Ultrafast creation of a light induced semimetallic state in strongly excited 1T-TiSe$_2$

TL;DR

This study demonstrates that intense optical excitation can rapidly induce a semimetallic state in 1T-TiSe$_2$ by reducing screening length, revealing a new ultrafast pathway to control quantum phases in correlated materials.

Contribution

It shows that ultrafast optical excitation can drive a charge density wave material into a semimetallic state by modulating screening, a novel dynamic control method.

Findings

Optical excitation induces a transition from gapped to semimetallic state.

The transition occurs almost instantly after excitation.

Reduction of screening length is likely responsible for the phase change.

Abstract

Screening, a ubiquitous phenomenon associated with the shielding of electric fields by surrounding charges, has been widely adopted as a means to modify a material's properties. While so far most studies have relied on static changes of screening through doping or gating, here we demonstrate that screening can also drive the onset of distinct quantum states on the ultrafast timescale. By using time and angle-resolved photoemission spectroscopy we show that intense optical excitation can drive 1T-TiSe$_2$, a prototypical charge density wave material, almost instantly from a gapped into a semimetallic state. By systematically comparing changes in bandstructure over time and excitation strength with theoretical calculations we find that the appearance of this state is likely caused by a dramatic reduction of the screening length. In summary, this work showcases how optical excitation enables the screening driven design of a non-equilibrium semimetallic phase in TiSe$_2$, possibly providing a general pathway into highly screened phases in other strongly correlated materials.