Anapole superconductivity from {{{{{{{mathcal{PT}}}}}}}}-symmetric mixed-parity interband pairing

Shota Kanasugi,Youichi Yanase

doi:10.1038/s42005-022-00804-7

Shota Kanasugi, Youichi Yanase

Open Access

https://doi.org/10.1038/s42005-022-00804-7

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Abstract

Recently, superconductivity with spontaneous time-reversal or parity symmetry breaking is attracting much attention owing to its exotic properties, such as nontrivial topology and nonreciprocal transport. Particularly fascinating phenomena are expected when the time-reversal and parity symmetry are simultaneously broken. This work shows that time-reversal symmetry-breaking mixed-parity superconducting states generally exhibit an unusual asymmetric Bogoliubov spectrum due to nonunitary interband pairing. For generic two-band models, we derive the necessary conditions for the asymmetric Bogoliubov spectrum. We also demonstrate that the asymmetric Bogoliubov quasiparticles lead to the effective anapole moment of the superconducting state, which stabilizes a nonuniform Fulde-Ferrell-Larkin-Ovchinnikov state at zero magnetic fields. The concept of anapole order employed in nuclear physics, magnetic materials science, strongly correlated electron systems, and optoelectronics is extended to superconductors by this work. Our conclusions are relevant for any multiband superconductors with competing even- and odd-parity pairing channels. Especially, we discuss the superconductivity in UTe2.

Highlights

Superconductivity with spontaneous time-reversal or parity symmetry breaking is attracting much attention owing to its exotic properties, such as nontrivial topology and nonreciprocal transport
We show that PT -symmetric mixed-parity superconducting states generally exhibit an asymmetric Bogoliubov spectrum (BS) in multiband systems, it is overlooked in single-band models
We have shown that an FFLO state is stabilized in the absence of an external magnetic field when the superconducting state belongs to a polar and time-reversal-odd irreducible representation (IR)

Summary

Introduction

Superconductivity with spontaneous time-reversal or parity symmetry breaking is attracting much attention owing to its exotic properties, such as nontrivial topology and nonreciprocal transport. This work shows that time-reversal symmetry-breaking mixed-parity superconducting states generally exhibit an unusual asymmetric Bogoliubov spectrum due to nonunitary interband pairing. Mixed-parity superconductivity with coexistent even- and odd-parity pairing channels has been widely discussed in noncentrosymmetric superconductors[6,7], ultracold fermion systems[8,9], and spin-orbit-coupled systems in the vicinity of the P-symmetry broken phase[10,11,12,13,14]. (Fig. 1a), when the spin-orbit coupling (SOC) due to noncentrosymmetric crystal structure is absent or weak This class of superconducting states spontaneously breaks both P- and T -symmetries but maintain the combined PT -symmetry. Evenparity T -symmetry breaking superconductors host topologically protected Bogoliubov Fermi surfaces in the presence of interband pairing[39,40]

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