(a) The longitudinal four-terminal resistance of HgTd/CdTe quantum wells as a function of gate voltage measured at T = 30 mK, from Ref. [5]. Device I is a topologically trivial quantum well. Devices II, III, and IV are topologically nontrivial quantum wells. In device IV (1.0 μm × 0.5 μm), at suitable gate voltage, quantum resistance was observed. (b) Transport properties of the 1D edge states in InAs/GaSb bilayers, from Ref. [8]. Conductance plateaus quantized to 2e2/h and 4e2/h, respectively, for the two device configurations shown in the inset, which both have length 2 μm and width 1 μm. |