90 research outputs found
Contact resistance dependence of crossed Andreev reflection
We show experimentally that in nanometer scaled superconductor/normal metal
hybrid devices and in a small window of contact resistances, crossed Andreev
reflection (CAR) can dominate the nonlocal transport for all energies below the
superconducting gap. Besides CAR, elastic cotunneling (EC) and nonlocal charge
imbalance (CI) can be identified as competing subgap transport mechanisms in
temperature dependent four-terminal nonlocal measurements. We demonstrate a
systematic change of the nonlocal resistance vs. bias characteristics with
increasing contact resistances, which can be varied in the fabrication process.
For samples with higher contact resistances, CAR is weakened relative to EC in
the midgap regime, possibly due to dynamical Coulomb blockade. Gaining control
of CAR is an important step towards the realization of a solid state entangler.Comment: 5 pages, 4 figures, submitted to PR
Permalloy-based carbon nanotube spin-valve
In this Letter we demonstrate that Permalloy (Py), a widely used Ni/Fe alloy,
forms contacts to carbon nanotubes (CNTs) that meet the requirements for the
injection and detection of spin-polarized currents in carbon-based spintronic
devices. We establish the material quality and magnetization properties of Py
strips in the shape of suitable electrical contacts and find a sharp
magnetization switching tunable by geometry in the anisotropic
magnetoresistance (AMR) of a single strip at cryogenic temperatures. In
addition, we show that Py contacts couple strongly to CNTs, comparable to Pd
contacts, thereby forming CNT quantum dots at low temperatures. These results
form the basis for a Py-based CNT spin-valve exhibiting very sharp resistance
switchings in the tunneling magnetoresistance, which directly correspond to the
magnetization reversals in the individual contacts observed in AMR experiments.Comment: 3 page
Large oscillating non-local voltage in multi-terminal single wall carbon nanotube devices
We report on the observation of a non-local voltage in a ballistic
one-dimensional conductor, realized by a single-wall carbon nanotube with four
contacts. The contacts divide the tube into three quantum dots which we control
by the back-gate voltage . We measure a large \emph{oscillating} non-local
voltage as a function of with zero mean. Though a classical
resistor model can account for a non-local voltage including change of sign, it
fails to describe the magnitude properly. The large amplitude of is
due to quantum interference effects and can be understood within the
scattering-approach of electron transport
Measurement of the spin polarization of the magnetic semiconductor EuS with zero-field and Zeeman-split Andreev reflection spectroscopy
We report measurements of the spin polarization (\textbf{\textit{P}}) of the
concentrated magnetic semiconductor EuS using both zero-field and Zeeman-split
Andreev reflection spectroscopy (ARS) with EuS/Al planar junctions. The
zero-field ARS spectra are well described by the modified (spin-polarized) BTK
model with expected superconducting energy gap and actual measurement
temperature (no additional spectral broadening). The fittings consistently
yield \textbf{\textit{P}} close to 80% regardless of the barrier strength.
Moreover, we performed ARS in the presence of a Zeeman-splitting of the
quasiparticle density of states in Al. To describe the Zeeman-split ARS
spectra, we develop a theoretical model which incorporates the solution to the
Maki-Fulde equations into the modified BTK analysis. The method enables the
determination of the magnitude as well as the sign of \textbf{\textit{P}} with
ARS, and the results are consistent with those from the zero-field ARS. The
experiments extend the utility of field-split superconducting spectroscopy from
tunnel junctions to Andreev junctions of arbitrary barrier strengths.Comment: 6 pages, 4 figure
Superconductivity enhanced conductance fluctuations in few layer graphene nanoribbons
We investigate the mesoscopic disorder induced rms conductance variance
in a few layer graphene nanoribbon (FGNR) contacted by two
superconducting (S) Ti/Al contacts. By sweeping the back-gate voltage, we
observe pronounced conductance fluctuations superimposed on a linear background
of the two terminal conductance G. The linear gate-voltage induced response can
be modeled by a set of inter-layer and intra-layer capacitances.
depends on temperature T and source-drain voltage .
