Surface quantum oscillations in silicon (100) inversion layers under uniaxial pressure

Surface quantum oscillations in (100) n-type silicon inversion layers were studied as a function of uniaxial compression. Due to an increase of the cyclotron mass the ratio of spin splitting to Landau splitting increases continuously with pressure. At p=3. 6 kbar, has roughly doubled. At zero pressure only the light-mass subband E₀ is occupied, whereas in the high-pressure limit only the heavy-mass subband E₀^' is populated. However, a simultaneous occupation of E₀ and E₀^' at medium pressures must be excluded, since the measured valley degeneracy factor is 2 in the whole pressure range investigated. An interaction between E₀ and E₀^' must be invoked, which generates a new twofold degenerate electron ground state at medium pressures. The pressure value at which the interaction becomes significant and also the cyclotron mass seem to depend on the magnetic field. Qualitatively, the experimental results can be explained by a theory of Kelly and Falicov which is based on the existence of charge-density waves in the silicon surface.