High-temperature quantum valley Hall effect with quantized conductance at zero magnetic field

Topological edge states offer an excellent platform to study 1D physics and develop functional elements for quantum electronics. Achieving a robust conductance quantization, the hallmark of ballistic transport, is challenging for helical edge states. Previous work from our lab [1-2] has demonstrated that Bernal-stacked bilayer graphene supports the quantum valley Hall effect through electrically defined band inversion, and the resulting topological edge channel, namely the kink states, can perform the operations of a valley valve, waveguide and tunable beam splitter. In this talk, I'll discuss our recent effort to achieve quantized resistance plateaus at zero magnetic field by improving device quality. The resistance plateau is wide in gate sweeps and remains constant as the temperature changes from mK to Kelvins. It changes by only 1% at 12 K and 3% at 46 K, due to the activation of bulk conduction. We demonstrate the operation of a topological switch toggling between conductance 0 and 4e²/h by controlling the existence/absence of the kink states. The excellent ballisticity and maneuverability of the kink states make it a good candidate for developing a quantum interconnect network.

[1] Li. et al., Nat. Nano. 11, 1060 (2016), [2] Li et al., Science 362, 1149 (2018)