Interlayer magnetophononic coupling in MnBi2Te4

TL;DR

This paper uncovers interlayer magnetophononic coupling in MnBi2Te4, revealing how phonons interact with magnetic states without structural changes, advancing control of magnetic topological phases.

Contribution

It demonstrates magnetophononic coupling in MnBi2Te4 through magneto-Raman spectroscopy and theoretical modeling, highlighting a new mechanism for manipulating magnetic topological materials.

Findings

Anomalies in phonon scattering across magnetic transitions

Detection of zone-boundary phonons via wave-mixing process

Observation of coherent phonons in ultrafast experiments

Abstract

The emergence of magnetism in quantum materials creates a platform to realize spin-based applications in spintronics, magnetic memory, and quantum information science. A key to unlocking new functionalities in these materials is the discovery of tunable coupling between spins and other microscopic degrees of freedom. We present evidence for interlayer magnetophononic coupling in the layered magnetic topological insulator MnBi2Te4. Employing magneto-Raman spectroscopy, we observe anomalies in phonon scattering intensities across magnetic field-driven phase transitions, despite the absence of discernible static structural changes. This behavior is a consequence of a magnetophononic wave-mixing process that allows for the excitation of zone-boundary phonons that are otherwise 'forbidden' by momentum conservation. Our microscopic model based on density functional theory calculations reveals that this phenomenon can be attributed to phonons modulating the interlayer exchange coupling. Moreover, signatures of magnetophononic coupling are also observed in the time domain through the ultrafast excitation and detection of coherent phonons across magnetic transitions. In light of the intimate connection between magnetism and topology in MnBi2Te4, the magnetophononic coupling represents an important step towards coherent on-demand manipulation of magnetic topological phases.