Ultrafast and helicity-controlled optical investigation on a charge-density wave Weyl semimetal (TaSe4)2I
일 시 : 2021년 12월 22일 수요일 16:00
연 사 : 김 소 연 박사 (Univ. Illinois at Urbana-Champaign)
장 소 : 747호 & 온라인 (줌 회의ID: 811 0183 4598 , 암호: 783734)
HOST : 문 순 재 교수님
초 록
In recent fields of condensed matter physics, the coupling between topological band structures and various degrees of freedom, such as lattice, charge, orbital, and spin, is highlighted. These understandingsare particularly appealing for the development of energy-efficient functional devices, as theycan be usedto controlthe dissipation-less electronic transport incorrelated topological materials. Identifying which degrees of freedom are coupled to a topological band is, however, a challenge. Investigating electrodynamics can overcome the difficultybecause many physical phenomena can be decoupled in time. (TaSe4)2I provides an excellent platform to exploretopology, lattice, and charge degrees of freedom. It is a nonmagnetic Weyl semimetal whichundergoesacharge-density-wave phase transition near260 Kon its structurally chiral lattice. The phase partof the CDW collective mode is expectedto follow the axion electrodynamics of high-energy physics [1,2], provided the pairs of Weyl fermions are coupled by a CDW modulation.From the axionic band structure, exciting phenomenasuch as chiral magnetoelectric and quantized photogalvanic effectsare proposed[3].
In this talk, we will first discuss the characteristics of topological Kramers-Weyl band structureand itspresence in (TaSe4)2I, which was examined via laser-based angle-resolved photoemission (ARPES) with full control of light helicity [4]. Next, we will consider a way to probe the CDW collective modes through ultrafast optical setups forTHz emission and THz-pump birefringence spectroscopies. The experimental results will be compared to the theoretically suggested axionic phase mode.
[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]S. Kimet al., arXiv:2108.10874 (2021).