bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Approach to the Rapid in situ Synthesis of Tungsten Carbide Nanopowder by Plasma Milling and Carbothermal Reduction
Authors: Zeng Meiqin , Pan Youtao , Liu Weifeng , Cui Jie , Lu Zhongchen , Zhu Min
Published: June 2022

This work prepares nanocrystalline tungsten carbide (WC) powder using conventional ball milling or plasma milling (P‐milling) to process tungsten trioxide (WO3)–carbon (C) mixtures, with subsequent carbothermal reduction. The aim is to assess the effects of a discharge plasma on the microstructure of these materials. The results indicates that WC powders with particle sizes of less than 100 nm could be fabricated through heating at a relatively low temperature of 1150 °C for 1 h under vacuum after P‐milling. This process is found to allow a lower processing temperature and provided more complete carburization in comparison with conventional ball milling. P‐milling is determined to produce more loosely adhering WO3 nanoparticles and a higher surface area, resulting in more reactive sites and a larger contact area between WO3 nanoparticles and C atoms. This technique simultaneously generates more oxygen vacancies and defects on the surfaces of the WO3 and C, respectively, based on the use of a plasma discharge. It is evident that this new technology permits nanocrystalline WC to be readily obtained from WO3 and C in a reduced time span and at a lower cost and greater efficiency. This technique could also be used to fabricate WC nanopowders on an industrial scale.
Heat Treatment‐Induced Wear Transition in Electroplated Ni–Co Coating on Copper
Authors: Zhang Chao , Zhang Jun , Hu Rong , Zhang Ming , Zhang Yuwen , Wu Wenhe , Li Guangshi , Lu Xionggang
Published: June 2022

Herein, the effect of heat treatment on the high‐temperature wear resistance of Ni–Co electroplating coating on copper surface is systematically investigated. Results show that the oxide layer formed on the surface of coating during heat treatment induces the wear mechanism transition of coating. Under the condition without oxide layer formation (heat treatment at 400 °C), the coating suffers severe adhesive wear due to the low hardness caused by grain growth. After heat treatment at 600 °C, the formation of CoO and Co3O4 oxide layers on the surface of coating improves wear resistance, and the wear mechanism changes to oxidative wear and adhesive wear. The density of the oxide layer determines the degree of adhesive wear. As the heat treatment temperature increases (900 °C), the formation of a denser NiCo2O4 oxide layer with higher hardness further inhibits the adhesive wear mechanism of the coating. Until more than 6 h, the formation of scale‐shaped NiCo2O4 and 3CoO·NiO oxide layers significantly improves the wear resistance of the coating and completely eliminates adhesive wear. The wear mechanism is transformed into oxidative wear.
Continuous Self‐Oxygenated Double‐Layered Hydrogel under Natural Light for Real‐Time Infection Monitoring, Enhanced Photodynamic Therapy, and Hypoxia Relief in Refractory Diabetic Wounds Healing
Authors: Zhu Zhongqiang , Wang Lu , Peng Yaou , Chu Xiaoying , Zhou Liyang , Jin Yingying , Guo Hanwen , Gao Qiang , Yang Jianhua , Wang Xinyi , Long Ziyue , Ge Yifan , Lu Si , Wang Bailiang
Published: June 2022

The human health is still threatened by refractory keratitis and diabetic foot ulcers caused by bacterial infections, hypoxia, and chronic inflammation, so that patients are exposed to the risk of amputation, vision loss, and even death. Herein, an oxygen‐producing double‐layered hydrogel is developed that can visualize bacterial infections and supply oxygen to enhance antimicrobial photodynamic therapy (PDT) and inflammation alleviation for diabetic wounds healing. The inner layer hydrogel (containing oxidized sodium alginate/carboxymethyl chitosan [CMCS] via Schiff‐base) is incorporated with a photodynamic metal–organic framework (PCN‐224) and a pH indicator (bromothymol blue). The outer layer hydrogel (containing agarose and CMCS) loads photosynthetic cyanobacteria that continuously generate oxygen to relieve hypoxia of tissue and enhance antimicrobial PDT efficiency. Meanwhile, some unique advantages are reflected by continuous oxygen supply under natural light, such as cell migration acceleration, inflammation relief, promotion of skin capillary formation, and wound tissue recovery. Therefore, the self‐oxygenated double‐layered hydrogel offers tremendous benefits in the synergistic treatment of refractory anaerobe wounds from timely infection monitoring to tissue repair.
Highly Efficient Flexible n‐Type Thermoelectric Films Formed by Encapsulation of Bi2Se3‐MWCNT Hybrid Networks in Polyvinyl Alcohol
Authors: Buks Krisjanis , Andzane Jana , Bugovecka Lasma , Katkov Mikhail V. , Smits Krisjanis , Starkova Olesja , Katkevics Juris , Bērziņš Agris , Brauna Loreta , Voikiva Vanda , Erts Donats
Published: June 2022

