MERCURY-BASED SUPERCONDUCTORS WITH QUASI-NORMAL OCCUPANCY

1995 ◽  
Vol 09 (18) ◽  
pp. 1175-1184
Author(s):  
M. MORENO ◽  
R.M. MÉNDEZ-MORENO ◽  
S. OROZCO ◽  
M.A. ORTÍZ
Keyword(s):  
Transition Temperature ◽  
Fermi Surface ◽  
Weak Coupling ◽  
Cuprate Superconductors ◽  
Energy Gap ◽  
Oxide Superconductors ◽  
Coupling Constant ◽  
Effective Coupling ◽  
Small Energy ◽  
Copper Oxide Superconductors

A model with anomalous occupancy is applied to Hg-based cuprate superconductors. The anomaly consists of a small energy gap near the Fermi surface, the scale of the gap anomaly is of order of the cutoff (v.g. Debye) energy. Values of the anomalous occupancy parameters for Hg-based superconductors are obtained for different values of the ratio R and the effective coupling constant, within the weak coupling. As these materials have the highest transition temperature known for layered copper-oxide superconductors, they serve as a new testing ground for various proposed models.

ENERGY BAND OVERLAPPING IN HIGH-Tc SUPERCONDUCTORS

1996 ◽  
Vol 10 (30) ◽  
pp. 1483-1490 ◽  
Author(s):  
M. MORENO ◽  
R. M. MÉNDEZ-MORENO ◽  
M. A. ORTIZ ◽  
S. OROZCO
Keyword(s):  
Weak Coupling ◽  
Cuprate Superconductors ◽  
Weak Coupling Limit ◽  
Band Model ◽  
Coupling Constant ◽  
High Tc Superconductors ◽  
Energy Bands ◽  
Effective Coupling ◽  
High Tc ◽  
Two Band Model

Multi-band superconductors are analyzed and the relevance of overlapping energy bands to the high-T c of these materials is studied. Within the BCS framework, a two band model with generalized Fermi surface topologies is developed. Values of the overlapped occupancy parameters for typical cuprate superconductors are obtained as a function of the ratio R and the effective coupling constant, λ, in the weak-coupling limit. The overlap scale is of the order or lower than the cutoff (Debye) energy. The typical behavior of the isotope effect is obtained. As these superconductors have transition temperatures above the phonon barrier, the results of this approach are important to the generic understanding of the high-T c superconducting mechanism.

THE ENERGY GAP IN THE HIGH-Tc COPPER OXIDE SUPERCONDUCTORS

1993 ◽  
Vol 07 (03) ◽  
pp. 143-153 ◽  
Author(s):  
YONGHONG LI ◽  
CHARLES M. LIEBER
Keyword(s):  
Transition Temperature ◽  
Energy Loss ◽  
High Temperature Superconductor ◽  
Energy Gap ◽  
Low Energy ◽  
Oxide Superconductors ◽  
High Tc ◽  
Resolution Electron ◽  
Copper Oxide Superconductors ◽  
Electron Energy Loss

We briefly review high-resolution electron energy loss spectroscopy (HREELS) studies of the low energy excitations in the high-temperature superconductor Bi 2 Sr 2 CaCu 2 O 8. HREELS has been used to determine the magnitude and temperature dependence of the energy gap (2Δ) for Bi 2 Sr 2 CaCu 2 O 8 single crystals. Below the transition temperature low-energy excitations are detected in the energy loss spectra. Because the energy loss spectra are proportional to the real part of the frequency dependent resistivity, ρR(ω), the energy gap can be determined directly from the HREEL data. At low temperature 2Δ = 6kT c and Δ develops sharply for T < T c . The constraints that these new results place on potential mechanisms of superconductivity are discussed.

Unrelated BCS-like pairing pseudogap and critical superconducting transition temperature in various cuprate compounds

2018 ◽  
Vol 32 (18) ◽  
pp. 1850195
Author(s):  
S. Dzhumanov ◽  
E. X. Karimboev ◽  
Sh. S. Djumanov
Keyword(s):  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
Order Parameter ◽  
Cuprate Superconductors ◽  
Energy Gap ◽  
Characteristic Temperature ◽  
Superconducting Order Parameter ◽  
Superconducting Transition ◽  
Gap Formation ◽  
Arpes Data

The smooth evolution of the energy gap observed in the tunneling and angle-resolved photoemission spectra (ARPES) of high-[Formula: see text] cuprates with lowering the temperature from a pseudogap state above the critical temperature [Formula: see text] to a superconducting state below [Formula: see text], has been poorly interpreted as the evidence that the pseudogap must have the same origin as the superconducting order parameter, and therefore, must be related to [Formula: see text]. We argue that such an explanation of the tunneling gap and ARPES data is misleading. We show that the BCS-like energy gap (or pseudogap) opening in the electronic excitation spectrum of underdoped-to-overdoped cuprates at a characteristic temperature [Formula: see text] and the true superconducting order parameter appearing only at [Formula: see text] are unrelated. The superconducting phenomenon in unconventional cuprate superconductors is fundamentally different from the BCS-like pairing of fermionic quasiparticles, and the superconducting transition temperature [Formula: see text] is not determined by the BCS-like gap formation. The unusual superconducting order parameter in these high-[Formula: see text] materials appears at [Formula: see text] and coexists with the BCS-like gap (or pseudogap) below [Formula: see text].

