Ultrasonic studies of the spin-triplet order parameter and the collective mode in Sr2RuO4 -: art. no. 060505

The elastic constant C-T and ultrasonic attenuation alpha (s) for (C-11-C-12)/2 have been measured on Sr2RuO4 with T-c*= 1.42 K. In contrast to the A(1g) and E-g strains, the B-1g strain (epsilon (xx)-epsilon (yy)) strongly couples to the superconducting state, which dominantly originate from hybridized Ru-4d(xy) electrons on the gamma Fermi surface. Taken into account impurity induced in-gap states, the T-3 dependence of alpha (s) is found to be consistent with an existence of line nodes. The large reduction in CT below T-c* evidences the two-component order parameter and chiral p-wave state. Anomalous C-T and alpha (s) around T-a = 1.34 K suggest a collective mode.