increases with decreasing T and . When lowering , a
pronounced cross-over at a voltage corresponding to the superconducting energy
gap is observed. For |V_{sd}|\ltequiv \Delta the fluctuations are
markedly enhanced. Expressed in the conductance variance of one
graphene-superconducutor (G-S) interface, values of 0.58 e^2/h are obtained at
the base temperature of 230 mK. The conductance variance in the sub-gap region
are larger by up to a factor of 1.4-1.8 compared to the normal state. The
observed strong enhancement is due to phase coherent charge transfer caused by
Andreev reflection at the nanoribbon-superconductor interface.Comment: 15 pages, 5 figure
Health lipid indices of dry fermented sausages made of pork meat
This research presents the results of a comparison assessment of the cholesterol content, fatty acid profile, and atherogenic (IA) and thrombogenic (IT) health lipid parameters of four dry fermented sausages produced from Mangalitsa and Swedish Landrace pork meat. The highest cholesterol level was found in Sremska sausage prepared from Landrace meat (64.92 mg/100g). Polyunsaturated fatty acid (PUFA) levels were considerably greater in Landrace meat sausages than in other kinds. The main cause of these variations was a higher overall n-6 PUFA concentration. The sausages made from Mangalitsa meat had the highest levels of monounsaturated fatty acid (MUFA) and unsaturated fatty acid (USFA). The highest saturated fatty acid (SFA) level was found in sausages prepared from Landrace meat. Fermented sausages made from Mangalitsa pork meat show better health lipid indices, atherogenic (IA), thrombogenic (IT), and PUFA/SFA ratios
Pseudospin Order in Monolayer, Bilayer, and Double-Layer Graphene
Graphene is a gapless semiconductor in which conduction and valence band
wavefunctions differ only in the phase difference between their projections
onto the two sublattices of the material's two-dimensional honeycomb crystal
structure. We explain why this circumstance creates openings for broken
symmetry states, including antiferromagnetic states in monolayer and bilayer
graphene and exciton condensates in double-layer graphene, that are momentum
space analogs of the real-space order common in systems with strong local
interactions. We discuss some similarities among, and some differences between,
these three broken symmetry states.Comment: 20 pages 4 figures. Contribution for the Proceedings of the Nobel
Symposium on Graphene. Updated reference
Quantum Hall Effects in Graphene-Based Two-Dimensional Electron Systems
In this article we review the quantum Hall physics of graphene based
two-dimensional electron systems, with a special focus on recent experimental
and theoretical developments. We explain why graphene and bilayer graphene can
be viewed respectively as J=1 and J=2 chiral two-dimensional electron gases
(C2DEGs), and why this property frames their quantum Hall physics. The current
status of experimental and theoretical work on the role of electron-electron
interactions is reviewed at length with an emphasis on unresolved issues in the
field, including assessing the role of disorder in current experimental
results. Special attention is given to the interesting low magnetic field limit
and to the relationship between quantum Hall effects and the spontaneous
anomalous Hall effects that might occur in bilayer graphene systems in the
absence of a magnetic field
An NMR strategy for fragment-based ligand screening utilizing a paramagnetic lanthanide probe
A nuclear magnetic resonance-based ligand screening strategy utilizing a paramagnetic lanthanide probe is presented. By fixing a paramagnetic lanthanide ion to a target protein, a pseudo-contact shift (PCS) and a paramagnetic relaxation enhancement (PRE) can be observed for both the target protein and its bound ligand. Based on PRE and PCS information, the bound ligand is then screened from the compound library and the structure of the ligandâprotein complex is determined. PRE is an isotropic paramagnetic effect observed within 30Â Ă
from the lanthanide ion, and is utilized for the ligand screening in the present study. PCS is an anisotropic paramagnetic effect providing long-range (~40Â Ă
) distance and angular information on the observed nuclei relative to the paramagnetic lanthanide ion, and utilized for the structure determination of the ligandâprotein complex. Since a two-point anchored lanthanide-binding peptide tag is utilized for fixing the lanthanide ion to the target protein, this screening method can be generally applied to non-metal-binding proteins. The usefulness of this strategy was demonstrated in the case of the growth factor receptor-bound protein 2 (Grb2) Src homology 2 (SH2) domain and its low- and high-affinity ligands
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