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Topological suppression of magnetoconductance oscillations in normal–superconductor junctions

Osca, Javier; Serra, Llorenç
Physica Status Solidi B , 1700135 (2017)

We show that the magnetoconductance oscillations of laterally- confined two-dimensional (2D) normal–superconductor (NS) junctions are completely suppressed when the superconduc- tor side enters a topological phase. This suppression can be attributed to the modification of the vortex structure of lo- cal currents at the junction caused by the topological transi- tion of the superconductor. The two regimes (with and without 1 Introduction Magnetoconductance oscillations are a central topic of the field of quantum transport in nanostruc- tures. Famous examples are the celebrated Aharonov–Bohm oscillations in a quantum ring and the Shubnikov–deHass os- cillations in the quantum Hall effect [1]. In a general sense, the accumulation of complex phases (angles) in the wave function during orbital motion in a perpendicular magnetic field is the basic cause behind the magnetoconductance oscil- lations. In presence of a superconductivity pairing gap, trans- port can be described as the propagation of electron and hole quasiparticles, with Andreev processes allowing the trans- formation of one type into the other. Andreev reflections in a normal–superconductor (NS) junction are affected by a mag- netic field acting on the normal side, the field thus modifying the magnetoconductance of the junction. The interplay of Andreev reflection and magnetic or- bital effects has received a long lasting attention [2–11]. In particular, Takagaki [3] studied the magnetoconductance of a two-dimensional (2D) NS junction, laterally confined to a width Ly and with the N terminal being a semicon- ductor. As the magnetic field is increased, the magnetocon- ductance tends to decrease in a stepwise manner due to the oscillations) could be seen in a semiconductor 2D junction with a cleaved-edge geometry, one of the junction arms having prox- imitized superconductivity. We predict similar oscillations and suppression as a function of the Rashba coupling. The oscilla- tion suppression is robust against differences in chemical po- tential and phases of lateral superconductors.