Superconductivity coexisting with ferromagnetism in a quasi-one dimensional non-centrosymmetric (TaSe$_4$)$_3$I

TL;DR

This study reports the coexistence of superconductivity and ferromagnetism in a non-centrosymmetric quasi-one-dimensional material, revealing a unique quantum phase that challenges conventional understanding of these phenomena.

Contribution

It demonstrates the first clear observation of both superconductivity and ferromagnetism coexisting in (TaSe$_4$)$_3$I, linked to inversion symmetry breaking and potential unconventional pairing.

Findings

Superconductivity and ferromagnetism coexist below 2.5 K.

Meissner effect detected despite ferromagnetic order.

Coexistence suggests potential for unconventional spin-triplet pairing.

Abstract

Low-dimensional materials with broken inversion symmetry and strong spin-orbit coupling can give rise to fascinating quantum phases and phase transitions. Here we report coexistence of superconductivity and ferromagnetism below 2.5\,K in the quasi-one dimensional crystals of non-centrosymmetric (TaSe$_4$)$_3$I (space group: $P\bar{4}2_1c$). The unique phase is a direct consequence of inversion symmetry breaking as the same material also stabilizes in a centro-symmetric structure (space group: $P4/mnc$) where it behaves like a non-magnetic insulator. The coexistence here upfront contradicts the popular belief that superconductivity and ferromagnetism are two apparently antagonistic phenomena. Notably, here, for the first time, we have clearly detected Meissner effect in the superconducting state despite the coexisting ferromagnetic order. The coexistence of superconductivity and ferromagnetism projects non-centrosymmetric (TaSe$_4$)$_3$I as a host for complex ground states of quantum matter including possible unconventional superconductivity with elusive spin-triplet pairing.