Disorder driven Charge Density Wave superlattice structure and potential Quantum Spin Liquid behavior in 1T-TaS₂ and 1T-TaSe₂

The transition metal dichalcogenide 1T-TaS_2-xSe_x is an interesting system due to the multiple phase transitions both as a function of doping and temperature, that includes charge density wave (CDW) states, Mott insulator, superconductivity and more recently, quantum spin liquid (QSL) state. 1T-TaS₂, undergoes a series of phase transitions upon cooling, acquiring a commensurate CDW (CCDW) phase below 183 K. Moreover, the CCDW transition is accompanied by a periodic lattice distortion that forms a √13×√13 supercell creating  the so-called Star-of-David motif. The Star-of-David formation alone cannot explain the electronic behavior of 1T-TaS₂ such as the QSL behavior, superconductivity, and the metal-insulator transition (MIT). From our recent work on this system, we observed clear evidence that the low-temperature crystal structure deviates from the long-range symmetry (P-3m1). Pair distribution function analysis suggests in-plane displacements of Ta atoms in 1T-TaS₂ in the CDW phase which shows significant differences from the model based on average structure. Distortions at the 12 Ta atoms making up the outer rim of the star are present in both 1T-TaS₂ and 1T-TaSe₂, which may very well lead to distortions in the spin structure.