16 research outputs found
Interplay between Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction
The interplay between the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction
and the Kondo effect is expected to provide the driving force for the emergence
of many phenomena in strongly correlated electron materials. Two magnetic
impurities in a metal are the smallest possible system containing all these
ingredients and define a bottom up approach towards a long term understanding
of concentrated / dense systems. Here we report on the experimental and
theoretical investigation of iron dimers buried below a Cu(100) surface by
means of low temperature scanning tunnelling spectroscopy (STS) combined with
density functional theory (DFT) and numerical renormalization group (NRG)
calculations. The Kondo effect, in particular the width of the Abrikosov-Suhl
resonance, is strongly altered or even suppressed due to magnetic coupling
between the impurities. It oscillates as function of dimer separation revealing
that it is related to the RKKY interaction mediated by the conduction
electrons. Simulations based on density functional theory support this concept
showing the same oscillation period and trends in the coupling strength as
found in the experiment
Theory of real space imaging of Fermi surfaces
A scanning tunneling microscope can be used to visualize in real space Fermi
surfaces with buried impurities far below substrates acting as local probes. A
theory describing this feature is developed based on the stationary phase
approximation. It is demonstrated how a Fermi surface of a material acts as a
mirror focusing electrons that scatter at hidden impurities.Comment: 10 pages, 4 figure
Long-range Kondo signature of a single magnetic impurity
The Kondo effect, one of the oldest correlation phenomena known in condensed
matter physics, has regained attention due to scanning tunneling spectroscopy
(STS) experiments performed on single magnetic impurities. Despite the
sub-nanometer resolution capability of local probe techniques one of the
fundamental aspects of Kondo physics, its spatial extension, is still subject
to discussion. Up to now all STS studies on single adsorbed atoms have shown
that observable Kondo features rapidly vanish with increasing distance from the
impurity. Here we report on a hitherto unobserved long range Kondo signature
for single magnetic atoms of Fe and Co buried under a Cu(100) surface. We
present a theoretical interpretation of the measured signatures using a
combined approach of band structure and many-body numerical renormalization
group (NRG) calculations. These are in excellent agreement with the rich
spatially and spectroscopically resolved experimental data.Comment: 7 pages, 3 figures + 8 pages supplementary material; Nature Physics
(Jan 2011 - advanced online publication
Graphene-metal contact resistivity on semi-insulating 6H-SiC(0001) measured with Kelvin probe force microscopy
We present Kelvin probe force microscopy measurements and resistance network simulations of the lateral charge transport across few-layer graphene on the semi-insulating 6H-SiC(0001) surface. After preparation of the SiC crystal by thermal decomposition, gold electrodes were prepared on the top of the graphene layers. The transport field is extracted by subtracting measurements of reverse lateral bias applied to the gold electrodes. Graphene sheet resistances as low as 0: 75 k Omega/sq were observed. By comparing the experimental transport measurements with a resistance network simulation the contact resistivity between graphene and a gold electrode can be determined to be < 1 x 10(-6) Omega cm(2). (C) 2013 AIP Publishing LLC
Origin of Schottky barriers in gold contacts on GaAs(110)
Gold contacts on n-type GaAs(110) have been investigated using scanning tunneling microscopy and spectroscopy in cross-sectional configuration. In spatially resolved current voltage spectroscopy the Schottky barrier potential is visible. We find signatures of delocalized gap states at the interface decaying into the semiconductor and observe a defect density at the interface below 3x10(13) cm(-2). Both findings support that the Fermi level pinning at the Au/GaAs(110) interface is dominated by metal-induced gap states
Intrinsic quantum dots in partially ordered bulk (GaIn)P
We present a photoluminescence study with 500 nm lateral resolution on partially ordered bulk (GaIn)P alloys at lattice temperatures 3-60 K, external magnetic fields 0-12 T, and excitation power 0.1-100 mu W. In the known ordering-induced low energy emission band we resolve narrow optical transition lines with 0.3-1.0 meV width. They show no thermal broadening, a diamagnetic shift with pronounced anisotropy, and biexci-tonic states. We demonstrate that the transitions are connected with intrinsic quasi-zero-dimensional electron-hole confinement formed at the antiphase-boundaries in the crystal