Excitations
An excitation is a state in which a system possesses more energy than its ground state. In quantum systems, excitations are quantized and correspond to the absorption of energy that promotes the system to a higher allowed energy level or to a collective mode. Excitations can be created by external perturbations such as photons, particle collisions, thermal energy, or applied fields, and they typically decay back toward the ground state over characteristic lifetimes.
Different systems support different kinds of excitations. In atoms and molecules, electronic excitations involve promoting electrons
Excitations are often described by their energy spectrum E(k) or E, their momentum, and their lifetime. Theoretical
Commonly cited examples include electronic transitions in atoms and semiconductors, phonons in crystals, and excitons in
Lifetime and decay pathways influence device performance, with some excitations persisting as long-lived states or contributing