Pressure-dependent topological superconductivity on the surface of FeTe_0.5Se_0.5

Abstract

FeTe1-xSex is a family of iron-based superconductors with its critical temperature (Tc) dependent on the composition of Se. A well-known Tc is 14.5 K for x = 0.45, which exhibits an s-wave superconducting gap between the topological superconducting surfaces states. Exchange interaction between the electrons has been proposed as the mechanism behind the formation of Cooper pairs for the sample of FeTe0.5Se0.5. In this article we provide further proof that exchange interaction, and hence the associated Tc, depends on the applied pressure on FeTe0.5Se0.5. Using density functional calculations for electrons and phonons and the Bardeen-Cooper-Schrieffer (BCS) theory for superconductivity, we found that Tc and superconducting gap for FeTe0.5Se0.5 soars under increasing compression, consistent with the results of experiment.

Exchange interaction for the triplet superconductor UTe2

“…In the particular example of FeTe 0.55 Se 0.45 10 , non-trivial topological surface states have been detected experimentally along with the associated topological superconductivity. Theoretical research on the more accessible FeTe 0.5 Se 0.5 not only produces accurate surface states 11 , 12 but provides evidence that exchange interaction 12 between electrons is driving the superconductivity, under ambient or higher pressures 13 . An extension of the theory to UTe 2 follows much the same reasoning, as one spin-triplet configuration— —consists also of two electrons having opposite spins, and therefore antisymmetric spatial wavefunction.…”