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Analytical Approach to the One-Dimensional Disordered Exclusion Process with Open Boundaries and Random Sequential Dynamics  [PDF]
M. Loulidi
Statistics , 2008, DOI: 10.1007/s10955-008-9538-7
Abstract: A one dimensional disordered particle hopping rate asymmetric exclusion process (ASEP) with open boundaries and a random sequential dynamics is studied analytically. Combining the exact results of the steady states in the pure case with a perturbative mean field-like approach the broken particle-hole symmetry is highlighted and the phase diagram is studied in the parameter space $(\alpha,\beta)$, where $\alpha$ and $\beta$ represent respectively the injection rate and the extraction rate of particles. The model displays, as in the pure case, high-density, low-density and maximum-current phases. All critical lines are determined analytically showing that the high-density low-density first order phase transition occurs at $\alpha \neq \beta$. We show that the maximum-current phase extends its stability region as the disorder is increased and the usual $1/\sqrt{\ell}$-decay of the density profile in this phase is universal. Assuming that some exact results for the disordered model on a ring hold for a system with open boundaries, we derive some analytical results for platoon phase transition within the low-density phase and we give an analytical expression of its corresponding critical injection rate $\alpha^*$. As it was observed numerically$^{(19)}$, we show that the quenched disorder induces a cusp in the current-density relation at maximum flow in a certain region of parameter space and determine the analytical expression of its slope. The results of numerical simulations we develop agree with the analytical ones.
Spin Transport in Disordered Two-Dimensional Hopping Systems with Rashba Spin-Orbit Interaction  [PDF]
U. Beckmann,T. Damker,H. Boettger
Physics , 2004, DOI: 10.1103/PhysRevB.71.205311
Abstract: The influence of Rashba spin-orbit interaction on the spin dynamics of a topologically disordered hopping system is studied in this paper. This is a significant generalization of a previous investigation, where an ordered (polaronic) hopping system has been considered instead. It is found, that in the limit, where the Rashba length is large compared to the typical hopping length, the spin dynamics of a disordered system can still be described by the expressions derived for an ordered system, under the provision that one takes into account the frequency dependence of the diffusion constant and the mobility (which are determined by charge transport and are independent of spin). With these results we are able to make explicit the influence of disorder on spin related quantities as, e.g., the spin life-time in hopping systems.
Ordered and Disordered Defect Chaos  [PDF]
Glen D. Granzow,Hermann Riecke
Physics , 1997, DOI: 10.1016/S0378-4371(97)00428-7
Abstract: Defect-chaos is studied numerically in coupled Ginzburg-Landau equations for parametrically driven waves. The motion of the defects is traced in detail yielding their life-times, annihilation partners, and distances traveled. In a regime in which in the one-dimensional case the chaotic dynamics is due to double phase slips, the two-dimensional system exhibits a strongly ordered stripe pattern. When the parity-breaking instability to traveling waves is approached this order vanishes and the correlation function decays rapidly. In the ordered regime the defects have a typical life-time, whereas in the disordered regime the life-time distribution is exponential. The probability of large defect loops is substantially larger in the disordered regime.
Hopping Conduction in Disordered Carbon Nanotubes  [PDF]
D. P. Wang,D. E. Feldman,B. R. Perkins,A. J. Yin,G. H. Wang,J. M. Xu,A. Zaslavsky
Physics , 2006, DOI: 10.1016/j.ssc.2007.02.028
Abstract: We report electrical transport measurements on individual disordered carbon nanotubes, grown catalytically in a nanoporous anodic aluminum oxide template. In both as-grown and annealed types of nanotubes, the low-field conductance shows as exp[-(T_{0}/T)^{1/2}] dependence on temperature T, suggesting that hopping conduction is the dominant transport mechanism, albeit with different disorder-related coefficients T_{0}. The field dependence of low-temperature conductance behaves an exp[-(xi_{0}/xi)^{1/2}] with high electric field xi at sufficiently low T. Finally, both annealed and unannealed nanotubes exhibit weak positive magnetoresistance at low T = 1.7 K. Comparison with theory indicates that our data are best explained by Coulomb-gap variable range hopping conduction and permits the extraction of disorder-dependent localization length and dielectric constant.
On the temperature dependence of the hopping thermopower in disordered semiconductors  [PDF]
O. E. Parfenov,F. A. Shklyaruk
Physics , 2006, DOI: 10.1134/S1063782607090035
Abstract: At low temperature using thermodynamics of irreversible processes the general expressions for the temperature dependence of the thermopower in the case of the hopping conductivity for disordered materials are found. The account of influence of impurity levels degeneration on the thermopower is lead. In a view of received results experimental data of the thermopower in amorphous and impurity semiconductors are discussed.
