Ultrafast generation of nonthermal magnons in iron: Ab initio parameterized calculations

Ultrafast laser excitation of ferromagnetic metals gives rise to correlated, highly non-equilibrium dynamics of electrons, spins and lattice, which are, however, poorly described by the widely used three-temperature model (3TM). Here, we develop a fully ab initio parameterized out-of-equilibrium theory based on a quantum kinetic approach -- termed (N+2) temperature model -- that describes magnon occupation dynamics due to electron-magnon scattering. We apply this model to perform quantitative simulations on the ultrafast, laser-induced generation of magnons in iron and demonstrate that on these timescales the magnon distribution is non-thermal: predominantly high-energy magnons are created, while the magnon occupation close to the center of the Brillouin zone even decreases, due to a repopulation towards higher energy states via a so-far-overlooked scattering term. Moreover, we show that the 3TM can be derived from our model and compare it with our microscopic calculations. In doing so, we demonstrate that the simple relation between magnetization and temperature computed at equilibrium does not hold in the ultrafast regime and that the 3TM greatly overestimates the demagnetization. Our ab initio-parametrized calculations show that ultrafast generation of non-thermal magnons provides a sizable demagnetization within 200 fs and, thus, emphasize the importance of magnon excitations for the ultrafast demagnetization process

Graph Concatenation for Quantum Codes

Graphs are closely related to quantum error-correcting codes: every stabilizer code is locally equivalent to a graph code, and every codeword stabilized code can be described by a graph and a classical code. For the construction of good quantum codes of relatively large block length, concatenated quantum codes and their generalizations play an important role. We develop a systematic method for constructing concatenated quantum codes based on "graph concatenation", where graphs representing the inner and outer codes are concatenated via a simple graph operation called "generalized local complementation." Our method applies to both binary and non-binary concatenated quantum codes as well as their generalizations.Comment: 26 pages, 12 figures. Figures of concatenated [[5,1,3]] and [[7,1,3]] are added. Submitted to JM

Einkommen und Armut von Familien und älteren Menschen

Die Einkommensposition von Familien hängt nicht nur von der Erwerbssituation der Haushaltsmitglieder ab, sondern auch vom Alter der Kinder. Dies zeigt eine Auswertung des vom DIW Berlin in Zusammenarbeit mit Infratest Sozialforschung erhobenen Sozio-oekonomischen Panels (SOEP). Zusammenlebende Paare mit Kindern kommen danach - gemessen an der gesamten Bevölkerung - auf ein durchschnittliches Einkommen. Das Armutsrisiko ist jedoch umso höher, je kleiner das jüngste Kind ist. Dieses Muster gilt auch für Alleinerziehende, die generell ein überdurchschnittliches Risiko für Einkommensarmut aufweisen, das sich zudem seit Mitte der 80er Jahre weiter erhöht hat. Die Einkommensposition der älteren Menschen in Deutschland hat sich hingegen in den vergangenen 20 Jahren deutlich verbessert. Abgesehen von alleinstehenden älteren Frauen ist die Armutsrate bei älteren Menschen geringer als in der Gesamtbevölkerung. Die in diesem Bericht angewandten Messverfahren werden im Wesentlichen auch im Armuts- und Reichtumsbericht der Bundesregierung verwendet.

Magnetic nanostructures by adaptive twinning in strained epitaxial films

We exploit the intrinsic structural instability of the Fe70Pd30 magnetic shape memory alloy to obtain functional epitaxial films exhibiting a self-organized nanostructure. We demonstrate that coherent epitaxial straining by 54% is possible. The combination of thin film experiments and large-scale first-principles calculations enables us to establish a lattice relaxation mechanism, which is not expected for stable materials. We identify a low twin boundary energy compared to a high elastic energy as key prerequisite for the adaptive nanotwinning. Our approach is versatile as it allows to control both, nanostructure and intrinsic properties for ferromagnetic, ferroelastic and ferroelectric materials.Comment: Final version. Supplementary information available on request or at the publisher's websit

