Physical Review Research (May 2021)

Spin-polarized tunneling in critically disordered Be-Al bilayers

  • F. N. Womack,
  • P. W. Adams,
  • G. Catelani

DOI
https://doi.org/10.1103/PhysRevResearch.3.023141
Journal volume & issue
Vol. 3, no. 2
p. 023141

Abstract

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We report spin-polarized tunneling density of states measurements of the proximity modulated superconductor-insulator transition in ultrathin Be-Al bilayers. The bilayer samples consisted of a Be film of varying thickness, d_{Be}=0.8–4.5nm, on which a 1 nm thick capping layer of Al was deposited. Detailed measurements of the Zeeman splitting of the BCS coherence peaks in samples with sheet resistances R∼h/4e^{2} revealed a superlinear Zeeman shift near the critical field. Our data suggests that critically disordered samples have a broad distribution of gap energies and that only the higher portion of the distribution survives as the Zeeman critical field is approached. This produces a counterintuitive field dependence in which the gap apparently increases with increasing parallel field.