Study Of Andreev Reflection On Carbon Based Materials Under Photoelectric Modulation

Andreev reflection is a fundamental scattering process that occurs in metallic superconductor heterojunctions and has become a research hotspot in recent years.The principle is that the incident electrons from the metal are reflected as holes at the interface of the metallic superconductor and form Cooper pairs in the superconductor.It has been found that Andreev reflection can occur in some new two-dimensional materials,such as graphene,silicene,transition metal disulfides,etc.,in addition to metal materials.Among them,the electrons in graphene have spin and charge degrees of freedom,and there are also valley degrees of freedom like spin degrees of freedom,so the presence of graphene makes Andreev reflection appear at the interface of graphene superconducting heterojunction.In the single-junction interface of graphene superconducting heterojunction,in addition to the foldback Andreev reflection of superconducting metal heterojunction,a unique specular Andreev reflection also occurs;while in the double-junction,in addition to the single-junction mentioned above local Andreev reflection,a non-local cross Andreev reflection also occurs.Based on this,this paper focuses on the Andreev reflections of single-junction and double-junction models of graphene/superconductor heterojunctions under the joint regulation of circularly polarized optical field,exchange field,and crossover potential.The main contents are as follows:1.The properties of folded-back Andreev reflection and specular Andreev reflection in the non-resonant circularly polarized light field,exchange field,and interleaving potential jointly regulated by graphene superconductor heterojunction are investigated.It is found that the band gap and the energy band are closely related between the foldback Andreev reflection and the specular Andreev reflection.The band gap between the foldback Andreev reflection and specular Andreev reflection can be changed by adjusting the optical field.Further,when the light field is equal to the crossover potential energy,the Dirac point appears in the energy band,making the transition point between the foldback Andreev reflection and the specular Andreev reflection appear.In addition,the position of the Dirac point can be controlled by exchanging the field.Therefore,the work in this paper can distinguish and regulate the foldback Andreev reflection and specular Andreev reflection well.2.The properties of crossed Andreev reflection as well as elastic co-tunneling conductivity are systematically investigated in a graphene superconducting heterojunction double-junction structure regulated by a non-resonant circularly polarized optical field,an exchange field,and a crossed potential.It is found that pure cross-Andreev reflection conductivity can be converted to pure elastic co-tunneling conductivity by changing the light on the right side from the left circularly polarized light to the right circularly polarized light.And by changing the exchange field,pure elastic co-tunneling and pure cross-Andreev reflection alone are achieved.Therefore,the structure can realize pure cross-Andreev reflection and spin-valley switching controlled by optical and exchange fields.In conclusion,the work in this paper provides some interesting insights into multi-interface correlated transport,and its findings are helpful for spintronic devices based on graphene materials.