Oscillations of differential resistance of a microscopic point contact in He II

Steady-state differential resistance oscillations of a normal point contact immersed in He II were studied experimentally. The oscillations are observed in the first and second derivatives of the characteristics as functions of current or voltage bias at a fixed bath temperature below Tλ or as a function of temperature T < Tλ at a fixed bias. In He I (for both equilibrium and subcooled vapor pressure) and in gas, stationary differential resistance oscillations are absent. The effect of contact resistance, electrode thickness, and surface state at the helium boundary on the oscillations is studied and a correlation with the phonon spectrum of the metal studied is noted. A model is presented, which takes account of features in heat transfer to He II from a microscopic point contact under significant overheating: differential resistance oscillations are related to the appearance of local vapor regions in the contact region at the helium boundary during transition to the film boiling regime in He II.

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