Electron drag between two two-dimensional electron gases in magnetic fields has been observed with a polarity opposite that for zero field. This negative drag requires that the electrons have a hole-like dispersion. Density dependence measurements in the integer quantum Hall regime show that drag is negative only when the upper Landau level of one layer is more than half filled while the other is less than half filled, indicating that hole-like dispersion is present in a half of each Landau level. Negative drag is argued to be a consequence of disorder. 73.40.Hm, 71.61.Ey, 73.20.Dx

Electron drag measurements of electron-electron scattering rates performed close to the Fermi temperature are reported. While evidence of an enhancement due to plasmons, as was recently predicted [K. Flensberg and B. Y.-K. Hu, Phys. Rev. Lett. 73, 3572 (1994)], is found, important differences with the random-phase approximation based calculations are observed. Although static correlation effects likely account for part of this difference, it is argued that correlation induced multiparticle excitations must be included to account for the magnitude of the rates and observed density dependences. 73.61.Ey, 73.20.Mf, 71.45.Gm, 72.80.Ey

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A novel numerical scheme including time and spatial discretization is offered for coupled Cahn-Hilliard and Navier-Stokes governing equation system in this paper. Variable densities and viscosities are considered in the numerical scheme. By introducing an intermediate velocity in both Cahn-Hilliard equation and momentum equation, the scheme can keep discrete energy law. A decouple approach based on pressure stabilization is implemented to solve the Navier-Stokes part, while the stabilization or convex splitting method is adopted for the Cahn-Hilliard part. This novel scheme is totally decoupled, linear, unconditionally energy stable for incompressible two-phase flow diffuse interface model. Numerical results demonstrate the validation, accuracy, robustness and discrete energy law of the proposed scheme in this paper.