Abstract

A hallmark of unconventional superconductivity, which can be understood as a macroscopic quantum phenomenon associated with superconducting pairing in which symmetries beyond the U(1) symmetry are broken, is the non-s-wave orbital pairing symmetry, the mathematical characteristics of the orbital part of the superconducting order parameter (OP). Sr2RuO4 and UTe2 are two promising candidates for establishing experimentally the exotic orbital pairing symmetry of odd party, which implies for these two materials also the spin-triplet pairing due to the presence of an inversion symmetry. While Sr2RuO4 is the first and for a long time the only layered perovskite superconductor without the presence of Cu, whose superconductivity was found in the 90’s, UTe2 is a heavy fermion superconductor discovered more recently. The normal electronic states on the Fermi surface in Sr2RuO4 were shown to evolve primarily from 4d orbitals of Ru, forming a highly anisotropic, cylindrical Fermi surface. However, the electronic properties in UTe2 are dominated by strongly correlated 5f electrons of U. In this talk I will give a brief overview of the superconducting properties of Sr2RuO4 and UTe2 and discuss our own work on the phase-sensitive determination of the orbital pairing symmetries of these two superconductors. I will also comment briefly on the ongoing debate on the symmetry properties of the spin part of the OP in Sr2RuO4.