Studying materials under the immense pressure of a diamond anvil cell (DAC) is key to discovering new states of matter, but a major hurdle has been the inability to directly measure their electronic properties. Our work overcomes this challenge by successfully implementing solid-state high harmonic generation (sHHG) spectroscopy inside a DAC.
By probing Molybdenum Disulfide (MoS₂) up to 30 GPa, we detected a pressure-induced crossover of its primary bandgap. This subtle electronic transition, confirmed by our first-principles simulations, manifested as a sharp, clear signal in our measurements—a minimum in harmonic intensity and a 30° rotation in the light’s polarization—all without any change to the material’s physical structure. Our results establish sHHG as a uniquely sensitive probe for exploring the electronic world of materials at high pressure.

The preprint can be found here: https://arxiv.org/abs/2506.14215