Fig. 3: Magnetic-field dependence of conductance and scanning tunnel spectroscopy (STS) spectra.
From: Room-temperature quantum spin Hall phase in laser-patterned few-layer 1T′- MoS2
a Out-of-plane magnetic-field (B⊥) dependence of conductance at gate voltages corresponding to the R plateaus in Fig. 2b, d (red and blue symbols) and away from them (black symbol). Insets: schematic views of band diagrams with the Fermi level (EF; red lines) near and away from Kramers degeneracy point (KDP) for each Vbg. Black symbols remain almost unchanged on increasing B⊥, suggesting that EF stays away from KDP (left upper inset). In contrast, red and blue symbols exponentially decrease with B⊥, suggesting that EF at B⊥ = 0 stays near KDP (left lower inset) as a Zeeman gap opens with increasing B⊥ (right inset). These results support our interpretation that the R plateau values in Fig. 2b, d originate from the quantum spin Hall (QSH) phase. b Examples of STS spectra for laser-irradiated 1T′ region. The two bulk signals (blue and green curves) were measured near the center of the 1T′ region, and the edge signals (red solid and dotted curves) were measured near the boundary of the 1T′/2H phases. Vbg was set to +35 V (R maximum) and +10 V (away from it) for the three solid curves and the dotted one, respectively. Insets: schematic views of band diagrams as in a. The red dotted curve with non-zero dI/dV values suggests that EF lies away from the bulk gap (upper inset). In contrast, gaps of varying magnitudes are manifest in the other three solid curves, suggesting that EF lies in the bulk gap near KDP, as expected for the QSH phase. c Distribution of bulk gaps Δ observed by STS on 10 different bulk points along the sample longitudinal direction in the 1T′ regions at T = 2 K and Vbg ∼35 V. Red and black symbols correspond to Δ values obtained under 4.6-mW- and 17-mW-power laser beam irradiation, respectively. Error bars show the dispersion obtained from measuring on three different spots (within ∼50 nm distance) at the same longitudinal position. The larger Δ values with the smaller dispersion of the red symbols suggest an improvement of the 1T′ crystal quality upon a reduction of laser power.
