Orbitalons

Orbitalons are a theoretical concept in condensed matter physics that describe localized excitations in the orbital degrees of freedom of strongly correlated electron systems. The term was introduced to explain phenomena observed in materials where electron interactions play a dominant role, such as certain transition metal oxides. Unlike conventional quasiparticles like phonons or magnons, orbitalons represent excitations in the arrangement of electron orbitals rather than their spin or charge.

In these materials, electrons occupy atomic orbitals, and their spatial arrangement can influence the material’s magnetic, electronic, and structural properties. Orbitalons arise when an electron transitions to a different orbital state, creating a localized disturbance in the orbital configuration. These excitations can propagate through the lattice, much like other quasiparticles, but their behavior is distinct due to the strong electron-electron interactions present in such systems.

Experimental evidence for orbitalons has been challenging to obtain, as they often coexist with other collective modes like spins and lattice vibrations. However, spectroscopic techniques such as resonant inelastic X-ray scattering (RIXS) and neutron scattering have provided indirect support for their existence in compounds like nickelates and certain perovskites. Theoretical models, including those based on the Hubbard and Heisenberg models with orbital degrees of freedom, have been used to describe their dynamics and interactions.

Orbitalons are particularly relevant in understanding phenomena such as orbital ordering, where electron orbitals align in a periodic manner, and orbital fluctuations, which can contribute to high-temperature superconductivity or colossal magnetoresistance in certain materials. Their study bridges the gap between electronic structure theory and macroscopic properties, offering insights into the complex behavior of strongly correlated electron systems.