Ultrafast Carrier Dynamics in Ba6Cr2S10 Modified by Toroidal Magnetic Phase Transition

Ba 6 Cr 2 S 10 is a recently discovered magnetic material, in which the spins are aligned ferromagnetically in the ab -plane and anti-parallelly in a paired form along the c -axis. It is characterized as a quasi-one dimensional (1D) dimerized structure with a ferrotoroidic order, forming the simplest candidate toroidal magnetic (TM) order and exhibiting an anti-ferromagnetic-like transition at around 10 K. Time-resolved ultrafast dynamics investigation of the novel A–Cr–S (A: metal elements) family of quantum materials has rarely been reported. Here, we investigate the time-resolved pump-probe ultrafast dynamics of a Ba 6 Cr 2 S 10 single crystal. A prominent change in the photo-excited carrier dynamics is observed at T c = 10 K, corresponding to the reported TM-paramagnetic phase transition. A potential unknown magnetic transition is also found at T * = 29 K. Our results provide new evidence for the TM magnetic transition in Ba 6 Cr 2 S 10 , and shed light on phase transitions in TM quantum materials.