meV

meV stands for milli-electronvolt, a unit of energy equal to one thousandth of an electronvolt. An electronvolt (eV) is defined as the amount of kinetic energy gained by an electron when accelerated through an electric potential difference of one volt. In SI energy units, 1 eV equals 1.602176634×10^-19 joules, so 1 meV equals 1.602176634×10^-22 J. Using E = h f, 1 meV corresponds to a frequency of about 0.2417 terahertz (THz) or 241.7 gigahertz. In terms of temperature via Boltzmann’s constant, 1 meV is about 11.6 kelvin, making the meV scale typical for low-temperature and solid-state phenomena.

The meV scale is widely used in condensed matter physics and materials science to describe low-energy excitations and features. It is common for characterizing phonons (lattice vibrations), magnons (spin excitations), superconducting gaps, and confined electronic or excitational structures in nanosystems. Because thermal energy at room temperature is about 25 meV, many meV-scale phenomena become especially relevant at cryogenic temperatures.

Measurement techniques frequently associated with meV energies include inelastic neutron scattering and inelastic X-ray scattering, terahertz and far-infrared spectroscopy, and electron energy loss spectroscopy at low energies. While some spectroscopies report energies in eV or higher, the meV range is essential for resolving subtle, low-energy dynamics and gap structures in quantum materials.