Valley-dependent tunneling through electrostatically created quantum dots in heterostructures of graphene with hexagonal boron nitride

Kelvin probe force microscopy (KPFM) has been employed to probe charge carriers in a graphene/hexagonal boron nitride (hBN) heterostructure [Nano Lett, 21, 5013 (2021)]. We propose an approach for operating valley filtering based on the KPFM-induced potential \(U_0\) instead of using external or induced pseudo-magnetic fields in strained graphene. Employing a tight-binding model, we investigate the parameters and rules leading to valley filtering in the presence of a graphene quantum dot (GQD) created by the KPFM tip. This model leads to a resolution of different transport channels in reciprocal space, where the electron transmission probability at each Dirac cone (\(K_1\)= -K and \(K_2\) = +K) is evaluated separately. The results show that U0 and the Fermi energy \(E_F\) control (or invert) the valley polarization, if electrons are allowed to flow through a given valley. The resulting valley filtering is allowed only if the signs of \(E_F\) and \(U_0\) are the same. If they are different, the valley filtering is destroyed and might occur only at some resonant states affected by \(U_0\). Additionally, there are independent valley modes characterizing the conductance oscillations near the vicinity of the resonances, whose strength increases with \(U_0\) and are similar to those occurring in resonant tunneling in quantum antidots and to the Fabry-Perot oscillations. Using KPFM, to probe the charge carriers, and graphene-based structures to control valley transport, provides an efficient way for attaining valley filtering without involving external or pseudo-magnetic fields as in previous proposals.