Presentation Information
[PCP1-07]Surface-localized topological superconductivity in nodal-loop materials: BdG analysis
*Takeru Matsushima1, Hiroki Tsuchiura1 (1. Department of Applied Physics, Tohoku University (Japan))
Keywords:
CaAgP,chiral p-wave superconductivity,nodal-line materials,drumhead surface states
Purpose
The exploration of nodal-line semimetals as potential hosts for unconventional superconductivity has recently gained momentum. In particular, CaAgP and its Pd-doped variants exhibit surface-localized superconductivity, motivating theoretical studies on how drumhead surface states may stabilize exotic pairing. We aim to clarify the underlying mechanism of surface-localized chiral p-wave superconductivity and provide experimentally testable predictions.
Method
We employ a minimal nodal-loop Hamiltonian with a toroidal Fermi surface and drumhead surface states. The Bogoliubov–de Gennes equations are solved self-consistently in a slab geometry, open along the z-axis and periodic in the x–y plane, assuming in-plane chiral p-wave pairing. The order parameter, quasiparticle spectrum, and local density of states (LDOS) are calculated with spatial resolution across the slab.
Results
Our calculations reveal that the superconducting order parameter Δ(z) is strongly enhanced at the surface layers but remains strongly suppressed in the bulk interior. This spatial profile directly reflects the large density of states associated with drumhead surface bands. The LDOS shows a clear superconducting gap on the surface states, whereas the central region remains almost gapless.
Discussion
The findings demonstrate that surface-localized superconductivity arises naturally from the interplay between chiral p-wave pairing symmetry and the flat-band character of drumhead states. The robustness of this mechanism was further tested by introducing dispersive components to the drumhead bands, which modifies the profile but does not eliminate the surface enhancement. These insights yield experimentally relevant signatures, such as thickness-dependent Tc, enhanced surface gaps observable in tunneling spectroscopy, and tunable asymmetry under mirror-symmetry breaking by gating.
Conclusion
We have established a self-consistent theoretical framework linking drumhead surface states to surface-localized chiral p-wave superconductivity in nodal-loop materials. Our results highlight CaAgP as a promising candidate for realizing topological superconductivity and offer concrete experimental diagnostics to test its surface-driven origin.
The exploration of nodal-line semimetals as potential hosts for unconventional superconductivity has recently gained momentum. In particular, CaAgP and its Pd-doped variants exhibit surface-localized superconductivity, motivating theoretical studies on how drumhead surface states may stabilize exotic pairing. We aim to clarify the underlying mechanism of surface-localized chiral p-wave superconductivity and provide experimentally testable predictions.
Method
We employ a minimal nodal-loop Hamiltonian with a toroidal Fermi surface and drumhead surface states. The Bogoliubov–de Gennes equations are solved self-consistently in a slab geometry, open along the z-axis and periodic in the x–y plane, assuming in-plane chiral p-wave pairing. The order parameter, quasiparticle spectrum, and local density of states (LDOS) are calculated with spatial resolution across the slab.
Results
Our calculations reveal that the superconducting order parameter Δ(z) is strongly enhanced at the surface layers but remains strongly suppressed in the bulk interior. This spatial profile directly reflects the large density of states associated with drumhead surface bands. The LDOS shows a clear superconducting gap on the surface states, whereas the central region remains almost gapless.
Discussion
The findings demonstrate that surface-localized superconductivity arises naturally from the interplay between chiral p-wave pairing symmetry and the flat-band character of drumhead states. The robustness of this mechanism was further tested by introducing dispersive components to the drumhead bands, which modifies the profile but does not eliminate the surface enhancement. These insights yield experimentally relevant signatures, such as thickness-dependent Tc, enhanced surface gaps observable in tunneling spectroscopy, and tunable asymmetry under mirror-symmetry breaking by gating.
Conclusion
We have established a self-consistent theoretical framework linking drumhead surface states to surface-localized chiral p-wave superconductivity in nodal-loop materials. Our results highlight CaAgP as a promising candidate for realizing topological superconductivity and offer concrete experimental diagnostics to test its surface-driven origin.