Coherent Transport in Y-Junction Graphene Waveguide

TL;DR

This paper investigates electron transport in Y-junction graphene waveguides using NEGF with tight-binding models, revealing conductance quantization and valley degeneracy effects influenced by geometry.

Contribution

It introduces a detailed theoretical analysis of Y-branch graphene waveguides employing NEGF with various tight-binding approximations, highlighting the impact of geometry and valley effects.

Findings

Pronounced conductance quantization with 4e^2/h spacing.

Deviations from multiples of 4e^2/h indicating valley degeneracy lift.

Geometry significantly influences energy channels and transport properties.

Abstract

We performed a series of theoretical transport studies on Y-branch electron waveguides which are embedded in mid-size armchair graphene nanoribbons (AGNRs). Non-equilibrium Greens function (NEGF) with different approximations of tight-binding (TB) Hamiltonian has been employed. Using the first nearest hopping approximation, we observed very pronounced conductance quantization, the structure of which depends on geometrical design and shows a spacing of $4e^2/h$, indicating the existence of valley degree of freedom. Moreover, by incorporating the third nearest approximation, we observed seminal plateaus deviated from multiples of $4e^2/h$ conductance, suggesting the lift of valley degeneracy. Finally, Quasi-one dimensional band structure calculations have been performed to study the availability of energy channels and the role of the major geometrical parameters on the transport.