Superconductivity is a fascinating state of matter in which an electrical current can flow without any resistance. Usually, it can exist in two forms. One is destroyed easily with a magnetic field and has "even parity" (i.e., it has a point symmetric wave function with respect to an inversion point). The other form is stable in magnetic fields applied in certain directions and has "odd parity" (i.e., it has an antisymmetric wave function). Consequently, the latter form should present a characteristic angle dependence of the critical field where superconductivity disappears. But odd-parity superconductivity is rare in nature; only a few materials support this state, and in none of them has the expected angle dependence been observed.
