Few-Electron bubbles in Superfluid helium gas

Scientists at the IISc Banglore discovered two species of Few-Electron Bubbles (FEBs) in Superfluid Helium Gas.

Few-Electron bubbles in Superfluid helium gas

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• The story: Scientists at the Indian Institute of Science (IISc), Banglore for the first time discovered two species of Few-Electron Bubbles (FEBs) in Superfluid Helium Gas.
• Helium: It is a chemical element with the symbol He and atomic number 2. The British chemist Sir William Ramsay discovered the existence of helium on Earth in 1895. It is a colourless, odourless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements.
• Electrons: All matter is made up of atoms, the basic units of chemical elements such as hydrogen, helium or oxygen. These are made up of three particles: Protons, Neutrons and Electrons, of which electrons are the subatomic particles that orbit the nucleus of an atom. They are generally negative in charge and much smaller than the nucleus.
• Electron Bubble: An electron bubble is the empty space created around a free electron in a cryogenic gas or liquid, such as neon or helium. They are typically very small, about 2 nm in diameter at atmospheric pressure. 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 (i.e. state of lowest energy). There are also multiple electron bubbles that contain thousands of electrons.
• Superfluidity: It is the frictionless flow and other exotic behaviour observed in liquid helium at temperatures near absolute zero (−273.15 °C), and similar frictionless behaviour of electrons in a superconducting solid. In each case the unusual behaviour arises from quantum mechanical effects.
• Few-Electron Bubbles: FEBs 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. FEBs form an interesting system that has both electron-electron interaction and electron-surface interaction. 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.
• Study properties: 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. There are several phenomena that FEBs can help scientists decipher, such as (i) Turbulent flows in superfluids and viscous fluids, or (ii) the flow of heat in superfluid helium. Just like how current flows without resistance in superconducting materials at very low temperatures, superfluid helium also conducts heat efficiently at very low temperatures.

 

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