Scientists at the University of California at San Diego (USA) found specimens of a new state of matter, which they call a coherent exciton gas. The study of its properties can significantly move us towards the exciton electronics. In a paper published March 29 in the journal Nature , scientists describe the emergence of “spontaneous coherence”, “spin texture” and “phase singularity” at the time when the excitons – a quasiparticle consisting of a bound pair of electrons and holes, and determining the special properties of semiconductors – cool almost to absolute zero (0.1 K). This is a coherent state of matter they believe hitherto unexplored, new-found.
Research group led Leonid Butov , a professor of the said university. In 2002, he found that the chilled excitons tend to organize themselves into a series of microscopic droplets, resembling a miniature pearl necklace.
At this time, using more efficient cooling instead of 1 K, as in 2002, it was possible to achieve even lower temperatures, and then using an interferometer to measure the coherence and the spin of each of these “drops”. It is found that the spin of the exciton homogeneous in space: it forms structures that the researchers have named “spin textures.” In addition, it appears that the structure of spontaneous coherence of the structures associated with the spin polarization of the phase singularities in coherent exciton gas.
“To see such a structure was a surprise – says lead researcher Alex Hay. – And another surprise was bόlshim polarization measurements, which showed that between coherence and polarization there is a strong correlation. ”
According to Leonid Butov, the physics of excitons is interesting in itself, but understanding the basic properties of excitons is needed to create the future of the exciton [optoelectronic] devices. Note that, theoretically, such devices would be used as a transistor, and even quasi-particle nuclear subatomic sizes.
Excitons themselves were created in the course of experiments with laser pulses that have been working on samples of gallium arsenide transistors are widely used in conventional cell phones. This creates a pair of negatively charged electrons, which knocks out a laser from its orbit, and the positive holes .
Mutual attraction holds the electron and hole together, giving the exciton, which they together make up the properties that differ from the properties of the electron and hole separately. However, sometimes the latter may merge: the electron takes a hole, and exciton cease to exist. To control this process, the team of Mr. Butov uses nanostructures, called ” quantum wells “, which can achieve stable existence of excitons in about 50 nanoseconds of the experiment. “It was during this time of excitons cooled, condensed form, and exhibit an interesting spin physics,” – commented the scientists. Then the merging of the electron and the hole in which they emit light, studied with the help of a complex system of mirrors – the interferometer, separating the resulting light beam into two spatial components.
It is this method and allow Californians during the experiment to see spontaneous coherence in the excitons, has never been pointed out by other scientists.