Anomalous proximity effect under Andreev and Majorana bound states

TL;DR

This paper investigates the behavior of zero-energy states and pair correlations in a Rashba nanowire junction, revealing how disorder and region lengths influence the robustness of Majorana versus Andreev bound states.

Contribution

It provides a theoretical analysis of the anomalous proximity effect, distinguishing trivial and topological phases through disorder effects on zero-energy peaks and pair correlations.

Findings

Zero-energy peaks are sensitive to disorder in trivial phases.

Long superconductor regions stabilize Majorana states against disorder.

Spin-triplet correlations are prominent near zero energy, suppressed by disorder.

Abstract

We theoretically study the anomalous proximity effect in a ballistic normal metal/diffusive normal metal/superconductor junction based on Rashba semiconductor nanowire model. The system hosts two distinct phases: a trivial helical phase with zero-energy Andreev Bound States and a topological phase with Majorana Bound States. We analyze the local density of states and induced pair correlations at the edge of the normal metal region. We investigate their behavior under scalar onsite disorder and changing the Superconductor and diffusive regions lengths in the trivial helical and topological phases. We find that both phases exhibit a zero-energy peak in the local density of states and spin-triplet pair correlations in the clean limit, which we attribute primarily to odd-frequency spin-triplet pairs. Disorder rapidly splits the zero-energy peak in the trivial helical phase regardless of the lengths of the superconductor and diffusive normal regions. The zero-energy peak in the topological phase show similar fragility when the superconductor region is short. However, for long superconductor regions, the zero-energy peak in the topological phase remain robust against disorder. In contrast, spin-singlet correlations are suppressed near zero energy in both phases. Our results highlight that the robustness of the zero-energy peak against scalar disorder, contingent on the Superconductor region length, serves as a key indicator distinguishing trivial Andreev bound states from topological Majorana bound states.