Topological energy barrier for skyrmion lattice formation in MnSi

We report the direct measurement of the topological skyrmion energy barrier through a hysteresis of the skyrmion lattice in the chiral magnet MnSi. Measurements were made using small-angle neutron scattering with a custom-built resistive coil to allow for high-precision minor hysteresis loops. The experimental data was analyzed using an adapted Preisach model to quantify the energy barrier for skyrmion formation and corroborated by the minimum-energy path analysis based on atomistic spin simulations. We reveal that the skyrmion lattice in MnSi forms from the conical phase progressively in small domains, each of which consisting of hundreds of skyrmions, and with an activation barrier of several eV.Comment: Final accepted versio

Lack of phylogeographic structure in the freshwater cyanobacterium <i>Microcystis aeruginosa</i> suggests global dispersal

Background: Free-living microorganisms have long been assumed to have ubiquitous distributions with little biogeographic signature because they typically exhibit high dispersal potential and large population sizes. However, molecular data provide contrasting results and it is far from clear to what extent dispersal limitation determines geographicstructuring of microbial populations. We aimed to determine biogeographical patterns of the bloom-forming freshwatercyanobacterium Microcystis aeruginosa. Being widely distributed on a global scale but patchily on a regional scale, this prokaryote is an ideal model organism to study microbial dispersal and biogeography.Methodology/Principal Findings: The phylogeography of M. aeruginosa was studied based on a dataset of 311 rDNAinternal transcribed spacer (ITS) sequences sampled from six continents. Richness of ITS sequences was high (239 ITS typeswere detected). Genetic divergence among ITS types averaged 4% (maximum pairwise divergence was 13%). Preliminary analyses revealed nearly completely unresolved phylogenetic relationships and a lack of genetic structure among all sequences due to extensive homoplasy at multiple hypervariable sites. After correcting for this, still no clear phylogeographic structure was detected, and no pattern of isolation by distance was found on a global scale. Concomitantly, genetic differentiation among continents was marginal, whereas variation within continents was high and was mostly shared with all other continents. Similarly, no genetic structure across climate zones was detected.Conclusions/Significance: The high overall diversity and wide global distribution of common ITS types in combination with the lack of phylogeographic structure suggest that intercontinental dispersal of M. aeruginosa ITS types is not rare, and that this species might have a truly cosmopolitan distribution

Vortex State and Field-Angle Resolved Specific Heat Oscillation for H // ab in d-Wave Superconductors

When magnetic field is applied parallel to the ab plane in d_{x^2-y^2}-wave superconductors, the transition of stable vortex lattice structure, spatial structure of local density of states, and specific heat oscillation by rotation of magnetic field orientation are investigated by quantitative calculations based on the selfconsistent Eilenberger theory. We estimate how the vortex state changes depending on the relative angle between the node-direction of the superconducting gap and magnetic field orientation. To reproduce the sign-change of specific heat oscillation observed in CeCoIn_5, our study is done by including strong paramagnetic effect. The quantitative theoretical calculations give decisive information to analyze the experimental data on the field-angle dependence, and establish the angle-resolved specific heat experiment as a spectroscopic means to identify the node-position of the superconducting gap.Comment: 9 pages, 13 figure

X-ray absorption spectroscopy systematics at the tungsten L-edge

A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, has been interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W&lt;sup&gt;0&lt;/sup&gt;(PMe&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;6&lt;/sub&gt;], [W&lt;sup&gt;II&lt;/sup&gt;Cl&lt;sub&gt;2&lt;/sub&gt;(PMePh&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt;], [W&lt;sup&gt;III&lt;/sup&gt;Cl&lt;sub&gt;2&lt;/sub&gt;(dppe)&lt;sub&gt;2&lt;/sub&gt;][PF&lt;sub&gt;6&lt;/sub&gt;] (dppe = 1,2-bis(diphenylphosphino)ethane), [W&lt;sup&gt;IV&lt;/sup&gt;Cl&lt;sub&gt;4&lt;/sub&gt;(PMePh&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;], [W&lt;sup&gt;V&lt;/sup&gt;(NPh)Cl&lt;sub&gt;3&lt;/sub&gt;(PMe&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;], and [W&lt;sup&gt;VI&lt;/sup&gt;Cl&lt;sub&gt;6&lt;/sub&gt;] correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio (EBR) of the L&lt;sub&gt;3,2&lt;/sub&gt;-edges and the L&lt;sub&gt;1&lt;/sub&gt; rising-edge energy with metal Z&lt;sub&gt;eff&lt;/sub&gt;, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W&lt;sup&gt;IV&lt;/sup&gt;(mdt)&lt;sub&gt;2&lt;/sub&gt;(CO)&lt;sub&gt;2&lt;/sub&gt;] and [W&lt;sup&gt;IV&lt;/sup&gt;(mdt)&lt;sub&gt;2&lt;/sub&gt;(CN)&lt;sub&gt;2&lt;/sub&gt;]&lt;sup&gt;2–&lt;/sup&gt; (mdt&lt;sup&gt;2–&lt;/sup&gt; = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W&lt;sup&gt;IV&lt;/sup&gt; species. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: 1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Z&lt;sub&gt;eff&lt;/sub&gt; in the species of interest; 2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS; 3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal-ligand distances, exaggerate the difference between formal oxidation state and metal Z&lt;sub&gt;eff&lt;/sub&gt; or, as in the case of [W&lt;sup&gt;IV&lt;/sup&gt;(mdt)&lt;sub&gt;2&lt;/sub&gt;(CO)&lt;sub&gt;2&lt;/sub&gt;], add other subtlety by modulating the redox level of other ligands in the coordination sphere

Outer-Sphere Contributions to the Electronic Structure of Type Zero Copper Proteins

Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called “type zero” sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding

Selberg Supertrace Formula for Super Riemann Surfaces III: Bordered Super Riemann Surfaces

This paper is the third in a sequel to develop a super-analogue of the classical Selberg trace formula, the Selberg supertrace formula. It deals with bordered super Riemann surfaces. The theory of bordered super Riemann surfaces is outlined, and the corresponding Selberg supertrace formula is developed. The analytic properties of the Selberg super zeta-functions on bordered super Riemann surfaces are discussed, and super-determinants of Dirac-Laplace operators on bordered super Riemann surfaces are calculated in terms of Selberg super zeta-functions.Comment: 43 pages, amste