Anomalous Fano Resonance in Double Quantum Dot System Coupled to Superconductor

Jan Barański,Konrad Jerzy Kapcia,Magdalena Barańska,Tomasz Zienkiewicz

doi:10.1038/s41598-020-59498-y

Jan Barański, Konrad Jerzy Kapcia + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-59498-y

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Abstract

We analyze the influence of a local pairing on the quantum interference in nanoscopic systems. As a model system we choose the double quantum dot coupled to one metallic and one superconducting electrode in the T-shape geometry. The analysis is particularly valuable for systems containing coupled objects with considerably different broadening of energy levels. In such systems, the scattering of itinerant electrons on a discrete (or narrow) energy level gives rise to the Fano-type interference. Systems with induced superconducting order, along well understood Fano resonances, exhibit also another features on the opposite side of the Fermi level. The lineshape of these resonances differs significantly from their reflection on the opposite side of the Fermi level, and their origin was not fully understood. Here, considering the spin-polarized tunneling model, we explain a microscopic mechanism of a formation of these resonances and discuss the nature of their uncommon lineshapes. We show that the anomalous Fano profiles originate solely from the pairing of nonscattered electrons with scattered ones. We investigate also the interplay of each type of resonances with the Kondo physics and discuss the resonant features in differential conductivity.

Highlights

Impurities or nanoobjects like quantum dots (QDs) hybridized to superconductors (SC) adopt some SC properties via proximity effects
As the interfacial quantum dot (i.e., QD1) is connected to superconducting reservoir, scattering on a side level is accompanied by the local pairing
In which the quantum dot is weakly connected to the Rashba chain, the scattering on the Majorana zero mode (MZM) suppresses the local density of states (LDOS) of QD only by one half[59,60]

Summary

Introduction

Impurities or nanoobjects like quantum dots (QDs) hybridized to superconductors (SC) adopt some SC properties via proximity effects. If one QD (QD1) is coupled to both metallic and superconducting electrodes and, side-coupled to the second quantum dot (QD2) with the spin-independent coupling (i.e., the system shown, but with t↑ = t↓), the combined effect of the electron scattering on discrete level and the local pairing gives rise to two resonant features on background of ABS states [see Fig. 2(a)]24,25.

Results

Conclusion