Majorana-assisted nonlocal electron transport through a floating topological superconductor

TL;DR

This paper demonstrates that a floating topological superconductor enables nonlocal electron transport mediated by Majorana modes without requiring additional charging energy, revealing distinct shot-noise characteristics in different regimes.

Contribution

It shows that nonlocal current correlations can be observed in a floating superconductor without charging energy, contrasting with previous models that required it.

Findings

Nonlocal correlations appear in floating superconductors without charging energy.

Peak conductance remains $e^2/h$ in both non-interacting and Coulomb-blockade regimes.

Shot noise is sub-Poissonian in Coulomb blockade, Poissonian in non-interacting regime.

Abstract

The nonlocal nature of the fermionic mode spanned by a pair of Majorana bound states in a one-dimensional topological superconductor has inspired many proposals aiming at demonstrating this property in transport. In particular, transport through the mode from a lead attached to the left bound state to a lead attached to the right will result in current cross-correlations. For ideal zero modes on a grounded superconductor, the cross-correlations are however completely suppressed in favor of purely local Andreev reflection. In order to obtain a non-vanishing cross-correlation, previous studies have required the presence of an additional global charging energy. Adding nonlocal terms in the form of a global charging energy to the Hamiltonian when testing the intrinsic nonlocality of the Majorana modes seems to be conceptually troublesome. Here, we show that a floating superconductor allows to observe nonlocal current correlations in the absence of charging energy. We show that the non-interacting and the Coulomb-blockade regime have the same peak conductance $e^2/h$ but different shot-noise power; while the shot noise is sub-Poissonian in the Coulomb-blockade regime in the large bias limit, Poissonian shot noise is generically obtained in the non-interacting case.