Competing phases in the high field phase diagram of (TMTSF)2_2ClO4_4

A model is presented for the high field phase diagram of (TMTSF)$_2$ClO$_4$, taking into account the anion ordering, which splits the Fermi surface in two bands. For strong enough field, the largest metal-SDW critical temperature corresponds to the N=0 phase, which originates from two intraband nesting processes. At lower temperature, the competition between these processes puts at disadvantage the N=0 phase vs. the N=1 phase, which is due to interband nesting. A first order transition takes then place from the N=0 to N=1 phase. We ascribe to this effect the experimentally observed phase diagrams.Comment: 5 pages, 3 figures (to appear in Phys. Rev. Lett.

Die Koordination von Interessenvielfalt im europäischen Entscheidungsprozeß und deren Ergebnis: Regulative Politik als "Patchwork"

Die europäische regulative Politik erwächst aus einem bunten Feld nationaler regulativer Traditionen und Interessen. Diese stoßen im europäischen Entscheidungsprozeß aufeinander und werden zum Ausgleich gebracht. Die informellen Muster, die - im Rahmen der europäischen institutionellen Strukturen - diesen Prozeß prägen, sind "die Strategie des ersten Schrittes", "Problemlösung", "negative Koordination/Verhandlung und Kompensation". Das Resultat dieses Prozesses ist der "Patchwork"-Charakter europäischer regulativer Politik. Am Beispiel zentraler Direktiven aus dem Bereich der europäischen Luftreinhaltepolitik im Bereich industrieller Emissionen werden diese Muster der Koordination europäischer Regulierungs- und Interessenvielfalt, deren Dynamik und Ergebnisse für die europäische regulative Politik diskutiert und illustriert.European regulatory policy-making unfolds in the context of diverse regulatory interests and traditions of member states. These diverse policy traditions clash in the European arena and have to be brought into balance. In the course of this process typical informal coordinative patterns emerge which - embedded in European institutions - are typical for regulatory policy making in Europe: a "first-mover strategy", "problem orientation" and "negative coordination, bargaining plus compensation". The result of the dynamics of these coordination patterns in regulatory policy making is a policy patchwork. The coordinative patterns of diversity, their typical paths and policy consequences will be illustrated by discussion European legislation in the field of clean air policy.Einleitung 1. Informelle Prozeßmuster der regulativen Politikgestaltung in Europa 1.1 "Strategie des ersten Schrittes" und "einseitige Anpassung" 1.2 Problemlösung 1.3 Negative Koordination, Verhandlung und Kompensation 1.4 Koordinationsmuster in der Langzeitperspektive 1.5 Folgen des regulativen Wettbewerbs: Policy-Merkmale 2. Empirische Beispiele: Die europäische Luftreinhaltepolitik im Bereich industrieller Emissionen 2.1 Emissionsgrenzwerte und Stand der Technik: Die Bundesrepublik als Schrittmacher 2.2 Betriebliche Selbstregulierung und Zugang zu Informationen: Großbritannien als Schrittmacher 2.3 Integrierter Umweltschutz: Der Konflikt zwischen britischem und deutschem Problemlösungsansatz Literatu

Nanoladder cantilevers made from diamond and silicon

We present a "nanoladder" geometry that minimizes the mechanical dissipation of ultrasensitive cantilevers. A nanoladder cantilever consists of a lithographically patterned scaffold of rails and rungs with feature size $\sim$ 100 nm. Compared to a rectangular beam of the same dimensions, the mass and spring constant of a nanoladder are each reduced by roughly two orders of magnitude. We demonstrate a low force noise of $158 (+62)(-42)\,$zN and $190 (+42)(-33)\,$zN in a one-Hz bandwidth for devices made from silicon and diamond, respectively, measured at temperatures between 100--150 mK. As opposed to bottom-up mechanical resonators like nanowires or nanotubes, nanoladder cantilevers can be batch-fabricated using standard lithography, which is a critical factor for applications in scanning force microscopy

the case of South Africa

Das Engagement und somit auch der Einfluss multinationaler Firmen in Entwicklungs- und Schwellenländern sind oftmals umstritten. In Hinblick auf umweltschädliche Auswirkungen gibt es vielfältige Belege dafür, dass Firmen schwache staatliche Regulierung im Umweltbereich ausnutzen; häufig mit verheerenden Folgen. Im Rahmen von freiwilligen CSR-Standards sind in letzter Zeit zunehmend Anstrengungen unternommen worden, um solchen Entwicklungen entgegenzuwirken. In unserer Recherche untersuchen wir das Wechselspiel freiwilliger CSRNormen mit öffentlicher Regulierung in Ländern begrenzter Staatlichkeit. Wir gehen dabei von folgender Frage aus: Fördern multinationale Unternehmen, die sich zu internationalen CSR-Normen verpflichtet haben, diese Standards auch aktiv in den Ländern, in denen sie operieren? Anhand der Situation im Bereich Umweltpolitik in Südafrika und beispielhaft anhand der Bergbau-, und Lebensmittelindustrie sollen zwei Fragen beantwortet werden: Erstens, bringen sich Firmen, die freiwillige Umweltstandards unterzeichnet haben, aktiv in die Förderung kollektiver Umweltregulierung ein und unter welchen Bedingungen? Und zweitens, falls sie dies tun, welche Modelle setzen sich durch: engagieren sich Firmen durch Einflussnahme auf den Staat, durch private Selbstregulierung oder in Formen öffentlich-privater Koregulierung

Intergovernmentalists in the Commission:Foxes in the Henhouse?

