Anharmonic strong-coupling effects at the origin of the charge density wave in CsV3Sb5

Ge He; Leander Peis; Emma Frances Cuddy; Zhen Zhao; Dong Li; Yuhang Zhang; Romona Stumberger; Brian Moritz; Haitao Yang; Hongjun Gao; Thomas Peter Devereaux; Rudi Hackl

doi:10.1038/s41467-024-45865-0

Anharmonic strong-coupling effects at the origin of the charge density wave in CsV₃Sb₅

Nat Commun. 2024 Mar 1;15(1):1895. doi: 10.1038/s41467-024-45865-0.

Authors

Ge He^#^{1

2}, Leander Peis^#^{3

4

5

6}, Emma Frances Cuddy^#^{7

8}, Zhen Zhao⁹, Dong Li⁹, Yuhang Zhang⁹, Romona Stumberger^{3

4

10}, Brian Moritz⁸, Haitao Yang^{11

12}, Hongjun Gao^{9

13}, Thomas Peter Devereaux^{14

15

16}, Rudi Hackl^{17

18

19}

Affiliations

¹ Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany. ghe@ucc.ie.
² Department of Physics, University College Cork, College Road, Cork, T12 K8AF, Ireland. ghe@ucc.ie.
³ Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany.
⁴ School of Natural Sciences, Technische Universität München, Garching, 85748, Germany.
⁵ IFW Dresden, Helmholtzstrasse 20, Dresden, 01069, Germany.
⁶ Capgemini, Frankfurter Ring 81, 80807, München, Germany.
⁷ Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA.
⁸ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.
⁹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
¹⁰ Robert Bosch GmbH, Robert-Bosch-Campus 1, 71272, Renningen, Germany.
¹¹ Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China. htyang@iphy.ac.cn.
¹² School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China. htyang@iphy.ac.cn.
¹³ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
¹⁴ Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA. tpd@stanford.edu.
¹⁵ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA. tpd@stanford.edu.
¹⁶ Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, 94305, USA. tpd@stanford.edu.
¹⁷ Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching, 85748, Germany. r.hackl@ifw-dresden.de.
¹⁸ School of Natural Sciences, Technische Universität München, Garching, 85748, Germany. r.hackl@ifw-dresden.de.
¹⁹ IFW Dresden, Helmholtzstrasse 20, Dresden, 01069, Germany. r.hackl@ifw-dresden.de.

^# Contributed equally.

Abstract

The formation of charge density waves is a long-standing open problem, particularly in dimensions higher than one. Various observations in the vanadium antimonides discovered recently further underpin this notion. Here, we study the Kagome metal CsV₃Sb₅ using polarized inelastic light scattering and density functional theory calculations. We observe a significant gap anisotropy with $2 Δ_{\max} / k_{B} T_{CDW} \approx 20$ , far beyond the prediction of mean-field theory. The analysis of the A_1g and E_2g phonons, including those emerging below T_CDW, indicates strong phonon-phonon coupling, presumably mediated by a strong electron-phonon interaction. Similarly, the asymmetric Fano-type lineshape of the A_1g amplitude mode suggests strong electron-phonon coupling below T_CDW. The large electronic gap, the enhanced anharmonic phonon-phonon coupling, and the Fano shape of the amplitude mode combined are more supportive of a strong-coupling phonon-driven charge density wave transition than of a Fermi surface instability or an exotic mechanism in CsV₃Sb₅.