Observing the Suppression of Superconductivity in RbEuFe_{4}As_{4} by Correlated Magnetic Fluctuations.

In this Letter, we describe quantitative magnetic imaging of superconducting vortices in RbEuFe_{4}As_{4} in order to investigate the unique interplay between the magnetic and superconducting sublattices. Our scanning Hall microscopy data reveal a pronounced suppression of the superfluid density near the magnetic ordering temperature in good qualitative agreement with a recently developed model describing the suppression of superconductivity by correlated magnetic fluctuations. These results indicate a pronounced exchange interaction between the superconducting and magnetic subsystems in RbEuFe_{4}As_{4}, with important implications for future investigations of physical phenomena arising from the interplay between them.

Tuning the structure of the Josephson vortex lattice in Bi2Sr2CaCu2O8+δ single crystals with pancake vortices.

In extremely anisotropic cuprate superconductors a lattice of stacks of pancake vortices nucleates when a magnetic field is applied perpendicular to the copper oxide layers, while an orthogonal lattice of highly elliptical Josephson vortices forms when the applied field is parallel to the layers. Under tilted magnetic fields these sublattices can interact in complex ways to form systems of vortex chains and composite vortex lattices. Here we have used high-resolution scanning Hall microscopy (SHM) to map the rich tilted-field vortex phase diagram in an underdoped Bi2Sr2CaCu2O8+δ single crystal. We find that the Josephson vortex lattice spacing has an unexpected non-monotonic dependence on the pancake vortex density reflecting the delicate balance between attractive and repulsive vortex interactions, and actually undergoes a field-driven structural transformation with increasing out-of-plane fields. We also identify particularly stable composite structures composed of vortex chains separated by an integer number of rows of interstitial pancake vortex stacks and are able to establish the precise evolution of vortex-chain phases as the out-of-plane field is increased at small in-plane fields. Our results are in good semi-quantitative agreement with theoretical models and could enable the development of vortex ratchets and lenses based on the interactions between Josephson and pancake vortices.

Superconducting and normal-state anisotropy of the doped topological insulator Sr0.1Bi2Se3.

SrxBi2Se3 and the related compounds CuxBi2Se3 and NbxBi2Se3 have attracted considerable interest, as these materials may be realizations of unconventional topological superconductors. Superconductivity with Tc ~3 K in SrxBi2Se3 arises upon intercalation of Sr into the layered topological insulator Bi2Se3. Here we elucidate the anisotropy of the normal and superconducting state of Sr0.1Bi2Se3 with angular dependent magnetotransport and thermodynamic measurements. High resolution x-ray diffraction studies underline the high crystalline quality of the samples. We demonstrate that the normal state electronic and magnetic properties of Sr0.1Bi2Se3 are isotropic in the basal plane while we observe a large two-fold in-plane anisotropy of the upper critical field in the superconducting state. Our results support the recently proposed odd-parity nematic state characterized by a nodal gap of Eu symmetry in SrxBi2Se3.

Isolation of Homogeneous Polysaccharide Monooxygenases from Fungal Sources and Investigation of Their Synergism with Cellulases when Acting on Cellulose.

Lytic polysaccharide monooxygenases (PMO) discovered several years ago are enzymes classified as oxidoreductases. In nature, they participate in microbial degradation of cellulose together with cellulases that belong to the hydrolytic type of enzymes (class of hydrolases). Three PMO from ascomycetes - Thielavia terrestris, Trichoderma reesei, and Myceliophthora thermophila - were isolated and purified to homogeneous state using various types of chromatography. The first two enzymes are recombinant proteins heterologously expressed by the Penicillium verruculosum fungus, while the third is a native PMO secreted by M. thermophila. When acting on microcrystalline cellulose, all these PMOs displayed synergism with the cellulase complex of the P. verruculosum fungus. Replacing 10% of cellulases (by protein concentration) with PMO in the presence of 6.25 mM gallic acid or 2.5 µM of cellobiose dehydrogenase from M. thermophila, used as electron donors for PMO, resulted in the 17-31% increase in the yield of reducing sugars after 24-48 h of the enzymatic reaction.

