Enhancement of electrical conductivity in MgO due to lithium impurities

The electrical conductivity of lithium-doped MgO crystals at room temperature is shown to be enhanced by the thermal creation of stable [Li]⁰ defects by oxidation at elevated temperatures. The current-voltage curves are found to be nonlinear at low voltages. The enhancement in conductivity is attributed to localized regions of high [Li]⁰ concentration in which the holes at the [Li]⁰ sites are thermally ionized into the valence band, causing these regions to be semiconducting.     

Direct measurement of the local density of states of a disordered one-dimensional conductor

One-dimensional electron systems (1DESs) containing two and one occupied subbands are found below the different types of [11;2] steps of the InAs(110) surface. Using low-temperature scanning tunneling spectroscopy, we determined the subband energies, the disorder potential, and the local density of states of these 1DESs. The rather complete knowledge of the 1DES allowed us to compare the measured LDOS with a single-particle calculation. Surprisingly, we did not find significant deviations from the calculation albeit the electron-electron interaction in the 1DESs is stronger than the electron-disorder interaction.     

Frequency conductivity of one-dimensional CDW with different types disorder

The low-frequency conductivity of one-dimensional charge density wave with disorder is calculated. The form of low-frequence conductivity peak is described.     

Electrical conductivity in a conductor 5 atoms thick

A single crystal 5 atoms thick comes close to the approximation of a quasi-two-dimensional system. Still, it retains some characteristics of the bulk material as revealed by the virtual absence of any contact effects as long as the contacts consist of thicker areas of the same crystal. Electrical conductivity and electron mobility are strongly influenced by adsorption on the surface. The onset of an additional conduction process at high current density and low temperature is reported.     

Spin-resolved polarized transport through a quasi one-dimensional mesoscopic quantum ring-shaped conductor with local Rashba spin-orbit interaction

We propose a quasi one-dimensional quantum ring-shaped model associated with Rashba spin-orbit (SO) interaction and Aharomov-Bohm flux to study a spin-dependent quantum transport. It is a possible candidate for spintronic current modulators. By tuning SO coupling strength and Fermi energy, we find there is a broad energy range of small vanishing spin transmission in the resonance and antiresonance interferences. More interestingly, the large on/off spin-resolved polarized conductance ratios are robust even in the presence of strong random on-site Anderson-type disorder in devices, which suggests a potential application in the real system.     

Stochastic properties of the resistivity in a one-dimensional disordered conductor

We investigate the stochastic properties of the resistanceR and its logarithm lnR for a one-dimensional disordered conductor of finite length and at zero temperature. In the model which we consider, the non-interacting electrons are scattered by a Gaussian random potential of vanishing correlation length. It is shown that for long samples, lnR is distributed according to a Gaussian law and the parameters of this distribution are calculated explicitly. For weak disorder potentials, we recover known relations between R>, ln<R>, and ln<R ^–1>, whereas for strong disorder new results are derived.     

Non-linear conduction in a quasi one-dimensional conductor at low temperatures

The current-voltage characteristics of a quasi one-dimensional organic system having asymmetric donor molecule like Qn-(TCNQ)₂ pellet with stoichiometry 1:2 grown from acetonitrile as a solvent have been studied atT=69 K. The characteristic curves show a pronounced deviation from ohmicity beyond a certain value of current. For higher values of currents a negative differential resistance region is observed.     

Mobility in a one-dimensional disorder potential

In this article the one-dimensional, overdamped motion of a classical particle is considered, which is coupled to a thermal bath and is drifting in a quenched disorder potential. The mobility of the particle is examined as a function of temperature and driving force acting on the particle. A framework is presented, which reveals the dependence of mobility on spatial correlations of the disorder potential. Mobility is then calculated explicitly for new models of disorder, in particular with spatial correlations. It exhibits interesting dynamical phenomena. Most markedly, the temperature dependence of mobility may deviate qualitatively from Arrhenius formula and a localization transition from zero to finite mobility may occur at finite temperature. Examples show a suppression of this transition by disorder correlations.Dedicated to Professor H. Wagner on the occasion of his 60th birthday     

Dynamic conductivity of a layered conductor in the quantum limit

The high-frequency conductivity of a layered conductor in the direction orthogonal to the layers is analytically calculated with the use of the model of a quasi-two-dimensional electron spectrum in the limit of strong magnetic fields (H) and low temperatures. It is shown that the conductivity can vanish for certain values of H.     

