@article{f530625ea9854960a8f372826f358bf0,
title = "Observation of a massive phason in a charge-density-wave insulator",
abstract = "The lowest-lying fundamental excitation of an incommensurate charge-density-wave material is believed to be a massless phason—a collective modulation of the phase of the charge-density-wave order parameter. However, long-range Coulomb interactions should push the phason energy up to the plasma energy of the charge-density-wave condensate, resulting in a massive phason and fully gapped spectrum1. Using time-domain terahertz emission spectroscopy, we investigate this issue in (TaSe4)2I, a quasi-one-dimensional charge-density-wave insulator. On transient photoexcitation at low temperatures, we find the material strikingly emits coherent, narrowband terahertz radiation. The frequency, polarization and temperature dependences of the emitted radiation imply the existence of a phason that acquires mass by coupling to long-range Coulomb interactions. Our observations underscore the role of long-range interactions in determining the nature of collective excitations in materials with modulated charge or spin order.",
author = "Soyeun Kim and Yinchuan Lv and Sun, {Xiao Qi} and Chengxi Zhao and Nina Bielinski and Azel Murzabekova and Kejian Qu and Duncan, {Ryan A.} and Nguyen, {Quynh L.D.} and Mariano Trigo and Shoemaker, {Daniel P.} and Barry Bradlyn and Fahad Mahmood",
note = "We thank P. Abbamonte, P. Armitage, D. Chaudhuri, T.-C. Chiang, L. Cooper, S. Kivelson, A. Kogar, P. Lee, V. Madhavan, D. Torchinsky and B. Wieder for insightful discussions. This work was supported by the Quantum Sensing and Quantum Materials, an Energy Frontier Research Center, funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0021238. F.M. acknowledges support from the EPiQS program of the Gordon and Betty Moore Foundation (grant GBMF11069). R.A.D. acknowledges support from the Bloch Postdoctoral Fellowship in Quantum Science and Engineering of the Stanford University Quantum Fundamentals, Architectures, and Machines initiative (Q-FARM), and from the Karel Urbanek and Marvin Chodorow Postdoctoral Fellowship of the Department of Applied Physics at Stanford University. X.-Q.S. acknowledges support from the Gordon and Betty Moore Foundation{\textquoteright}s EPiQS Initiative through grant GBMF8691. We acknowledge the use of the spectroscopic ellipsometry setup at the Institute for Basic Science (IBS) in Korea (grant no. IBS-R009-D1).",
year = "2023",
month = apr,
doi = "10.1038/s41563-023-01504-5",
language = "English (US)",
volume = "22",
pages = "429--433",
journal = "Nature Materials",
issn = "1476-1122",
publisher = "Nature Publishing Group",
number = "4",
}