[Novel Enzyme Preparations with High Pectinase and Hemicellulase Activity Based on Penicillium canescens Strains].

Recombinant strains of Penicillium canescens producing homologous pectin lyase A and heterologous endo- 1,5-α-arabinase A and endo- 1,4-α-polygalacturonase, as well as enzymes of the host strain (α-L-arabinofuranosidases, xylanases, and others), were obtained by genetic engineering. The enzyme preparations (EPs) obtained from the cultural medium of recombinant P. canescens strains efficiently hydrolyzed raw plant material with a high content of pectin compounds. It was shown that the yield of reducing sugars and arabinose increased 16 and 22% in comparison with the control EP based on the host strain when one of the obtained EPs was used for beet pulp hydrolysis. It was established that the most active EP consisted of pectin lyase (10%), endo-1,5-arabinase (26%), α-L-arabinofuranosidase and arabinoxylan-arabinofuranohydrolase (12%), and xylanase (10%). The activities of pectin lyase, polygalacturonase, and arabinase of the EP in reactions with various substrates were determined. The specificity, pH and T-optima, and thermal stability of the homogenous recombinant endo- 1,5-α-arabinase were investigated. The kinetic parameters (K(m), K(cat)) of the linear arabinan hydrolysis were determined.

[Construction of Producers of Cellulolytic and Pectinolytic Enzymes Based on the Fungus Penicillium verruculosum].

Based on the fungus Penicillium verruculosum, we created strains with a complex of extracellular enzymes that contains both cellulolytic enzymes of the fungus and heterologous pectin lyase A from P. canescens and endo- 1,4-α-polygalacturonase from Aspergillus niger. The endopolygalacturonase and pectin lyase activities of enzyme preparations obtained from culture media of the producer strains reached 46-53 U/mg of protein and 1.3-2.3 U/mg of protein, respectively. The optimal temperature and pH values for recombinant pectin lyase and endopolygalacturonase corresponded to those described in the literature for these enzymes. The content of heterologous endopolygalacturonase and pectin lyase in the studied enzyme preparations was 4-5% and 23% of the total protein content, respectively. The yield of reducing sugars upon the hydrolysis of sugar beet and apple processing wastes with the most efficient preparation was 41 and 71 g/L, respectively, which corresponded to a polysaccharide conversion of 49% and 65%. Glucose was the main product of the hydrolysis of sugar beet and apple processing wastes.

[Cultivation of a novel cellulase/xylanase producer, Trichoderma longibrachiatum mutant TW 1-59-27: production of the enzyme preparation and the study of its properties].

As a result of gamma-mutagenesis of Trichoderma longibrachiatum TW1 and the subsequent selection of improved producers, a novel mutant strain, TW1-59-27, capable of efficiently secreting cellulase and xylanase was obtained. In a fed-batch cultivation, the new TW1-59-27 mutant was significantly more active compared with the original TW1 strain. For instance, the activities of cellulase (towards carboxymethylcellulose) and xylanase in the culture broth (CB) increased by 1.8 and two times, respectively, and the protein content increased by 1.47 times. The activity of these enzymes in the dry enzyme preparation derived from the CB of the TW1-59-27 mutant was 1.3-1.8 times higher than that in the preparation derived from the original TW1 strain. It was established that the cellulase from the enzyme preparation of the mutant strain demonstrated the maximum activity at 55-65 degrees C; it occurred in xylanase at 60 degrees C. The pH optima of these enzymes were pH 4.5-5.0 and pH 5.0-6.0, respectively. It was shown that the content of endoglucanases in the enzyme preparation increased from 7% to 13.5%; the effect is largely driven by the secretion of endoglucanase-1. An enzyme preparation with increased endoglucanase-1 content is promising for use as a feed additive in agriculture.

