Odd-parity superconductivity underpinned by antiferromagnetism in heavy fermion metal YbRh$_2$Si$_2$

TL;DR

This study provides evidence for odd-parity, spin-triplet topological superconductivity in YbRh$_2$Si$_2$, driven by antiferromagnetism, with multiple superconducting states and a topological helical phase identified through high-resolution impedance measurements.

Contribution

It demonstrates the coexistence of antiferromagnetism and odd-parity superconductivity, revealing a topological helical state in a heavy fermion metal for the first time.

Findings

Multiple superconducting states suppressed differently by magnetic field

Superconductivity abruptly ends at the antiferromagnetic critical field

Evidence for a topological helical superconducting state

Abstract

Topological superconductors are essential elements of the periodic table of topological quantum matter. However, the relevant odd-parity spin-triplet superconductors are rare. We report high-resolution measurements of the complex electrical impedance of YbRh$_2$Si$_2$ down to 0.4 mK, that reveal the presence of several superconducting states, suppressed differently by magnetic field, both Pauli-limited and beyond the Pauli limit. Superconductivity is abruptly switched off at the critical field of the primary antiferromagnetic order. The onset of electro-nuclear spin density wave order enhances the superconductivity, which we account for by the simultaneous formation of a spin-triplet pair density wave. Together these observations provide compelling evidence for odd-parity superconductivity, and its underpinning by antiferromagnetism, and allow us to identify the topological helical state.