multisubband

Multisubband refers to systems in which several quantized transverse energy levels, or subbands, are occupied and contribute to physical properties. Quantization arises from confinement in one dimension in structures such as quantum wells, quantum wires, nanoribbons, or nanotubes. The confinement produces discrete subband energies E_n with associated wavefunctions; the spacing ΔE depends on well width, material, and geometry. When the Fermi level or external excitation exceeds multiple ΔE, several subbands are populated.

Consequences of multisubband occupation include multiple conducting channels in transport, which affect conductance steps, mobility, and scattering. In low-temperature experiments, Shubnikov-de Haas oscillations may reflect several occupied subbands. In optics, intersubband transitions between subbands produce absorption or emission lines in the infrared to terahertz range.

Modeling multisubband systems typically uses the envelope-function or effective mass approximations, solving the Schrödinger equation with the confinement potential. Self-consistent Schrödinger-Poisson methods are common for heterostructures. For transport, multi-subband Boltzmann or Kubo formalisms can be employed, with intersubband coupling and many-body effects sometimes playing a significant role.

Applications and examples of multisubband physics include infrared detectors and quantum cascade lasers that rely on transitions between subbands, as well as fundamental studies of two-dimensional electron gases in quantum wells. Materials commonly studied include GaAs/AlGaAs, Si/SiGe, and graphene nanoribbons, where multiple subbands can be occupied under appropriate conditions.