Intravalley Andreev reflection in the multi-terminal device with Y-shaped Kekulé graphene superlattices

Abstract

Using the tight-binding model, a multi-terminal superconductor (S) device is proposed, where the structures of the center region are primitive graphene (G) or Y-shaped Kekulé graphene superlattice (GS). The intravalley Andreev reflection is studied in this model through the utilization of the non-equilibrium Green's function method. In the G/S device, due to the time-reverse symmetry the dominant process of Andreev reflection is intervalley reflection. In the three-terminal GS/S device, it has been observed that with the time reversal symmetry the coefficient of intravalley Andreev reflection can surpass that of intervalley reflection in Andreev specular reflection. This is attributed to the coupling between valleys K and -K within the first Brillouin zone, resulting in enhanced intervalley scattering. The valley-dependent transport of Andreev reflection can be influenced by the phase difference between superconductor terminals. The valley polarization of the Andreev retro-reflection and the Andreev specular reflection could be controlled by adjusting the structure of the central region.