Abstract:

A hallmark for unconventional superconductivity is the non-s-wave pairing symmetry of the superconducting order parameter (OP). The s-wave pairing was assumed in the original BCS theory of superconductivity. Sr₂RuO₄ and UTe₂, for which a non-s-wave pairing is quite well established, are two promising candidates for the more exotic odd-party, spin-triplet superconductors. While Sr₂RuO₄ is the first and only layered perovskite superconductor with the normal electronic states on the Fermi surface formed primarily out of 4d orbitals, UTe₂ is a (recently discovered) heavy fermion superconductor possessing a highly anisotropic Fermi surface with electronic states dominated by strongly correlated 5f electrons of U. Both Sr₂RuO₄ and UTe₂ are furthermore likely candidates for the spin-fluctuation-mediated pair formation proposed originally for superfluid ³He. In this talk I will give a brief overview of the experimental work on Sr₂RuO₄ and UTe₂ that is most relevant to the unconventional nature of superconductivity and discuss our own work on the phase-sensitive determination of the symmetry properties of the OP in these two superconductors.