Unraveling Magneto-Phononic Coupling and Photoinduced Magnetic Control in Antiferromagnetic Kondo Semimetal CeBi

TL;DR

This study uses ultrafast optical spectroscopy to explore magneto-phononic interactions and photoinduced magnetic control in CeBi, revealing strong coupling effects and a threshold for non-thermal magnetic state manipulation.

Contribution

It demonstrates the use of coherent phonons as sensitive probes of magnetic order and shows photoinduced, non-thermal control of antiferromagnetism in CeBi.

Findings

Phonon anomalies near AFM transition temperatures in CeBi.

Identification of a pump fluence threshold for magnetic state quenching.

Evidence of strong magneto-phononic coupling in CeBi.

Abstract

We report an ultrafast optical spectroscopy study on the coherent phonon dynamics in the topological semimetal CeBi and its nonmagnetic isostructural compound LaBi, revealing profound insights into their electronic and magnetic interactions. Both materials exhibit prominent $A_{1g}$ longitudinal optical phonons with characteristic anharmonic temperature dependencies. However, in CeBi, the $A_{1g}$ phonon frequency and amplitude show clear anomalies near its antiferromagnetic (AFM) ordering temperatures ($T_{N1}$ $\simeq$ 25 K and $T_{N2}$ $\simeq$ 12 K), which unequivocally demonstrate strong magneto-phononic coupling. Crucially, in the AFM state at 4 K, CeBi exhibits a pump fluence threshold of $F_C$ $\approx$ 44 $\mu$J/cm$^2$, above which the rate of phonon softening accelerates and the amplitude increases sharply. This unique threshold, absent in paramagnetic CeBi and LaBi, points to a photoinduced, non-thermal quenching of the AFM order. Our findings establish coherent phonons as highly sensitive probes of intertwined orders in heavy fermion systems, highlighting the transformative potential of ultrafast pulses in dynamically controlling magnetic states in correlated electron materials and paving the way for the manipulation of emergent quantum phases.