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cleaved edge realizes the sharp edge limit, where the Chklovskii picture relevant for soft etched or gated edges is no longer valid.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

Direct evidence for superconductivity in the organic charge density-wave compound alpha-(BEDT-TTF)_2KHg(SCN)_4 under hydrostatic pressure

We present direct evidence of a superconducting state existing in the title compound below 300 mK under quasi-hydrostatic pressure. The superconducing transition is observed in the whole pressure range studied, 0 < P < 4 kbar. However, the character of the transition drastically changes with suppressing the charge-density wave state.Comment: 2 pages, 2 figure

Magnetic Field Induced Coherence-Incoherence Crossover in the Interlayer Conductivity of a Layered Organic Metal

The angle-dependent interlayer magnetoresistance of the layered organic metal $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$ is found to undergo a dramatic change from the classical conventional behavior at low magnetic fields to an anomalous one at high fields. This field-induced crossover and its dependence on the sample purity and temperature imply the existence of two parallel channels in the interlayer transport: a classical Boltzmann conductivity $\sigma_{c}$ and an incoherent channel $\sigma_{i}$. We propose a simple model for $\sigma_{i}$ explaining its metallic temperature dependence and low sensitivity to the inplane field component.Comment: 5 page

Feasibility limits of using low-grade industrial waste heat in symbiotic district heating and cooling networks

Abstract: Low-grade waste heat is an underutilized resource in process industries, which may consider investing in urban symbiosis projects that provide heating and cooling to proximal urban areas through district energy networks. A long distance between industrial areas and residential users is a barrier to the feasibility of such projects, given the high capital intensity of infrastructure, and alternative uses of waste heat, such as power generation, may be more profitable, in spite of limited efficiency. This paper introduces a parametric approach to explore the economic feasibility limits of waste heat-based district heating and cooling (DHC) of remote residential buildings depending on network extension. A parametric model for the comparative water\u2013energy\u2013carbon nexus analysis of waste heat-based DHC and Organic Rankine Cycles is also introduced, and applied to an Italian and to an Austrian setting. The results show that, for a generic 4\ua0MW industrial waste heat flow steadily available at 95\ua0\ub0C, district heating and cooling is the best option from an energy\u2013carbon perspective in both countries. Power generation is the best option in terms of water footprint in most scenarios, and is economically preferable to DHC in Italy. Maximum DHC feasibility threshold distances are in line with literature, and may reach up to 30\ua0km for waste heat flows of 30\ua0MW in Austria. However, preferability threshold distances, above which waste heat-to-power outperforms DHC from an economic viewpoint, are shorter, in the order of 20\ua0km in Austria and 10\ua0km in Italy for 30\ua0MW waste heat flows. Graphic abstract: [Figure not available: see fulltext.]

Magnetic Breakdown in the electron-doped cuprate superconductor Nd2−x_{2-x}Cex_xCuO4_4: the reconstructed Fermi surface survives in the strongly overdoped regime

We report on semiclassical angle-dependent magnetoresistance oscillations (AMRO) and the Shubnikov-de Haas effect in the electron-overdoped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_4$. Our data provide convincing evidence for magnetic breakdown in the system. This shows that a reconstructed multiply-connected Fermi surface persists, at least at strong magnetic fields, up to the highest doping level of the superconducting regime. Our results suggest an intimate relation between translational symmetry breaking and the superconducting pairing in the electron-doped cuprate superconductors.Comment: 5 pages, 4 figures, submitted to PR

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

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