Quasiparticles in Semiconductors

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The term quasiparticles describe a physical concept, which treats elementary excitations of a combination of strongly interacting particles, called quasi-particles. This new class of quasiparticles which acts as a single subatomic particle could help researchers better understand semiconductor that is essential for most modern electronic devices

Concept of Quasiparticles

In the beginning, it sounded interesting to treat excitations as particles. But let‘s think about what matter is. According to Einstein’s theory of relativity, we know that matter and energy are essentially the same. The matter can be converted into energy, as in fission and fusion reactors, or else, energy can be converted into matter.

The introduction of this concept has considerably simplified the methods for describing the variety of processes in many particle systems with great interaction. The idea of quasiparticles has reduced the complex dynamics of systems composed of strongly interacting particles to simpler dynamic systems.

Differences Between Quasiparticles and Elementary Particles

The quasiparticles and the usual elementary particles have both similarities and key differences. Like normal particles, quasiparticles can be confined in space and maintain their localization in motion; they can interact with both particles and other quasiparticles. In contrast, quasiparticles cannot exist outside of a medium, whose elementary excitations are essential for their existence.

Quasiparticles are studied in connection with modern solid-state physics and nuclear physics because they play a significant role in determining the properties of matter. However, that all particles may really be disturbances in some original medium.

Quasiparticle can be divided into two classes by their internal structure: single-particle excitations (electron-hole) and collective excitations, i.e. sets of equal components (e.g. exciton, plasmon, etc.).

Measurement of Quasiparticles

An experimental technique for measuring quasiparticles is Raman spectroscopy: the sample is exposed to laser light from which a small part of inelastic scattering. The laser light photons can give off energy to produce a quasiparticle or take the energy from an already existing one. In the Raman spectra, processes can be linked to Stokes (creation of quasiparticle) and Anti-Stoke Peaks.

Examples of quasiparticles include a phonon, plasmon, exciton, hole, and magnon. There also more complex quasiparticles representing combinations of the above examples. The two types of quasiparticles consist in one system have similar values of energy and momentum, they hybridize quasiparticles with the formation of two new quasiparticles, each having certain characteristics of the two original quasiparticles. Examples of these quasiparticles are; photon mixed with an exciton or an optical phonon results in the formation of polaritons and mixing a photon with a magnon results in the formation of photomagnons.

New Kind of Quasiparticles

A new kind of quasiparticle found in semiconducting crystals known as collexon. These quasiparticles can exhibit unique optical features and unusual physical properties, which are of interested to both applied and fundamental science.

Christian Nenstiel and colleagues, Technical University of Berlin, they inserted germanium atoms into a gallium nitride semiconductor, a similar to silicon. The team realized that a large number of free electron in germanium help to steady excitons to form the new kind of quasiparticle.

Collexons could be recognized as a common feature of semiconducting materials. Since semiconductors being fundamental to modern technology, improving our understanding of their electronic structure could be useful to both theorists and experimentalists.

It is too early to forecasting the applications of quasiparticles; a lot of interesting physics is still waiting for us.

Gordon Callsen, Federal Polytechnic School of Lausanne, Switzerland

Sources and Further Reading

Updated on 18/09/18

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