Localization In Two-dimensional Systems Research Articles

Nondiffusive weak localization in two-dimensional systems with spin-orbit splitting of the spectrum

The effect of spin splitting caused by structural asymmetry (Rashba’s contribution) and bulk asymmetry (Dresselhaus’s contribution) on the magnetoconductance of two-dimensional structures with high mobility of charge carriers is studied. The theory of weak localization with regard to both of the contributions is developed. The theory is valid in the entire region of classically low magnetic fields for arbitrary relations between the frequencies of spin precession and elastic collisions. The suppression of the correction for antilocalization is demonstrated in the case of equal contributions of structural anisotropy and bulk anisotropy to the spin splitting. The effect of the contribution, cubic in the wave vector, to the spin splitting on the quantum magnetoresistance is studied.

Nonuniversality of the interference quantum correction to conductivity beyond the diffusion regime

Results of numerical simulation of the weak localization in two-dimensional systems in wide range of magnetic filed are presented. Three cases are analyzed: (i) the isotropic scattering and randomly distributed scatterers; (ii) the anisotropic scattering and randomly distributed scatterers; (iii) the isotropic scattering and the correlated distribution of the scatterers. It is shown that the behavior of the conductivity beyond the diffusion regime strongly depends on the scattering anisotropy and correlation in the scatterer distribution.

Epitaxial strain effects on the metal–insulator transition in V 2O 3 thin films

Effects of epitaxial stress on the metal–insulator transition of V 2O 3 have been studied for in the form of epitaxial thin films grown on α-Al 2O 3 (0001) and LiTaO 3 (0001) substrates. A metallic phase is stabilized down to 2 K in the V 2O 3 thin film on α-Al 2O 3 (0001), where the a-axis is compressed by 4% owing to large epitaxial stress. On the other hand, the transition temperature T MI is raised by 20 K from the value of 170 K in bulk samples in the film on LiTaO 3 (0001), where the a-axis is expanded. These results suggest an intimate relationship between the a-axis length and T MI in V 2O 3. The conductivity of the metallic ultrathin films shows logarithmic temperature dependence below 20 K, probably due to the Anderson localization in two-dimensional systems.

Effect of intersubband scattering on weak localization in two-dimensional systems

The theory of weak localization is generalized for multilevel 2D systems taking into account intersubband scattering. It is shown that weak intersubband scattering which is negligible in a classical transport, affects strongly the weak-localization correction to conductivity. The anomalous magnetoresistance is calculated in the whole range of classically low magnetic fields. This correction to conductivity is shown to depend strongly on the ratios of occupied level concentrations. It is demonstrated that at relatively low population of the excited subband, it is necessary to use the present theory because the high-field limit asimptotics is shown to be achieved only in classical magnetic fields.

Vibration mode localization in two-dimensional systems with multiple substructural modes

Free vibration mode localization in randomly disordered weakly coupled two-dimensional cantilever-mesh-spring arrays, in which S substructural modes are considered for each cantilever, is studied in this paper. A method of regular perturbation is applied to determine the localization factors, which are defined in terms of the angles of orientation and characterize the average exponential rates of growth or decay of the amplitudes of vibration. Iterative formulations are derived to determine the amplitudes of vibration of the cantilevers. In the diagonal directions, a transfer matrix formulation is obtained. The localization behaviour of the system in the diagonal directions is similar to that of a one-dimensional cantilever-spring array with multiple substructural modes. Applicability of the single-substructural-mode and two-substructural-modes approximations is investigated.

Vibration Mode Localization in Two-Dimensional Systems

Vibration Mode Localization in Two-Dimensional Systems

Low-temperature properties of organic conductor (DTEDT) 3SbF 6

The electrical resistivity of (DTEDT) 3SbF 6 shows a metallic temperature dependence down to 10 K. After showing a resistance minimum, the resistivity increases with log T dependence, which is followed by a decrease below ∼0.2 K. The log T dependence is ascribed to weak localization in two-dimensional system. The decrement was suppressed by a magnetic field less than ∼1 T, suggesting that it is due to a superconducting transition.

