Plasmon (physics)

The quantized fluctuations in the charge carrier density in the solid are called plasmons ; quantum mechanically they are treated as boson quasiparticles . The term is a common abbreviation for plasma oscillation quanta . What the photon represents for electromagnetic waves , the plasmon is for vibrations in the Fermigas of metals.

One differentiates:

• Particle plasmon (localized surface plasmon)
• Surface plasmon
• Volume plasmon

The first two belong to the plasmon polaritons , since fluctuations in the electron density couple with electromagnetic fields outside the metal. Strictly speaking, the words "surface and particle plasmons" should therefore have the addition polariton, but this addition is usually left out.

Explanation

Classically , one can think of plasmons as oscillations of electrons that oscillate relative to the positive ions .

For better clarity, imagine a cubic metal block in a field facing to the right . The free electrons now move to the left until the field inside is balanced. Positive ions are exposed on the right edge. If you switch off the external field, the electrons migrate to the right again as a result of mutual repulsion and the attraction by the positive ions. The electrons now oscillate back and forth at the plasma frequency until the energy is used up by friction or other damping . Plasmons are the quantization of this natural oscillation .

As collective suggestions in the context of solid-state physics (electron gas in metals) they were treated in the early 1950s by David Pines and David Bohm , (volume) plasmons in silver by Herbert Fröhlich and H. Pelzer in 1955 and surface plasmons for the first time by Rufus Ritchie in 1957, the also reported with Eldridge in 1962 on the emission of photons from irradiated metal foils.

energy

Plasmons have approximately the energy

${\displaystyle E_{p}=\hbar \cdot \omega _{p}=\hbar {\sqrt {\frac {ne^{2}}{m\varepsilon _{0}}}}\,.}$

It is

• ${\displaystyle \hbar }$the Planck constant and
• ${\displaystyle \omega _{p}}$the plasma frequency
• ${\displaystyle n}$the density of valence electrons
• ${\displaystyle e}$the elementary charge
• ${\displaystyle m}$the electron mass
• ${\displaystyle \varepsilon _{0}}$the absolute dielectric constant of the vacuum.

literature

• VM Shalaev, S. Kawata: Nanophotonics with Surface Plasmons . Elsevier, 2006, ISBN 978-0-08-046799-3 ( limited preview in Google Book Search).
• D. Sarid, W. Challener: Modern Introduction to Surface Plasmons . Cambridge University Press, 2010, ISBN 978-0-521-76717-0 ( limited preview in Google Book Search).