Terahertz surface plasmon excitation over a bismuth thin film by an electron beam

The excitation of terahertz surface plasma wave (SPW) over bismuth thin film-glass structure by a parallel propagating electron beam is studied. The SPW phase velocity is sensitive to the thickness of bismuth film and it is driven via the Cerenkov resonance. The growth rate for terahertz radiation generation by an electron beam is obtained under small signal approximation.     

Hole-majority condition and magnetic field dependence of the electron/hole density and magnetization in a bismuth thin film

The electrons and holes in a bismuth thin film placed in a transverse magnetic field assume three-dimensionally quantized energy spectra. Peculiar magnetic field dependence of the carrier density and magnetization has been re-calculated using the hole-majority condition, replacing the conventional charge-neutrality condition. Some of the new results seem to be physically significant.     

Positive conductivity type in bismuth film

The Hall effect and thermoelectric power have been measured over the temperature range 77–300K for two kinds of bismuth films (99.9999% purity), one prepared at 150° C and the other at room temperature on a glass substrate. The former films exhibit an enhancement of positive nature of the conductivity as the film thickness is decreased, indicating the presence of a number of local acceptor states. From the present results it becomes apparent that the transport properties of evaporated films are structure-sensitive.     

Electron-electron interaction effects in bismuth

Measurements of the far infrared magneto-optical transmission spectra of bismuth at 311 and 337 μ and in fields up to 100 kG at 4°K are described. The sensitivity of the spectra of transmitted magneto plasma waves to the electron scattering in bismuth is discussed. Particular attention is drawn to excitonic effects associated with weakly allowed hole cyclotron resonance absorption lines observed in the spectra. A simple Cooper pair like argument is given to illustrate the nature of these inter subband excitons. The features entering into a more complete theory of the excitons are also briefly discussed.     

Electron-electron interaction effects in bismuth

Measurements of the far infrared magneto-optical transmission spectra of bismuth at 311 and 337 and in fields up to 100 kG at 4°K are described. The sensitivity of the spectra of transmitted magneto plasma waves to the electron scattering in bismuth is discussed. Particular attention is drawn to excitonic effects associated with weakly allowed hole cyclotron resonance absorption lines observed in the spectra. A simple Cooper pair like argument is given to illustrate the nature of these inter subband excitons. The features entering into a more complete theory of the excitons are also briefly discussed.Work supported by the National Science Foundation under Grant #GH40968     

Tunnel current in size-quantized bismuth film

Interpretation of experimental results of the electron tunneling in thin bismuth films (Lutskii et al. 1975) is given. It is shown that the tunnel characteristics are described well in the framework of the Abrikosov-Cohen spectrum.     

Polarization effects associated with two-wave interaction in bismuth titanate and bismuth silicate crystals

Polarization effects associated with two-wave interaction in Bi₁₂TiO₂₀ and Bi₁₂SiO₂₀ crystals are investigated. The experimental data are subjected to the required theoretical analysis. A new procedure is proposed for determining the density of acceptor centers (N _A) in photorefractive crystals. The values of N _A obtained by this procedure are in good agreement with published data. Fiz. Tverd. Tela (St. Petersburg) 39, 1990–1994 (November 1997)     

Anomalous energy dependence of the electron relaxation time in bismuth

The relaxation time of highly nonequilibrium electrons whose excitation energy |Δε| is of the order of the Fermi energy ε _F is measured. The measurements are made on bismuth samples with the aid of transverse electron focusing with micron intercontact separations. The dependence of the electron collision frequency on the excitation energy is found to be close to linear. The possibility of observing the topological restructuring of a closed isoenergetic surface into an open surface in Bi with an increase in the electron energy is discussed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 12, 835–840 (25 December 1996)     

Quadrupole interaction of tantalum impurities in bismuth metal

The time differential perturbed angular correlation technique has been used in the measurement of the electric quadrupole interaction of Ta impuritiy in bismuth metal. The interaction frequencies at 293, 400 and 500 K have been observed to be 288±1.5, 266.9±3 and 244.5±4.3 MHz respectively. The electric field gradient at 293 K is 4.75±0.3 × 10¹⁷ V/cm² with the temperature coefficientB=2.2±0.2 × 10⁻⁵ (K)^−3/2.     

Weak electron localization and electron-electron interaction effects in metallic glasses at temperatures just above superconducting transition

Electrical resistance and magnetoresistance (MR) of metallic glasses Zr_xBe_1−x (x = 0.6; 0.7) and Zr₇₅Rh₂₅ in the temperature range of 4.2–12 K and in the magnetic field of 7.4T have been studied. It has experimentally been shown that in accordance with the theory of weak localization of electrons (WEL) and electron-electron interaction (EEI) temperature dependences of conductivity and magnetic conductivity (MC) are determined by localization effects and EEI in the Cooper and Diffusion channels. The comparison of theoretical and experimental values of coefficients at temperature laws of the conductivity variation points out to the need to take into account the Maki-Thompson (MT) temperature correction in the absence of a magnetic field.     

