SPIN-POLARON PAIRING AND HIGH-TEMPERATURE SUPERCONDUCTIVITY

1988 ◽  
Vol 02 (05) ◽  
pp. 699-709 ◽  
Author(s):  
Hiroshi Kamimura
Keyword(s):  
High Temperature ◽  
Exchange Interaction ◽  
High Temperature Superconductivity ◽  
Spin Polaron ◽  
S Wave ◽  
Wave Pairing ◽  
Spin Singlet ◽  
Atomic Exchange ◽  
Spin Polarons ◽  
The Right

In this paper a review is given on the mechanism of high temperature superconductivity recently developed by Kamimura, Matsuno, and Saito. In this mechanism spin-polarons associated with itinerant holes in the e v band (Cu dz 2- Op π band) are created in CuO 2 layers by strong intra-atomic exchange interaction (Hund's coupling) with localized dx 2− y 2 holes. Then the interplay of Hund's coupling and superexchange between Cu 2+( dx 2− y 2) spins gives rise to an attractive exchange interaction between spin-polarons, which leads to the formation of spin-singlet spin-polarons pairs. This contributes to high temperature superconductivity. Further the s-wave pairing reproduces the observed x dependence of T c as well as the right magnitudes of T c in ( La 1−x Sr x )2 CuO 4 satisfactorily.

THE SPIN-POLARON PAIRING AND THE x DEPENDENCE OF THE Tc IN (La1-xSrx)2CuO4

1992 ◽  
Vol 06 (18) ◽  
pp. 1131-1136
Author(s):  
R. MOTA ◽  
G. A. R. LIMA ◽  
A. FAZZIO
Keyword(s):  
Critical Temperature ◽  
Exchange Interaction ◽  
Hole Concentration ◽  
Ladder Approximation ◽  
Attractive Interaction ◽  
Spin Polaron ◽  
Spin Singlet ◽  
Atomic Exchange ◽  
Spin Polarons ◽  
Superconducting Correlations

We present a study of superconducting correlations associated to the mechanism of spin-polaron pairing resulting from an attractive exchange interaction between spin-polarons. The spin-polarons associated with itinerant holes in CuO 2 are assumed to be created by strong intra-atomic exchange interaction with quasi-localized spins. The interplay of Hund's coupling and superexchange between quasi-localized spins gives rise to an attractive interaction between spin-polarons which leads to the formation of spin-singlet spin-polaron-pairs. The two-particle Green function in the ladder approximation for the itinerant holes with this attractive interaction is used to calculate in ( La 1-x Sr x)2 CuO 4 the dependence on the hole concentration of the critical temperature T c . The obtained results reproduce the experimental observations satisfactorily.

scholarly journals GINZBURG–LANDAU LIKE THEORY OF HIGH TEMPERATURE SUPERCONDUCTIVITY IN THE CUPRATES: EMERGENT d-WAVE ORDER

2012 ◽  
Vol 26 (10) ◽  
pp. 1230005
Author(s):  
T. V. RAMAKRISHNAN
Keyword(s):  
High Temperature ◽  
Cooper Pair ◽  
Nearest Neighbor ◽  
High Temperature Superconductivity ◽  
Transition Curve ◽  
Hole Doping ◽  
Positive Interaction ◽  
Long Wavelength ◽  
Spin Singlet ◽  
D Wave

High temperature superconductivity in the cuprates remains one of the most widely investigated, constantly surprising and poorly understood phenomena in physics. Here, we describe briefly a new phenomenological theory inspired by the celebrated description of superconductivity due to Ginzburg and Landau and believed to describe its essence. This posits a free energy functional for the superconductor in terms of a complex order parameter characterizing it. We propose that there is, for superconducting cuprates, a similar functional of the complex, in plane, nearest neighbor spin singlet bond (or Cooper) pair amplitude ψij. Further, we suggest that a crucial part of it is a (short range) positive interaction between nearest neighbor bond pairs, of strength J′. Such an interaction leads to nonzero long wavelength phase stiffness or superconductive long range order, with the observed d-wave symmetry, below a temperature Tc~z J′ where z is the number of nearest neighbors; d-wave superconductivity is thus an emergent, collective consequence. Using the functional, we calculate a large range of properties, e.g., the pseudogap transition temperature T* as a function of hole doping x, the transition curve Tc(x), the superfluid stiffness ρs(x, T), the specific heat (without and with a magnetic field) due to the fluctuating pair degrees of freedom and the zero temperature vortex structure. We find remarkable agreement with experiment. We also calculate the self-energy of electrons hopping on the square cuprate lattice and coupled to electrons of nearly opposite momenta via inevitable long wavelength Cooper pair fluctuations formed of these electrons. The ensuing results for electron spectral density are successfully compared with recent experimental results for angle resolved photo emission spectroscopy (ARPES), and comprehensively explain strange features such as temperature dependent Fermi arcs above Tc and the "bending" of the superconducting gap below Tc.

scholarly journals Unusual symmetries of the order parameter in cuprates

2020 ◽  
Vol 2 (4) ◽  
pp. 207-212
Author(s):  
Tran Van Luong ◽  
Nguyen Thi Ngoc Nu
Keyword(s):  
High Temperature ◽  
Order Parameter ◽  
Cuprate Superconductors ◽  
High Temperature Superconductivity ◽  
Spin Fluctuation ◽  
High Temperature Superconductors ◽  
Coulomb Repulsion ◽  
Bcs Theory ◽  
S Wave ◽  
Wave Symmetry

The BCS superconducting theory, introduced by J. Bardeen, L. Cooper and R. Schriffer in 1957, succeeded in describing and satis-factorily explaining the nature of superconductivity for low-temperature superconductors. However, the BCS theory cannot explain the properties of high-temperature superconductors, discovered by J. G. Bednorz and K. A. Müller in 1986. Although scientists have found a lot of new superconductors and their transition temperatures are constantly increasing, most high-temperature superconductors are found by experiment and so far no theory can fully explain their properties. Many previous studies have suggested that the order parameter in high-temperature copper-based superconductors (cuprate superconductors - cuprates) is in the form of d-wave symmetry, but recent results show that the order parameter has an extended s-wave symmetry (extended s wave). Studying the symmetric forms of order parameters in cuprate can contribute to understanding the nature of high-temperature superconductivity. In this article, the authors present an overview of the development of high-temperature supercon-ductors over the past 30 years and explains unusual symmetries of the order parameter in copper-based superconductors. The com-petition of three coupling mechanisms of electrons in cuprates (the mechanism of coupling through coulomb repulsion, electron-phonon mechanism and spin-fluctuation mechanism) affects the unusual symmetry of the order parameter. The solution of the self-consistency equation in simple cases has been found and the ability to move the phase within the superconducting state has been shown.

Occurrence ofd-Wave Pairing in the Phonon-Mediated Mechanism of High Temperature Superconductivity in Cuprates

1996 ◽  
Vol 77 (4) ◽  
pp. 723-726 ◽  
Author(s):  
Hiroshi Kamimura ◽  
Shunichi Matsuno ◽  
Yuji Suwa ◽  
Hideki Ushio
Keyword(s):  
High Temperature ◽  
High Temperature Superconductivity ◽  
Wave Pairing
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