Topologically protected Landau level in the vortex lattice of a Weyl superconductor

The question whether the mixed phase of a gapless superconductor can support a Landau level is a celebrated problem in the context of $\mathit{\text{d}}$-wave superconductivity, with a negative answer: The scattering of the subgap excitations (massless Dirac fermions) by the vortex lattice obscures the Landau level quantization. Here we show that the same question has a positive answer for a Weyl superconductor: The chirality of the Weyl fermions protects the zeroth Landau level by means of a topological index theorem. As a result, the heat conductance parallel to the magnetic field has the universal value $G=\frac{1}{2}{g}_0\mathrm{\Phi }\mathrm{/}{\mathrm{\Phi }}_0$, with $\mathrm{\Phi }$ the magnetic flux through the system, ${\mathrm{\Phi }}_0$ the superconducting flux quantum, and $g_0$ the thermal conductance quantum.