Topological Superconductivity in Sn/Si(111) driven by non-local Coulomb interactions

TL;DR

This paper investigates how non-local Coulomb interactions influence topological superconductivity in Sn/Si(111), revealing various pairing symmetries driven by charge fluctuations and proposing experimental verification methods.

Contribution

It provides a detailed analysis of the impact of extended Hubbard interactions on superconducting pairing symmetries in a topological system, using the random-phase approximation.

Findings

Chiral d-wave pairing near half-filling with weak extended interactions.

Chiral p-wave and f-wave pairings at different doping levels with stronger Coulomb interactions.

Charge fluctuations significantly influence the formation of Cooper pairs.

Abstract

Superconductivity was recently observed in boron-doped ($\sqrt{3}\times\sqrt{3}$)Sn/Si(111). The material can be described by an extended Hubbard model on a triangular lattice. Here, we use the random-phase approximation to investigate the charge and spin fluctuations as well as the superconducting properties of the system with respect to filling and the relative strength of the extended versus the on-site Hubbard interactions. Our calculations reveal that near half-filling and weak extended Hubbard interactions, the superconducting ground state exhibits chiral $d$-wave pairing. Far from half-filling and for stronger nearest-neighbor Coulomb interactions, the system shows chiral $p$-wave (hole-doping) and $f$-wave (electron-doping) pairings. The dependence of the pairing symmetry on the extended Hubbard interactions suggests that charge fluctuations play an important role in the formation of Cooper pairs. Finally, the temperature dependence of the Knight shift is calculated for all observed superconducting textures and put forward as an experimental method to examine the symmetry of the superconducting gap function.