2,517 research outputs found
Probing of the Kondo peak by the impurity charge measurement
We consider the real-time dynamics of the Kondo system after the local probe
of the charge state of the magnetic impurity. Using the exactly solvable
infinite-degeneracy Anderson model we find explicitly the evolution of the
impurity charge after the measurement.Comment: 4 pages, 1 eps figure, revte
Dynamical conductance in the two-channel Kondo regime of a double dot system
We study finite-frequency transport properties of the double-dot system
recently constructed to observe the two-channel Kondo effect [R. M. Potok et
al., Nature 446, 167 (2007)]. We derive an analytical expression for the
frequency-dependent linear conductance of this device in the Kondo regime. We
show how the features characteristic of the 2-channel Kondo quantum critical
point emerge in this quantity, which we compute using the results of conformal
field theory as well as numerical renormalization group methods. We determine
the universal cross-over functions describing non-Fermi liquid vs. Fermi liquid
cross-overs and also investigate the effects of a finite magnetic field.Comment: 11 pages in PRB forma
Composition of the nuclear periphery from antiproton absorption
Thirteen targets with mass numbers from 58 to 238 were irradiated with the
antiproton beam from the Low Energy Antiproton Ring facility at CERN leading to
the formation of antiprotonic atoms of these heavy elements. The antiproton
capture at the end of an atomic cascade results in the production of more or
less excited residual nuclei. The targets were selected with the criterion that
both reaction products with one nucleon less than the proton and neutron number
of the target be radioactive. The yield of these radioactive products after
stopped-antiproton annihilation was determined using gamma-ray spectroscopy
techniques. This yield is related to the proton and neutron density in the
target nucleus at a radial distance corresponding to the antiproton
annihilation site. The experimental data clearly indicate the existence of a
neutron-rich nuclear periphery, a "neutron halo", strongly correlated with the
target neutron separation energy Bn and observed for targets with Bn < 10 MeV.
For two-target nuclei 106Cd and 144Sm, with larger neutron binding energies, a
proton-rich nuclear periphery was observed. Most of the experimental data are
in reasonable agreement with calculations based on current antiproton-nucleus
and pion-nucleus interaction potentials and on nuclear densities deduced with
the help of the Hartree-Fock-Bogoliubov approach. This approach was, however,
unable to account for the 106Cd and 144Sm results.Comment: Latex (RevTeX,aps style), 13 pages + 12 Postscript figure
Quantum Yu-Shiba-Rusinov dimers
Magnetic adatoms on a superconducting substrate undergo a quantum phase
transition as their exchange coupling to the conduction electrons increases.
For quantum spins, this transition is accompanied by screening of the adatom
spin. Here, we explore the consequences of this screening for the phase
diagrams and subgap excitation spectra of dimers of magnetic adatoms coupled by
hybridization of their Yu-Shiba-Rusinov states and spin-spin interactions. We
specifically account for higher spins, single-ion anisotropy,
Ruderman-Kittel-Kasuya-Yosida coupling, and Dzyaloshinsky-Moriya interactions
relevant in transition-metal and rare-earth systems. Our flexible approach
based on a zero-bandwidth approximation provides detailed physical insight and
is in excellent qualitative agreement with available numerical-renormalization
group calculations on monomers and dimers. Remarkably, we find that even in the
limit of large impurity spins or strong single-ion anisotropy, the phase
diagrams for dimers of quantum spins remain qualitatively distinct from phase
diagrams based on classical spins, highlighting the need for a theory of
quantum Yu-Shiba-Rusinov dimers.Comment: 17 pages, 12 figure
Más cuentos escogidos / Cristobal Schmid ; ilustraciones de J. Ortega Hernández y Manuel Picolo.
Contiene: Rosa de Tanemburgo - Genoveva de Brabante - Fridolín el bueno y Thierry el malo - El canastillo de flore
Stochastic Resonance in an Extended FitzHugh-Nagumo System: the Role of Selective Coupling
Here we present a study of stochastic resonance in an extended
FitzHugh-Nagumo system with a field dependent activator diffusion. We show that
the system response (here measured through the output signal-to-noise ratio) is
enhanced due to the particular form of the non-homogeneous coupling. Such a
result supports previous ones obtained in a simpler scalar reaction-diffusion
system and shows that such an enhancement, induced by the field dependent
diffusion -or selective coupling-, is a robust phenomenon.Comment: 14 pages, 19 figure
Persistent currents with long-range hopping in 1D single-isolated-diffusive rings
We show from exact calculations that a simple tight-binding Hamiltonian with
diagonal disorder and long-range hopping integrals, falling off as a power
of the inter-site separation, correctly describes the experimentally
observed amplitude (close to the value of an ordered ring) and flux-periodicity
() of persistent currents in single-isolated-diffusive normal metal rings
of mesoscopic size. Long-range hopping integrals tend to delocalize the
electrons even in the presence of disorder resulting orders of magnitude
enhancement of persistent current relative to earliar predictions.Comment: 4 pages, 3 figure
Strange behavior of persistent currents in small Hubbard rings
We show exactly that small Hubbard rings exhibit unusual kink-like structures
giving anomalous oscillations in persistent current. Singular behavior of
persistent current disappears in some cases. In half-filled systems mobility
gradually drops to zero with interaction, while it converges to some finite
value in non-half-filled cases.Comment: 7 pages, 6 figure
What is the Thouless Energy for Ballistic Systems?
The Thouless energy, \Ec characterizes numerous quantities associated with
sensitivity to boundary conditions in diffusive mesoscopic conductors. What
happens to these quantities if the disorder strength is decreased and a
transition to the ballistic regime takes place? In the present analysis we
refute the intuitively plausible assumption that \Ec loses its meaning as an
inverse diffusion time through the system at hand, and generally disorder
independent scales take over. Instead we find that a variety of (thermodynamic)
observables are still characterized by the Thouless energy.Comment: 4 pages REVTEX, uuencoded file. To appear in Physical Review Letter
Analyzing the success of T-matrix diagrammatic theories in representing a modified Hubbard model
We present a systematic study of various forms of renormalization that can be
applied in the calculation of the self-energy of the Hubbard model within the
T-matrix approximation. We compare the exact solutions of the attractive and
repulsive Hubbard models, for linear chains of lengths up to eight sites, with
all possible taxonomies of the T-matrix approximation. For the attractive
Hubbard model, the success of a minimally self-consistent theory found earlier
in the atomic limit (Phys. Rev. B 71, 155111 (2005)) is not maintained for
finite clusters unless one is in the very strong correlation limit. For the
repulsive model, in the weak correlation limit at low electronic densities --
that is, where one would expect a self-consistent T-matrix theory to be
adequate -- we find the fully renormalized theory to be most successful. In our
studies we employ a modified Hubbard interaction that eliminates all Hartree
diagrams, an idea which was proposed earlier (Phys. Rev. B 63, 035104 (2000)).Comment: Includes modified discussion of 1st-order phase transition. Accepted
for publication in J. Phys.: Condensed Matte
- …