Magnetic-order-mediated carrier and phonon dynamics in MnBi2Te4

TL;DR

This study uses ultrafast optical spectroscopy to explore how magnetic order influences carrier, spin, and phonon dynamics in MnBi2Te4, revealing anomalous responses associated with antiferromagnetic transition.

Contribution

It uncovers the impact of antiferromagnetic order on quasiparticle, spin, and phonon dynamics, including modulation of carrier processes and phonon energy renormalization.

Findings

Carrier decay and recombination are modulated by AFM order.

A long spin-lattice relaxation process emerges below TN.

Unusual phonon energy shifts are linked to spin coupling.

Abstract

We investigate the quasiparticle dynamics in MnBi2Te4 single crystal using the ultrafast optical spectroscopy. Our results show that there exist anomalous dynamical optical responses below the antiferromagnetic (AFM) ordering temperature TN. In specific, we reveal that both the initial carrier decay and recombination processes can be modulated via introducing the AFM order in sub-picosecond and picosecond timescales, respectively. We also discover a long relaxation process emerging below TN with a timescale approaching to the nanosecond regime, and can be attributed to the T-dependent spin-lattice interaction. There also emerges an unusual phonon energy renormalization below TN , which is found to arise from its coupling the spin degree via the exchange interaction and magnetic anisotropy. Our findings provide key information for understanding the dynamical properties of non-equilibrium carrier, spin and lattice in MnBi2Te4.