Gap Structure of the Spin-Triplet Superconductor Sr₂RuO ₄ Determined from the Field-Orientation Dependence of the Specific Heat

The inplane anisotropy in the superconducting (SC) gap of the spin-triplet superconductor Sr₂RuO₄ from the field-orientation dependence of the specific heat at low temperatures was analyzed. A magnetic field was aligned parallel to the RuO₂ planes with high accuracy. Single crystals of the compound were grown by a floating-zone method in an infrared image furnace. The gap structure in the active band was determined and the multiband superconductivity was identified. The SC state of the compound had a band-dependent gap and the gap of its active SC band had strong inplane anisotropy with a minimum along the [100] direction.