Browsing by Subject "Bose gas"

Now showing 1 - 4 of 4

Open Access
Counterflow in Bose gas bilayers: collective modes and dissipationless drag
(American Institute of Physics, 2020) Abedinpour, S. H.; Tanatar, Bilal
We investigate the collective density oscillations and dissipationless drag effect in bilayer structures of ultra-cold bosons in the presence of counterflow. We consider different types of inter-particle interactions and obtain the drag coefficient and effect of counterflow on the sound velocity. We observe that counterflow enhances (suppresses) the energy of symmetric (asymmetric) density mode and drives the homogeneous system towards instability. The dependence of the drag coefficient on the spacing between two layers is determined by the form of particle-particle interaction.
Open Access
Many-body properties of one-dimensional systems with contact interaction
(1999) Demirel, Ekrem
The one-dimensional electron systems are attracting a lot of interest because of theoretical and technological implications. These systems are usually fabricated on two-dimensional electron systems by confining the electrons in one of the remaining free directions by using nanolithographic techniques. There are also naturally occuring orgnanic conductors such as TTF-TCNQ whose conductivity is thought to be largely one-dimensional. The one-dimensional electron systems are important theoretically since they constitute one of the simplest many-body systems of interacting fermions with properties very different from three- and two-dimensional systems. The one-dimensional electron gas with a repulsive contact interaction model can be a useful paradigm to investigate these peculiar many-body properties. The system of bosons are also very interesting because of the macroscopic effects such as Bose-Einstein condensation and superfluidity. Another motivation to study one-dimensional Bose gas is the theoretical thought that one-dimensional electron gas gives boson gas characteristics. This work is based on the study of correlation effects in one-dimensional electron and boson gases with repulsive contact interactions. The correlation effects are described by a localfield correction which takes into account the short-range correlations. We use Vashishta-Singwi approach to calculate static correlation effects in onedimensional electron and boson gases. We find that Vashishta-Singwi approach gives better results than the other approximations. We also study the dynamical correlation effects in a one-dimensional electron gas with contact interaction within the quantum version of the self-consistent scheme of Singwi et al. (STLS) We calculate frequency dependent local-field corrections for both density and spin fluctuations. We investigate the structure factors, spin-dependent pair-correlation functions, and collective excitations. We compare our results with other theoretical approaches.
Open Access
Strongly interacting one-dimensional Bose condensates
(2000) Erkan, Kamil
Recent observation of Bose-Einstein condensation in dilute alkali gzises led to a great interest in this area both experimentally and theoretically. The most important characteristics of a Bose-Einstein condensate is that it consists of a large number of atoms occupying a single quantum state. This kind of a feature seen in photons led to the production of widely-used photon lasers. Coherent state of atoms may lead to the production of atom lasers in near future. The well-known Bogoliubov model to explain the nature of Bose-Einstein condensates of trapped dilute gases is valid when the interaction between particles is weak. However, as the number of atoms is increased, the interaction effects lead to a significant contribution in the system. Several attempts were made to improve the Bogoliubov model and to explain strongly interacting systems but these treatments are accurate up to a finite strength of the coupling . One-dimensional Bose systems is important because exact solution of the homogenous problem exists. Also it is a good testing ground to study interaction effects since only two-body interactions play role in these systems. Furthermore, experimental realization of one-dimensional systems are attracting a great deal of interest into the present problem. We investigate a somewhat different method to study the properties of strongly coupled Bose condensates in one-dimensional space. It uses the socalled Kohn-Sham theory to solve the problem by considering the exact solution of the homogenous one-dimensional Bose gas. The new approach reveals that interactions are expressed by a ■0^ term in the strongly coupled regime in contrast to a 0^ term in weak coupling regime. The model is applied to several types of trap potentials by performing a numerical minimization. We also improve the model for the case of a finite temperature. We observe that the system has a non-zero critical temperature which suggests a real phase transition in onedimensional space. In the last part, we work on the stability of a two-component condensate in a harmonic trap potential. We find that for a wide range of system parameters either a coexisting or a phase-segregated mixture can be obtained.
Open Access
Variational Monte Carlo study of two dimensional charged bosons
(2014-09) Karakuzu, Seher
We studied the ground state properties of 2D charged Bosons interacting via Coulomb potential using the Variational Monte Carlo method. We start with the paper of McMillan [1] in which there are 3D Bosons interacting via Lennard-Jones potential. We calculate ground state energy and pair distribution function of the system and our results are compared with the original work. We also reproduce the paper of Liu et al. [2] and study the 2D Bosons interacting with the same potential. Our results are compared with the original work. In order to evaluate long-range potentials in periodic systems we introduce Ewald summation method for 2D system and Natoli-Ceperley method which evaluates potentials optimally. We compare our Natoli-Ceperley results with the Holzmann et al. [3]. We also investigate 2D charged Boson system interacting via Coulomb potential using the RPA pseudo potential. Our results are compared with de Palo et al. [4]. We try to optimize the wave function further introducing a Kinetic Energy projection to the original RPA wave function. We show that it is very difficult to optimize it further since it is a very good wave function.