Spin-filtered and Spatially Distinguishable Crossed Andreev Reflection in a Silicene-Superconductor Junction

TL;DR

This paper theoretically demonstrates spin-polarized, spatially distinguishable crossed Andreev reflection in a silicene-superconductor junction, revealing high-efficiency nonlocal quantum interference and Josephson oscillations due to topological edge states.

Contribution

It introduces a novel mechanism for achieving high-fraction, spin-polarized crossed Andreev reflection with spatial separation in silicene nanoribbons, leveraging topological edge states and symmetry breaking.

Findings

Crossed Andreev reflection fraction exceeds 50% in narrow silicene nanoribbons.

Transport channels are spatially separated and spin-polarized due to helicity conservation.

Josephson oscillations with near 100% efficiency are observed when connecting superconducting leads.

Abstract

We theoretically investigate the quantum transports in a junction between a superconductor and a silicene nanoribbon, under the effect of a magnetic exchange field. We find that for a narrow nanoribbon of silicene, remarkable crossed Andreev reflection (with a fraction $>50\%$) can be induced in the energy window of the elastic cotunneling, by destroying some symmetries of the system. Since the energy responses of electrons to the exchange field are opposite for opposite spins, these transport channels can be well spin polarized. Moreover, due to the helicity conservation of the topological edge states, these three transport channels are spatially separated in three different locations of the device, making them experimentally distinguishable. This crossed Andreev reflection is a nonlocal quantum interference between opposite edges through evanescent modes. If two superconducting leads with different phases are connected to two edges of the silicene nanoribbon, the crossed Andreev reflection can present Josephson type oscillations, with a maximal fraction $\sim 100\%$.