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WHEN IS A METAL A GOOD METAL? - THE CASE OF BISMUTH SURFACES

One of the most fascinating aspects in the study of surfaces is the effect of reduced co-ordination and dimensionality on the geometric and electronic structure. This can lead to a situation where the properties of the surface are drastically different from those of the bulk. A particularly interesting example of this are the surfaces of bismuth.

Bismuth is a group V semimetal with a very low density of states at the Fermi level and a carrier concentration which is about five orders of magnitude lower than that of a "good" metal such as copper. In sharp contrast to this, many low-index surfaces support electronic states crossing the Fermi level, which turn them into much better metals than the bulk. It will be shown that this is caused by the strong spin-orbit interaction in the heavy element Bi combined with the loss of inversion symmetry at the surface. The surfaces can thus be viewed as a nearly two-dimensional metals, but with a peculiar spin structure. Some properties of such metals will be explored, such as the formation of standing electron waves and the electric conduction through the surface layer.