arXiv subjects

D. López

Publications and source records attributed to D. López.

11 recordsLinked to original sources

arXiv2015

Thermodynamic evidence for the Bose glass transition in twinned YBa$_2$Cu$_3$O$_{7-δ}$ crystals

We used a micromechanical torsional oscillator to measure the magnetic response of a twinned YBa$_2$Cu$_3$O$_{7-δ}$ single crystal disk near the Bose glass transition. We observe an anomaly in the temperature dependence of the magnetization consistent with the appearance of a magnetic shielding perpendicular to the correlated pinning of the twin boundaries. This effect is related to the thermodynamic transition from the vortex liquid phase to a Bose glass state.

cond-mat.dis-nn↗

arXiv2011

Capacitance measurements and electrostatic calibrations in experiments measuring the Casimir force

We compare the results of capacitance measurements in the lens-plane and sphere-plane configurations with theoretical predictions from various models of a spherical surface. It is shown that capacitance measurements are incapable of discriminating between models of perfect and modified spherical surfaces in an experiment demonstrating the anomalous scaling law for the electric force. Claims to the contrary in the recent literature are explained by the use of irregular comparison. The data from capacitance measurements in an experiment measuring the Casimir force using a micromechanical torsional oscillator are shown to be in excellent agreement with theoretical predictions using the model of a perfect spherical surface.

quant-ph↗

arXiv2009

Application of the proximity force approximation to gravitational and Yukawa-type forces

We apply the proximity force approximation, which is widely used for the calculation of the Casimir force between bodies with nonplanar boundary surfaces, to gravitational and Yukawa-type interactions. It is shown that for the gravitational force in a sphere-plate configuration the general formulation of the proximity force approximation is well applicable. For a Yukawa-type interaction we demonstrate the validity of both the general formulation of the proximity force approximation, and a simple mapping between the sphere-plate and plate-plate configurations. The claims to the contrary in some recent literature are thus incorrect. Our results justify the constraints on the parameters of non-Newtonian gravity previously obtained from the indirect dynamic measurements of the Casimir pressure.

quant-ph↗

arXiv2008

Comment on "Anomalies in electrostatic calibration for the measurement of the Casimir force in a sphere-plane geometry"

Recently W. J. Kim, M. Brown-Hayes, D. A. R. Dalvit, J. H. Brownell, and R. Onofrio [Phys. Rev. A, v.78, 036102(R) (2008)] performed electrostatic calibrations for a plane plate above a centimeter-size spherical lens at separations down to 20-30 nm and observed "anomalous behavior". It was found that the gradient of the electrostatic force does not depend on separation as predicted on the basis of a pure Coulombian contribution. Some hypotheses which could potentially explain the deviation from the expected behavior were considered, and qualitative arguments in favor of the influence of patch surface potentials were presented. We demonstrate that for the large lenses at separations of a few tens nanometers from the plate, the electrostatic force law used by the authors is not applicable due to possible deviations of the mechanically polished and ground lens surface from a perfect spherical shape. A model is proposed which explains the observed "anomalous behavior" using the standard Coulombian force.

quant-ph↗

arXiv2008

Comment on "Possible resolution of the Casimir force finite temperature correction "controversies""

The recently suggested modification of the transverse electric contribution to the Lifshitz formula (S. K. Lamoreaux, arXiv:0801.1283) is discussed. We show that this modification is inconsistent with the data of two precise experiments, and violates the Nernst heat theorem. The preprint's suggestion concerning the resolution of the "apparent violation of the Third Law of Thermodynamics" is shown to be incorrect.

quant-ph↗

arXiv2008

Stronger constraints on non-Newtonian gravity from the Casimir effect

We review new constraints on the Yukawa-type corrections to Newtonian gravity obtained recently from gravitational experiments and from the measurements of the Casimir force. Special attention is paid to the constraints following from the most precise dynamic determination of the Casimir pressure between the two parallel plates by means of a micromechanical torsional oscillator. The possibility of setting limits on the predictions of chameleon field theories using the results of gravitational experiments and Casimir force measurements is discussed.

hep-th↗

arXiv2007

Tests of new physics from precise measurements of the Casimir pressure between two gold-coated plates

A micromechanical torsion oscillator has been used to strengthen the limits on new Yukawa forces by determining the Casimir pressure between two gold-coated plates. By significantly reducing the random errors and obtaining the electronic parameters of the gold coatings, we were able to conclusively exclude the predictions of large thermal effects below 1 $μ$m and strengthen the constraints on Yukawa corrections to Newtonian gravity in the interaction range from 29.5 nm to 86 nm.

hep-ph↗

arXiv2006

Comment on "On the temperature dependence of the Casimir effect"

Recently, Brevik et al. [Phys. Rev. E 71, 056101 (2005)] adduced arguments against the traditional approach to the thermal Casimir force between real metals and in favor of one of the alternative approaches. The latter assumes zero contribution from the transverse electric mode at zero frequency in qualitative disagreement with unity as given by the thermal quantum field theory for ideal metals. Those authors claim that their approach is consistent with experiments as well as with thermodynamics. We demonstrate that these conclusions are incorrect. We show specifically that their results are contradicted by four recent experiments and also violate the third law of thermodynamics (the Nernst heat theorem).

quant-ph↗

arXiv2005

Casimir Effect as a Test for Thermal Corrections and Hypothetical Long-Range Interactions

We have performed a precise experimental determination of the Casimir pressure between two gold-coated parallel plates by means of a micromachined oscillator. In contrast to all previous experiments on the Casimir effect, where a small relative error (varying from 1% to 15%) was achieved only at the shortest separation, our smallest experimental error ($\sim 0.5$%) is achieved over a wide separation range from 170 nm to 300 nm at 95% confidence. We have formulated a rigorous metrological procedure for the comparison of experiment and theory without resorting to the previously used root-mean-square deviation, which has been criticized in the literature. This enables us to discriminate among different competing theories of the thermal Casimir force, and to resolve a thermodynamic puzzle arising from the application of Lifshitz theory to real metals. Our results lead to a more rigorous approach for obtaining constraints on hypothetical long-range interactions predicted by extra-dimensional physics and other extensions of the Standard Model. In particular, the constraints on non-Newtonian gravity are strengthened by up to a factor of 20 in a wide interaction range at 95% confidence.

quant-ph↗

arXiv2003

Measurement of the Casimir force between dissimilar metals

The first precise measurement of the Casimir force between dissimilar metals is reported. The attractive force, between a Cu layer evaporated on a microelectromechanical torsional oscillator, and an Au layer deposited on an Al$_2$O$_3$ sphere, was measured dynamically with a noise level of 6 fN/$\sqrt{\rm{Hz}}$. Measurements were performed for separations in the 0.2-2 $μ$m range. The results agree to better than 1% in the 0.2-0.5 $μ$m range with a theoretical model that takes into account the finite conductivity and roughness of the two metals. The observed discrepancies, which are much larger than the experimental precision, can be attributed to a lack of a complete characterization of the optical properties of the specific samples used in the experiment.

quant-ph↗

arXiv1994

Flux-Cutting in YBa$_{2}$Cu$_{3}$O$_{7-δ}$ single crystals: Experiment and Phenomenological model

We measured the current induced loss of vortex correlation in YBCO crystals using the pseudo DC flux transformer geometry. We find that the current $I_{cut}$ at which the top and bottom voltage differ is a linear function of temperature independent of pinning. Although the vortex correlation length at $I_{cut}$ coincides with the sample thickness, the experimental data show that $I_{cut}$ is sample thickness independent. The observed behavior with temperature, magnetic field and thickness is described by a phenomenological model.

cond-mat↗