[Use of Endoglucanase IV from Trichoderma reesei to Enhance the Hydrolytic Activity of a Cellulase Complex from the Fungus Penicillium verruculosum].

The effect of polysaccharide monooxygenase (endoglucanase IV) from the fungus Trichoderma reesei on the hydrolysis of polysaccharide substrates by cellulases secreted by the fungus Penicillium verruculosum has been investigated. Supplementation of the enzyme complex from P. verruculosum by endoglucanase IV from T. reesei has been shown to elevate the efficiency of cellulose hydrolysis by 45%.

Combination of a spectrometer-on-chip and an array of Young's interferometers for laser spectrum monitoring.

This Letter presents the design and experimental results for an on-chip photonic device for laser spectrum monitoring that combines a nanospectrometer and an array of Young's interferometers. The array of Young's interferometers and the spectrometer measure the width and wavelength of a spectrum in visible light, respectively. The accuracy of spectral width measurements is around 10% for FWHM higher than 2.5 pm. The spectrometer-on-chip is based on a digital planar hologram, and provides a resolution around 145 pm within the spectral range of 719-861 nm (142 nm bandwidth). The performance of the device is demonstrated for distinguishing between the single- and two-longitudinal mode operation of a fiber Bragg grating laser diode with 23 pm mode separation.

Stripe domains and first-order phase transition in the vortex matter of anisotropic high-temperature superconductors.

We report the direct imaging of a novel modulated flux striped domain phase in a nearly twin-free YBCO crystal. These domains arise from instabilities in the vortex structure within a narrow region of tilted magnetic fields at small angles from the in-plane direction. By comparing the experimental and theoretically derived vortex phase diagrams we infer that the stripe domains emerge from a first-order phase transition of the vortex structure. The size of domains containing vortices of certain orientations is controlled by the balance between the vortex stray field energy and the positive energy of the domain boundaries. Our results confirm the existence of the kinked vortex chain phase in an anisotropic high temperature superconductor and reveal a sharp transition in the state of this phase resulting in regular vortex domains.

Huge critical current density and tailored superconducting anisotropy in SmFeAsO0.8F0.15 by low-density columnar-defect incorporation.

Iron-based superconductors could be useful for electricity distribution and superconducting magnet applications because of their relatively high critical current densities and upper critical fields. SmFeAsO0.8F0.15 is of particular interest as it has the highest transition temperature among these materials. Here we show that by introducing a low density of correlated nano-scale defects into this material by heavy-ion irradiation, we can increase its critical current density to up to 2 × 107 A cm⁻² at 5 K--the highest ever reported for an iron-based superconductor--without reducing its critical temperature of 50 K. We also observe a notable reduction in the thermodynamic superconducting anisotropy, from 8 to 4 upon irradiation. We develop a model based on anisotropic electron scattering that predicts that the superconducting anisotropy can be tailored via correlated defects in semimetallic, fully gapped type II superconductors.

[Development of complex enzymatic preparations of pactinases and celulases for sugar beet marc digestion].

Complex enzymatic preparations demonstrating activities homologous to pectinlyase A and heterologous to endo-1,4-beta-glucanase from Penicilliumverruculosum and beta-glycosidase from Aspergillusniger have been obtained on the basis of recombinant strains of the fungus Penicilliumcanescens. Two approaches were utilized: development of an enzymatic preparation on the basis of a new strain, which produced all three enzymes, and development of an enzymatic preparation via combined cultivation of three strains, each of which produced one of the enzymes.

[Production of enzyme preparations on the basis of Penicillum canescens recombinant strains with a high ability for the hydrolysis of plant materials].

