Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session M35: Casimir Effect and Dispersive Interactions |
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Sponsoring Units: DAMOP Chair: Justin Wilson, University of Maryland Room: 210B |
Wednesday, March 4, 2015 11:15AM - 11:27AM |
M35.00001: The repulsive Casimir effect in Weyl semimetals Justin Wilson, Andrew Allocca, Victor Galitski Weyl semimetals are a proposed topological material with broken time-reversal symmetry. Due to this, they experience a particular bulk Hall effect as well as a weak longitudinal conductance. In such a situation, one can see a repulsive Casimir effect between two Weyl semimetals (similar to what has been studied for topological insulators and quantum hall materials), and the effect can be tuned from attractive to repulsive with chemical potential or magnetic field. We consider, separately, a simplified bulk description and a thin film geometry taking into account the band structure. [Preview Abstract] |
Wednesday, March 4, 2015 11:27AM - 11:39AM |
M35.00002: Weak localization as a definitive test of diffusive models in the Casimir effect Andrew Allocca, Justin Wilson, Victor Galitski Results from many measurements of the Casimir effect suggest that the metallic plates in these experiments should be modeled with the plasma model of free electrons as opposed to the naive diffusive Drude model, while other experiments seem to indicate the exact opposite, with results more in line with a diffusive model. We study the Casimir effect at low temperatures between a thick disordered plate and purely two-dimensional disordered system where the Drude conductivity decreases logarithmically at low temperatures due to weak localization. This effect can be tuned with either temperature or applied magnetic field leading to a measurable change in the Casimir force. On the other hand, a ballistic model cannot experience such an effect and is only weakly dependent on temperature and magnetic field. As a result, we propose that an experiment would unambiguously differentiate between diffusive and ballistic models by measuring the effect at low temperatures with an applied magnetic field. Additionally, we calculate the impact that fluctuations in the disorder distribution have on the Casimir effect. Assuming the validity of a diffusive model, we find that the Drude model is a good approximation of a more exact treatment of disorder. [Preview Abstract] |
Wednesday, March 4, 2015 11:39AM - 11:51AM |
M35.00003: Is it plasma or Drude? Experimental answer using rotating engineered samples Ricardo Decca Measurements done between a Ni covered sphere and a Au coated rotating sample made of sectors of Au and Ni are presented. This approach follows the proposal made by G. Bimonte.\footnote{G. Bimonte, Phys. Rev. Lett. 112, 240401 (2014).} Many samples with different thicknesses $t$ of the top Au film ($t\in [20,84]$~nm) were prepared to measure the interaction. The Ni-coated sapphire sphere was mounted on a sensitive mechanical torsional oscillator. Measurements were done for separations between the sphere and the Au-coated engineered sample in the \{200--1000\}~nm range. With integration times $\sim 1000$~s and after accounting for a systematic, once-per-revolution impulsive signal from the air-bearing spindle, the error in the measurement is $\sim 0.3$~fN. In all cases it was observed that a plasma-like model provides good agreement with the experiment, while the Drude model is off by factors as large as 1000. The experimental apparatus and the potential source of errors will be briefly discussed. [Preview Abstract] |
Wednesday, March 4, 2015 11:51AM - 12:03PM |
M35.00004: Casimir effect and radiative heat transfer between Chern Insulators Pablo Rodriguez Lopez, Adolfo Grushin, Wang-Kong Tse, Diego Dalvit Chern Insulators are a class of two-dimensional topological materials. Their electronic properties are different from conventional materials, and lead to interesting new physics as quantum Hall effect in absence of an external magnetic field. Here we will review some of their special properties and, in particular, we will discuss the radiative heat transfer and the Casimir effect between two planar Chern Insulators sheets. Finally, we will see how to control the intensity and sign of this Casimir force and the requirements to observe a repulsive Casimir force in the lab with those materials. [Preview Abstract] |
Wednesday, March 4, 2015 12:03PM - 12:15PM |
M35.00005: Conformal field theory of critical Casimir forces Thorsten Emig, Giuseppe Bimonte, Mehran Kardar Thermal fluctuations of a critical system induce long-ranged Casimir forces between objects that couple to the underlying field. For two dimensional conformal field theories (CFT) we derive exact results for the Casimir interaction for a deformed strip and for two compact objects of arbitrary shape in terms of the free energy of a standard region (circular ring or flat strip) whose dimension is determined by the mutual capacitance of two conductors with the objects' shape; and a purely geometric energy that is proportional to conformal charge of the CFT, but otherwise super-universal in that it depends only on the shapes and is independent of boundary conditions and other details. The effect of inhomogenous boundary conditions is also discussed. [Preview Abstract] |
