bipolaron

A bipolaron is a quasiparticle that consists of two polarons bound together. Polarons are quasiparticles formed when an electron or hole interacts strongly with the lattice vibrations of a crystal, causing the lattice to distort around the charge carrier. A bipolaron is formed when two such polarons interact and bind together, resulting in a composite particle with a reduced effective mass and altered electronic properties.

Bipolarons are particularly relevant in the study of strongly correlated electron systems, such as high-temperature superconductors and certain types of semiconductors. They can significantly influence the electrical and thermal properties of these materials. The formation of bipolarons can lead to the opening of a gap in the electronic band structure, which can affect the material's conductivity and superconducting properties.

The stability and properties of bipolarons depend on various factors, including the strength of the electron-phonon interaction, the lattice structure, and the temperature. At high temperatures, thermal fluctuations can break apart the bipolaron, leading to a transition to a state where the polarons are more mobile. This transition can have important implications for the material's electronic and superconducting behavior.

Bipolarons have been studied using various experimental techniques, such as optical spectroscopy, transport measurements, and scanning tunneling microscopy. Theoretical models, including the Holstein-Hubbard model and the Peierls-Hubbard model, have been developed to describe the formation and properties of bipolarons. These models provide insights into the underlying mechanisms that govern the behavior of bipolarons in different materials.