Average nucleotide identity of genome sequences supports the description of Rhizobium lentis sp. nov., Rhizobium bangladeshense sp. nov. and Rhizobium binae sp. nov. from lentil (Lens culinaris) nodules

Rhizobial strains isolated from effective root nodules of field-grown lentil (Lens culinaris) from different parts of Bangladesh were previously analysed using sequences of the 16S rRNA gene, three housekeeping genes (recA, atpD and glnll) and three nodulation genes (nodA, nodC and nodD), DNA fingerprinting and phenotypic characterization. Analysis of housekeeping gene sequences and DNA fingerprints indicated that the strains belonged to three novel clades in the genus Rhizobium. In present study, a representative strain from each clade was further characterized by determination of cellular fatty acid compositions, carbon substrate utilization patterns and DNA DNA hybridization and average nucleotide identity (ANI) analyses from whole-genome sequences. DNA DNA hybridization showed 50-62 % relatedness to their closest relatives (the type strains of Rhizobium etli and Rhizobium phaseoh) and 50-60 % relatedness to each other. These results were further supported by ANI values, based on genome sequencing, which were 87-92 % with their close relatives and 88-89 % with each other. On the basis of these results, three novel species, Rhizobium lentis sp. nov. (type strain BLR27(T)=LMG 28441(T)=DSM 29286(T)), Rhizobium bangladeshense sp. nov. (type strain BLR175(T)=LMG 28442(T)=DSM 29287(T)) and Rhizobium binae sp. nov. (type strain BLR195(T)=LMG 28443(T)=DSM 29288(T)), are proposed. These species share common nodulation genes (nodA, nodC and nodD) that are similar to those of the symbiovar viciae

Using random testing to manage a safe exit from the COVID-19 lockdown

We argue that frequent sampling of the fraction of infected people (either by random testing or by analysis of sewage water), is central to managing the COVID-19 pandemic because it both measures in real time the key variable controlled by restrictive measures, and anticipates the load on the healthcare system due to progression of the disease. Knowledge of random testing outcomes will (i) significantly improve the predictability of the pandemic, (ii) allow informed and optimized decisions on how to modify restrictive measures, with much shorter delay times than the present ones, and (iii) enable the real-time assessment of the efficiency of new means to reduce transmission rates. Here we suggest, irrespective of the size of a suitably homogeneous population, a conservative estimate of 15000 for the number of randomly tested people per day which will suffice to obtain reliable data about the current fraction of infections and its evolution in time, thus enabling close to real-time assessment of the quantitative effect of restrictive measures. Still higher testing capacity permits detection of geographical differences in spreading rates. Furthermore and most importantly, with daily sampling in place, a reboot could be attempted while the fraction of infected people is still an order of magnitude higher than the level required for a relaxation of restrictions with testing focused on symptomatic individuals. This is demonstrated by considering a feedback and control model of mitigation where the feed-back is derived from noisy sampling data.Comment: 18 pages, 6 figures, 2 appendices. Phys. Biol. (2020

Néel vector switching and terahertz spin-wave excitation in Mn2Au due to femtosecond spin-transfer torques

Efficient and fast manipulation of antiferromagnets has to date remained a challenging task, hindering their application in spintronic devices. For ultrafast operation of such devices, it is highly desirable to be able to control the antiferromagnetic order within picoseconds—a timescale that is difficult to achieve with electrical circuits. Here, we demonstrate that bursts of spin-polarized hot-electron currents emerging due to laser-induced ultrafast demagnetization are able to efficiently excite spin dynamics in antiferromagnetic Mn2Au by exerting a spin-transfer torque on femtosecond timescales. We combine quantitative superdiffusive transport and atomistic spin-model calculations to describe a spin-valve-type trilayer consisting of Fe|Cu|Mn2Au. Our results demonstrate that femtosecond spin-transfer torques can switch the Mn2Au layer within a few picoseconds. In addition, we find that spin waves with high frequencies up to several THz can be excited in Mn2Au