1T-TaS 2 undergoes successive phase transitions upon cooling and eventually enters an insulating state of mysterious origin. Some consider this state to be a band insulator with interlayer stacking order, yet others attribute it to Mott physics that support a quantum spin liquid state. Here, we determine the electronic and structural properties of 1T-TaS 2 using angle-resolved photoemission spectroscopy and X-Ray diffraction. At low temperatures, the 2π/2c-periodic band dispersion, along with half-integer-indexed diffraction peaks along the c axis, unambiguously indicates that the ground state of 1T-TaS 2 is a band insulator with interlayer dimerization. Upon heating, however, the system undergoes a transition into a Mott insulating state, which only exists in a narrow temperature window. Our results refute the idea of searching for quantum magnetism in 1T-TaS 2 only at low temperatures, and highlight the competition between on-site Coulomb repulsion and interlayer hopping as a crucial aspect for understanding the material's electronic properties.

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Abstract. On the foundation of the theory of the intuitionistic fuzzy set, this paper uses the triangular fuzzy number to denote the membership degree and the non-membership degree and proposes the triangular intuitionistic fuzzy number. Then the operation rules of triangular intuitionistic fuzzy numbers are defined. The weighted arithmetic averaging operator and the weighted geometric average operator are presented and used to the decision making area after defined the score function and the accuracy function. An effective solution is offered for multi-attitude decision-making problem and an active try is made.

The effect of both remote phonon originating from and the screening of extrinsic charged impurity by substrate and gate dielectric on the electron dynamics of single layer MoS2 are investigated with Monte Carlo method. The temperature-dependent mobility curve measured by Hall effect is reproduced by taking the two counter roles played by substrate and gate dielectric into consideration. Based on the analysis of remote phonon effect and charged impurity screening, an optimized transistor structure which is composed of single HfO2 gate dielectric with interfacial layer and absence of SiO2 substrate is proposed for the realization of mobility approaching intrinsic value and best device performance.