Flux-periodicity crossover from h/2e to h/e in aluminium nano-loops

C Espy,Y Yeshurun,R Garreis,E Scheer,A Shaulov,P Leiderer,J Braun,O J Sharon,F Strigl

doi:10.1088/1742-6596/969/1/012063

C Espy, Y Yeshurun + Show 7 more

Open Access

https://doi.org/10.1088/1742-6596/969/1/012063

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Abstract

We study the magnetoresistance of aluminium ‘double-networks’ formed by connecting the vertexes of nano-loops with relatively long wires, creating two interlaced subnetworks of small and large loops (SL and LL, respectively). Far below the critical temperature, Aharonov-Bohm like quantum interference effects are observed for both the LL and the SL subnetworks. When approaching Tc, both exhibit the usual Little-Parks oscillations, with periodicity of the superconducting flux quantum Φ0=h/2e. For one sample, with a relatively large coherence length, ξ, at temperatures very close to Tc, the Φ0 periodicity of the SL disappears, and the waveform of the first period is consistent with that predicted recently for loops with a size a < ξ, indicating a crossover to 2Φ0 periodicity.

Highlights

In a multiply connected superconductor, the fluxoid, defined as the sum of the magnetic flux and the line integral of the screening current, is quantized in units of Φ0 = h/2e, where the 2e is a hallmark of electron pairing in the superconductor
In the present study we focus on aluminium, a low-Tc superconductor with a relatively large bulk coherence length (ξ0 = 1.6 μm)
Critical field and coherence length where wwffffff is the width of the wire

Summary

Introduction

In the present study we focus on aluminium, a low-Tc superconductor with a relatively large bulk coherence length (ξ0 = 1.6 μm). In nanostructures made of diffusive thin films the coherence length is reduced due to the finite mean free path, and simultaneously the penetration depth λL is enhanced. I.e. when the lateral dimensions are in the order of the penetration depth λL, the critical field Bc may increase to a few hundred mT. Taking these considerations together, we fabricated 'double-networks' [3], see figure 1, with small loops of order of 400 x 400 nm, connected by wires of ~ 1600 nm length. An applied field of ~ 10 mT corresponds to a flux of h/2e through the small loops

Sample fabrication

Transport measurements

Results

Little Parks effect

Aharonov-Bohm effect in small loops

Conclusions