Subelectronvolt

Subelectronvolt is a descriptor used for energies, particles, or excitations that lie below one electronvolt (eV). Since 1 eV corresponds to about 11,600 kelvin in thermal units, the subelectronvolt range covers energies from tens of millielectronvolts down to microelectronvolts and below. The term is common in discussions of low-energy phenomena in condensed matter physics, atomic and molecular physics, and certain areas of particle physics.

In solid-state systems, many fundamental excitations are subelectronvolt. Phonons and magnons in crystals typically reside in the meV range, while the energy splittings in superconducting qubits and other quantum devices often lie in the μeV range. Infrared and terahertz radiation, and various spectroscopic probes, explore subeV photons. The subeV scale also governs thermal and electronic processes at cryogenic temperatures, where kBT can be well below 1 eV.

In particle physics and cosmology, the term is used for discussions of particles or fields with masses or energy scales under an eV, such as subeV neutrino masses or ultralight dark matter candidates. However, such usage is contextual and not a precise physical boundary; the exact relevance of the subelectronvolt scale depends on the system and experimental capabilities.

Overall, subelectronvolt denotes a broad, informal energy regime highlighting phenomena and measurements simpler or more pronounced at low energies, relative to typical atomic and molecular transitions in the eV scale.