Ultrafast transmission electron microscopy on dynamic process of a CDW transition in 1T-TaSe2

TL;DR

This study uses 4D ultrafast transmission electron microscopy to observe rapid structural changes during a charge-density-wave phase transition in 1T-TaSe2, revealing transient states and second-order transition characteristics.

Contribution

It provides real-time visualization of the CDW phase transition dynamics in 1T-TaSe2 with unprecedented temporal resolution, highlighting transient states and structural features.

Findings

Observation of a 3 ps transition from C to IC phase

Identification of a structurally isosbestic point at qiso

Evidence of second-order transition behavior

Abstract

Four-dimensional ultrafast transmission electron microscopy (4D-UTEM) measurements reveal a rich variety of structural dynamic phenomena at a phase transition in the charge-density-wave (CDW) 1T-TaSe2. Through the photoexcitation, remarkable changes on both the CDW intensity and orientation are clearly observed associated with the transformation from a commensurate (C) into an incommensurate (IC) phase in a time-scale of about 3 ps. Moreover, the transient states show up a notable "structurally isosbestic point" at a wave vector of qiso where the C and IC phases yield their diffracting efficiencies in an equally ratio. This fact demonstrates that the crystal planes parallel to qiso adopts visibly common structural features in these two CDW phases. The second-order characters observed in this nonequilibrium phase transition have been also analyzed based on the time-resolved structural data.