Creation of a novel inverted charge density wave state

TL;DR

This paper reports the discovery of a new inverted charge density wave state in 1T-TaSe2 induced by femtosecond laser over-driving, revealing unique lattice, charge, and electronic properties through advanced spectroscopy and theoretical analysis.

Contribution

It introduces a novel inverted CDW state created by ultrafast laser excitation, with detailed experimental and theoretical characterization of its unique properties.

Findings

Identification of a new inverted CDW state in 1T-TaSe2

Enhanced density of states near the Fermi level

Increased metallicity and altered electron-phonon coupling

Abstract

Charge density wave (CDW) order is an emergent quantum phase that is characterized by a periodic lattice distortion and charge density modulation, often present near superconducting transitions. Here we uncover a novel inverted CDW state by using a femtosecond laser to coherently over-drive the unique star-of-David lattice distortion in 1T-TaSe$_2$. We track the signature of this novel CDW state using time- and angle-resolved photoemission spectroscopy and time-dependent density functional theory, and validate that it is associated with a unique lattice and charge arrangement never before realized. The dynamic electronic structure further reveals its novel properties, that are characterized by an increased density of states near the Fermi level, high metallicity, and altered electron-phonon couplings. Our results demonstrate how ultrafast lasers can be used to create unique states in materials, by manipulating charge-lattice orders and couplings.