Fluctuation and strain effects in a chiral p -wave superconductor

For a tetragonal material, order parameters of pₓ and py symmetry are related by rotation and hence have the same Tc at a mean-field level. This degeneracy can be lifted by a symmetry-breaking field, such as (uniaxial) in-plane strain, such that at Tc, the order parameter is only of pₓ or py symmetry. Only at a lower temperature also the respective other order parameter condenses to form a chiral p-wave state. At the mean-field level, the derivative of Tc with strain is discontinuous at zero strain. We analyze the consequences of (thermal) fluctuations on the strain-temperature phase diagram within a Ginzburg-Landau approach. We find that the order-parameter fluctuations can drive the transition to be weakly first order, rounding off this discontinuity. We discuss the possibility of a second-order transition into a nonsuperconducting time-reversal-symmetry-breaking phase and consequences for the spin-triplet superconductor Sr₂RuO₄.