bulkphoton

Bulkphoton is not a standard term in mainstream physics. When used, it may refer to a photon-like excitation associated with the bulk of a material, i.e., a mode that propagates through the three-dimensional interior rather than being confined to a surface or interface. It could also describe a quantum of the bulk electromagnetic field in a medium or a collective excitation that behaves like a photon within the bulk.

In practice, the idea of a bulk photon could appear in several contexts. In condensed-matter photonics and in photonic crystals or metamaterials, researchers distinguish bulk modes that extend through the interior from localized surface states or edge modes. In this sense, a bulkphoton would be the delocalized bulk counterpart to surface-bound modes such as surface plasmon polaritons. The term might also arise in discussions of polaritons, where photons strongly couple to material excitations (for example, exciton-polaritons or phonon-polaritons), giving rise to mixed light–matter quasiparticles that can propagate through the bulk.

The concept overlaps with established ideas rather than introducing a new fundamental particle. For instance, photons in a medium can be described with an effective mass or altered dispersion, and bulk polaritons are commonly discussed in optics and solid-state physics. Any use of the term bulkphoton typically requires clear definition of dispersion, polarization, and spatial extent to avoid confusion with ordinary bulk photons or surface-bound excitations.

Because there is no widely accepted definition, researchers should specify the intended meaning of bulkphoton in their work, including how it differs from known bulk modes and surface states. As consensus evolves, the usage may become more precise or be replaced by more established terminology.