Contrary to the dominant view in the scholarly literature on European institutions, where the European Commission is generally described as a unitary actor whose acts are primarily influenced by a political agenda and/or considerations of self-interest, this article argues that a variety of opinions coexist within the Commission staff. Based on the largest attitudinal survey ever conducted on Commission officials, it documents the existence of a sizeable minority of intergovernmentalists and analyzes their attitude towards the institution they serve and their views on its place in the integration process

Phase Diagram for Charge Density Waves in a Magnetic Field

The influence of an external magnetic field on a quasi one-dimensional system with a charge density wave (CDW) instability is treated within the random phase approximation which includes both CDW and spin density wave correlations. We show that the CDW is sensitive to both orbital and Pauli effects of the field. In the case of perfect nesting, the critical temperature decreases monotonously with the field, and the wave vector of the instability starts to shift above some critical value of magnetic field. Depending on the ratio between the spin and charge coupling constants and on the direction of the applied magnetic field, the wave vector shift is either parallel ($CDW_x$ order) or perpendicular ($CDW_y$ order) to the most conducting direction. The $CDW_x$ order is a field dependent linear combination of the charge and spin density waves and is sensible only to the Pauli effect. The wave vector shift in $CDW_y$ depends on the interchain coupling, but the critical temperature does not. This order is affected by the confinement of the electronic orbits. By increasing the relative strength of the orbital effect with respect to the Pauli effect, one can destroy the $CDW_y$, establishing either a $CDW_x$, or a $CDW_0$ (corresponding to perfect nesting wave vector). We also show that by increasing the imperfect nesting parameter, one passes from the regime where the critical temperature decreases with the field to the regime where it is initially enhanced by the orbital effect and eventually suppressed by the Pauli effect. For a bad nesting, the quantized phases of the field-induced CDW appear.Comment: 30 pages (LaTeX) + 15 figure

Magnetic resonance force microscopy with a one-dimensional resolution of 0.9 nanometers

Magnetic resonance force microscopy (MRFM) is a scanning probe technique capable of detecting MRI signals from nanoscale sample volumes, providing a paradigm-changing potential for structural biology and medical research. Thus far, however, experiments have not reached suffcient spatial resolution for retrieving meaningful structural information from samples. In this work, we report MRFM imaging scans demonstrating a resolution of 0.9 nm and a localization precision of 0.6 nm in one dimension. Our progress is enabled by an improved spin excitation protocol furnishing us with sharp spatial control on the MRFM imaging slice, combined with overall advances in instrument stability. From a modeling of the slice function, we expect that our arrangement supports spatial resolutions down to 0.3 nm given suffcient signal-to-noise ratio. Our experiment demonstrates the feasibility of sub-nanometer MRI and realizes an important milestone towards the three-dimensional imaging of macromolecular structures.Comment: 17 pages, 4 figure

Sign reversals of the quantum Hall effect and helicoidal magnetic-field-induced spin-density waves in quasi-one-dimensional organic conductors

We study the effect of umklapp scattering on the magnetic-field-induced spin-density-wave phases, which are experimentally observed in the quasi-one-dimensional organic conductors of the Bechgaard salts family. Within the framework of the quantized nesting model, we show that umklapp processes may naturally explain sign reversals of the quantum Hall effect (QHE) observed in these conductors. Moreover, umklapp scattering can change the polarization of the spin-density wave (SDW) from linear (sinusoidal SDW) to circular (helicoidal SDW). The QHE vanishes in the helicoidal phases, but a magnetoelectric effect appears. These two characteristic properties may be utilized to detect the magnetic-field-induced helicoidal SDW phases experimentally.Comment: 4 pages, latex, 3 figure

Quantum phase transitions in Bose-Einstein condensates from a Bethe ansatz perspective

We investigate two solvable models for Bose-Einstein condensates and extract physical information by studying the structure of the solutions of their Bethe ansatz equations. A careful observation of these solutions for the ground state of both models, as we vary some parameters of the Hamiltonian, suggests a connection between the behavior of the roots of the Bethe ansatz equations and the physical behavior of the models. Then, by the use of standard techniques for approaching quantum phase transition - gap, entanglement and fidelity - we find that the change in the scenery in the roots of the Bethe ansatz equations is directly related to a quantum phase transition, thus providing an alternative method for its detection.Comment: 26 pages, 13 figure

Field-induced spin density wave in (TMTSF)2_2NO3_3

Interlayer magnetoresistance of the Bechgaard salt (TMTSF)$_2$NO$_3$ is investigated up to 50 teslas under pressures of a few kilobars. This compound, the Fermi surface of which is quasi two-dimensional at low temperature, is a semi metal under pressure. Nevertheless, a field-induced spin density wave is evidenced at 8.5 kbar above $\sim$ 20 T. This state is characterized by a drastically different spectrum of the quantum oscillations compared to the low pressure spin density wave state.Comment: to be published in Phys. Rev. B 71 (2005