Superconductivity in SrTiO3: Dielectric Function Method for Non-Parabolic Bands

Abstract

The dielectric function method for superconductivity has been applied to SrTiO3 accounting for the non-parabolic dispersion of charge carriers in the conduction band and for the dispersion of optical phonons based on density functional theory calculations. The obtained critical temperatures of the superconducting phase transition in SrTiO3 are in agreement with experiments in the density range n ∼ 5 × 10 18 to 5 × 10 20 cm −3 . The dielectric function method predicts also the sign of the anomalous isotope effect in strontium titanate, in line with recent observations.

Superconductivity mediated by polar modes in ferroelectric metals

“…Comments: Since this work was completed, further experimental studies 34,[64][65][66] and theoretical studies [67][68][69] have been reported that are generally in keeping with our conclusions. A theoretical expression for the integration cut-off in the Eliashberg gap equation has been discussed 69 and leads to numerical values of ω c for SrTiO 3 of the same order of magnitude as those used in our analyses in the density range near to the dome maximum (see also "Methods" section and Supplementary Information).…”

Giant Grüneisen parameter in a superconducting quantum paraelectric

“…The recent debate about appropriate models [10][11][12][13][14][15][16][17][18][19][20][21]7] mostly swirls around the question of which phonons provide the superconducting pairing and how. Showing experimentally which phonons are the most relevant is not a trivial task either: Some recent experiments on approaching the quantum paraelectric to ferroelectric phase transition show correlations of the ferroelectric phase with superconductivity [22][23][24][25][26][27][28].…”

“…In other words, the relationship between the anomalous responses of critical temperature and mode Grüneisen parameter to strain indicates that the ferroelectric soft-mode must be the key element in a theory that can correctly describe the pairing. This is true whether that theory is a direct [10,68], multi-phonon [21], screening [20] or any other scenario, even if they include couplings to other phonon modes.…”

Isotope tuning of the superconducting dome of strontium titanate

“…1 Although the coupling to the LO1 mode at 22 meV is very small (λ = 0.003), 28,29 the main features of the phase diagram have been reproduced in a hybrid model of coupling to plasmons and the LO1 mode. 15,22,30,31 In this approach the electron-electron interaction is treated in the random phase approximation. Since this approximation has been shown to strongly overestimate the stability of the superconducting state, 32 further analysis of the hybrid phonon-plasmon model is required taking into account exchange and correlation terms.…”