135 research outputs found
Exchange cotunneling through quantum dots with spin-orbit coupling
We investigate the effects of spin-orbit interaction (SOI) on the exchange
cotunneling through a spinful Coulomb blockaded quantum dot. In the case of
zero magnetic field, Kondo effect is shown to take place via a Kramers doublet
and the SOI will merely affect the Kondo temperature. In contrast, we find that
the breaking of time-reversal symmetry in a finite field has a marked influence
on the effective Anderson, and Kondo models for a single level. The nonlinear
conductance can now be asymmetric in bias voltage and may depend strongly on
direction of the magnetic field. A measurement of the angle dependence of
finite-field cotunneling spectroscopy thus provides valuable information about
orbital, and spin degrees of freedom and their mutual coupling.Comment: 5 pages, 2 figure
Field efficacy of new compounds to replace copper for scab control in organic apple production
Efficacy of compounds was investigated in field experiments in Denmark and the Netherlands according to EPPO guidelines. Some Yucca extracts and potassium bicarbonate had an efficacy similar to sulphur on leaves. Addition of sulphur to Yucca 1 and to potassium bicarbonate increased the level of efficacy to that of copper. This confirms results from earlier years. Although a dose increase resulted in better efficacy, this was more prominent for Yucca1 than for potassium bicarbonate
Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots
By means of sequential and cotunneling spectroscopy, we study the tunnel
couplings between metallic leads and individual levels in a carbon nanotube
quantum dot. The levels are ordered in shells consisting of two doublets with
strong- and weak-tunnel couplings, leading to gate-dependent level
renormalization. By comparison to a one- and two-shell model, this is shown to
be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a
parallel magnetic field is shown to reduce this mixing and thus suppress the
effects of tunnel renormalization.Comment: 5 pages, 3 figures; revised version as publishe
Superconductivity-enhanced bias spectroscopy in carbon nanotube quantum dots
We study low-temperature transport through carbon nanotube quantum dots in
the Coulomb blockade regime coupled to niobium-based superconducting leads. We
observe pronounced conductance peaks at finite source-drain bias, which we
ascribe to elastic and inelastic cotunneling processes enhanced by the
coherence peaks in the density of states of the superconducting leads. The
inelastic cotunneling lines display a marked dependence on the applied gate
voltage which we relate to different tunneling-renormalizations of the two
subbands in the nanotube. Finally, we discuss the origin of an especially
pronounced sub-gap structure observed in every fourth Coulomb diamond
Probing Transverse Magnetic Anisotropy by Electronic Transport through a Single-Molecule Magnet
By means of electronic transport, we study the transverse magnetic anisotropy
of an individual Fe single-molecule magnet (SMM) embedded in a
three-terminal junction. In particular, we determine in situ the transverse
anisotropy of the molecule from the pronounced intensity modulations of the
linear conductance, which are observed as a function of applied magnetic field.
The proposed technique works at temperatures exceeding the energy scale of the
tunnel splittings of the SMM. We deduce that the transverse anisotropy for a
single Fe molecule captured in a junction is substantially larger than the
bulk value.Comment: 18 pages with 16 figures; version as publishe
Prevention and control of apple scab
Improved prevention and control of apple scab caused by Venturia inaequalis is aimed at without the use of copper containing products in the Repco-project. Substantial progress is made in selection of potential products against summer epidemics. A patent application is made for E73. New effective biocontrol agents are selected to reduce inoculum during winter. The product potassium bicarbonate has shown good efficacy and Repco contributes to the registration of this product in Europe. Earthworms tended to be stimulated to consume apple leaves treated with amino acids or beetpulp, especially when applied fresh under controlled environmental condi-tons
Nonequilibrium transport through a spinful quantum dot with superconducting leads
We study the nonlinear cotunneling current through a spinful quantum dot
contacted by two superconducting leads. Applying a general nonequilibrium Green
function formalism to an effective Kondo model, we study the rich variation in
the IV-characteristics with varying asymmetry in the tunnel coupling to source
and drain electrodes. The current is found to be carried respectively by
multiple Andreev reflections in the symmetric limit, and by spin-induced
Yu-Shiba-Russinov bound states in the strongly asymmetric limit. The interplay
between these two mechanisms leads to qualitatively different
IV-characteristics in the cross-over regime of intermediate symmetry,
consistent with recent experimental observations of negative differential
conductance and re-positioned conductance peaks in sub-gap cotunneling
spectroscopy.Comment: 5 pages, 3 fig
- …