arXiv subjects

Nicolas Sandeau

Publications and source records attributed to Nicolas Sandeau.

11 recordsLinked to original sources

arXiv2021

A Novel Treatment of the Josephson Effect

A new picture of the Josephson effect is devised. The radio-frequency (RF) signal, observed in a Josephson junction, is shown to stem from bound electrons, tunneling periodically through the insulating film. This holds also for the microwave mediated tunneling. The Josephson effect is found to be conditioned by the same prerequisite worked out previously for persistent currents, thermal equilibrium and occurence of superconductivity. The observed negative resistance behaviour is shown to originate from the interplay between normal and superconducting currents.

cond-mat.mes-hall↗

arXiv2020

Towards room-temperature superconductivity

By taking advantage of a stability criterion established recently, the critical temperature $T_c$ is reckoned with help of the microscopic parameters, characterising the normal and superconducting electrons, namely the independent-electron band structure and a \textit{repulsive} two-electron force. The emphasis is laid on the sharp $T_c$ dependence upon electron concentration and inter-electron coupling, which might offer a practical route toward higher $T_c$ values and help to understand why high-$T_c$ compounds exhibit such remarkable properties.

physics.gen-ph↗

arXiv2020

Thermal Stability of Superconductors

A stability criterion is worked out for the superconducting phase. The validity of a prerequisite, established previously for persistent currents, is thereby confirmed. Temperature dependence is given for the specific heat and concentration of superconducting electrons in the vicinity of the critical temperature $T_c$. The isotope effect, mediated by electron-phonon interaction and hyperfine coupling, is analyzed. Several experiments, intended at validating this analysis, are presented, including one giving access to the specific heat of high-$T_c$ compounds.

cond-mat.supr-con↗

arXiv2020

Comment on "`Inconsistency of the conventional theory of superconductivity"' by Hirsch J.E

A rebuttal of a recent article by Hirsch J.E. is presented below. To begin with, the main assumption, regarding the Meissner effect, which the whole argument relies upon, is disproved. Besides, the subsequent analysis misconstrues an original view of the Meissner effect by other authors [2]. Finally, the discussion of the Joule effect turns out to violate the first law of thermodynamics.

physics.gen-ph↗

arXiv2019

Study of the superconducting to normal transition

A model, based on classical mechanics and thermodynamics and valid for \textit{all} superconductors, is devised to investigate the properties of the \textit{current-driven}, superconducting to normal transition. This process is shown to be reversible. An original derivation of the BCS variational procedure is given. Two different critical temperatures are introduced. The temperature dependence of the critical current is worked out and found to agree with observation. The peculiar transport properties of high-$T_c$ compounds in the normal state and old magnetoelastic data are also interpreted within this framework. A novel experiment is proposed to check the relevance of this analysis to high-$T_c$ superconductivity.

physics.gen-ph↗

arXiv2019

An observable prerequisite for the existence of persistent currents

A classical model is presented for persistent currents in superconductors. Their existence is argued to be warranted because their decay would violate the second law of thermodynamics. This conclusion is achieved by analyzing comparatively Ohm's law and the Joule effect in normal metals and superconducting materials. Whereas Ohm's law applies in identical terms in both cases, the Joule effect is shown to cause the temperature of a superconducting sample to \textit{decrease}. An experiment is proposed to check the validity of this work in superconductors of both types I and II.

physics.gen-ph↗

arXiv2018

Revisiting low-frequency susceptibility data in superconducting materials

Old susceptibility data, measured in superconducting materials at low-frequency, are shown to be accounted for consistently within the framework of a recently published\cite{sz1} analysis of the skin effect. Their main merit is to emphasize the significance of the skin-depth measurements, performed \textit{just beneath} the critical temperature $T_c$, in order to disprove an assumption, which thwarted any understanding of the skin-depth data, achieved so far by conventional high-frequency methods, so that those data might, from now on, give access to the temperature dependence of the concentration of superconducting electrons.

cond-mat.supr-con↗

arXiv2018

Comparative study of the Meissner and skin effects in superconductors

The Meissner effect is studied by using an approach based on Newton and Maxwell's equations. The objective is to assess the relevance of London's equation and shed light on the connection between the Meissner and skin effects. The properties of a superconducting cylinder, cooled in a magnetic field, are accounted for within the same framework. The radial Hall effect is predicted. The energy, associated with the Meissner effect, is calculated and compared with the binding energy of the superconducting phase with respect to the normal one.

cond-mat.supr-con↗

arXiv2016

Study of the skin effect in superconducting materials

The skin effect is analyzed to provide the numerous measurements of the penetration depth of the electromagnetic field in superconducting materials with a theoretical basis. Both the normal and anomalous skin effects are accounted for within a single framework. The emphasis is laid on the conditions required for the penetration depth to be equal to London's length, which enables us to validate an assumption widely used in the interpretation of all current experimental results.

cond-mat.supr-con↗

arXiv2015

On the physical significance of London's equation

The Meissner effect is analysed by using an approach based on Newton and Maxwell's equations, in order to assess the relevance of London's equation. The Hall effect is predicted. Two test experiments are proposed in detail to check the validity of this theory and to measure London's length.

cond-mat.supr-con↗

arXiv2006

Axial localization of luminophores by partial coherence interferometry

We propose a solution for increasing the axial resolution of confocal microscopes. In the experimental set-up described in this paper an interference phenomenon between two counterpropagating beams is used to determine the axial position of a luminophore. The optical path difference between the two waves, which is related to the position of the luminophore, is recovered thanks to a second interferometer by using partial coherence interferometry demodulation technique. The proposed solution can find applications in biology for localizing with nanometric resolution a small number of tagged species.

physics.bio-ph↗