Superflow-stabilized nonlinear NMR in rotating 3He-B

Nonlinear spin precession has been observed in 3He−B in large counterflow of the normal and superfluid fractions. The new precessing state is stabilized at a high rf excitation level and displays frequency-locked precession over a large range of frequency shifts, with the magnitude of magnetization at its equilibrium value. Comparison to analytical and numerical calculation indicates that in this state the orbital angular momentum L of the Cooper pairs is oriented transverse to the external magnetic field in a “non-Leggett” configuration with broken spin-orbit coupling. The resonance shift depends on the tipping angle θ of the magnetization as ω−ωL=(Ω2B/2ωL)(cosθ−1/5). The phase diagram of the precessing modes with arbitrary orientation of L is constructed.