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Few-Electron Bubbles in Superfluid Helium Gas

  • 14 Jul 2021
  • 4 min read

Why in News

Recently, 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.


  • 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.


  • Matter is made up of atoms, which are the basic units of chemical elements such as hydrogen, helium or oxygen.
  • Atoms are made up of three particles: Protons, Neutrons and Electrons.
  • Hence, electrons are the subatomic particles that orbit the nucleus of an atom. They are generally negative in charge and are much smaller than the nucleus of the atom.

Key Points

  • 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 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, 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.
      • 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.
  • Significance:
    • 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.
    • Decipher Phenomenons:
      • 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.
        • Just like how current flows without resistance in superconducting materials at very low temperatures, superfluid helium also conducts heat efficiently at very low temperatures.

Source: DTE

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