H3S has much higher Tc than H2S for which the VHS is absent, the constant DOS approximation employed so far seriously overestimates (underestimates) Tc by ˜60 K (˜10 K) for H3S (H2S ). We then discuss the impact of the strong electron-phonon coupling on the electronic structure with and without the VHS and how it affects the superconductivity. In particular, we focus on (1) the feedback effect in the self-consistent calculation of the self-energy, (2) the effect of the energy shift due to the zero-point motion, and (3) the effect of the changes in the phonon frequencies due to strong anharmonicity. We show that the effect of (1)-(3) on Tc is about 10-30 K for both H3S and H2S . Eventually, Tc is estimated to be 181 K for H3S at 250 GPa and 34 K for H2S at 140 GPa, which explains the pressure dependence of Tc observed in the experiment. In addition, we evaluate the lowest-order vertex correction beyond the Migdal-Eliashberg theory and discuss the validity of the Migdal approximation for sulfur hydrides.

  12. Performance of a polarised neutron cryo-flipper using a high TcYBCO film

    NASA Astrophysics Data System (ADS)

    Parnell, S. R.; Washington, A. L.; Kaiser, H.; Li, F.; Wang, T.; Hamilton, W. A.; Baxter, D. V.; Pynn, R.

    2013-09-01

    It is well-known that the Meissner effect in superconducting materials can be used to provide a well-defined, non-adiabatic, magnetic-field transition. This can be utilised to produce a highly efficient neutron spin flipper that is suitable for use with neutrons of multiple wavelengths. Devices of this type using superconducting niobium have been deployed on neutron diffractometers for several decades but have required liquid helium to maintain the correct temperature. The use of high Tc materials, which removes the need for cryogens and simplifies the device, was first explored by Fitzsimmons et al. in [1]. In this communication, we describe a π flipper which uses commercially available films consisting of a 350-nm-thick YBCO film capped with 100 nm of gold on a 78×100×0.5 mm sapphire substrate. We discuss the design and performance of this device. 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 He refrigerator. The part of the vacuum chamber, where the YBCO film is located, is 5 cm wide, which allows us to minimise the distance from the film to the magnetic guide fields. Negligible small angle neutron scattering is observed from the flipper and its transmission is measured to be greater than 98.5% over a wide band of neutron wavelengths. In this design, the maximum neutron beam size that can be used is 42×42 mm2 and we can easily switch from a vertical to a horizontal guide field (both perpendicular to the neutron beam) on either side of the YBCO film. Data are reported for neutron wavelengths between 4 and 8.5 Å and flipping efficiencies under a variety of conditions are discussed. Under optimum conditions an efficiency of 99.5±0.3% was achieved for 4-8 Å neutrons on a pulsed source and 99.4±0.5% was achieved at a monochromatic source using a neutron wavelength of 4.2 Å.

  13. Large low-symmetry polarons of the high-Tc, copper oxides: Formation, mobility and ordering

    NASA Astrophysics Data System (ADS)

    Bersuker, Gennadi I.; Goodenough, John B.

    1997-02-01

    A microscopic model of the evolution from antiferromagnetic insulator to superconductor on oxidation of the parent-phase (CuO 2) 2- sheets of a cuprate superconductor starts with the assumption that strong electron-lattice interactions are dominant and give a heterogeneous electronic distribution. Introduction of pseudo-Jahn-Teller vibronic coupling associated with the δ holes in the (CuO 2) (2-δ) - sheets is shown to stabilize, below a critical temperature Tp ≈ 850 K, large non-adiabatic polarons containing 5 to 7 copper centers; cooperative low-symmetry in-plane vibrations also stabilize an elastic attractive force between polarons that can overcome the longer-range Coulomb repulsion between polarons. Utilizing established parameters for isolated CuO 6 complexes gives a calculated polaron size of 5 to 7 copper centers, which compares with a measured mean size of 5.3 copper centers in underdoped samples 0 < δ ≤ 0.10. A large polaron is shown to move by a piece-wise tunneling of a fraction of itself across a peripheral CuO vibronic bond rather than by an activated hopping. This type of motion, which is not described by conventional transport theories, gives a linear increase of the resistivity with temperature above a temperature Tϱ due to scattering of the polaron at its own border, which separates regions inside and outside the polaron of slightly different mean CuO bond length. At lower temperatures, the polaron mobility becomes activated, but at higher concentrations this change is obscured because the elastic interpolaron attractive force causes the polarons to condense into a “polaron liquid,” and below some critical temperature Td ≥ Tc the polarons undergo long-range ordering into one-dimensional <110> polaronic stripes separated by stripes of the parent phase, which support antiferromagnetic spin fluctuations. The zig-zag polaron stripes consist of polaron pairs oriented alternately along [100] and [010] axes of a CuO 2 sheet. Formation

  14. Fragile surface zero-energy flat bands in three-dimensional chiral superconductors

    NASA Astrophysics Data System (ADS)

    Kobayashi, Shingo; Tanaka, Yukio; Sato, Masatoshi

    2015-12-01

    We study surface zero-energy flat bands in three-dimensional chiral superconductors with pz(px+i py) ν -wave pairing symmetry (ν is a nonzero integer), based on topological arguments and tunneling conductance. It is shown that the surface flat bands are fragile against (i) the surface misorientation and (ii) the surface Rashba spin-orbit interaction. The fragility of (i) is specific to chiral SCs, whereas that of (ii) happens for general odd-parity SCs. We demonstrate that these flat-band instabilities vanish or suppress a zero-bias conductance peak in a normal/insulator/superconductor junction, which behavior is clearly different from high-Tc cuprates and noncentrosymmetric superconductors. By calculating the angle-resolved conductance, we also discuss a topological surface state associated with the coexistence of line and point nodes.

  15. The Composition and Structure of Y-Ba-Cu-O Superconductors

    NASA Astrophysics Data System (ADS)

    Hua, Z. Y.; Jia, C. L.; Cheng, H. S.; Cai, Y. M.; Jiang, A. R.

    High Tc superconductors of Y-Ba-Cu-O system with (Y+Ba):Cu=1~2 have been investigated. Results show that any sample in this system with a proportion of Y:Cu between 0.6 and 1.2 is oxygen-deficient and will be superconductive after sintering in an oxygen flow. In this system all superconductors with different nominal composition have a superconductive phase of perovskite-1ike YBa2Cu3O7 (Phase A), and the difference of constituents is shown in another phase (Phase B) which acts as a gettering center. When the composition has an excess of Y, there will be a third phase (Phase C) which has been identified as small particles of Y2O3. For an exact nominal proportion of Y:Ba:Cu=1:2:3, single-phase superconductors can be prepared.

  16. Infrared detection with high-[Tc] bolometers and response of Nb tunnel junctions to picosecond voltage pulses

    SciTech Connect

    Verghese, S.

    1993-05-01

    Oxide superconductors with high critical temperature [Tc] make sensitive thermometers for several types of infrared bolometers. The authors built composite bolometers with YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta

  17. Shining light on CuO for exploring high-Tc multiferroics

    NASA Astrophysics Data System (ADS)

    Stucky, A.; Ubaldini, A.; Levallois, J.; Tran, M. K.; van der Marel, D.; Giannini, E.

    2014-12-01

    Searching for a 3D multiferroic material with a strong magnetoelectric coupling and high critical temperature is a major challenge in modern condensed matter research. CuO is the building block of high-temperature superconductors and triggered a new interest when it was established as potential high temperature multiferroic. We have succeeded in growing high quality single crystals of CuO with two different methods, namely the floating zone under high oxygen pressure and the chemical vapor transport growth. The fact that we are able to grow crystals of the same compound by different techniques makes it possible to study the effect of slightly different chemical compositions, various kinds of defects and variable strain on the final properties of the compound. Optical spectroscopy has been deployed to study the optical response of cupric oxide. Thereby we achieved a deeper insight of the optical, electronic and structural properties by measuring the infrared reflectivity under a magnetic field and the Raman shift under hydrostatic high pressure.

  18. Photo-enhanced antinodal conductivity in the pseudogap state of high-Tc cuprates

    PubMed Central

    Cilento, F.; Dal Conte, S.; Coslovich, G.; Peli, S.; Nembrini, N.; Mor, S.; Banfi, F.; Ferrini, G.; Eisaki, H.; Chan, M. K.; Dorow, C. J.; Veit, M. J.; Greven, M.; van der Marel, D.; Comin, R.; Damascelli, A.; Rettig, L.; Bovensiepen, U.; Capone, M.; Giannetti, C.; Parmigiani, F.

    2014-01-01

    A major challenge in understanding the cuprate superconductors is to clarify the nature of the fundamental electronic correlations that lead to the pseudogap phenomenon. Here we use ultrashort light pulses to prepare a non-thermal distribution of excitations and capture novel properties that are hidden at equilibrium. Using a broadband (0.5–2 eV) probe, we are able to track the dynamics of the dielectric function and unveil an anomalous decrease in the scattering rate of the charge carriers in a pseudogap-like region of the temperature (T) and hole-doping (p) phase diagram. In this region, delimited by a well-defined T*neq(p) line, the photoexcitation process triggers the evolution of antinodal excitations from gapped (localized) to delocalized quasiparticles characterized by a longer lifetime. The novel concept of photo-enhanced antinodal conductivity is naturally explained within the single-band Hubbard model, in which the short-range Coulomb repulsion leads to a k-space differentiation between nodal quasiparticles and antinodal excitations. PMID:25014895

  19. Recrystallization of high temperature superconductors

    SciTech Connect

    Kouzoudis, D.

    1996-05-09

    Currently one of the most widely used high {Tc} superconductors is the Bi-based compounds Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub z} (known as BSCCO 2212 and 2223 compounds) with {Tc} values of about 85 K and 110 K respectively. Lengths of high performance conductors ranging from 100 to 1000 m long are routinely fabricated and some test magnets have been wound. An additional difficulty here is that although Bi-2212 and Bi-2223 phases exist over a wide range of stoichiometries, neither has been prepared in phase-pure form. So far the most successful method of constructing reliable and robust wires or tapes is the so called powder-in-tube (PIT) technique [1, 2, 3, 4, 5, 6, 7] in which oxide powder of the appropriate stoichiometry and phase content is placed inside a metal tube, deformed into the desired geometry (round wire or flat tape), and annealed to produce the desired superconducting properties. Intermediate anneals are often incorporated between successive deformation steps. Silver is the metal used in this process because it is the most compatible with the reacting phase. In all of the commercial processes for BSCCO, Ag seems to play a special catalytic role promoting the growth of high performance aligned grains that grow in the first few micrometers near the Ag/BSCCO interface. Adjacent to the Ag, the grain alignment is more perfect and the current density is higher than in the center of the tape. It is known that Ag lowers the melting point of several of the phases but the detailed mechanism for growth of these high performance grains is not clearly understood. The purpose of this work is to study the nucleation and growth of the high performance material at this interface.

  20. Effects of the Electronic Doping In the Stability of the Metal Hydride NaH

    NASA Astrophysics Data System (ADS)

    Olea-Amezcua, Monica-Araceli; Rivas-Silva, Juan-Francisco; de La Peña-Seaman, Omar; Heid, Rolf; Bohnen, Klaus-Peter

    2015-03-01

    Despite metal hydrides light weight and high hydrogen volumetric densities, the Hydrogen desorption process requires excessively high temperatures due to their high stability. Attempts for improvement the hydrogenation properties have been focus on the introduction of defects, impurities and doping on the metal hydride. We present a systematic study of the electronic doping effects on the stability of a model system, NaH doped with magnesium, forming the alloying system Na1-xMgxH. We use the density functional theory (DFT) and the self-consistent version of the virtual crystal approximation (VCA) to model the doping of NaH with Mg. The evolution of the ground state structural and electronic properties is analyzed as a function of Mg-content. The full-phonon dispersion, calculated by the linear response theory (LRT) and density functional perturbation theory (DFPT), is analyzed for several Mg-concentrations, paying special attention to the crystal stability and the correlations with the electronic structure. Applying the quasiharmonic approximation (QHA), the free energy from zero-point motion is obtained, and its influence on the properties under study is analyzed. This work is partially supported by the VIEP-BUAP (OMPS-EXC14-I) and CONACYT-Mexico (No. 221807) projects.

  1. Lattice-mismatch Strain Effects in Electron-Doped Calcium Manganese Oxide Thin Films

    NASA Astrophysics Data System (ADS)

    Hart, Cacie; Yong, Grace; Warecki, Zoey; Chaudhry, Adeel; Sharma, Prakash; Johnson, Anthony; Schaefer, David; Kolagani, Rajeswari

    2015-03-01

    Electron-doped Calcium Manganese Oxide (CaMnO3-δ) thin films are of interest for use as photocatalysts and fuel cell electrodes in renewable energy applications. Oxygen stoichiometry of the films is a key parameter for the functionality in these applications. Currently, we are investigating the properties of (CaMnO3-δ) films grown by pulsed laser deposition. The thin films are epitaxially grown on LaAlO3 and SrTiO3 substrates. Both of these substrates have larger in-plane lattice parameters than CaMnO3-δ, which leads to bi-axial tensile strain in the thin films. We have characterized the thickness dependence of structural, electrical, and morphological properties of these films using high resolution x-ray diffraction, temperature dependent electrical resistivity measurements, and atomic force microscopy. The thickness dependence is characteristically different from what has been preciously observed in thin films of hole-doped manganites. Our results suggest that coupling between tensile strain and oxygen deficiency affect the electrical and structural properties of the material. NSF Grant ECCS1128586.

  2. Stabilization of Ferromagnetic States by Electron Doping in ZnO-Based Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2001-03-01

    In order to investigate functionality of ZnO as a diluted magnetic semiconductor (DMS), we had studied the magnetism in ZnO doped with 3d transition metal atoms (TM) and showed that it was also a candidate for a new functional magnetic material [1]. In this paper, we develop our previous work and give detailed materials design with ZnO-based DMS based on ab initio calculations. The electronic structure of a TM-doped ZnO was calculated within the local density approximation by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation. Total energies of Zn_1-xTM^\\uparrow_xO and Zn_1-xTM^\\uparrow_x/2TM^downarrow_x/2O, where up and down arrows mean the directions of respective atomic magnetic moments, were compared and appearance of the ferromagnetism was discussed. Effects of carrier doping to these systems were also considered. It was found that their magnetic states were controllable by changing the carrier density. In particular, ferromagnetic states were stabilized by electron doping in the case of Fe, Co or Ni doped ZnO. From the point of practical applications, it is favorable feature to realize high Curie temperature ferromagnet, because n-type ZnO is easily available. [1] K. Sato and H. Katayama-Yoshida, Jpn. J. Appl. Phys. 39 (2000) L555.

