845 research outputs found
Coulomb Drag Between Parallel Ballistic Quantum Wires
The Coulomb drag between parallel, {\it ballistic} quantum wires is studied
theoretically in the presence of a perpendicular magnetic field B. The
transresistance R_D shows peaks as a function of the Fermi level and splitting
energy between the 1D subbands of the wires. The sharpest peaks appear when the
Fermi level crosses the subband extrema so that the Fermi momenta are small.
Two other kinds of peaks appear when either {\it intra}- or {\it inter}-subband
transitions of electrons have maximum probability; the {\it intra}-subband
transitions correspond to a small splitting energy. R_D depends on the field B
in a nonmonotonic fashion: it decreases with B, as a result of the suppression
of backscattering, and increases sharply when the Fermi level approaches the
subband bottoms and the suppression is outbalanced by the increase of the
Coulomb matrix elements and of the density of states.Comment: Text 14 pages in Latex/Revtex format, 4 Postscript figures. Phys.
Rev. B,in pres
Frictional drag between non-equilibrium charged gases
The frictional drag force between separated but coupled two-dimensional
electron gases of different temperatures is studied using the non-equilibrium
Green function method based on the separation of center-of-mass and relative
dynamics of electrons. As the mechanisms of producing the frictional force we
include the direct Coulomb interaction, the interaction mediated via virtual
and real TA and LA phonons, optic phonons, plasmons, and TA and LA
phonon-electron collective modes. We found that, when the distance between the
two electron gases is large, and at intermediate temperature where plasmons and
collective modes play the most important role in the frictional drag, the
possibility of having a temperature difference between two subsystems modifies
greatly the transresistivity.Comment: 8figure
BCS theory for s+g-wave superconductivity borocarbides Y(Lu)NiBC
The s+g mixed gap function \Delta_k=\Delta {[(1-x)-x\sin^4\theta\cos4\phi]}
(x: weight of g-wave component) has been studied within BCS theory. By suitable
consideration of the pairing interaction, we have confirmed that the
coexistence of s- and g-wave, as well as the state with equal s and g
amplitudes (i.e., x=1/2) may be stable. This provides the semi-phenomenological
theory for the s+g-wave superconductivity with point nodes which has been
observed experimentally in borocarbides YNi_2B_2C and possibly in LuNi_2B_2C.Comment: 5 pages, 3 figure
Black hole thermodynamics with generalized uncertainty principle
In the standard viewpoint, the temperature of a stationary black hole is
proportional to its surface gravity, . This is a
semiclassical result and the quantum gravity effects are not taken into
consideration. This Letter explores a unified expression for the black hole
temperature in the sense of a generalized uncertainty principle(GUP). Our
discussion involves a heuristic analysis of a particle which is absorbed by the
black hole. Besides a class of static and spherically symmetric black holes, an
axially symmetric Kerr-Newman black hole is considered. Different from the
existing literature, we suggest that the black hole's irreducible mass
represent the characteristic size in the absorption process. The information
capacity of a remnant is also discussed by Bousso's D-bound in de Sitter
spacetime.Comment: 18 pages, great improvement on the first version; a Kerr-Newman black
hole is considere
Electron-electron interactions and two-dimensional - two-dimensional tunneling
We derive and evaluate expressions for the dc tunneling conductance between
interacting two-dimensional electron systems at non-zero temperature. The
possibility of using the dependence of the tunneling conductance on voltage and
temperature to determine the temperature-dependent electron-electron scattering
rate at the Fermi energy is discussed. The finite electronic lifetime produced
by electron-electron interactions is calculated as a function of temperature
for quasiparticles near the Fermi circle. Vertex corrections to the random
phase approximation substantially increase the electronic scattering rate. Our
results are in an excellent quantitative agreement with experiment.Comment: Revtex style, 21 pages and 8 postscript figures in a separate file;
Phys. Rev. B (in press
Preparation of decoherence-free, subradiant states in a cavity
The cause of decoherence in a quantum system can be traced back to the
interaction with the environment. As it has been pointed out first by Dicke, in
a system of N two-level atoms where each of the atoms is individually dipole
coupled to the environment, there are collective, subradiant states, that have
no dipole coupling to photon modes, and therefore they are expected to decay
slower. This property also implies that these type of states, which form an N-1
dimensional subspace of the atomic subsytem, also decohere slower. We propose a
scheme which will create such states. First the two-level atoms are placed in a
strongly detuned cavity and one of the atoms, called the control atom is
excited. The time evolution of the coupled atom-cavity system leads to an
appropriately entangled state of the atoms. By applying subsequent laser pulses
at a well defined time instant, it is possible to drive the atomic state into
the subradiant, i. e., decoherence free subspace. Up to a certain average
number of the photons, the result is independent of the state of the cavity.
The analysis of the conditions shows that this scheme is feasible with present
day techniques achieved in atom cavity interaction experiments.Comment: 5 page
Correlations, compressibility, and capacitance in double-quantum-well systems in the quantum Hall regime
In the quantum Hall regime, electronic correlations in double-layer
two-dimensional electron systems are strong because the kinetic energy is
quenched by Landau quantization. In this article we point out that these
correlations are reflected in the way the partitioning of charge between the
two-layers responds to a bias potential. We report on illustrative calculations
based on an unrestricted Hartree-Fock approximation which allows for
spontaneous inter-layer phase coherence. The possibility of studying
inter-layer correlations by capacitive coupling to separately contacted
two-dimensional layers is discussed in detail.Comment: RevTex style, 21 pages, 6 postscript figures in a separate file;
Phys. Rev. B (in press
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