BISTABLE SELF-ORGANIZATION OF NUCLEAR SPINS IN CONDUCTING SOLIDS

Under suitable conditions the dynamic nuclear polarization by the Over hauser effect in conductors is responsible for a bistable hysteresis o f the electron spin resonance (ESR) line of conduction electrons [Phys . Rev. B 47, 15 023 (1993)]. We study in this work the dynamics of the phenomenon in terms of the bistable self-organization of nuclear spin s and the microwave field. The deterministic evolution of the nuclear field is described as an overdamped motion in a potential U. It is sho wn that the shape of the ESR line, in both monostable and bistable reg imes, is proportional to the second derivative of this potential. By t aking into account the fluctuations of the nuclear field, a Schrodinge r equation for the self-organized spin-field system is derived. For th e monostable Overhauser effect, this equation is that of the quantum m echanical harmonic oscillator. The self-organized spin-field system ca n thus be compared with a ''vibrating molecule'' in the nuclear field space, in which the steady state nuclear held corresponds to the equil ibrium ''interatomic distance.'' With this analogy, the bistable spin- field system may also be compared to a ''mixed valence molecular compl ex,'' in which the two stable configurations of the ''complex'' corres pond to the two stable steady states of the nuclear field.