Abstract
In a noncentrosymmetric system, an intrinsic electric
polarization is allowed and may lead to
unusual nonreciprocal charge transport phenomena. As a result, a current-dependent resistance,
arising from the magnetoelectric anisotropy term of k · E × B, appears and acts as a current
rectifier with the amount of rectification being linearly proportional to the magnitude of both
current and applied magnetic field. In this work, a different type of nonreciprocal transport effect
was demonstrated in a graphene-based device, which requires no external magnetic field. Owing to
the unique pseudospin (valley) degree of freedom in chiral fermions with trigonal warping, a large
nonreciprocal transport effect was uncovered in a gapped bilayer graphene, where electric-field
tunabilities of the band gap and valley polarization play an important role. The exact cancellation
of nonreciprocal effect between two different valleys is effectively removed by breaking the inversion
symmetry via electric gatings. The magnitude of the current rectification appears to be at a
maximum when the Fermi surface undergoes a Lifshitz transition near the band edges, which is
proportional to the current and the displacement field strength. The full electric-field tuning of the
nonreciprocal transport effect without a magnetic field opens up a new direction for valleytronics
in two-dimensional based devices.