Phonon bottle-neck

K. The resonance was saturated at 6.8 GHz, producing a phonon bottle-neck in which the effective temperature of the resonant phonons was raised to 150K. The bandwidth was 270 MHz, of the same order as the unsaturated line width of the cerium resonance. Measurements of Brillouin scattering in CaW04 containing Nd are described by Geschwind (1972). 

Roinel et al. (1985) have made a detailed study of the relaxation rates for the enhanced Tm (/ = ) nuclear spins as a function of temperature from 0.05 up to 2 K, in fields up to 4 T perpendicular to the c-axis. The variation of the relaxation rate is rather complex at 50-100 mK recovery is generally non-exponential. At fields below 0.5 T, relaxation is dominated by interactions with electronic impurities, but above 1T effects are attributed to a bottle-neck between phonons and bath. It is concluded that the relaxation rate at low fields would be too short to allow study of a nuclear ordered state, produced by adiabatic demagnetization of the enhanced Tm nuclear spins. 

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