The use of organic–inorganic nanocomposites has shown the greatest potential for engineering efficient flexible thermoelectric devices. In this work, a novel approach of encapsulation of as‐grown bismuth selenide‐multiwalled carbon nanotubes (Bi2Se3‐MWCNT) hybrid network in polyvinyl alcohol for fabrication of n‐type flexible thermoelectric films is demonstrated as a successful alternative to the mechanically mixed counterparts. The developed stable flexible n‐type thermoelectric material has a Seebeck coefficient and power factor at room temperature as high as −85 μV K−1 and 0.4 μW m−1 K−2, and figure‐of‐merit, exceeding the value shown by the mixed counterpart by ≈2 orders of magnitude, while requiring 3–4 times less inorganic material in comparison with mixed composites. Charge carrier transport mechanisms and contribution of Bi2Se3 and MWCNT components of not encapsulated and encapsulated hybrid networks to the total Seebeck coefficient, electrical conductance, and power factor are studied. In addition, the fabricated flexible thermoelectric films show good environmental stability at relative humidity levels up to 60%, as well as great mechanical and electrical stability with the increase of resistance within 0.5% and deviations of the Seebeck coefficient within 2% from the initial value during the 100 repetitive bending cycles.
Electrochemical Exfoliation of Naturally Occurring Layered Mineral Stibnite (Sb2S3) for Highly Sensitive and Fast Room‐Temperature Acetone Sensing
Authors: Li Jialong , Niu Yue , Zeng Junwei , Wang Jianqiang , Wang Quan , Liu Xiangcheng , Li Hao , de Rooij Nicolaas Frans , Wang Yao , Zhou Guofu
Published: June 2022

The analysis of exhaled acetone is used as a noninvasive diagnosis for diabetes. Compared with traditional breath analysis tools, chemiresistive gas sensors have attracted more attention for real‐time monitoring, owing to the possibility of integration and facile operation. However, most reported room‐temperature acetone gas sensors suffer from complicated preparation, costly raw materials, or relatively long response and recovery time. In this work, naturally occurring layered mineral stibnite is used to prepare Sb2S3 by a one‐step method of electrochemical cathodic exfoliation. As‐prepared Sb2S3 displays an amorphous feature with porous, hierarchical nanostructure, and its formation mechanism is rationally proposed. The porous, hierarchical and amorphous Sb2S3‐based gas sensors show excellent gas sensing performance toward acetone at room temperature, with the high response up to 1.46 toward 100 ppm acetone, and fast gas response and recovery toward acetone at room temperature (7 s for response and 30 s for one response–recovery cycle), which is one of the top three shortest response times among the reported room‐temperature acetone gas sensors. The electrochemical cathodic exfoliation may offer a new strategy for facile preparation of mineral materials, and the discussed devices may hold great promise for developing cost‐effective and high‐performance acetone sensors at room temperature.
Robust Microfluidic Integrated Electrolyte‐Gated Organic Field‐Effect Transistor Sensors for Rapid, In Situ and Label‐Free Monitoring of DNA Hybridization
Authors: Doumbia Amadou , Webb Michelle , Behrendt Jonathan M. , Wilson Richard J. , Turner Michael L.
Published: June 2022

Electrolyte‐gated organic field‐effect transistors (EGOFETs) are subject to intense research for biosensing in fluids. The ability of these devices to quantify a variety of chemical and biological molecules sensitively and selectively, but ex situ, has been widely demonstrated. However, continuous monitoring of analyte‐receptor interactions in real time by EGOFETs, in high demand for practical applications, has rarely been explored. Here, an EGOFET array integrated with a microfluidic device, for real‐time detection of the hybridization of DNA is presented. The integrated devices exhibit highly reproducible electrical performance in the array and can operate under different electrical stresses over >1 h with 85–96% figures of merit retention. The utility of the devices is demonstrated to detect the hybridization of a complementary target DNA in 10 × 10−3 m phosphate‐buffered saline (1× PBS) selectively with a temporal resolution of <1 s in a flow of analyte with no incubation step. The detection time is <30 s and the relative standard deviation of the sensing reproducibility is <15% under the target concentration of 100 × 10−9 m.
Photocatalysis‐Induced Nanopores toward Highly Reliable Organic Electrochemical Metallization Memory
Authors: Zeng Tao , Su Riya , Tao Ye , Lin Ya , Shan Xuanyu , Cheng Yankun , Wang Zhongqiang , Zhao Xiaoning , Xu Haiyang , Liu Yichun
Published: June 2022

Organic electrochemical metallization (ECM) memory that possesses high reliable switching performance is in great demand for the future smart wearable and flexible electronics. The resistive switching (RS) behavior of organic ECM memory is determined by the micro‐morphology evolution of metal conductive filaments (CFs) during the operating process. However, the morphology controllability of CFs is generally deteriorated by their random distribution and unexpected overgrowth. Herein, a kind of nanoporous PVC/TiO2 nanocomposite is developed using photocatalytic method for improving the RS reliability of organic ECM memory. The introduction of engineered nanopores can effectively simplify the CFs morphology to obtain excellent uniformity, good retention, and low cycling degradation. In addition, taking advantage of the multilevel RS behavior and 200 × 200 memristive array artificial neural network (ANN), alphabetic data storage and image pattern recognition are successfully realized. The proposed approach is expected to provide novel platforms for the advance of highly reliable flexible electronics and ANN for intelligence applications.
Back‐End‐of‐Line SiC‐Based Memristor for Resistive Memory and Artificial Synapse
Authors: Kapur Omesh , Guo Dongkai , Reynolds Jamie , Han Yisong , Beanland Richard , Jiang Liudi , de Groot C. H. (Kees) , Huang Ruomeng
Published: June 2022

