Few-Electron Bubbles in Superfluid Helium Gas

• 14 Jul 2021

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.

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

• 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