254 research outputs found
Theoretical Investigation of Local Electron Temperature in Quantum Hall Systems
In this work we solve thermo-hydrodynamical equations considering a two
dimensional electron system in the integer quantum Hall regime, to calculate
the spatial distribution of the local electron temperature. We start from the
self-consistently calculated electrostatic and electrochemical potentials in
equilibrium. Next, by imposing an external current, we investigate the
variations of the electron temperature in the linear-response regime. Here a
local relation between the electron density and conductivity tensor elements is
assumed. Following the Ohm's law we obtain local current densities and by
implementing the results of the thermo-hydrodynamical theory, calculate the
local electron temperature. We observe that the local electron temperature
strongly depends on the formation of compressible and incompressible strips.Comment: 10 pages, 4 figure
Hydrodynamic Equations in Quantum Hall Systems at Large Currents
Hydrodynamic equations (HDEQs) are derived which describe spatio-temporal
evolutions of the electron temperature and the chemical potential of
two-dimensional systems in strong magnetic fields in states with large diagonal
resistivity appearing at the breakdown of the quantum Hall effect. The
derivation is based on microscopic electronic processes consisting of drift
motions in a slowly-fluctuating potential and scattering processes due to
electron-electron and electron-phonon interactions. In contrast with the usual
HDEQs, one of the derived HDEQs has a term with an energy flux perpendicular to
the electric field due to the drift motions in the magnetic field. As an
illustration, the current distribution is calculated using the derived HDEQs.Comment: 10 pages, 2 Postscript figures, to be published in J. Phys. Soc. Jpn.
71 (2002) No.
Interaction effects in multi-subband quantum wires
We investigate the effect of electron-electron interactions on the transport
properties of disordered quasi one-dimensional quantum wires with two or more
subbands occupied. We apply two alternative methods to solve the logarithmic
divergent problem, namely the parquet graph theory and a renormalization group
calculation. We solve the group equations analytically in the weak coupling
limit and find a power-law for the temperature dependent conductivity of a
multi-channel system. The exponent is roughly equal to the inverse of the
number of the occupied subbands.Comment: 4 pages, style-files included. No figure. Appears in J. Phys. Soc.
Japan (Letter
Superconductivity of Quasi-One-Dimensional Electrons in Strong Magnetic Field
The superconductivity of quasi-one-dimensional electrons in the magnetic
field is studied. The system is described as the one-dimensional electrons with
no frustration due to the magnetic field. The interaction is assumed to be
attractive between electrons in the nearest chains, which corresponds to the
lines of nodes of the energy gap in the absence of the magnetic field. The
effective interaction depends on the magnetic field and the transverse
momentum. As the magnetic field becomes strong, the transition temperature of
the spin-triplet superconductivity oscillates, while that of the spin-singlet
increases monotonically.Comment: 15 pages, RevTeX, 3 PostScript figures in uuencoded compressed tar
file are appende
Linear conductance in Coulomb-blockade quantum dots in the presence of interactions and spin
We discuss the calculation of the linear conductance through a
Coulomb-blockade quantum dot in the presence of interactions beyond the
charging energy. In the limit where the temperature is large compared with a
typical tunneling width, we use a rate-equations approach to describe the
transitions between the corresponding many-body states. We discuss both the
elastic and rapid-thermalization limits, where the rate of inelastic scattering
in the dot is either small or large compared with the elastic transition rate,
respectively. In the elastic limit, we find several cases where a closed
solution for the conductance is possible, including the case of a constant
exchange interaction. In the rapid-thermalization limit, a closed solution is
possible in the general case. We show that the corresponding expressions for
the linear conductance simplify for a Hamiltonian that is invariant under spin
rotations.Comment: 11 pages, no figures, revtex
Evidence of Spin-Filtering in Quantum Constrictions with Spin-Orbit Interaction
A new type of blockade effect - spin-orbit blockade (SOB) - is found in the
conduction of a quantum dot (QD) made of a material with spin-orbit
interaction. The blockade arises from spin-filtering effect in a quantum point
contact (QPC), which is a component of the QD. Hence the appearance of the
blockade itself evidences the spin-filtering effect in the QPC. The lower bound
of filtering efficiency is estimated to be above 80%.Comment: 4 pages, 4 figure
Elasticity Theory Connection Rules for Epitaxial Interfaces
Elasticity theory provides an accurate description of the long-wavelength
vibrational dynamics of homogeneous crystalline solids, and with supplemental
boundary conditions on the displacement field can also be applied to abrupt
heterojunctions and interfaces. The conventional interface boundary conditions,
or connection rules, require that the displacement field and its associated
stress field be continuous through the interface. We argue, however, that these
boundary conditions are generally incorrect for epitaxial interfaces, and we
give the general procedure for deriving the correct conditions, which depend
essentially on the detailed microscopic structure of the interface. As a simple
application of our theory we analyze in detail a one-dimensional model of an
inhomogeneous crystal, a chain of harmonic oscillators with an abrupt change in
mass and spring stiffness parameters. Our results have implications for phonon
dynamics in nanostructures such as superlattices and nanoparticles, as well as
for the thermal boundary resistance at epitaxial interfaces.Comment: 7 pages, Revte
Mesoscopic Tunneling Magnetoresistance
We study spin-dependent transport through
ferromagnet/normal-metal/ferromagnet double tunnel junctions in the mesoscopic
Coulomb blockade regime. A general transport equation allows us to calculate
the conductance in the absence or presence of spin-orbit interaction and for
arbitrary orientation of the lead magnetizations. The tunneling
magnetoresistance (TMR), defined at the Coulomb blockade conductance peaks, is
calculated and its probability distribution presented. We show that mesoscopic
fluctuations can lead to the optimal value of the TMR.Comment: 5 pages, 3 eps figures included using epsf.sty. Revised text and
improved notation, fig. 2 removed, explicit equations for the GSE case adde
Aharonov-Bohm Effect for Parallel and T-shaped Double Quantum Dots
We investigate the Aharonov-Bohm (AB) effect for the double quantum dots in
the Kondo regime using the slave-boson mean-field approximation. In contrast to
the non-interacting case, where the AB oscillation generally has the period of
4 when the two-subring structure is formed via the interdot tunneling
, we find that the AB oscillation has the period of 2 in the Kondo
regime. Such effects appear for the double quantum dots close to the T-shaped
geometry even in the charge-fluctuation regime. These results follow from the
fact that the Kondo resonance is always fixed to the Fermi level irrespective
of the detailed structure of the bare dot-levels.Comment: 3 pages, 4 figures; minor change
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