surfacestate

Surfacestate, or surface state, is an electronic state localized at the surface or interface of a solid. Its wavefunction decays into the bulk, and its energy lies within a bulk band gap or near the projected bulk bands. Surface states arise when translational symmetry is terminated, creating boundary conditions that cannot be satisfied by bulk states alone.

Conventional surface states include Tamm states, arising from potential termination, and Shockley states, associated with surface termination in simple band-structure pictures. They often form a two-dimensional electron system at the surface and can influence surface reactivity and electronic transport. In semiconductors, such states can pin the Fermi level and govern surface recombination.

Topological surface states are a distinct class found in topological insulators, where robust, gapless Dirac-like states exist at the boundary between a topological and a trivial insulator. These states are protected by time-reversal symmetry and exhibit spin-momentum locking, making them resistant to non-magnetic scattering.

Modeling and observation: surface states are studied with slab calculations in density functional theory or tight-binding models; they can be probed by angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM).

Significance: surface states influence catalysis, corrosion resistance, and the design of two-dimensional electron systems and nanoelectronic devices.