Elektronphonon

Electron-phonon interaction, or electron-phonon coupling, describes the interaction between itinerant electrons and lattice vibrations (phonons) in crystalline solids. Through this coupling, electrons can scatter by exchanging energy and momentum with phonons, while phonons can be driven by electronic motion. The strength and details of the interaction depend on material properties and on the character of the phonon modes, such as acoustic or optical vibrations and whether the lattice potential is polar.

Theoretical treatments usually start from perturbation theory for weak coupling and extend to more comprehensive frameworks for stronger coupling. A central concept is the electron self-energy, which captures how coupling to phonons renormalizes the effective mass and gives finite lifetimes to electronic states. The Eliashberg formalism introduces the spectral function α^2F(ω), which combines the phonon density of states with the coupling strength and yields a frequency-dependent coupling constant λ = 2 ∫ α^2F(ω)/ω dω. In polar materials, long-range Fröhlich coupling to optical phonons can be significant, while in many metals deformation-potential coupling to various phonon modes dominates.

Consequences of electron-phonon coupling include a temperature-dependent electrical resistivity arising from phonon scattering, renormalization of electronic dispersion observable as kinks in spectroscopic data, and, most notably, conventional phonon-mediated superconductivity described by BCS and Eliashberg theory. In strong coupling, carrier mass enhancement and, in some cases, polaronic effects may occur. Phonon engineering is also used to tailor thermoelectric and superconducting properties.

Experimental probes include resistivity measurements, angle-resolved photoemission spectroscopy, inelastic neutron scattering, Raman spectroscopy, and tunneling spectroscopy, all providing insight into phonon spectra and coupling strength. Electron-phonon coupling is fundamental to the behavior of many metals, doped semiconductors, and conventional superconductors, while remaining an active area of research in other materials systems.