  3. THz emission from a slice of high-Tc superconducting single crystal

    NASA Astrophysics Data System (ADS)

    Wang, Huabing

    2008-03-01

    Copper oxide superconductors possess intrinsically a layered crystalline structure, in which superconducting and non-superconducting layers interleave each other. Therefore the crystal itself consists of a number of superconducting junctions sequentially stacked along the c axis of the crystal, and these junctions are often referred to as intrinsic Josephson junctions (IJJs). In the case of Bi2Sr2CaCu2O8+δ (BSCCO), each IJJ measures approximately 1.5 nm thick. Many groups have been exploring the possibilities to develop terahertz (THz) detectors and oscillators based on IJJs, due to the high collective plasma frequencies (up to THz region), the uniformity in junction properties, the easiness to make a large junction array, and the low loss at high frequencies. Some years ago, in IJJs singled out from inside a slice of BSCCO single crystal with a double-sided process, THz response was successfully observed as sharp Shapiro steps at frequencies up to 2.5 THz, and harmonic mixings were carried out with harmonic numbers as large as 90. Recently observed have been THz oscillations in various structures of BSCCO IJJs, which can be excited by dc bias, in-plane magnetic fields, or microwave irradiations at several gigahertz. Needless to say, for practical applications, it is necessary to synchronize the emissions from IJJs, couple the THz oscillations into a finite space, guide them in a controllable way, monitor the frequencies and power levels, and preferably do the jobs using an integrated system. We have been making extensive efforts to explore these ideas, and will report our latest results at the meeting.

  4. Direct angle resolved photoemission spectroscopy and superconductivity of strained high-Tc films

    NASA Astrophysics Data System (ADS)

    Pavuna, Davor; Ariosa, Daniel; Cloetta, Dominique; Cancellieri, Claudia; Abrecht, Mike

    2008-02-01

    Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T_{c} superconductors (HTSC) under different degrees of epitaxial ({compressive vs. tensile}) strain. In overdoped and underdoped in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La_{2-x}Sr_{x}CuO_{4} (LSCO) films we almost double T_{c} to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES data under {tensile} strain exhibit the dispersion that is three-dimensional, yet T_{c} drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO_{2} plane, enhances the two-dimensional character of the dispersion and increases T_{c}, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual lattice of cuprates is like a `Napoleon-cake', i.e. rigid CuO_{2 } planes alternating with softer `reservoir', that distort differently under strain, our data rule out all oversimplified two-dimensional (rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T_{c}.

  5. Upper critical field of electron-doped Pr2-xCexCuO4-δ in parallel magnetic fields

    NASA Astrophysics Data System (ADS)

    Li, Pengcheng; Balakirev, F. F.; Greene, R. L.

    2007-05-01

    We report a systematic study of the resistive superconducting transition in the electron-doped cuprates Pr2-xCexCuO4-δ down to 1.5K for magnetic field up to 58T applied parallel to the conducting ab planes. We find that the zero-temperature parallel critical field [Hc2‖ab(0)] exceeds 58T for the underdoped and optimally doped films. For the overdoped films, 58T is sufficient to suppress the superconductivity. We also find that the Zeeman energy μBHc2‖ab(0) reaches the superconducting gap (Δ0) , i.e., μBHc2‖ab(0)≃Δ0 , for all the dopings, strongly suggesting that the parallel critical field is determined by the Pauli paramagnetic limit in electron-doped cuprates.

  6. Theoretical insights on the electron doping and Curie temperature in La-doped Sr2CrWO6.

    PubMed

    Wang, Jing; Meng, Jian; Wu, Zhijian

    2011-11-30

    The structure and electronic and magnetic properties of La(x)Sr(2-x)CrWO(6) (x = 0.0, 0.5, 1.0, 1.5, 2.0) were investigated by using the density functional theory. With the increase of La doping, the extra electrons are injected into W 5d orbitals, which makes the spin moments of W increase. In addition, the calculated Curie temperature and total magnetic moments decrease with the increase of the electron doping, in agreement with the experimental observation. This also means that the decrease of Curie temperature with the electron doping is intrinsic. Half metallic properties are obtained for x = 0.0, 0.5, 1.5, and 2.0, whereas for x = 1.0, the compound is semiconducting.

  7. Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR.

    PubMed

    Wiecki, P; Roy, B; Johnston, D C; Bud'ko, S L; Canfield, P C; Furukawa, Y

    2015-09-25

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using ^{75}As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe_{2}As_{2} families of iron-pnictide superconductors. These FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of T_{c} and the shape of the superconducting dome in these and other iron-pnictide families. PMID:26451577

  8. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    DOE PAGES

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud’ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting domemore » in these and other iron-pnictide families.« less

  9. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    SciTech Connect

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud’ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-22

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. Furthermore, these FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting dome in these and other iron-pnictide families.

  10. Current-induced nonlinear conduction of two-electron doped manganites Ca1-xCexMnO3

    NASA Astrophysics Data System (ADS)

    Yamato, Y.; Matsukawa, M.; Murano, Y.; Kobayashi, S.; Suryanarayanan, R.

    2010-04-01

    We have investigated the current-induced nonlinear conduction in a charge-ordered phase of two-electron doped manganites Ca1-xCexMnO3 (x = 0.1 and 0.167). The substitution of Ce4+ ion for Ca2+site of the parent matrix causes two-electron doping with the chemical formula Ca^{2+}_{1-x}Ce^{4+}_{x}Mn^{4+}_{1-2x}Mn^{3+}_{2x}O_3 . Seebeck coefficient data of Ca0.9Ce0.1MnO3 are, in both its temperature dependence and its magnitude, very similar to those of Ca0.8Sm0.2MnO3, leading to further evidence for two-electron doping. The VI characteristics measured using a long pulsed current show a negative differential resistance and its associated giant electroresistance effect. It is demonstrated that a temperature rise across the samples due to Joule heating is not responsible for a huge decrease in resistance observed here.

  11. Transport and magnetic properties of electron-doped manganites CaMn1-xSbx03

    NASA Astrophysics Data System (ADS)

    Murano, Y.; Matsukawa, M.; Kobayashi, S.; Nimori, S.; Suryanarayanan, R.

    2010-01-01

    We report transport and magnetic properties of electron-doped manganites CaMn1-xSbxO3. The substitution of Sb5+ ion for Mn 4+site of the parent matrix causes one-electron doping with the chemical formula CaMn4+1-2xMn3+xSb5+x03. Single phase samples (x = 0.02, 0.05, 0.08 and 0.1) are prepared with a solid-state reaction method. Upon increasing the doping level of Sb, the resistivity is suppressed at high temperatures, accompanied by carrier doping. However, it is strongly enhanced at low temperatures because the presence of the Sb ion prevents moving of carriers on the MnO network. Seebeck coefficient of the samples studied shows a negative value over a whole range of temperatures, indicating the electron doping. An anomalous diamagnetic behavior is observed at x = 0.02 0.05 and 0.08, as it has been reported in the V doped manganites. These findings are close to the variation of eg orbital state due to the local lattice distortion associated with the Sb doping.

  12. Collective pinning behavior of intergranular Josephson vortices and the intergranular irreversibility line of high-{Tc} superconducting ceramics

    SciTech Connect

    Miu, L.

    1995-02-01

    The supercurrent-transport properties of YBa{sub 2}Cu{sub 3}O{sub {approximately}7} (Y:123) polycrystalline bulk sintered samples with random grain orientation were thoroughly investigated. The dissipation process in these materials occurs due to intergranular flux motion, rather than by weak-link quenching. It was found that the model which takes into consideration collective creep of intergranular vortices is self-consistent in describing the low-voltage-level current-voltage characteristics and the intergranular irreversibility line of high-{Tc} superconducting ceramics.

  13. Fine uniform filament superconductors

    DOEpatents

    Riley, Jr., Gilbert N.; Li, Qi; Roberts, Peter R.; Antaya, Peter D.; Seuntjens, Jeffrey M.; Hancock, Steven; DeMoranville, Kenneth L.; Christopherson, Craig J.; Garrant, Jennifer H.; Craven, Christopher A.

    2002-01-01

    A multifilamentary superconductor composite having a high fill factor is formed from a plurality of stacked monofilament precursor elements, each of which includes a low density superconductor precursor monofilament. The precursor elements all have substantially the same dimensions and characteristics, and are stacked in a rectilinear configuration and consolidated to provide a multifilamentary precursor composite. The composite is thereafter thermomechanically processed to provide a superconductor composite in which each monofilament is less than about 50 microns thick.

  14. Superconductor rotor cooling system

    DOEpatents

    Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.

    2002-01-01

    A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.

  15. Photothermal measurements of superconductors

    SciTech Connect

    Kino, G.S.; Studenmund, W.R.; Fishman, I.M.

    1996-12-31

    A photothermal technique has been used to measure diffusion and critical temperature in high temperature superconductors. The technique is particularly suitable for determining material quality and inhomogeneity.

  16. Superconductor rotor cooling system

    DOEpatents

    Gamble, Bruce B.; Sidi-Yekhlef, Ahmed; Schwall, Robert E.; Driscoll, David I.; Shoykhet, Boris A.

    2004-11-02

    A system for cooling a superconductor device includes a cryocooler located in a stationary reference frame and a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with a rotating reference frame in which the superconductor device is located. A method of cooling a superconductor device includes locating a cryocooler in a stationary reference frame, and transferring heat from a superconductor device located in a rotating reference frame to the cryocooler through a closed circulation system external to the cryocooler. The closed circulation system interfaces the stationary reference frame with the rotating reference frame.

  17. Ultra-sensitive sensors for weak electromagnetic fields using high-{Tc} SQUIDS for biomagnetism, NDE, and corrosion currents

    SciTech Connect

    Kraus, R.H. Jr.; Flynn, E.R.; Espy, M.; Jia, Q.X.; Wu, X.D.; Reagor, D.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The research has directly contributed to a new DOE supported project, three patents (one granted and two submitted), and several potential opportunities for new program funding at the Laboratory. The authors report significant developments extending from basic understanding of and fabrication techniques for high critical-temperature (high-{Tc}) SQUID devices to the development of high-level applications such as the SQUID Microscope. The development of ramp edge geometry and silver-doped YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) electrodes has tremendously improved the performance of high-{Tc} SQUIDS. Recent experiments have proven and quantified the LANL-patented superconducting imaging plane gradiometry concept. A SQUID microscope, developed largely under this project, has recently acquired data that demonstrated exceptional sensitivity a nd resolution. New techniques for background noise suppression, needed to use the extraordinarily sensitive SQUID sensors in unshielded environments, have also been developed. Finally, initial investigations to use SQUIDs in a basic physics experiment to measure the electric dipole moment of the neutron were very successful.

  18. Structure, stoichiometry and spectroscopy of oxide superconductors

    NASA Astrophysics Data System (ADS)

    Rao, C. N. R.

    In the new oxide superconductors, structure and oxygen stoichiometry play the most crucial role. Thus, all the high-temperature oxide superconductors are orthorhombic perovskites with low-dimensional features. Oxygen stoichiometry in YBa2Cu3O7-δ has an important bearing on the structure as well as superconductivity. This is equally true in the La3-xBa3+xCu 6O14+δ system of which only the 123 oxide (x = 1) with the orthorhombic structure shows high Tc. Orthorhombicity though not essential, is generally found ; it is necessary for the formation of twins. The nature of oxygen and copper in the cuprates has been examined by electron spectroscopy. Copper in these cuprates is only in 1 + and 2 + states. It seems likely that oxygen holes are responsible for superconductivity of the cuprates as well as Ba(Bi, Pb)O3. High Tc superconductivity is also found in oxides of the Bi-(Ca, Sr)-Cu-O and related oxides possessing Cu-O sheets. Dans les nouveaux oxydes supraconducteurs, la structure et la stoechiométrie de l'oxygène jouent un rôle absolument crucial. Ainsi, tous les oxydes supraconducteurs à haute température critique sont des pérovskites orthorhombiques possédant des propriétés de basse dimensionnalité. La stoechiométrie de l'oxygène dans YBa2Cu3O7- δ a une influence importante tant sur la structure que sur la supraconductibilité. Ceci est également valable pour les composés du type La3 -xBa3 + xCu 6O14 + δ parmi lesquels seul l'oxyde 123 (x = 1) à structure orthorhombique présente un grand T. Bien que ce ne soit pas essentiel, cette orthorhombicité est fréquente ; elle est nécessaire à la formation de macles. La nature de l'oxygène et du cuivre a été observée par spectroscopie électronique... Dans ces cuprates, le cuivre est dans les seuls états de valence + 1 et + 2. Vraisemblablement, les trous logés sur l'oxygène sont responsables de la supraconductibilité des cuprates comme de Ba(Bi, Pb)O3. La supraconductibilité existe aussi

  19. Scanning tunneling spectroscopic evidence for a magnetic field-revealed microscopic order in the high-TC superconductor YBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Beyer, A. D.; Grinolds, M. S.; Teague, M. L.; Yeh, N.-C.; Tajima, S.

    2009-03-01

    We present spatially resolved scanning tunneling spectroscopic measurements of YBa2Cu3O7-δ as a function of magnetic field and at T<

  20. High-Tc Superconductivity near the Anion Height Instability in Fe-Based Superconductors: Analysis of LaFeAsO1-xHx

    NASA Astrophysics Data System (ADS)

    Onari, Seiichiro; Yamakawa, Youichi; Kontani, Hiroshi

    2014-05-01

    The isostructural transition in the tetragonal phase with a sizable change in the anion height, is realized in heavily H-doped LaFeAsO and (La,P) codoped CaFe2As2. In these compounds, the superconductivity with higher Tc (40-50 K) is realized near the isostructural transition. To find the origin of the anion-height instability and the role in realizing the higher-Tc state, we develop the orbital-spin fluctuation theory by including the vertex correction. We analyze LaFeAsO1-xHx and find that the non-nematic orbital fluctuations, which induce the anion-height instability, are automatically obtained at x ˜0.5, in addition to the conventional nematic orbital fluctuations at x˜0. The non-nematic orbital order triggers the isostructural transition, and its fluctuation would be a key ingredient to realize higher-Tc superconductivity of order 50 K.

  1. Photoinduced Melting of Superconductivity in the High-Tc Superconductor La2−xSrxCuO4 Probed by Time-resolved Optical and Terahertz Techniques

    SciTech Connect

    Logvenov, G.; Beyer, M.; Staedter, D.; Beck, M.; Schaefer, H.; Kabanov, V.V.; Bozovic, I.; Koren, G.; Demsar, J.

    2011-06-13

    The dynamics of depletion and recovery of a superconducting state in La{sub 2-x}Sr{sub x}CuO{sub 4} thin films is investigated utilizing optical pump-probe and optical pump-THz-probe techniques as a function of temperature and excitation fluence. The absorbed energy density required to suppress superconductivity is found to be about eight times higher than the thermodynamically determined condensation energy density and nearly temperature independent between 4 and 25 K. These findings indicate that, during the time when the superconducting state suppression takes place ({approx}0.7 ps), a large part (nearly 90%) of the energy is transferred to the phonons with energy lower than twice the maximum value of the superconducting gap and only 10% is spent on Cooper pair breaking.

  2. Structural changes upon electrochemical insertion of lithium into the Bi2Sr2CaCuO8+y high Tc superconductor

    NASA Astrophysics Data System (ADS)

    Fleischer, Niles A.; Manassen, Joost; Coppens, Philip; Lee, Peter; Gao, Yan

    1992-04-01

    The insertion compound LixBi2Sr2CaCu2O8+y (x≤2) was prepared by electrochemical insertion of lithium into Bi2Sr2CaCu2O8+y pellets at room temperature in galvanic cells. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists, but the superconducting fraction appears to be lower in the reacted samples. The lithiated product was analyzed by crystallographic and chemical measurements. The results show that insertion of Li ions is accompanied by an expansion of the interlayer spacing between Bi-O planes and a small increase in the a- and b-cell parameters. This change is consistent with some, but not all, of the donated electrons entering the Cu-O planes, with a corresponding reduction in hole concentration. At higher levels of Li content, a substantial breakdown of the lattice is observed.