Two‐terminal memristor has emerged as one of the most promising neuromorphic artificial electronic devices for their structural resemblance to biological synapses and ability to emulate many synaptic functions. In this work, a memristor based on the back‐end‐of‐line (BEOL) material silicon carbide (SiC) is developed. The thin film memristors demonstrate excellent binary resistive switching with compliance‐free and self‐rectifying characteristics which are advantageous for the implementation of high‐density 3D crossbar memory architectures. The conductance of this SiC‐based memristor can be modulated gradually through the application of both DC and AC signals. This behavior is demonstrated to further emulate several vital synaptic functions including paired‐pulse facilitation (PPF), post‐tetanic potentiation (PTP), short‐term potentiation (STP), and spike‐rate‐dependent plasticity (SRDP). The synaptic function of learning‐forgetting‐relearning processes is successfully emulated and demonstrated using a 3 × 3 artificial synapse array. This work presents an important advance in SiC‐based memristor and its application in both memory and neuromorphic computing.
The Impact of Nanoscale Percolation in Yttrium‐Doped BaZrO3 on the Oxygen Ion and Proton Conductivities: A Density Functional Theory and Kinetic Monte Carlo Study
Authors: Draber Fabian M. , Denninger Johannes R. , Müller Peter C. , Sommerfeld Isabel K. , Martin Manfred
Published: June 2022

Yttrium‐doped BaZrO3 is known for its high proton conductivity, making it an advanced energy material for various applications, like electrolyzers, fuel cells, or methane conversion cells. In the previous study, density functional theory (DFT) and kinetic Monte Carlo simulations (KMC) show that nanoscale percolation of Y ions enhances the proton mobility by providing fast migration pathways for protons. To investigate the general impact of nanoscale percolation on ionic conductivities, the same methods, DFT and KMC, are now used to calculate oxygen ion conductivity of Y‐doped BaZrO3. The results explain on a microscopic level why the macroscopic oxygen ion conductivity exhibits a higher activation energy than the proton conductivity, as known experimentally. They also show that nanoscale percolation pathways are not beneficial for oxygen ion conduction due to trapping of oxygen vacancies by single Y ions and blocking of their motion by nanoscale percolation of Y ions. Finally, the understanding and comparison of the microscopic jump processes of oxygen vacancies and of protons in acceptor‐doped BaZrO3 are used to propose a simple descriptor for the influence of a dopant on the ionic conductivities, of oxygen ions and of protons as well. This new descriptor allows an easy screening of various dopants.
Lung cancer and mesothelioma risks in a prospective cohort of workers with asbestos‐related lung or pleural diseases
Authors: Taeger Dirk , Wichert Katharina , Lehnert Martin , Casjens Swaantje , Pesch Beate , Weber Daniel G. , Brüning Thomas , Johnen Georg , Behrens Thomas
Published: June 2022

Background

Asbestos causes mesothelioma and lung cancer. In the European Union, asbestos was banned in 2005, but it is still in use in many other countries. The aim of this study was to estimate the lung cancer and mesothelioma incidence risk of men with benign asbestos‐related lung or pleural diseases.

Methods

Between 2008 and 2018, 2439 male participants of a German surveillance program for asbestos workers were included in the cohort. All participants had a recognized occupational asbestos‐related disease of the pleura or lung. We estimated the mesothelioma and lung cancer risks by calculating standardized incidence ratios (SIR) with corresponding 95% confidence intervals (95% CI).

Results

We observed 64 incident lung cancer and 40 mesothelioma cases in the cohort. An SIR of 17.60 (95% CI: 12.57–23.96) was estimated for mesothelioma and 1.27 (95% CI: 0.98–1.62) for lung cancer. The presence of pleural plaques was associated with a strongly increased risk (SIR: 13.14; 95% CI: 8.51–19.40) for mesothelioma, but not for lung cancer (SIR: 1.05; 95% CI: 0.76–1.41). The highest lung‐cancer risk (SIR: 2.56; 95% CI 1.10–5.04) was revealed for cohort members with less than 40 years since first asbestos exposure. Lung cancer risks by duration of asbestos exposure did not show a consistent time trend, but for time since last exposure a trend for mesothelioma was seen.

Conclusions

Compared to the general population, we demonstrated an association between benign asbestos‐related lung or pleural disease and mesothelioma risk in workers with a history of occupational asbestos exposure. Because lung‐cancer risk is dominated by smoking habits, a possible effect of asbestos exposure may have been masked. Efforts should be made to ban production and use of asbestos worldwide and to establish safe handling rules of legacy asbestos.
Electromagnetic waves in a rotating frame of reference
Authors: Hauck J.C. , Mashhoon B.
Published: June 2022

We discuss the electromagnetic measurements of rotating observers and study the propagation of electromagnetic waves in a uniformly rotating frame of reference. The phenomenon of helicity‐rotation coupling is elucidated and some of the observational consequences of the coupling of the spin of a particle with the rotation of a gravitational source are briefly examined.
The Reeh–Schlieder property for ground states
Authors: Jäkel C.D.
Published: June 2022

Recently it has been shown that the Reeh–Schlieder property w.r.t. thermal equilibrium states is a direct consequence of locality, additivity and the relativistic KMS condition. Here we extend this result to ground states.
Mirages, anti‐mirages, and further surprises in quantum corrals with non‐magnetic impurities
Authors: Schmid M. , Kampf A.P.
Published: June 2022

We investigate the local density of states (LDOS) for non‐interacting electrons in a hard‐wall ellipse in the presence of a single non‐magnetic scattering center. Using a T‐matrix analysis we calculate the local Green's function and observe a variety of quantum mirage effects for different impurity positions. Locating the impurity near positions with LDOS maxima for the impurity free corral can either lead to a reduction or an ehancement of the LDOS at the mirror image point, i.e. a mirage or anti‐mirage effect, or even suppress LDOS maxima in the entire area of the corral.
Four‐dimensional couplings among BF and matter theories from BRST cohomology
Authors: Bizdadea C. , Ciobîrcă C.C. , Cioroianu E.M. , Saliu S.O. , Săraru S.C.
Published: June 2022