Vibration mode localization in two-dimensional systems

Vibration mode localization in two-dimensional systems

Universal Behaviour of Magnetoconductance due to Weak Localization in Two-Dimensional Systems - Example of GaInAs Quantum Wells

Weak localization corrections to conductivity of a two-dimensional electroii gas are studied by measurements of the magnetic field dependence of the conductivity in GalnAs quantum wells. We observe that, when presented as a function of the normalized magnetic field (x = B/Btr , where B is the magnetic field, B« = h/4eτD, D is the dichusion constant and τ is momentum relaxation time), dicherent samples show very similar high field behaviour. A theoretical description is developed that allows one to describe in a consistent way high and low field behaviour. The theory predicts universal (B -1 /2 ) behaviour of the conductivity correction for all 2D systems in the high field limit (r > 1). Low field behaviour depends strongly on spin and phase relaxation mechanisms. Comparison of the theory with experiment confirms the universal behaviour in the high fleld limit and allows one to estimate the spin and phase relaxatioii times for dicherent GalnAs quantum wells.

Universal critical normal sheet resistance in ultrathin films.

A simple analysis is given to ultrathin-film systems. Based on the physical picture proposed that the superconducting-insulating phase transition at T-0 is a combined effect of the pairing and localization in two-dimensional systems, the normal-state sheet resistance is evaluated in the vicinity of the transition. It is found to be universal and equal to h/(2e${)}^{2}$, independent of the details of different samples as observed in experiments. A similar formulation can be also used to explain the quantized conductance in narrow channels.

Localization in Two-Dimensional Systems in Quantum Hall Regime

A recent development in understanding the problem of electron localization in two-dimensional systems in strong magnetic fields is reviewed mainly from a theoretical point of view with emphasis on relation to the quantum Hall effect. The results of numerical study are described in detail, but other theoretical approaches like perturbation theory are discussed more briefly.

Positive Magnetoresistance of Thin Gold Films at Low Temperatures

The electrical resistance of ultra thin gold films increases as the temperature is lowered below 6 K. The magnetoresistance is positive and anisotropic. A logarithmic dependence of the resistance on magnetic field has been observed. The results are inqualitative agreement with the recent theories of the electron localization in two-dimensional systems.

A self-consistent treatment of Anderson localization

Anderson localization in two-dimensional systems is discussed with the use of Feynman graph method. A self-consistent treatment of diffusion propagator leads to an expression for dynamical conductivity which vanishes at zero frequency while exhibiting well known logarithmic dependence at higher frequency. It is applied to three-dimensional systems, too, and a discussion is given on mobility edge.

Temperature and electric field dependences of conductivity in 1 T TaS2

Systematic measurements are made on temperature and electric field dependences of conductivity for various samples of 1 TTaS 2. Logarithmic dependences on both variables are observed in the region T ≳ 20 K for small E and E ≳ 40 V cm −1 for small T. This behavior seems to be compatible with the recent scaling theory on the Anderson localization in two-dimensional system. On the other hand it is found that the values of the logarithmic slopes are obviously smaller than the theoretical value and show good correlation with the conductivity of each sample. These results suggest that 1 TTaS 2 may be regarded as “quasi” two-dimensional electronic system.

Electron localization in disordered systems: critical behavior and macroscopic manifestations

The review deals with new results in the theory of electron localization in disordered systems and with experiments which have been stimulated by these results. An elementary scaling theory of localization and its consequences are discussed. Attention is concentrated on the phenomenon of localization in two-dimensional systems. The main experiments on the conductivity of thin metal wires and films, demonstrating qualitatively new behavior associated with localization, are discussed. The review concludes with a brief look at the problems of deriving a self-consistent scaling theory of critical behavior at a mobility edge.

Some aspects of localization in two-dimensional systems

Some aspects of localization in two-dimensional systems