  3. Matching field effects at tesla-level magnetic fields in critical current density in high-Tc superconductors containing self-assembled columnar defects

    SciTech Connect

    Sinclair, J.; Zuev, Yuri L; Cantoni, Claudia; Wee, Sung Hun; Varanasi, C. V.; Thompson, James R; Christen, David K

    2012-01-01

    We have investigated the superconductive transport properties of YBa2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC.H/ data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC.H/. The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.

  4. Deviations from Fermi-liquid behavior in (2+1)-dimensional quantum electrodynamics and the normal phase of high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Aitchison, I. J. R.; Mavromatos, N. E.

    1996-04-01

    We argue that the gauge-fermion interaction in multiflavor quantum electrodynamics in (2+1) dimensions is responsible for non-Fermi-liquid behavior in the infrared, in the sense of leading to the existence of a nontrivial (quasi)fixed point that lies between the trivial fixed point (at infinite momenta) and the region where dynamical symmetry breaking and mass generation occurs. This quasifixed-point structure implies slowly varying, rather than fixed, couplings in the intermediate regime of momenta, a situation which resembles that of (four-dimensional) ``walking technicolor'' models of particle physics. The inclusion of wave-function renormalization yields marginal O(1/N) corrections to the ``bulk'' non-Fermi-liquid behavior caused by the gauge interaction in the limit of infinite flavor number. Such corrections lead to the appearance of modified critical exponents. In particular, at low temperatures there appear to be logarithmic scaling violations of the linear resistivity of the system of order O(1/N). The connection with the anomalous normal-state properties of certain condensed-matter systems relevant for high-temperature superconductivity is briefly discussed. The relevance of the large (flavor) N expansion to the Fermi-liquid problem is emphasized. As a partial result of our analysis, we point out the absence of charge-density-wave instabilities from the effective low-energy theory, as a consequence of gauge invariance.

  5. Advanced tensile testing methods for bulk superconductors at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Kasaba, K.; Teshima, H.; Hokari, T.; Sato, T.; Katagiri, K.; Shoji, Y.; Murakami, A.; Hirano, H.

    2006-10-01

    Tensile tests of bulk high Tc superconductors at room temperature have been generally performed by gluing the bulk specimens to Al-alloy rods. Because of the difference in the coefficient of thermal expansion, thermal stresses were induced at cryogenic temperatures especially near the interface between the specimen and the rods. In this study, tensile testing methods with minimized effect of the thermal stress were tried by using specimens cut from Dy-Ba-Cu-O superconductors. These were: (1) The rod material of Al-alloy was replaced with Ti-alloy, which has the coefficient close to the bulk. (2) The interlayer made of the identical bulk superconductor was inserted between the specimen and the Ti-alloy rod. The nominal tensile strength at the liquid nitrogen temperature (LNT) of the specimen glued to the Ti-alloy rods was significantly higher than that glued to the Al-alloy rods. The application of the interlayers increased the strength significantly. The FEM analysis showed that the thermal tensile stress component in the direction of loading axis within the specimen at LNT is markedly reduced by the method (1) and substantially eliminated in the method (2).

  6. Electronic structure, irreversibility line and magnetoresistance of Cu0.3Bi2Se3 superconductor

    SciTech Connect

    Hemian, Yi; Gu, Genda; Chen, Chao -Yu; Sun, Xuan; Xie, Zhuo -Jin; Feng, Ya; Liang, Ai -Ji; Peng, Ying -Ying; He, Shao -Long; Zhao, Lin; Liu, Guo -Dong; Dong, Xiao -Li; Zhang, Jun; Chen, Chuang -Tian; Xu, Zu -Yan; Zhou, X. -J.

    2015-06-01

    CuxBi2Se3 is a superconductor that is a potential candidate for topological superconductors. We report our laser-based angle-resolved photoemission measurement on the electronic structure of the CuxBi2Se3 superconductor, and a detailed magneto-resistance measurement in both normal and superconducting states. We find that the topological surface state of the pristine Bi2Se3 topological insulator remains robust after the Cu-intercalation, while the Dirac cone location moves downward due to electron doping. Detailed measurements on the magnetic field-dependence of the resistance in the superconducting state establishes an irreversibility line and gives a value of the upper critical field at zero temperature of ~4000 Oe for the Cu0.3Bi2Se3 superconductor with a middle point Tc of 1.9K. The relation between the upper critical field Hc2 and temperature T is different from the usual scaling relation found in cuprates and in other kinds of superconductors. Small positive magneto-resistance is observed in Cu0.3Bi2Se3 superconductors up to room temperature. As a result, these observations provide useful information for further study of this possible candidate for topological superconductors.

  7. Fabrication of high temperature superconductors

    DOEpatents

    Balachandran, Uthamalingam; Dorris, Stephen E.; Ma, Beihai; Li, Meiya

    2003-06-17

    A method of forming a biaxially aligned superconductor on a non-biaxially aligned substrate substantially chemically inert to the biaxially aligned superconductor comprising is disclosed. A non-biaxially aligned substrate chemically inert to the superconductor is provided and a biaxially aligned superconductor material is deposited directly on the non-biaxially aligned substrate. A method forming a plume of superconductor material and contacting the plume and the non-biaxially aligned substrate at an angle greater than 0.degree. and less than 90.degree. to deposit a biaxially aligned superconductor on the non-biaxially aligned substrate is also disclosed. Various superconductors and substrates are illustrated.

  8. Divergent nematic susceptibility of optimally doped Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Chu, Jiun-Haw; Kuo, Hsueh-Hui; Fisher, Ian

    2015-03-01

    By performing differential elastoresistivity measurements on a wider range of iron based superconductors, including electron doped (Ba(Fe1-xCox)2As2, Ba(Fe1-xNix)2As2),holedoped(Ba1-xKxFe2As2), isovalent substituted pnictides (BaFe2(As1-xPx)2) and chalcogenides (FeTe1-xSex), we show that a divergent nematic susceptibility in the B2g symmetry channel appears to be a generic feature of optimally doped compositions. For the specific case of optimally ``doped'' BaFe2(As1-xPx)2, the nematic susceptibility can be well fitted by a Curie-Weiss temperature dependence with critical temperature close to zero, consistent with expectations of quantum critical behavior in the absence of disorder. However for all the other optimal doped iron based superconductors, the nematic susceptibility exhibits a downward deviation from Curie-Weiss behavior, suggestive of an important role played by disorder.

  9. Maximum repulsed magnetization of a bulk superconductor with low pulsed field

    NASA Astrophysics Data System (ADS)

    Tsuchimoto, M.; Kamijo, H.; Fujimoto, H.

    2005-10-01

    Pulsed field magnetization of a bulk high- Tc superconductor (HTS) is important technique especially for practical applications of a bulk superconducting magnet. Full magnetization is not obtained for low pulsed field and trapped field is decreased by reversed current in the HTS. The trapped field distribution by repulsed magnetization was previously reported in experiments with temperature control. In this study, repulsed magnetization technique with the low pulsed field is numerically analyzed under assumption of variable shielding current by the temperature control. The shielding current densities are discussed to obtain maximum trapped field by two times of low pulsed field magnetizations.

  10. Simulation of magnetization process of Pure-type superconductor magnet undulator based on T-method

    NASA Astrophysics Data System (ADS)

    Deri, Yi; Kawaguchi, Hideki; Tsuchimoto, Masanori; Tanaka, Takashi

    2015-11-01

    For the next generation Free Electron Laser, Pure-type undulator made of high Tc superconductors (HTSs) was considered to achieve a small size and high intensity magnetic field undulator. In general, it is very difficult to adjust the undulator magnet alignment after the HTS magnetization since the entire undulator is installed inside a cryostat. The appropriate HTS alignment has to be determined in the design stage. This paper presents the development of a numerical simulation code for magnetization process of the Pure-type HTS undulator to assist the design of the optimal size and alignment of the HTS magnets.

  11. Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi

    High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their magnets cooled by LH2. As the first step of the study, an experimental setup which can be used for investigating heat transfer characteristics of LH2 in a pool and also in forced flow (circulation loop with a pump), and also for evaluation of electro-magnetic properties of LH2 cooled superconductors under external magnetic field (up to 7 T). In this paper, we will show a short sketch of the experimental set-up, practical experiences in safety operation of liquid hydrogen cooling system and example test results of critical current evaluation of HTC superconductors cooled by LH2.

  12. Test Status for Proposed Coupling of a Gravitational Force to Extreme Type II YBCO Ceramic Superconductors

    NASA Technical Reports Server (NTRS)

    Noever, David; Li, Ning; Robertson, Tony; Koczor, Ron; Brantley, Whitt

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.

  13. Fabrication and voltage divider operation of a T flip-flop using high-Tc interface-engineered Josephson junctions

    NASA Astrophysics Data System (ADS)

    Kim, Jun Ho; Hyeob Kim, Sang; Sung, Gun Yong

    2002-09-01

    We designed and fabricated a rapid-single-flux-quantum T flip-flop (TFF) with high-Tc interface-engineered Josephson junctions. Y1Ba2Cu3O7-d and Sr2AlTaO6 were deposited for the superconducting layer and the insulating layer, respectively. The Josephson junction was formed through an interface treatment process using Ar ion milling and vacuum annealing. We simulated a TFF circuit and designed a physical layout using WRspice and Xic. The fabricated TFF has a minimum junction width of 3 μm. Through the measurement of the voltage divider operation, the maximum operation frequency was estimated to be 53 GHz at 22 K and 106 GHz at 12 K.

  14. Magnetic relaxation with vortex creep observed by the magneto-optical image method for high Tc superconducting films

    NASA Astrophysics Data System (ADS)

    Lee, Wongi; Lee, Jhinhwan; Youm, Dojun; Yoo, Jaeun

    2016-06-01

    The relaxation of magnetic flux in high Tc superconducting films was investigated. After the samples were cooled in the applied magnetic fields, the magnetic field was turned off and the changes of the remaining magnetic flux distribution were observed by using the magneto-optical image method. The induced current density was examined which varies with the logarithmic-time dependence associated with the creep motions of vortices. The overall magnitude of the induced current density is observed to decrease as the external magnetic field applied during cooling is increased. The range of external fields examined was 30-50 mT. This could be explained by taking into account the formation of meandering shapes of vortices which develop during the period of transition to the creep mode. The results of the numerical simulation for this effect are in good agreement with the experimental results.

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

    NASA Technical Reports Server (NTRS)

    Haertling, Gene; Grabert, Gregory; Gilmour, Phillip

    1993-01-01

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

  16. Probing commensurate ground states of Josephson vortex in layered superconductors.

    PubMed

    Takahashi, Y; Luo, M-B; Nishizaki, T; Kobayashi, N; Hu, X

    2014-04-01

    Because of the commensurability condition between the vortex lattice constant determined by external magnetic field and the nano-scale layered structure, interlayer Josephson vortices (JVs) in high-Tc cuprate superconductors can take various configurations. We have simulated with Langevin scheme the in-plane flux-flow dynamics of JVs subject to point-like pinning centers. Oscillation in resistivity is found with the applied magnetic field, where the resistivity peaks occur around commensurate JV configurations. We have also measured the resistivity experimentally using single crystals of underdoped YBa2Cu3Oy with the anisotropy parameter gamma approximately equal to 50. A unique JV lattice has been detected for the first time.

  17. Upper critical field in electron-doped Pr2-xCexCuO4-δ in parallel magnetic fields

    NASA Astrophysics Data System (ADS)

    Li, Pengcheng; Balakirev, F. F.; Greene, R. L.

    2007-03-01

    We report a comprehensive study of the resistive superconducting transition in the electron-doped Pr2-xCexCuO4-δ films down to 1.5K for magnetic field up to 58T applied parallel to the conducting ab-planes. We find that the parallel critical field (Hc2//ab) exceeds 58T for underdoped and optimally doped films. For the overdoped films, 58T is sufficient to suppress the superconductivity. An Hc2//ab -T phase diagram is established. A comparison between our experimental results and theories for orbital and spin pairbreaking effects will be presented.

  18. High-Field Hall Resistivity and Magnetoresistance of Electron-Doped Pr2-xCexCuO4-δ

    NASA Astrophysics Data System (ADS)

    Li, Pengcheng; Balakirev, F. F.; Greene, R. L.

    2007-07-01

    We report resistivity and Hall effect measurements in electron-doped Pr2-xCexCuO4-δ films in magnetic field up to 58 T. In contrast to hole-doped cuprates, we find a surprising nonlinear magnetic field dependence of Hall resistivity at high field in the optimally doped and overdoped films. We also observe a crossover from quadratic to linear field dependence of the positive magnetoresistance in the overdoped films. A spin density wave induced Fermi surface reconstruction model can be used to qualitatively explain both the Hall effect and magnetoresistance.

  19. Defects in correlated metals and superconductors

    NASA Astrophysics Data System (ADS)

    Alloul, H.; Bobroff, J.; Gabay, M.; Hirschfeld, P. J.

    2009-01-01

    In materials with strong local Coulomb interactions, simple defects such as atomic substitutions strongly affect both macroscopic and local properties of the system. A nonmagnetic impurity, for instance, is seen to induce magnetism nearby. Even without disorder, models of such correlated systems are generally not soluble in two or three dimensions, and so few exact results are known for the properties of such impurities. Nevertheless, some simple physical ideas have emerged from experiments and approximate theories. Here the authors review what we can learn about this problem from one-dimensional (1D) antiferromagnetically correlated systems. Experiments on the high- Tc cuprate normal state which probe the effect of impurities on local charge and spin degrees of freedom are discussed, and compared with theories of single impurities in correlated hosts, as well as phenomenological effective Kondo descriptions. Subsequently, theories of impurities in d -wave superconductors including residual quasiparticle interactions are reviewed and compared with experiments in the superconducting state. Existing data exhibit a remarkable similarity to impurity-induced magnetism in the 1D case, implying the importance of electronic correlations for the understanding of these phenomena, and suggesting that impurities may provide excellent probes of the still poorly understood ground state of the cuprates.

  20. Large area bulk superconductors

    DOEpatents

    Miller, Dean J.; Field, Michael B.

    2002-01-01

    A bulk superconductor having a thickness of not less than about 100 microns is carried by a polycrystalline textured substrate having misorientation angles at the surface thereof not greater than about 15.degree.; the bulk superconductor may have a thickness of not less than about 100 microns and a surface area of not less than about 50 cm.sup.2. The textured substrate may have a thickness not less than about 10 microns and misorientation angles at the surface thereof not greater than about 15.degree.. Also disclosed is a process of manufacturing the bulk superconductor and the polycrystalline biaxially textured substrate material.