The local and manifestly covariant Lagrangian interactions in four spacetime dimensions that can be added to a “free” model that describes a generic matter theory and an abelian BF theory are constructed by means of deforming the solution to the master equation on behalf of specific cohomological techniques.
Vacuum electrodynamics of accelerated systems: Nonlocal Maxwell's equations
Authors: Mashhoon B.
Published: June 2022

The nonlocal electrodynamics of accelerated systems is discussed in connection with the development of Lorentz‐invariant nonlocal field equations. Nonlocal Maxwell's equations are presented explicitly for certain linearly accelerated systems. In general, the field equations remain nonlocal even after accelerated motion has ceased.
The quantum supersymmetric vector multiplet and some problems in non‐Abelian supergauge theory
Authors: Grigore D.R. , Scharf G.
Published: June 2022

We consider the supersymmetric vector multiplet in a purely quantum framework. We obtain some discrepancies with respect to the literature in the expression of the super‐propagator and we prove that the model is consistent only for positive mass. The gauge structure is constructed purely deductive and leads to the introduction of scalar ghost superfields, in analogy to the usual gauge theories. The construction of a consistent supersymmetric gauge theory based on the vector model depends crucially on the definition of gauge invariance. We find some significant difficulties to impose a supersymmetric gauge invariance condition for the usual expressions from the literature.
Exact solution of position dependent mass Schrödinger equation by supersymmetric quantum mechanics
Authors: Koç R. , Tütüncüler H.
Published: June 2022

A supersymmetric technique for the solution of the effective mass Schrödinger equation is proposed. Exact solutions of the Schrödinger equation corresponding to a number of potentials are obtained. The potentials are fully isospectral with the original potentials. The conditions for the shape invariance of the potentials are discussed.
Why the cuprate superconductors are unusual: an ionic approach
Authors: Geballe T.H. , Moyzhes B.Y.
Published: June 2022

A new mobile charge carrier in hole‐doped high Tc cuprates is proposed. The configuration is based upon electrostatic considerations which show that a doped hole binds to an exciton and forms a linear, charge one singlet. In an ionic representation this exciton‐ hole (eh) particle is represented as O‐1Cu+1O‐1. The eh particle lives mostly in one dimension, being confined to either [10] rows and [01] columns of Cu‐O ions in the CuO2 layer. This model provides a simple qualitative understanding of the transport behavior reported in the literature for (La,Sr)2CuO4 and a natural explanation for the two relaxation rates suggested by the Hall data. It further offers a model for why coherence in two dimensions requires d‐wave symmetry. However additional pairing interactions in the intervening layers between the CuO2 layers are required to explain why the Tcs found in some cuprates are enhanced beyond what is expected by comparison with other cuprates. It is postulated that these interactions are based on eh partictles which occur in double chains of the 248 cuprates, and in negative U center ions in the charge reservoir layers of all the other cuprates with enhanced Tc > 100 K. We are lead to speculate that all cuprates with Tc > 100 K have pairing interactions off as well as on the CuO2 layers. The model suggests a much more enhanced Tc would be achieved with proper doping if the CuO2 layers could be modified by the addition of Cu to form Cu2O2 layers.
In situ synchrotron X‐ray studies of PbTiO3 thin films
Authors: Fong D.D. , Thompson C. , Streiffer S.K. , Eastman J.A. , Auciello O. , Fuoss P.H. , Stephenson G.B.
Published: June 2022

We have used in situ synchrotron x‐ray scattering to investigate PbTiO3 films grown epitaxially on SrTiO3 (001) substrates. When the films are cooled below a thickness‐dependent Curie temperature, the ferroelectric phase forms as 180° stripe domains with a well‐defined period. With further cooling, the period changes fairly abruptly from a lower to a higher value, suggesting a transition between two stripe domain phases. The periods of both stripe phases are observed to depend on the square root of film thickness, in agreement with theory.
SrBi2Nb2O9 thin films epitaxially grown on Pt epitaxial bottom layers: structural characteristics and nanoscale characterization of the ferroelectric behaviour by AFM
Authors: Duclère J.‐R. , Guilloux‐Viry M. , Bouquet V. , Perrin A. , Gautier B.
Published: June 2022

SrBi2Nb2O9 (SBN) films were grown by pulsed laser deposition on (100) and (110) Pt epitaxial bottom layers. In both cases x‐ray diffraction evidenced the epitaxial growth of SBN in spite of the coexistence of mainly two orientations. SBN films on (100) Pt present usually a dominant (001) orientation with the (115) one. AFM piezoresponse images agree with the crystallographic data, i.e. only the (115) oriented grains show a piezoelectric contrast. The SBN films grown on (110) Pt lead to a more homogenous piezoresponse imaging, in agreement with the preferential (116) orientation and the microstructure.
Thermoelectric power of La2‐xSrxCuO4 at high temperatures
Authors: Kim J.S. , Kim B.H. , Kim D.C. , Park Y.W.
Published: June 2022

