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TT: Fachverband Tiefe Temperaturen

TT 39: Correlated Electrons: Charge Order

TT 39.4: Talk

Wednesday, March 20, 2024, 10:15–10:30, H 3025

Giant circular dichroism induced by electronic chirality in TiSe₂ — Qian Xiao¹, •Oleg Janson², Sonia Francoual³, Qingzheng Qiu¹, Qizhi Li¹, Shilong Zhang¹, Wu Xie^3,4, Pablo Bereciartua³, Jeroen van den Brink^2,5,6, Jasper van Wezel⁶, and Yingying Peng^1,7 — ¹Peking University, Beijing, China — ²Institute for Theoretical Solid State Physics, Leibniz IFW Dresden, Germany — ³DESY, Hamburg, Germany — ⁴Zhejiang University, Hangzhou, China — ⁵Würzburg-Dresden Cluster of Excellence ct.qmat, Germany — ⁶Institute for Theoretical Physics, University of Amsterdam, The Netherlands — ⁷Collaborative Innovation Center of Quantum Matter, Beijing, China

The quasi-2D van-der-Waals material 1T-TiSe₂ is known for its well-studied transition into a commensurate 2×2×2 charge density wave (CDW) state. Several experimental and theoretical studies suggested that the charge order may be chiral, yet no bulk measurement so far provided direct evidence for intrinsic broken inversion symmetry and chirality. In a resonant elastic x-ray scattering (REXS) experiment, we observe giant circular dichroism up to ∼40% at a Bragg peak forbidden in the centrosymmetric CDW structure. By performing first-principles calculations for the earlier proposed chiral structural model, we find excellent quantitative agreement with the experimental azimuthal angle dependence for different polarizations. In this way, we accurately estimate the magnitude of the inversion-breaking distortion and confirm that bulk 1T-TiSe₂ has chiral electronic order.

Keywords: charge density wave (CDW); inversion symmtery breaking; orbital ordering; resonant elastic x-ray scattering (REXS); transition-metal dichalcogenides (TMD)