Tunneling conductance of a magnetized zigzag graphene nanoribbon/superconductor junction

Abstract

The zigzag graphene nanoribbon (ZGNR) has very peculiar electronic structure and transport properties such as the edge state, spontaneous magnetization, and the even-odd effect. In this work, we report a theoretical study on the interplay between the magnetization and pseudoparity of the particle, and their combined effect on the tunneling conductance spectra of the ZGNR/superconductor junction. It is shown that the magnetization in ZGNR can significantly modify the original even-odd effect in nonmagnetic ZGNR due to the definite pseudoparity of the particles. For the ferromagnetic ZGNR that can be obtained by an external magnetic field or the proximity effect through a ferromagnet on ZGNR, the Andreev reflection (AR), which is entirely prohibited in the nonmagnetic ZGNR with an even zigzag chain number, is now allowed only for one kind of spin; thus the system resembles a spin-diode device in which only one spin species AR can occur under positive bias while the other spin species AR occurs under negative bias. For the antiferromagnetic ZGNR with weak magnetization, the conductance gap appears at Fermi energy due to the insulating property of ZGNR; in addition, AR is also possible for the even ZGNR, and two conductance peaks appear in the superconductor energy gap, which is attributed to the pseudoparity of the edge state destroyed by the antiferromagnetic ordering in ZGNR. For the odd ZGNR, either ferromagnetic or antiferromagnetic magnetization has no qualitative influence on the conductance spectra of the junction. Our findings may shed light on devising spin devices based on magnetized graphene nanoribbons.