Thermoelectric power (TEP) of high‐Tc superconductors has been investigated in a wide range of temperature (Tc < T < 700 K) for La2‐xSrxCuO4. For wide doping level from underdoping to heavily overdoping, TEP follows the linear‐T dependence above the broad peak temperature, Tp. At high temperatures, however, TEP shows deviation from the linear‐T dependence at a certain temperature Th, which is pronounced with doping up to x ∼ 0.2 and turns to be suppressed for further doping. The systematic change of the characteristic temperatures, Tc, Tp, and Th discussed in terms of the crossover behavior from a pseudogap state to strange metal in the underdoped regime and from strange metal to conventional metal in the overdoped regime.
Colossal magnetoresistive manganite thin‐films for infrared detection and imaging
Authors: Todd M.A. , Donohue P.P. , Wright P.J. , Crosbie M.J. , Lane P.A. , Jo M.‐H. , Pang B.S.H. , Blamire M.G.
Published: June 2022

The sharp metal‐to‐insulator transition observed in several colossal magnetoresistive manganite (CMR) materials has led to interest in the use of CMR thin‐films as bolometric detectors of infrared radiation. We have confirmed that with optimum growth and processing conditions, both high TCR (up to 30%/K) and low excess noise properties can be achieved in pulsed‐laser deposited La0.7Ca0.3MnO3 thin films. These offer unprecendented levels of performance if used as resistance bolometers, however a degree of cooling from room temperature will be required to achieve maximum bolometer performance. We have shown that LaxBa1‐xMnO3 is a candidate for uncooled bolometer operation and demonstrated room‐temperature TCR values of 5%/K in both laser‐deposited and liquid‐delivery CVD deposited LBMO films. Further enhancement to these figures is expected with optimised processing.
Modelling the electric field effect in superconducting films
Authors: Pavlenko N.
Published: June 2022

We present a phenomenological model of periodic ferroelectric‐superconductor (FE‐S) heterostructures containing two alternating ferroelectric and superconducting layers. The interaction at the FE‐S contacts is described as a coupling of the local carrier density of the superconductor with the spontaneous ferroelectric polarization near the FE‐S interface. For the stronger coupling, we find a stable symmetric domain‐type phase exhibiting the ferroelectric domain structure. With a further increase of the coupling energy, we obtain the complete suppression of the superconducting state in the S‐film. The behavior of the system is discussed for different thicknesses of the S‐films.
Pulsed laser deposited SrBi2Nb2O9 thin films grown on various substrates compatible with microwaves applications
Authors: Rousseau A. , Duclère J.‐R. , Guilloux‐Viry M. , Bouquet V. , Perrin A.
Published: June 2022

SrBi2Nb2O9 (SBN) films were grown by pulsed laser deposition on various substrates suitable for microwaves applications. Pure c‐axis oriented SBN films on (100) MgO and (100) LaAlO3 are epitaxially grown. The crystalline quality evaluated by the rocking curves width is strongly correlated to the film‐substrate mismatch (Δohgr; = 0.9–2° on MgO and Δω = 0.3–0.4° on LaAlO3). SBN growth on sapphire is more complex. In fact, on R‐plane as well as on C‐plane, XRD evidences the coexistence of various orientations of the SBN films. In spite of the coexistence of several orientations epitaxial growth was evidenced, strongly influencing the microstructure.
Advances of pulsed laser deposition of ZnO thin films
Authors: Lorenz M. , Hochmuth H. , Schmidt‐Grund R. , Kaidashev E.M. , Grundmann M.
Published: June 2022

Advances in Pulsed Laser Deposition (PLD) equipment and process design for the epitaxy of ZnO thin films on a‐, and c‐oriented sapphire substrates are reported. The achieved improvement of device relevant ZnO layer properties is directly related to our equipment design and novel process schemes. First results on growth and reflectivity of ZnO‐MgO based dielectric Bragg resonators for future ZnO‐based light emitter devices are shown.
Electro‐optical properties of ZnO‐BaTiO3‐ZnO heterostructures grown by pulsed laser deposition
Authors: Schubert M. , Ashkenov N. , Hofmann T. , Lorenz M. , Hochmuth H. , v. Wenckstern H. , Grundmann M. , Wagner G.
Published: June 2022

Electro‐optical birefringence measurements by spectroscopic ellipsometry on ZnO‐BaTiO3‐ZnO heterostructures, grown by pulsed laser deposition on (0001) sapphire are reported. Wurtzite‐structure ZnO layers serve as transparent conducting electrodes. An interesting hysteresis is observed, tentatively assigned due to coupling between wurtzite and ferroelectric polarization, and ferroelectric phase transition.
Making the transition temperature of cuprate superconductors higher by using the field‐effect‐transistor geometry
Authors: Hayashi M.
Published: June 2022

We present a possibility to raise the transition temperature of cuprate superconductors by using the field‐effect‐transistor type devices. The basic mechanism is based on the proximity effect of the two off‐diagonal‐long‐range‐orders in the superconducting phase of the cuprates, namely, the singlet resonating‐valence‐bond order and the bose condensation. Our model is based on the mean field theory of the t‐J model.
Magnetism of SrRuO3 thin films under high hydrostatic pressure
Authors: Demuer A. , Jaccard D. , Reiner J.W. , Ahn C.H. , Triscone J.‐M.
Published: June 2022

We report on resistivity and Hall measurements performed on epitaxial thin films of the weak ferromagnet SrRuO3 under hydrostatic pressure up to 21.4 GPa. In the low pressure range (< 13GPa), we observe a linear pressure dependence of the Curie temperature with a rate ‐6K GPa‐1 similar to that found in the bulk material. At higher pressures, the hysteretic loop observed in the Hall measurement, related to the magnetization via the extraordinary Hall effect, supports our previous observation concerning the unexpected persistence of ferromagnetic order above 70 K.
Influence of film thickness and strain on magnetic properties of epitaxial La0.7A0.3CoO3 (A = Ca, Sr, Ba) thin films
Authors: Morán O. , Fuchs D. , Adelmann P. , Schneider R.
Published: June 2022

