Browsing by Subject "Atomic physics"

Now showing 1 - 10 of 10

Open Access
Anti-de sitter-wave solutions of higher derivative theories
(American Physical Society, 2013) Gürses, M.; Hervik, S.; Şişman, T. Ç.; Tekin, B.
We show that the recently found anti-de Sitter (AdS)-plane and AdS-spherical wave solutions of quadratic curvature gravity also solve the most general higher derivative theory in D dimensions. More generally, we show that the field equations of such theories reduce to an equation linear in the Ricci tensor for Kerr-Schild spacetimes having type-N Weyl and type-N traceless Ricci tensors. © 2013 American Physical Society.
Open Access
Atomic and electronic structure of carbon strings
(IOP Publishing Ltd., 2005) Tongay, S.; Dag, S.; Durgun, Engin; Senger, R. T.; Çıracı, Salim
This paper presents an extensive study of various string and tubular structures formed by carbon atomic chains. Our study is based on first-principles pseudopotential plane wave and finite-temperature ab initio molecular dynamics calculations. Infinite- and finite-length carbon chains exhibit unusual mechanical and electronic properties such as large cohesive energy, axial strength, high conductance, and overall structural stability even at high temperatures. They are suitable for structural and chemical functionalizations. Owing to their flexibility and reactivity they can form linear chain, ring, helix, two-dimensional rectangular and honeycomb grids, three-dimensional cubic networks, and tubular structures. Metal-semiconductor heterostructures and various quantum structures, such as multiple quantum wells and double-barrier resonant tunnelling structures, can be formed from the junctions of metallic carbon and semiconducting BN linear chains. Analysis of atomic and electronic structures of these periodic, finite, and doped structures reveals fundamentally and technologically interesting features, such as structural instabilities and chiral currents. The double covalent bonding of carbon atoms depicted through self-consistent charge density analysis underlies the chemical, mechanical, and electronic properties.
Open Access
Atomic strings of group IV, III-V, and II-VI elements
(American Institute of Physics, 2004) Tongay, S.; Durgun, Engin; Çıracı, Salim
A systematic first-principles study of atomic strings made by group IV, III-V, and II-VI elements has revealed interesting mechanical, electronic, and transport properties. The double bond structure underlies their unusual properties. We found that linear chain of C, Si, Ge, SiGe, GaAs, InSb, and CdTe are stable and good conductor, although their parent diamond (zincblende) crystals are covalent (polar) semiconductors but, compounds SiC, BN, AlP, and ZnSe are semiconductors. First row elements do not form zigzag structures.
Open Access
Canonical-covariant Wigner function in polar form
(OSA - The Optical Society, 2000) Hakioǧlu, T.
The two-dimensional Wigner function was investigated in polar canonical coordinates. The covariance properties under the action of affine canonical transformations were derived. The polar canonical phase-space representations were considered important for paraxial optical systems as well as other systems in which a rotational symmetry around a particular axis was present.
Open Access
Diodelike asymmetric transmission of linearly polarized waves using magnetoelectric coupling and electromagnetic wave tunneling
(American Physical Society, 2012-05-24) Mutlu, M.; Akosman, A. E.; Serebryannikov, A. E.; Özbay, Ekmel
An asymmetric, reciprocal, diffraction-free transmission of linearly polarized waves in a new diodelike, three-layer, ultrathin, chiral structure is studied theoretically and experimentally. The exploited physical mechanism is based on the maximization of the cross-polarized transmission in one direction due to the polarization selectivity dictated by the peculiar eigenstate combination, which is efficiently controlled by the electromagnetic tunneling through the metallic subwavelength mesh sandwiched between these layers. Simulation and microwave experiment results demonstrate a nearly total intensity transmission at normal incidence in one direction and a small intensity transmission in the opposite direction.
Open Access
Energy dissipation in atomic force microscopy and atomic loss processes
(American Physical Society, 2001) Hoffmann, P. M.; Jeffery, S.; Pethica, J. B.; Özer, H. Ö.; Oral, A.
Atomic scale dissipation is of great interest in nanomechanics and atomic manipulation. We present dissipation measurements with a linearized, ultrasmall amplitude atomic force microscope which is capable of measuring dissipation at chosen, fixed separations. We show that the dynamic dissipation in the noncontact regime is of the order of a few 10–100 meV per cycle. This dissipation is likely due to the motion of a bistable atomic defect in the tip-surface region. In the contact regime we observe dc hysteresis associated with nanoscale plasticity. We find the hysteretic energy loss to be 1 order of magnitude higher for a silicon surface than for copper.
Open Access
Generation of long-living entanglement between two separate three-level atoms
(The American Physical Society, 2005) Çakir, Ö.; Dung, H. T.; Knöll, L.; Welsch, Dirk- Gunnar
A scheme for nonconditional generation of long-living maximally entangled states between two spatially well separated atoms is proposed. In the scheme, A-type atoms pass a resonatorlike equipment of dispersing and absorbing macroscopic bodies giving rise to body-assisted electromagnetic field resonances of well-defined heights and widths. Strong atom-field coupling is combined with weak atom-field coupling to realize entanglement transfer from the dipole-allowed transitions to the dipole-forbidden transitions, whereby the entanglement is preserved when the atoms depart from the bodies and from each other. The theory is applied to the case of atoms passing by a microsphere.
Open Access
Ground-state properties and collective excitations in a 2D Bose-Einstein condensate with gravity-like interatomic attraction
(Springer, 2008) Keleş, Ahmet; Sevinçli, Sevilay; Tanatar, Bilal
We study the ground-state properties of a Bose-Einstein condensate (BEC) with the short-range repulsion and gravitylike 1/r interatomic attraction in two-dimensions (2D). Using the variational approach, we obtain the ground-state energy and show that the condensate is stable for all interaction strenghts 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 (TF-G) and gravity (G) regimes.
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
Persistent perfect entanglement in atomic systems
(IOP, 2004) Çakır, Özgür; Can, M. Ali; Klyachko, Alexander A.; Shumovsky, Alexander S.
It is shown that the system of an even number of three-level atoms in the Λ configuration in a cavity can evolve into a persistent maximum entangled state. The time of formation of such an entangled state is estimated.