scholarly journals Electronic Structure and Thermodynamic Properties of High Temperature Superconductors

2021 ◽  
Author(s):  
◽  
James Glenn Storey
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Isotope Effect ◽  
High Temperature Superconductivity ◽  
Hole Concentration ◽  
Ac Susceptibility ◽  
High Temperature Superconductors ◽  
Phonon Modes ◽  
Bulk Properties ◽  
Doping Dependence

<p>The generic doping dependence of the thermodynamic, electrodynamic and transport properties of high-temperature superconductors remains a puzzle despite many years of study. We are still awaiting a rigorous scientific theory that explains the resistance-free flow of electric current in these novel materials. In conventional superconductors, observations of the predicted dependence of the superconducting transition temperature on isotopic mass played a key role in identifying a phononic pairing mechanism. In order to elucidate the role of phonons in the high-Tc superconductors, the oxygen isotope effect in the separate components of the penetration depth tensor of the high-temperature superconductor YBa2Cu4O8 was determined from AC susceptibility measurements, performed on biaxially-aligned powders set in epoxy. The results, extracted after assuming values for the upper cut-off radii in the particle size distributions, show that the isotope effect in the bc-plane is negligible compared to those of the ab- and ac-planes. This suggests that the electrons prefer to couple to phonon modes in which the motion of the atoms is perpendicular to the plane of transport. The electronic entropy, superfluid density, Raman response, spin susceptibility and thermoelectric power were calculated from energy-momentum dispersions determined by angle-resolved photoemission spectroscopy (ARPES). An excellent match with experimental data was obtained. This is a highly significant result because it provides the first comprehensive link between these bulk properties and the ARPES measurements which are dominated by the outermost CuO2 layer. Thus, in most respects surface effects do not appear to seriously modify or obscure the band structure which governs bulk properties. The calculations reveal the presence of a van Hove singularity (vHs) at the Fermi level (EF ) in the heavily overdoped regime to be a universal feature of the cuprates. The evolution of these properties with temperature and doping can be fully explained by the retreat of EF from the vHs and the opening of a normal state pseudogap as doping is decreased. Consequently, the pairing potential amplitude is found to be a strongly decreasing function of hole concentration, similar to the doping dependence of the exchange interaction, J. The pairing interaction is possibly a universal function of the EF â EvHs with the maximum in the transition temperature (Tc) governed by the exact magnitude of the density of states on the flanks of the vHs. These are key new discoveries which may provide a route forward to solving the puzzle of high-temperature superconductivity.</p>

scholarly journals Electronic Structure and Thermodynamic Properties of High Temperature Superconductors

2021 ◽  
Author(s):  
◽  
James Glenn Storey
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Isotope Effect ◽  
High Temperature Superconductivity ◽  
Hole Concentration ◽  
Ac Susceptibility ◽  
High Temperature Superconductors ◽  
Phonon Modes ◽  
Bulk Properties ◽  
Doping Dependence

