Browsing by Subject "Density-wave instability"

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Open Access
Density and pseudo-spin rotons in a bilayer of soft-core bosons
(Institute of Physics, 2023-05-26) Pouresmaeeli, F.; Abedinpour, S. H.; Tanatar, Bilal
We study the dynamics of a bilayer system of bosons with repulsive soft-core Rydberg-dressed interactions within the mean-field Bogoliubov-de Gennes approximation. We find roton minima in both symmetric and asymmetric collective density modes of the symmetric bilayer. Depending on the density of bosons in each layer and the spacing between two layers, the homogeneous superfluid phase becomes unstable in either (or both) of these two channels, leading to density and pseudo-spin-density wave instabilities in the system. Breaking the symmetry between two layers, either with a finite counterflow or a density imbalance renormalizes the dispersion of collective modes and makes the system more susceptible to density-wave instability.
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
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.