Isotope effect due to the super-exchange interaction and van Hove singularity in high-Tc superconductors

2013 ◽  
Vol 114 (6) ◽  
pp. 063901
Author(s):  
A. Bechlaghem ◽  
D. Bourbie
Keyword(s):  
Exchange Interaction ◽  
Isotope Effect ◽  
Van Hove Singularity ◽  
High Tc Superconductors ◽  
High Tc ◽  
Super Exchange Interaction

THE VAN HOVE SINGULARITY IN HIGH Tc SUPERCONDUCTORS

1995 ◽  
Vol 09 (09) ◽  
pp. 1067-1080 ◽  
Author(s):  
M.L. HORBACH ◽  
H. KAJÜTER
Keyword(s):  
Energy Scale ◽  
Measured Temperature ◽  
Van Hove Singularity ◽  
High Tc Superconductors ◽  
Electronic Density ◽  
High Tc ◽  
Scattering Rate ◽  
Weakly Coupled ◽  
Coherence Lengths

Experimental indications for the role of the van Hove singularity (vHs) in the electronic density of states of high Tc superconductors are discussed. It is argued that (i) like the resistivity, the measured temperature and doping dependences of the normal state electronic specific heat of YBCO are consistent with the existence of a vHs and (ii) the doping dependence of Tc in the underdoped and optimally doped regimes may be accounted for mainly by a vHs. Further, we discuss the suppression of the quasiparticle scattering rate below Tc, and the coherence lengths in the hole-doped materials and NCCO. Assuming that the same mechanism for superconductivity operates in the electron-doped and the hole-doped cuprates, we argue that the bosonic mode that causes the superconductivity is strongly influenced by the doping in the overdoped regime. We further argue that this boson involves an energy scale larger than that of phonons and is only weakly coupled to the charge carriers.

THEORY OF THE ISOTOPE EFFECT AND SUPERCONDUCTING TRANSITION TEMPERATURE IN HIGH-Tc OXIDES

2011 ◽  
Vol 25 (26) ◽  
pp. 2069-2078 ◽  
Author(s):  
A. BECHLAGHEM ◽  
D. BOURBIE
Keyword(s):  
Experimental Data ◽  
Transition Temperature ◽  
Fermi Level ◽  
Isotope Effect ◽  
Qualitative Agreement ◽  
Superconducting Transition Temperature ◽  
Superconducting Transition ◽  
Van Hove Singularity ◽  
High Tc ◽  
Analytical Expressions

Analytical expressions for the superconducting transition temperature Tc and the isotope coefficient α have been obtained for the case where the Fermi level is close to the van Hove singularity. In this approach, we consider two interactions, the first related to the phonons and the second relevant to the magnetic excitations. Our result shows that the isotope coefficient α decreases with the superconducting transition temperature Tc in qualitative agreement with experimental data.

The Isotope Effect within the Anharmonic Model for High-Tc Superconductors

1987 ◽  
Vol 144 (2) ◽  
pp. K113-K117 ◽  
Author(s):  
S. L. Drechsler ◽  
N. M. Plakida
Keyword(s):  
Isotope Effect ◽  
High Tc Superconductors ◽  
High Tc

GAP ENERGY, ISOTOPE EFFECT AND COHERENCE LENGTH IN HIGH Tc-OXIDES

1999 ◽  
Vol 13 (32) ◽  
pp. 3915-3925 ◽  
Author(s):  
A. BECHLAGHEM ◽  
M. MOSTEFA ◽  
Y. ZANOUN
Keyword(s):  
Effective Mass ◽  
Isotope Effect ◽  
Coherence Length ◽  
High Temperature Superconductors ◽  
Constant Term ◽  
Realistic Model ◽  
Bcs Theory ◽  
Van Hove Singularity ◽  
High Tc ◽  
Gap Energy

The model recently developed by Getino et al. to study the gap energy in the van Hove scenario in high-T c oxides is extended to study the isotope effect and the coherence length in these materials. We propose a more realistic model by: (1) adding a constant term to the singular logarithmic contribution, within the weak coupling BCS theory and a phonon mediated interaction; (2) assuming the Fermi level lies close to a van Hove singularity for optimal doping. The equations obtained from this approach, are applicable to low as well as high temperature superconductors successfully the superconducting temperature transition T c , the gap energy Δ, the isotope effect α and the coherence length ξ. For high-T c oxides, it is found that when the effective mass of carriers tends to be large, α and ξ tend to be small where T c and Δ became larges. We shown that when the effective mass of carriers is enclosed between 5 m e and 15 m e , the values obtained for these parameters are in agreement with experimental data.

NUMERICAL SIMULATION OF THE ISOTOPE EFFECT IN THE HIGH-Tc SUPERCONDUCTORS

1989 ◽  
Vol 03 (06) ◽  
pp. 897-908 ◽  
Author(s):  
T. GALBAATAR ◽  
R-J. RAKAUSKAS ◽  
J. SULSKUS
Keyword(s):  
Numerical Simulation ◽  
Isotope Effect ◽  
Quadrupole Moments ◽  
High Tc Superconductors ◽  
High Tc ◽  
Oxygen Ions ◽  
Electron Phonon Interaction ◽  
Local Vibrational Mode ◽  
Anharmonic Potential ◽  
The Matrix

The results of a numerical simulation are presented for the oxygen isotope effect in the high-T c oxides by solving the Schrödinger equation for a local vibrational mode of oxygen ions in a double well anharmonic potential of the form −Ax2/2+Bx4/4. The features of the energy spectrum, eigenfunctions and the matrix elements of the dipole and quadrupole moments are discussed. The applicability region of a two-level approximation to describe the electron-phonon interaction is given. The constant of the isotope effect α is determined to be comparable to that of La 2−x Sr x CuO 4 but in disagreement with the up-to-date experimental observations for the YBaCuO system.

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