  1. A two-phase charge-density real-space-pairing model of high-Tc superconductivity.

    PubMed

    Humphreys

    1999-03-01

    It is usually assumed that high-T(c) superconductors have a periodic band structure and a periodic charge density, although amorphous low-T(c) superconductors are known. In this paper, it is suggested that the CuO(2) conduction planes of cuprate superconductors consist of regions of two different charge densities which do not normally repeat periodically. It is suggested that the pairing of holes occurs in real space in cuprate superconductors. It is proposed that the hole-pairing mechanism is magnetic exchange coupling and the pairing force is strong, the pairing energy being greater than kT at room temperature. The bound hole pair is essentially a bipolaron. A real-space model is very tentatively suggested in which the CuO(2) planes of YBa(2)Cu(3)O(7) contain nanodomains of a 3 x 3 hole lattice surrounded by interfaces one unit cell wide in which the holes are paired. In the superconducting state in this model, the existing hole pairs condense and move coherently and collectively around the insulating nanodomains, like trams running around blocks of houses, with one hole on each tramline. The hole pairs move in an elegant manner with hole pairs hopping from oxygen to oxygen via adjacent copper sites. The model explains the superconducting current being in the ab plane and it also explains the very short coherence lengths. Because the pairing force is strong, the model suggests that room-temperature superconductivity might be possible in carefully designed new oxide materials.

  2. Direct correlation of structural and electrical properties of electron-doped individual VO2 nanowires on devised TEM grids

    NASA Astrophysics Data System (ADS)

    Jo, Y.-R.; Kim, M.-W.; Kim, B.-J.

    2016-10-01

    Nano-scale VO2 wires with controlled parameters such as electron-doping have attracted intense interest due to their capability of suppressing the temperature of the metal-insulator transition (MIT). However, because their diameters are smaller than the spatial resolutions of the conventional measuring equipment, the ability to perform a thorough examination of the wires has been hindered. Here, we report the fabrication of a transmission electron microscopy (TEM) grid with an optimum design of Si3N4 windows on which the photolithography for individual electron-doped VO2 nanowire devices can be safely accomplished, allowing the cross-examination of the structural and electrical properties. TEM dark-field imaging was used to quantitatively investigate the fractions of rutile and M1 phases, and their lattice alignments were observed using high-resolution TEM (HRTEM) with small area diffraction. Moreover, electron energy loss spectroscopy (EELS) revealed that the rutile domain would be created by the strain induced by oxygen vacancies. Importantly, we successfully tuned the transition temperature by changing the rutile fraction while maintaining a high level of resistivity change. The resistivity at room temperature linearly decreased with the rutile fraction, following a simple model. Furthermore, the T dependence of the threshold voltage can be attributed to the Joule heating, exhibiting an identical thermal dependence, irrespective of the rutile fraction.

  3. Influence of electron doping on the ground state of (Sr1-xLax)2IrO4

    DOE PAGES

    Chen, Xiang; Hogan, Tom; Walkup, D.; Zhou, Wenwen; Pokharel, M.; Yao, Mengliang; Tian, Wei; Ward, Thomas Zac; Zhao, Y.; Parshall, Dr. D.; et al

    2015-08-17

    The evolution of the electronic properties of electron-doped (Sr1-xLax)2IrO4 is experimentally explored as the doping limit of La is approached. As electrons are introduced, the electronic ground state transitions from a spin-orbit Mott phase into an electronically phase separated state, where long-range magnetic order vanishes beyond x = 0:02 and charge transport remains percolative up to the limit of La substitution (x =0:06). In particular, the electronic ground state remains inhomogeneous even beyond the collapse of the parent state's long-range antiferromagnetic order, while persistent short-range magnetism survives up to the highest La-substitution levels. Furthermore, as electrons are doped into Sr2IrO4,more » we observe the appearance of a low temperature magnetic glass-like state intermediate to the complete suppression of antiferromagnetic order. Universalities and di erences in the electron-doped phase diagrams of single layer and bilayer Ruddlesden-Popper strontium iridates are discussed.« less

  4. Influence of Electron Doping on Magnetic Order in CeRu2Al10

    SciTech Connect

    Kobayashi, Riki; Kaneko, Koji; Saito, Kotaro; Mignot, Jean-Michel; André, Gilles; Robert, Julien; Wakimoto, Shuichi; Matsuda, Masaaki; Chi, Songxue; Haga, Yoshinori; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Nishioka, Takashi; Matsumura, Masahiro; Tanida, Hiroshi; Sera, Masafumi

    2014-09-17

    The effect of electron doping by the substitution of Rh for Ru on unconventional magnetic order in CeRu2Al10 was investigated via neutron powder diffraction. In Ce(Ru1-xRhx)2Al10 with x = 0.05, 0.12, and 0.2, reorientation of the ordered moment from the c- to the a-axis takes place in all samples, while the ordering vector q=(0 1 0) remains unchanged within this concentration range. The moment reorientation is accompanied by an enhancement in its size by a factor of ~2.4, from μ=0.43 μB at x=0 to μ =1.06, 1.04, and 1.02 μB for x=0.05, 0.12 and 0.2, respectively. The continuous decrease in N´eel temperature T0(TN), despite an abrupt increase in μ , underlines the strong anisotropy in the exchange interaction in CeRu2Al10, and the fact that this anisotropy is easily suppressed by electron doping.

  5. Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

    PubMed

    Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

    2015-01-14

    Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.

  6. Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

    PubMed

    Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

    2015-01-14

    Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors. PMID:25532066

  7. Practical superconductor development for electrical power applications, annual report for FY 1994

    SciTech Connect

    Balachandran, U.

    1994-10-01

    Development of useful high-critical-temperature 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 in the Y-Ba-Cu, (Bi,Pb)-Sr-Ca-Cu, (Tl,Pb,Bt)-(Ba,Sr)-Ca-Cu. and Hg-Ba-Ca-Cu-0 oxide systems. Topics discussed are synthesis and heat treatment of high-Tc superconductors, formation of monolithic and composite conductors. characterization of structures and superconducting and mechanical properties, and fabrication and testing of prototype components. Collaborations with industry and academia are documented.

  8. Scaling relation for the superfluid density of cuprate superconductors: Origins and limits

    NASA Astrophysics Data System (ADS)

    Tallon, J. L.; Cooper, J. R.; Naqib, S. H.; Loram, J. W.

    2006-05-01

    A universal scaling relation, ρs∝σ(Tc)×Tc has been reported by Homes [Nature (London) 430, 539 (2004)] where ρs is the superfluid density and σ(T) is the dc conductivity. The relation was shown to apply to both c -axis and in-plane dynamics for high- Tc superconductors as well as to the more conventional superconductors Nb and Pb, suggesting common physics in these systems. We show quantitatively that the scaling behavior has several possible origins, including marginal Fermi-liquid behavior, Josephson coupling, dirty-limit superconductivity, and unitary impurity scattering for a d -wave order parameter. However, the relation breaks down seriously in overdoped cuprates, and possibly even at lower doping.

  9. The refrigeration of high temperature superconductors between 25K and 65K

    SciTech Connect

    Richardson, R.N.; Scurlock, R.G.; Tavner, A.C.R.

    1996-12-31

    The present state of the art indicates that acceptable j - H characteristics for power applications of the new high Tc superconductors will only be achieved using materials at temperatures below liquid nitrogen temperature. A boiling point of 27.1K and high specific cooling capacity make neon an eminently suitable choice of refrigerant at these temperatures. A cryostat has been constructed which employs a two stage Gifford-McMahon cooler to liquefy neon gas. The cryostat contains up to 5 litres of liquid neon which can be used for {open_quote}in-situ{close_quote} experiments or transfer to another cryostat. Another set of cryostats are being used with liquid nitrogen/oxygen mixtures at reduced pressure for temperatures down to 50K. All these cryostats provide a core facility for characterising and operating high T{sub c} superconductors at Southampton.

  10. The intercalation chemistry of layered iron chalcogenide superconductors

    NASA Astrophysics Data System (ADS)

    Vivanco, Hector K.; Rodriguez, Efrain E.

    2016-10-01

    The iron chalcogenides FeSe and FeS are superconductors composed of two-dimensional sheets held together by van der Waals interactions, which makes them prime candidates for the intercalation of various guest species. We review the intercalation chemistry of FeSe and FeS superconductors and discuss their synthesis, structure, and physical properties. Before we review the latest work in this area, we provide a brief background on the intercalation chemistry of other inorganic materials that exhibit enhanced superconducting properties upon intercalation, which include the transition metal dichalcogenides, fullerenes, and layered cobalt oxides. From past studies of these intercalated superconductors, we discuss the role of the intercalates in terms of charge doping, structural distortions, and Fermi surface reconstruction. We also briefly review the physical and chemical properties of the host materials-mackinawite-type FeS and β-FeSe. The three types of intercalates for the iron chalcogenides can be placed in three categories: 1.) alkali and alkaline earth cations intercalated through the liquid ammonia technique; 2.) cations intercalated with organic amines such as ethylenediamine; and 3.) layered hydroxides intercalated during hydrothermal conditions. A recurring theme in these studies is the role of the intercalated guest in electron doping the chalcogenide host and in enhancing the two-dimensionality of the electronic structure by spacing the FeSe layers apart. We end this review discussing possible new avenues in the intercalation chemistry of transition metal monochalcogenides, and the promise of these materials as a unique set of new inorganic two-dimensional systems.

  11. Continuous lengths of oxide superconductors

    DOEpatents

    Kroeger, Donald M.; List, III, Frederick A.

    2000-01-01

    A layered oxide superconductor prepared by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon. A continuous length of a second substrate ribbon is overlaid on the first substrate ribbon. Sufficient pressure is applied to form a bound layered superconductor precursor powder between the first substrate ribbon and the second substrate ribbon. The layered superconductor precursor is then heat treated to establish the oxide superconducting phase. The layered oxide superconductor has a smooth interface between the substrate and the oxide superconductor.

  12. Instabilities of High Temperature Superconductors

    PubMed Central

    Matthias, B. T.; Corenzwit, E.; Cooper, A. S.; Longinotti, L. D.

    1971-01-01

    We have observed the transition temperature of both the cubic and tetragonal phases of several high-temperature β-W superconductors. The instability of the cubic lattice appears to be characteristic of high-temperature superconductors. PMID:16591897

  13. Voltage divider based on submicron slits in a high Tc superconducting film and two bicrystal grain boundaries

    NASA Astrophysics Data System (ADS)

    Kaplunenko, V. K.; Ivanov, Z. G.; Stepantsov, E. A.; Claeson, T.; Wikborg, E.

    1995-07-01

    Experiments on a model of rapid single flux quantum (RSFQ) flip-flop cell, based on high-Tc (HTS) Josephson junctions show that it can operate as a voltage divider at frequency up to 400 GHz. The junctions were formed in YBaCuO film, deposited on novel Y-ZrO2 bicrystals with two asymmetric 32° grain boundaries, about 10 μm apart, and allow a new design of RSFQ logic based on a single HTS layer. Small inductances (≂10 pH) were made as narrow, submicron size slits. The junction widths were between 4 and 10 μm and for ten junctions located close to the tested circuits, the linear critical current densities at T=4.4 K were 10.7 μA/μm±50% for one grain boundary and 8.3 μA/μm±50% for the other one. IcRn was about 1 mV±50%. A current density of half the expected value meant that the test circuit did not act as an ideal flip-flop down to the lowest frequency. As a voltage divider it gave a half value division up to 0.82 mV at T=4.4 K and to 0.4 mV at 30 K.

  14. Direct angle resolved photoelectron spectroscopy (DARPES) on high-Tc films: doping, strains, Fermi surface topology and superconductivity

    NASA Astrophysics Data System (ADS)

    Pavuna, D.; Ariosa, D.; Cancellieri, C.; Cloetta, D.; Abrecht, M.

    2008-03-01

    Since 1997 we systematically perform Direct ARPES ( = DARPES) on in-situ grown, non-cleaved, ultra-thin (<25nm) cuprate films. Specifically, we probe low energy electronic structure and properties of high-Tc films under different degree of epitaxial (compressive vs tensile) strain. In overdoped in-plane compressed La2-xSrxCuO4 (LSCO) thin films we double Tc from 20K to 40K, yet the Fermi surface (FS) remains essentially 2-dimensional (2D). In contrast, tensile strained films show 3-dimensional (3D) dispersion, while Tc is drastically reduced. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the 2D character of the dispersion and increases Tc, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3D. We have the FS topology for both cases. As the actual lattice of cuprates is 'Napoleon-cake' -like i.e. rigid CuO2 planes alternate with softer 'reservoir' (that strains distort differently) our results tend to rule out 2D rigid lattice mean field models. Finally, we briefly discuss recent successful determination of the FS topology from the observed wavevector quantization by DARPES in cuprate films thinner than 18 units cells (<24nm). Such an approach is of broader interest as it can be extended to other similar confined (ultra-thin) functional oxide systems.

  15. Development of high Tc (greater than 110K) Bi, Tl and Y-based materials as superconducting circuit elements

    NASA Technical Reports Server (NTRS)

    Haertling, Gene H.; Lee, Burtrand; Grabert, Gregory; Gilmour, Phillip

    1991-01-01

    This report is presented in two parts. Part 1 deals primarily with Bi-based materials and a small amount of work on a Y-based composition while Part 2 covers work on Tl-based materials. In Part 1, a reliable and reproducible process for producing bulk bismuth-based superconductors has been developed. It is noted however, that a percentage of the tapecast material experiences curling and fracturing after a 30 hour sintering period and is thus in need of further examination. The Bi-Sr-Ca-Cu-O (BSCCO) material has been characterized by critical temperature data, X-ray diffraction data, and surface morphology. In the case of T sub c, it is not critical to anneal the material. It appears that the BSCCO material has the possibility of producing a better grounding strap than that of the 123 material. Attempts to reproduce near room temperature superconductors in the Y-Ba-Cu-O system were unsuccessful. In Part 2, several methods of processing the high temperature superconductor Tl2Ba2Ca2Cu3O10 were investigated; i.e., different precursor compositions were sintered at various sintering times and temperatures. The highest superconductig temperature was found to be 117.8K when fired at 900 C for three hours. Higher sintering temperatures produced a melted sample which was nonsuperconducting at liquid nitrogen temperature. Also, a preliminary study found Li2O substitutions for copper appeared to increase the transition temperature and create fluxing action upon sintering. It was suggested that lower sintering temperatures might be obtained with lithium additions to produce reliable Tl2Ba2Ca2Cu3O10 processing methods.

  16. Development of high Tc (greater than 110K) Bi, Tl and Y-based materials as superconducting circuit elements

    NASA Astrophysics Data System (ADS)

    Haertling, Gene H.; Lee, Burtrand; Grabert, Gregory; Gilmour, Phillip

    1991-06-01

    This report is presented in two parts. Part 1 deals primarily with Bi-based materials and a small amount of work on a Y-based composition while Part 2 covers work on Tl-based materials. In Part 1, a reliable and reproducible process for producing bulk bismuth-based superconductors has been developed. It is noted however, that a percentage of the tapecast material experiences curling and fracturing after a 30 hour sintering period and is thus in need of further examination. The Bi-Sr-Ca-Cu-O (BSCCO) material has been characterized by critical temperature data, X-ray diffraction data, and surface morphology. In the case of T sub c, it is not critical to anneal the material. It appears that the BSCCO material has the possibility of producing a better grounding strap than that of the 123 material. Attempts to reproduce near room temperature superconductors in the Y-Ba-Cu-O system were unsuccessful. In Part 2, several methods of processing the high temperature superconductor Tl2Ba2Ca2Cu3O10 were investigated; i.e., different precursor compositions were sintered at various sintering times and temperatures. The highest superconductig temperature was found to be 117.8K when fired at 900 C for three hours. Higher sintering temperatures produced a melted sample which was nonsuperconducting at liquid nitrogen temperature. Also, a preliminary study found Li2O substitutions for copper appeared to increase the transition temperature and create fluxing action upon sintering. It was suggested that lower sintering temperatures might be obtained with lithium additions to produce reliable Tl2Ba2Ca2Cu3O10 processing methods.

