Light-field-driven non-Ohmic current and Keldysh crossover in a Weyl semimetal

Abstract

In recent years, coherent electrons driven by light fields have attracted significant interest in exploring novel material phases and functionalities1–4. However, observing coherent light-field-driven electron dynamics5,6 in solids is challenging because the electrons are scattered within several ten femtoseconds in ordinary materials, and the coherence between light and electrons is disturbed. However, when we use Weyl semimetals7–11, the electron scattering becomes relatively long (several hundred femtoseconds - several picoseconds), owing to the suppression of the back-scattering process12. This study presents the light-field-driven dynamics by the THz pulse (~1 ps) to Weyl semimetal Co3Sn2S213–20, where the intense THz pulse of a monocycle electric field nonlinearly generates direct current (DC) via coherent acceleration without scattering5,6 and non-adiabatic excitation1,5,21,22 (Landau–Zener Transition). In other words, the non-Ohmic current appears in the Weyl semimetal with a combination of the long relaxation time and an intense THz pulse. This nonlinear DC generation also demonstrates a Keldysh crossover23 from a photon picture to a light-field picture by increasing the electric field strength.