Protection of Ising spin-orbit coupling in bulk misfit superconductors

Ising superconductivity is present due to the combined effect of broken-inversion symmetry and spin-orbit coupling that locks the spins out of plane, features that are associated with two-dimensional materials. We show that bulk misfit superconductors, ${(\mathrm{LaSe})}_{1.14}(\mathrm{Nb}{\mathrm{Se}}_{2})$ and ${(\mathrm{LaSe})}_{1.14}{(\mathrm{Nb}{\mathrm{Se}}_{2})}_{2}$, comprising monolayers and bilayers of $\mathrm{Nb}{\mathrm{Se}}_{2}$, exhibit unexpectedly strong Ising protection with a Pauli-limit violation comparable to monolayer $\mathrm{Nb}{\mathrm{Se}}_{2}$. We establish these misfit compounds as Ising superconductors using complementary experimental methods in combination with first-principles calculations. A concerted effect of charge-transfer, defects, reduction of interlayer hopping, and stacking enables Ising superconductivity in these compounds and therefore provides a possible pathway to design of bulk superconductors that are resilient to magnetic fields.