Electron Bubbles in Helium
At room temperature, electrons in noble gasses move about freely, limited only by collisions with the weakly interacting atoms. Their mobility, which depends on the gas density and temperature, is well described by classical kinetic theory. As the temperature is lowered the electron mobility decreases, since the helium atoms slow down at lower temperature and do not interact with the electron as often.
Below a critical temperature, the mobility of the electrons drops quickly to a value much below what is expected classically. This discrepancy led to the development of the electron bubble theory. At low temperatures, electrons injected into liquid helium do not move freely as one might expect, but rather form small vacuum bubbles around themselves.
Read more about this topic: Electron Bubble
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