Browsing by Subject "Collective modes"

Now showing 1 - 6 of 6

Open Access
Collective modes in a bilayer dipolar fermi gas and the dissipationless drag effect
(Springer, 2013) Tanatar, Bilal
We consider the collective modes of a bilayer dipolar Fermi system in which the particles interact via long range (∼1/r 3) interaction. Assuming that each layer has a background flow which varies little and that the dynamics of the superfluid near T=0 is the same as that of a normal fluid, we obtain the dispersion relations for the collective modes in the presence of background flow. Decomposing the background flow into two parts, the center-of-mass flow and counterflow, we focus on the properties of the counterflow. We first find an estimate of the change in the zero-point energy ΔE ZP due to counterflow for a unit area of bilayer. Combining this with the free energy F of the system and taking the partial derivatives with respect to background velocities in the layers, we determine the current densities which reveal the fact that current in one layer does not only depend on the velocity in the same layer but also on the velocity of the other layer. This is the drag effect and we calculate the drag coefficient.
Open Access
Correlations in charged fermion-boson mixture in dimensionalities D = 2 and D = 3
(Elsevier B.V., 2006) Asgari, R.; Tanatar, Bilal
We numerically study the correlation effects in a two-component charged fermion-boson mixture at zero temperature investigating the role played by the statistical effects and Coulomb correlations in a model with different fermion and boson mass ratios in two and three dimensions. The local-field factors describing the correlation effects and collective excitation modes are determined through the self-consistent scheme. We find that the effects of correlations and statistics are more pronounced in two-dimensional mixtures.
Open Access
Density-wave instability and collective modes in a bilayer system of antiparallel dipoles
(IOP Publishing, 2018-01) Akatürk, E.; Abedinpour, S. H.; Tanatar, Bilal
We consider a bilayer of dipolar particles in which the polarization of dipoles is perpendicular to the planes, in the antiparallel configuration. Using accurate static structure factor S q( ) data from hypernetted-chain (HNC) and Fermi HNC calculations, respectively for an isolated layer of dipolar bosons and dipolar fermions, we construct effective screened intralayer interactions. Adopting the random-phase approximation for interlayer interactions, we investigate the instability of these homogeneous bilayer systems towards the formation of density waves by studying the poles of the density–density response function. We have also studied the collective modes of these systems and find that the dispersion of their antisymmetric collective mode signals the emergence of the density wave instability as well.
Open Access
Drag effect in double-layer dipolar fermi gases
(IOP, 2014) Tanatar, Bilal; Renklioğlu, Başak; Öktel, M. Özgür
We consider two parallel layers of two-dimensional spin-polarized dipolar Fermi gas without any tunneling between the layers. The effective interactions describing screening and correlation effects between the dipoles in a single layer (intra-layer) and across the layers (interlayer) are modeled within the Hubbard approximation. We calculate the rate of momentum transfer between the layers when the gas in one layer has a steady flow. The momentum transfer induces a steady flow in the second layer which is assumed initially at rest. This is the drag effect familiar from double-layer semiconductor and graphene structures. Our calculations show that the momentum relaxation time has temperature dependence similar to that in layers with charged particles which we think is related to the contributions from the collective modes of the system.
Open Access
Phase diagram and dynamics of Rydberg-dressed fermions in two dimensions
(American Physical Society, 2017) Khasseh, R.; Abedinpour, S. H.; Tanatar, Bilal
We investigate the ground-state properties and the collective modes of a two-dimensional two-component Rydberg-dressed Fermi liquid in the dipole-blockade regime. We find instability of the homogeneous system toward phase-separated and density ordered phases, using the Hartree-Fock and random-phase approximations, respectively. The spectral weight of collective density oscillations in the homogenous phase also signals the emergence of density-wave instability. We examine the effect of exchange hole on the density-wave instability and on the collective-mode dispersion using the Hubbard local-field factor.
Open Access
Quantum Monte Carlo simulations of ultracold atomic systems
(2019-07) Akatürk, Emre
Here, we present our work and findings on ultracold atomic systems. We first present a semi-analytical work on density wave instability (DWI) and collective modes of a bilayer dipolar system of bosons and fermions. We then show our results for quantum Monte Carlo (QMC) simulations on a bosonic system with an impurity in two-dimensions (2D). We investigate DWI on two parallel layers with antiparallel dipoles that have little to no pairing between interlayer particles. We observe that for both fermionic and bosonic bilayers, below a threshold intralayer coupling strength, no density wave instability emerges. At higher couplings, DWI forms below a critical layer spacing. We also investigate collective modes in this system. For the second problem, we present our investigations of a 2D Bose polaron, which is a system with bosonic particles and a mobile impurity. We use diffusion Monte Carlo (DMC) simulations to calculate physical quantities such as polaron energy and effective mass of the polaron as well as quantities that give insight to structural properties of the system such as pair correlation function and density profile. We model the boson-boson and boson-impurity interaction with hard spheres.