New semiconductor quasiparticles

The discovery improves our understanding of the interactions between electrons in a variety of situations, including understanding their behavior within opto-electronic devices.

Physicists have used a high-speed laser to reveal new quasi-particles of semiconductors - particles that quickly crystallize into liquid-like droplets. The discovery improves our understanding of the interactions between electrons in a variety of situations, including understanding their behavior within opto-electronic devices.

Physicists from the Joint Institute for Laboratory Astrophysics (JILA) in the US used a multi-speed laser to discover new quasi-particles of semiconductors that eventually form a liquid droplet. Quasi-particles consist of smaller particles that are trapped inside solid materials and can behave in a predictable way. A small example is an exciton, the pair consisting of an electron and the "hole" from which it came, which is a niche in the energy structure of the material where the electron was supposed to be, but it was absent from there.

 

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The new quasi-particle, described in an article published on February 27.02.2014, 25 in the prestigious scientific journal Nature, is a microscopic coupling of electrons and holes in an unpaired and innovative array. The researchers call this new state a "quantum droplet" because it has known quantum properties, such as highly ordered energy levels, but it also has several properties of a liquid. The state, for example, can create waves, similar to a liquid. The situation is different from ordinary liquids, for example water, since the quantum tip has a finite size, outside of which the connection between the electrons and the holes disappears. Although the lifetime of the new state is extremely short at XNUMX picoseconds (trillionths of a second), the quantum typhoon is stable enough for researchers to study how light shone on it reacts with these special forms of matter.

"Electron-hole droplets are known in semiconductor materials, but they typically contain thousands of millions of electrons and holes," explains physicist Steven Cundiff. "In the new case we are talking about droplets with only five electrons and five holes." The researchers created the new quasi-particle by exciting a gallium arsenide semiconductor with a high-speed red laser beamed at a frequency of 100 million pulses per second. In the first step, the laser creates excitons, which move inside the semiconductors. As the laser power increases, more and more electron-hole pairs are formed and the quantum droplets are formed when the exciton density reaches a threshold value. At this point the coupling disappears and a number of electrons are positioned in a specific array relative to a given hole. The droplets behave like bubbles held together by pressure coming from the plasma surrounding them.

The experimental data obtained by the researchers regarding the energy levels of an individual drop corresponded to the theoretical calculations made even earlier. The researchers discovered that they can affect any energy level by changing the quantum properties of the laser pulses. It seems on the face of it that the typhoon is stable enough to carry out future ongoing studies regarding the interrelationships between radiation and specially defined states of matter stored within it. In addition, quasi-particles can have exotic properties that do not exist in other known materials, and thanks to these properties allow control of the behavior of larger systems and devices.
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