Molecular aspects of superconductivity: The role of the one‐particle term at the gap formation

Svrček, Michal; Baňacký, Pavol; Zajac, Anton

doi:10.1002/qua.560430309

Cited by 9 publications

(8 citation statements)

References 8 publications

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“…In this case, for matrix elements of the symmetric matrix ⍀, the following inequalities hold [36,37]:…”

Section: Nonadiabatic Effectsmentioning

confidence: 98%

“…[35][36][37][38]. To keep the present study consistent as much as possible, the Appendix outlines only the final equations that are relevant to the study of MgB 2 .…”

Section: Preliminariesmentioning

confidence: 98%

“…With respect to the nonadiabatic theory of electron-vibration interactions [35][36][37][38], in the following discussion, instead of the EP coupling constant , we need matrix elements of EP coupling U PQ (r) (Q). Directly available is only the total value of the EP coupling that can be extracted from the dependence of the total "core" energy/unit cell on the deformation displacement of atoms out of the equilibrium positions according to normal mode vibrations.…”

Section: Nonadiabatic Effectsmentioning

confidence: 99%

“…Under these circumstances, the original E F can be destroyed and a gap in the one-particle spectrum can be opened. This has been shown [36] at the derivation of the gap equation and at simulation of the temperature dependence of the photoemission and tunneling spectra of the HTSs [43]. In principle, the mentioned mechanism can result in metal-insulator, metal-metal transitions (the transitions are accompanied by charge or spin-density wave formation), but also in metal-superconductor transition.…”

Section: Introduction Imentioning

confidence: 98%

“…In 1992 we published a series of papers on the molecular nonadiabatic theory of electron-vibration interactions elaborated for some aspects of superconductivity [35][36][37][38]. The key point of this treatment is that in an ensemble of interacting electrons and nuclei (a molecular or solid-state system), the motion of the electrons is studied to be explicitly dependent not only on the operators of instantaneous nuclear coordinates, but on the operators of instantaneous nuclear velocity-momenta as well.…”

Section: Introduction Imentioning

confidence: 99%

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Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB₂

Baňacký

2004

Int J of Quantum Chemistry

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ABSTRACT:The theory of the nonadiabatic electron-vibration interactions has been applied to the study of MgB 2 superconducting state transition. It has been shown that at nonadiabatic conditions in which the Born-Oppenheimer approximation is not valid and electronic motion is dependent not only on the nuclear coordinates but also on the nuclear momenta, the fermionic ground-state energy of the studied system can be stabilized by nonadiabatic electron-phonon interactions at broken translation symmetry. Moreover, the new arising state is geometrically degenerate; i.e., there are an infinite number of different nuclear configurations with the same fermionic ground-state energy. The model study of MgB 2 yields results that are in a good agreement with the experimental data. For distorted lattice, with 0.016 Å/atom of in-plane out-of-phase BOB atoms displacements out of the equilibrium (E 2g phonon mode) when the nonadiabatic interactions are most effective, it has been calculated that the new arising state is 87 meV/unit cell more stable than the equilibrium-high symmetry clumped nuclear structure at the level of the Born-Oppenheimer approximation. The calculated T c is 39.5 K. The resulting density of states exhibits two-peak character, in full agreement with the tunneling spectra. The peaks are at Ϯ4 meV, corresponding to the change of the band density of states, and at Ϯ7.6 meV, corresponding to the band. The superconducting state transition can be characterized as a nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization (NASICKELES).

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“…In this case, for matrix elements of the symmetric matrix ⍀, the following inequalities hold [36,37]:…”

Section: Nonadiabatic Effectsmentioning

confidence: 98%

“…[35][36][37][38]. To keep the present study consistent as much as possible, the Appendix outlines only the final equations that are relevant to the study of MgB 2 .…”

Section: Preliminariesmentioning

confidence: 98%

Section: Nonadiabatic Effectsmentioning

confidence: 99%

Section: Introduction Imentioning

confidence: 98%

Section: Introduction Imentioning

confidence: 99%

See 3 more Smart Citations

Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB₂

Baňacký

2004

Int J of Quantum Chemistry

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Effect of nonadiabaticity on the Fermi-edge photoemission and tunneling spectra of superconductors

ack

Szcs

1996

Int. J. Quantum Chem.

