Asymmetric valley-resolved beam splitting and incident modes in slanted graphene junctions

Abstract

Electron injection into a graphene sheet through a slanted armchair graphene nanoribbon (AGNR) is investigated. An incident mode, or subband, in the AGNR is valley-unpolarized. Our attention is on the valley-resolved nature of the injected electron beams and its connection to the incident mode. It is known for a normal injection that an incident mode will split symmetrically into two valley-resolved beams of equal intensity. We show, in contrast, that slanted injections result in asymmetric valley-resolved beam splitting. The most asymmetric beam splitting cases, when one of the valley-resolved beams has basically disappeared, are found and the condition derived. This is shown not due to trigonal warping because it holds even in the low incident energy regime, as long as collimation allows. These most asymmetric beam splitting cases occur at energies within an energy interval near and include the subband edge of an incident mode. The physical picture is best illustrated by a projection of the slanted AGNR subband states onto that of the 2D graphene sheet. It follows that the disappearing of a valley-resolved beam coincides with the situation that the group velocities of the projected states in the corresponding valley are in backward directions.

Valley-polarized quantum transport generated by gauge fields in graphene

“…Their interpretation proposes that the formation of bulk topological valley cur rents is intertwined with the presence of a Berry curvature generated by the mass term [22], a scenario which is however under serious questioning [23][24][25][26]. Accordingly to date, despite the wealth of theoretical proposals of valley dependent effects [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], exper imental fingerprints of PMF on quantum transport and unambiguous demonstration of a valley Hall effect in graphene remain elusive.…”

“…Their interpretation proposes that the formation of bulk topological valley currents is intertwined with the presence of a Berry curvature generated by the mass term [23], a scenario which is under questioning [24,25]. Accordingly to date, despite the wealth of theoretical proposals of valley dependent effects [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], experimental fingerprints of PMF on quantum transport and unambiguous demonstration of a valley Hall effect in graphene remain elusive.Here, we predict that once the electronic structure of Dirac fermions embeds a strain-related gauge field, it is possible to fine-tune the superposition of an external real magnetic field to reach a resonant effect, where the sum of valley-dependent effective magnetic fields either sum up or cancel each other. This results in a remarkable valley-polarized quantum transarXiv:1705.09085v2 [cond-mat.mes-hall] 1 Jul 2017…”

Valley Filtering and Electronic Optics Using Polycrystalline Graphene

“…In analogy with spintronics, manipulating carriers in these two valleys can be used to encode data, i.e., to represent the zeroes and ones in digital computing. To date, many strategies [5][6][7][8][9] have been proposed to break the valley degeneracy for creating and detecting the valley polarization in graphene. They mainly rely on the valley filtering effects and/or the generation of spatially-separated valley-resolved currents in graphene nanostructures.…”

Charge, Spin and Valley Hall Effects in Disordered Graphene

“…This phenomenon can be exploited to realize valley filters, where the valley selection is performed by changing the direction of the magnetic field generated by ferromagnetic stripes [219,220,[222][223][224]. Other proposals are based on the valley-dependent anisotropy introduced by trigonal warping [225,226], slanted graphene junctions [227] or bilayer graphene [228][229][230][231].…”