AC Josephson effect without superconductivity

TL;DR

This paper predicts a mesoscopic analog of the AC Josephson effect in normal conductors, where a DC voltage induces high-frequency current oscillations, potentially enabling tunable terahertz signals without superconductivity.

Contribution

It introduces a theoretical framework showing that normal conductors can exhibit Josephson-like oscillations under DC bias, independent of superconductivity.

Findings

Current oscillates at frequency eV_b/h in a mesoscopic interferometer.

Effect is not limited by a superconducting gap.

Potential to generate tunable terahertz signals.

Abstract

Superconductivity derives its most salient features from the coherence of its macroscopic wave function. The associated physical phenomena have now moved from exotic subjects to fundamental building blocks for quantum circuits such as qubits or single photonic modes. Here, we theoretically find that the AC Josephson effect---which transforms a DC voltage $V_b$ into an oscillating signal $cos(2eV_b t/ \hbar)$---has a mesoscopic counterpart in normal conductors. We show that on applying a DC voltage $V_b$ to an electronic interferometer, there exists a universal transient regime where the current oscillates at frequency $eV_b/h$. This effect is not limited by a superconducting gap and could, in principle, be used to produce tunable AC signals in the elusive $0.1-10$ THz "terahertz gap".