Nonequilibrium carrier and phonon dynamics in the ferrimagnetic semiconductor Mn$_3$Si$_2$Te$_6$

TL;DR

This study explores ultrafast carrier and phonon behaviors in the ferrimagnetic semiconductor Mn$_3$Si$_2$Te$_6$, revealing complex relaxation processes and phonon dynamics influenced by magnetic ordering, with implications for optoelectronic and spintronic applications.

Contribution

It provides the first detailed analysis of nonequilibrium carrier and phonon dynamics in Mn$_3$Si$_2$Te$_6$, highlighting the effects of magnetic order on relaxation processes.

Findings

Prolonged electron-phonon thermalization due to hot-phonon bottleneck.

Identification of two non-radiative recombination mechanisms.

Observation of temperature-dependent relaxation components.

Abstract

We investigate the ultrafast carrier and phonon dynamics in the ferrimagnetic semiconductor Mn$_3$Si$_2$Te$_6$ using time-resolved optical pump-probe spectroscopy. Our results reveal that the electron-phonon thermalization process with a subpicosecond timescale is prolonged by the hot-phonon bottleneck effect. We identify the subsequent relaxation processes associated with two non-radiative recombination mechanisms, i.e., phonon-assisted electron-hole recombination and defect-related Shockley-Read-Hall recombination. Temperature-dependent measurements indicate that all three relaxation components show large variation around 175 and 78 K, which is related to the initiation of spin fluctuation and ferrimagnetic order in Mn$_3$Si$_2$Te$_6$. In addition, two pronounced coherent optical phonons are observed, in which the phonon with a frequency of 3.7 THz is attributed to the $A_{1g}$ mode of Te precipitates. Applying the strain pulse propagation model to the coherent acoustic phonons yields a penetration depth of 506 nm and a sound speed of 2.42 km/s in Mn$_3$Si$_2$Te$_6$. Our results develop understanding of the nonequilibrium properties of the ferrimagnetic semiconductor Mn$_3$Si$_2$Te$_6$, and also shed light on its potential applications in optoelectronic and spintronic devices.