PhD Seminar - Emergence of a Fermi-surface in the current-driven hidden state of 1T-TaS2

1T-TaS₂ undergoes a metal-insulator transition at low temperatures, forming a correlated insulating state whose underlying nature remains a topic of active debate. This state, however, is fragile, and the system can be driven into a meta-stable metallic state through the application of a current pulse, emerging from the commensurate charge-density wave (C-CDW) state.

Using nano-ARPES, we have, for the first time, directly measured the emergence of a Fermi surface in this hidden metallic state. Our data reveal that, despite distinct morphological differences, the hidden-metallic state bears a strong resemblance to the nearly commensurate CDW (NC-CDW) phase. Moreover, by comparing the out-of-plane dispersion of these two states, we find that while the unit cell size in the C-CDW state is twice the interlayer separation—suggesting possible dimerization—in the metallic state, the atomic unit size is restored.

Our results emphasize the critical role of interlayer interactions in this system and strongly support interlayer dimerization as the origin of the insulating ground state in 1T-TaS₂.