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We report a non-monotonic and strongly temperature dependent magneto-resistance observed in clean quantum point contacts. At the same time the conductance of the point contact varies linearly with temperature. This unexpected behavior may be related to electron-electron interactions.

A planar Maxwell–Chern–Simons–Proca model endowed with a Lorentz-violating background is taken as framework to investigate the electron–electron interaction. The Dirac sector is introduced exhibiting a Yukawa and a minimal coupling with the scalar and the gauge fields, respectively. The electron–electron interaction is then exactly evaluated as the Fourier transform of the Möller scattering amplitude (carried out in the nonrelativistic limit) for the case of a purely timelike background. The interaction potential exhibits a totally screened behavior far from the origin as consequence of massive character of the physical mediators. The total interaction (scalar plus gauge potential) can always be attractive, revealing that this model may lead to the formation of electron–electron bound states.

X-ray diffraction patterns of melt-spun Fe-Cu-Nb-Si-B (FINEMET-type) alloys reveal that crystallites of Fe₂Si and Fe₃B phases with average sizes of 15(5) and 20(2) nm are present in the surface layer of thickness ≈ 10 Å and these nanocrystallites occupy 5–10% of the total volume. The results of an elaborate analysis of the high-resolution electrical resistivity data taken in a temperature range from 13 K to 300 K and their discussion in the light of existing theories demonstrates that the enhanced electron–electron interaction (EEI), quantum interference (QI) effects, inelastic electron–phonon scattering, coherent electron–magnon (and/or electron-spin fluctuation) scattering are the main mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron–phonon scattering is the most effective mechanism to destroy phase coherence of electron wavefunctions. The physical quantities such as diffusion constant, density of states at the Fermi level and the phase-breaking time, determined for the first time for the alloys in question, exhibit a systematic variation with the copper concentration.

By using the extended Hubbard model under the Hartree–Fock approximation, we theoretically investigate the effect of electron–electron interaction on the polarization of the single-photon excited state of the charged $\pi$-conjugated oligomer. In the framework of one-dimensional tight-binding model, a uniform weak electric field is applied for polarization. The results show that the polarization property will vary with the electron–electron interaction. For example, with the increase of on-site Coulomb interaction strength, the value of the induced dipole moment is decreased. Its physical origin is revealed by analyzing the wavefunction of the localized energy level. In addition, the relation between the critical electric field for the dissociation of the single-photon excited state of the charged oligomer and the electron–electron interaction strength is also discussed.

We here report the manifestation of weak localization effects in the electrical resistivity of TaN(001) films grown on MgO(001) substrates by a pulsed laser deposition technique. These films were characterized by X-ray diffraction and Rutherford backscattering. High precision electrical resistivity measurements were performed on these films in the temperature range 12–300 K. A careful analysis of data showed these films to lie in the weakly localized regime with negative temperature coefficient of resistivity throughout the whole temperature range of study. A crossover from 2D localization at lower temperatures to 3D localization at higher temperatures was observed.

In order to study the higher order quantized plateaus in the acoustoelectric current induced by the surface acoustic wave (SAW), we consider in this paper, the Coulomb interaction of electrons trapped in the SAW-induced quantum dot at the Hartree approximation level. The Hartree self-consistent potential that originates from the electron–electron interactions in the quantum dot satisfies the Poisson equation and can be solved numerically together with the Schrödinger equation; following which, the conventional tunneling mechanism can be used to interpret the step-like acoustoelectric current, in which the escape of electrons from the quantum dot determines the deviation of the current from the quantized value. It should be noted that the quantum dot is formed by both the SAW-induced potential and the Hartree self-consistent potential in our paper, which is different from previous works. We have also calculated the first and the second quantized plateaus by use of this method.

By using a Hamiltonian of interaction between fermions via bosons¹ we derive some properties of the electro-phonon and electron-photon interaction and also of the electron-electron interaction. We have obtained that in a degenerate electron gas there is an attraction between two electrons via acoustical phonons. Also, in certain conditions, there may be an attraction between two electrons via longitudinal optical phonons. Although our expressions for the polaron energy in both cases of the acoustical and longitudinal optical phonons are different from that obtained in the standard theory, their magnitudes are the same with these and they are in good agreement with experimental data. The total emission rate of an electron against a phonon system at absolute zero is directly proportional to the electron momentum. Also, an attraction between two electrons may appear via photons.

We study a two-electron system of a quantum ring under the influence of a perpendicular homogeneous magnetic field. Calculations are made by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. A ground-state behavior (spin singlet–triplet transitions) as a function of the strength of a magnetic field is investigated. We find that the ring radius R₀ and the ring width W are important for the singlet–triplet transition of the ground-state.

We investigated temperature and magnetic field dependences of conductivity of multi-walled carbon nanotubes (MWNTs) with different average outer diameter. We separated out the quantum corrections to magnetoconductivity for interaction electrons and determined the dependence of constant of electron–electron interaction λ versus curvature of graphene layers in MWNTs.

The electrical resistivity ρ(T) of La_0.8C_0.2MnO₃ manganite nanoparticles (particle size 18 nm and 70 nm) significantly depends on temperature and size of nanoparticles. ρ(T) of 70 nm La_0.8C_0.2MnO₃ manganite exhibits metallic phase in low temperature regime (T < 250 K), develops a maxima near 250 K and decrease with T at high temperatures (250 K < T < 300 K). However, the ρ(T) of 18 nm La_0.8C_0.2MnO₃ manganite shows insulating phase in overall temperature regime, where resistivity decrease with temperature. The resistivity in metallic phase is theoretically analyzed by considering the strong spin fluctuations effect which is modelled using Drude–Lorentz type function. In addition to the spin fluctuation-induced contribution the electron-phonon and electron-electron ρ_e-e(T) = BT² contributions are also incorporated for complete understanding of experimental data. The contributions to the resistivity by inherent acoustic phonons (ρ_ac) as well as high frequency optical phonons (ρ_op) were estimated using Bloch–Gruneisen [BG] model of resistivity. It is observed that the resistivity contribution due to electron-electron interaction shows typical quadratic temperature dependence. Resistivity in Semiconducting/insulating phase is discussed with small polaron conduction (SPC) model. Finally the theoretically calculated resistivity compared with experimental data which found consistent in wide range of temperature.

We report a non-monotonic and strongly temperature dependent magneto-resistance observed in clean quantum point contacts. At the same time the conductance of the point contact varies linearly with temperature. This unexpected behavior may be related to electron-electron interactions.