6 research outputs found
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. Here, we report evidence of
unconventional superconductivity emerging from a spin-3/2 quasiparticle
electronic structure in the half-Heusler semimetal YPtBi, a low-carrier density
noncentrosymmetric cubic material with a high symmetry that preserves the
-like manifold in the Bi-based 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 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
model of the fermions to explain how a dominant =3 septet pairing
state is the simplest solution that naturally produces nodes in the mixed
even-odd parity gap. Together with the underlying topologically non-trivial
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 generation of topological superconductors.Comment: 12 pages, 10 figures, supplementary info include
Unconventional nodal superconductivity in miassite RhS
Unconventional superconductivity has long been believed to arise from a
lab-grown correlated electronic system. Here we report compelling evidence of
unconventional nodal superconductivity in a mineral superconductor \rhs. We
investigated the temperature-dependent London penetration depth
and disorder evolution of the critical temperature and
upper critical field in synthetic miassite \rhs. We found a
power-law behavior of with at low
temperatures below ( = 5.4 K), which is consistent with the
presence of lines of the node in the superconducting gap of \rhs. The nodal
character of the superconducting state in \rhs~was supported by the observed
pairbreaking effect in and in samples with the controlled
disorder that was introduced by low-temperature electron irradiation. We
propose a nodal sign-changing superconducting gap in the irreducible
representation, which preserves the cubic symmetry of the crystal and is in
excellent agreement with the superfluid density,