Source capture
Authors Zhongyi Zhang, Congcong Le, Hoi Chun Po, Jiangping Hu, Xianxin Wu, Shengshan Qin
arXiv / Publisher https://arxiv.org/abs/2610.03601
PDF https://arxiv.org/pdf/2610.03601
Relevance score 5.082
Primary category cond-mat.supr-con
Published 2026-10-05
Research paradigm Theoretical
Sample form Thin Film

Summary

Based on a first-principles-derived two-orbital model, this study investigates the mechanism of topological superconductivity in substrate-supported bilayer nickelate thin films (La3Ni2O7). Under the assumption of dominant interlayer pairing, the substrate-induced layer-asymmetric potential and layer-staggered Rashba spin-orbit coupling drive the system into a time-reversal-invariant topological superconducting phase of class DIII, which is protected by diagonal mirror symmetry. This nontrivial topology originates from the reversal of the pairing sign on the spin-split bonding Fermi surface, manifesting as a nonzero diagonal mirror winding number and Majorana Kramers pairs at the [11] edge. Furthermore, orbital hybridization gives rise to bulk Dirac nodes and zero-energy flat bands that deviate from the diagonal direction. The research establishes the potential of bilayer nickelates as a platform for topological superconductivity, where tunable topological transitions and boundary modes provide a new avenue for probing unconventional pairing.

Materials

Methods

  • First-principles calculations
  • Effective two-orbital model
  • Tight-binding Hamiltonian
  • Bogoliubov-de Gennes (BdG) Hamiltonian
  • Topological analysis
  • Fermi-surface formula
  • Numerical edge-state calculations
  • STM
  • Spin-resolved angle-resolved photoemission spectroscopy (ARPES) (proposed probe)

Keywords

  • topological superconductivity
  • time reversal invariant topological superconducting phase
  • layer asymmetry
  • layer asymmetric potential
  • layer staggered rashba spin orbit coupling
  • interlayer pairing
  • dominant interlayer pairing
  • mirror symmetry
  • diagonal mirror symmetry
  • majorana kramers pair
  • mirror winding number
  • pairing sign reversal
  • bulk gap nodes
  • dirac nodes
  • chiral charge
  • zero energy flat bands
  • class diii
  • unconventional pairing
  • high tc superconductivity
  • nodal topological superconductivity
  • orbital hybridization
  • chiral symmetry
  • particle hole symmetry
  • time reversal symmetry

Highlights

  • The substrate naturally provides the layer-asymmetric potential and layer-staggered Rashba spin-orbit coupling needed for the topological phase.
  • Realizing the topological superconductivity does not require strong layer asymmetry or SOC, because the topological window is set by comparable energy scales of order meV.
  • The Majorana Kramers pair at the [11] edge could survive even when mirror symmetry is broken, provided the time-reversal-protected index stays unchanged.
  • The topological regime exhibits a V-shaped bulk tunneling spectrum and zero-energy peaks at the [11] and [21] edges but not at the [10] edge, resembling d-wave signatures but distinguished by layer polarization of the nodal quasiparticles.
  • An external electric field that reverses the layer-asymmetric potential can transfer the nodal quasiparticle spectral weight to the opposite layer, changing the top-layer spectrum from V-shaped to nearly fully gapped.
  • The layer-uniform Rashba term only weakly affects the topological window and shifts helicity branches without changing their layer composition.
  • The authors note a related work on nodal orbital-anti-phase pairing in a mirror-symmetric spinless bilayer nickelate model, but in their case they obtain a nonzero mirror winding number and a Majorana Kramers pair at the [11] edge.

Conclusions

  • Substrate-supported bilayer nickelate thin films can host an intrinsic time-reversal-invariant topological superconducting phase protected by diagonal mirror symmetry.
  • A modest layer-asymmetric potential and layer-staggered Rashba spin-orbit coupling drive the system into this topological phase over a broad parameter range with a dominant interlayer pairing.
  • The nontrivial topology arises from a reversal of the pairing sign on one of the spin-split bonding Fermi surfaces and is characterized by a nonzero mirror winding number along the diagonal direction, as well as a Majorana Kramers pair at the [11] edge.
  • The phase also features bulk gap nodes located slightly away from the diagonal directions, featuring chiral charge and zero-energy flat bands.
  • The Dirac nodes arise from the combined effects of orbital hybridization, the layer-asymmetric potential, and the staggered Rashba spin-orbit coupling, and they carry topological charges protected by chiral symmetry.
  • High-Tc bilayer nickelates are a promising platform for topological superconductivity, where tunable topological transitions and Majorana boundary modes can provide probes of unconventional pairing.

