Induced Half-Metallicity and Gapless Topological Superconductivity in the CrI$_3$-Pb Interface

Abstract: We study a two-dimensional heterostructure comprised of a monolayer of the magnetic insulator chromium triiodide (CrI$_3$) on a superconducting lead (Pb) substrate. Through first-principles computation and a tight-binding model, we demonstrate that charge transfer from the Pb substrate dopes the CrI$_3$ into an effective half-metal, allowing for the onset of a gapless topological superconductivity phase via the proximity effect. This phase, in which there exists a superconducting gap only in part of the Fermi surface, is shown to occur generically in 2D half-metal-superconductor heterostructures which lack two-fold in-plane rotational symmetry. However, a sufficiently large proximity-induced pairing amplitude can bring such a system into a fully-gapped topological superconducting phase. As such, these results are expected to better define the optimal 2D component materials for future proposed TSC heterostructures.