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We investigate the effect of exchange and correlation ͑XC͒ on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a different approach, which employs dynamic XC kernels in the calculation of the bilayer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. The spectrum of bilayer plasmons and the drag resistivity are calculated in a broad range of temperatures taking into account both intra-and interlayer correlation effects. We observe that both plasmon modes are strongly affected by XC corrections. After the inclusion of the complex dynamic XC kernels, a decrease of the electron density induces shifts of the plasmon branches in opposite directions. This is in stark contrast with the tendency observed within random phase approximation that both optical and acoustical plasmons move away from the boundary of the particle-hole continuum with a decrease in the electron density. We find that the introduction of XC corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the random phase approximation is found to disappear when the XC corrections are included. Our numerical results at low temperatures are in good agreement with the results of recent experiments by Kellogg et al. ͓Solid State Commun. 123, 515 ͑2002͔͒.
We investigate the effect of exchange and correlation ͑XC͒ on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a different approach, which employs dynamic XC kernels in the calculation of the bilayer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. The spectrum of bilayer plasmons and the drag resistivity are calculated in a broad range of temperatures taking into account both intra-and interlayer correlation effects. We observe that both plasmon modes are strongly affected by XC corrections. After the inclusion of the complex dynamic XC kernels, a decrease of the electron density induces shifts of the plasmon branches in opposite directions. This is in stark contrast with the tendency observed within random phase approximation that both optical and acoustical plasmons move away from the boundary of the particle-hole continuum with a decrease in the electron density. We find that the introduction of XC corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the random phase approximation is found to disappear when the XC corrections are included. Our numerical results at low temperatures are in good agreement with the results of recent experiments by Kellogg et al. ͓Solid State Commun. 123, 515 ͑2002͔͒.
We study the spin Coulomb drag in a quasi-two-dimensional electron gas of finite transverse width, including local field corrections beyond the random phase approximation (RPA). We find that the finite transverse width of the electron gas causes a significant reduction of the spin Coulomb drag. This reduction, however, is largely compensated by the enhancement coming from the inclusion of many-body local field effects beyond the RPA, thereby restoring good agreement with the experimental observations by C. P. Weber et al. [Nature (London) Lately a number of spin-based devices have been designed and studied with the goal of combining memory and logical functions in a single device [1][2][3][4][5]. A crucial requirement for most spin devices is the existence of a robust population of spin-polarized carriers [6] as well as the feasibility of moving the spins in the device by means of spin currents. In this context, understanding the various scattering processes which control the relaxation of the spin and the spin current has emerged as an important theoretical and practical problem. In this Letter we focus on the spin current relaxation caused by electron-electron scattering in quasi-two-dimensional quantum wells of finite width.It is now well established [5,7,8] that the Coulomb interaction induces momentum transfer between the carrier populations of ''up'' and ''down'' spin. This results in a spin Coulomb drag (SCD) effect within a single twodimensional electron gas (2DEG) layer, in close analogy to the conventional charge Coulomb drag, which occurs between spatially separated layers. Because the inherent friction between the two spin components leads to a decay of the spin current even in the absence of impurities, the SCD has recently become a subject of experimental and theoretical investigations [9][10][11][12][13]. In particular, the SCD is known to reduce the spin diffusion constant relative to the conventional density diffusion constant, and thus to prolong the time during which a spin packet can be effectively manipulated. Indeed a significant reduction in the spin diffusion constant was measured by Weber et al. [9] and found to be in quantitative agreement with the SCD reduction calculated for a strictly 2DEG in the random phase approximation (RPA) [10].The agreement between the RPA theory for an electron gas of zero width and the experiment is encouraging, but also somewhat puzzling. Quantum wells in which the experiments have been performed are not strictly twodimensional but have finite transverse widths of the order of 10 nm. In contrast to the conventional charge Coulomb drag, where the interlayer spacing causes an exponential suppression of large angle scattering events, the main contribution to the SCD comes from events with a momentum transfer of the order of the Fermi momentum. At such values of the momentum transfer, the form factor that takes into account the width of the 2DEG is significantly smaller than 1, and should cause a significant reduction of the SCD even at relatively high temper...
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