Physical Science

Two species of few-electron bubbles (FEB) in superfluid helium

These FEBs can serve as a useful model to study how the energy states of electrons and interactions between them in a material influence its properties

August 19, 2021
The Scitech
 

In a new study, scientists at the Indian Institute of Science (IISc) have experimentally shown the existence of two species of few electron bubbles (FEBs) in superfluid helium for the first time. These FEBs can serve as a useful model to study how the energy states of electrons and interactions between them in a material influence its properties. The research team included Neha Yadav, a former PhD student at the Department of Physics, Prosenjit Sen, Associate Professor at the Centre for Nano Science and Engineering (CeNSE), and Ambarish Ghosh, Professor at CeNSE. The study was published in Science Advances. An electron injected into a superfluid form of helium creates a single electron bubble (SEB) – a cavity that is free of helium atoms and contains only the electron. The shape of the bubble depends on the energy state of the electron. For instance, the bubble is spherical when the electron is in the ground state (1S). There are also MEBs – multiple electron bubbles that contain thousands of electrons, says IISc statement. FEBs, on the other hand, are nanometre-sized cavities in liquid helium containing just a handful of free electrons. The number, state, and interactions between free electrons dictate the physical and chemical properties of materials. Studying FEBs, therefore, could help scientists better understand how some of these properties emerge when a few electrons present in a material interact with each other. According to the authors, understanding how FEBs are formed can also provide insights into the self-assembly of soft materials, which can be important for developing next-generation quantum materials. However, scientists have only theoretically predicted the existence of FEBs so far. “We have now experimentally observed FEBs for the first time and understood how they are created,” says Neha Yadav,

The researchers first applied a voltage pulse to a tungsten tip on the surface of liquid helium. Then they generated a pressure wave on the charged surface using an ultrasonic transducer. This allowed them to create 8EBs and 6EBs, two species of FEBs containing eight and six electrons respectively. These FEBs were found to be stable for at least 15 milliseconds (quantum changes typically happen at much shorter time scales) which would enable researchers to trap and study them. There are several phenomena that FEBs can help scientists decipher, such as turbulent flows in superfluids and viscous fluids, or the flow of heat in superfluid helium.

Source: India Science Wire