  17. SU(2) symmetry in a realistic spin-fermion model for cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Kloss, T.; Montiel, X.; Pépin, C.

    2015-05-01

    We consider the pseudogap (PG) state of high-Tc superconductors in the form of a composite order parameter fluctuating between 2 pF -charge ordering and superconducting (SC) pairing. In the limit of linear dispersion and at the hot spots, both order parameters are related by a SU(2) symmetry, and the eight-hot-spot model of Efetov et al. [Nat. Phys. 9, 442 (2013), 10.1038/nphys2641] is recovered. In the general case, however, curvature terms of the dispersion will break this symmetry, and the degeneracy between both states is lifted. Taking the full momentum dependence of the order parameter into account, we measure the strength of this SU(2) symmetry breaking over the full Brillouin zone. For realistic dispersion relations including curvature we find generically that the SU(2) symmetry breaking is small and robust to the fermiology and that the symmetric situation is restored in the large paramagnon mass and coupling limit. Comparing the level splitting for different materials, we propose a scenario that could account for the competition between the PG and SC states in the phase diagram of high-Tc superconductors.

  18. Advances in fabrication of mono- and multifilament Ag-CLAD BSCCO superconductors

    SciTech Connect

    Balachandran, U.; Iyer, A.N.; Jammy, R.; Haldar, P.; Hoehn, J.G. Jr.; Suenaga, M.

    1995-07-01

    Fabricating long lengths of robust and high-quality conductors is imperative for various applications of high-{Tc} superconductors. Long lengths of mono- and multifilament Ag-clad Bi-Sr-Ca-Cu-0 conductors have been fabricated by the powder-in-tube technique. High values for critical current density (J{sub c}) have been achieved in both short- and long-length conductors. J{sub c} values up to 12,000 A/cm{sup 2} have been achieved in an 850-m-long multifilament conductor. Pancake-shaped coils and test magnets fabricated from long-length conductors were characterized at various temperatures and applied magnetic fields. A magnet containing 770 m of high-{Tc} conductor generated a record high field of {approx} 1 T at 4.2 K in a background field of {approx} 20 T. In-situ tensile and bending characteristics of both mono- and multifilament conductors have also been studied. Multifilament conductors exhibited better axial strain tolerance ({var_epsilon} {approx} 1%) than that of monofilament conductor ({var_epsilon} {approx} 0.2%), while retaining 90% of their initial critical current. An analysis of the results is presented, along with effects of parameters such as thickness, superconductor/Ag ratio, and microstructural details.

  19. Synthesis of high {Tc} superconducting coatings and patterns by melt writing and oxidation of metallic precursor alloys

    DOEpatents

    Gao, W.; Vander Sande, J.B.

    1998-07-28

    A method is provided for fabrication of superconducting oxides and superconducting oxide composites and for joining superconductors to other materials. A coating of a molten alloy containing the metallic elements of the oxide is applied to a substrate surface and oxidized to form the superconducting oxide. A material can be contacted to the molten alloy which is subsequently oxidized joining the material to the resulting superconducting oxide coating. Substrates of varied composition and shape can be coated or joined by this method. 5 figs.

  20. THE 2D HEISENBERG ANTIFERROMAGNET IN HIGH-Tc SUPERCONDUCTIVITY:. A Review of Numerical Techniques and Results

    NASA Astrophysics Data System (ADS)

    Barnes, T.

    In this article we review numerical studies of the quantum Heisenberg antiferromagnet on a square lattice, which is a model of the magnetic properties of the undoped “precursor insulators” of the high temperature superconductors. We begin with a brief pedagogical introduction and then discuss zero and nonzero temperature properties and compare the numerical results to analytical calculations and to experiment where appropriate. We also review the various algorithms used to obtain these results, and discuss algorithm developments and improvements in computer technology which would be most useful for future numerical work in this area. Finally we list several outstanding problems which may merit further investigation.

  1. Reduction in bearing size due to superconductors in magnetic bearings

    NASA Technical Reports Server (NTRS)

    Rao, Dantam K.; Lewis, Paul; Dill, James F.

    1991-01-01

    A design concept that reduces the size of magnetic bearings is assessed. The small size will enable magnetic bearings to fit into limited available bearing volume of cryogenic machinery. The design concept, called SUPERC, uses (high Tc) superconductors or high-purity aluminum conductors in windings instead of copper. The relatively high-current density of these conductors reduces the slot radial thickness for windings, which reduces the size of the bearings. MTI developed a sizing program called SUPERC that translates the high-current density of these conductors into smaller sized bearings. This program was used to size a superconducting bearing to carry a 500 lb. load. The sizes of magnetic bearings needed by various design concepts are as follows: SUPERC design concept = 3.75 in.; magnet-bias design concept = 5.25 in.; and all electromagnet design concept = 7.0 in. These results indicate that the SUPERC design concept can significantly reduce the size of the bearing. This reduction, in turn, reduces the weight and yields a lighter bearing. Since the superconductors have inherently near-zero resistance, they are also expected to save power needed for operation considerably.

  2. Effect of granularity and annealing conditions on the magneto-resistance of the electron doped superconductor Nd1.85Ce0.15CuO4

    NASA Astrophysics Data System (ADS)

    Raveendran, N. Radhikesh; Amaladass, E. P.; Janaki, J.; Mani, Awadhesh

    2016-05-01

    A single phase polycrystalline sample of Nd1.85Ce0.15CuO4 has been synthesized and well characterized. Detailed studies on electrical resistivity behavior of this system as a function of temperature and magnetic field reveal interesting features attributable to the granularity effects. These features have been qualitatively understood based on the interplay of Josephson junction coupling and quasi particle tunneling which dictates the evolution of the observed temperature and field dependent resistivity behavior of Nd1.85Ce0.15CuO4 system. The studies also reveal significant changes with respect to annealing conditions, indicating that such compounds are very sensitive to annealing conditions. It has been observed that prolonged annealing in Argon atmosphere leads to a decrease in normal state resistivity. This is associated with a decrease in the S-I-S type Josephson tunnel junctions perhaps due to improved inter-granular coupling, nevertheless they could not be completely eliminated.

  3. c -axis longitudinal magnetoresistance of the electron-doped superconductor Pr1.85Ce0.15CuO4

    NASA Astrophysics Data System (ADS)

    Yu, W.; Liang, B.; Greene, R. L.

    2006-12-01

    We report c -axis resistivity and longitudinal magnetoresistance measurements of superconducting Pr1.85Ce0.15CuO4 single crystals. In the temperature range 13⩽T⩽32K , a negative magnetoresistance is observed at fields just above HC2 . Our studies suggest that this negative magnetoresistance is caused by superconducting fluctuations. At lower temperatures (T⩽13K) , a different magnetoresistance behavior and a resistivity upturn are observed, whose origin is still unknown.

  4. Microscopic Examinations of Co Valences and Spin States in Electron-Doped LaCoO3

    NASA Astrophysics Data System (ADS)

    Tomiyasu, Keisuke; Koyama, Syun-Ichi; Watahiki, Masanori; Sato, Mika; Nishihara, Kazuki; Takahashi, Yuki; Onodera, Mitsugi; Iwasa, Kazuaki; Nojima, Tsutomu; Nojiri, Hiroyuki; Okamoto, Jun; Huang, Di-Jing; Yamasaki, Yuuichi; Nakao, Hironori; Murakami, Youichi

    2016-09-01

    We studied the Co valences and spin states in electron-doped LaCo1-yTeyO3 by measuring X-ray absorption spectra and electron spin resonance. The low-temperature insulating state involves the low-spin Co3+ state (S = 0) and the high-spin Co2+ state, where the latter is described by g = 3.8 and jeff = 1/2. The results, in concurrence with the electron-hole asymmetry confirmed in the electrical resistivity, coincide with the spin-blockade phenomenon in this system. Furthermore, we discuss the g factor in terms of the strong covalent-bonding nature and consider multiple origins of this phenomenon.

  5. Strain-controlled electronic properties and magnetorelaxor behaviors in electron-doped CaMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Xiang, P.-H.; Yamada, H.; Sawa, A.; Akoh, H.

    2009-02-01

    We have fabricated epitaxial thin films of electron-doped manganite Ca1-xCexMnO3 (CCMO) with 0≤x≤0.08. The transport properties of CCMO films are very sensitive to substrate-controlled epitaxial strain. For the CCMO(x =0.05) film, the metallic transport characteristic is observed only on a nearly lattice-matched NdAlO3 (NAO) substrate, while tensilely and compressively stressed films are insulating. The CCMO(x =0.06) film on the NAO substrate shows a large magnetoresistance characteristic of a magnetorelaxor. This behavior can be explained in terms of the phase separation and the irreversible growth of the metallic domain in antiferromagnetic insulating matrix.

  6. Unusual superconducting state at 49 K in electron-doped CaFe2As2 at ambient pressure.

    PubMed

    Lv, Bing; Deng, Liangzi; Gooch, Melissa; Wei, Fengyan; Sun, Yanyi; Meen, James K; Xue, Yu-Yi; Lorenz, Bernd; Chu, Ching-Wu

    2011-09-20

    We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe(2)As(2) via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at 49 K, which has a low critical field < 4 Oe, and the other at 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe(2)As(2) (or Ae122), where Ae = Ca, Sr, or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (T(c)) only up to 38 K and pressurization has been reported to produce superconductivity with a T(c) up to 30 K. The unusual 49 K phase detected will be discussed. PMID:21911404

  7. Granular Superconductors and Gravity

    NASA Technical Reports Server (NTRS)

    Noever, David; Koczor, Ron

    1999-01-01

    As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

  8. Fermi surface nesting induced strong pairing in iron-based superconductors

    PubMed Central

    Terashima, K.; Sekiba, Y.; Bowen, J. H.; Nakayama, K.; Kawahara, T.; Sato, T.; Richard, P.; Xu, Y.-M.; Li, L. J.; Cao, G. H.; Xu, Z.-A.; Ding, H.; Takahashi, T.

    2009-01-01

    The discovery of high-temperature superconductivity in iron pnictides raised the possibility of an unconventional superconducting mechanism in multiband materials. The observation of Fermi-surface (FS)-dependent nodeless superconducting gaps suggested that inter-FS interactions may play a crucial role in superconducting pairing. In the optimally hole-doped Ba0.6K0.4Fe2As2, the pairing strength is enhanced simultaneously (2Δ/Tc≈7) on the nearly nested FS pockets, i.e., the inner hole-like (α) FS and the 2 hybridized electron-like FSs, whereas the pairing remains weak (2Δ/Tc≈3.6) in the poorly nested outer hole-like (β) FS. Here, we report that in the electron-doped BaFe1.85Co0.15As2, the FS nesting condition switches from the α to the β FS due to the opposite size changes for hole- and electron-like FSs upon electron doping. The strong pairing strength (2Δ/Tc≈6) is also found to switch to the nested β FS, indicating an intimate connection between FS nesting and superconducting pairing, and strongly supporting the inter-FS pairing mechanism in the iron-based superconductors. PMID:19359490

  9. Lightning in superconductors

    PubMed Central

    Vestgården, J. I.; Shantsev, D. V.; Galperin, Y. M.; Johansen, T. H.

    2012-01-01

    Crucially important for application of type-II superconductor films is the stability of the vortex matter – magnetic flux lines penetrating the material. If some vortices get detached from pinning centres, the energy dissipated by their motion will facilitate further depinning, and may trigger a massive electromagnetic breakdown. Up to now, the time-resolved behaviour of these ultra-fast events was essentially unknown. We report numerical simulation results revealing the detailed dynamics during breakdown as within nanoseconds it develops branching structures in the electromagnetic fields and temperature, with striking resemblance of atmospheric lightning. During a dendritic avalanche the superconductor is locally heated above its critical temperature, while electrical fields rise to several kV/m as the front propagates at instant speeds near up to 100 km/s. The numerical approach provides an efficient framework for understanding the ultra-fast coupled non-local dynamics of electromagnetic fields and dissipation in superconductor films. PMID:23185691

  10. Charge density waves in the graphene sheets of the superconductor CaC(6).

    PubMed

    Rahnejat, K C; Howard, C A; Shuttleworth, N E; Schofield, S R; Iwaya, K; Hirjibehedin, C F; Renner, Ch; Aeppli, G; Ellerby, M

    2011-01-01

    Graphitic systems have an electronic structure that can be readily manipulated through electrostatic or chemical doping, resulting in a rich variety of electronic ground states. Here we report the first observation and characterization of electronic stripes in the highly electron-doped graphitic superconductor, CaC(6), by scanning tunnelling microscopy and spectroscopy. The stripes correspond to a charge density wave with a period three times that of the Ca superlattice. Although the positions of the Ca intercalants are modulated, no displacements of the carbon lattice are detected, indicating that the graphene sheets host the ideal charge density wave. This provides an exceptionally simple material-graphene-as a starting point for understanding the relation between stripes and superconductivity. Furthermore, our experiments suggest a strategy to search for superconductivity in graphene, namely in the vicinity of striped 'Wigner crystal' phases, where some of the electrons crystallize to form a superlattice. PMID:22127054

  11. How Electron Spectroscopy with Synchrotron Light Can Help Us Understand High-Tc Superconductivity and Other Complex States of Matter

    SciTech Connect

    Campuzano, Juan Carlos

    2012-03-07

    All the physical, chemical, and mechanical properties of materials are controlled by electrons that occupy the highest energy levels in solids, those near the Fermi energy. Many techniques were developed to study those electrons, leading to the great successes of condensed matter physics. Newer and complex materials, such as the high-temperature superconductors, tend to exhibit very large anisotropies in their physical properties, requiring a more detailed knowledge of the behavior of electrons not only as a function of their energy, but also their momentum. Angle-resolved photoemission can contribute to our understanding by providing a great deal of information on many of the momentum-dependent properties of electrons and their interactions. In this talk, I will present a brief overview of how a long-term and focused collaboration between scientists at Argonne and other institutions has contributed to making angle-resolved photoemissions a most useful tool in the study of complex states of matter.

  12. Bose-glass melting in the cubic (K,Ba)BiO3 high-Tc oxide with columnar defects

    NASA Astrophysics Data System (ADS)

    Klein, T.; Conde-Gallardo, A.; Joumard, I.; Marcus, J.; van der Beek, C. J.; Konczykowski, M.

    2000-02-01

    The Bose-glass transition in the fully isotropic (K,Ba)BiO3 superconductor with columnar defects produced by irradiation with 7.2 GeV Ta ions was studied by transport and nonlinear susceptibility measurements. For fields smaller than the dose equivalent field Bφ, the Bose-glass transition line HBG(T) shifts progressively upwards with increasing dose, dHBG/dT~1+αB1/2φ. The critical exponents have been deduced from the scaling properties of the transport measurements; we obtain z=5.3+/-0.3 and ν=1.1+/-0.2. For tilted magnetic fields, the transition temperature scales as TBG(0)-TBG(θ)~\\|sin(θ)\\|1/ν, as recently suggested by Lidmar and Wallin.

