Fyzikální ústav Akademie věd ČR

The electrical activity of superfluid ⁴He induced by the relative motion of normal and superfluid components has been recently observed. It was induced in two different types of experiments. In a first experiment the electric potential oscillations were generated by a wave of second-sound, the out-of-phase oscillation of the normal and superfluid components. In a second experiment liquid helium was involved in motion by a torsional oscillator whose walls affected the normal component only. We note that observation of electrical activity is unusual for liquid helium becasue it has spherically symmetrical and electrically neutral atoms, and may indicate new electro-physical properties of helium.

We suggest to study the appearance of periodic electrical polarization in He II with different ways of second-sound generation. Thermal oscillations are not the only way to generate a second-sound wave. For several years our group successfully used second-sound capacitor sensors based on nuclepore membrane as a powerful tool for experimental investigation of quantum turbulence in He II. Such sensors have relatively simple construction and can be used as speaker and receiver of second sound waves. The given sensors can generate quantized vortices by themselves, which provides a possibility to analyze the connection between quantized vortex lines and electrical activity of superfluid helium.

Newly approved project, started in Spring 2013