Journal Article

PUBDB-2025-01328

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Non-equilibrium states and interactions in the topological insulator and topological crystalline insulator phases of NaCd$_4$As$_3$

Kafle, T. R. (Corresponding author) ; Zhang, Y. ; Wang, Y.-y. ; Shi, X. ; Li, N. ; Sapkota, R. ; Thurston, J. ; You, W. ; Gao, S. ; Dong, Q. ; Rossnagel, K.DESY* ; Chen, G.-F. ; Freericks, J. ; Kapteyn, H. C. ; Murnane, M. M.

2025
AIP Publishing LLC Melville, NY

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Please use a persistent id in citations: doi:10.1063/4.0000273  doi:10.3204/PUBDB-2025-01328

Abstract: 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 NaCd$_4$As$_3$: 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.

Note: M.M.M. and H.C.K. acknowledge support by the U.S.Department of Energy, Office of Science, Basic Energy Sciences x-ray Scattering Program Award DE-SC0002002 for this research.The ARPES setup was supported by the NSF through JILA PhysicsFrontiers Center PHY-2317149. J.K.F. was supported by theDepartment of Energy, Basic Energy Sciences under Award DE-FG02-08ER46542. J.K.F. was also supported by the McDevittbequest at Georgetown University.

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Contributing Institute(s):

1. FS-SXQM (FS-SXQM)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2025

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