Physics Seminar

“Ultrafast optical studies on CDW collective modes of the Weyl-CDW (TaSe₄)₂I”

Soyeun Kim

Department of Physics,

Univ. Illinois at Urbana-Champaign (UIUC)

Jan. 11th (Tue), 15:00, E6 #1501

(TaSe₄)₂I provides an excellent platform to explore topology, lattice, and charge degrees of freedom. It is a non-magnetic Weyl semimetal with a quasi-1D charge-density wave phase transition (T_C ~ 260 K) on its structurally chiral lattice. Because the pairs of Weyl fermions are coupled by a CDW modulation, the phase part of the CDW collective mode is suggested to follow the axion electrodynamics described by θE·B [1,2]. As a result, exciting phenomena such as negative magnetoresistance, quantized photogalvanic and piezomagnetic effects have been proposed [1,3,4]. In this talk, we will investigate the CDW collective modes of (TaSe₄)₂I using ultrafast optical tools of THz emission and THz-pump birefringence spectroscopy. The experimental results will be discussed and compared to the theoretically suggested magnetoelectric effects in the Weyl-CDW system.

[1] J. Gooth et al., Nature 575, 315 (2019).
[2] W. Shi et al., Nat. Phys. 17, 381 (2021).
[3] D. M. Nenno et al., Nat. Rev. Phys. 2, 682 (2020).
[4] Yu et al., Phys. Rev. B 104, 174406 (2021).

Contact: Eunjung Jo, (jojo@kaist.ac.kr)