Superflow-Stabilized Nonlinear NMR in Rotating 3He-B

TL;DR

This paper reports the observation of a stabilized nonlinear spin precession in superfluid 3He-B under large counterflow, revealing a new precessing state with unique frequency locking and broken spin-orbit coupling.

Contribution

It introduces a novel stabilized nonlinear precessing state in 3He-B, characterized by transverse orbital angular momentum and broken spin-orbit coupling, supported by analytical and numerical analysis.

Findings

Observation of frequency-locked precession over large frequency shifts

Identification of a non-Leggett configuration with transverse orbital angular momentum

Derivation of the resonance shift dependence on magnetization tipping angle

Abstract

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 high rf excitation level and displays frequency-locked precession over a large range of frequency shifts, with the 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 theta of the magnetization as omega - omega_L = (Omega_B^2 / 2 omega_L)(cos(theta) - 1/5). The phase diagram of the precessing modes with arbitrary orientation of L is constructed.