Phase-resolved frequency-domain analysis of the photoemission spectra for photoexcited 1T-TaS2 in the Mott insulating charge density wave state

TL;DR

This study uses frequency-domain photoemission spectroscopy to analyze how photoexcitation affects the electronic structure and Mott gap in 1T-TaS2, revealing coherent phonon oscillations and the robustness of the CDW phase.

Contribution

It introduces frequency-domain ARPES analysis to dynamically study the interplay between charge density waves and Mott insulating states in 1T-TaS2.

Findings

Photoexcitation collapses the Mott gap, inducing metallicity.

Coherent phonons modulate the band structure in sync with the CDW amplitude mode.

The CDW phase remains robust despite Mott gap reduction.

Abstract

We investigate the nonequilibrium electronic structure of 1T-TaS2 by time- and angle-resolved photoemission spectroscopy. We observe that strong photoexcitation induces the collapse of the Mott gap, leading to the photo-induced metallic phase. It is also found that the oscillation of photoemission intensity occurs as a result of the excitations of coherent phonons corresponding to the amplitude mode of the charge density wave (CDW). To study the dynamical change of the band dispersions modulated by the CDW amplitude mode, we perform analyses by using frequency-domain angle-resolved photoemission spectroscopy (FDARPES). We find that two different peak structures exhibit anti-phase oscillation with respect to each other by retrieving the amplitude and phase parts of the FDARPES spectra. They are attributed to the minimum and maximum band positions in energy, where the single band is oscillating between them synchronizing with the CDW amplitude mode. We further find that the flat band constructed as a result of CDW band folding survives during the oscillation while the Mott gap is significantly reduced. Our results suggest the CDW phase is robust, and the lattice modulation corresponding to the CDW amplitude mode dynamically modulates the Mott gap.