Signature of electron-phonon interaction in high temperature superconductors

Ashokan, Vinod; Indu, B. D.; Dimri, A. K.

doi:10.1063/1.3610642

Cited by 36 publications

(13 citation statements)

References 59 publications

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“…35,67,68 The anharmonicity coefficients V s (k 1 , k 2 · · · k s ) are the Fourier transform of sth order anharmonic force constant and are symmetric with respect to the pair of lattice vibration indices k s . 66,67 In order to obtain the line shape of phonon spectrum, let us consider the evaluation of the double time temperature-dependent retarded Green's function 59,70 …”

Section: Theorymentioning

confidence: 99%

Anharmonic phonon–electron effects on phonon density of states in La2−xSrxCuO4

Ashokan

Indu

2015

Mod. Phys. Lett. B

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In the present work, the phonon density of states (PDOS) for La 2−x SrxCuO 4 crystal is investigated by using the double time thermodynamic Green's function method via a non-perturbative approach. A newly formulated Hamiltonian is considered for the lattice dynamics of phonon, which includes the effects of electron-phonon interactions, lattice anharmonicities and the interacting isotopic impurities. The automated emergence of pairons and d x 2 −y 2 wave pairing mechanism appears as a salient features of the theory. The PDOS is found to be dependent on temperature, impurity concentration, electronphonon coupling coefficient and renormalized frequencies, and the numerical investigations on PDOS exhibits fairly good agreements with the inelastic neutron scattering experimental observations. Mod. Phys. Lett. B Downloaded from www.worldscientific.com by RUTGERS UNIVERSITY on 10/03/15. For personal use only. V. Ashokan & B. D. Induinvolved either via diagonal or off-diagonal interactions or van Hove scenario or rattling phonon modes. It has also been observed that there is a large body of experimental evidence showing strong electron-phonon coupling in HTS 18-22 and their role in describing superconducting properties. [2][3][4][23][24][25][26][27] In these studies, the electron-phonon interaction in the photoemission spectra is not directly addressed. Some of the remarkable investigations 2,3,28-33 reveal that the anharmonicity of less than 1% can induce superconductivity even in the presence of coulomb repulsion, which makes the problem more exciting on new grounds. Further, the effects of disorders and defects are well known which drastically change the frequency (energy) spectrum of solids may also play decisive role in understanding the problem in a wider perspective. 34,35The d-wave paring mechanism in HTS has attracted considerable attention of physicists in the past few years, because of its experimental verifiability. 36,37 The only way to find the order parameter in HTS is to study the phonon interaction between electrons, which leads to pairing. The d x 2 −y 2 pairing state has two exceptional properties that makes it a feasible candidate for explaining the anomalous behavior of the cuprates, firstly, it exhibits nodes in the energy gap that lead to an excess of excitations at low temperatures which has been firmly established by transport experiments, temperature dependent London penetration depth in YBa 2 Cu 3 O 7−δ , 38 the infrared and Raman scattering experiments, 39 Josephson tunneling 40 and thermodynamic measurements. Secondly, the d-wave symmetry is implied by a number of possible superconducting pairing mechanisms like magnetic interactions, spin fluctuations, that are known to be important in the cuprates. Many more ideas for the allowed symmetries have been discussed in the literatures 9,41-43 and give naive approach to establish the importance of d x 2 −y 2 pairing states. Further, a phenomenological model proposed by Pines and co-workers 44-46 and Moriya et al. using self-consistent renormalizat...

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Section: Theorymentioning

confidence: 99%

Anharmonic phonon–electron effects on phonon density of states in La2−xSrxCuO4

Ashokan

Indu

2015

Mod. Phys. Lett. B

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“…In the above expressions , and are renormalized mode, perturbed mode, and pairon energies, respectively. Δ ( ) and Γ ( ) are the electron energy line shis and widths, respectively [11]. e electron energy line width Γ ( ) has the form:…”

Section: The Hamiltonian and Green's Functionsmentioning

confidence: 99%

Electrons and Phonons in High Temperature Superconductors

Singh

Ashokan

et al. 2013

Journal of Materials

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The defect-induced anharmonic phonon-electron problem in high-temperature superconductors has been investigated with the help of double time thermodynamic electron and phonon Green’s function theory using a comprehensive Hamiltonian which includes the contribution due to unperturbed electrons and phonons, anharmonic phonons, impurities, and interactions of electrons and phonons. This formulation enables one to resolve the problem of electronic heat transport and equilibrium phenomenon in high-temperature superconductors in an amicable way. The problem of electronic heat capacity and electron-phonon problem has been taken up with special reference to the anharmonicity, defect concentration electron-phonon coupling, and temperature dependence.

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“…Let us consider the double-time thermodynamic electron retarded Green's function [6,7] ( ) ( H , respectively are unperturbed electron-, unperturbed phonon-, electronphonon-, anharmonic (upto quartic terms)-, and defect contributions to the Hamiltonian H and are expressible in the form [8]…”

Section: Quantum Dynamics Of Electronsmentioning

confidence: 99%

Theory of Electron Density of States of High Temperature Impurity Induced Anharmonic Superconductors

Singh¹,

Singh²,

Ashokan³

et al. 2012

AMPC

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The expression for the electron density of states (EDOS) of high temperature superconductors (HTS) has been derived taking the disorder and anharmonicity effects as a central problem. This has been dealt with the help of double time thermodynamic Green’s function theory for electrons via a generalized Hamiltonian which consists of the contribution due to 1) unperturbed electrons; 2) unperturbed phonons; 3) isotopic impurities; 4) anharmonicities (no BCS type Hamiltonian has been taken up in the formulation); and 5) electron-phonon interactions. The renormalization effects and emergence of pairons appears as a unique feature of the theory and dependence of EDOS on impurity concentration and temperature has been discussed in details with special reference to the HTS.

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Signature of electron-phonon interaction in high temperature superconductors

Cited by 36 publications

References 59 publications

Anharmonic phonon–electron effects on phonon density of states in La2−xSrxCuO4

Anharmonic phonon–electron effects on phonon density of states in La2−xSrxCuO4

Electrons and Phonons in High Temperature Superconductors

Theory of Electron Density of States of High Temperature Impurity Induced Anharmonic Superconductors

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