Odd-parity superconductivity in Weyl semimetals

Unconventional superconducting states of matter are realized in the presence of strong spin-orbit coupling. In particular, nondegenerate bands can support odd-parity superconductivity with rich topological content. Here we study whether this is the case for Weyl semimetals. These are systems whose low-energy sector, in the absence of interactions, is described by linearly dispersing chiral fermions in three dimensions. The energy spectrum has nodes at an even number of points in the Brillouin zone. Consequently both intranodal finite momentum pairing and internodal BCS superconductivity are allowed. For local attractive interaction the finite momentum pairing state with chiral $p$-wave symmetry is found to be most favorable at finite chemical potential. The state is an analog of the superfluid ${}^3$He $A$ phase, with Cooper pairs having finite center-of-mass momentum. For chemical potential at the node the state is preempted by a fully gapped charge density wave. For nonlocal attraction the BCS state wins out for all values of the chemical potential.

Figure 1

The interaction shown in Eq. (3) is a function of three vectors ($\widehat{q}$, ${\widehat{e}}_{\vec{q}}^1$, and ${\widehat{e}}_{\vec{q}}^2$) that form a right-handed coordinate system. Each vector couples to an operator of distinct symmetry in the particle-hole channel.