MILLIMETER WAVEBAND SPECTROSCOPY-OF LIQUID HE II

摘要

Low temperature experiments [1-4] on the interaction of electromagnetic field with liquid helium have produced a number of interesting and unexpected results that have yet to be explained in a conventional manner. One of such effects is the resonance absorption and radiation of electromagnetic waves in superfluid helium at a frequency f corresponding to the roton gap of the energy, spectrum, ε= Δ/h . For Δ =8.65 K, which corresponds to a temperature of the order of 1.4 K, f= 2ω≈180.3:GHz, The temperature dependence of this absorption near the temperature of transition to superfluid state coincides precisely with temperature dependence of the roton gap obtained in neutron scattering experiments [5,6] Since at this frequency the photon momentum p_(pt) 3.8 x 10~3 cm~(-1) is many orders of magnitude smaller than the roton momentum p_r = 1.9 x 10~8 cm~(-1), the question of how the momentum conservation law can be obeyed in a such process must be addressed.