Quantum-torque-induced breaking of magnetic interfaces in ultracold gases

TL;DR

This paper demonstrates how ultracold bosonic gases can simulate magnetic interfaces and spin dynamics, revealing quantum torque effects and magnetic wave formation in a highly controllable environment.

Contribution

It introduces ultracold gases as a new platform to study far-from-equilibrium spin dynamics and magnetic interface phenomena, highlighting quantum torque effects.

Findings

Magnetic interfaces form rapidly from polarized states.

Quantum torque induces short-wavelength magnetic waves.

Strong spatial anticorrelations in magnetization observed.

Abstract

A rich variety of physical effects in spin dynamics arises at the interface between different magnetic materials. Engineered systems with interlaced magnetic structures have been used to implement spin transistors, memories and other spintronic devices. However, experiments in solid state systems can be difficult to interpret because of disorder and losses. Here, we realize analogues of magnetic junctions using a coherently-coupled mixture of ultracold bosonic gases. The spatial inhomogeneity of the atomic gas makes the system change its behavior from regions with oscillating magnetization -- resembling a magnetic material in the presence of an external transverse field -- to regions with a defined magnetization, as in magnetic materials with a ferromagnetic anisotropy stronger than external fields. Starting from a far-from-equilibrium fully polarized state, magnetic interfaces rapidly form. At the interfaces, we observe the formation of short-wavelength magnetic waves. They are generated by a quantum torque contribution to the spin current and produce strong spatial anticorrelations in the magnetization. Our results establish ultracold gases as a platform for the study of far-from-equilibrium spin dynamics in regimes that are not easily accessible in solid-state systems.