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.

SUPERFLUIDITY IN SEMI-LOCALIZED 2D ELECTRON SYSTEM WITH CIRCULAR MOLECULAR ORBITS

2002 ◽  
Vol 16 (11n12) ◽  
pp. 1731-1738
Author(s):  
MASANORI SUGAHARA ◽  
NIKOLAI N. BOGOLUBOV
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
High Temperature Superconductors ◽  
Electron System ◽  
Circular Orbits ◽  
New Model ◽  
New Type

Recently discovered new type of high temperature superconductors have circular molecular orbits in each unit site of 2D s/p electron system. We discuss a new model of superconductivity caused by the correlated state of electrons in the 2D interconnection of circular orbits. This model gives an estimation of the superfluidity transition temperature: T c ≈ 70-200  K for fcc C 60, and T c ≈50-150  K for MgB2 .

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>

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.

scholarly journals Square Lattice Iridates

2019 ◽  
Vol 10 (1) ◽  
pp. 315-336 ◽  
Author(s):  
Joel Bertinshaw ◽  
Y.K. Kim ◽  
Giniyat Khaliullin ◽  
B.J. Kim
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Single Layer ◽  
Square Lattice ◽  
Spin Orbit Coupling ◽  
Fermi Arcs ◽  
Firm Evidence ◽  
Energy Physics ◽  
Strong Spin

Over the past few years, Sr2IrO4, a single-layer member of the Ruddlesden–Popper series iridates, has received much attention as a close analog of cuprate high-temperature superconductors. Although there is not yet firm evidence for superconductivity, a remarkable range of cuprate phenomenology has been reproduced in electron- and hole-doped iridates including pseudogaps, Fermi arcs, and d-wave gaps. Furthermore, many symmetry-breaking orders reminiscent of those decorating the cuprate phase diagram have been reported using various experimental probes. We discuss how the electronic structures of Sr2IrO4 through strong spin-orbit coupling leads to the low-energy physics that had long been unique to cuprates, what the similarities and differences between cuprates and iridates are, and how these advance the field of high-temperature superconductivity by isolating essential ingredients of superconductivity from a rich array of phenomena that surround it. Finally, we comment on the prospect of finding a new high-temperature superconductor based on the iridate series.

Electron-Doped High Tc Superconductors

MRS Bulletin ◽  
1990 ◽  
Vol 15 (6) ◽  
pp. 60-67 ◽  
Author(s):  
M. Brian Maple
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Building Blocks ◽  
The United States ◽  
Charge Carriers ◽  
Critical Temperatures ◽  
High Tc ◽  
Prevailing View ◽  
Identical Crystal

Since the discovery of high temperature superconductivity in layered copper-oxide compounds in the latter part of 1986, an enormous amount of research has been carried out on these remarkable materials. Prior to 1989, the prevailing view was that the charge carriers responsible for superconductivity in these materials were holes that move through conducting CuO2 planes. The CuO2 planes are the basic building blocks of the crystal structures of all the presently known oxides with superconducting critical temperatures Tc greater than ~30 K. Recently, new superconducting materials have been discovered in Japan and the United States in which the charge carriers involved in the superconductivity appear to be electrons, rather than holes, that reside within the conducting CuO2 planes. These findings could have important implications regarding viable theories of high temperature superconductivity as well as strategies for finding new high temperature superconductors.The new electron-doped materials have the chemical formula Ln2-xMxCuO4-y and exhibit superconductivity with superconducting critical temperatures Tc as high as ~25 K for x ≍ 0.15 and y ≍ 0.02. Superconductivity has been discovered for M = Ce and Ln = Pr, Nd, Sm, and Eu, and for M = Th and Ln = Pr, Nd, and Sm. A related compound with the identical crystal structure, Nd2CuO4-x-y Fx, has also been found to display superconductivity withTc ≍ 25 K. Recently, it has been observed that superconductivity with Tc ≍ 25 K can even be induced in nonsuperconducting Nd2-xCexCuO4-y compounds by substituting Ga or In for Cu. Thus, it appears that the CuO2 planes can be doped with electrons, rendering the Ln2CuO4-y parent compounds metallic and superconducting, by substituting electron donor elements at sites within, as well as outside, the CuO2 planes; i.e., by substituting (1) Ce4+ or Th4+ ions for Ln3+ ions; (2) F1- ions for O2- ions; and (3) Ga3+ or In3+ ions for Cu2+ ions.

EFFECTIVE THEORY FOR HIGH-TEMPERATURE SUPERCONDUCTIVITY BASED ON DUALITY AT S = 1/2 ANTIFERROMAGNETIC HEISENBERG MODEL

2005 ◽  
Vol 19 (12) ◽  
pp. 571-579 ◽  
Author(s):  
TAKAO MORINARI
Keyword(s):  
High Temperature ◽  
Heisenberg Model ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Parent Compound ◽  
High Energy ◽  
Field Application ◽  
Effective Theory ◽  
Dirac Fermions ◽  
Antiferromagnetic Heisenberg Model

It is argued that in two-dimension duality connects the CP1 representation of the S = 1/2 antiferromagnetic Heisenberg model with the Schwinger model in which Dirac fermions are interact via a U(1) gauge field. Application of this duality to underdoped high-temperature superconductors suggests that the high-energy fermionic excitation at the Mott insulating parent compound turns out to be a low-lying excitation in the spin disordered regime. A picture for high-temperature superconductivity is proposed.

Crystal Growth of High Temperature Superconductors

MRS Bulletin ◽  
1988 ◽  
Vol 13 (10) ◽  
pp. 56-61 ◽  
Author(s):  
H.J. Scheel ◽  
F. Licci
Keyword(s):  
High Temperature ◽  
Critical Current Density ◽  
Single Crystals ◽  
Critical Current ◽  
Current Density ◽  
Large Scale ◽  
High Temperature Superconductivity ◽  
High Temperature Superconductors ◽  
Superconducting Transition ◽  
Theoretical Understanding

The discovery of high temperature superconductivity (HTSC) in oxide compounds has confronted materials scientists with many challenging problems. These include the preparation of ceramic samples with critical current density of about 106 A/cm2 at 77 K and sufficient mechanical strength for large-scale electrotechnical and magnetic applications and the preparation of epitaxial thin films of high structural perfection for electronic devices.The main interest in the growth of single crystals is for the study of physical phenomena, which will help achieve a theoretical understanding of HTSC. Theorists still do not agree on the fundamental mechanisms of HTSC, and there is a need for good data on relatively defect-free materials in order to test the many models. In addition, the study of the role of defects like twins, grain boundaries, and dislocations in single crystals is important for understanding such parameters as the critical current density. The study of HTSC with single crystals is also expected to be helpful for finding optimum materials for the various applications and hopefully achieving higher values of the superconducting transition temperature Tc than the current maximum of about 125 K. It seems unlikely at present that single crystals will be used in commercial devices, but this possibility cannot be ruled out as crystal size and quality improve.

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