NMR lineshifts and spontaneously broken spin-orbit symmetry. I. General concepts

The condition for the position of the nuclear magnetic resonance line observed in a many-body system to shift away from the Larmor value gamma H 0 is studied. It is shown that shifts of the order of magnitude of that recently observed in liquid 3 He below 3 mK are possible only if the system possesses a peculiar ordering property, not hitherto seen in any many-body system, which is called 'spontaneously broken spin-orbit symmetry'. Some general aspects of the behaviour of systems with this property are studied, without making any particular assumptions about the microscopic dynamics.