We prepared La0.7A0.3CoO3 (A=Ca, Sr, Ba) films with a thickness ranging from 50 up to 1000 monolayers (∼ 20–400 nm) by pulsed laser deposition (PLD) on (001)‐oriented single crystal substrates of SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7 and LaAlO3 and studied the in‐plane and out‐of‐plane magnetization as function of thickness and of the strain provided by the substrate‐film lattice mismatch. The Curie temperature TC decreases slightly with thickness according to the finite size scaling 1 – TC / T∞ = (N0 / N)λ, where T∞ is the bulk Curie temperature and N is the number of monolayers. We obtain a critical exponent λ = 0.9 ± 0.2, consistent with the theoretical mean field value, and a spin‐spin coupling range N0 = 2–3.
Surface electronic structure and Verwey‐transition of magnetite studied by photoemission spectroscopy
Authors: Schrupp D. , Sing M. , Tsunekawa M. , Fujiwara H. , Kasai S. , Sekiyama A. , Suga S. , Muro T. , Brabers V.A.M. , Claessen R.
Published: June 2022

We report on a detailed study of single crystal surfaces with (111) and (100) orientations by means of photoemission spectroscopy (PES). The surfaces were prepared by sputtering, annealing, and post‐oxidizing and characterized using LEED, XPS, and STM. The surface electronic structure turns out to be strongly dependent on the surface orientation and preparation conditions. This also holds for more bulk sensitive PES measurements using photons with an energy at the Fe 2p resonance threshold. Thus we conclude that the surface region extends much deeper into the bulk than the topmost atomic layer.
The microstructure of La0.67Sr0.33MnO3 grain boundaries on SrTiO3 bicrystal substrates
Authors: Liljenfors T. , Gunnarsson R. , Ivanov Z. , Olsson E.
Published: June 2022

The aim of this study is to characterize the grain boundary microstructure of artificial La0.67Sr0.33MnO3 (LSMO) grain boundaries obtained by epitaxial growth on SrTiO3 (STO) bicrystal substrates. The films were deposited on STO bicrystal substrates using pulsed laser deposition. The substrates were (001) oriented and the boundaries were symmetrical [001]‐tilt boundaries with nominal tilt angle 24° and 37° respectively. The microstructures were characterized using a transmission electron microscope. The thickness of the LSMO films was 32 and 37 nm respectively. The films were relatively smooth and the interface between the substrate and the films was sharp without any evidence of chemical reaction or interdiffusion.
Correlation of the electrical transport in epitaxial La2/3Ca1/3MnO3 thin films with magnetization
Authors: Morán O. , Fuchs D. , Hott R. , Grube K. , Schneider R. , Bacca E. , Prieto P.
Published: June 2022

We measured the magnetization M(T,H) and resistivity ρ(T,H) of epitaxial c‐axis oriented films of the metallic ferromagnetic perovskite La2/3Ca1/3MnO3 as function of temperature and external magnetic field. The films were prepared by dc‐sputtering at high oxygen pressure onto (001) SrTiO3 substrates without additional oxygen annealing. Ferromagnetic ordering was observed below a temperature TC ≈ 260 K where a negative magnetoresistance ratio of 50% was achieved in a magnetic field of 6 T. Above TC, the zero field resistivity exhibits polaron‐hopping like activated conduction. The relation ρ(T,H) ∝ exp[‐M(H,T)/M0] observed below TC suggests a direct connection between magnetization and resistivity.
Novel effects observed in heavy ion irradiated Bi2Sr2‐xLaxCuOy thin films
Authors: Raffy H. , Murrills C. , Pomar A. , Li Z.Z.
Published: June 2022

The superconducting properties of Bi2Sr2‐xLaxCuOy thin films irradiated by 1 GeV heavy ions have been investigated. Firstly, irradiation produces dramatic changes in Tc and in R(T). This fact is attributed to a self‐doping effect of the sample by oxygen liberated from the ion tracks. Secondly, the pinning properties of the columnar defects allowed us to probe different vortex behaviours for films with increasing La content (0 ≤ x ≤ 0.4). From the angular dependence of R(H) and Jc(H) in the mixed state, for a given column density, a directional pinning effect, or linear vortex behaviour, is observed for low x values, whereas no directional effect is seen for large x values and 2D scaling properties, characteristic of pancake vortices, are then observed. Importantly this reveals that changes in x induce large changes in the material anisotropy.
Strain dependence of transport critical exponent in RuO2‐glass systems
Authors: Vionnet S. , Grimaldi C. , Maeder T. , Ryser P. , Strässler S.
Published: June 2022

A vast class of disordered conducting‐insulating compounds close to the percolation threshold is characterized by nonuniversal values of transport critical exponents. The lack of universality implies that critical indexes may depend on material properties such as microstructure, composition etc., and that in principle they can be influenced by suitable applied perturbations leading to important informations about the origin of nonuniversality. Here we show that RuO2‐glass compounds can have nonuniversal values of transport critical exponents which can be altered by an applied mechanical strain leading to a logarithmically divergent piezoresistive response at the percolation threshold. This finding supports the tunneling‐percolation theory of nonuniversality proposed several years ago.
Behavior of the APSG electronic wavefunction near the electron‐electron coalescence point
Authors: Pernal K. , Cioslowski J.
Published: June 2022

