24378 research outputs found
Sort by
Non hermiticity in spintronics oscillation death in coupled spintronic nano oscillators through emerging exceptional points
Get PDFThe emergence of exceptional points EPs in the parameter space of a non hermitian 2D eigenvalue problem has long been interest in mathematical physics, however, only in the last decade entered the scope of experiments. In coupled systems, EPs give rise to unique physical phenomena, and enable the development of highly sensitive sensors. Here, we demonstrate at room temperature the emergence of EPs in coupled spintronic nanoscale oscillators and exploit the system s non hermiticity. We observe amplitude death of self oscillations and other complex dynamics, and develop a linearized non hermitian model of the coupled spintronic system, which describes the main experimental features. The room temperature operation, and CMOS compatibility of our spintronic nanoscale oscillators means that they are ready to be employed in a variety of applications, such as field, current or rotation sensors, radiofrequeny and wireless devices, and in dedicated neuromorphic computing hardware. Furthermore, their unique and versatile properties, notably their large nonlinear behavior, open up unprecedented perspectives in experiments as well as in theory on the physics of exceptional points expanding to strongly nonlinear system
Optical constants of TiN, amorphous SiO2, and SiN in the extreme ultraviolet range
Get PDFUsing reflectometry, we studied the optical constants of TiN and amorphous SiO2 thin films in the spectral range 5 24 nm ca. 250 eV ca. 52 eV , and for SiN in the spectral range 5 33 nm ca. 250 eV ca. 37 eV . The films elemental concentration depth profiles were measured using elastic recoil detection analysis ERDA . The reflectance was measured using monochromatized synchrotron radiation. For the analysis of reflectivity data, Markov chain Monte Carlo MCMC based Bayesian inferences Bayesian inferences were used to obtain the optical constants and their model uncertainties. For SiO2 and SiN, dispersion profiles were sampled with sub amp; Aring;ngstr amp; ouml;m resolution in certain intervals around the Si L1 and Si L2,3 transitions. The obtained optical constants are compared with literature values and with estimations based on the independent atom approximation IA
Magneto ionic modulation of the interlayer exchange interaction in synthetic antiferromagnets
No full textThe electric field control of magnetism is a highly promising and potentially effective approach for realizing energy efficient applications. Recent interest has focused on the magneto ionic effect in synthetic antiferromagnets, driven by its potential to enable high density data storage devices with ultra low power consumption. However, the underlying mechanism responsible for the magneto ionic effect on the interlayer exchange coupling remains elusive. In our work, we find that the modulation of the interlayer exchange coupling is highly sensitive to the thickness of the ferromagnetic layer. We have identified that the changes in the interlayer exchange coupling induced by the gate voltage can be associated with the magneto ionic effects on the top ferromagnetic layer of the synthetic antiferromagnet. The direct contact between the high ion mobility oxide and the top ferromagnetic layer plays a crucial role in facilitating these effects, largely modifying the anisotropy of the layers. Our findings highlight the important role of magneto ionic control over the properties of the top ferromagnetic layer in governing the observed modifications in the interlayer exchange coupling. This study provides crucial insight into the intricate interplay between stack structure and magneto ionic effect on magnetic properties in synthetic antiferromagnetic thin film system
A Bioinspired Nonheme FeIII O22 CuII Complex with an St 1 Ground State
Get PDFCytochrome c oxidase CcO is a heme copper oxidase HCO that catalyzes the natural reduction of oxygen to water. A profound understanding of some of the elementary steps leading to the intricate 4e 4H reduction of O2 is presently lacking. A total spin St 1 FeIII O22 CuII IP intermediate is proposed to reduce the overpotentials associated with the reductive O O bond rupture by allowing electron transfer from a tyrosine moiety without the necessity of any spin surface crossing. Direct evidence of the involvement of IP in the CcO catalytic cycle is, however, missing. A number of heme copper peroxido complexes have been prepared as synthetic models of IP, but all of them possess the catalytically nonrelevant St 0 ground state resulting from antiferromagnetic coupling between the S 1 2 FeIII and CuII centers. In a complete nonheme approach, we now report the spectroscopic characterization and reactivity of the FeIII O22 CuII intermediates 1 and 2, which differ only by a single amp; 8722;CH3 versus amp; 8722;H substituent on the central amine of the tridentate ligands binding to copper. Complex 1 with an end on peroxido core and ferromagnetically St 1 coupled FeIII and CuII centers performs H bonding mediated O O bond cleavage in the presence of phenol to generate oxoiron IV and exchange coupled copper II and PhO moieties. In contrast, the amp; 956; amp; 951;2 amp; 951;1 peroxido complex 2, with a St 0 ground state, is unreactive toward phenol. Thus, the implications for spin topology contributions to O O bond cleavage, as proposed for the heme FeIII O22 CuII intermediate in CcO, can be extended to nonheme chemistr
A green solvent enables precursor phase engineering of stable formamidinium lead triiodide perovskite solar cells
