Strain effects on the electronic structure of the iron selenide superconductor

Abstract

The influence of various strains on crystal and electronic structures of superconducting FeSe has been studied ab initio. We consider changes in the Fermi surface nesting with a vector Q = (0.5, 0.5) × (2π/a) as crucial for rising superconductivity (SC) mediated by spin-fluctuations (SF). Our results indicate that the c-axis strained FeSe exhibits the most imperfect nesting, which enhances SF and, hence, also SC. In turn, the ab-plane compressive strain slightly weakens this nesting while the tensile strain destroys it completely. These findings are consistent with reported earlier experimental dependencies of superconducting transition temperatures on strain in FeSe thin films.

Strain effects on electronic structure and superconductivity in the iron telluride

“…Thus, the strain-induced changes of N(E F ) in iron chalcogenides seem to be irrelevant for the SC phenomenon. Similar conclusions have also been drawn for FeSe [23] and FeSe 0.5 Te 0.5 [24].…”

“…Our former studies on influence of various kinds of strain on electronic structure of FeSe [23] and FeSe 0.5 Te 0.5 [24] showed relations between the FS-nesting modifications and possibly SF-mediated SC properties in iron chalcogenides. In these compounds compressive strain diminishes intensity of nesting vector q ∼ (0.5, 0.5) × (2π/a), while the tensile strain in the ab-plane completely destroys these subtle features.…”

Strain effects on the electronic structure of the FeSe0.5Te0.5 superconductor

“…Since the nesting properties that can determine these phenomena are very subtle, their modifications can be described, both qualitatively and quantitatively, by theoretical studies. Our previous results for the pure FeSe [29] showed precise nesting function changes under different pressure and strain conditions being connected with either suppression or enhancement of the SC in this parent compound for all iron chalcogenide superconductors.…”

“…99) under various stress conditions was performed with the Abinit package [35,36], using Projector Augmented Wave (PAW) pseudopotentials, generated with Atompaw software [37]. The local density approximation (LDA) [38], employed here, seems to be adequate for electronic structure calculations for the 11-type systems, as discussed earlier [29]. The 3s3p3d;4s4p states for both Fe and Se atoms as well as the 4s4p4d;5s5p states for the Te atom were selected as a valence-band basis.…”

“…In particular, SC can be mediated by antiferromagnetic spin fluctuations (SF), observed experimentally by e.g. NMR [33,34], which are driven by the imperfect nesting with the q ∼ (π, π) vector, spanning the above FS sheets in iron chalcogenides [24,26,27,29].…”