3,668 research outputs found
Kondo effect of a Co atom on Cu(111) in contact with an Fe tip
Single Co atoms, which exhibit a Kondo effect on Cu(111), are contacted with
Cu and Fe tips in a low-temperature scanning tunneling microscope. With Fe
tips, the Kondo effect persists with the Abrikosov-Suhl resonance significantly
broadened. In contrast, for Cu-covered W tips, the resonance width remains
almost constant throughout the tunneling and contact ranges. The distinct
changes of the line width are interpreted in terms of modifications of the Co d
state occupation owing to hybridization with the tip apex atoms.Comment: 4 pages, 3 figure
Quantized Conductance of a Single Magnetic Atom
A single Co atom adsorbed on Cu(111) or on ferromagnetic Co islands is
contacted with non-magnetic W or ferromagnetic Ni tips in a scanning tunneling
microscope. When the Co atom bridges two non-magnetic electrodes conductances
of 2e^2/h are found. With two ferromagnetic electrodes a conductance of e^2/h
is observed which may indicate fully spin-polarized transport.Comment: 3 pages, 2 figure
Isotropization in the approach to big rip singularities for Cardassian models
Cardassian models are an alternative to general relativity which have been proposed as an approach to explaining accelerated cosmic expansion while avoiding directly introducing dark energy. They are generally formulated only in the homogeneous and isotropic case. In this paper an extension of the usual formulation to general spatially homogeneous geometries is given. A characteristic feature of many classes of Cardassian models is the occurrence of big rip singularities where the scale factor tends to infinity after a finite time. It is shown that big rip singularities are also widespread in more general homogeneous cases. It is also shown that there is isotropization in the approach to a big rip singularity which bears a strong resemblance to the late-time isotropization observed in cosmological spacetimes which accelerate forever in the future
Controlled Contact to a C60 Molecule
The conductance of C60 on Cu(100) is investigated with a low-temperature
scanning tunneling microscope. At the transition from tunneling to the contact
regime the conductance of C60 adsorbed with a pentagon-hexagon bond rises
rapidly to 0.25 conductance quanta G0. An abrupt conductance jump to G0 is
observed upon further decreasing the distance between the instrument's tip and
the surface. Ab-initio calculations within density functional theory and
non-equilibrium Green's function techniques explain the experimental data in
terms of the conductance of an essentially undeformed C60. From a detailed
analysis of the crossover from tunneling to contact we conclude that the
conductance in this region is strongly affected by structural fluctuations
which modulate the tip-molecule distance.Comment: 4 pages, 3 figure
Controlling the Kondo Effect in CoCu_n Clusters Atom by Atom
Clusters containing a single magnetic impurity were investigated by scanning
tunneling microscopy, spectroscopy, and ab initio electronic structure
calculations. The Kondo temperature of a Co atom embedded in Cu clusters on
Cu(111) exhibits a non-monotonic variation with the cluster size. Calculations
model the experimental observations and demonstrate the importance of the local
and anisotropic electronic structure for correlation effects in small clusters.Comment: 4 pages, 4 figure
Hot electron cascades in the scanning tunneling microscope
The nonequilibrium distribution of electrons at the junction of a scanning tunneling microscope is investigated by detecting photons with energies hv > eV, where V is the bias voltage. Electrons are found at energies exceeding the Fermi level by almost eV. While their distribution deviates from a Fermi-Dirac function it is consistent with a model of hot electrons and holes that diffuse in energy and real space
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