Interaction effects on a Majorana zero mode leaking into a quantum dot

David A. Ruiz-Tijerina, E. Vernek, Luis G. G. V. Dias da Silva, J. C. Egues

Published 2014-12-04Version 1

We have recently shown [Phys. Rev. B {\bf 89}, 165314 (2013)] that a non--interacting quantum dot coupled to a 1D topological superconductor can sustain a Majorana mode even when the dot charge is removed by a gate voltage. This is due to the Majorana bound state of the wire leaking into the quantum dot. Here we extend this previous work by investigating the low--temperature quantum transport through an {\it interacting} quantum dot connected to source and drain leads and side--coupled to a topological wire. We explore the signatures of a Majorana zero--mode leaking into the quantum dot for a wide range of dot parameters, using a recursive Green's function approach. We then study the Kondo regime using numerical renormalization group calculations. We observe the interplay between the Majorana mode and the Kondo effect for different dot--wire coupling strengths, gate voltages and Zeeman fields. Our results show that a "0.5" conductance signature appears in the dot due to the presence of the Majorana mode, and that it persists for a wide range of dot parameters. The Kondo effect, on the other hand, is suppressed by both Zeeman fields and gate voltages. We show that the zero--bias conductance as a function of the magnetic field follows a well--known universality curve. This can be measured experimentally, and we propose that the universal conductance drop followed by a persistent conductance of $0.5\,e^2/h$ are evidence for the presence of Majorana--Kondo physics. These results confirm that the Majorana signature in the dot remains even in the presence of the Kondo effect.