Ultrafast Carrier Dynamics in Ba₆Cr₂S₁₀ Modified by Toroidal Magnetic Phase Transition

Ba₆Cr₂S₁₀ 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 Ba₆Cr₂S₁₀ 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 Ba₆Cr₂S₁₀, and shed light on phase transitions in TM quantum materials.