Anomalous Proximity Effect and Theoretical Design for its Realization

TL;DR

This paper provides a microscopic understanding of the anomalous proximity effect in a superconductor with Dresselhaus spin-orbit coupling, highlighting the role of chiral symmetry and zero-energy states in the presence of disorder.

Contribution

It introduces a theoretical framework explaining how zero-energy states with chiral symmetry penetrate into dirty normal metals, revealing conditions for perfect Andreev reflection.

Findings

Zero-energy states are robust against disorder due to chiral symmetry.

All zero-energy states at an edge share the same chirality under large Zeeman fields.

Perfect Andreev reflection occurs at zero-energy in the dirty normal metal.

Abstract

We discuss the stability of zero-energy states appearing in a dirty normal metal attached to a superconducting thin film with Dresselhaus [110] spin-orbit coupling under the in-plane Zeeman field. The Dresselhaus superconductor preserves an additional chiral symmetry and traps more than one zero-energy state at its edges. All the zero-energy states at an edge belong to the same chirality in large Zeeman field due to the effective $p$-wave pairing symmetry. The pure chiral nature in the wave function enables the penetration of the zero-energy states into the dirty normal metal with keeping their high degree of degeneracy. By applying a theorem, we prove the the perfect Andreev reflection into the dirty normal metal at the zero-energy. This paper gives a microscopic understanding of the anomalous proximity effect.