Multigap superconductivity in Ising superconductors: The case of (LaSe)1.14(NbSe2)m misfit layer compounds

Abstract

Strong spin-orbit coupling and broken inversion symmetry in transition metal dichalcogenides give rise to Ising superconductivity, a spin-protected pairing state first identified in monolayer NbSe₂ through in-plane critical fields far exceeding the Pauli limit. More recently, Ising superconductivity has been proposed as a potential route to unconventional and even topological superconductivity in bulk misfit compounds. Here, we investigate the superconducting order parameter of layered misfit compounds composed of alternating transition metal dichalcogenide and rocksalt layers, which host extremely doped, electronically decoupled NbSe₂ sheets within a three-dimensional crystal. Using directional scanning tunneling spectroscopy on the misfit superconductors (LaSe)_1.14(NbSe₂) and (LaSe)_1.14(NbSe₂)₂, we uncover a strongly anisotropic multigap superconducting state: a fragile gap on the Γ-centered Fermi-surface pocket coexists with a robust, intrinsic gap on the K and K' pockets. These features are in quantitative agreement with momentum-resolved gaps Δ(k) obtained from anisotropic Migdal-Eliashberg calculations. The marked fragility of the Γ-centered gap, combined with the strong sensitivity of the critical temperature to non-magnetic disorder, points to pairing beyond conventional s-wave symmetry, potentially involving a topological order parameter. These results establish NbSe₂-based misfit compounds as a tunable bulk platform for multigap, unconventional superconductivity, with Ising protection offering a promising route toward topological pairing.

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BibTeX RIS

BibTeX

@misc{palaciomorales2026multigap,
  title = {{Multigap superconductivity in Ising superconductors: The case of (LaSe)1.14(NbSe2)m misfit layer compounds}},
  author = {Alexandra Palacio-Morales and Tomas Samuely and Ludovica Zullo and Raphaël T. Leriche and Pavol Szabó and Shunsuke Sasaki and Cesare Tresca and Hugo Le Du and Christophe Brun and François Debontridder and Giovanni Marini and Marek Kuzmiak and Jozef Kačmarčík and Laurent Cario and Matteo Calandra and Tristan Cren and Peter Samuely},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.15446},
  eprint = {2609.15446},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.15446},
  note = {CC BY-NC-ND 4.0},
}

RIS

TY  - UNPB
TI  - Multigap superconductivity in Ising superconductors: The case of (LaSe)1.14(NbSe2)m misfit layer compounds
AU  - Alexandra Palacio-Morales
AU  - Tomas Samuely
AU  - Ludovica Zullo
AU  - Raphaël T. Leriche
AU  - Pavol Szabó
AU  - Shunsuke Sasaki
AU  - Cesare Tresca
AU  - Hugo Le Du
AU  - Christophe Brun
AU  - François Debontridder
AU  - Giovanni Marini
AU  - Marek Kuzmiak
AU  - Jozef Kačmarčík
AU  - Laurent Cario
AU  - Matteo Calandra
AU  - Tristan Cren
AU  - Peter Samuely
PY  - 2026
DA  - 2026/09/22
PB  - arXiv
DO  - 10.48550/arxiv.2609.15446
UR  - https://arxiv.org/abs/2609.15446
AB  - Strong spin-orbit coupling and broken inversion symmetry in transition metal dichalcogenides give rise to Ising superconductivity, a spin-protected pairing state first identified in monolayer NbSe_2 through in-plane critical fields far exceeding the Pauli limit. More recently, Ising superconductivity has been proposed as a potential route to unconventional and even topological superconductivity in bulk misfit compounds. Here, we investigate the superconducting order parameter of layered misfit compounds composed of alternating transition metal dichalcogenide and rocksalt layers, which host extremely doped, electronically decoupled NbSe_2 sheets within a three-dimensional crystal. Using directional scanning tunneling spectroscopy on the misfit superconductors (LaSe)_1.14(NbSe_2) and (LaSe)_1.14(NbSe_2)_2, we uncover a strongly anisotropic multigap superconducting state: a fragile gap on the Γ-centered Fermi-surface pocket coexists with a robust, intrinsic gap on the K and K' pockets. These features are in quantitative agreement with momentum-resolved gaps Δ(k) obtained from anisotropic Migdal-Eliashberg calculations. The marked fragility of the Γ-centered gap, combined with the strong sensitivity of the critical temperature to non-magnetic disorder, points to pairing beyond conventional s-wave symmetry, potentially involving a topological order parameter. These results establish NbSe_2-based misfit compounds as a tunable bulk platform for multigap, unconventional superconductivity, with Ising protection offering a promising route toward topological pairing.
ER  -

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