scholarly journals ELECTRONIC BOUND STATES IN PARITY-PRESERVING QED3 APPLIED TO HIGH-Tc CUPRATE SUPERCONDUCTORS

2003 ◽  
Vol 18 (05) ◽  
pp. 725-741 ◽  
Author(s):  
H. R. CHRISTIANSEN ◽  
O. M. DEL CIMA ◽  
M. M. FERREIRA ◽  
J. A. HELAYËL-NETO
Keyword(s):  
Bound States ◽  
Cuprate Superconductors ◽  
Energy Scale ◽  
Spontaneous Breaking ◽  
Electron Interaction ◽  
Oxide Superconductors ◽  
S Wave ◽  
High Tc ◽  
Pair Condensation ◽  
Copper Oxide Superconductors

We consider a parity-preserving QED 3 model with spontaneous breaking of the gauge symmetry as a framework for the evaluation of the electron–electron interaction potential underlying high-T c superconductivity. The fact that the resulting potential, -CsK0(Mr), is non-confining and "weak" (in the sense of Kato) strongly suggests the mechanism of pair-condensation. This potential, compatible with an s-wave order parameter, is then applied to the Schrödinger equation for the sake of numerical calculations, thereby enforcing the existence of bound states. The results worked out by means of our theoretical framework are checked by considering a number of phenomenological data extracted from different copper oxide superconductors. The agreement may motivate a deeper analysis of our model viewing an application to quasiplanar cuprate superconductors. The data analyzed here suggest an energy scale of 1–10 meV for the breaking of the U(1)-symmetry.

scholarly journals Paramagnetic Resonance as a Probe of the Spin Gap in Normal State of Superconductor

2011 ◽  
Vol 2011 ◽  
pp. 1-3
Author(s):  
Frank J. Owens
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Transition Temperature ◽  
Normal State ◽  
Oxide Superconductors ◽  
Superconducting Transition ◽  
Paramagnetic Resonance ◽  
Spin Gap ◽  
Order Of Magnitude ◽  
Copper Oxide Superconductors ◽  
Electron Paramagnetic

It is shown that electron paramagnetic resonance (EPR) can be used to observe the spin gap in copper oxide superconductors. The electron paramagnetic resonance spectra of the Cu2+ ion in underdoped show a pronounced decrease in intensity in the normal state as the temperature is lowered to 133 K, the superconducting transition temperature of the material. The decrease is attributed to a pairing of the Cu2+   spins to form a spin gap. A spin gap of 0.0533 eV is estimated from the data which is in order of magnitude agreement with values obtained from NMR measurements.

scholarly journals Effect of Multiple Orders on Superconducting Transition Temperature of Hole Doped Cuprates

2017 ◽  
Vol 9 (4) ◽  
pp. 341-349
Author(s):  
I. Qabid ◽  
S. H. Naqib
Keyword(s):  
Transition Temperature ◽  
Superconducting Transition Temperature ◽  
Cuprate Superconductors ◽  
Energy Gap ◽  
Density Wave ◽  
Spin Density Wave ◽  
Superconducting Transition ◽  
Electronic Density ◽  
Special Cases ◽  
Multiple Orders

Hole doped high-Tc cuprate superconductors are strongly correlated electronic systems. In these materials, various electronic orders are often found, but whether they support or compete with superconducting order is not unambiguous. Superconductivity normally manifests itself by a superconducting gap in the electronic density of states (EDOS). In cuprates, a gap appears even in the normal state called the pseudogap (PG). For certain doping range, spin density wave and charge density wave coexist with superconductivity by inducing corresponding additional gaps in the EDOS. In this study, we have tried to obtain expression for superconducting transition temperature, Tc by solving the BCS (Bardeen-Cooper-Schrieffer) energy gap equation in the presence of depleted EDOS of various origins and types. We have been successful to solve the weak-coupling BCS integral equation analytically in some special cases and also in the general case by using numerical integration. We have found that depending on conditions these non-pairing gaps/orders can enhance as well as reduce Tc.

SINGLE-PARTICLE AND OPTICAL EXCITATIONS IN DOPED MOTT- HUBBARD INSULATORS

1992 ◽  
Vol 06 (05n06) ◽  
pp. 589-602 ◽  
Author(s):  
WALTER STEPHAN ◽  
PETER HORSCH
Keyword(s):  
Optical Properties ◽  
Band Structure ◽  
Fermi Surface ◽  
Copper Oxide ◽  
Hubbard Model ◽  
Optical Conductivity ◽  
Single Particle ◽  
Oxide Superconductors ◽  
Two Dimensional ◽  
Copper Oxide Superconductors

Recent numerical results for the single-particle spectral function and optical conductivity of the two-dimensional Hubbard and t−J models are reviewed. Already for two holes in systems of sixteen to twenty sites (≥ 10% doping) a large electronic Fermi surface, compatible with Luttinger’s theorem, is observed. The full single-particle Green’s function is examined, and is shown to exhibit quasiparticle-like behavior, with dispersion consistent with the band structure of the non-interacting limit, and band width scaling approximately as J for J smaller than t. The optical conductivity of the Hubbard and t−J models is shown to have many features in common with recent experiments on copper oxide superconductors. The importance of the often neglected 3-site terms which arise in the derivation of the t−J model from the Hubbard model for optical properties is discussed.

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