Electrically Tunable Picosecond-scale Octupole Fluctuations in Chiral Antiferromagnets

TL;DR

This paper develops a theory for the ultrafast relaxation dynamics of octupole order in chiral antiferromagnets, revealing mechanisms and enabling electrical control for potential spintronic applications.

Contribution

It introduces a combined analytical and simulation framework to understand and control octupole relaxation times in chiral AFMs, highlighting electrical tunability.

Findings

Octupole moments relax on picosecond timescales.

Two relaxation mechanisms identified: barrier escape and precessional dephasing.

Electrical tuning of relaxation times demonstrated through analogy with Josephson junctions.

Abstract

We present a theory for the relaxation time of the octupole order parameter in nanoscale chiral antiferromagnets (AFMs) coupled to thermal baths and spin injection sources. Using stochastic spin dynamics simulations, we demonstrate that the octupole moment relaxes through two distinct mechanisms$-$escape over a barrier and precessional dephasing$-$as the barrier for octupole fluctuations is lowered relative to the thermal energy. Notably, the octupole moment relaxes orders of magnitude faster than the typical dipolar order parameters, reaching picosecond timescales. By combining Langer's theory with an effective low-energy description of octupole dynamics in chiral AFMs, we derive analytical expressions for the relaxation times. We find that relaxation in chiral AFMs parallels dipole relaxation in XY magnets, with exchange fields serving the role of the dipole fields. Further, by drawing on the analogy between order parameter dynamics in XY magnets under spin injection and current-biased Josephson junctions, we propose a new scheme for electrically tuning the octupole relaxation times. Our work offers fundamental insights for the development of next-generation spintronic devices that harness octupole order parameters for information encoding, especially in octupole-based probabilistic computing.