Supercurrent as a Probe for Topological Superconductivity in Magnetic Adatom Chains

TL;DR

This paper demonstrates that supercurrent and spin polarization in magnetic adatom chains coupled to superconductors can serve as indicators of topological superconductivity and Majorana states, providing new experimental probes.

Contribution

It introduces the use of supercurrent and spin polarization profiles as novel signatures for detecting topological superconductivity in magnetic adatom chains.

Findings

Supercurrent reverses direction at a critical exchange coupling.

Enhanced supercurrent occurs in the topological regime with Majorana states.

Spin polarization aligns with the triplet pairing d-vector near the chain.

Abstract

A magnetic adatom chain, proximity coupled to a conventional superconductor with spin-orbit coupling, exhibits locally an odd-parity, spin-triplet pairing amplitude. We show that the singlet-triplet junction, thus formed, leads to a net spin accumulation in the near vicinity of the chain. The accumulated spins are polarized along the direction of the local $\mathbf{d}$-vector for triplet pairing and generate an enhanced persistent current flowing around the chain. The spin polarization and the "supercurrent" reverse their directions beyond a critical exchange coupling strength at which the singlet superconducting order changes its sign on the chain. The current is strongly enhanced in the topological superconducting regime where Majorana bound states appear at the chain ends. The current and the spin profile offer alternative routes to characterize the topological superconducting state in adatom chains and islands.