The behavior of electronic wave functions within the antisymmetrized product of strongly orthogonal geminals (APSG) approximation at the point of the electron‐electron coalescence is examined. Its elucidation allows one to understand the origins of the previously reported satisfactory performance of APSG wavefunctions as reference states in the connected moments expansion method (CMX). It is shown that the failure to satisfy the electron‐electron cusp condition causes divergence of certain type of integrals that enter the CMX formulae, which in turn brings about significant deterioration of the quality of the resulting estimates for the ground‐state energy in finite basis sets.
Local information‐distance thermodynamics of molecular fragments
Authors: Nalewajski R.F.
Published: June 2022

The Fisher information contained in a probability distribution is summarized. The corresponding measures of the information distance, relative to the reference probability density, are introduced and discussed. These concepts are designed as analogues of the Kullback‐Leibler directed divergence and Kullback's divergence. For these alternative measures of the missing information the equilibrium (“stockholder”) scheme of Hirshfeld, of a division of the molecular electron density into the subsystem components, is derived from the minimum principle of the local or global entropy deficiency relative to the free‐subsystem (“promolecule”) reference. The local information distance densities are used to describe instantaneous electron distributions in molecular subsystems within a thermodynamic‐like approach to the density fluctuations and irreversible processes. The key concepts of such a local irreversible “thermodynamics” are introduced. They include the corresponding local affinities (forces) and the conjugate fluxes (responses), which together determine the local entropy deficiency source. These quantities depend on the adopted measure of the information distance and selected state‐parameters. For each such representation the relevant Onsager‐type reciprocity relations can be derived, which reflect the symmetries between the linear effects of affinities on fluxes.
Electric/magnetic flux tube on the background of magnetic/electric field
Authors: Dzhunushaliev V.
Published: June 2022

It is argued that the phenomenon of a flux tube in quantum chromodynamics is closely connected with a spontaneously symmetry breakdown of gauge theory. It is shown that in the presence of a mass term in the SU(2) gauge theory the Nielsen‐Olesen equations describe the flux tube surrounded by an external field.
Electronic structure and transport properties of quantum dots
Authors: Tews M.
Published: June 2022

The subject of this paper are electronic properties of isolated quantum dots as well as transport properties of quantum dots coupled to two electronic reservoirs. Thereby special focus is put on the effects of Coulomb interaction and possible correlations in the quantum dot states. First, the regime of sequential tunneling to the reservoirs is investigated. It is shown that in case degenerate states participate in transport, the resonance positions in the differential conductance generally depend on temperature and the degree of degeneracy. This effect can be used to directly probe degeneracies in a quantum dot spectrum. A further effect, characteristic for sequential tunneling events, is the complete blocking of individual channels for transport. A generalisation of the well known spin blockade is found for correlated dot states transitions through which are not directly spin‐forbidden. In the second part, the electronic structure of spherical quantum dots is calculated. In order to account for correlation effects, the few‐particle Schrödinger equation is solved by an exact diagonalization procedure. The calculated electronic structure compares to experimental findings obtained on colloidal semiconductor nanocrystals by Scanning Tunneling Spectroscopy. It is found that the electric field induced by the tunneling tip is gives rise to a Stark effect which can break the spherical symmetry of the electronic ground state density which is in agreement with wave‐function mapping experiments. The symmetry breaking depends on the competition between exchange energy and the Stark energy. Moreover, a systematic dependence on particle number is found for the excitation energies of optical transitions which explains recent experimental findings on self‐organized quantum dots. In the last part, co‐tunneling in the Coulomb blockade regime is studied. For this end the tunneling current is calculated up to the forth order perturbation theory in the tunnel coupling by a real‐time Green's function approach for the non‐equilibrium case. The differential conductance calculated for a quantum dot containing up to two interacting electrons shows complex signatures of the excitation spectrum which are explained by a combination of co‐tunneling and sequential tunneling processes. Thereby the calculations show a peak structure within the Coulomb blockade regime which has also been observed in experiment.
QCD universality recovered via the Total Available Quadri‐Scalar
Authors: Appignani C.
Published: June 2022

After presenting a brief review of the phenomenology of the Leading Effect, we define a new variable, the “Total Available Quadri‐Scalar” (ATOT) and propose it as the invariant quantity effectively available for the production of the multihadronic final states. The introduction and definition of this new varaible is justified by means of simple geometrical‐kinematical considerations and we show that ATOT reduces to the so‐called effective energy in the single specific situation where the use of the latter applies. Using ATOT to re‐plot existing data, the quantity  is shown to be a “Universality Feature” – that is, independent from the colliding particles, the collider nominal energy, and even from the hadronic invariant mass – as imposed by QCD universality.
Electron excitation cross section of atomic transitions in the two‐state approximation
Authors: Kamli A. , Bougouffa S.
Published: June 2022

The cross section of the 3s → 3p transition of sodium produced by electron impact has been calculated by performing a numerical integration of the coupled differential equations. The potential functions have been calculated exactly using the hydrogen‐like wave functions for the valence electron of the sodium with an effective charge adjusted to fit the experimental 3s → 3p line strength. The results compare very well with experimental data and with those obtained using more elaborate and sophisticated models.
Novel properties of wave propagation in biaxially anisotropic left‐handed materials
Authors: Shen J.Q.
Published: June 2022

