Ultrafast Modulations And Detection of a Ferro-rotational Charge Density Wave Using Time-resolved Electric Quadrupole Second Harmonic Generation

TL;DR

This paper demonstrates ultrafast modulations of a ferro-rotational charge density wave in 1T-TaS2 using time-resolved electric quadrupole second harmonic generation, revealing dynamic phase transitions and mode frequencies.

Contribution

It introduces a novel application of EQ RA-SHG to track ultrafast charge density wave modulations and phase transitions in 1T-TaS2.

Findings

Ultrafast breathing and rotation of EQ RA-SHG patterns at specific frequencies.

Photo-induced transient CDW phase observed at a critical pump fluence.

Significant shifts in mode frequencies indicating phase transition.

Abstract

We show the ferro-rotational nature of the commensurate charge density wave (CCDW) in $1T$-$\mathrm{TaS}_2$ and track its dynamic modulations by temperature-dependent and time-resolved electric quadrupole rotation anisotropy-second harmonic generation (EQ RA-SHG), respectively. The ultrafast modulations manifest as the breathing and the rotation of the EQ RA-SHG patterns at three frequencies around the reported single CCDW amplitude mode frequency. A sudden shift of the triplet frequencies and a dramatic increase in the breathing and rotation magnitude further reveal a photo-induced transient CDW phase across a critical pump fluence of ~ 0.5 mJ/cm$^2$.