We investigate the superconducting gap structure in bilayer nickelates within a model where conduction bands of dx2-y2 symmetry coexist with localized d3z2-r2 spins. Strong interlayer coupling drives the local moments into a singlet ground state, whose virtual singlet-triplet excitations ("triplons") mediate the pairing interaction between conduction electrons. This yields interband s+- pairing, with opposite signs of the order parameter on the two (alpha and beta) bands. Our theory naturally explains the key experimental features: a larger gap on the alpha band despite its smaller density of states, and pronounced gap anisotropy arising from nonlocal Kondo coupling. The results support triplon-mediated pairing as the microscopic origin of superconductivity in bilayer nickelates.
@article{arxiv.2602.23989,
title = {Triplon-mediated pairing and the superconducting gap structure in bilayer nickelates},
author = {Huimei Liu and Giniyat Khaliullin},
journal= {arXiv preprint arXiv:2602.23989},
year = {2026}
}
Comments
6 pages, 5 figures. Discussion of the tunneling spectra and Fig. 5 are added