Wohlleben Effect and Emergent Pi junctions in superconducting Boron doped Diamond thin films

TL;DR

This paper investigates the Wohlleben effect and emergent Pi junctions in superconducting boron-doped diamond thin films, revealing possible spin-related mechanisms and phase glass states through magnetic and electrical measurements.

Contribution

It provides evidence for the emergence of Pi junctions and related phenomena in BDD, linking magnetic anomalies to spin flip scattering and phase frustration in disordered superconductors.

Findings

Observation of paramagnetic Meissner effect in BDD

Detection of spin glass-like susceptibility anomalies

Evidence supporting the presence of Pi junctions in BDD

Abstract

Diamond is an excellent band insulator. However, boron (B) doping is known to induce superconductivity. We present two interesting effects in superconducting B doped diamond (BDD) thin films: i) Wohlleben effect (paramagnetic Meissner effect, PME) and ii) a low field spin glass like susceptibility anomaly. We have performed electrical and magnetic measurements (under pressure in one sample) at dopings (1.4 , 2.6 and 3.6) X 1021 cm-3, in a temperature range 2 - 10 K. PME, a low field anomaly in inhomogeneous superconductors could arise from flux trapping, flux compression, or for non-trivial reason such as emergent Josephson Pi junctions. Joint occurrence of PME and spin glass type anomalies points to possible emergence of Pi junctions. BDD is a disordered s-wave superconductor; and Pi junctions could be produced by spin flip scattering of spin half moments when present at weak superconducting regions (Bulaevski et al. 1978). A frustrated network of 0 and Pi junctions will result (Kusmartsev et al. 1992) in a distribution of spontaneous equilibrium supercurrents, a phase glass state. Anderson localized spin half spinons embedded in a metallic fluid (two fluid model of Bhatt et al.) could create Pi junction by spin flip scattering. Our findings are consistent with presence of Pi junctions, invoked to explain their (Bhattacharyya et al.) observation of certain resistance anomaly in BDD.