  13. Superconductivity and chemical composition of the high-Tc phase (Tc = 111 K) in the Sb-Pb-Bi-Sr-Ca-Cu-O system

    NASA Astrophysics Data System (ADS)

    Kijima, Naota; Gronsky, Ronald; McKernan, Steffen K.; Endo, Hozumi; Oguri, Yasuo

    1991-01-01

    A superconducting phase with a critical temperature of 111 K in the Sb-Pb-Bi-Sr-Ca-Cu-O system has been synthesized by means of a long firing period. Its crystal structure is similar to the high-Tc phase (107 K) in the Pb-Bi-Sr-Ca-Cu-O system, and its average chemical composition is 4.3, 2.6, 19.2, 21.4, 15.8 and 36.9 percent for Sb, Pb, Bi, Sr, Ca, and Cu, respectively. The summation of the Sb concentration and the Ca concentration is approximately the same for all the samples of this phase, implying that Sb substitutes for Ca, and oxygen atoms are introduced to compensate the oxygen deficiency in the central Cu-O layer sandwiched by the two Ca layers in the crystal structure of the high-Tc phase.

  14. Method for preparing superconductors

    DOEpatents

    Dahlgren, Shelley D.

    1976-01-01

    A superconductor having an equiaxed fine grain beta-tungsten crystalline structure found to have improved high field critical current densities is prepared by sputter-depositing superconductive material onto a substrate cooled to below 200.degree. C. and heat-treating the deposited material.

  15. Quantum phenomena in superconductors

    SciTech Connect

    Clarke, J.

    1987-08-01

    This paper contains remarks by the author on aspects of macroscopic quantum phenomena in superconductors. Some topics discussed are: Superconducting low-inductance undulatory galvanometer (SLUGS), charge imbalance, cylindrical dc superconducting quantum interference device (SQUIDS), Geophysics, noise theory, magnetic resonance with SQUIDS, and macroscopic quantum tunneling. 23 refs., 4 figs. (LSP)

  16. SIS (Superconductor-Insulator-Superconductor) mixer research

    NASA Astrophysics Data System (ADS)

    Feldman, M. J.

    1987-03-01

    Theoretical and experimental research has been conducted to elucidate the basic physics behind the properties of superconductor-insulator- superconductor (SIS) tunnel junction receiving devices. The quantum theory of mixing was employed to calculate the saturation behavior of the SIS mixer and the SIS direct detector. The direct detector was found to saturate at far higher powers than previously believed, permitting practical application of this device. Experiments verified the saturation theory. The mixer saturation expression led to the formulation of frequency scaling regions. The origin of quantum noise sources is completely minimized. The mixer quantum noise limit was shown to be reached in only two special cases. Computer calculations determined that the behavior of SIS receivers divides into two regimes, low and high frequencies, the cross-over frequency depending upon junction quality. The properties of these two regimes were delineated. All previous SIS receivers have operated in the low frequency regime. Plasma-etched niobium nitride edge junctions have been fabricated using a novel barrier formation process. These junctions have excellent current-voltage characteristics.

  17. Use of a high-Tc SQUID-based nuclear magnetic resonance spectrometer in magnetically unshielded environments to discriminate tumors in rats, by characterizing the longitudinal relaxation rate

    NASA Astrophysics Data System (ADS)

    Huang, K.-W.; Chen, H.-H.; Yang, H.-C.; Horng, H.-E.; Liao, S.-H.; Chieh, J.-J.; Yang, S. Y.

    2012-06-01

    This study uses a sensitive, high-Tc SQUID-detected nuclear magnetic resonance spectrometer in magnetically unshielded environments to discriminate liver tumors in rats, by characterizing the longitudinal relaxation rate, T1-1. The high-Tc SQUID-based spectrometer has a spectral line width of 0.9Hz in low magnetic fields. It was found that relaxation rate for tumor tissues is (3.6 ± 0.02) s-1 and the relaxation rate for normal tissues is (7.7 ± 0.02) s-1. The difference in the longitudinal relaxation rates suggests that water structures around the DNA of cancer cells are different from those of normal tissues. The optimized detection sensitivity for the established system is 0.21 g at the present stage. It is concluded that T1-1 can be used to distinguish cancerous tissues from normal tissues. The high-Tc, SQUID-detected NMR and MRI in magnetically unshielded environments may also be useful for discriminating other tumors.

  18. Non-conventional superconducting fluctuations in Ba(Fe1-xRhx)2As2 iron-based superconductors.

    PubMed

    Bossoni, L; Romanó, L; Canfield, P C; Lascialfari, A

    2014-10-01

    We measured the static uniform spin susceptibility of Ba(Fe(1-x)Rh(x))(2)As(2) iron-based superconductors, over a broad range of doping (0.041 ⩽ x ⩽ 0.094) and magnetic fields. At small fields (H ⩽ 1 kOe) we observed, above the transition temperature Tc, the occurrence of precursor diamagnetism, which is not ascribable to the Ginzburg-Landau theory. On the contrary, our data agree with a phase fluctuation model, which has been used to interpret a similar phenomenology occurring in the high-Tc cuprate superconductors. Additionally, in the presence of strong fields, the unconventional fluctuating diamagnetism is suppressed, whereas Ginzburg-Landau fluctuations are found, in agreement with literature. PMID:25229750

  19. Theoretical study of large proximity-induced s -wave-like pairing from a d -wave superconductor

    NASA Astrophysics Data System (ADS)

    Li, Wan-Ju; Chao, Sung-Po; Lee, Ting-Kuo

    2016-01-01

    We use the proximity effect to generate effective topological superconductors by placing metals with strong spin-orbit coupling in contact with a superconductor, aiming to produce Majorana zero modes useful for topologically protected quantum computation. In recent experiments, several quintuple layers of Bi2Se3 were epitaxially grown on the high-Tc material Bi2Sr2CaCu2O8+δ , and conflicting experimental results were reported. We use the standard mean-field approach to study this heterostructure and find it is unlikely to have a large proximity-induced superconducting gap. Despite the seemingly correct temperature dependence, the s -wave gap claimed to be observed may not be purely superconducting in origin. Future work on the proximity-induced bulk superconducting gap and the interfacial band structure should shed light on this issue.

  20. Nanostructured organic light-emitting diodes with electronic doping, transparent carbon nanotube charge injectors, and quantum dots

    NASA Astrophysics Data System (ADS)

    Williams, Christopher D.

    Organic light-emitting diodes (OLEDs) and polymeric light-emitting diodes (PLEDs) are rapidly-emerging technologies which are being studied extensively in industrial, academic, and government laboratories for applications in displays and solid-state lighting. Their thin film structure (with total thickness of active layers less than a micron) and the inherent flexibility of the constituent materials give them promise in the flat panel display industry as well as open new areas of possible applications for flexible transparent displays and even textile displays. The materials also show high electroluminescence efficiency, and with proper device engineering these devices demonstrate efficiencies and lifetimes which surpass current methods of lighting such at incandescent bulbs, which average approximately 1% efficiency. Lastly, the materials offer easy processing through well studied and developed methods such as thermal evaporation, solution spin-casting and ink jet printing. Ink jet printing of polymeric layers in PLEDs offers many advantages when considering mass production of display and lighting panels, as it allows uniform films to be produced on large area substrates using a simple roll-to-roll method. In this dissertation, we discuss several new methods and procedures which we have developed and used to produce OLEDs and PLEDs. More specifically these are electronic doping of transport layers, fluorescent doping of emissive layers by semiconductor nanocrystals (NC) (also known as quantum dots (QD)), and electrode engineering, namely by the use of transparent carbon nanotube sheets as charge injectors. We expand on the existing field of molecular doping and introduce a doped device with a very thick hole transport layer. Such a device is more resistant to failure due to excessive current density. We also investigate the effects of the presence of dopant molecules in the emissive layer of a multilayer OLED. This portion of the work introduces the negative

  1. Platform for engineering topological superconductors: Superlattices on Rashba superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Yao; He, Wen-Yu; Xu, Dong-Hui; Lin, Nian; Law, K. T.

    2016-07-01

    The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose an experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without or with little fine tuning of the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.

  2. Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca0.9La0.1FeAs2

    NASA Astrophysics Data System (ADS)

    Liu, Z. T.; Xing, X. Z.; Li, M. Y.; Zhou, W.; Sun, Y.; Fan, C. C.; Yang, H. F.; Liu, J. S.; Yao, Q.; Li, W.; Shi, Z. X.; Shen, D. W.; Wang, Z.

    2016-07-01

    CaFeAs2 is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal system for the realization of Majorana modes. We performed a systematical angle-resolved photoemission spectroscopy and first-principles calculation study of the slightly electron-doped CaFeAs2. We found that the zigzag As chain of 112-type iron-based superconductors play a considerable role in the low-energy electronic structure, resulting in the characteristic Dirac-cone like band dispersion as the prediction. Our experimental results further confirm that these Dirac cones only exist around the X but not Y points in the Brillouin zone, breaking the S4 symmetry at iron sites. Our findings present the compelling support to the theoretical prediction that the 112-type iron-based superconductors might host the topological nontrivial edge states. The slightly electron doped CaFeAs2 would provide us a unique opportunity to realize and explore Majorana fermion physics.

  3. Ambient-pressure organic superconductor

    DOEpatents

    Williams, Jack M.; Wang, Hsien-Hau; Beno, Mark A.

    1986-01-01

    A new class of organic superconductors having the formula (ET).sub.2 MX.sub.2 wherein ET represents bis(ethylenedithio)-tetrathiafulvalene, M is a metal such as Au, Ag, In, Tl, Rb, Pd and the like and X is a halide. The superconductor (ET).sub.2 AuI.sub.2 exhibits a transition temperature of 5 K which is high for organic superconductors.

  4. Superconductor stability 90: A review

    SciTech Connect

    Dresner, L.

    1990-01-01

    This paper reviews some recent developments in the field of stability of superconductors. The main topics dealt with are hydrodynamic phenomena in cable-in-conduit superconductors, namely, multiple stability, quench pressure, thermal expulsion, and thermal hydraulic quenchback, traveling normal zones in large, composite conductors, such as those intended for SMES, and the stability of vapor-cooled leads made of high-temperature superconductors. 31 refs., 5 figs.

  5. Electron doping evolution of structural and antiferromagnetic phase transitions in NaFe1 -xCoxAs iron pnictides

    NASA Astrophysics Data System (ADS)

    Tan, Guotai; Song, Yu; Zhang, Chenglin; Lin, Lifang; Xu, Zhuang; Hou, Tingting; Tian, Wei; Cao, Huibo; Li, Shiliang; Feng, Shiping; Dai, Pengcheng

    2016-07-01

    We use transport and neutron diffraction to study the electronic phase diagram of NaFe1 -xCoxAs . In the undoped state, NaFeAs exhibits a tetragonal-to-orthorhombic structural transition below Ts followed by a collinear antiferromagnetic (AF) order below TN. Upon codoping to form NaFe1 -xCoxAs ,Ts and TN are gradually suppressed, leading to optimal superconductivity near Co-doping x =0.025 . While transport experiments on these materials reveal an anomalous behavior suggesting the presence of a quantum critical point (QCP) near optimal superconductivity, our neutron diffraction results indicate that commensurate AF order becomes transversely incommensurate with TN>Tc before vanishing abruptly at optimal superconductivity. These results are remarkably similar to electron-doping and isovalent-doping evolution of the AF order in BaFe2 -xNixAs2 and BaFe2(As1 -xPx)2 , thus suggesting a universal behavior in the suppression of the magnetic order in iron pnictides as superconductivity is induced.

  6. Superconductivity below 20 K in heavily electron-doped surface layer of FeSe bulk crystal.

    PubMed

    Seo, J J; Kim, B Y; Kim, B S; Jeong, J K; Ok, J M; Kim, Jun Sung; Denlinger, J D; Mo, S-K; Kim, C; Kim, Y K

    2016-01-01

    A superconducting transition temperature (Tc) as high as 100 K was recently discovered in one monolayer FeSe grown on SrTiO3. The discovery ignited efforts to identify the mechanism for the markedly enhanced Tc from its bulk value of 8 K. There are two main views about the origin of the Tc enhancement: interfacial effects and/or excess electrons with strong electron correlation. Here, we report the observation of superconductivity below 20 K in surface electron-doped bulk FeSe. The doped surface layer possesses all the key spectroscopic aspects of the monolayer FeSe on SrTiO3. Without interfacial effects, the surface layer state has a moderate Tc of 20 K with a smaller gap opening of 4.2 meV. Our results show that excess electrons with strong correlation cannot induce the maximum Tc, which in turn reveals the need for interfacial effects to achieve the highest Tc in one monolayer FeSe on SrTiO3. PMID:27050161

  7. Enhanced carrier collection efficiency and reduced quantum state absorption by electron doping in self-assembled quantum dot solar cells

    SciTech Connect

    Li, Tian E-mail: dage@ece.umd.edu; Dagenais, Mario E-mail: dage@ece.umd.edu; Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati

    2015-02-02

    Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In{sub 0.5}Ga{sub 0.5}As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.

  8. Probing Topological Superconductors

    NASA Astrophysics Data System (ADS)

    Schmeltzer, David

    2015-03-01

    The presence of attractive interaction on the surface of a 3D topological insulator which is characterized by spinors carrying a Berry phase of π gives rise to superconductivity that support space time half vortices (Majorana zero modes). We construct the effective dual action for the superconductor with the vortices, and show that the 2 n Majorana fermions are localized and can be replaced with n spinless fermions. The effect of the Majorana zero modes can be observed trough the the Andreev cross reflection when metallic leads are attached to the superconductor. The presence of the Majorana fermions can be detected with transverse sound waves. We have computed the effect of elastic strain fields and obtain an anomalous response indicating the presence of the Majorana fermions.

  9. Analytic holographic superconductor

    NASA Astrophysics Data System (ADS)

    Herzog, Christopher P.

    2010-06-01

    We investigate a holographic superconductor that admits an analytic treatment near the phase transition. In the dual 3+1-dimensional field theory, the phase transition occurs when a scalar operator of scaling dimension two gets a vacuum expectation value. We calculate current-current correlation functions along with the speed of second sound near the critical temperature. We also make some remarks about critical exponents. An analytic treatment is possible because an underlying Heun equation describing the zero mode of the phase transition has a polynomial solution. Amusingly, the treatment here may generalize for an order parameter with any integer spin, and we propose a Lagrangian for a spin-two holographic superconductor.

  10. Vortex cutting in superconductors

    NASA Astrophysics Data System (ADS)

    Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; Crabtree, G. W.

    2016-08-01

    Vortex cutting and reconnection is an intriguing and still-unsolved problem central to many areas of classical and quantum physics, including hydrodynamics, astrophysics, and superconductivity. Here, we describe a comprehensive investigation of the crossing of magnetic vortices in superconductors using time dependent Ginsburg-Landau modeling. Within a macroscopic volume, we simulate initial magnetization of an anisotropic high temperature superconductor followed by subsequent remagnetization with perpendicular magnetic fields, creating the crossing of the initial and newly generated vortices. The time resolved evolution of vortex lines as they approach each other, contort, locally conjoin, and detach, elucidates the fine details of the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.

