Title | Beyond triplet: Unconventional superconductivity in a spin-3/2 topological semimetal |
Publication Type | Journal Article |
Year of Publication | 2018 |
Authors | H. Kim, K. Wang, Y. Nakajima, R. Hu, S. Ziemak, P. Syers, L. Wang, H. Hodovanets, J. D. Denlinger, P. M. R. Brydon, D. F. Agterberg, M. A. Tanatar, R. Prozorov, and J. Paglione |
Journal | SCIENCE ADVANCES |
Volume | 4 |
Pagination | eaao4513 |
Date Published | APR |
Type of Article | Article |
ISSN | 2375-2548 |
Abstract | In all known fermionic superfluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to formeither spinsinglet 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 formquintet or septet pairs. We report evidence of unconventional superconductivity emerging from a spin-3/2 quasi-particle electronic structure in the half-Heusler semimetal YPtBi, a low-carrier density noncentrosymmetric cubic material with a high symmetry that preserves the p-like j = 3/2 manifold in the Bi-based Gamma(8) band in the presence of strong spin-orbit coupling. With a striking linear temperature dependence of the London penetration depth, the existence of line nodes in the superconducting order parameter Delta is directly explained by a mixed-parity Cooper pairing model with high total angular momentum, consistent with a high-spin fermionic superfluid state. We propose a k.p model of the j = 3/2 fermions to explain how a dominant J = 3 septet pairing state is the simplest solution that naturally produces nodes in the mixed even-odd parity gap. Together with the underlying topologically nontrivial band structure, the unconventional pairing in this system represents a truly novel form of superfluidity that has strong potential for leading the development of a new series of topological superconductors. |
DOI | 10.1126/sciadv.aao4513 |