Wednesday, March 4, 2015 12:15PM - 12:27PM |
M35.00006: Efficient near-field energy transfer and relieved Casimir stiction between sub-wavelength gratings Xianglei Liu, Bo Zhao, Zhuomin Zhang The promising applications of near-field heat transfer in thermophotovoltaic devices, thermal imaging, thermal rectifiers, and local thermal management have motivated the search for nanostructures capable of supporting higher efficiency or greater heat flux than simple planar substances. In this work, efficient and delocalized radiative heat transfer between two aligned 1D sub-wavelength gratings is demonstrated based on the scattering theory using the rigorous coupled-wave analysis (RCWA). It is shown that the heat flux can be greatly enhanced and the accurate prediction may differ significantly from that of the geometry-based Derjaguin's proximity approximation (PA). The underlying mechanism is attributed to the excitation of hyperbolic modes that increase the energy transmission by supporting propagation of waves with large parallel wavevectors and. Besides efficient energy transport, the performance is robust, insensitive to the relative lateral shift. In addition, the Casimir stiction considering both quantum and thermal fluctuations is found to be relieved compared with bulks. [Preview Abstract] |
Wednesday, March 4, 2015 12:27PM - 12:39PM |
M35.00007: Possibilities of Verifying Dynamical Casimir Effect with Nonlinear Materials in Microwave Cavities Viktor Dodonov I evaluate the number of ``Casimir quanta'' that could be created in high-quality electromagnetic cavities containing materials with big third-order nonlinear optical coefficients, due to the parametric amplification of the microwave vacuum field, if the effective refractive index of the material is modulated by periodic high-intensity short laser pulses. The main result is that the expected total number of created microwave photons depends neither on the laser beam shape, nor on the duration or power of individual pulses, but it is determined by the total energy of all pulses, provided the duration of each pulse is much shorter than the period of field oscillations in the selected resonant mode. The experiment can be feasible in small cavities with high resonance frequencies. Possible spurious effects will be discussed, too. [Preview Abstract] |
Wednesday, March 4, 2015 12:39PM - 12:51PM |
M35.00008: Electrostatic patch potentials in Casimir force measurements Joseph Garrett, David Somers, Jeremy Munday Measurements of the Casimir force require the elimination of the electrostatic force between interacting surfaces. The force can be minimized by applying a potential to one of the two surfaces. However, electrostatic patch potentials remain and contribute an additional force which can obscure the Casimir force signal [1-2]. We will discuss recent measurements of patch potentials made with Heterodyne Amplitude-Modulated Kelvin Probe Force Microscopy that suggest patches could be responsible for \textgreater 1{\%} of the signal in some Casimir force measurements, and thus make the distinction between different theoretical models of the Casimir force (e.g. a Drude-model or a plasma-model for the dielectric response) difficult to discern [3].\\[4pt] [1] C. C. Speake and C. Trenkel, Phys. Rev. Lett. 90, 160403 (2003).\\[0pt] [2] R. O. Behunin, F. Intravaia, D. A. R. Dalvit, P. A. Maia Neto, and S. Reynaud, Phys. Rev. A 85, 012504 (2012).\\[0pt] [3] J. L. Garrett, D. Somers, and J. N. Munday, J. Phys. Condens. Matter (in press) arXiv:1409.5012 (2014). [Preview Abstract] |
Wednesday, March 4, 2015 12:51PM - 1:03PM |
M35.00009: Tunable Casimir-Polder Forces and Spontaneous Emission Rates Felipe Rosa, Wilton Kort-Kamp, Felipe Pinheiro, Tarik Cysne, Diego Oliver, Carlos Farina We investigate the dispersive Casimir-Polder interaction between a Rubidium atom and a graphene sheet subjected to an external magnetic field ${\bf B}$. We demonstrate that this concrete physical system allows for a high degree of control of dispersive interactions at micro and nanoscales. Indeed, we show that the application of an external magnetic field can induce a $80\%$ reduction of the Casimir-Polder energy relative to its value without the field. We also show that sharp discontinuities emerge in the Casimir-Polder interaction energy for certain values of the applied magnetic field at low temperatures. In addition, we also show that atomic spontaneous emission rates can be greatly modified by the action of the magnetic field, with an order of magnitude enhancement or suppression depending on the dipole's moment orientation. [Preview Abstract] |
Wednesday, March 4, 2015 1:03PM - 1:15PM |
M35.00010: Suppression of chaos assisted stiction in Casimir oscillators due to surface roughness Wijnand Broer, George Palasantzas, Jasper Knoester, Holger Waalkens, Vitaly B. Svetovoy At separations below 100 nm, the Casimir force strongly influences the actuation dynamics of Micro Mechanical systems (MEMS) in dry vacuum conditions. This theoretical analysis includes the effects of both the material optical response and that of surface roughness in an experimentally relevant way. Moreover, energy gains and losses during actuation are considered via driving and damping, respectively. We show that the system can exhibit chaotic motion for certain actuation parameter values due to the nonlinearity of the Casimir force. Surface roughness of the interacting components turns out to make the MEMS actuation less susceptible to chaotic motion than that of flat surfaces. [Preview Abstract] |
