Valley-selective Channels in Strained Graphene Wrinkles

Pristine graphene has two degenerate valleys with linear dispersion. Under the influence of strain, the shift of the carbon atoms generates a vector potential which can give rise to a so-called pseudo-magnetic (PM) field. Unlike a real magnetic field, the PM field has opposite signs in the two valleys and provides a handle to control the valley degree of freedom. Theory has shown that in a strained wrinkle with Gaussian shape, the propagation of carriers along the wrinkle is valley-selective [1]. The carriers from one valley can only move in one direction while the ones from the other valley move in the opposite direction. By transferring single-layer graphene on top of an array of pillars fabricated on the surface of hBN, we generate strained wrinkles in a controllable way [2]. Measuring the magneto and Hall resistance as a function of field and carrier density at low temperatures, we observe a series of quantum conductance plateaus. Surprisingly, we find that all the plateaus are shifted by two units of quantum conductance. Using the Landauer-Buttiker formalism we show that this shift is a direct consequence of a valley selective channel along the wrinkle.
[1] Phys. Rev. B 94, 125422 (2016)
[2] Nano Lett. 17, 2839 (2017)