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Enhancement of superconducting stiffness in hybrid superconducting-metallic bilayers

J. E. Ebot1, Lorenzo Pizzino2, Sam Mardazad1, Johannes S. Hofmann3, Thierry Giamarchi2, and Adrian Kantian1

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Phys. Rev. B 114, 264507 – Published 10 November, 2026

DOI: https://doi.org/10.1103/9tsf-lrgd

Abstract

Boosting superconductivity by metallic reservoirs is the essence of Kivelson's bilayer proposal. One layer provides pairing to the electrons, while the weakly coupled metal provides additional phase coherence to those pairs by mediating extended-range pair-pair coupling. Demonstrating significant and unambiguous performance gains with strong-coupling methods for such setups had been difficult. In the present work, we study these systems doped away from half filling, corresponding to a partially spin-polarized 1D Anderson or Kondo lattice. We show that this breaks the coexistence of dominant superconducting and density-density correlations decisively in favor or the former. Consequently, we provide evidence that in this doped regime, superconducting near-long-range order is not precluded by a small charge gap in the thermodynamic limit, as we have recently shown to be the case at half filling. We study the complex manner in which the enhancement of superconductivity in the pairing layer depends on the parameters of the metal, and especially that both pairing-limited and stiffness-limited regimes may appear in these systems. In addition to superconducting bilayers, our results are relevant, via a particle-hole transformation, for heavy-fermion Kondo-lattice materials in magnetic fields, as we provide previously lacking insight on the competition between antiferromagnetic and easy-plane magnetism, as well as a route for comprehensive indirect tests of Kivelson's bilayer proposal well beyond previous capabilities.

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Phys. Rev. B 114, 264507– Published 10 November, 2026
  • Received 1 May 2026
  • Revised 22 October 2026
  • Accepted 27 October 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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