Non-equilibrium states and interactions in the topological insulator and topological crystalline insulator phases of NaCd₄As₃

TY - JOUR

T1 - Non-equilibrium states and interactions in the topological insulator and topological crystalline insulator phases of NaCd4As3

AU - Kafle, Tika R.

AU - Zhang, Yingchao

AU - Wang, Yi Yan

AU - Shi, Xun

AU - Li, Na

AU - Sapkota, Richa

AU - Thurston, Jeremy

AU - You, Wenjing

AU - Gao, Shunye

AU - Dong, Qingxin

AU - Rossnagel, Kai

AU - Chen, Gen Fu

AU - Freericks, James

AU - Kapteyn, Henry C.

AU - Murnane, Margaret M.

N1 - Publisher Copyright: © 2025 Author(s).

PY - 2025/1/1

Y1 - 2025/1/1

N2 - Topological materials are of great interest because they can support metallic edge or surface 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) phase 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 leading band edge shift of >150 meV that slowly builds up and reaches a maximum 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 directly excited electronic states and the probed electronic states are weakly coupled. Both couplings are likely due to a partial relaxation of the lattice distortion, which is known to be associated with the TI phase. In contrast, no distinct excited state is observed in the TCI phase immediately or after photoexcitation, which we attribute to the low density of states and phase space available near the Fermi level. Our results show how ultrafast laser excitation can reveal the distinct excited states and interactions in phase-rich topological materials.

AB - Topological materials are of great interest because they can support metallic edge or surface 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) phase 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 leading band edge shift of >150 meV that slowly builds up and reaches a maximum 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 directly excited electronic states and the probed electronic states are weakly coupled. Both couplings are likely due to a partial relaxation of the lattice distortion, which is known to be associated with the TI phase. In contrast, no distinct excited state is observed in the TCI phase immediately or after photoexcitation, which we attribute to the low density of states and phase space available near the Fermi level. Our results show how ultrafast laser excitation can reveal the distinct excited states and interactions in phase-rich topological materials.

UR - https://www.scopus.com/pages/publications/85217208180

U2 - 10.1063/4.0000273

DO - 10.1063/4.0000273

M3 - Article

AN - SCOPUS:85217208180

SN - 2329-7778

VL - 12

JO - Structural Dynamics

JF - Structural Dynamics

IS - 1

M1 - 014501

ER -