<p>The generic doping dependence of the thermodynamic, electrodynamic and transport properties of high-temperature superconductors remains a puzzle despite many years of study. We are still awaiting a rigorous scientific theory that explains the resistance-free flow of electric current in these novel materials. In conventional superconductors, observations of the predicted dependence of the superconducting transition temperature on isotopic mass played a key role in identifying a phononic pairing mechanism. In order to elucidate the role of phonons in the high-Tc superconductors, the oxygen isotope effect in the separate components of the penetration depth tensor of the high-temperature superconductor YBa2Cu4O8 was determined from AC susceptibility measurements, performed on biaxially-aligned powders set in epoxy. The results, extracted after assuming values for the upper cut-off radii in the particle size distributions, show that the isotope effect in the bc-plane is negligible compared to those of the ab- and ac-planes. This suggests that the electrons prefer to couple to phonon modes in which the motion of the atoms is perpendicular to the plane of transport. The electronic entropy, superfluid density, Raman response, spin susceptibility and thermoelectric power were calculated from energy-momentum dispersions determined by angle-resolved photoemission spectroscopy (ARPES). An excellent match with experimental data was obtained. This is a highly significant result because it provides the first comprehensive link between these bulk properties and the ARPES measurements which are dominated by the outermost CuO2 layer. Thus, in most respects surface effects do not appear to seriously modify or obscure the band structure which governs bulk properties. The calculations reveal the presence of a van Hove singularity (vHs) at the Fermi level (EF ) in the heavily overdoped regime to be a universal feature of the cuprates. The evolution of these properties with temperature and doping can be fully explained by the retreat of EF from the vHs and the opening of a normal state pseudogap as doping is decreased. Consequently, the pairing potential amplitude is found to be a strongly decreasing function of hole concentration, similar to the doping dependence of the exchange interaction, J. The pairing interaction is possibly a universal function of the EF â EvHs with the maximum in the transition temperature (Tc) governed by the exact magnitude of the density of states on the flanks of the vHs. These are key new discoveries which may provide a route forward to solving the puzzle of high-temperature superconductivity.</p>

PAIRING STATE AND HIGH TEMPERATURE SUPERCONDUCTIVITY OF SEMI-LOCALIZED 2D ELECTRON SYSTEM WITH CIRCULAR MOLECULAR ORBITS

2002 ◽  
Vol 16 (10n11) ◽  
pp. 351-362 ◽  
Author(s):  
MASANORI SUGAHARA ◽  
NIKOLAI N. BOGOLUBOV
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Upper Bound ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Electron System ◽  
Circular Orbits ◽  
New Model ◽  
Pairing State ◽  
The Stability

Recently, new types of high temperature superconductors have been found which are characterized by the existence of circular molecular orbits in each unit site of 2D s/p electron system. In view of the characteristic, a new model of superconductivity is studied based on the stability of the correlated state of electrons in the 2D interconnection of circular orbits. This model gives an estimation of the upper bound of superfluidity transition temperature: T c ~ 130-400 K for fcc C 60, and T c ~ 110-340 K for hole-doped MgB 2.

scholarly journals High temperature superconductivity in sulfur hydride under ultrahigh pressure: A complex superconducting phase beyond conventional BCS

2016 ◽  
Vol 2 (1) ◽  
Author(s):  
Annette Bussmann-Holder ◽  
Jürgen Köhler ◽  
M.-H. Whangbo ◽  
Antonio Bianconi ◽  
Arndt Simon
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Transition Temperature ◽  
Hydrogen Bonds ◽  
Pressure Dependence ◽  
High Temperature Superconductivity ◽  
Superconducting Phase ◽  
Ultrahigh Pressure ◽  
Phonon Modes ◽  
Interband Coupling

AbstractThe recent report of superconductivity under high pressure at the record transition temperature of Tc =203 K in pressurized H2S has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms cannot account for the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope coefficient. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active.

Doping dependence ofTcand its related isotope effect in high-temperature superconductors

1997 ◽  
Vol 55 (17) ◽  
pp. 11751-11755 ◽  
Author(s):  
A. Bussmann-Holder ◽  
A. R. Bishop ◽  
L. Genzel ◽  
A. Simon
Keyword(s):  
High Temperature ◽  
Isotope Effect ◽  
High Temperature Superconductors ◽  
Doping Dependence

scholarly journals High-temperature superconductivity using a model of hydrogen bonds

2018 ◽  
Vol 115 (22) ◽  
pp. 5709-5713 ◽  
Author(s):  
Daniel Kaplan ◽  
Yoseph Imry
Keyword(s):  
High Temperature ◽  
Matrix Element ◽  
Simple Model ◽  
Hydrogen Bonds ◽  
Isotope Effect ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Superconducting Gap ◽  
Gap Equation ◽  
The Matrix

