Exploring multichannel superconductivity in ThFeAsN

Schrodi, Fabian; Kabeer, Fairoja Cheenicode; Aperis, Alex; Oppeneer, Peter M.

doi:10.1103/physrevb.104.094516

Cited by 8 publications

(12 citation statements)

References 59 publications

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“…If we go to some more realistic model of electron spectrum, like tight -binding approximation in some definite crystal lattice (not in infinite dimensions! ), we can obtain instability of phonon spectrum at some finite value of phonon wave vector k [21][22][23]41]. The appearance of such instabilities, as is well known, usually corresponds to formation in the system of charge density waves (CDW) [20].…”

Section: Strong Coupling and Lattice Instabilitymentioning

confidence: 90%

“…In self -consistent derivation of Eliashberg equations we have to use the diagram of Fig. 1, where the the phonon Green's function is taken in "dressed" form (40) or (41) and describes the physical (renormalized) phonon spectrum. In this case we do not have to include corrections to this function due to electron -phonon interaction, as they are already taken into account in phonon spectrum (37).…”

Section: Strong Coupling and Lattice Instabilitymentioning

confidence: 99%

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Limits of Eliashberg Theory and Bounds for Superconducting Transition Temperature

Sadovskii

2021

Preprint

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The discovery of record -breaking values of superconducting transition temperature Tc in quite a number of hydrides under high pressure was an impressive demonstration of capabilities of electron -phonon mechanism of Cooper pairing. This lead to an increased interest to foundations and limitations of Eliashberg -McMillan theory as the main theory describing superconductivity in a system of electrons and phonons. Below we shall consider both elementary basics of this theory and a number of new results derived only recently. We shall discuss limitations on the value of the coupling constant related to lattice instability and a phase transition to another phase (CDW, bipolarons). Within the stable metallic phase the effective pairing constant may acquire arbitrary values. We consider extensions beyond the traditional adiabatic approximation. It is shown that Eliasberg -McMillan theory is also applicable in the strong antiadiabatic limit. The limit of very strong coupling, being most relevant for the physics of hydrides, is analyzed in details. We also discuss the bounds for Tc appearing in this limit.

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Section: Strong Coupling and Lattice Instabilitymentioning

confidence: 90%

Section: Strong Coupling and Lattice Instabilitymentioning

confidence: 99%

Limits of Eliashberg Theory and Bounds for Superconducting Transition Temperature

Sadovskii

2021

Preprint

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“…We therefore want to discuss here the possibility of vertex corrections to the EPI, that potentially can contribute positively to the superconducting gap size and eventually T c . In a recent work by some of the authors it was shown for a model system that unconventional gap symmetries, such as s ± -wave, can arise from isotropic EPI when taking vertex corrections into account [29]. We therefore want to obtain here an estimate of the vertex function when considering the non-interacting state of the system.…”

Section: B Possibility Of Non-adiabatic Effectsmentioning

confidence: 99%

“…The characteristic energy scale of the phonon spectrum is ω log ≃ 17 meV (value taken from DFT calculation), from which we can define the isotropic EPI kernel V m−m ′ = 2g 2 0 ω log /(ω 2 log + q 2 m−m ′ ). Taking into consideration the shallowness of our system, ǫ F ≃ 52 meV, we get a non-adiabaticity ratio of α = ω log /ǫ F ∼ 0.33, which is an indicator for the nonnegligible relevance of vertex corrections [29]. For simplicity let us further assume that the system is in the non-interacting state, which translates into an electron Green's function Ĝ…”

Section: B Possibility Of Non-adiabatic Effectsmentioning

confidence: 99%

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Exploring multichannel superconductivity in ThFeAsN

Schrodi,

Kabeer,

Aperis

et al. 2021

Preprint

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We investigate theoretically the superconducting state of the undoped Fe-based superconductor ThFeAsN. Using input from ab initio calculations, we solve the Fermi-surface based, multichannel Eliashberg equations for Cooper-pair formation mediated by spin and charge fluctuations, and by the electron-phonon interaction (EPI). Our results reveal that spin fluctuations alone, when coupling only hole-like with electron-like energy bands, can account for a critical temperature Tc up to ∼ 7.5 K with an s±-wave superconducting gap symmetry, which is a comparatively low Tc with respect to the experimental value T exp c = 30 K. Other combinations of interaction kernels (spin, charge, electronphonon) lead to a suppression of Tc due to phase frustration of the superconducting gap. We qualitatively argue that the missing ingredient to explain the gap magnitude and Tc in this material is the first-order correction to the EPI vertex. In the noninteracting state this correction adopts a form supporting the s± gap symmetry, in contrast to EPI within Migdal's approximation, i.e., EPI without vertex correction, and therefore it enhances tendencies arising from spin fluctuations.

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Doping dependence and multichannel mediators of superconductivity: calculations for a cuprate model

Schrodi,

Aperis,

Oppeneer

2024

Electron. Struct.

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We study two aspects of the superconductivity in a cuprate model system, its doping dependence and the influence of competing pairing mediators. We first include electron-phonon interactions beyond Migdal’s approximation and solve self- consistently, as a function of doping and for an isotropic electron-phonon coupling, the full-bandwidth, anisotropic vertex-corrected Eliashberg equations under a non-interacting state approximation for the vertex correction. Our results show that such pairing interaction supports the experimentally observed dx2−y2-wave symmetry of the superconducting gap, but only in a narrow doping interval of the hole-doped system. Depending on the coupling strength, we obtain realistic values for the gap magnitude and superconducting critical temperature Tc close to optimal doping, rendering the electron-phonon mechanism an important candidate for mediating superconductivity in this model system. Second, for a doping near optimal hole doping, we study multichannel superconductivity, by including both vertex-corrected electron- phonon interaction and spin and charge fluctuations as pairing mechanisms. We find that both mechanisms cooperate to support an unconventional d-wave symmetry of the order parameter, yet the electron-phonon interaction is mainly responsible for the Cooper pairing and high critical temperature Tc. Spin fluctuations are found to have a suppressing effect on the gap magnitude and critical temperature due to their repulsive interaction at small coupling wave vectors.

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Exploring multichannel superconductivity in ThFeAsN

Cited by 8 publications

References 59 publications

Limits of Eliashberg Theory and Bounds for Superconducting Transition Temperature

Limits of Eliashberg Theory and Bounds for Superconducting Transition Temperature

Exploring multichannel superconductivity in ThFeAsN

Doping dependence and multichannel mediators of superconductivity: calculations for a cuprate model

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