Main claims

  • Substrate-supported bilayer nickelate thin films can host an intrinsic time-reversal-invariant topological superconducting phase protected by diagonal mirror symmetry.
    • Evidence: Abstract and full text state that the authors demonstrate substrate-supported bilayer nickelate thin films can host an intrinsic time-reversal-invariant topological superconducting phase protected by diagonal mirror symmetry.,Using a two-orbital model derived from first-principles calculations, the authors analyze the system and find the topological phase.
  • A modest layer-asymmetric potential and layer-staggered Rashba spin-orbit coupling drive the system into a topological phase over a broad parameter range with dominant interlayer pairing.
    • Evidence: Abstract: a modest layer-asymmetric potential and layer-staggered Rashba spin-orbit coupling drive the system into this topological phase over a broad parameter range with a dominant interlayer pairing.,Full text: substrate-induced mirror-symmetry breaking and layer-staggered Rashba SOC are incorporated into the effective model, and the topological phase diagram is calculated.
  • The nontrivial topology arises from a pairing-sign reversal on one spin-split bonding Fermi surface and is characterized by a nonzero mirror winding number and a Majorana Kramers pair at the [11] edge.
    • Evidence: Abstract: the nontrivial topology arises from a reversal of the pairing sign on one of the spin-split bonding Fermi surfaces and is characterized by a nonzero mirror winding number along the diagonal direction, as well as a Majorana Kramers pair at the [11] edge.,Full text: mirror winding number calculation and edge-state analysis show a Majorana Kramers pair at the projecting point of the diagonal on the [11] edge.
  • The topological phase features bulk gap nodes slightly away from the diagonal directions, carrying chiral charge and giving rise to zero-energy flat bands.
    • Evidence: Abstract: the phase also features bulk gap nodes located slightly away from the diagonal directions, featuring chiral charge and zero-energy flat bands.,Full text: the Dirac nodes carry topological charge protected by chiral symmetry, and zero-energy flat bands appear on the [21] edge.
  • The topological phase can be realized and tuned experimentally, and its tunable topological transitions and Majorana boundary modes can probe unconventional pairing.
    • Evidence: Discussion: substrate selection and strain, distance from the interface, and external electric fields can tune the relevant parameters.,Discussion: STM spectra may distinguish U-shaped and V-shaped behavior, and layer polarization of nodal quasiparticles can serve as evidence for dominant interlayer pairing.

Workflow

  • system_and_first_principles — Substrate and interface effects define the low-energy electronic structure used for modeling.
    • Materials: La3Ni2O7 bilayer thin films on SrLaAlO4 substrate; NiO2 bilayers near the interface; Ni dz2 and dx2-y2 orbitals
    • Methods: First-principles calculations; Band-structure analysis; Identification of spin splitting
    • Observations: Low-energy states are dominated by Ni dz2 and dx2-y2 orbitals; Bonding and antibonding bands show spin splitting along the diagonal
  • effective_model_construction — The effective model incorporates the substrate-induced symmetry breaking and interlayer pairing needed to analyze topology.
    • Materials: La3Ni2O7 bilayer film on SrLaAlO4 substrate; Two-orbital low-energy subspace
    • Methods: Two-orbital tight-binding Hamiltonian; Add layer-asymmetric potential; Add layer-staggered Rashba spin-orbit coupling; Add layer-uniform Rashba term; Fit model parameters to first-principles bands; Construct BdG Hamiltonian in Nambu basis with spin-singlet pairing
    • Observations: Effective model captures band structure and spin splittings; Fitted substrate and Rashba parameters are meV-scale; Layer-staggered Rashba term produces opposite spin textures in the two layers
  • topological_analysis — Layer asymmetry and layer-staggered Rashba spin-orbit coupling drive intrinsic topological superconductivity in the effective model.
    • Materials: BdG Hamiltonian; Mirror-symmetry sectors
    • Methods: Symmetry classification in class DIII; Mirror winding number calculation; Fermi-surface formula; Topological phase diagram calculation; Edge-state calculations
    • Observations: Topological superconducting phase occurs over a broad parameter range; Nonzero mirror winding number along the diagonal direction; Majorana Kramers pair at the [11] edge; Bulk Dirac nodes slightly off the diagonal directions; Zero-energy flat bands on the [21] edge
  • interpretation_and_experimental_probes — Tunable topological transitions and Majorana boundary modes can provide probes of unconventional pairing in bilayer nickelates.
    • Materials: Topological superconducting state; Bulk nodes; Majorana boundary modes
    • Methods: Discussion of experimental routes; Proposed ARPES, STM, and electric-field tuning probes; Comparison of layer-polarization signatures
    • Observations: Topological phase is experimentally accessible with moderate parameters; Nodal quasiparticles are layer-polarized; STM spectra may be U-shaped or V-shaped depending on layer position; Electric field can transfer spectral weight between layers