0428同步年報-2021-全

012 ACTIVITY REPORT 2021 Fig. 3 : CDW–Mott insulator phase in monolayer 1T-TaSe 2 robust against electron doping. (a–c) K-deposition dependence of ARPES intensity along the ΓK cut for monolayer 1T-TaSe 2 [potassium coverage d K = 0 (pristine), 3.2 × 10 13 and 6.4 × 10 13 atoms/cm 2 , respectively], measured at T = 300 K with h ν = 51 eV. (d–f) Same as (a–c), but obtained on taking the second derivative of EDC. (g) EDC at the Γ point for each d K . (h) Plots of intensity at E F with respect to that at LHB, I EF / I LHB , as a function of d K , estimated from the EDC in (g). The I EF / I LHB values for bulk TaS 2 measured at T = 30 and 300 K are also plotted. Error bars reflect uncertainties originating from the energy resolution and statistics of data. [Reproduced from Ref. 4] Fig. 2 : CDW–Mott phase of monolayer 1T-TaSe 2 robust against temperature variation. (a−c) Near- E F ARPES intensity along the ΓK cut measured at T = 40, 300 and 450 K, respectively. (d) Temperature dependence of EDC at the Γ point. EDC for bulk 1T-TaS 2 ( T = 30 and 300 K); bulk 1T-TaSe 2 ( T = 30 K) is also shown as a reference. (e) Squared leading-edge midpoint Δ LEM at the Γ point plotted against T for monolayer 1T-TaSe 2 (blue circles), with results of numerical fitting with the semi- phenomenological (blue solid curve) BCS gap functions. Δ LEM and fitting results are also plotted for bulk 1T-TaS 2 (red). We obtained { T CDW-Mott , A} = {530 K, 1.01} and {180 K, 1.50} for monolayer 1T-TaSe 2 and bulk 1T-TaS 2 , respectively. Error bars in (e) reflect uncertainties originating from energy resolution and standard deviation in the peak positions of EDC. [Reproduced from Ref. 4] The authors further confirmed that the electronic band structure of the CDW-Mott phase was stable also under photoexcitation, using laser-based pump-probe ARPES measurements. From a careful analysis of all the data, the authors showed that the enhanced transition temperature, as well as the Mott-Hubbard and CDW gaps for monolayer 1T-TaSe 2 , originate from (i) a lattice distortion in combination with enhanced electron-electron correlations, and (ii) a disappearance of interlayer hopping in the monolayer limit compared to the bulk. The study 4 thus established an effective method to