Browsing by Subject "Collective excitations"

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Open Access
Collective excitations and density-wave instabilities in one-dimensional soft-core boson systems
(2024-07) Mohammadi, Zohreh
We investigated the dynamics of bosons interacting with Rydberg-dressed potentials in single-wire and double-wire structures. Specifically, we aimed to understand how the addition of Rydberg dressing, with its soft-core nature and van der Waals tail at long distances, influences the behavior of single-wire and doublewire systems of bosons. This investigation was conducted using the random phase approximation (RPA) and the Bogoliubov-de Gennes (BdG) mean-field approximation at zero temperature, focusing on the emergence of collective modes and density-wave instabilities. We examined the dispersions of collective modes in single-wire and double-wire structures of bosons with Rydberg-dressed interactions. In the long-wavelength limit, symmetric and anti-symmetric modes show linear behavior in wave vectors with distinct sound velocities. A prominent maxon-roton feature appears at intermediate wave vectors, especially at large coupling constants. The influence of wire spacing on mode dispersion is significant: smaller spacings lead to the disappearance of the asymmetric mode with free-particle-like dispersion, while larger spacings result in mode degeneracy in symmetric bi-wires due to diminished inter-wire coupling. The system becomes unstable toward density-waves at strong couplings, indicated by the vanishing roton energy, affecting both symmetric and antiymmetric branches. Additionally, density imbalances between wires shift the energy of the excitation branches and destabilize the homogeneous superfluid phase at lower coupling constants. While the roton softening observed suggests instability toward densitymodulated phases, more sophisticated numerical methods are needed to characterize these phases accurately.
Open Access
Ground-state properties, vortices, and collective excitations in a two-dimensional Bose-Einstein condensate with gravitylike interatomic attraction
(The American Physical Society, 2008) Keleş, A.; Sevinçli, S.; Tanatar, Bilal
We study the ground-state properties of a Bose-Einstein condensate with short-range repulsion and gravitylike 1/r interatomic attraction in two-dimensions (2D). Using the variational approach we obtain the ground-state energy and analyze the stability of the condensate for a range of interaction strengths in 2D. We also determine the collective excitations at zero temperature using the time-dependent variational method. We analyze the properties of the Thomas-Fermi-gravity and gravity regimes, and we examine the vortex states, finding the coherence length and monopole mode frequency for these regimes. Our results are compared and contrasted with those in 3D condensates.
Open Access
Hybridization of fano and vibrational resonances in surface-enhanced infrared absorption spectroscopy of streptavidin monolayers on metamaterial substrates
(2014) Alici, K. B.
We present spectral hybridization of organic and inorganic resonant materials and related bio-sensing mechanism. We utilized a bound protein (streptavidin) and a Fano-resonant metasurface to illustrate the concept. The technique allows us to investigate the vibrational modes of the streptavidin and how they couple to the underlying metasurface. This optical, label-free, nonperturbative technique is supported by a coupled mode-theory analysis that provides information on the structure and orientation of bound proteins. We can also simultaneously monitor the binding of analytes to the surface through monitoring the shift of the metasurface resonance. All of this data opens up interesting opportunities for applications in biosensing, molecular electronics and proteomics. © 2014 IEEE.