Yu. F. Komnik

Transition from strong to weak electron localization in a percolating gold film under the influence of an electric field

The low-temperature (0.5–55 K) conductivity of a semicontinuous gold film near the percolation threshold is studied. It is found that the film resistance is very sensitive to the applied voltage U. By varying U, the film can be reversibly transformed from the insulating to the metallic type conductivity. This makes it possible to study the metal–insulator transition (MIT) by tuning the electric field. For low U⩽0.05u2009V, the film behaves as an insulator with the sheet resistance R□ up to 10u2009MΩ. In this state, the dependences R(T)∝exp(1/T) (for T⩽20u2009K) and R(U)∝exp(1/U) (for T⩽1u2009K and U>0.1u2009V) are observed. At high voltages (U≃10u2009V), the film has the resistance R□≃5u2009kΩ and behaves like a “dirty” metal. The magnetoresistance (MR) in the metallic state is positive and corresponds to the weak localization effect. In the insulating state, the MR is negative and is described by the formula ΔR(H)/R(0)∝−H2/T. The negative MR manifests itself for nearest-neighbor hopping. Such behavior is unusual, and its nature is ...

Spin-orbit interaction in thin bismuth films

The magnetic-field dependences of the resistance of thin (100–700 A thick) bismuth films at low temperatures are analyzed using quantum corrections to the conductivity with weak electron localization. It is shown that the spin-orbit scattering time τso is much shorter than the phase relaxation time τφ of the electrons (the case of a strong spin-orbit interaction). It is found that τso tends to increase with the film thickness. This shows that the surface scattering of the electrons plays a dominant role in spin-orbit processes. Apparently, strong spin relaxation in the presence of surface scattering is due to the gradient of the internal crystal-field potential near the surface of the metal, resulting in lifting of the spin degeneracy and in the appearance of a spin gap (Rashba mechanism).The magnetic-field dependences of the resistance of thin (100–700 A thick) bismuth films at low temperatures are analyzed using quantum corrections to the conductivity with weak electron localization. It is shown that the spin-orbit scattering time τso is much shorter than the phase relaxation time τφ of the electrons (the case of a strong spin-orbit interaction). It is found that τso tends to increase with the film thickness. This shows that the surface scattering of the electrons plays a dominant role in spin-orbit processes. Apparently, strong spin relaxation in the presence of surface scattering is due to the gradient of the internal crystal-field potential near the surface of the metal, resulting in lifting of the spin degeneracy and in the appearance of a spin gap (Rashba mechanism).

Negative magnetoresistance in the nearest-neighbour hopping conduction in granular gold film

Abstract The low-temperature (0.5–55xa0K) conduction of semicontinuous gold film vacuum deposited at T ≈50xa0K is studied. The film is near the percolation threshold (thickness 3.25xa0nm). Its resistance is extremely sensitive to the applied voltage U . At low enough U the film behaves as an insulator (two-dimensional granular metal). In this state the dependences R ( T )∝exp(1/ T ) (for T ⩽20xa0K) and R ( U )∝exp(1/ U )) (for T ⩽1xa0K and U >0.1xa0V) are observed. Magnetoresistance (MR) is negative and can be described by Δ R ( H )/ R (0)∝− H 2 / T . This negative MR which manifests itself for nearest-neighbour hopping is rather uncommon and, up to now, has not been clarified. The possible mechanisms of such case of negative MR are discussed.

Peculiarities in the electron properties of δ〈Sb〉-layers in epitaxial silicon. III. Electron–phonon relaxation

Complex studies of weak electron localization, electron–electron interaction, and electron overheating in Si crystals containing a δ〈Sb〉-layer with various concentrations of Sb atoms are carried out in order to obtain information on the characteristic times of inelastic electron relaxation. The temperature dependence of the electron–phonon relaxation time τep derived from the electron overheating effect can be described by the dependence τep∝T−p, where p≅3.7±0.3, which corresponds to the case qTl<1 (qT is the wave vector of the thermal phonon and l the electron mean free path).

Investigation of heat transfer from current-carrying point contact to cryogenic liquid

Abstract It is shown here that there is a possibility of studying the heat transfer from a current-carrying point contact to a cryogenic liquid through investigation of the electron-phonon relaxation in the point contact. The character of the relaxation processes in the point contact was controlled using cyclotron spectroscopy of the electron-phonon interaction. Three types of heat transfer to cryogenic liquid convection, nucleate boiling or film boiling - were observed depending on the power in the region of the current-carrying point contact. The dependences of the degree of non-equilibrium of the injected electrons upon the injection current and the bath temperature are described. Quantitative estimates of the overheating temperature of the point contact are given.

Peculiarities of electronic properties of δ〈Sb〉 layers in epitaxial silicon. IV. Hopping conductivity and nonlinear effects

The temperature dependence of the kinetic electronic characteristics (conductivity, magnetoresistance, Hall e.m.f.) is studied in the temperature interval 3–50 K on epitaxial silicon crystals having a δu2009〈Sb〉 layer with sheet concentrations of Sb atoms 1×1013 and 5×1012u2009cm−2. The shape of the current–voltage characteristics is determined at various temperatures. It is found that the low-temperature kinetic phenomena in these objects are governed by the hopping mechanism of conductivity. A variable range hopping conductivity is observed at sufficiently low temperatures (<10u2009K). The nonlinearity of the current–voltage characteristics is explained by the theory of non-Ohmic hopping conductivity in moderately strong electric fields.

Surface energy relaxation of conduction electrons in bismuth using transverse electron focusing technique

The position of the first and second lines of transverse electron focusing on the scale of magnetic fields is analyzed to determine the loss of excess energy of conduction electrons in bismuth as a result of collisions with the crystal boundary upon normal incidence as well as the shape of the functional dependence of this quantity on the initial excess energy. It is found that beginning from relatively low values of excess energy (∼3u2009meV), a sharp drop in energy occurs upon reflection of electrons at the boundary.

Relaxation and effects of potential gradient in a Bi point contact

It is shown that electron relaxation in an emitter-type point contact strongly affects the position of the first line of transverse electron focussing (EF) in Bi on the magnetic field scale. As a result, the energy of electrons leaving the point contact region is lower than the energy eV determined by the voltage applied to the point contact. In the case of strong currents, the intrinsic field of the current also affects the position of the EF line. The additional shift of the EF line under the action of this factor depends on V nonlinearly in view of strong nonlinearity of the current–voltage characteristics of Bi point contacts. It is shown that this nonlinearity can be explained by an increase in the concentration of charge carriers in the point contact region under the action of the gradient of potential distribution and interband tunneling. These mechanisms give an accurate description of the nonlinearity of the current–voltage characteristics of Bi point contacts.