244 research outputs found
The structure of a single sharp quantum Hall edge probed by momentum-resolved tunneling
Momentum resolved magneto-tunnelling spectroscopy is performed at a single
sharp quantum Hall edge. We directly probe the structure of individual integer
quantum Hall (QH) edge modes, and find that an epitaxially overgrown cleaved
edge realizes the sharp edge limit, where the Chklovskii picture relevant for
soft etched or gated edges is no longer valid. The Fermi wavevector in the
probe quantum well probes the real-space position of the QH edge modes, and
reveals inter-channel distances smaller than both the magnetic length and the
Bohr radius. We quantitatively describe the lineshape of principal conductance
peaks and deduce an edge filling factor from their position consistent with the
bulk value. We observe features in the dispersion which are attributed to
fluctuations in the ground energy of the quantum Hall system.Comment: 4 pages, 3 figure
Magnetic Transformations in the Organic Conductor kappa-(BETS)2Mn[N(CN)2]3 at the Metal-Insulator Transition
A complex study of magnetic properties including dc magnetization, 1H NMR and
magnetic torque measurements has been performed for the organic conductor
kappa-(BETS)2Mn[N(CN)2]3 which undergoes a metal-insulator transition at
T_MI~25K. NMR and the magnetization data indicate a transition in the manganese
subsystem from paramagnetic to a frozen state at T_MI, which is, however, not a
simple Neel type order. Further, a magnetic field induced transition resembling
a spin flop has been detected in the torque measurements at temperatures below
T_MI. This transition is most likely related to the spins of pi-electrons
localized on the organic molecules BETS and coupled with the manganese 3d spins
via exchange interaction.Comment: 6 pages, 5 Figures, 1 Table; Submitted to Phys.Rev.B (Nov.2010
Probing the Electrostatics of Integer Quantum Hall Edges with Momentum-Resolved Tunnel Spectroscopy
We present measurements of momentum-resolved magneto-tunneling from a
perpendicular two-dimensional (2D) contact into integer quantum Hall (QH) edges
at a sharp edge potential created by cleaved edge overgrowth. Resonances in the
tunnel conductance correspond to coincidences of electronic states of the QH
edge and the 2D contact in energy-momentum space. With this dispersion relation
reflecting the potential distribution at the edge we can directly measure the
band bending at our cleaved edge under the influence of an external voltage
bias. At finite bias we observe significant deviations from the flat-band
condition in agreement with self-consistent calculations of the edge potential
Grid based energy system setup optimisation with Rivus in dedicated regions
Within the project IDEE (Integrated Design Efficient Energy systems in urban regions) the expertise of four cross-border (Italia & Austria) research centres and one public authority is bundled up to support the planning of new setups or the extension of existing setups in grid based sustainable energy systems for pilot regions inside the project areas. A special focus within the project is the optimization of network topologies in district heating setups. First scenarios on possible system setups for the pilot regions have been calculated outlining the topology of optimal pipe setups as well as the load of (Heat-) pipes at different time steps with the objective to minimise overall system costs.
Keywords: District heating, Optimization, Network calculation, MIL
Correlation between Fermi surface transformations and superconductivity in the electron-doped high- superconductor NdCeCuO
Two critical points have been revealed in the normal-state phase diagram of
the electron-doped cuprate superconductor NdCeCuO by exploring
the Fermi surface properties of high quality single crystals by high-field
magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas
effect shows that the weak superlattice potential responsible for the Fermi
surface reconstruction in the overdoped regime extrapolates to zero at the
doping level corresponding to the onset of superconductivity.
Second, the high-field Hall coefficient exhibits a sharp drop right below
optimal doping where the superconducting transition
temperature is maximum. This drop is most likely caused by the onset of
long-range antiferromagnetic ordering. Thus, the superconducting dome appears
to be pinned by two critical points to the normal state phase diagram.Comment: 9 pages; 7 figures; 1 tabl
Field-induced charge-density-wave transitions in the organic metal α-(BEDT-TTF)₂KHg(SCN)₄ under pressure
Successive magnetic-field-induced charge-density-wave transitions in the layered molecular conductor α-(BEDT-TTF)₂KHg(SCN)₄ are studied in the hydrostatic pressure regime, in which the zero field chargedensity-wave (CDW) state is completely suppressed. The orbital effect of the magnetic field is demonstrated to restore the density wave, while the orbital quantization induces transitions between different CDW states at changing the field strength. The latter appear as distinct anomalies in the magnetoresistance as a function of field. The interplay between the orbital and Pauli paramagnetic effects acting, respectively, to enhance and to suppress the CDW instability is particularly manifest in the angular dependence of the field-induced anomalies
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