|Quasiparticles and more quasiparticles|
|Contact: Paul Preuss, (510) 486-6249, [email protected]|
Quasiparticles are mathematical entities used to predict realistic electronic behavior by including properties, like finite range, that real electrons do not possess. In metals under ordinary conditions, so-called Landau quasiparticles closely resemble familiar electrons; as Crommie's "quantum corral" showed, an STM can clearly image their interference upon scattering.
In conventional low-temperature superconductivity the situation grows more complex. Superconductivity is carried by Cooper pairs -- usually described as pairs of electrons -- that move through the crystal lattice without resistance. A broken Cooper pair is called a Bogoliubov quasiparticle. It differs from the conventional quasiparticle in metal because it combines the properties of a negatively charged electron and a positively charged hole (an electron void).
Physical objects like impurity atoms, from which quasiparticles scatter in an ordinary metal, only weakly affect the energy of a Cooper pair in a conventional superconductor. In conventional superconductors, interference between Bogoliubov quasiparticles is hard for an STM to see.
Because of their complex global electronic structures, however, high-Tc cuprate superconductors are another matter. Thus Davis and his colleagues were able to resolve distinctive patterns of quasiparticle interference in Bi-2212.