Quantum oscillations induced by heating electrons on Rydberg states at the surface of superfluid 4He

The relaxation of excited Rydberg states of hot surface electrons on superfluid 4 He is theoretically studied using different models for the ripplon spectrum in the short-wavelength range discussed in the literature. Besides magneto-oscillations caused by the alignment of the staircases of Landau levels of different surface subbands, novel oscillations are found to be possible for a ripplon spectrum with a roton threshold ωrot or with any other upper limitation. The sharp changes in the relaxation rate occur when the total electron excitation energy, including Rydberg states and Landau levels, passes over the doubled threshold energy. The amplitude of these oscillations increases with electron temperature. As a result, the occupancy of the first excited Rydberg state becomes a remarkable periodic function with three distinct periods of sharp variations. This effect can be used for experimental testing theoretical models describing the ripplon spectrum at q≳1Å−1.