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 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=½g₀Φ/Φ₀, with Φ the magnetic flux through the system, Φ₀ the superconducting flux quantum, and g₀ the thermal conductance quantum.