Inverted David Stars in van der Waals charge-density wave materials:
Rashba flat bands, spin Hall effect, Chern insulator, and spin liquids
2D Van der Waals charge-density wave materials demonstrated a surprisingly diverse set of emergent quantum phenomena, including superconductivity, Mott insulators, topological insulators, and spin liquids [1-4, 7]. For example, the low-dimensional domain walls and its conducting channels in these materials give rise to the unusually-stable flat bands [1, 2] and non-Fermi liquids [3]. When the domain walls are gapped due to appropriate perturbations, they can realize the higher-order topological insulators with corner states [2, 4-6]. In understanding these phenomena, the formation of a very particular CDW, known as the David star, was essential. In this talk, I will present our recent studies [7] on a possible alternative charge density wave of monolayer 1T-Transition Metal Dichalcogenides (TMD). While the David star has been conventionally considered as the underlying charge order in the literature, recent tunneling probe experiments on monolayer samples have motivated us to explore an alternative structure: the inverted David star. In sharp contrast with the David star, the inverted David star manifestly breaks the inversion symmetry, resulting in flat bands with pronounced Rashba spin-orbit couplings. These distinctive features unlock novel possibilities and functionalities for 1T-TMDs, including the giant spin Hall effect, the emergence of Chern bands, and spin liquids that can break rotational or time-reversal symmetries.
[1] Emergent honeycomb network of topological excitations in correlated charge density wave, Nature Communications 10, 4038 (2019)
[2] Stable flatbands, topology, and superconductivity of magic honeycomb networks, Physical Review Letters 124, 137002 (2020)
[3] Non-Fermi liquids in conducting two-dimensional networks, Physical Review Letters 126, 186601 (2021)
[4] Mobile kink solitons in a van der Waals charge-density wave layer, Advanced Materials, 2300160 (2023)
[5] Higher-order topological insulators in twisted bilayer graphene, Physical Review Letters 123, 216803 (2019)
[6] Many-body invariants for Chern and chiral hinge insulators, Physical Review Letters 126, 016402 (2021)
[7] Electronic States of Inverted David Stars in 1T-Transition Metal Dichalcogenides, in preparation