Browsing by Author "Das, A. K."

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Open Access
Collective excitations and screened interactions in two-dimensional charged Bose systems
(Institute of Physics Publishing Ltd., 1995) Tanatar, Bilal; Das, A. K.
We study the collective excitation spectrum of a two-dimensional charged Bose gas interacting via long- and short-range potentials. The resulting plasmon dispersions depend on the type of interaction. Extending our results to a double-layer system, we calculate the dispersion relations of ensuing optical and acoustic plasmons, and screened interactions. The effective interactions exhibit attractive parts which may have interesting consequences. Comparison of our results with a two-dimensional electron gas is made.
Open Access
Drag effect for a bilayer charged-Bose-gas system
(American Physical Society, 1996) Tanatar, Bilal; Das, A. K.
The Coulomb-drag effect, which has previously been considered theoretically and experimentally for a system of two electron gas layers, is studied for a system of two charged-Bose-gas (CBG) layers within an analytically solvable model. We consider a bilayer CBG in the presence of counterflow which, in superfluid mixtures and in spatially separated superconductors, leads to a drag effect. We investigate the effects of counterflow on the collective excitations, interaction energy, screened interactions, induced charge densities, and plasmon density of states in the bilayer CBG. These quantities, many of which have not been considered in connection with Coulomb drag in a bilayer electron gas, show how the many-body properties are affected, and thus provide additional insights into the drag effect.
Open Access
Effects of disorder on collective modes in single-and double-layer Bose systems
(Institute of Physics Publishing Ltd., 1996) Tanatar, Bilal; Das, A. K.
We report some new results from our study of two-dimensional (2D) Bose systems, particularly the collective excitations in 2D charged Bose gas, in the presence of disorder. The effects of disorder are taken into account through collisions the Bose particles suffer due to disorder; these collisions are considered in the relaxation-time approximation within a number-conserving scheme in the random-phase approximation (RPA) at T = 0. The dependence of the plasmon dispersion on the boson interparticle potential, and the critical wave vector below which the plasma excitations cannot propagate, are investigated. The static structure factor S(q) in the presence of disorder is evaluated in closed form. We consider single- and double-layer systems and compare our results with the corresponding electron gas systems. A double-layer system in which one layer is disordered while the other is disorder-free exhibits results analogous to the 'drag effect'. Many-body extensions beyond the RPA are also discussed.
Open Access
Many-body properties of a disordered charged Bose gas superlattice
(Academic Press, 2000) Tanatar, Bilal; Das, A. K.
We study some many-body properties of a disordered charged Bose gas (CBG) superlattice-an infinite array of CBG layers each of which containing disorder. The latter is assumed to cause collisions with the charged bosons, the effect of collisions being taken into account through a number-conserving relaxation time approximation incorporated within the random phase approximation (RPA) at T = 0. We go beyond the RPA and include a local-field correction G(q, q z) which is assumed to be collision independent, as an approximation. The resulting density-density correlation function is then used to calculate a number of many-body quantities of physical interest, e.g. (a) collective modes, (b) static structure factor, (c) energy-loss function, (d) plasmon density of states, and (e) groundstate energy. The effects of collisions on these quantities are discussed, and the results are compared with the corresponding results for an electron gas superlattice.
Open Access
Self-consistent theory of localization and Coulomb drag effect
(American Physical Society, 2000) Tanatar, Bilal; Das, A. K.
We study the Coulomb drag rate for electrons in a double-quantum-well structure in the presence of disorder. The self-consistent theory of localization is used to obtain the frequency dependence of the generalized diffusion coefficient which influences the response functions. The interplay between screening effects and disorder at low temperature gives rise to an enhanced drag rate as the system goes from a weakly localized to a strongly localized phase with increasing disorder. The change in the interlayer momentum transfer rate may be used as a probe to investigate localization properties of coupled quantum-well systems. ©2000 The American Physical Society.