MAGNETIC-FIELD STUDIES OF LATERAL AND VERTICAL SUPERLATTICES

The increased succes in growing and manufacturing short period superlattices and laterally patterned structures has allowed physicists to demonstrate many of the properties first predicted when work on superlattices began. In addition new phenomena have emerged, such as coherently propagating edge states. Magnetic fields play a vital role in demonstrating and studying these phenomena. The construction of new superlattice band structures now consists in using far more properties than merely layer thickness. Strain, magnetic exchange, spin and electric field can all be built into individual layers. This allows us to look at zone-folding and mini-band formation, metal-semiconductor transitions, spin alignment, piezo-electric band modification, modified electron-phonon coupling and may other effects. Cyclotron motion through the structures and the resulting energy quantisation provide the means to map out these phenomena. The most direct spectoscopic information comes from studies such as inter and intra-band magneto-optics, which allow us measure mini-band widths and zone-folding. Magnetotransport gives us information on the charge transfer and energy levels in structures, and can also demonstrate radical changes in the superlattice properties when large magnetic fields are applied. Lateral patterning, particularly when magnetic fields are applied, allows us to study 1-D and 2-D superlattice potentials in a plane. This can be used to study both individual quantum dots or connected lines or arrays which can exhibit controlled tunnelling or metal-insulator transitions.