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Temperature dependence of the experimental photoemission spectra of the high-T, superconductors have been interpreted and simulated by the recently formulated molecular nonadiabatic theory of the electron-vibrational interaction. The change of the spectral feature below T,, particularly formation of the narrow, near Fermi surface (FS) edge, peak separated by the dip from a broad spectral band at higher binding energies has been shown to be the consequence of the nonadiabatic electron-phonon coupling and corresponding properties of the nonadiabatic polarons. Simulation yields very good fit to the experimental temperature-dependent spectra, with the calculated value of the gap 30.5 meV.

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Microscopic insight into the pump–probe relaxation dynamics of superconductors: Model study of MgB₂ relaxation within nonlinear response theory

Baňacký

Szöcs

2016

Physica Status Solidi (b)

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ReceivedHere we present a quantum-statistical formulation of relaxation dynamics of superconductors related to pump-probe (PP) spectroscopy. The method is based on the perturbation expansion of the non-equilibrium density matrix for calculation of multi-time correlation functions, and the corresponding response function. As a model for our study, the high-temperature superconductor MgB 2 has been selected. Knowledge of the electronic structure and of the corresponding Eliashberg function of electron-phonon (EP) interactions enabled us to distinguish nonequilibrium processes in a sequence of interactions with laser pulses on a microscopic level. Temperature-dependent relaxation dynamics as a function of delay time between the pump and probe pulses have been derived. We have shown that an abrupt increase of the relaxation time at T c is the direct consequence of sudden changes in the character of EP coupling in transition from an adiabatic to a stabilized superconducting anti-adiabatic state, as it predicts the anti-adiabatic theory of electron-vibration interactions. The BCS model, which is based on adiabatic character of EP coupling, is basically unable to reflect the enormous sudden increase of the relaxation time at T c . Differences in the optical pump-optical probe and the optical pump-terahertz probe settings of PP relaxation dynamics are discussed within diagrammatic perturbation theory.Keywords: pump-probe spectroscopy; relaxation dynamics of superconductors; electron-phonon coupling; theory of superconductivity; anti-adiabatic theory of superconductivity IntroductionPump-probe (PP) spectroscopy, a method of nonlinear optics, is an important experimental tool in the study of ultrafast relaxation dynamics of excited states in condensed matter systems [1,2]. The interpretation of experimental results relies on various types of phenomenological equations of motion for the relaxation of "hot electrons" and/or high-energy phonons in coupling to bosonic degrees of freedom [3][4][5][6][7]. The assumption of quasi-equilibrium, which is often behind these methods, is discussed in [8], where the authors present an analytic solution of excited state relaxation dynamics within the Boltzmann kinetic equation, the method of which deals with electrons and phonons out of equilibrium.In general, however, phenomenological treatments not only ignore nonlinear aspects of processes running in PP experiments, but ignore also the microscopic character of nonequilibrium states -coherences and/or populations, which can evolve in the studied system over a sequence of different time periods via the interaction of matter with the incident fields. In these circumstances, mainly in the case of superconductors, it is difficult to disclose the relationship between the derived relaxation parameters, i.e. relaxation times, or electron-phonon (EP) coupling constants (), and the microscopic mechanism of the superconducting state transition. The theory of high-temperature superconductors (e.g. cuprates, pnictides) is far from being settled,...

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Molecular aspects of superconductivity: The role of the one‐particle term at the gap formation

Cited by 9 publications

References 8 publications

Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB₂

Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB₂

Effect of nonadiabaticity on the Fermi-edge photoemission and tunneling spectra of superconductors

Microscopic insight into the pump–probe relaxation dynamics of superconductors: Model study of MgB₂ relaxation within nonlinear response theory

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Molecular aspects of superconductivity: The role of the one‐particle term at the gap formation

Cited by 9 publications

References 8 publications

Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB2

Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB2

Effect of nonadiabaticity on the Fermi-edge photoemission and tunneling spectra of superconductors

Microscopic insight into the pump–probe relaxation dynamics of superconductors: Model study of MgB2 relaxation within nonlinear response theory

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Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB₂

Nonadiabatic sudden increase of the cooperative kinetic effect at lattice energy stabilization—Microscopic mechanism of superconducting state transition: Model study of MgB₂

Microscopic insight into the pump–probe relaxation dynamics of superconductors: Model study of MgB₂ relaxation within nonlinear response theory