Condensed matter dark state with two pairs of sublattices

Yoonah Chung

In quantum physics, there are quantum states of matter undetectable by a spectroscopic means, which is called dark states. By extending this concept of dark states to condensed matter, we found a novel concept of condensed matter dark states that cannot be measured by angle-resolved photoemission spectroscopy (ARPES) under any experimental conditions, such as light polarization and scattering geometry. Our model to explain the mechanism of dark states is based on the tight-binding approximation that condensed matter dark states arise from double destructive interference of initial-state wavefunctions between two pairs of sublattices. We demonstrate this mechanism in palladium diselenides (PdSe₂) as a model system. In the unit cell, there are four sublattices of palladium that are connected by multiple glide-mirror symmetries. The ARPES signal from the valence band of PdSe₂ is not detected in some of the entire Brillouin zones. The relative phases between sublattices are completely polarized to one of the four kinds in each Brillouin zone, arranged zone by zone in the checkerboard patterns. We generalize the mechanism of dark states to the other materials having similar structural properties such as cuprates.