Photo-excitation band-structure engineering of 2H-NbSe$_2$ probed by time- and angle-resolved photoemission spectroscopy

TL;DR

This study uses time- and angle-resolved photoemission spectroscopy to explore how strong photo-excitation modulates the electronic band structure of 2H-NbSe$_2$, revealing potential for light-controlled material functionalities.

Contribution

It demonstrates band structure engineering in 2H-NbSe$_2$ through photo-excitation and correlates structural changes with electronic dynamics, supported by DFT calculations.

Findings

Photo-excitation increases photoelectron intensities near E_F.

Variation in Se height significantly affects band structure.

Faster carrier relaxation at K-centered Fermi surface.

Abstract

We investigated the nonequilibrium electronic structure of 2H-NbSe$_2$ by time- and angle-resolved photoemission spectroscopy. We find that the band structure is distinctively modulated by strong photo-excitation, as indicated by the unusual increase in the photoelectron intensities around E$_F$. In order to gain insight into the observed photo-induced electronic state, we performed DFT calculations with modulated lattice structures, and found that the variation of the Se height from the Nb layer results in a significant change in the effective mass and band gap energy. We further study the momentum-dependent carrier dynamics. The results suggest that the relaxation is faster at the K-centered Fermi surface than at the $\Gamma$-centered Fermi surface, which can be attributed to the stronger electron-lattice coupling at the K-centered Fermi surface. Our demonstration of band structure engineering suggests a new role for light as a tool for controlling the functionalities of solid-state materials.