Direct measurement of the Hall effect in a free-electron-like surface state

We have succeeded in directly measuring the Hall effect in a single-atomic layer on a Si (111) crystal surface. Our four-point-probe transport measurements under magnetic field showed that the behavior of majority carriers in the surface state changed from electronlike to holelike during the structural conversion from the root 3 x root 3-Ag to root 21 x root 21-(Ag, Au) surface superstructure. This is due to a change in the Fermi surface caused by band folding. The results are discussed quantitatively and shown to be consistent with the electronic structure obtained by photoemission spectroscopy.