A proposed experimental diagnosing of specular Andreev reflection using the spin orbit interaction.

Yanling Yang,Bing Zhao,Xiaoguang Xu,Ziyu Zhang,Yong Jiang,Chunxu Bai

doi:10.1038/srep29279

Abstract

Based on the Dirac-Bogoliubov-de Gennes equation, we theoretically investigate the chirality-resolved transport properties through a superconducting heterojunction in the presence of both the Rashba spin orbit interaction (RSOI) and the Dresselhaus spin orbit interaction (DSOI). Our results show that, if only the RSOI is present, the chirality-resolved Andreev tunneling conductance can be enhanced in the superconducting gap, while it always shows a suppression effect for the case of the DSOI alone. In contrast to the similar dependence of the specular Andreev zero bias tunneling conductance on the SOI, the retro-Andreev zero bias tunneling conductance exhibit the distinct dependence on the RSOI and the DSOI. Moreover, the zero-bias tunneling conductances for the retro-Andreev reflection (RAR) and the specular Andreev reflection (SAR) also show a qualitative difference with respect to the barrier parameters. When the RSOI and the DSOI are finite, three orders of magnitude enhancement of specular Andreev tunneling conductance is revealed. Furthermore, by analyzing the balanced SOI case, we find that the RAR is in favor of a parabolic dispersion, but a linear dispersion is highly desired for the SAR. These results shed light on the diagnosing of the SAR in graphene when subjected to both kinds of SOI.

Highlights

Based on the Dirac-Bogoliubov-de Gennes equation, we theoretically investigate the chirality-resolved transport properties through a superconducting heterojunction in the presence of both the Rashba spin orbit interaction (RSOI) and the Dresselhaus spin orbit interaction (DSOI)
Besides the Desselhaus spin orbit interaction (DSOI) induced by bulk inversion asymmetry, which can be tuned by exploiting interfacial interactions[17], there is another type of spin orbit interaction (SOI) induced by structure inversion asymmetry, the Rashba spin orbit interaction (RSOI), which can be tuned by the external gate voltages[12,13,14,15], adatoms[18], and substrate emerging[19]
The component of momentum kx excitation spectrum εγ+ and in the left, central, εγ− originate from and right lead corresponds to the conduction band and the valence band, respectively. It is well-known that the specular Andreev reflection (SAR) occurs when the reflected hole travels in the valence band below the neutrality point, while the retro-Andreev reflection (RAR) corresponds to a conduction band hole

Summary

Graphene flake

Along with the metallic, semiconducting, and topological insulating states, superconducting state is one of the major and the amazing states in graphene. A considerable experimental progress has been steadily made in hunting the SAR where an unprecedentedly clean bilayer graphene-based superconducting heterojunction has been developed and a key point for the transition between the usual retro-Andreev reflection (RAR) and the special SAR has been revealed[43]. The sub-gap tunneling conductance for the SAR case, in sharp contrast to its counterpart in conventional RAR case where it always increases with increasing incident energy, becomes non-monotonic and reaches a maximum at a certain finite incident energy The emergence of those qualitative differences resulted from the acquisition of the AR hole localized in which band (conduction or valance) may give birth to a new way to diagnose the SAR in the actual experiments

Model and Basic Formalism

Results and Discussion

Conclusion

Additional Information