Understanding and enhancing superconductivity in FeSe/SrTiO$_3$ by quantum size effects


Type
Article
Change log
Authors
Murta, B 
Garcia Garcia, AM 
Abstract

Superconductivity in one-atom-layer iron selenide (FeSe) on a strontium titanate (STO) substrate is enhanced by almost an order of magnitude with respect to bulk FeSe. There is recent experimental evidence suggesting that this enhancement persists in FeSe/STO nanoislands. More specifically, for sizes L ~ 10 nm, the superconducting gap is a highly nonmonotonic function of L with peaks well above the bulk gap value. This is the expected behavior only for weakly-coupled metallic superconductors such as Al or Sn. Here we develop a theoretical formalism to describe these experiments based on three ingredients: Eliashberg theory of superconductivity in the weak coupling limit, pairing dominated by forward scattering, and periodic orbit theory to model spectral fluctuations. We obtain an explicit analytical expression for the size dependence of the gap that describes quantitatively the experimental results with no free parameters. This is a strong suggestion that superconductivity in FeSe/STO is mediated by STO phonons. We propose that, since FeSe/STO is still a weakly coupled superconductor, quantum size effects can be used to further enhance the bulk critical temperature in this interface.

Description
Keywords
cond-mat.supr-con, cond-mat.supr-con, cond-mat.mes-hall
Journal Title
Physical Review B - Condensed Matter and Materials Physics
Conference Name
Journal ISSN
2469-9950
2469-9969
Volume Title
94
Publisher
American Physical Society
Sponsorship
Engineering and Physical Sciences Research Council (EP/I004637/1)