Neha Yadav

Working with
Prof. Ambarish Ghosh

Experimental Observation of Few Electron Bubbles
in Liquid Helium


An electron entering liquid helium experiences a repulsive potential of 1 eV. This originates in the interaction between the injected electron and electrons of the closed shells of helium atoms through Pauli exclusion principle. If the energy of the electron exceeds 1 eV, it can penetrate the liquid, form a cavity free from helium atoms and subsequently localize itself within the cavity. This is known as a single electron bubble (SEB). In another configuration, a system of electrons of energy less than 1 eV can form a floating charged layer above the surface of liquid helium: a two-dimensional system that has been studied in great detail over last few decades. If the number of electrons in this layer exceeds a critical value of 2 × 1013 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠/𝑚2 , an electro hydrodynamical instability sets in, giving rise to multielectron bubbles (MEBs), referring to micron to mm sized cavities containing a large number of electrons. In the experiments to be discussed in my talk, the primary technique is based on cavitation of liquid helium using pulsed ultrasound. We have observed a new species of electron bubble which cavitates at a negative pressure approximately 80 percent lower magnitude than SEBs. We conclude that these are multielectron bubbles with small (less than 20) number of electrons; I’ll be presenting various evidences supporting this claim and compare our results with related experiments previously reported.



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