Improved tetrahedron method for the Brillouin-zone integration applicable to response functions

Kawamura, Masaya; Gohda, Yoshihiro; Tsuneyuki, Shinji

doi:10.1103/physrevb.89.094515

Cited by 123 publications

(82 citation statements)

References 31 publications

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“…This value is consistent with the value of 0.33 (eV·spin·atom) −1 in McMillan’s study3. We also calculated the Fermi surface35 to see the volume change effect on the electronic structure.…”

Section: Methodssupporting

confidence: 89%

Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain

Mito

Matsui

Tsuruta

et al. 2016

Sci Rep

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Finding a physical approach for increasing the superconducting transition temperature (Tc) is a challenge in the field of material science. Shear strain effects on the superconductivity of rhenium were investigated using magnetic measurements, X-ray diffraction, transmission electron microscopy, and first-principles calculations. A large shear strain reduces the grain size and simultaneously expands the unit cells, resulting in an increase in Tc. Here we show that this shear strain approach is a new method for enhancing Tc and differs from that using hydrostatic strain. The enhancement of Tc is explained by an increase in net electron–electron coupling rather than a change in the density of states near the Fermi level. The shear strain effect in rhenium could be a successful example of manipulating Bardeen–Cooper–Schrieffer-type Cooper pairing, in which the unit cell volumes are indeed a key parameter.

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Section: Methodssupporting

confidence: 89%

Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain

Mito

Matsui

Tsuruta

et al. 2016

Sci Rep

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show abstract

“…Various interpolation techniques are available to circumvent this difficulty, such as Fourier interpolation by maximally localized Wannier functions [34][35][36] or by using the auxiliary phonon linewidths, 37 and an improved tetrahedron method. 38 We use the method in Ref. 37 (as it is already implemented in the Quantum espresso package) to compute λ q on a dense 24×24×1 q grid that is needed for the summation in Eq.…”

Section: Model and Methodsmentioning

confidence: 99%

Ab initiostudy of cross-interface electron-phonon couplings in FeSe thin films onSrTiO3andBaTiO3

et al. 2016

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We study the electron-phonon coupling strength near the interface of monolayer and bilayer FeSe thin films on SrTiO3, BaTiO3, and oxygen-vacant SrTiO3 substrates, using ab initio methods. The calculated total electron-phonon coupling strength λ = 0.2-0.3 cannot account for the high Tc ∼ 70 K observed in these systems through the conventional phonon-mediated pairing mechanism. In all of these systems, however, we find that the coupling constant of a polar oxygen branch peaks at q = 0 with negligible coupling elsewhere, while the energy of this mode coincides with the offset energy of the replica bands measured recently by angle-resolved photoemission spectroscopy experiments. But the integrated coupling strength for this mode from our current calculations is still too small to produce the observed high Tc, even through the more efficient pairing mechanism provided by the forward scattering. We arrive at the same qualitative conclusion when considering a checkerboard antiferromagnetic configuration in the Fe layer. In light of the experimental observations of the replica band feature and the relatively high Tc of FeSe monolayers on polar substrates, our results point towards a cooperative role for the electron-phonon interaction, where the crossinterface interaction acts in conjunction with a purely electronic interaction. We also discuss a few scenarios where the coupling strength obtained here may be enhanced.

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“…[27] with the Wannier interpolation for the electron-phonon matrix elements [80], and λ = 1.97 in Ref. [26] with the optimized tetrahedron method [81] for the electron delta function in Eq. (18) in Im3m-H 3 S).…”

Section: A Electronic Structurementioning

confidence: 99%

Effect of Van Hove singularities on high- Tc superconductivity in H3S

et al. 2016

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One of interesting open questions for the high transition temperature (Tc) superconductivity in sulfur hydrides is why high pressure phases of H3S have extremely high Tc's. Recently, it has been pointed out that the presence of the van Hove singularities (vHs) around the Fermi level is crucial. However, while there have been quantitative estimates of Tc based on the Migdal-Eliashberg theory, the energy dependence of the density of states (DOS) has been neglected to simplify the Eliashberg equation. In this study, we go beyond the constant DOS approximation and explicitly consider the electronic structure over 40 eV around the Fermi level. In contrast with the previous conventional calculations, this approach with a sufficiently large number of Matsubara frequencies enables us to calculate Tc without introducing the empirical pseudo Coulomb potential. We show that while H3S has much higher Tc than H2S for which the vHs is absent, the constant DOS approximation employed so far seriously overestimates (underestimates) Tc by ∼ 60 K (∼ 10 K) for H3S (H2S). We then discuss the impact of the strong electron-phonon coupling on the electronic structure with and without the vHs and how it affects the superconductivity. Especially, we focus on (1) the feedback effect in the self-consistent calculation of the self-energy, (2) the effect of the energy shift due to the zero-point motion, and (3) the effect of the changes in the phonon frequencies due to strong anharmonicity. We show that the effect of (1)- (3) on Tc is about 10-30 K for both H3S and H2S. Eventually, Tc is estimated to be 181 K for H3S at 250 GPa and 34 K for H2S at 140 GPa, which explains the pressure dependence of Tc observed in the experiment. In addition, we evaluate the lowest order vertex correction beyond the Migdal-Eliashberg theory and discuss the validity of the Migdal approximation for sulfur hydrides.

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Improved tetrahedron method for the Brillouin-zone integration applicable to response functions

Cited by 123 publications

References 31 publications

Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain

Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain

Ab initiostudy of cross-interface electron-phonon couplings in FeSe thin films onSrTiO3andBaTiO3

Effect of Van Hove singularities on high- Tc superconductivity in H3S

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