Physicists at Kiel University discover an unusual state of matter
The existence of an unusual state of matter, a crystal that consists entirely of holes, has been proven at Kiel University. As reported in the latest issue of Physical Review Letters (December 2nd , 2005), an international team led by Professor Michael Bonitz has, for the first time, demonstrated with the help of extensive computer simulations that this exotic phenomenon, the existence of which was hitherto only a subject of speculation, should certainly occur. The physicists have also been able to predict the conditions for its formation.
"We now know that this effect occurs in semiconductors with a certain type of band structure", says Bonitz. "In normal solids, the electrons and holes (which are formed when electrons are excited) are both far extended inside the solid - a consequence of quantum mechanics. Electrons and holes penetrate the material like a liquid". However, when the mass of a hole exceeds a certain critical value - 80 times the mass of an electron - the hole liquid undergoes a spontaneous change to become a crystal. Furthermore, there are strong indications that in semiconductor systems of this kind, a reduction of pressure can result in the formation of Bose condensates of bound electron-hole pairs (so-called excitons). Anticipating the next stage of the research, the physicist explains that "the next exciting problem is to set up an experiment that will confirm our prediction of the crystal of holes". Suitable materials systems for this have already been suggested.
Susanne Schuck | alfa
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