An enzyme preparation has been produced on the basis of Penicillium canescens strains with the activity of cellibiohydrolase I, II; endo-1,4-beta-gluconase of Penicillium verruculosum; and beta-glucosidase of Aspergillus niger. It was shown that for the most effective hydrolysis of aspen wood pulp the optimal ratio of cellobiohydrolase and endo- 1,4-3-gluconase in enzyme preparations was 8 : 2 (by protein). It was also established that the homologous xylanase secreted by the Penicillium canescens fungus is a required component for the enzyme complex for hydrolysis of the hemicellulose matrix of aspen wood.

Multiband wavelength demultiplexer based on digital planar holography for on-chip spectroscopy applications.

A novel type of multiband wavelength demultiplexer for on-chip spectroscopy applications is proposed, and first results of the device fabrication and characterization are reported. The devices are based on computer-designed digital planar holograms, which involve millions of lines specifically located and oriented in order to direct output light into designed focal channels according to the wavelength. Devices operate in four individual bandwidths within the visible range (477.2-478.0 nm, 528.8-529.9 nm, 586.4-587.7 nm, 628.9-630.4 nm) with 96 channels and spectral channel spacing down to 0.0375 nm/channel.

Magnetoresistance anisotropy of a one-dimensional superconducting niobium strip.

We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross section. When its transverse dimensions are comparable to the superconducting coherence length, the angle dependent magnetoresistances at a fixed temperature can be scaled as R(theta,H) = R(H/Hctheta) where Hctheta =Hc0(cos2theta + gamma(-2)sin2theta)(-1/2) is the angular dependent critical field, gamma is the width to thickness ratio, and Hc0 is the critical field in the thickness direction at theta=0 degrees . The results can be understood in terms of the anisotropic diamagnetic energy for a given field in a one-dimensional superconductor.

Emission of coherent THz radiation from superconductors.

Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to approximately 50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.

Radiation due to Josephson oscillations in layered superconductors.

We derive the power of direct radiation into free space induced by Josephson oscillations in intrinsic Josephson junctions of layered superconductors. We consider the superradiation regime for a crystal cut in the form of a thin slice parallel to the c axis. We find that the radiation correction to the current-voltage characteristic in this regime depends only on crystal shape. We show that at a large number of junctions oscillations are synchronized providing high radiation power and efficiency in the terahertz frequency range. We discuss the crystal parameters and bias current optimal for radiation power and crystal cooling.

Microscopic theory of thermal phase slips in clean narrow superconducting wires.

We consider the structure of a thermal phase-slip center for a simple microscopic model of a clean one-dimensional superconductor in which superconductivity occurs only within one conducting channel or several identical channels. Surprisingly, the Eilenberger equations describing the saddle-point configuration allow for an exact analytical solution in the whole temperature and current range. This solution allows us to derive a closed expression for the free-energy barrier, which we use to compute its temperature and current dependences.

[Use of a preparation from fungal pectin lyase in the food industry].

A new enzyme preparation of fungal pectin lyase (EC 4.2.2.10) was shown to be useful for the production of cranberry juice and clarification of apple juice in the food industry. A comparative study showed that the preparation of pectin lyase is competitive with commercial pectinase products. The molecular weight of homogeneous pectin lyase was 38 kDa. Properties of the homogeneous enzyme were studied. This enzyme was most efficient in removing highly esterified pectin.

[Application of neutral-alkaline pectate lyases to cotton fabric boil off].

Commercial and pilot pectate lyase preparations (EC 4.2.2.2) have been compared. They differ in their effect on pectins with different esterification degrees (ED). The activity of the pilot preparation with respect to a substrate with ED = 70% is tenfold lower than with respect to unesterified polygalacturonic acid. For commercial preparations, this activity ratio ranged within 1.5-2. At equal pectate lyase activities, the commercial preparations better remove pectin from crude cotton fabric during its boil off. The laboratory preparation is more efficient for improving the capillarity (wettability) of the fabric owing to the cooperative effect of the pectate lyase, cellulase, and hemicellulase present in the preparation.