Magneto-acoustic rotation of transverse waves in ³He-B

In superfluid ³He-B, the off-resonant coupling of the J = 2^-, M = ± 1 order parameter collective modes to transverse current excitations stabilizes propagating transverse waves with low damping for frequencies above that of the J = 2^- modes. Right- (RCP) and left circularly polarized (LCP) transverse modes are degenerate in zero field; however, a magnetic field with H∥q lifts this degeneracy giving rise to the acoustic analog of circular birefringence and an acoustic Faraday effect for linearly polarized transverse sound waves (Moores and Sauls, J. Low Temp. Phys. 91 (1993) 13). We present theoretical results for the temperature, pressure and field dependence of the Faraday rotation angle, and compare the theory with recent measurements (Lee et al., Nature 400 (1999) 431). The analysis provides a direct measurement of the Landé g-factor for the J = 2^- modes, and new information on the magnitude of f-wave pairing correlations in ³He-B.