Mechanism, time-reversal symmetry and topology of superconductivity in noncentrosymmetric systems

TL;DR

This paper investigates how symmetry, magnetic doping, and competing interactions influence the topological and time-reversal properties of superconductivity in noncentrosymmetric materials, providing criteria for topological superconductor design.

Contribution

It establishes that electron-phonon coupling yields trivial, fully gapped, time-reversal symmetric superconductors, and explores how magnetic doping and competing instabilities can induce topological phases.

Findings

Pure electron-phonon coupling leads to trivial superconductivity.

Magnetic doping can induce topologically nontrivial states.

Time-reversal symmetry of the order parameter affects the superconducting properties.

Abstract

We analyze the possible interaction-induced superconducting instabilities in noncentrosymmetric systems based on symmetries of the normal state. It is proven that pure electron-phonon coupling will always lead to a fully gapped superconductor that does not break time-reversal symmetry and is topologically trivial. We show that topologically nontrivial behavior can be induced by magnetic doping without gapping out the resulting Kramers pair of Majorana edge modes. In case of superconductivity arising from the particle-hole fluctuations associated with a competing instability, the properties of the condensate crucially depend on the time-reversal behavior of the order parameter of the competing instability. When the order parameter preserves time-reversal symmetry, we obtain exactly the same properties as in case of phonons. If it is odd under time-reversal, the Cooper channel of the interaction will be fully repulsive leading to sign changes of the gap and making spontaneous time-reversal symmetry breaking possible. To discuss topological properties, we focus on fully gapped time-reversal symmetric superconductors and derive constraints on possible pairing states that yield necessary conditions for the emergence of topologically nontrivial superconductivity. These conditions might serve as a tool in the search for topological superconductors. We also discuss implications for oxides heterostructures and single-layer FeSe.