Mode-Selective Spontaneous Oscillation of Bandgap in Dirac Wedge Semimetals

This article studies the time-dependent behavior of semimetal Zr₃AgX₃F₂₀ [X=Cd and Hg], M(MoS)₃ and M(MoSe)₃ [M=Li, Na, K, Rb, Tl, In, I] using time-dependent density functional theory. The results show half-occupied Dirac wedge bands. Due to the one-dimensional character, the materials oscillate in a selective mode at a finite temperature. The wedge bands couple to such a phonon mode, resulting in spontaneous oscillation in a rigid period. Especially, the bandgap periodically closes and opens in a large scale, supporting a pulsed current even under a constant biased voltage. Besides, these systems might be long sought time crystals in condensed matters.