Spin-dependent electron localization in crystals

The possibilities of spatially localizing spin-polarized electrons in two-dimensional and three-dimensional systems due to spin-orbit interaction are studied theoretically. Using simple one-dimensional potentials as examples, it is demonstrated that electrons with a definite helicity can be localized so that carrier separation by spin is accomplished. The magnetic field effect is studied, and it is shown that the position of bound levels depends substantially on this effect.     

Testing weak interaction models after the null bismuth result

The theories advanced to explain the absence of parity violation in bismuth vapour need further experiments to discriminate between them. We show that any observed asymmetry in ep scattering with polarized electrons must have a specific y-dependence if it is to be consistent with the bismuth experiments. Different charge asymmetries in e⁺e^? → μ⁺μ^? and μ^±p → μ^±X are also predicted in the different types of theory.     

Relativistic electron localization and the lack of Zitterbewegung

Using space-time resolved solutions to relativistic quantum field theory we analyze the electron-positron pair creation process from vacuum. For early times the entangled electron-positron wave function can be obtained analytically. We show that there are, in principle, no limitations to the localization length of an electron and demonstrate that its spatial probability density can be much narrower than the Compton wavelength. We also find that quantum field theory prohibits the occurrence of Zitterbewegung for an electron.     

Phonon and electron transport in aluminum thin film: Influence of film thickness on electron and lattice temperatures

Influence of film thickness on non-equilibrium energy transport in the aluminum thin film is examined. The solutions of Boltzmann equation and the modified two-equation model are presented to predict electron and phonon temperatures in the film for various film thicknesses. It is found that electron and phonon temperatures predicted from the Boltzmann equation differ from the solution of two-equation model in the film for small film thickness. As the film thickness increases, this difference becomes negligibly small. Two-equation model predicts higher electron and phonon temperatures than those obtained from the solutions of the Boltzmann equation in the vicinity of the high temperature edge. This becomes opposite in the region of the low temperature edge.     

Atomic-force microscopy of bismuth film defects decorated by oxidation

A method has been developed for revealing intercrystalline boundaries and mutual orientation of crystallites in bismuth films with the use of natural oxidation in combination with atomic-force microscopy. For bismuth films prepared through vacuum thermal evaporation on mica substrates, the block boundaries have been revealed, the sizes of blocks have been determined, and their mutual crystallographic orientation has been established. The results obtained have been used to determine thermal evaporation conditions that ensure a higher perfection of the film structure.     

Fano resonances and electron localization in heterobarriers

A study is made of electron tunneling in semiconductor heterostructures having a complex dispersion law. A generalized Fabry-Perot approach is used to describe tunneling across the barrier. Mixing of electron states at the heterojunctions is responsible for the asymmetric resonant structure of the transmission which is characterized by a resonance-antiresonance pair. The resonance corresponds to a pole while the antiresonance corresponds to a zero of the scattering amplitude in the complex energy plane, i.e., near the pole and the zero the transmission of the heterobarrier has a Fano resonance structure. It is shown that for certain barrier parameters the resonances may collapse and localized states may appear in the heterobarrier, which is observed on the current-voltage characteristics of the barriers. The two-valley model of a GaAs/Al_xGa_1?x As/GaAs heterostructure is considered as an example. An analysis is made of the resonance structure in the barrier as a function of the type of boundary conditions used for the heterojunctions. The low-temperature current-voltage characteristic of the barrier is calculated.     

On electron localization criteria in the Anderson model

The averaged Green function and the conductivity for the Anderson model are calculated for a simple cubic lattice within the CPA. The results are used to investigate the behaviour of the mobility edge on the basis of the two rather different approaches of the minimum metallic conductivity idea due to Mott and the Economou-Cohen localization theory.     

Weak localization and interaction in doped CdTe

We study weak localization and electron interaction in CdTe:In by low temperature magnetoconductance experiments to quantify the phase breaking length and the importance of interactions in CdTe. Then we study superconducting contacts to CdTe:In by transport measurements at very low temperature. The conductance-voltage characteristics of the superconducting contact exhibits the main features of a SIN junction, with a superimposed zero bias anomaly. This anomaly in the density of states of CdTe is very sensitive to magnetic field and probably induced by the proximity of the superconducting contact. Received 6 May 1998 and Received in final form 20 October 1998     

Investigation of ultrafast electron dynamics of nickel film and micro-nano-structure film

The electron thermalization and relaxation processes in ferromagnetic nickel thin film and micro-nano- structure film have been studied by measuring the transient change after excitation by a femtosecond laser pulse. The measurements indicate that the electron thermalization time is between 18 and 47 fs. This is somewhat faster than the value reported before. And the thermalization time of the micro-nano-structure film is much longer than the nickel film. We deduce that it is caused by the discontinuity of the electron band close to the Fermi level in the micro-nano-structure nickel film.