Opto- and magneto-tunable exceptional degeneracies in non-Hermitian ferromagnet/$p$-wave magnet junctions

TL;DR

This paper investigates how external magnetic fields and circularly polarized light can dynamically control exceptional points in non-Hermitian junctions involving unconventional p-wave magnets, revealing new tunable topological features.

Contribution

It introduces a novel non-Hermitian ferromagnet/UPM junction model demonstrating opto- and magneto-tunable exceptional degeneracies, highlighting the unique properties of UPMs compared to even-parity magnets.

Findings

Exceptional points can be modulated by magnetic fields and circularly polarized light.

UPMs exhibit distinct EP formation conditions due to their symmetry properties.

CPL enables dynamic, global re-normalization of EPs, unlike magnetic fields.

Abstract

Unconventional $p$-wave magnets (UPMs) with odd-parity spin textures have attracted interest for their zero net magnetization and anisotropic spin-split Fermi surfaces. Here, we explore a non-Hermitian open quantum system composed of a ferromagnet and a UPM, subjected to an external magnetic field and off-resonant circularly polarized light (CPL), serving as tunable control parameters. We demonstrate the emergence of exceptional points (EPs) in the proposed junction, whose locations can be modulated by the intrinsic properties of the UPM. These EPs exhibit different multiplicities and formation conditions compared to those in even-parity magnets (dubbed $d$- wave altermagnets), a distinction attributable to the preserved time-reversal and broken inversion symmetries characteristic of UPMs. We find that both the unidirectional magnetic field (with adjustable strength and orientation) and the CPL induce momentum-direction-dependent modifications to the EPs, such as their shifting, tilting, merging, or annihilation, supported by analyses of spin projection and eigenvector overlap. Although both perturbations influence the EP structure, they operate via distinct mechanisms: CPL induces a global Floquet re-normalization, enabling dynamic tunability through light, whereas the unidirectional magnetic field selectively alters orientation-aligned terms, lacking such tunability. Beyond revealing EP dynamics in UPM-based junctions, our results highlight UPMs as promising platforms for non-Hermitian phenomena in future spintronics.