1,394 research outputs found
Fluctuations, dissipation and the dynamical Casimir effect
Vacuum fluctuations provide a fundamental source of dissipation for systems
coupled to quantum fields by radiation pressure. In the dynamical Casimir
effect, accelerating neutral bodies in free space give rise to the emission of
real photons while experiencing a damping force which plays the role of a
radiation reaction force. Analog models where non-stationary conditions for the
electromagnetic field simulate the presence of moving plates are currently
under experimental investigation. A dissipative force might also appear in the
case of uniform relative motion between two bodies, thus leading to a new kind
of friction mechanism without mechanical contact. In this paper, we review
recent advances on the dynamical Casimir and non-contact friction effects,
highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in
Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni,
David Roberts, and Felipe da Rosa. Minor changes, a reference adde
Engineering of electromagnetic interactions in three-dimensional plasmonic metamaterials
Thesis (Ph.D.)--Boston UniversityField of nanoplasmonics study the interaction of light with nanoscale metallic structures and it possesses the great potential of being the key element in future, highly integrated, on-chip nanophotonic aevices. Several major breakthroughs have been demonstrated in the past decade regarding the utilization of plasmonics for purposes ranging from optical nanoantennas to enhanced biochemical sensing platforms. So far, studies are generally focused on two-dimensional (2D) arrangement of plasmonic nanostructures. However, engineering of materials in three dimensions (3D) by integrating different kinds of plasmonic resonances in multi-layers, offers additional degrees of freedom in our design space, resulting in remarkable effects
This thesis research investigates the outcomes of the tailoring of electromagnetic interactions between multiple plasmonic structures in three-dimensions. We are mainly focused on a coherence phenomenon termed as Farro resonance. Farro resonances are generally studied in atomic physics, which occur due to an interference between multiple excitation pathways where a discrete resonant state is coupled to a broad continuum. Fano resonances are inherently linked to an atomic physics concept termed as Electromagnetically Induced Transparency (EIT). Recently, a plasmonic analogue of the EIT effect was proposed and drew great attention. Plasmon Induced Transparency (PIT) enables one to mimic the extremely dispersive spectral characteristics of EIT, on-chip and without any stringent requirements.
In the first two parts of this work, we show that by a precise engineering of the near-field interactions of plasmonic elements, PIT effect can be carried simultaneously to multiple spectral domains. This effect has many potential applications ranging from enhanced non-linearities to novel optical communication systems. In the third part, we investigate a multi-spectral Fano resonant plasmonic structure's non-linear response by embedding a nanoscale Kerr medium to the design. We show that a unique set of effects can be achieved through the interplay of Fano resonances and embedded optical non-linearity. In the last part, we develop a unifying theory to describe Fano resonances in both purely plasmonic structures and also in other systems which are comprised of plasmonic structures coupled to molecular resonances. The developed theory provides an invaluable intuition to Fano resonances and their utilization in applications such as biosensing and spectroscopy
Schwinger boson theory of anisotropic ferromagnetic ultrathin films
Ferromagnetic thin films with magnetic single-ion anisotropies are studied
within the framework of Schwinger bosonization of a quantum Heisenberg model.
Two alternative bosonizations are discussed. We show that qualitatively correct
results are obtained even at the mean-field level of the theory, similar to
Schwinger boson results for other magnetic systems. In particular, the
Mermin-Wagner theorem is satisfied: a spontaneous magnetization at finite
temperatures is not found if the ground state of the anisotropic system
exhibits a continuous degeneracy. We calculate the magnetization and effective
anisotropies as functions of exchange interaction, magnetic anisotropies,
external magnetic field, and temperature for arbitrary values of the spin
quantum number. Magnetic reorientation transitions and effective anisotropies
are discussed. The results obtained by Schwinger boson mean-field theory are
compared with the many-body Green's function technique.Comment: 14 pages, including 7 EPS figures, minor changes, final version as
publishe
Wetting on a spherical wall: influence of liquid-gas interfacial properties
We study the equilibrium of a liquid film on an attractive spherical
substrate for an intermolecular interaction model exhibiting both fluid-fluid
and fluid-wall long-range forces. We first reexamine the wetting properties of
the model in the zero-curvature limit, i.e., for a planar wall, using an
effective interfacial Hamiltonian approach in the framework of the well known
sharp-kink approximation (SKA). We obtain very good agreement with a mean-field
density functional theory (DFT), fully justifying the use of SKA in this limit.
We then turn our attention to substrates of finite curvature and appropriately
modify the so-called soft-interface approximation (SIA) originally formulated
by Napi\'orkowski and Dietrich [Phys. Rev. B 34, 6469 (1986)] for critical
wetting on a planar wall. A detailed asymptotic analysis of SIA confirms the
SKA functional form for the film growth. However, it turns out that the
agreement between SKA and our DFT is only qualitative. We then show that the
quantitative discrepancy between the two is due to the overestimation of the
liquid-gas surface tension within SKA. On the other hand, by relaxing the
assumption of a sharp interface, with, e.g., a simple smoothing of the density
profile there, markedly improves the predictive capability of the theory,
making it quantitative and showing that the liquid-gas surface tension plays a
crucial role when describing wetting on a curved substrate. In addition, we
show that in contrast to SKA, SIA predicts the expected mean-field critical
exponent of the liquid-gas surface tension
Quasiclassical Green's function approach to mesoscopic superconductivity
Recent experiments on mesoscopic normal-metal--superconductor
heterostructures resolve properties on length scales and at low temperatures
such that the temperature is below the Thouless energy . We
describe the properties of these systems within the framework of quasiclassical
many-body techniques. Diffusive and ballistic systems are covered, both in
equilibrium and nonequilibrium situations. Thereby we demonstrate the common
physical basis of various subtopics.Comment: 38 pages, LaTeX, sup.sty-style file included, to appear in
Superlattices and Microstructures; several minor changes and corrections of
typographical errors, two updated figure
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