Time-reversal symmetry-breaking in noncentrosymmetric superconductors.

In this paper we examine the appearance of time-reversal symmetry-breaking (TRSB) states in the bulk and at the surface of a noncentrosymmetric superconductor. We utilize a Ginzburg-Landau theory, with coefficients derived from a microscopic model of the superconductor. We show that suppression of the triplet order parameter at the surface stabilizes a TRSB state by locally tuning the system into the bulk TRSB phase.

Beyond triplet: Unconventional superconductivity in a spin-3/2 topological semimetal.

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 beyond spin-triplet, with higher spin quasi-particles combining to form quintet or septet pairs.

Topological surface states in nodal superconductors.

Topological superconductors have become a subject of intense research due to their potential use for technical applications in device fabrication and quantum information. Besides fully gapped superconductors, unconventional superconductors with point or line nodes in their order parameter can also exhibit nontrivial topological characteristics. This article reviews recent progress in the theoretical understanding of nodal topological superconductors, with a focus on Weyl and noncentrosymmetric superconductors and their protected surface states.