New form of matter ‘excitonium’ discovered

  • Scientists have proven the existence of new form of matter called excitonium – which was first theorised almost 50 years ago.
  • Researchers from University of California and University of Illinois studied non-doped crystals of a transition metal— dichalcogenide titanium diselenide (1T-TiSe2).
  • Excitonium exhibits macroscopic quantum phenomena, like a superconductor and is made up of excitons, particles that are formed in a very strange quantum mechanical pairing.
  • When an electron, seated at the edge of the crowded-with-electrons valence band in a semiconductor, gets excited and jumps over the energy gap to the otherwise empty conduction band, it leaves behind a “hole” in the valence band. That hole behaves as though it were a particle with positive charge, and it attracts the escaped electron. When the escaped electron with its negative charge, pairs up with the hole, the two remarkably form a composite particle, a boson – an exciton.
  • The team used a novel technique called momentum-resolved electron energy-loss spectroscopy (M-EELS) for the study. With their new technique, the group was able to measure collective excitations of the low-energy bosonic particles, the paired electrons and holes.