Quantum Interference Breaks Bias Symmetry at Extended Superconducting Interfaces

TL;DR

Quantum interference at extended superconducting interfaces causes bias asymmetry in conductance, challenging the assumption of particle-hole symmetry enforcing symmetric transport, and offers a spectroscopic probe of interface physics.

Contribution

This work reveals that extended interfaces induce bias asymmetry through quantum interference, providing a new interferometric method to probe nonlocal interface physics and superconducting energy scales.

Findings

Bias asymmetry arises from quantum interference at extended interfaces.

The interface acts as an effective Andreev interferometer with damped oscillations.

Bias dependence is governed by the superconducting gap, serving as a spectroscopic tool.

Abstract

Particle-hole symmetry of the Bogoliubov-de~Gennes Hamiltonian is widely assumed to enforce bias-symmetric transport at superconducting interfaces. We show that this expectation fails generically for interfaces with finite spatial extent due to quantum interference. Using a tight-binding scattering formalism that preserves exact particle-hole symmetry, we demonstrate that propagation through an extended interface causes electrons and holes to accumulate unequal phases, leading to intrinsic bias-asymmetric conductance. The interface thereby acts as an effective Andreev interferometer with characteristic damped oscillations arising from coherent multiple reflections within the barrier. While the asymmetry originates from normal-state interference, its bias dependence is governed by the superconducting gap, which emerges as a sharp crossover scale that can be clearly resolved even when conventional coherence peaks are weak or absent. Thus we present bias asymmetry as an interferometric, spectroscopic probe of nonlocal interface physics and superconducting energy scales in hybrid and topological systems where extended interfaces are unavoidable.