Unconventional orbital-charge density wave mechanism in transition metal dichalcogenide 1T-TaS₂

The transition metal dichalcogenide 1T-TaS₂ attracts growing attention because of the formation of rich density-wave (DW) and superconducting transitions. However, the origin of the incommensurate DW state below T_IC≈550K, which is the ``parent state'' of the rich physical phenomena, are still uncovered. Here, we attack this fundamental problem by focusing on the spin-fluctuation-driven DW mechanism that has been developed in the study of Fe-based and cuprate superconductors [1-2]. We derive the optimized form factor, which is DW order parameter with momentum, orbital, and energy dependences, by applying the DW equation method developed in Refs. [1-2] to the eight-orbital Hubbard model for 1T-TaS_2. The obtained triple-q orbital-charge DW state satisfactorily explains the incommensurate DW state in 1T-TaS₂. The predicted orbital-selective form factor with unconventional sign-reversal in both momentum and energy spaces would be measurable by the ARPES study. The present study gives a fundamental information to understand the rich physics in 1T-TaS₂. [1] S. Onari and H. Kontani, Phys. Rev. Lett. 109, 137001 (2012). [2] S. Onari and H. Kontani, Phys. Rev. Research 2, 042005 (2020).