Mesoscopic pairing without superconductivity

TL;DR

This paper investigates pairing phenomena in mesoscopic nanowires, revealing a crossover between bulk and mesoscopic regimes and introducing the parity parameter as a key measure, with implications for understanding superconductivity signatures.

Contribution

It introduces the parity parameter as a unifying measure for pairing in mesoscopic systems and connects theoretical predictions with recent experimental conductance data.

Findings

Parity parameter can be extracted from conductance oscillations.

System exhibits a crossover from bulk to mesoscopic pairing regimes.

Experiment is in the fluctuation-dominated mesoscopic regime on the BCS side.

Abstract

We discuss pairing signatures in mesoscopic nanowires with variable attractive pairing interaction. Depending on wire length, density, and interaction strength, these systems realize a simultaneous bulk-to-mesoscopic and BCS-BEC crossover, which we describe in terms of the parity parameter that quantifies the odd-even energy difference and generalizes the bulk Cooper pair binding energy to mesoscopic systems. We show that the parity parameter can be extracted from recent measurements of conductance oscillations in SrTiO$_3$ nanowires by G. Cheng et al. [Nature 521, 196 (2015)], where it marks the critical magnetic field that separates pair and single-particle currents. Our results place the experiment in the fluctuation-dominated mesoscopic regime on the BCS side of the crossover.