scholarly journals Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides

2013 ◽  
Vol 4 (1) ◽  
Author(s):  
Meng Wang ◽  
Chenglin Zhang ◽  
Xingye Lu ◽  
Guotai Tan ◽  
Huiqian Luo ◽  
...  
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
Iron Pnictides ◽  
Doping Dependence ◽  
Spin Excitations

scholarly journals Review on origin of the unusual high-Tc superconductivity in Ca1−xRExFe2As2 (RE = La, Ce, Pr, Nd)

2015 ◽  
Vol 1 (1) ◽  
Author(s):  
W. Zhou ◽  
Z. X. Shi
Keyword(s):  
High Temperature ◽  
Transition Temperature ◽  
Crystal Structures ◽  
High Temperature Superconductivity ◽  
Iron Pnictides ◽  
Iron Based Superconductors ◽  
High Tc ◽  
High Tc Superconductivity ◽  
Iron Based

AbstractSince the discovery of high temperature superconductivity in iron pnictides in 2008, many iron-based superconductors (IBSs) with various crystal structures have been exploited.Among them, superconductivity with the onset transition temperature T

QUANTIZATION OF THE HOPF COEFFICIENT IN EFFECTIVE GAUGE THEORIES OF DOPED MOTT INSULATORS

1989 ◽  
Vol 04 (06) ◽  
pp. 521-527 ◽  
Author(s):  
I. J. R. AITCHISON ◽  
N. E. MAVROMATOS
Keyword(s):  
High Temperature ◽  
Gauge Theories ◽  
High Temperature Superconductivity ◽  
Quantization Condition ◽  
Physical Significance ◽  
Mott Insulators ◽  
Abelian Gauge ◽  
A Value ◽  
Spin Excitations ◽  
High Temperature Expansion

A quantization condition is given for the coefficient of the Hopf invariant which arises in effective (Abelian) gauge theories of doped Mott insulators formulated on S2 × S1 (as a result of a high temperature expansion). A value 1/2 for the spin of the relevant excitations is obtained among the allowed values. This may explain the origin of neutral fermions in paramagnetic insulators which are believed to play a major role in high temperature superconductivity. Other fractional spin excitations, however, are allowed as well, whose physical significance is not yet transparent.

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>

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