The Kondo effect is studied theoretically in the framework of the non-equilibrium Green function formalism. The system under consideration consists of a single quantum dot asymmetrically coupled to ferromagnetic electrodes, whose magnetic moments are non-collinear. The spin-dependent density of states, as well as the transport characteristics such as differential conductance and tunneling magnetoresistance through the system are obtained using the equation of motion method. Numerical illustration of the mentioned quantities for several magnetic configurations and coupling strengths is presented and discussed.
The poor man's scaling technique is applied to the problem of electronic transport through a single quantum dot (with finite Coulomb repulsion) asymmetrically coupled to electrodes. The considered quantum dot is coupled to ferromagnetic electrodes, whose magnetic moments are non-collinear. The analysis and numerical illustration of spin splitting of the dot level as well as of the Kondo temperature on the coupling asymmetry is presented and discussed.
We demonstrate experimentally that conductance steps can occur in nanowires formed at metal-semiconductor junctions, between a cobalt tip and a germanium surface revealing long-duration plateaus at reproducible levels. The high reproducibility of the conductance traces obtained leads to very sharp peaks in the conductance histogram suggesting formation of stable atomic configurations. We develop a new type of correlation analysis of the preferred conductance values that provide new type of information on a few-atomic-nanocontact formation dynamics.
Kondo effect in a single-level quantum dot attached to magnetic leads is studied theoretically by the "poor man's scaling" and non-equilibrium Green function methods. From the scaling equations we derive the Kondo temperature as a function of the model parameters - in particular as a function of the angle between magnetic moments. Transport characteristics, i.e. differential conductance and tunnel magnetoresistance associated with magnetization rotation, were calculated within the non-equilibrium Green function formalism based on the equation of motion method.
Linear and non-linear conductance of quantum dots attached to magnetic leads is considered theoretically in the Kondo regime. The considerations are based on the non-equilibrium Green function formalism and the relevant equation of motion method. Splitting of the Kondo anomaly due to coupling of the dot to ferromagnetic electrodes, and its dependence on magnetic configuration of the system and on the lead's spin polarization is studied numerically.
Conductance quantization of heterocontacts between tungsten (W) tip and cubic RCu_5 (R = Gd, Ho, Lu) binary compounds prepared by melt-spinning was observed in nanowires produced dynamically using piezoelectric actuator. The conductance stepwise behaviour of the nanowires was directly observed with a storage oscilloscope. Quantum units of the nanowires conductance measured in their paramagnetic states are presented and discussed in terms of the Landauer formalism.
We present a method of measurement of the current-voltage (I-V) and conductance-voltage (G-V) characteristics of nanowires with quantum point contact formed at the Co-Ge_{99.99}Ga_{0.01} interface. The effect of the Fermi level pinning leads to the formation of an ohmic contact between Co and Ge_{99.99}Ga_{0.01}. On the measured characteristics, above the threshold value of voltage an exponential current growth is observed. Such effect could be useful in the production of the electronic nanodevices.
Spin effects in electronic transport properties of artificial magnetic structures, like nanopillar spin valves, tunnel junctions, mesoscopic double-barrier junctions (single-electron transistors) are briefly discussed. Two classes of spin effects are distinguished; i.e. magnetoresistance phenomena due to magnetization rotation, and current-induced magnetic switching and magnetic dynamics.
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