Some physically interesting properties and effects (including the quantum effects) of wave propagation in biaxially anisotropic left‐handed materials are investigated in this paper: (i) we show that in the biaxially gyrotropic left‐handed material, the left‐right coupling of circularly polarized light arises due to the negative indices in permittivity and permeability tensors of gyrotropic media; (ii) it is well known that the geometric phases of photons inside a curved fiber in previous experiments often depend on the cone angles of solid angles subtended by a curve traced by the direction of wave vector of light, at the center of photon momentum space. Here, however, for the light propagating inside certain anisotropic left‐handed media we will present a different geometric phase that is independent of the cone angles; (iii) the extra phases of electromagnetic wave resulting from the instantaneous helicity inversion at the interfaces between left‐ and right‐handed (LRH) media is also studied in detail by using the Lewis‐Riesenfeld invariant theory. Some interesting applications (e.g., controllable position‐dependent frequency shift, detection of quantum‐vacuum geometric phases and helicity reversals at the LRH interfaces etc.) of above effects and phenomena in left‐handed media is briefly discussed.
Current‐density patterns induced by avalanche injection phenomena in high‐voltage diodes during turn‐off
Authors: Niedernostheide F.‐J. , Falck E. , Schulze H.‐J. , Kellner‐Werdehausen U.
Published: June 2022

The turn‐off behavior of two types of high‐voltage diodes is investigated by means of numerical simulations. Basic self‐organized structures appearing as transient patterns during the turn‐off period are quasi‐stationary or traveling current‐density filaments and periodic current‐density distributions. Additionally, we find evolution of more complex patterns that can be considered to be a superposition of basic structures. Examples of such complex structures are presented and mechanisms leading to their evolution are discussed.
Pattern formation in a reaction‐advection model with delay: a continuum approach to myxobacterial rippling
Authors: Börner U. , Bär M.
Published: June 2022

Standing wave oscillations of the cell density (rippling) are observed in premature aggregates of developing myxobacteria. Recently the underlying pattern formation mechanism was shown to be based on the interplay between active cell motion and local interactions triggering reversals in the cells' direction of motion. The propagation of information through the system is mediated by the internal state of moving cells rather than by diffusible chemical signals. Discrete cellular automata and coupled‐map lattices have been investigated earlier and indicate the importance of a minimum refractory period between subsequent reversals of a cell. In this paper we consider the continuum limit of the process, that yields a set of hyperbolic partial differential equations with a a single discrete time delay. The time delay corresponds to the duration of the mentioned refractory period of the cells. According to linear stability analysis a minimal time delay is required for a wave instability to occur. The results of the continuum model are in reasonable agreement with the findings in the discrete models adding credibility to the earlier studies.
Reaction‐diffusion waves in neuronal tissue and the window of cortical excitability
Authors: Dahlem M.A. , Müller S.C.
Published: June 2022

Spreading depression (SD) is a dynamic wave phenomenon occurring in all gray matter regions of the central nervous systems (CNS). It is characterized by a sudden breakdown of neuronal activity and accompanied by a massive influx and efflux of ions across the membrane of neurons. The retina is a constituent of the CNS in which one can easily observe the dynamic behavior of the SD wave fronts, because SD changes the optical properties of the tissue. There is ample evidence that SD belongs to the self‐organization processes due to the coupling of reaction with diffusion in excitable medium. It is assumed that the occurrence of SD is associated with some neurological symptoms of migraine with aura. A frequently reported aura symptom is a traveling visual blind region (scotoma) with a preceding figure of scintillating line segments. The characteristic form and development of the scotoma suggests that the underlying phenomenon is a wave propagating through the primary visual cortex, most likely the cortical spreading depression. In this article we discuss similarities between SD waves and the migraine aura on the basis of properties of reaction‐diffusion waves known from other excitable media. In particular, the propagation velocities, the shape and the dynamics of the waves are compared with each other. We find that the assumption of the neuronal tissue to be in a state of only weak excitability explains some properties of the migraine aura, such as the confined appearance and its propagation with a stable velocity.
Anomalous statistics in turbulence, financial markets and other complex systems
Authors: Peinke J. , Böttcher F. , Barth St.
Published: June 2022

The meaning of non‐Gaussian statistics of disordered systems is discussed. The risks of heavy tailed probability distributions of wind gusts are presented together with the discussion of an eventual power law behavior of such heavy tailed distributions. We summarize the argumentation connecting such probability distributions with Levy processes and the meaning of non‐existing moments. Based on turbulence and financial market data, stochastic cascade processes are presented, which lead to anomalous statistics with heavy tails, too. Finally we show how for disordered complex systems with an underlying hierarchical structure, like the cascade structure in turbulence, a stochastic equation can be estimated directly from the data. The numerical solution of this reconstructed stochastic process gives back the anomalous statistics.
The vanadium Magnéli phases VnO2n‐1
Authors: Schwingenschlögl U. , Eyert V.
Published: June 2022

To compare the metal‐insulator transitions (MITs) of VO2 and V2O3 we analyze the relations between the structural and electronic properties of the vanadium Magnéli phases. These materials set up the homologous series VnO2n‐1 (3 ≤ n ≤ 9) and have crystal structures comprising typical dioxide‐like and sesquioxide‐like regions. As the MITs of the vanadium Magnéli phases are accompanied by structural transformations, we are able to discuss the effects of characteristic changes in the local atomic environments. The systematic investigation of the transport properties is based on a new and unifying description of the crystal structures of the Magnéli phases including VO2 and V2O3. Our results lead to a comprehensive understanding of the MITs in the Magnéli class and shed new light on the role of particular electronic states for the MIT of V2O3.