@article{13478, author = {Tika Kafle and Yingchao Zhang and Qing-Xing Dong and Xun Shi and Na Li and Richa Sapkota and Jeremy Thurston and Wenjing You and Shunye Gao and Kai Rossnagel and Gen-Fu Chen and James Freericks and Henry Kapteyn and Margaret Murnane}, title = {Non-equilibrium States and Interactions in the Topological Insulator and Topological Crystalline Insulator Phases of NaCd4As3}, abstract = {

Topological materials are of great interest because they can support metallic states that are robust against perturbations, with the potential for technological applications. Here we experimentally explore the light-induced non-equilibrium properties of two distinct topological phases in NaCd4As3: a topological crystalline insulator (TCI) and a topological insulator (TI) phase. This material has surface states that are protected by mirror symmetry in the TCI phase at room temperature, while it undergoes a structural phase transition to a TI phase below 200 K. After exciting the TI phase by an ultrafast laser pulse, we observe a chemical potential shift >150 meV, that slowly builds up and maximizes after ~0.6 ps, and that persists for ~8 ps. The slow rise time of the excited electron population and electron temperature suggests that the electronic and structural orders are strongly coupled in this TI phase. It also suggests that the excited electronic states immediately and ~0.6 ps after excitation belong to different orbitals, likely due to partial relaxation of the lattice distortion that is known to be associated with the TI phase. In contrast, no distinct excited state is observed in the TCI phase after photoexcitation, which we attribute to the low density of states and phase space available near the Fermi level. Our results show how ultrafast excitation can probe the excited states and interactions within phase rich topological materials.

}, year = {2024}, journal = {Submitted}, url = {https://arxiv.org/abs/2407.19404}, }