  11. Reversible tuning of the collapsed tetragonal phase transition in CaF e2A s2 by separate control of chemical pressure and electron doping

    NASA Astrophysics Data System (ADS)

    Zhao, K.; Stingl, C.; Manna, R. S.; Jin, C. Q.; Gegenwart, P.

    2015-12-01

    Single crystals of Ca (Fe1-xR ux ) 2A s2(0 ≤x ≤0.065 ) and C a1 -yL ay(Fe0.973Ru0.027 ) 2A s2(0 ≤y ≤0.2 ) have been synthesized and studied with respect to their structural, electronic, and magnetic properties. The partial substitution of Fe by Ru induces a decrease of the c -axis constant leading for x ≤0.023 to a suppression of the coupled magnetic and structural (tetragonal to orthorhombic) transitions. At xcr=0.023 a first-order transition to a collapsed tetragonal (CT) phase is found, which behaves like a Fermi liquid and which is stabilized by further increase of x . The absence of superconductivity near xcr is consistent with truly hydrostatic pressure experiments on undoped CaF e2A s2 . Starting in the CT regime at x =0.027 , we investigate the additional effect of electron doping by partial replacement of Ca by La. Most remarkably, with increasing y the CT phase transition is destabilized and the system is tuned back into a tetragonal ground state at y ≥ 0.08. This effect is ascribed to a weakening of interlayer As-As bonds by electron doping. Upon further electron doping filamentary superconductivity with Tc of 41 K at y =0.2 is observed.

  12. Effect of pressure on the magnetic, transport, and thermal-transport properties of the electron-doped manganite CaMn1-xSbxO3

    NASA Astrophysics Data System (ADS)

    Murano, Yuh; Matsukawa, Michiaki; Ohuchi, Syuya; Kobayashi, Satoru; Nimori, Shigeki; Suryanarayanan, Ramanathan; Koyama, Keiichi; Kobayashi, Norio

    2011-02-01

    We have demonstrated the effect of hydrostatic pressure on magnetic and transport properties, and thermal-transport properties in the electron-doped manganite CaMn1-xSbxO3. The substitution of Sb5+ ion for Mn 4+ site of the parent matrix causes one-electron doping with the chemical formula CaMn1-2x4+Mnx3+Sbx5+O3 accompanied by a monotonous increase in unit-cell volume as a function of x. Upon increasing the doping level of Sb, the magnitudes of both electrical resistivity and negative Seebeck coefficient are suppressed at high temperatures, indicating the electron doping. Anomalous diamagnetic behaviors at x=0.05 and 0.08 are clearly observed in the field cooled dc magnetization. The effect of hydrostatic pressure on dc magnetization is in contrast to the chemical pressure effect due to Sb doping. The dynamical effect of ac magnetic susceptibility measurement points to the formation of the magnetically frustrated clusters such as FM clusters embedded in canted AFM matrix.

  13. Processing of Superconductor-Normal-Superconductor Josephson Edge Junctions

    NASA Technical Reports Server (NTRS)

    Kleinsasser, A. W.; Barner, J. B.

    1997-01-01

    The electrical behavior of epitaxial superconductor-normal-superconductor (SNS) Josephson edge junctions is strongly affected by processing conditions. Ex-situ processes, utilizing photoresist and polyimide/photoresist mask layers, are employed for ion milling edges for junctions with Yttrium-Barium-Copper-Oxide (YBCO) electrodes and primarily Co-doped YBCO interlayers.

  14. Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors

    PubMed Central

    Shibauchi, Takasada; Krusin-Elbaum, Lia; Hasegawa, Masashi; Kasahara, Yuichi; Okazaki, Ryuji; Matsuda, Yuji

    2008-01-01

    In high-transition-temperature (Tc) superconductivity, charge doping is a natural tuning parameter that takes copper oxides from the antiferromagnet to the superconducting region. In the metallic state above Tc, the standard Landau's Fermi-liquid theory of metals as typified by the temperature squared (T2) dependence of resistivity appears to break down. Whether the origin of the non-Fermi-liquid behavior is related to physics specific to the cuprates is a fundamental question still under debate. We uncover a transformation from the non-Fermi-liquid state to a standard Fermi-liquid state driven not by doping but by magnetic field in the overdoped high-Tc superconductor Tl2Ba2CuO6+x. From the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid features appear above a sufficiently high field that decreases linearly with temperature and lands at a quantum critical point near the superconductivity's upper critical field—with the Fermi-liquid coefficient of the T2 dependence showing a power-law diverging behavior on the approach to the critical point. This field-induced quantum criticality bears a striking resemblance to that in quasi-two-dimensional heavy-Fermion superconductors, suggesting a common underlying spin-related physics in these superconductors with strong electron correlations. PMID:18480261

  15. Higgs mechanism, phase transitions, and anomalous Hall effect in three-dimensional topological superconductors

    NASA Astrophysics Data System (ADS)

    Nogueira, Flavio S.; Sudbø, Asle; Eremin, Ilya

    2015-12-01

    We demonstrate that the Higgs mechanism in three-dimensional topological superconductors exhibits unique features with experimentally observable consequences. The Higgs model we discuss has two superconducting components and an axionlike magnetoelectric term with the phase difference of the superconducting order parameters playing the role of the axion field. Due to this additional term, quantum electromagnetic and phase fluctuations lead to a robust topologically nontrivial state that holds also in the presence of interactions. In this sense, we show that the renormalization flow of the topologically nontrivial phase cannot be continuously deformed into a topologically nontrivial one. One consequence of our analysis of quantum critical fluctuations is the possibility of having a first-order phase transition in the bulk and a second-order phase transition on the surface. We also explore another consequence of the axionic Higgs electrodynamics, namely, the anomalous Hall effect. In the low-frequency London regime an anomalous Hall effect is induced in the presence of an applied electric field parallel to the surface. This anomalous Hall current is induced by a Lorentz-like force arising from the axion term, and it involves the relative superfluid velocity of the superconducting components. The anomalous Hall current has a negative sign, a situation reminiscent of but quite distinct in physical origin from the anomalous Hall effect observed in high-Tc superconductors. In contrast to the latter, the anomalous Hall effect in topological superconductors is nondissipative and occurs in the absence of vortices.

  16. Sm-Ba-Cu-O bulk superconductors melt-processed in air

    NASA Astrophysics Data System (ADS)

    Fujimoto, Hiroyuki; Cai, Chuanbing; Ohtabara, Emi

    2002-08-01

    Recent development shows that melt-processed YBaCuO (Y123) and light rare-earth (LRE) BaCuO superconductors have a high Jc at 77 K and high magnetic field. Solidification processes for producing RE123 superconductors are effective for obtaining high Jc and are very promising for high field application as a superconducting permanent magnet with the liquid nitrogen refrigeration. LRE BaCuO bulk superconductors melt-processed in a reduced oxygen atmosphere, named oxygen-controlled-melt-growth process, have a high Tc and Jc. However, processing in air is preferable for practical applications. In this study, we discuss Sm123 bulks melt-processed in air, and their characteristic superconducting properties. Isothermal undercooling growth in air with oxygen annealing and Nd123/MgO thin film cold seeding technique were applied in Sm 1.8Ba 2.4Cu 3.4O y/Ag system to seek the high efficiency of process, homogeneity of composition, and feasibility of batch production. Single-domain growth was achieved using this technique. The result implies that melt-processed in air applying isothermal method and thin film seeding in Sm system is fit for producing larger bulks in large scale applications.

  17. Theory of nodal s±-wave pairing symmetry in the Pu-based 115 superconductor family

    PubMed Central

    Das, Tanmoy; Zhu, Jian-Xin; Graf, Matthias J.

    2015-01-01

    The spin-fluctuation mechanism of superconductivity usually results in the presence of gapless or nodal quasiparticle states in the excitation spectrum. Nodal quasiparticle states are well established in copper-oxide, and heavy-fermion superconductors, but not in iron-based superconductors. Here, we study the pairing symmetry and mechanism of a new class of plutonium-based high-Tc superconductors and predict the presence of a nodal s+− wave pairing symmetry in this family. Starting from a density-functional theory (DFT) based electronic structure calculation we predict several three-dimensional (3D) Fermi surfaces in this 115 superconductor family. We identify the dominant Fermi surface “hot-spots” in the inter-band scattering channel, which are aligned along the wavevector Q = (π, π, π), where degeneracy could induce sign-reversal of the pairing symmetry. Our calculation demonstrates that the s+− wave pairing strength is stronger than the previously thought d-wave pairing; and more importantly, this pairing state allows for the existence of nodal quasiparticles. Finally, we predict the shape of the momentum- and energy-dependent magnetic resonance spectrum for the identification of this pairing symmetry. PMID:25721375

  18. Theory of nodal s±-wave pairing symmetry in the Pu-based 115 superconductor family

    DOE PAGES

    Das, Tanmoy; Zhu, Jian -Xin; Graf, Matthias J.

    2015-02-27

    The spin-fluctuation mechanism of superconductivity usually results in the presence of gapless or nodal quasiparticle states in the excitation spectrum. Nodal quasiparticle states are well established in copper-oxide, and heavy-fermion superconductors, but not in iron-based superconductors. Here, we study the pairing symmetry and mechanism of a new class of plutonium-based high-Tc superconductors and predict the presence of a nodal s⁺⁻ wave pairing symmetry in this family. Starting from a density-functional theory (DFT) based electronic structure calculation we predict several three-dimensional (3D) Fermi surfaces in this 115 superconductor family. We identify the dominant Fermi surface “hot-spots” in the inter-band scattering channel,more » which are aligned along the wavevector Q = (π, π, π), where degeneracy could induce sign-reversal of the pairing symmetry. Our calculation demonstrates that the s⁺⁻ wave pairing strength is stronger than the previously thought d-wave pairing; and more importantly, this pairing state allows for the existence of nodal quasiparticles. Finally, we predict the shape of the momentum- and energy-dependent magnetic resonance spectrum for the identification of this pairing symmetry.« less

  19. Fundamental studies of superconductors using scanning magnetic imaging

    NASA Astrophysics Data System (ADS)

    Kirtley, J. R.

    2010-12-01

    In this review I discuss the application of scanning magnetic imaging to fundamental studies of superconductors, concentrating on three scanning magnetic microscopies—scanning SQUID microscopy (SSM), scanning Hall bar microscopy (SHM) and magnetic force microscopy (MFM). I briefly discuss the history, sensitivity, spatial resolution, invasiveness and potential future developments of each technique. I then discuss a selection of applications of these microscopies. I start with static imaging of magnetic flux: an SSM study provides deeper understanding of vortex trapping in narrow strips, which are used to reduce noise in superconducting circuitry. Studies of vortex trapping in wire lattices, clusters and arrays of rings and nanoholes show fascinating ordering effects. The cuprate high-Tc superconductors are shown to have predominantly d-wave pairing symmetry by magnetic imaging of the half-integer flux quantum effect. Arrays of superconducting rings act as a physical analog for the Ising spin model, with the half-integer flux quantum effect helping to eliminate one source of disorder in antiferromagnetic arrangements of the ring moments. Tests of the interlayer tunneling model show that the condensation energy available from this mechanism cannot account for the high critical temperatures observed in the cuprates. The strong divergence in the magnetic fields of Pearl vortices allows them to be imaged using SSM, even for penetration depths of a millimeter. Unusual vortex arrangements occur in samples comparable in size to the coherence length. Spontaneous magnetization is not observed in Sr2RuO4, which is believed to have px ± ipy pairing symmetry, although effects hundreds of times bigger than the sensitivity limits had been predicted. However, unusual flux trapping is observed in this superconductor. Finally, unusual flux arrangements are also observed in magnetic superconductors. I then turn to vortex dynamics: imaging of vortices in rings of highly underdoped

  20. Studies of nonlinear electrodynamics of high-temperature superconductors

    SciTech Connect

    Lam, Quan-Chiu H.

    1991-08-01

    Nonlinear electrodynamics of high-{Tc} superconductors are studied both theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an arc field, H{sub 1} cos({omega}t), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a superposing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field P{sub nf}(H{sub dc}), is indeed experimentally observed in powdered YBa{sub 2}Cu{sub 3}O{sub 7}. Other experimental aspects also agree with model predictions. For bulk sintered cylindrical samples, a generalized critical state model is presented. In this model, the nonlinear electrodynamics are due to flux-pinning, somewhat similar to low-temperature type-II superconductors, but with a more generalized critical current densities' dependence on magnetic field -- J{sub c}(H){approximately}H{sub local}{sup -{beta}}, with {beta} being an adjustable parameter. Experiments in ac and dc magnetic fields on a sintered cylindrical rod of YBa{sub 2}Cu{sub 3}O{sub 7} yield unambiguous evidence of independent inter- and intragranular contributions to the complex harmonic permeability {tilde {mu}}{sub n} = {mu}{prime}{sub n} -i{mu}{double prime}{sub n}. Temperature- dependence measurements reveal that, while the intragranular supercurrents disappear at {Tc}{ge}91.2 K, the intergranular supercurrents disappear at T{ge}86.6 K. This result is, to our knowledge, the first clear measurement of the phase-locking temperature of the 3-D matrix formed by YBa{sub 2}Cu{sub 3}O{sub 7} grains, which are in electrical contact with one another through weak links.

  1. Studies of nonlinear electrodynamics of high-temperature superconductors

    SciTech Connect

    Lam, Quan-Chiu H.

    1991-08-01

    Nonlinear electrodynamics of high-{Tc} superconductors are studied both theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an arc field, H{sub 1} cos({omega}t), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a superposing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field P{sub nf}(H{sub dc}), is indeed experimentally observed in powdered YBa{sub 2}Cu{sub 3}O{sub 7}. Other experimental aspects also agree with model predictions. For bulk sintered cylindrical samples, a generalized critical state model is presented. In this model, the nonlinear electrodynamics are due to flux-pinning, somewhat similar to low-temperature type-II superconductors, but with a more generalized critical current densities` dependence on magnetic field -- J{sub c}(H){approximately}H{sub local}{sup -{beta}}, with {beta} being an adjustable parameter. Experiments in ac and dc magnetic fields on a sintered cylindrical rod of YBa{sub 2}Cu{sub 3}O{sub 7} yield unambiguous evidence of independent inter- and intragranular contributions to the complex harmonic permeability {tilde {mu}}{sub n} = {mu}{prime}{sub n} -i{mu}{double_prime}{sub n}. Temperature- dependence measurements reveal that, while the intragranular supercurrents disappear at {Tc}{ge}91.2 K, the intergranular supercurrents disappear at T{ge}86.6 K. This result is, to our knowledge, the first clear measurement of the phase-locking temperature of the 3-D matrix formed by YBa{sub 2}Cu{sub 3}O{sub 7} grains, which are in electrical contact with one another through weak links.

