90 research outputs found
Electron transport through single Mn12 molecular magnets
We report transport measurements through a single-molecule magnet, the Mn12
derivative [Mn12O12(O2C-C6H4-SAc)16(H2O)4], in a single-molecule transistor
geometry. Thiol groups connect the molecule to gold electrodes that are
fabricated by electromigration. Striking observations are regions of complete
current suppression and excitations of negative differential conductance on the
energy scale of the anisotropy barrier of the molecule. Transport calculations,
taking into account the high-spin ground state and magnetic excitations of the
molecule, reveal a blocking mechanism of the current involving non-degenerate
spin multiplets.Comment: Accepted for Phys. Rev. Lett., 5 pages, 4 figure
Multimodal nonlinear imaging of atherosclerotic plaques differentiation of triglyceride and cholesterol deposits
Cardiovascular diseases in general and atherothrombosis as the most common of its individual disease entities is the leading cause of death in the developed countries. Therefore, visualization and characterization of inner arterial plaque composition is of vital diagnostic interest, especially for the early recognition of vulnerable plaques. Established clinical techniques provide valuable morphological information but cannot deliver information about the chemical composition of individual plaques. Therefore, spectroscopic imaging techniques have recently drawn considerable attention. Based on the spectroscopic properties of the individual plaque components, as for instance different types of lipids, the composition of atherosclerotic plaques can be analyzed qualitatively as well as quantitatively. Here, we compare the feasibility of multimodal nonlinear imaging combining two-photon fluorescence (TPF), coherent anti-Stokes Raman scattering (CARS) and second-harmonic generation (SHG) microscopy to contrast composition and morphology of lipid deposits against the surrounding matrix of connective tissue with diffraction limited spatial resolution. In this contribution, the spatial distribution of major constituents of the arterial wall and atherosclerotic plaques like elastin, collagen, triglycerides and cholesterol can be simultaneously visualized by a combination of nonlinear imaging methods, providing a powerful label-free complement to standard histopathological methods with great potential for in vivo application
Spintronic magnetic anisotropy
An attractive feature of magnetic adatoms and molecules for nanoscale
applications is their superparamagnetism, the preferred alignment of their spin
along an easy axis preventing undesired spin reversal. The underlying magnetic
anisotropy barrier --a quadrupolar energy splitting-- is internally generated
by spin-orbit interaction and can nowadays be probed by electronic transport.
Here we predict that in a much broader class of quantum-dot systems with spin
larger than one-half, superparamagnetism may arise without spin-orbit
interaction: by attaching ferromagnets a spintronic exchange field of
quadrupolar nature is generated locally. It can be observed in conductance
measurements and surprisingly leads to enhanced spin filtering even in a state
with zero average spin. Analogously to the spintronic dipolar exchange field,
responsible for a local spin torque, the effect is susceptible to electric
control and increases with tunnel coupling as well as with spin polarization.Comment: 6 pages with 4 figures + 26 pages of Supplementary Informatio
The numerical renormalization group method for quantum impurity systems
In the beginning of the 1970's, Wilson developed the concept of a fully
non-perturbative renormalization group transformation. Applied to the Kondo
problem, this numerical renormalization group method (NRG) gave for the first
time the full crossover from the high-temperature phase of a free spin to the
low-temperature phase of a completely screened spin. The NRG has been later
generalized to a variety of quantum impurity problems. The purpose of this
review is to give a brief introduction to the NRG method including some
guidelines of how to calculate physical quantities, and to survey the
development of the NRG method and its various applications over the last 30
years. These applications include variants of the original Kondo problem such
as the non-Fermi liquid behavior in the two-channel Kondo model, dissipative
quantum systems such as the spin-boson model, and lattice systems in the
framework of the dynamical mean field theory.Comment: 55 pages, 27 figures, submitted to Rev. Mod. Phy
High prevalence of Trichomonas gallinae in wild columbids across western and southern Europe
Avian trichomonosis is known as a widespread disease in columbids and passerines, and recent findings have highlighted the pathogenic character of some lineages found in wild birds. Trichomonosis can affect wild bird populations including endangered species, as has been shown for Mauritian pink pigeons Nesoenas mayeri in Mauritius and suggested for European turtle doves Streptopelia turtur in the UK. However, the disease trichomonosis is caused only by pathogenic lineages of the parasite Trichomonas gallinae. Therefore, understanding the prevalence and distribution of both potentially pathogenic and non-pathogenic T. gallinae lineages in turtle doves and other columbids across Europe is relevant to estimate the potential impact of the disease on a continental scale
Superconductivity in a single C60 transistor
Single molecule transistors (SMTs) are currently attracting enormous
attention as possible quantum information processing devices. An intrinsic
limitation to the prospects of these however is associated to the presence of a
small number of quantized conductance channels, each channel having a high
access resistance of at best =12.9 k. When the
contacting leads become superconducting, these correlations can extend
throughout the whole system by the proximity effect. This not only lifts the
resistive limitation of normal state contacts, but further paves a new way to
probe electron transport through a single molecule. In this work, we
demonstrate the realization of superconducting SMTs involving a single C60
fullerene molecule. The last few years have seen gate-controlled Josephson
supercurrents induced in the family of low dimensional carbon structures such
as flakes of two-dimensional graphene and portions of one-dimensional carbon
nanotubes. The present study involving a full zero-dimensionnal fullerene
completes the picture.Comment: 12 pages, 3 figure
Signatures of Molecular Magnetism in Single-Molecule Transport Spectroscopy
Single-molecule transistors provide a unique experimental tool to investigate
the coupling between charge transport and the molecular degrees of freedom in
individual molecules. One interesting class of molecules for such experiments
are the single-molecule magnets, since the intramolecular exchange forces
present in these molecules should couple strongly to the spin of transport
electrons, thereby providing both new mechanisms for modulating electron flow
and also new means for probing nanoscale magnetic excitations. Here we report
single-molecule transistor measurements on devices incorporating Mn12
molecules. By studying the electron-tunneling spectrum as a function of
magnetic field, we are able to identify clear signatures of magnetic states and
their associated magnetic anisotropy. A comparison of the data to simulations
also suggests that electron flow can strongly enhance magnetic relaxation of
the magnetic molecule
- …