Duality symmetries and effective dynamics in disordered hopping models  [PDF]
Robert L. Jack,Peter Sollich
Statistics , 2009, DOI: 10.1088/1742-5468/2009/11/P11011
Abstract: We identify a duality transformation in one-dimensional hopping models that relates propagators in general disordered potentials linked by an up-down inversion of the energy landscape. This significantly generalises previous results for a duality between trap and barrier models. We use the resulting insights into the symmetries of these models to develop a real-space renormalisation scheme that can be implemented computationally and allows rather accurate prediction of propagation in these models. We also discuss the relation of this renormalisation scheme to earlier analytical treatments.
Hopping in Disordered Media: A Model Glass Former and A Hopping Model  [PDF]
Thomas B. Schroeder
Physics , 2000,
Abstract: Two models involving particles moving by ``hopping'' in disordered media are investigated: I) A model glass-forming liquid is investigated by molecular dynamics under (pseudo-) equilibrium conditions. ``Standard'' results such as mean square displacements, intermediate scattering functions, etc. are reported. At low temperatures hopping is present in the system as indicated by a secondary peak in the distribution of particle displacements during a time interval 't'. The dynamics of the model is analyzed in terms of its potential energy landscape (potential energy as function of the 3N particle coordinates), and we present direct numerical evidence for a 30 years old picture of the dynamics at sufficiently low temperatures. Transitions between local potential energy minima in configuration space are found to involve particles moving in a cooperative string-like manner. II) In the symmetric hopping model particles are moving on a lattice by doing thermally activated hopping over energy barriers connecting nearest neighbor sites. This model is analyzed in the extreme disorder limit (i.e. low temperatures) using the Velocity Auto Correlation (VAC) method. The VAC method is developed in this thesis and has the advantage over previous methods, that it can calculate a diffusive regime in finite samples using periodic boundary conditions. Numerical results using the VAC method are compared to three analytical approximations, including the Diffusion Cluster Approximation (DCA), which is found to give excellent agrement with the numerical results.
Mechanism of hopping transport in disordered Mott insulators  [PDF]
S. Nakatsuji,V. Dobrosavljevic,D. Tanaskovic,M. Minakata,H. Fukazawa,Y. Maeno
Physics , 2004, DOI: 10.1103/PhysRevLett.93.146401
Abstract: By using a combination of detailed experimental studies and simple theoretical arguments, we identify a novel mechanism characterizing the hopping transport in the Mott insulating phase of Ca$_{2-x}$Sr$_x$RuO$_4$ near the metal-insulator transition. The hopping exponent $\alpha$ shows a systematic evolution from a value of $\alpha=1/2$ deeper in the insulator to the conventional Mott value $\alpha=1/3$ closer to the transition. This behavior, which we argue to be a universal feature of disordered Mott systems close to the metal-insulator transition, is shown to reflect the gradual emergence of disorder-induced localized electronic states populating the Mott-Hubbard gap.
Hopping transport of interacting carriers in disordered organic materials  [PDF]
Sergey V. Novikov
Physics , 2007, DOI: 10.1002/pssc.200777575
Abstract: Computer simulation of the hopping charge transport in disordered organic materials has been carried out explicitly taking into account charge-charge interactions. This approach provides a possibility to take into account dynamic correlations that are neglected by more traditional approaches like mean field theory. It was found that the effect of interaction is no less significant than the usually considered effect of filling of deep states by non-interacting carriers. It was found too that carrier mobility generally increases with the increase of carrier density, but the effect of interaction is opposite for two models of disordered organic materials: for the non-correlated random distribution of energies with Gaussian DOS mobility decreases with the increase of the interaction strength, while for the model with long range correlated disorder mobility increases with the increase of interaction strength.
Structural, Magnetic and Electron Transport Properties of Ordered-Disordered Perovskite Cobaltites  [PDF]
Asish K. Kundu,B. Raveau
Physics , 2010,
Abstract: Rare earth perovskite cobaltites are increasingly recognized as materials of importance due to rich physics and chemistry in their ordered-disordered structure for the same composition. Apart from colossal magnetoresistance effect, like manganites, the different forms of cobaltites exhibit interesting phenomena including spin, charge and orbital ordering, electronic phase separation, insulator-metal transition, large thermoelectric power at low temperature. Moreover, the cobaltites which display colossal magnetoresistance effect could be used as read heads in magnetic data storage and also in other applications depending upon their particular properties. The A-site ordereddisordered cobaltites exhibit ferromagnetism and metal-insulator transitions as well as other properties depending on the composition, size of A-site cations and various external factors such as pressure, temperature, magnetic field etc. Ordered cobaltites, having a 112-type layered structure, are also reported to have an effectively stronger electron coupling due to layered A-site cationic ordering. Most importantly for the present article we focus on La-Ba-Co-O based ordered-disordered perovskite phases, which exhibit interesting magnetic and electron transport properties with ferromagnetic transition, TC ~ 177K, and it being the first member of lanthanide series. Zener double exchange mechanism considered to be crucial for understanding basic physics of the ferromagneticmetallic phase, yet does not explain clearly the insulating-type phase. In terms of electron transport the ferromagnetic-metallic or insulating/semiconducting states have been discussed in the present article with different types of hopping model.
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