Electron Interactions In Metals Research Articles

On quantum approach to modeling of plasmon photovoltaic effect

Surface plasmons in metallic nanostructures including metallically nanomodified solar cells are conventionally studied and modeled by application of the Mie approach to plasmons or by the finite element solution of differential Maxwell equations with imposed boundary and material constraints (e.g., upon commercial COMSOL software system). Both approaches are essentially classical ones and neglect quantum particularities related to plasmon excitations in metallic components. We demonstrate that these quantum plasmon effects are of crucial importance especially in theoretical simulations of plasmon-aided photovoltaic phenomena. Quantum corrections considerably improve both the Mie and COMSOL approaches in this case. We present the semiclassical random phase approximation description of plasmons in metallic nanoparticles and apply the quantum Fermi golden rule scheme to assess the sunlight energy transfer to the semiconductor solar cell mediated by surface plasmons in metallic nanoparticles deposited on the top of the battery. In addition, short-ranged electron–electron interaction in metals is discussed in the framework of the semiclassical hydrodynamic model. The significance of the related quantum corrections is illustrated by the quantumly improved COMSOL simulations.

Теорія взаємодії фононів з електронами в металах

Теорія взаємодії фононів з електронами в металах

SUPERCONDUCTIVITY: FROM ELECTRON INTERACTION TO NUCLEAR SUPERFLUIDITY

I present an expanded version of a talk given at the Urbana symposium that celebrated the fiftieth anniversary of the publication of the microscopic theory of superconductivity by Bardeen, Cooper, and Schrieffer — BCS. I recall at some length, the work with my Ph.D. mentor, David Bohm, and my postdoctoral mentor, John Bardeen, on electron interaction in metals during the period 1948–55 that helped pave the way for BCS, describe the immediate impact of BCS on a small segment of the Princeton physics community in the early spring of 1957, and discuss the extent to which the Bardeen–Pines–Frohlich effective electron-electron interaction provided a criterion for superconductivity in the periodic system. I describe my lectures on BCS at Niels Bohr's Institute of Theoretical Physics in June 1957 that led to the proposal of nuclear superfluidity, discuss nuclear and cosmic superfluids briefly, and close with a tribute to John Bardeen, whose birth centennial we celebrated in 2008, and who was my mentor, close colleague, and dear friend.

Electron-Phonon vs. Electron-Impurity Interactions with Small Electron Bandwidths

It is a common practice to try to understand electron interactions in metals by defining a hierarchy of energy scales. Very often, the Fermi energy is considered the largest, so much so that frequently bandwidths are approximated as infinite. The reasoning is that attention should properly be focused on energy levels near the Fermi level, and details of the bands well away from the Fermi level are unimportant. However, a finite bandwidth can play an important role for low frequency properties: following a number of recent papers, we examine electron–impurity and electron–phonon interactions in bands with finite widths. In particular, we examine the behavior of the electron self-energy, spectral function, density of states, and dispersion, when the phonon spectral function is treated realistically as a broad Lorentzian function. With this phonon spectrum, impurity scattering has a significant nonlinear effect.

Asymmetry of Compton profiles

The asymmetry and observed anomalous broadening of experimental Compton profiles measured at synchrotron radiation sources have raised questions on the validity of the impulse approximation and the strength of the electron–electron interaction in metals. However, asymmetry and broadening can also be introduced by experimental artifacts. In order to address these issues we have made a systematic study on simple systems using various incident photon energies and different spectrometers. In addition, we have performed simulations on the effect of dead time and an asymmetric instrument function in the measured Compton profiles. We conclude that the observed asymmetry of Compton profiles of Be and Na does not originate from any experimental artifacts, but is due to the failure of the impulse approximation. This is confirmed by quasi-self consistent field calculations of the core electron Compton profiles, which agree quite well with the experimental results.

Superconductivity mediated by spin fluctuations in the heavy-fermion compound UPd2 Al3

It is well known that any weak attractive electron–electron interaction in metals can in principle cause the formation of Cooper pairs, which then condense into a superconducting ground state1. In conventional superconductors, this attractive interaction is mediated by lattice vibrations (phonons). But for the heavy-fermion and high-temperature superconductors, alternative pairing interactions are considered to be possible2. For example, the low-temperature properties of heavy-fermion systems are dominated by antiferromagnetic spin fluctuations, which have been considered theoretically3 as a possible cause for Cooper-pair formation. This picture recently received some experimental support: the resistivity behaviour under pressure of two cerium-based heavy-fermion compounds was shown to be consistent with a magnetically mediated pairing mechanism4. Here we use tunnelling spectroscopy to investigate the superconducting order parameter of a uranium-based heavy-fermion superconductor—epitaxial thin films of UPd2 Al3. Our observation of a strong-coupling feature in the tunnelling conductivity, combined with recent inelastic neutron scattering data13,14,15 strongly suggest a pairing interaction mediated by spin fluctuations.

Spin-dependent electron interactions in metals across the compressibility and spin-susceptibility anomalies.

We carry out explicit calculations to determine the phase boundaries on the density-temperature plane associated with divergence of the isothermal compressibility and the spin susceptibility of the electron liquid in metallic substances. It is shown that the signs and magnitudes of the spin-dependent and phonon-induced electron interactions exhibit remarkable changes across the phase boundaries. We point out that the strong attractive interaction between electrons with parallel spins appears near the spin-susceptibility anomaly, which may take place at $n\ensuremath{\simeq}2\ifmmode\times\else\texttimes\fi{}{10}^{20}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ for $T\ensuremath{\lesssim}150$ K.

Precise measurement of low temperature diffusion of positive muons in Cu: Evidence for the effect of muon-electron interaction in metals

The diffusion rate of positive muons in high purity Cu was measured by means of the zero field muon spin relaxation method for temperatures from 69 mK to 135 K. We found that with decreasing temperature the rate reaches a minimum at around 20 K and increases down to 0.5 K, where it clearly levels off. The origin of the observed temperature dependence is discussed in the light of recently developed theories taking into account the μ +-conduction electron interaction in metals, where the basic coupling constant K is determined to be 0.32.