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We show that the dispersive force between a spherical nanoparticle (with a radius $le$ 100 nm) and a substrate is enhanced by several orders of magnitude when the sphere is near to the substrate. We calculate exactly the dispersive force in the non-retarded limit by incorporating the contributions to the interaction from of all the multipolar electromagnetic modes. We show that as the sphere approaches the substrate, the fluctuations of the electromagnetic field, induced by the vacuum and the presence of the substrate, the dispersive force is enhanced by orders of magnitude. We discuss this effect as a function of the size of the sphere.
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The role of geometry on dispersive forces is investigated by calculating the energy between different spheroidal particles and planar surfaces, both with arbitrary dielectric properties. The energy is obtained in the non-retarded limit using a spectral representation formalism and calculating the interaction between the surface plasmons of the two macroscopic bodies. The energy is a power-law function of the separation of the bodies, where the exponent value depends on the geometrical parameters of the system, like the separation distance between bodies, and the aspect ratio among minor and major axes of the spheroid.
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Cecilia Noguez
, Carlos E. Roman-Velazquez
, Raul Esquivel-Sirvent andn Carlos Villarreal
2003
We calculate exactly the Casimir force or dispersive force, in the non-retarded limit, between a spherical nanoparticle and a substrate beyond the Londons or dipolar approximation. We find that the force is a non-monotonic function of the distance between the sphere and the substrate, such that, it is enhanced by several orders of magnitude as the sphere approaches the substrate. Our results do not agree with previous predictions like the Proximity theorem approach.
There is today a growing need to accurately model the angular scattering response of metasurfaces for optical analog processing applications. However, the current metasurface modeling techniques are not well suited for such a task since they are limited to small angular spectrum transformations, as shall be demonstrated. The goal of this work is to overcome this limitation by improving the modeling accuracy of these techniques and, specifically, to provide a better description of the angular response of metasurfaces. This is achieved by extending the current methods, which are restricted to dipolar responses and weak spatially dispersive effects, so as to include quadrupolar responses and higher-order spatially dispersive components. The accuracy of the newly derived multipolar model is demonstrated by predicting the angular scattering of a dielectric metasurface. This results in a modeling accuracy that is at least two times better than the standard dipolar model.
We present a lattice QCD study for the cutoff effects on nuclear forces. Two-nucleon forces are determined from Nambu-Bethe-Salpeter (NBS) wave functions using the HAL QCD method. Lattice QCD simulations are performed employing N_f = 2 clover fermion configurations at three lattice spacings of a = 0.108, 0.156, 0.215 fm on a fixed physical volume of L^3 x T = (2.5 fm)^3 x 5 fm with a large quark mass corresponding to m_pi = 1.1 GeV. We observe that while the discretization artifact appears at the short range part of potentials, it is suppressed at the long distance region. The cutoff dependence of the phase shifts and scattering length is also presented.
Polarisable atoms and molecules experience the Casimir-Polder force near magnetoelectric bodies, a force that is induced by quantum fluctuations of the electromagnetic field and the matter. Atoms and molecules in relative motion to a magnetoelectric surface experience an additional, velocity-dependent force. We present a full quantum-mechanical treatment of this force and identify a generalised Doppler effect, the time delay between photon emission and reabsorption, and the Roentgen interaction as its three sources. For ground-state atoms, the force is very small and always decelerating, hence commonly known as quantum friction. For atom and molecules in electronically excited states, on the contrary, both decelerating and accelerating forces can occur depending on the magnitude of the atomic transition frequency relative to the surface plasmon frequency.
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