664 research outputs found
Underscreened Kondo effect in quantum dots coupled to ferromagnetic leads
We analyze the equilibrium transport properties of underscreened Kondo effect
in the case of a two-level quantum dot coupled to ferromagnetic leads. Using
the numerical renormalization group (NRG) method, we have determined the gate
voltage dependence of the dot's spin and level-resolved spectral functions. We
have shown that the polarization of the dot is very susceptible to spin
imbalance in the leads and changes sign in the middle of the S=1 Coulomb
valley. Furthermore, we have also found that by fine-tuning an external
magnetic field one can compensate for the presence of ferromagnetic leads and
restore the Kondo effect in the case of Coulomb valley. However, the
underscreened Kondo effect cannot be fully recovered due to its extreme
sensitivity with respect to the magnetic field.Comment: 7 pages, 6 figure
Tunnel magnetoresistance of a supramolecular spin valve
We theoretically study the transport properties of a supramolecular spin
valve, consisting of a carbon nanotube with two attached magnetic molecules,
weakly coupled to metallic contacts. The emphasis is put on analyzing the
change of the system's transport properties with the application of an external
magnetic field, which aligns the spins of the molecules. It is shown that
magnetoresistive properties of the considered molecular junction, which are
associated with changing the state of the molecules from superparamagnetic to
the ferromagnetic one, strongly depend on the applied bias voltage and the
position of the nanotube's orbital levels, which can be tuned by a gate
voltage. A strong dependence on the transport regime is also found in the case
of the spin polarization of the current flowing through the system. The
mechanisms leading to those effects are explained by invoking appropriate
molecular states responsible for transport. The analysis is done with aid of
the real-time diagrammatic technique up to the second order of expansion with
respect to tunneling processes
Interplay of the Kondo Effect and Spin-Polarized Transport in Magnetic Molecules, Adatoms and Quantum Dots
We study the interplay of the Kondo effect and spin-polarized tunneling in a
class of systems exhibiting uniaxial magnetic anisotropy, such as magnetic
molecules, magnetic adatoms, or quantum dots coupled to a single localized
magnetic moment. Using the numerical renormalization group method we calculate
the spectral functions and linear conductance in the Kondo regime. We show that
the exchange coupling between conducting electrons and localized magnetic core
generally leads to suppression of the Kondo effect. We also predict a
nontrivial dependence of the tunnel magnetoresistance on the strength of
exchange coupling and on the anisotropy constant.Comment: 4 pages with 4 EPS figures (version as accepted for publication in
Physical Review Letters
Co-tunneling current through the two-level quantum dot coupled to magnetic leads: A role of exchange interaction
The co-tunneling current through a two-level doubly occupied quantum dot
weakly coupled to ferromagnetic leads is calculated in the Coulomb blockade
regime. It is shown that the dependence of the differrential conductance on
applied voltage has a stair-case structure with different sets of "stairs" for
parallel and anti-parallel configurations of magnetization of the leads.
Contributions to the current from elastic and inelastic processes are
considered distinctly. It is observed that the interference part of the
co-tunneling current involves terms corresponding to inelastic processes.
Dependence of the co-tunneling current on the phases of the tunneling
amplitudes is studied.Comment: LaTex, 14 page
Kondo effect in a quantum dot coupled to ferromagnetic leads and side-coupled to a nonmagnetic reservoir
Equilibrium transport properties of a single-level quantum dot tunnel-coupled
to ferromagnetic leads and exchange-coupled to a side nonmagnetic reservoir are
analyzed theoretically in the Kondo regime. The equilibrium spectral functions
and conductance through the dot are calculated using the numerical
renormalization group (NRG) method. It is shown that in the antiparallel
magnetic configuration, the system undergoes a quantum phase transition with
increasing exchange coupling , where the conductance drops from its maximum
value to zero. In the parallel configuration, on the other hand, the
conductance is generally suppressed due to an effective spin splitting of the
dot level caused by the presence of ferromagnetic leads, irrespective of the
strength of exchange constant. However, for ranging from J=0 up to the
corresponding critical value, the Kondo effect and quantum critical behavior
can be restored by applying properly tuned compensating magnetic field.Comment: (8 pages, 8 figs) to appear in PR
Comment on "Deuterium--tritium fusion reactors without external fusion breeding" by Eliezer et al
Inclusion of inverse Compton effects in the calculation of
deuterium-deuterium burn under the extreme conditions considered by Eliezer et
al. [Phys. Lett. A 243 (1998) 298] are shown to decrease the maximum burn
temperature from about 300 keV to only 100--150 keV. This decrease is such that
tritium breeding by the DD --> T + p reaction is not sufficient to replace the
small amount of tritium that is initially added to the deuterium plasma in
order to trigger ignition at less than 10 keV.Comment: 6 pages, 1 tabl
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