Oral: Photoinduced transient reflective anisotropy and its prolonged lifetime in CaMnBi₂

A transient anisotropic reflectivity is induced after photoexcitation on the ab-plane of CaMnBi₂, which is a tetragonal layered Bi-based pnictide. The observed relaxation time is prolonged with no significant relaxation observed up to 1.5 ns at around 50 K, above which the behavior vanishes. This temperature is referred to the critical temperature for several phenomena observed in CaMnBi₂, including magnetoresistance, spin canting, and the transition of transport domination to Dirac carriers. However, this anisotropic reflectivity persists with Na doping but not with Cu doping. While both Na and Cu doping was indicated to induce spin canting, our measurement excludes spin canting as an origin of the transient optical anisotropy. Additionally, it was reported that the Dirac carriers in CaMnBi₂ may exhibit 1D transport behavior, pointing to a feasible origin of our photoinduced optical anisotropy. We discovered suppressed relaxation as pump fluence increase; meanwhile, the signal reaches saturation. This onset fluence of saturation decreases with the rising temperature, implying Dirac carrier density may play a role in the observed transient optical anisotropy. Further studies might be required to gain deeper understanding of this intriguing phenomenon.