Ferroelectricity in magnon Bose-Einstein condensate: non-reciprocal superfluidity, exceptional points and Majorana bosons

TL;DR

This paper explores a ferroelectric transition in a magnon Bose-Einstein condensate driven by electric field interactions, revealing non-reciprocal superfluidity, exceptional points, and Majorana bosons, with implications for quantum materials.

Contribution

It introduces a novel ferroelectric phase in magnon superfluids mediated by the Aharonov-Casher phase, highlighting spontaneous symmetry breaking and topological features.

Findings

Spontaneous ferroelectric transition in magnon superfluid.

Nonreciprocal quasiparticle spectrum in the ferroelectric phase.

Identification of exceptional points and Majorana boson analogs.

Abstract

We investigate a ferroelectric instability of a magnon Bose-Einstein condensate, mediated by its interaction with an electric field through a geometric Aharonov-Casher (AC) phase. A distinct feature of the system is the positive feedback loop in which an electric field induces magnon orbital motion via the AC phase, generating electric polarization that in turn enhances the original field. Based on bosonic Bogoliubov-de Gennes (BdG) mean-field theory, we show that this feedback drives a spontaneous ferroelectric transition in the magnon superfluid, accompanied by a persistent magnon supercurrent. In the resulting ferroelectric phase, the quasiparticle excitation spectrum becomes nonreciprocal, reflecting spontaneous breaking of spatial inversion symmetry. At the critical point of the transition, the bosonic BdG Hamiltonian exhibits coalescence of both eigenvalues and eigenvectors, forming an exceptional point. The corresponding eigenvector is an equally weighted superposition of bosonic quasiparticle and quasihole states and is invariant under particle-hole transformation, allowing it to be interpreted as a bosonic analog of a Majorana fermion.