Loi de Coulomb (électrostatique)

Résumé

thumb| Dans les deux cas, la force est proportionnelle au produit des charges et varie en carré inverse de la distance entre les charges. La loi de Coulomb exprime, en électrostatique, la force de l'interaction électrique entre deux particules chargées électriquement. Elle est nommée d'après le physicien français Charles-Augustin Coulomb qui l'a énoncée en 1785 et elle forme la base de l'électrostatique. Elle peut s'énoncer ainsi : Détermination expérimentale historique thumb|Balance de Coulomb. Charles-Augustin Coulomb énonce la loi d'interaction électrostatique en 1785 à la suite de nombreuses mesures réalisées grâce à la balance de Coulomb qu'il a mise au point pour détecter des forces d'interaction très faibles. Il s'agit d'une balance de torsion pour laquelle la mesure de l'angle de torsion à l'équilibre permet de déterminer l'intensité de forces répulsives. Dans le cas de forces attractives, c'est l'étude des oscillations du système qui permet de déterminer l'intens

Source officielle

https://fr.wikipedia.org/wiki/Loi_de_Coulomb_(%C3%A9lectrostatique)

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Explaining the mechanism of superconductivity in the high-T-c cuprates requires an understanding of what causes electrons to form Cooper pairs. Pairing can be mediated by phonons, the screened Coulomb force, spin or charge fluctuations, excitons, or by a combination of these. An excitonic pairing mechanism has been postulated, but experimental evidence for coupling between conduction electrons and excitons in the cuprates is sporadic. Here we use resonant inelastic x-ray scattering to monitor the temperature dependence of the dd exciton spectrum of Bi2Sr2CaCu2O8-x crystals with different charge carrier concentrations. We observe a significant change of the dd exciton spectra when the materials pass from the normal state into the superconductor state. Our observations show that the dd excitons start to shift up (down) in the overdoped (underdoped) sample when the material enters the superconducting phase. We attribute the superconductivity-induced effect and its sign reversal from underdoped to overdoped to the exchange coupling of the site of the dd exciton to the surrounding copper spins.

AMER PHYSICAL SOC2022

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We investigate the ground state properties of large atoms and quantum dots described by a d-dimensional N-body Hamiltonian of confinement ZV. In atoms, d = 3 and V is the Coulomb interaction; in dots, d = 2 and V is phenomenologically determined. We express the grand-canonical partition function in a path integral approach, and evaluate its expansion in Z-1. The problem can be seen as that of field theory possessing a saddle point. This saddle point results in a mean-field contribution to the energy, while the fluctuations result in the correlation energy. The mean-field contribution to the energy is self-consistently determined by the Hartree potential and contains an exchange term. Its smooth contribution is evaluated by a semiclassical method, with ε = Z-1/d in the role of ℏ, while its oscillating contribution can be related to the periodic orbits in the corresponding classical Hamiltonian. In the case of atoms, the leading order in ε of the correlation energy contains a term in Z ln Z1/3, which is essential in reproducing the behaviour shown by reference values, and a term in Z. While we have evaluated the contribution to the Z-term provided by the leading fluctuation order, the numerical evaluation of the contributions provided by higher order fluctuations remains an open problem. The self-consistent contribution to the energy corresponds to the statistical atom, composed of Thomas-Fermi and its corrections, comprehensively analysed, including oscillations, by Schwinger and Englert. In the case of dots, the leading order in ε of the correlation energy is a universal contribution of order Z, which we obtain in closed form. We then determine the expansion in ε of the smooth contributions down to this correlation order. We apply the approach to dots of quadratic and quartic confinement, including the oscillating contribution in the case of a chaotic quartic confinement.

EPFL2009

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Spin-correlated electronic state on the surface of a spin-orbit Mott system

Jan Hugo Dil, Chang Liu

We use angle-resolved photoemission spectroscopy to show that the near-surface electronic structure of a bulk insulating iridate Sr3Ir2O7 lying near a metal-Mott insulator transition exhibits weak metallicity signified by finite electronic spectral weight at the Fermi level. The surface electrons exhibit a spin structure resulting from an interplay of spin-orbit, Coulomb interaction and surface quantum magnetism. Our results shed light on understanding the exotic quantum entanglement and transport phenomena in iridate-based oxide devices.

2014

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