Giant Microwave Absorption in d-Wave Superconductors

We discuss a new mechanism of microwave absorption in d-wave superconductors which arises in the presence of a dc supercurrent. This mechanism produces a contribution to the ac conductivity that is proportional to the inelastic quasiparticle relaxation time and determines the supercurrent dependence of the conductivity. This new contribution may also be much larger than the conventional contribution because, in superconductors, the inelastic relaxation time typically exceeds the elastic one by several orders of magnitude. We show that the calculation of the aforementioned contribution to the conductivity can be reduced to the calculation of the single particle density of states in the presence of a dc supercurrent. Our results may enable determination of the inelastic relaxation time in superconductors from microwave absorption measurements.