  2. Magnetic and pairing properties of a two-orbital model for the pnictide superconductors: a quantum Monte Carlo study.

    PubMed

    Liu, Guang-Kun; Huang, Zhong-Bing; Wang, Yong-Jun

    2014-08-13

    Using the constrained-path Monte Carlo method, a two-orbital model for the pnictide superconductors is studied at half filling and in both the electron- and hole-doped cases. At half filling, a stable (π, 0)/(0, π) magnetic order is explicitly observed and the system tends to be in an orthomagnetic order rather than the striped antiferromagnetic order on increasing the Coulomb repulsion U. In the electron-doped case, the (π, 0)/(0, π) magnetic order is enhanced upon doping and suppressed eventually and a s(±) pairing state dominates all the possible nearest-neighbour-bond pairings. Whereas in the hole-doped case, the magnetic order is straightforwardly suppressed and two nearly degenerate A(1g) and B(1g) intraband pairings become the dominant ones. PMID:25029986

  3. Electronic structure of rare-earth doped SrFBiS2 superconductors from photoemission spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Mishra, P.; Lohani, H.; Jha, Rajveer; Awana, V. P. S.; Sekhar, B. R.

    2016-06-01

    The electronic structure study of the Rare Earth (La, Ce) doped SrFBiS2 superconductors using valence band photoemission in conjugation with the band structure calculations have been presented. The spectral features shift towards higher binding energy, consistent with the electron doping, for the doped compounds. An enhanced metallicity in addition to the shift in the Fermi level towards the conduction band occurs for the Rare Earth (RE) doped compounds. Further, the degeneracy of bands along X-M direction at valence band maximum (VBM) and conduction band minimum (CBM) is lifted due to RE doping. An enhanced spectral weight near EF accompanied by a decrease in density of states at higher binding energy occurs for the doped compounds. This unusual spectral weight shift is substantiated by the change in Fermi surface topology and reduced distortion of Bi-S plane for the doped compounds.

  4. Chemical Substitution and High Pressure Effects on Superconductors in the LnOBiS$_2$ (Ln = La-Nd) System

    SciTech Connect

    Fang, Yuankan; Wolowiec, Christian T.; Yazici, Duygu; Maple, M. Brian

    2015-12-14

    A large number of compounds which contain BiS$_2$ layers exhibit enhanced superconductivity upon electron doping. Much interest and research effort has been focused on BiS$_2$-based compounds which provide new opportunities for exploring the nature of superconductivity. Important to the study of BiS2-based superconductors is the relation between structure and superconductivity. By modifying either the superconducting BiS$_2$ layers or the blocking layers in these layered compounds, one can effectively tune the lattice parameters, local atomic environment, electronic structure, and other physical properties of these materials. In this article, we will review some of the recent progress on research of the effects of chemical substitution in BiS$_2$-based compounds, with special attention given to the compounds in the LnOBiSS$_2$ (Ln = La-Nd) system. Strategies which are reported to be essential in optimizing superconductivity of these materials will also be discussed.

  5. Topological insulators and superconductors

    NASA Astrophysics Data System (ADS)

    Teo, Jeffrey C. Y.

    We study theoretical properties of robust low energy electronic excitations associated with topological insulators and superconductors. The bulk materials are described by non-interacting single particle band Hamiltonians with a finite excitation gap. Their topological phases are classifed according to symmetries and dimensions, characterized by discrete bulk invariants, and correspond to topologically protected gapless excitations bounded to boundaries, interfaces or other kinds of defects. In particular, we study the metallic surface states of the three dimensional topological insulator Bi1-- xSbx, critical edge transport behavior of quantum spin Hall insulators (QSHI) using point contact geometry, Majorana bound states in three dimensions and their resemblance to Ising statistics, and various gapless modes accompanying topological defects in insulators and superconductors. We illustrate the topological phase of Bi1-- xSbx by calculating its surface energy spectrum numerically from a previously proposed tight binding model. An odd number of surface Dirac cones occupy the surface Brillouin zone and exhibit the strong topological nature of the material. We investigate the critical conductance behavior of a point contact in QSHI using a spinful Luttinger liquid description along the edges. For weak interactions, a novel intermediate fixed point controls the pinch-off transition, and the universal crossover scaling function of conductance is extracted from the solvable limits for the Luttinger parameter g = 1 -- epsilon, g = 1/2 + epsilon, and g = 1/ 3 . Majorana fermions are studied as zero energy quasiparticle excitations associated with pointlike topological defects in 3D superconductors. The low energy modes are described phenomenologically in a Dirac-type Bogoliubov de Gennes (BdG) framework, and the Majorana bound states are shown to exhibit Ising non-Abelian statistics despite living in (3 + 1) dimensions. In particular, novel braidless operations are shown to

  6. Universality class of the structural phase transition in the normal phase of cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Najafi, M. N.; Tavana, A.

    2016-08-01

    The tetragonal-orthorhombic structural phase transition of oxygen atoms in the basal plane of YBa2Cu3O6 +δ high-TC cuprate superconductors is studied numerically. By mapping the system onto the asymmetric next-nearest-neighbor Ising model, we characterize this phase transition. Results indicate the degrees of critical behavior. We show that this phase transition occurs at the temperature TC≃0.148 eV in the thermodynamic limit. By analyzing the critical exponents, it is found that this universality class displays some common features, with the two-dimensional three-state Potts model universality class, although the possibility of other universality classes cannot be ruled out. Conformal invariance at T =Tc is investigated using the Schramm-Loewner evolution (SLE) technique, and it is found that the SLE diffusivity parameter for this system is 3.34 ±0.01 .

  7. Transport and structural properties of the Ho1Ba2Cu3O9 - delta superconductor

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Ik; Golben, John P.; Song, Yi; Lee, Sang Young; Noh, Tae W.; Chen, Xiao-dong; Testa, Joe; Gaines, J. R.; Tettenhorst, Rodney T.

    1987-07-01

    The compound Ho1Ba2Cu3O9-δ has been found to be a high Tc superconductor. The onset of the superconducting transition is 88 K with zero resistance achieved at 87 K. The x-ray diffraction spectrum of this material shows it to be a single-phase perovskite similar to the Y1Ba2Cu3O9-δ compound but different from the K2NiF4 perovskite which is believed to be the superconducting phase for the La2(1-x) Ba2xCuO4-δ system. Possible oxygen deficiencies in several of the unit cell planes are discussed. The room-temperature resistance, the superconducting onset temperature, and the emergence of the single phase all depend upon the sample preparation firing conditions.

  8. Surface state and normal layer effects in high T{sub c} superconductors

    SciTech Connect

    Klemm, R.A.; Ledvij, M.; Liu, Samuel H.

    1996-01-01

    In addition to the conducting CuO{sub 2} (S) layers, most high-{Tc}, superconductors also contain other conducting (N) layers, which are only superconducting due to the proximity effect. The combination of S and N layers can give rise to complicated electronic densities of states, leading to quasilinear penetration depth and NMR relaxation rate behavior at low temperatures. Surface states can also complicate the analysis of tunneling and photoemission measurements. Moreover, geometrical considerations and inhomogeneously trapped flux are possible explanations of the paramagnetic Meissner effect and of corner and ring SQUID experiments. Hence, all of the above experiments could be consistent with isotropic s-wave superconductive within the S layers.

  9. Reassessment of the electronic state, magnetism, and superconductivity in high-Tc cuprates with the Nd2CuO4 structure

    NASA Astrophysics Data System (ADS)

    Naito, Michio; Krockenberger, Yoshiharu; Ikeda, Ai; Yamamoto, Hideki

    2016-04-01

    The electronic phase diagram of the cuprates remains enigmatic and is still a key ingredient to understand the mechanism of high-Tc superconductivity. It has been believed for a long time that parent compounds of cuprates were universally antiferromagnetic Mott insulators (charge-transfer insulators) and that high-Tc superconductivity would develop upon doping holes or electrons in a Mott-Hubbard insulator ("doped Mott-insulator scenario"). However, our recent discovery of superconductivity in the parent compounds of square-planar cuprates with the Nd2CuO4 (T') structure and the revised electronic phase diagram in T' cuprates urged a serious reassessment to the above scenario. In this review, we present the main results derived from our synthesis and experiments on T' cuprates in the undoped or heavily underdoped regime over 20 years, including material issues and basic physics. The key material issue is how to remove excess oxygen ions at the apical site without introducing oxygen vacancies in the CuO2 planes. In order to put this into practice, the basic knowledge of complex solid-state chemistry in T' cuprates is required, which is also included in this review.

  10. Surface Optimization of RBa2Cu3O7-δ (R=Y, Nd) Epitaxial High Tc Films for In Situ Photoemission Studies

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Schmauder, T.; Ariosa, D.; Touzelet, O.; Rast, S.; Onellion, M.; Pavuna, D.

    One of the intrinsic difficulties for in situ photoemission studies of high Tc oxide films is the surface volatility, especially the oxygen loss. In order to solve this problem, we have constructed a dedicated system for high Tc film surface studies, in particular for ARPES measurements. Here we briefly describe our pulsed laser deposition (PLD) system that is linked to the photoemission chamber at the Synchrotron Radiation Center (SRC) in Wisconsin, and discuss crystallographic and electronic properties measured on epitaxial YBa2Cu3O7-δ (YBCO) and NdBa2Cu3O7-δ (NBCO) films. Resistivity and XRD studies show that the best c axis epitaxial films, with Tc (onset)=92 K (Tc0=90.5 K), are monophase and single crystalline with crystal coherence up to almost 1 µm. Initial core level photoemission study indicates that, for YBCO on SrTiO3 (without any buffer layer), the Ba oxide layer tends to be the dominant surface layer. Further experiments are underway to reproducibly detect sharp Fermi edge and perform ARPES study on optimally doped film surfaces.

  11. High-Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides

    DOE PAGES

    Di Castro, D.; Cantoni, C.; Ridolfi, F.; Aruta, C.; Tebano, A.; Yang, N.; Balestrino, G.

    2015-09-28

    At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case can oxygen ions be incorporated in themore » interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. In addition, a detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1–2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explaining the dependence of Tc on the number of CuO2 planes in these systems.« less

  12. Gap-modulation infrared spectroscopy of high transition temperature superconductors

    PubMed Central

    Little, William A.; Collman, James P.

    1988-01-01

    Conventional methods of determining the coupling factor α2(ω)F(ω) for the newly discovered high transition temperature (Tc) cuprate superconductors by using tunneling and infrared measurements have thus far failed to show the cause of the very high Tc of these compounds. This is due in part to difficulties in sample preparation for tunneling studies and to difficulties in obtaining good data at relatively high tunneling voltages. Also, in IR (infrared) measurements, small differences in absorptivity between the normal and superconducting state can be masked by changes in the phonon occupation at high and low temperatures. Here we propose a technique for determing the coupling constant, which should be less dependent on the surface quality of the sample than with tunneling and should allow measurements at higher energies with greater precision than do tunneling or simple IR observations. This should make possible a definitive determination of any possible exciton contribution to this coupling term, which would appear at energies well above the range where conventional IR or tunneling measurements are effective. PMID:16593950

  13. Scanning Tunneling Microscopy and Spectroscopy of Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    Hoffman, Jennifer

    2010-03-01

    Two decades after the discovery of high-Tc superconductivity in the cuprates, superconductivity was discovered up to 55, in a second family of materials: the iron-pnictides. This recent discovery has generated tremendous excitement for several reasons. First, there is hope that the iron-pnictides will finally provide the foil necessary to understand the enormous yet puzzling body of research on the cuprates. Second, reports of low anisotropy and strong vortex pinning in these new materials have spurred optimism that the iron-pnictides may finally lead to the widespread technological applications which have been elusive for cuprates. In this talk, I will present the first scanning tunneling spectroscopic imaging study of a single crystal iron-pnictide superconductor in high magnetic fields. We study optimally doped BaCo0.2Fe1.8As2 with Tc= 25.3,, finding a ˜6, superconducting gap with nanoscale inhomogeneity, which leads to an average reduced gap of 2δ/kBTc˜5.7. We further observe a static disordered vortex lattice at 9,, and demonstrate that vortices are pinned in the bulk of this material, a promising observation for practical application.

  14. Conventional magnetic superconductors

    DOE PAGES

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

    2015-07-01

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

  15. Hybrid superconductor magnet bearings

    SciTech Connect

    Chu, W.

    1995-04-01

    Hybrid superconductor magnet bearings (HSMB`s) utilize high temperature superconductors (HTS`s) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS`s, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, the authors present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.

  16. Hybrid superconductor magnet bearings

    NASA Technical Reports Server (NTRS)

    Chu, Wei-Kan

    1995-01-01

    Hybrid superconductor magnet bearings (HSMB's) utilize high temperature superconductors (HTS's) together with permanent magnets to form a frictionless interface between relatively rotating parts. They are low mass, stable, and do not incur expenditure of energy during normal operation. There is no direct physical contact between rotor and stator, and hence there is no wear and tear. However, just as any other applications of HTS's, it requires a very cold temperature to function. Whereas this might be perceived as a disadvantage on earth, it is of no great concern in space or on the moon. To astronomers, the moon is an excellent site for an observatory, but the cold and dusty vacuum environment on the moon precludes the use of mechanical bearings on the telescope mounts. Furthermore, drive mechanisms with very fine steps, and hence bearings with extremely low friction are needed to track a star from the moon, because the moon rotates very slowly. All aspects considered, the HSMB is about the only candidate that fits in naturally. Here, we present a design for one such bearing, capable of supporting a telescope that weighs about 3 lbs on Earth.

  17. Conventional magnetic superconductors

    SciTech Connect

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

    2015-07-01

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

  18. Materials design for new superconductors

    NASA Astrophysics Data System (ADS)

    Norman, M. R.

    2016-07-01

    Since the announcement in 2011 of the Materials Genome Initiative by the Obama administration, much attention has been given to the subject of materials design to accelerate the discovery of new materials that could have technological implications. Although having its biggest impact for more applied materials like batteries, there is increasing interest in applying these ideas to predict new superconductors. This is obviously a challenge, given that superconductivity is a many body phenomenon, with whole classes of known superconductors lacking a quantitative theory. Given this caveat, various efforts to formulate materials design principles for superconductors are reviewed here, with a focus on surveying the periodic table in an attempt to identify cuprate analogues.

  19. Dynamics of quasiparticles and antiferromagnetic correlations in electron-doped cuprate La2-xCexCuO4+/-δ (LCCO)

    NASA Astrophysics Data System (ADS)

    Vishik, I. M.; Mahmood, F.; Alpichshev, Z.; Higgins, J. S.; Greene, R. L.; Gedik, N.

    We studied quasiparticle dynamics in thin films of the electron-doped cuprate La2-xCexCuO4 (LCCO) via optical pump-probe spectroscopy. In underdoped LCCO, the quasiparticle recombination dynamics imply a nodeless superconducting gap, which can be realized with dx2-y2 symmetry if a nodal hole-pocket is absent. Meanwhile, optimally doped LCCO shows recombination dynamics consistent with line nodes. Above Tc, fluence-dependent dynamics indicate a fully-formed gap in the density of states, which is associated with antiferromagnetic correlations, and limits can be placed on the correlation length and time.

  20. Electron spin susceptibility of superconductors

    SciTech Connect

    Levitov, L.S.; Nazarov, Y.V.; Eliashberg, G.M.

    1985-03-10

    The effect of spin polarization due to the Meissner currents on the electron spin susceptibility of a superconductor is studied. This effect accounts for a susceptibility considerably stronger than that of a normal metal. The spin distribution is discussed.