Temperature and Magnetic Field Dependencies*

Topological materials (TMs) have recently gained significant attention for their potential in spintronics devices and quantum computing applications which are characterized by their conductive surface states protected by time-reversal symmetry. These gapless surface states emerge from band inversion and the influence of spin-orbit coupling. Here, we present our work on the ultrafast carrier dynamics in single crystals of the topological material EuCd₂Sb₂, achieved through the utilization of a two-color optical pump-optical probe (OP-OP) technique. The time-domain traces of transient reflectivity (ΔR/R) of the probe pulses were recorded in the temperature range of 2-300 K. In addition, we also applied different magnetic fields (1, 2, 3, 4, 5, and 6 T) parallel to c-axis of the sample and performed the OP-OP measurements in the temperature range of 2-300 K. The significant observations from the OP-OP measurements include, (i) transition from positive ΔR/R signal to a negative ΔR/R signal at around 120 K, (ii) appearance of a slow frequency mode of 0.03 THz at all temperatures and fields, and (iii) origin of a new frequency mode at 0.16 THz after application of 6 T. The detailed analysis of these results will be carried out to have a deeper understanding on the ultrafast dynamics of EuCd₂Sb₂ single crystals. Further, we will also carry out a detailed magnetic measurements using superconducting quantum interference devices to elucidate the magnetic phase transitions