Interband Proximity Effect and Nodes of Superconducting Gap inSr2RuO4

The power-law temperature dependences of the specific heat, the nuclear relaxation rate, and the thermal conductivity suggest the presence of line nodes in the superconducting gap of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. These recent experimental observations contradict the scenario of a nodeless $\left(k_x{+ik}_y\right)$-type superconducting order parameter. We propose that interaction of superconducting order parameters on different sheets of the Fermi surface is a key to understanding the above discrepancy. A full gap exists in the active band, which drives the superconducting instability, while line nodes develop in passive bands by the interband proximity effect.