Get PDFPerovskite solar cells PSCs offer an efficient, inexpensive alternative to current photovoltaic technologies, with the potential for manufacture via high throughput coating methods. However, challenges for commercial scale solution processing of metal halide perovskites include the use of harmful solvents, the expense of maintaining controlled atmospheric conditions, and the inherent instabilities of PSCs under operation. Here, we address these challenges by introducing a high volatility, low toxicity, biorenewable solvent system to fabricate a range of 2D perovskites, which we use as highly effective precursor phases for subsequent transformation to amp; 945; formamidinium lead triiodide amp; 945; FAPbI3 , fully processed under ambient conditions. PSCs utilising our amp; 945; FAPbI3 reproducibly show remarkable stability under illumination and elevated temperature ISOS L 2 and damp heat ISOS D 3 stressing, surpassing other state of the art perovskite compositions. We determine that this enhancement is a consequence of the 2D precursor phase crystallisation route, which simultaneously avoids retention of residual low volatility solvents such as DMF and DMSO and reduces the rate of degradation of FA in the material. Our findings highlight both the critical role of the initial crystallisation process in determining the operational stability of perovskite materials, and that neat FA based perovskites can be competitively stable despite the inherent metastability of the amp; 945; phas
Structural Elucidation of a Metagenomic Urethanase and Its Engineering Towards Enhanced Hydrolysis Profiles
No full textWhile plastics like polyethylene terephthalate can already be degraded efficiently by the activity of hydrolases, other synthetic polymers like polyurethanes PUs and polyamides PAs largely resist biodegradation. In this study, we solved the first crystal structure of the metagenomic urethanase UMG SP 1, identified highly flexible loop regions to comprise active site residues, and targeted a total of 20 potential hot spots by site saturation mutagenesis. Engineering campaigns yielded variants with single mutations, exhibiting almost 3 and 8 fold improved activity against highly stable N aryl urethane and amide bonds, respectively. Furthermore, we demonstrated the release of the corresponding monomers from a thermoplastic polyester PU and a PA nylon amp; 8197;6 by the activity of a single, metagenome derived urethanase after short incubation times. Thereby, we expanded the hydrolysis profile of UMG SP 1 beyond the reported low molecular weight carbamates. Together, these findings promise advanced strategies for the bio based degradation and recycling of plastic materials and waste, aiding efforts to establish a circular economy for synthetic polymer
Distribution and diversity of classical deacylases in bacteria
No full textClassical Zn2 dependent deac et ylases play fundamental regulatory roles in life and are well characterized in eukaryotes regarding their structures, substrates and physiological roles. In bacteria, however, classical deacylases are less well understood. We construct a Generalized Profile GP and identify thousands of uncharacterized classical deacylases in bacteria, which are grouped into five clusters. Systematic structural and functional characterization of representative enzymes from each cluster reveal high functional diversity, including polyamine deacylases and protein deacylases with various acyl chain type preferences. These data are supported by multiple crystal structures of enzymes from different clusters. Through this extensive analysis, we define the structural requirements of substrate selectivity, and discovered bacterial de d l lactylases and long chain deacylases. Importantly, bacterial deacylases are inhibited by archetypal HDAC inhibitors, as supported by co crystal structures with the inhibitors SAHA and TSA, and setting the ground for drug repurposing strategies to fight bacterial infections. Thus, we provide a systematic structure function analysis of classical deacylases in bacteria and reveal the basis of substrate specificity, acyl chain preference and inhibitio
Combining geometric constraint and redox non innocence within an ambiphilic PBiP pincer ligand
No full textThe synthesis of the first pincer ligand featuring a strictly T shaped group 15 element and its coordination behaviour towards transition metals is described. The platform is itself derived from a trianionic redox non innocent NNN scaffold. In addition to providing a rigid coordination environment to constrain a Bi centre in a T shaped geometry to manipulate its frontier molecular orbital constitution, the NNN chelate displays highly covalent bonding towards the geometrically constrained Bi centre. The formation of intriguing ambiphilic Bi M bonding interactions is demonstrated upon formation of a pincer complex as well as a multimetallic cluster. All compounds are comprehensively characterised by spectroscopic methods including X ray Absorption Near Edge Structure XANES spectroscopy and complemented by DFT calculation
Flat band induced quantum criticality in a nonsuperconducting iron pnictide
No full textFlat electronic bands at the Fermi energy amp; 119864;F can induce interaction driven instabilities and further result in the emergence of a plethora of new quantum phases such as Mott insulators, ferromagnetism, fractional quantum Hall states even at high temperatures, and superconductivity. Except for flat bands in amp; 119891; electron systems and special geometric lattices, however, the materials with quantum criticality induced by flat bands just at amp; 119864;F remain elusive. Here, by using angle resolved photoemission spectroscopy and band structure calculations, we present a comprehensive study of the low energy electronic structure of a nonsuperconducting iron pnictide, Ba amp; 8290; Fe1 3 amp; 8290;Co1 3 amp; 8290;Ni1 3 2 amp; 8290;As2 , which is a quantum critical 3 amp; 8290; amp; 119889; transition metal alloy. We demonstrate the existence of a dispersionless flat band of amp; 119905;2 amp; 8290; amp; 119892; orbitals just at amp; 119864;F which is responsible for quantum critical behaviors. Our findings will promote studies of emergent physics induced by flat bands, such as non Fermi liquid behaviors and quantum critical phenomena in 3 amp; 8290; amp; 119889; transition metal