Skyrmion Lattice in a Chiral Magnet

Skyrmions represent topologically stable field configurations with particle-like properties. We used neutron scattering to observe the spontaneous formation of a two-dimensional lattice of skyrmion lines, a type of magnetic vortices, in the chiral itinerant-electron magnet MnSi. The skyrmion lattice stabilizes at the border between paramagnetism and long-range helimagnetic order perpendicular to a small applied magnetic field regardless of the direction of the magnetic field relative to the atomic lattice. Our study experimentally establishes magnetic materials lacking inversion symmetry as an arena for new forms of crystalline order composed of topologically stable spin states

Analytische Modellierung des Zeitverhaltens und der Verlustleistung von CMOS-Gattern

In modernen CMOS-Technologien werden die Verzögerungszeit, die Ausgangsflankensteilheit und der Querstrom eines Gatters sowohl durch die Lastkapazität als auch durch die Steilheit des Eingangssignals beeinflusst. Die heute verwendeten Technologiebibliotheken beinhalten Tabellenmodelle mit 25 oder mehr Stützpunkten dieser Abhängigkeiten, woraus durch Interpolation die benötigten Zwischenwerte berechnet werden. Bisherige Versuche, analytische Modelle abzuleiten beruhten darauf, den Querstrom zu vernachlässigen oder Transistorströme als stückweise linear anzunähern. Der hier gezeigte Ansatz beruht auf einer näherungsweisen Lösung der Differentialgleichung, die aus den beiden Transistorströmen und einer Lastkapazität besteht und damit das Schaltverhalten eines Inverters beschreibt. Mit wenigen Technologieparametern können daraus für einen beliebig dimensionierten Inverter die für eine Timing- und Verlustleistungsanalyse notwendigen Größen berechnet werden. Das Modell erreicht bei einem Vergleich zu Referenzwerten aus SPICE Simulationen eine Genauigkeit von typischerweise 5%.</p><p style=&quot;line-height: 20px;&quot;>In modern CMOS-technologies the gate delay, output transition time and the short-circuit current depend on the capacitive load as well as on the input transition time. Today’s technology libraries use table models with 25 or more samples for these dependencies. Intermediate values have to be calculated through interpolation. Attempts to derive analytical models are based on neglecting the short-circuit current or approximating it by piecewise linear functions. The approach shown in this paper provides an approximate solution for the differential equation describing the dynamic behavor of an inverter circuit. It includes the influence of both transistor currents and a single load capacitance. The required values for timing and power analysis can be calculated with a small set of technology parameters for an arbitrary designed inverter. Compared to reference values extracted from SPICE simulations, the model achieves a typical precision of 5%

Fallacies, Irrelevant Facts, and Myths in the Discussion of Capital Regulation: Why Bank Equity is Not Expensive

We examine the pervasive view that “equity is expensive,” which leads to claims that high capital requirements are costly and would affect credit markets adversely. We find that arguments made to support this view are either fallacious, irrelevant, or very weak. For example, the return on equity contains a risk premium that must go down if banks have more equity. It is thus incorrect to assume that the required return on equity remains fixed as capital requirements increase. It is also incorrect to translate higher taxes paid by banks to a social cost. Policies that subsidize debt and indirectly penalize equity through taxes and implicit guarantees are distortive. Any desirable public subsidies to banks’ activities should be given directly and not in ways that encourage leverage. Finally, suggestions that high leverage serves a necessary disciplining role are based on inadequate theory lacking empirical support. We conclude that bank equity is not socially expensive, and that high leverage is not necessary for banks to perform all their socially valuable functions, including lending, taking deposits and issuing money-like securities. To the contrary, better capitalized banks suffer fewer distortions in lending decisions and would perform better. The fact that banks choose high leverage does not imply that this is socially optimal, and, viewed from an ex ante perspective, high leverage may not even be privately optimal for banks. Setting equity requirements significantly higher than the levels currently proposed would entail large social benefits and minimal, if any, social costs. Approaches based on equity dominate alternatives, including contingent capital. To achieve better capitalization quickly and efficiently and prevent disruption to lending, regulators must actively control equity payouts and issuance. If remaining challenges are addressed, capital regulation can be a powerful tool for enhancing the role of banks in the economy.capital regulation, financial institutions, capital structure, too big to fail, systemic risk, bank equity, contingent capital, Basel.

Uniaxial pressure dependence of magnetic order in MnSi

We report comprehensive small angle neutron scattering (SANS) measurements complemented by ac susceptibility data of the helical order, conical phase and skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all crystallographic orientations uniaxial pressure favours the phase for which a spatial modulation of the magnetization is closest to the pressure axis. Uniaxial pressures as low as 1kbar applied perpendicular to the magnetic field axis enhance the skyrmion lattice phase substantially, whereas the skyrmion lattice phase is suppressed for pressure parallel to the field. Taken together we present quantitative microscopic information how strain couples to magnetic order in the chiral magnet MnSi.Comment: 23 pages, includes supplemen

Spin Transfer Torques in MnSi at Ultra-low Current Densities

Spin manipulation using electric currents is one of the most promising directions in the field of spintronics. We used neutron scattering to observe the influence of an electric current on the magnetic structure in a bulk material. In the skyrmion lattice of MnSi, where the spins form a lattice of magnetic vortices similar to the vortex lattice in type II superconductors, we observe the rotation of the diffraction pattern in response to currents which are over five orders of magnitude smaller than those typically applied in experimental studies on current-driven magnetization dynamics in nanostructures. We attribute our observations to an extremely efficient coupling of inhomogeneous spin currents to topologically stable knots in spin structures