Wednesday, March 4, 2015 1:15PM - 1:27PM |
M35.00011: Influence of dissipation on two-atom dispersion interactions Pablo Barcellona, Stefan Yoshi Buhmann We consider the dispersion interaction between two neutral, ground-state atoms at zero and finite temperature by means of a dynamical approach. Our result differs from the previous ones obtained with time-independent perturbation theory because it correctly accounts for the influence of dissipation via the atomic decay rates. Modern measurements of Casimir force seem to suggest a suppressed influence of dissipation. Our new result shows similar features and can hence help resolve the Drude-plasma debate. We also consider the interaction between a ground-state atom and an excited atom. There are discordant results in the literature for the retarded potential: one oscillating and one monotonous. Our dynamical result uniquely leads to the oscillating result when taking into account the decay rates. [Preview Abstract] |
Wednesday, March 4, 2015 1:27PM - 1:39PM |
M35.00012: Giant vacuum forces via transmission lines Ephraim Shahmoon, Igor Mazets, Gershon Kurizki Quantum electromagnetic fluctuations induce forces between neutral particles, namely, the van der Waals (vdW) and Casimir interactions. Here we show that these fundamental interactions can be enhanced by many orders of magnitude upon changing the character of the mediating vacuum photon-modes. We consider two dipoles in the vicinity of any standard electric transmission line and find analytically that the interaction scales non-trivially with the inter-dipolar distance, resulting in a strong and long-range interaction. This may have profound implications on the non-additivity of vdW and Casimir interactions in many-particle systems, and opens the door for Casimir Physics in 1d. We discuss the possibilities of measuring this effect, e.g. in a coplanar waveguide line. [Preview Abstract] |
Wednesday, March 4, 2015 1:39PM - 1:51PM |
M35.00013: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 1:51PM - 2:03PM |
M35.00014: Negative Casimir Entropies in Nanoparticle Interactions Kimball Milton, Romain Guerout, Gert-Ludwig Ingold, Astrid Lambrecht, Serge Reynaud Negative entropy has been known in Casimir systems for some time. For example, it can occur between parallel metallic plates modelled by a realistic Drude permittivity. Less well known is that negative entropy can occur purely geometrically, say between a perfectly conducting sphere and a conducting plate. The latter effect is most pronounced in the dipole approximation, which occurs when the size of the sphere is small compared to the separation between the sphere and the plate. Therefore, here we examine cases where negative entropy can occur between two electrically and magnetically polarizable nanoparticles or atoms, which need not be isotropic, and between such a small object and a conducting plate. Negative entropy can occur even between two perfectly conducting spheres, between two electrically polarizable nanoparticles if there is sufficient anisotropy, between a perfectly conducting sphere and a Drude sphere, and between a sufficiently anisotropic electrically polarizable nanoparticle and a transverse magnetic conducting plate. [Preview Abstract] |
(Author Not Attending)
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M35.00015: Probing the Casimir force with optical tweezers Paulo Maia Neto, DIney Ether, Luis Pires, Yareni Ayala, Felipe Rosa, Stefan Umrath, Gert Ingold, Nathan Viana, Moyses Nussenzveig Optical tweezers (OT) are single-beam laser traps for neutral particles, usually applied to dielectric microspheres immersed in a fluid. The stiffness is proportional to the trapping beam power, and hence can be tuned to very small values, allowing one to measure femtonewton forces, once the device is carefully calibrated. We employ OT to measure the Casimir (or retarded van der Waals) force between polystyrene beads in ethanol, for distances between 50 nanometers and 1 micrometer. The spherical beads have diameters ranging from 3 to 7 micrometers. We find a rather large correction to the widely employed Proximity Force approximation (PFA), since the ratio between distances and sphere radii is much larger than the typical values probed in recent experiments. For the comparison with experimental data, we compute the Casimir force using the scattering approach applied to the spherical geometry, including the contribution of double-layer forces. We also present experimental results for the total force between a mercury microdroplet and a polystyrene bead immersed in ethanol, with similar distances and diameters. In short, we probe the Casimir force with different materials in a regime far from the validity of PFA, such that the spherical geometry plays a non-trivial role. [Preview Abstract] |
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