Conduction Electrons In Solids Research Articles

Low-temperature dielectric anomaly arising from electronic phase separation at the Mott insulator-metal transition

Coulomb repulsion among conduction electrons in solids hinders their motion and leads to a rise in resistivity. A regime of electronic phase separation is expected at the first-order phase transition between a correlated metal and a paramagnetic Mott insulator, but remains unexplored experimentally as well as theoretically nearby T = 0. We approach this issue by assessing the complex permittivity via dielectric spectroscopy, which provides vivid mapping of the Mott transition and deep insight into its microscopic nature. Our experiments utilizing both physical pressure and chemical substitution consistently reveal a strong enhancement of the quasi-static dielectric constant ε1 when correlations are tuned through the critical value. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory. Our findings suggest a similar ’dielectric catastrophe’ in many other correlated materials and explain previous observations that were assigned to multiferroicity or ferroelectricity.

Dielectric function for free electron gas: comparison between Drude and Lindhard models

The interaction between light and metals or heavily doped semiconductors is largely determined by their free conduction electrons. The frequency and wave vector dependent complex dielectric function is an essential ingredient of the description of its optical and transport properties. The aim of this paper is to give a didactic introduction how the conduction electrons in solids responds to an external time dependent electric field and to make a comparison between Drude and Lindhard dielectric function models for the electron gas. In within framework of Lindhard model we derived an expression for dielectric function that is similar to the familiar Drudes's formula. In particular, the differences and similarities between the complex conductivity obtained from the two models are analyzed.

Polarization-dependent hard X-ray photoemission spectroscopy of solids

We have developed a linear polarization-dependent hard X-ray photoemission (HAXPES) measurement system, by which the orbital contribution in the valence bands as well as the conduction electrons in solids can be revealed. Our experimental set up, recent progress and a few examples of the linear polarization dependence of HAXPES spectra are shown. It is also shown that the polarization dependence of the core-level spectra is fairly explained by theoretical calculations of photoelectron angular distributions for single atoms.

Electronic stopping powers of solids for slow atoms

Based on the dielectric response theory, electronic stopping powers of solids for slow atoms have been studied. Using a local-field-correction dielectric function, we have calculated these stopping powers by including the correlation and exchange effects. The screening of shellwise electron charge densities of slow atoms by the conduction electrons in solids was estimated using a Thomas-Fermi screening model. In this model, atomic shellwise electron densities were constructed by a superposition of several Yukawa potentials. Stopping powers of Al, Ni, Ag, and Au were calculated for atoms with atomic number between 6 and 18. Calculated results showed that stopping powers oscillated with atomic number consistent with experimental data. Present results also indicated that our approach is much improved over other theoretical calculations. A comparison of presently calculated results with available theoretical and experimental data was made and discussed.

Bistable Magnetic Resonance of Conduction Electrons in Solids

The phenomenon of bistable hysteresis in magnetic resonance of conduction electrons in solids is discussed, particularly the case of gallium oxide β-Ga2O3. This memory effect is a consequence of the dynamic polarization of nuclei by the Overhauser effect and manifests itself by a hysteresis of the ESR line provided that particular conditions for the external (or control) and internal (or material) parameters are satisfied. The influence of all these parameters on bistability is studied in detail. It is shown that magnetic resonance of conduction electrons in solids containing nonzero nuclear spins is an intrinsically bistable phenomenon. The reasons why bistability is so strong in gallium oxide even at room temperature, compared to other identified compounds where bistability exists only at very low temperature, are discussed in terms of electronic and crystallographic structure.

Tunable bistable hysteresis of the magnetic resonance of conduction electrons in solids

Under dynamic nuclear polarisation by the Overhauser effect, conduction electrons in solids can exhibit a hysteresis of their magnetic resonance. In the case of polycrystalline samples of β-Ga2 O3 , a giant hysteresis can be achieved corresponding to a situation where the electron spins absorb the electromagnetic field when the magnetic field is swept downward and no absorption occurs in the reverse sweep direction. It is shown that this phenomenon is a general property of conducting solids containing elements with non-zero nuclear spins.

A Monte Carlo Simulation of Ion-Induced Kinetic Electron Emission with a Stochastic Excitation of Electrons in Solids

A Monte Carlo simulation is performed for the study of the proton-induced kinetic secondary electron emission from solids. In this simulation, the excitation of conduction electrons in solids is stochastically treated by using the excitation function with the Lindhard dielectric theory. The calculated electron yields are about 30 percent larger than experimental yields at incident energy of 1 keV. The simulation, however, enables the calculation of angular and energy distributions of emitted electrons; the angular distribution calculated follows a cosine law. The energy distribution peaks at an energy of 2∼3 eV, which is consistent with the experimental ones, while the FWHM (full width at half-maximum) of the calculated distribution is larger than those. In addition, the depth distribution of secondary electrons is analogous to that obtained with electron bombardment.

Second-Harmonic Generation of Ultrasound in Degenerate Piezoelectric Semiconductors

We study second-harmonic generation of ultrasound in degenerate piezoelectric semiconductors using a quantum treatment which is valid at high frequencies and in strong magnetic fields. The effects of electron scattering on the electron-phonon interaction are neglected so that this quantum treatment is valid for the high-frequency region such that $\ensuremath{\omega}\ensuremath{\tau}\ensuremath{\gg}1$, where $\ensuremath{\omega}$ is the is sound frequency and $\ensuremath{\tau}$ is the relaxation time of electrons. It is found that the magnitude of the second-harmonic generation depends strongly upon the dc magnetic field and is considerably enhanced using the nonparabolic model for the energy bands of a degenerate semiconductor. Some in the dependence of the acoustic intensity on the magnetic field can be observed for both parabolic and nonparabolic band structures at the region of high frequencies and strong magnetic fields. These can be interpreted as the so-called giant quantum oscillations which arise because the conduction electrons in solids can resonantly absorb or emit phonons. It can also be seen that some discontinuities occur at strong magnetic fields in the acoustic intensity of the second-harmonic generation for the nonparabolic band structure. This is due to the fact that the linear and nonlinear conductivity tensors have singularities of purely quantum origin related to the degeneracy of the electron gas.

Combined Effects of Sound and Electric Fields upon the Conduction Electrons in Solids

The Boltzmann equation for the electronic distribution function in the presence of ultrasonic sound and a dc electric field is solved to produce a unified picture of the different effects resulting from the combined action of these two external disturbances. The response of the electronic system is described by the sum of various dc and ac current densities. Specifically it is shown which parts of the distribution function give rise to ultrasonic attenuation and to the acoustoelectric effect for both zero and nonzero external dc field. The Weinreich relation is found to be valid except for small correction terms due to collision drag. The orders of magnitude of the acoustoelectric field and the acoustoresistive effect are discussed for metals and semiconductors.

Interaction of conduction electrons in solids

It is shown that the influence of the interaction of conduction electrons with phonons can be partly included in the potential energy of their interaction. The “effective” potential energy found is used to study the possibility of the existence of bound states of two electrons in polar, homopolar and metallic crystals.