Recently, there has been much interest in high-temperature superconductors and more recently in hydrogen-based superconductors. This work offers a simple model that explains the behavior of the superconducting gap based on naive BCS (Bardeen–Cooper–Schrieffer) theory and reproduces most effects seen in experiments, including the isotope effect and Tc enhancement as a function of pressure. We show that this is due to a combination of the factors appearing in the gap equation: the matrix element between the proton states and the level splitting of the proton.

scholarly journals Isotope Effect in the Translation-Invariant Bipolaron Theory of High-Temperature Superconductivity

2020 ◽  
Vol 5 (4) ◽  
pp. 80
Author(s):  
Victor D. Lakhno
Keyword(s):  
High Temperature ◽  
Isotope Effect ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Superconducting Transition ◽  
Strong Electron ◽  
Translation Invariant ◽  
Electron Phonon Interaction ◽  
Theory Of Superconductivity

It is shown that the translation-invariant bipolaron theory of superconductivity can explain the dependence of the isotope coefficient in high-temperature superconductors on the critical temperature of a superconducting transition: in the case of strong electron–phonon interaction, the isotope coefficient is low when doping is optimal and high when it is weak. It is demonstrated that in the case of London penetration depth, the absolute value of the isotope coefficient behaves in the opposite way. A conclusion of the great role of non-adiabaticity in the case of weak doping is made. The criteria for d-wave phonon input into the isotope effect is established.

Hole Concentration - Tc Relationships for Nd and Zn Substitutions in YBa2Cu3Oy

1989 ◽  
Vol 156 ◽  
Author(s):  
Merrill W. Shafer ◽  
T. Penney ◽  
B. L. Olson ◽  
R. L. Greene
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Master Curve ◽  
Hole Concentration ◽  
High Temperature Superconductors ◽  
Major Effect ◽  
Zn Substitution ◽  
Sheet Copper ◽  
The Relationship

ABSTRACTOne of the intriguing questions involving the copper containing high temperature superconductors is the relationship between the hole concentration and the transition temperature, Tc. We address this question in terms of a proposed “master curve” on a Tc, vs hole concentration plot. This curve shows a maximum at 90K at a hole concentration of approximately 0.2 – 0.22 holes per sheet copper for the 1–2–3 system. In this work we studied the Nd1+xBa2−xCu3Oy and YBa2Cu3−xZnxOy systems to check the validity of this “master curve”. Both Nd and Zn substitutions lower Tc, Nd by reducing the number of holes, consistent with the model given by the curve. The effect of Zn substitution is ambiguous, since both the holes are increased and the Cu-O planes are perturbed. Compensation doping, using both Nd and Zn, shows that the major effect of Zn is to disrupt the Cu-O planes.

Frequency response of AC susceptibility in high temperature superconductors

2005 ◽  
Vol 135 (3) ◽  
pp. 203-207 ◽  
Author(s):  
S.L. Liu ◽  
G.J. Wu ◽  
X.B. Xu ◽  
J. Wu ◽  
H.M. Shao ◽  
...  
Keyword(s):  
High Temperature ◽  
Frequency Response ◽  
Ac Susceptibility ◽  
High Temperature Superconductors

scholarly journals Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder

Materials ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 5830
Author(s):  
Andrzej Ślebarski ◽  
Maciej M. Maśka
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
High Temperature Superconductors ◽  
Superconducting Phase ◽  
Length Scale ◽  
Superconducting Transition ◽  
Atomic Disorder ◽  
Strong Inhomogeneity ◽  
Related Compounds

We investigated the effect of enhancement of superconducting transition temperature Tc by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (La3M4Sn13, Ca3Rh4Sn13, Y5Rh6Sn18, Lu5Rh6Sn18; M= Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale ξ in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with Tc⋆>Tc (dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of Tc⋆∼2Tc (dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase Tc⋆ in respect to the bulk Tc one and proposed a model that explains the Tc⋆>Tc behavior in the series of nonmagnetic skutterudite-related compounds.

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