Observation of a massive phason in a charge-density-wave insulator

Soyeun Kim, Yinchuan Lv, Xiao Qi Sun, Chengxi Zhao, Nina Bielinski, Azel Murzabekova, Kejian Qu, Ryan A. Duncan, Quynh L.D. Nguyen, Mariano Trigo, Daniel P. Shoemaker, Barry Bradlyn, Fahad Mahmood

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)429-433
Number of pages5
JournalNature Materials
Issue number4
StatePublished - Apr 2023

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • General Chemistry
  • General Materials Science


Dive into the research topics of 'Observation of a massive phason in a charge-density-wave insulator'. Together they form a unique fingerprint.

Cite this