Electron transport in a multichannel one-dimensional conductor: molybdenum selenide nanowires

We have measured electron transport in small bundles of identical conducting molybdenum selenide nanowires where the number of weakly interacting one-dimensional chains ranges from 1 to 300. The linear conductance and current in these nanowires exhibit a power-law dependence on temperature and bias voltage, respectively. The exponents governing these power laws decrease as the number of conducting channels increase. These exponents can be related to the electron-electron interaction parameter for transport in multichannel 1D systems with a few defects.     

Electrical conductivity and permittivity of the one-dimensional superionic conductor LiCuVO<Subscript>4</Subscript>

The electrical conductivity σ^a and permittivities ?^a, ?^b, and ?^c of a LiCuVO₄ single crystal have been measured along the a, b, and c crystallographic axes, respectively, in the temperature range 300–390 K at a frequency of 10³ Hz. The temperature dependences σ(T) and ?(T) were found to be typical for superionics.     

Leontovich-Levin equation taking into account finite conductivity of a conductor

A generalization of the Leontovich-Levin equation for current in an ideally conducting linear vibrator to the case of a finite-conductivity conductor is considered. This generalization is valid for strong and weak skin effects, as well as for inhomogeneous conductors with an axisymmetric conductivity distribution (in particular, for carbon nanotubes, CNTs). The internal structure of the conductor is fully described by the internal impedance per unit length. A recurrent scheme is proposed for calculating such an impedance for layer-inhomogeneous conductors. A particular case of the impedance for metallic achiral CNTs is considered, and substantial differences between this case and the macroscopic model of a conductor with full skin effect are indicated.     

Spin polarization of the current in a correlated one-dimensional conductor with an impurity

The spin transport as the current flows through an impurity in a one-dimensional conductor is analyzed. The interacting electrons are described in terms of the Luttinger liquid theory. Both the Coulomb and short-range interactions are considered; the latter appears when the gate screens the long-range part of the Coulomb potential. The cases of magnetic and nonmagnetic impurities are considered. It has been revealed that, for a magnetic impurity, the electric current flow induces the generation of the spin current, which has direct and alternating components. At low temperatures and voltages, the current can be completely spin-polarized. For a nonmagnetic impurity, the spin current generation is absent. The spin current flowing though the wire affects the current-voltage characteristic for both magnetic and nonmagnetic impurities. The results have been obtained for a rather strong electron-electron interaction.     

Band-hopping transition in the quasi one-dimensional conductor TMTSF-DMTCNQ?

It has been reported that under pressure ? 10 kb, TMTSF-DMTCNQ shows at some temperature an S-shaped anomaly in the conductivity and a change in the slope of thermopower vs temperature. These changes have been taken to indicate a transition from one metallic phase to another. I give evidence that the transition these changes signal is from band to hopping conduction in the DMTCNQ chains.     

Different behaviour of local tunneling conductivity for deep and shallow impurities due to Coulomb interaction

Spatial distribution of local tunneling conductivity was investigated for deep and shallow impurities on semiconductor surfaces. Non-equilibrium Coulomb interaction and interference effects were taken into account and analyzed theoretically with the help of Keldysh formalism. Two models were investigated: mean field self-consistent approach for shallow impurity state and Hubbard-I model for deep impurity state. We have found that not only above the impurity but also at the distances comparable to the lattice period both effects interference between direct and resonant tunneling channels and on-site Coulomb repulsion of localized electrons strongly modifies form of tunneling conductivity measured by the scanning tunneling microscopy/spectroscopy (STM/STS).     

Resistance fluctuation in a one-dimensional disordered conductor in the presence of an electric field

The influence of small electric field on the nature of resistance fluctuations in a one-dimensional disordered system is studied. It is shown that for a bounded random potential the mean resistance saturates for large lengths, in agreement with the recent numerical results. We further obtain an asymptotic expression for the full probability distribution of resistance.