Temperature dependent ultrafast dynamics of topological materials SrCd₂Sb₂ and EuCd₂Sb₂

Hung-Viet Khuc^1*, Jiun-Haw Chu³, Cheng-Chien Chen⁷, Yu-Sheng Kuo¹, Wen-Yen Tzeng⁸, Chien-Ming Tu², Chih-Wei Luo^2,3,4,5,6, Jiunn-Yuan Lin¹

¹Institute of Physics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
²Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
³Department of Physics, University of Washington, Seattle, Washington 98195, USA
⁴Taiwan Consortium of Emergent Crystalline Materials (TCECM), National Science and Technology Council, Taiwan
⁵Institute of Physics and Center for Emergent Functional Matter Science, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
⁶National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan
⁷University of Alabama at Birmingham, Birmingham, Alabama, USA
⁸Department of Electronic Engineering, National Formosa University, Yunlin 632, Taiwan

* Presenter:Hung-Viet Khuc, email:hungvietdhsptn@gmail.com

Topological materials (TMs) have attracted much attention due to their potential applications in optoelectronics, spintronics, and quantum computing. Theoretical calculations by J. M. DeStefano et al. showed SrCd₂As₂ as a narrow bandgap semiconductor under ambient conditions. Applying negative pressure to SrCd₂As₂ can reduce the bandgap and induce band inversion. Alloying Sb at the As site thus transforms SrCd₂As₂ into a TM. This study reports on ultrafast carrier dynamics in TM SrCd₂Sb₂ single crystals using a 400 nm-800 nm optical pump-probe (OP-OP) technique. The transient reflectivity (ΔR/R) curves of SrCd₂Sb₂ display electronic structure transitions around 150 K. Above 150 K, SrCd₂Sb₂ single crystals are TM, and below 150 K, SrCd₂Sb₂ single crystals exhibit semiconductor-like behavior similar to SrCd₂As₂.

EuCd₂Sb₂ and SrCd₂Sb₂ share similar single-crystal structures, with Eu atoms replacing Sr. Identified as an ideal magnetic Weyl semimetal, EuCd₂Sb₂ may serve as a promising platform for exploring magnetism-electronic structure interactions. From 2 K to 300 K, ΔR/R curves of EuCd₂Sb₂ reveal electronic transitions near 150 K, analogous to SrCd₂Sb₂. We are investigating EuCd₂Sb₂’s magnetic field responses.

Keywords: Topological materials, Weyl semimetal, ultrafast carrier dynamics