Isostructural electronic transition in MoS$_2$ probed by solid-state high harmonic generation spectroscopy

TL;DR

This study demonstrates that solid-state high harmonic generation spectroscopy can directly probe pressure-induced electronic transitions in MoS$_2$ within diamond anvil cells, revealing a crossover in the material's electronic structure without structural change.

Contribution

The paper introduces the use of sHHG spectroscopy inside DACs to detect electronic transitions under high pressure, providing a new optical method for studying quantum phenomena in materials.

Findings

Identification of a pressure-induced crossover from K-point to Gamma-point in MoS$_2$

Observation of a sharp minimum in harmonic intensity at transition pressure

Detection of a 30-degree rotation in harmonic polarization anisotropy

Abstract

Studying materials under extreme pressure in diamond anvil cells (DACs) is key to discovering new states of matter, yet no method currently allows the direct measurement of the electronic structure in this environment. Solid-state high harmonic generation (sHHG) offers a new all-optical window into the electronic structure of materials. We demonstrate sHHG spectroscopy inside a DAC by probing $2H$-MoS$_2$, up to 30 GPa, revealing a pressure-induced crossover of the lowest direct bandgap from the $\textbf{K}$-point to the $\Gamma$-point. This transition manifests as a sharp minimum in harmonic intensity and a 30{\deg} rotation of the sHHG polarization anisotropy, despite the absence of a structural phase change. First-principles simulations attribute these features to interference between competing excitation pathways at distinct points in the Brillouin zone. Our results establish sHHG as a sensitive probe of electronic transitions at high pressure, enabling access to quantum phenomena that evade detection by conventional techniques.