Pure thermal spin current and perfect spin-filtering with negative differential thermoelectric resistance induced by proximity effect in graphene/silicene junctions

Zainab Gholami,Farhad Khoeini

doi:10.1038/s41598-020-80616-3

Abstract

The spin-dependent Seebeck effect (SDSE) and thermal spin-filtering effect (SFE) are now considered as the essential aspects of the spin caloritronics, which can efficiently explore the relationships between the spin and heat transport in the materials. However, there is still a challenge to get a thermally-induced spin current with no thermal electron current. This paper aims to numerically investigate the spin-dependent transport properties in hybrid graphene/silicene nanoribbons (GSNRs), using the nonequilibrium Green’s function method. The effects of temperature gradient between the left and right leads, the ferromagnetic exchange field, and the local external electric fields are also included. The results showed that the spin-up and spin-down currents are produced and flow in opposite directions with almost equal magnitudes. This evidently shows that the carrier transport is dominated by the thermal spin current, whereas the thermal electron current is almost disappeared. A pure thermal spin current with the finite threshold temperatures can be obtained by modulating the temperature, and a negative differential thermoelectric resistance is obtained for the thermal electron current. A nearly zero charge thermopower is also obtained, which further demonstrates the emergence of the SDSE. The response of the hybrid system is then varied by changing the magnitudes of the ferromagnetic exchange field and local external electric fields. Thus, a nearly perfect SFE can be observed at room temperature, whereas the spin polarization efficiency is reached up to 99%. It is believed that the results obtained from this study can be useful to well understand the inspiring thermospin phenomena, and to enhance the spin caloritronics material with lower energy consumption.

Highlights

The spin caloritronics has constructed the subject of many researches in recent y ears[1,2,3]
A hybrid nanoribbon system is first defined and subjected to different local external fields, including the perpendicular electric (EZ) and ferromagnetic exchange (Mz) fields, which are applied to the central region
A ferromagnetic exchange field can be created by the proximity with a ferromagnetic insulator EuO as suggested for GE74

Summary

Introduction

The spin caloritronics has constructed the subject of many researches in recent y ears[1,2,3]. GE has uncommon transport properties, which are related to its unusual electronic s tructure[29,30] This is especially true around the Fermi level, where the charge carriers behave similar to massless particles. SE and GE have similar electronic structures near the Fermi level and can result in the massless Dirac fermions[38] This concept is widely used for developing the high-performance field-effect transistors[39]. One of the properties of SE is that it has a larger bandgap, induced by the spin–orbit interaction (SOI) This establishes the quantum spin Hall e ffect[40], and has a significant role in spin transport and spintronic devices. Several studies have been carried out by researchers to investigate the charge and spin thermal transport properties of the SE43–45

Objectives

Results

Conclusion