High-spin superconductivity in topological half-Heusler semimetals*

In all known fermionic superfluids, Cooper pairs are composed of spin-1/2 quasi-particles that
pair to form either spin-singlet or spin-triplet bound states. The "spin" of a Bloch electron, however, is fixed by the
symmetries of the crystal and the atomic orbitals from which it is derived, and in some cases can behave as if it were
a spin-3/2 particle. The superconducting state of such a system allows pairing states to form "beyond triplet", with
higher spin quasi-particles combining to form quintet or even septet pairs. I will present evidence for the first experimentally realized case of a high-spin fermionic superfluid in the exotic superconducting state of the half-Heusler compound YPtBi, as well as the rich
landscape of ground states and intertwined orders found in the X-Y-Z family of materials.