Superconductivity in the ferromagnetic semiconductor SmN

TL;DR

This paper reports the discovery of superconductivity in heavily doped ferromagnetic semiconductor SmN, which maintains ferromagnetism and exhibits unconventional triplet pairing, offering new insights into quantum phases and spintronic applications.

Contribution

It demonstrates for the first time that a ferromagnetic semiconductor, SmN, can become superconducting while preserving ferromagnetism, revealing an unconventional triplet pairing mechanism.

Findings

Superconductivity coexists with ferromagnetism in SmN.

Superconducting pairing likely has p-wave symmetry.

Charge carriers are inferred to be heavy mass.

Abstract

The discovery of materials that simultaneously host different phases of matter has often initially confounded, but ultimately enhanced, our basic understanding of the coexisting types of order. The associated intellectual challenges, together with the promise of greater versatility for potential applications, have made such systems a focus of modern materials science. In particular, great efforts have recently been devoted to making semiconductors ferromagnetic and metallic ferromagnets superconducting. Here we report the unprecedented observation of a heavily donor-doped ferromagnetic semiconductor, SmN, becoming superconducting with ferromagnetism remaining intact. The extremely large exchange splitting of the conduction and valence bands in this material necessitates that the superconducting order hosted by SmN is of an unconventional triplet type, most likely exhibiting p-wave symmetry. Short range spin fluctuations, which are thought to be the cause of pairing interactions in currently known triplet superconductors, are quenched in SmN, suggesting its superconductivity to be the result of phonon- or Coulomb-mediated pairing mechanisms. This scenario is further supported by the inferred heavy mass of superconducting charge carriers. The unique near-zero magnetisation associated with the ferromagnetic state in SmN further aids its coexistence with superconductivity. Presenting this novel material system where semiconducting, ferromagnetic and superconducting properties are combined provides a versatile new laboratory for studying quantum phases of matter. Moreover it is a major step towards identifying materials that merge superconductivity and spintronics, urgently needed to enable the design of electronic devices with superior functionality.