Chiral Pseudogap Metal Emerging from a Disordered Van der Waals Mott Insulator 1T-TaSSe.

The emergence of a pseudogap is a hallmark of anomalous electronic states formed through substantial manybody interaction but the mechanism of the pseudogap formation and its role in related emerging quantum states such as unconventional superconductivity remain largely elusive. Here, the emergence of an unusual pseudogap in a representative van der Waals chiral charge density wave (CDW) materials with strong electron correlation, 1T-TaS is reported, through isoelectronic substitute of S. The evolution of electronic band dispersions of 1T-TaSSe (0 ⩽ x ⩽ 2) is systematically investigated using angle-resolved photoemission spectroscopy (ARPES). The results show that the Se substitution induces a quantum transition from an insulating to a pseudogap metallic phase with the CDW order preserved. Moreover, the asymmetry of the pseudogap spectral function is found, which reflects the chiral nature of CDW structure. The present observation is contrasted with the previous suggestions of a Mott transition driven by band width control or charge transfer. Instead, the pseudogap phase is attributed to a disordered Mott insulator in line with the recent observation of substantial lateral electronic disorder. These findings provide a unique electronic system with chiral pseudogap, where the complex interplay between CDW, chirality, disorder, and electronic correlation may lead to unconventional emergent physics.