magnetic topological insulator*

MnBi₂Te₄ is recently identified as an intrinsic antiferromagnetic (AFM) topological insulator which is considered as a suitable material for the study of novel topological quantum phenomena whose possible behavior and ultrafast dynamics could be investigated through a versatile femtosecond time-resolved spectroscopy under applied magnetic field and temperature. In this work, topological quantum phase transition is studied in the magnetic topological insulator, MnBi_2-xSb_xTe₄ (x=0.19), which is MnBi₂Te₄ mixed with antimony. It focusses on the phase transition induced by chemical substitution, magnetic field, and ultrafast lasers. The optical pump-probe (OP-OP) measurements are performed in the magneto-optical closed-cycle cryostat (Opti-Cool) to reveal and study the ultrafast dynamics about MnBi_2-xSb_xTe₄ (x=0.19) at room temperature and low temperature (2 K). A continuously increasing magnetic field upto 7 T is also applied during the low temperature condition to observe the changing ultrafast dynamics crossing the spin-flop situation. In addition, we also plan to perform the Superconducting Quantum Interference Device (SQUID) to confirm the magnetic moment of anti-ferromagnetic (AFM) state at Neel temperature and magnetic level for the origin of spin-flop situation.