Coulomb drag effect in coupled quantum wire systems: Finite-[formula omitted] and exchange–correlation effects

Abstract

In this paper, we study the Coulomb drag in GaAs-based coupled electron–electron (e–e) and electron–hole (e–h) quantum wire systems by calculating the drag rate over a wide range of temperature T, particle (electron/hole) number density, and some selected values of inter-wire separation. The exchange–correlations among particles are treated within the self-consistent mean-field approximation of Singwi et al. (the STLS theory) and the inter-wire interaction potential is assumed to be statically screened. We find that the drag rate increases with decrease in particle number density and/or inter-wire separation due to the increased intra- and inter-wire coupling among particles. Further, the drag rate is found to be more for coupled e–h than the e–e quantum wire system due to the stronger e–h correlations on behalf of hole’s larger effective mass. As an important finding, we assert that the drag rate abruptly enhances at the critical system parameters for which the charge-density-wave (CDW) instability has been recently reported to occur in the e–h system. On the other side, the random-phase approximation (RPA) underestimates the drag rate in comparison to the STLS theory and the difference is seen to be more in the particle’s strong coupling domain i.e. at low inter-wire spacing and/or particle number density. In addition, we report for the first time the plasmon dispersion of both the coupled e–h and e–e systems at non-zero T and find that the plasma modes get dispersed into four branches among which two are recognized as optic (in-phase) and remaining two as the acoustic (out-of-phase) plasma modes. All the four plasma energy modes show a consistent blue shift with rise in T, however, the uppermost branches of the optical and acoustic plasma modes seem to repel each other as inter-wire spacing and/or particle number density is lowered. Interestingly, the inclusion of exchange–correlations in the RPA causes a red (blue)-shift in the upper (lower) branch of both the optic and acoustic plasma modes for each of the system leading to an overall enhancement in the Coulomb drag rate.