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Condens. Matter, Volume 4, Issue 2 (June 2019)

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Cover Story (view full-size image) Novel large-area silicon drift detectors (SDDs) for high-precision X-ray spectroscopy were [...] Read more.
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Open AccessReview
The Ancient Romans’ Route to Charge Density Waves in Cuprates
Condens. Matter 2019, 4(2), 60; https://doi.org/10.3390/condmat4020060
Received: 30 May 2019 / Revised: 16 June 2019 / Accepted: 21 June 2019 / Published: 25 June 2019
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Abstract
An account is given of the main steps that led the research group in Rome, to which the author belongs, to the formulation of the charge-density-wave scenario for high-Tc superconducting cuprates. The early finding of the generic tendency of strongly correlated [...] Read more.
An account is given of the main steps that led the research group in Rome, to which the author belongs, to the formulation of the charge-density-wave scenario for high- T c superconducting cuprates. The early finding of the generic tendency of strongly correlated electron systems with short range interactions to undergo electron phase separation was subsequently contrasted with the homogenizing effect of the long-range Coulomb interaction. The two effects can find a compromise in the formation of incommensurate charge density waves. These charge density waves are inherently dynamical and are overdamped as a consequence of the possibility to decay in electron-hole pairs, yet tend to maintain a (quantum) critical character, which is mirrored in their marked momentum and frequency dependence and in their strong variation with temperature and doping. These dynamical incommensurate charge density waves act as mediators of pairing lading to high- T c superconductivity, and provide the scattering mechanism that produces the observed violation of the Fermi-liquid paradigm in the metallic phase. Full article
(This article belongs to the Special Issue From cuprates to Room Temperature Superconductors)
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Open AccessEditorial
High Precision X-Ray Measurements
Condens. Matter 2019, 4(2), 59; https://doi.org/10.3390/condmat4020059
Received: 17 June 2019 / Revised: 20 June 2019 / Accepted: 22 June 2019 / Published: 25 June 2019
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Abstract
Since their discovery in 1895, the detection of X-rays has had a strong impact and various applications in several fields of science and human life [...] Full article
(This article belongs to the Special Issue High Precision X-Ray Measurements)
Open AccessArticle
Efficient Spatial Sampling for AFM-Based Cancer Diagnostics: A Comparison between Neural Networks and Conventional Data Analysis
Condens. Matter 2019, 4(2), 58; https://doi.org/10.3390/condmat4020058
Received: 22 April 2019 / Revised: 13 June 2019 / Accepted: 19 June 2019 / Published: 21 June 2019
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Abstract
Atomic force microscopy (AFM) in spectroscopy mode receives a lot of attention because of its potential in distinguishing between healthy and cancer tissues. However, the AFM translational process in clinical practice is hindered by the fact that it is a time-consuming technique in [...] Read more.
Atomic force microscopy (AFM) in spectroscopy mode receives a lot of attention because of its potential in distinguishing between healthy and cancer tissues. However, the AFM translational process in clinical practice is hindered by the fact that it is a time-consuming technique in terms of measurement and analysis time. In this paper, we attempt to address both issues. We propose the use of neural networks for pattern recognition to automatically classify AFM force–distance (FD) curves, with the aim of avoiding curve-fitting with the Sneddon model or more complicated ones. We investigated the applicability of this method to the classification of brain cancer tissues. The performance of the classifier was evaluated with receiving operating characteristic (ROC) curves for the approach and retract curves separately and in combination with each other. Although more complex and comprehensive models are required to demonstrate the general applicability of the proposed approach, preliminary evidence is given for the accuracy of the results, and arguments are presented to support the possible applicability of neural networks to the classification of brain cancer tissues. Moreover, we propose a possible strategy to shorten measurement times based on the estimation of the minimum number of FD curves needed to classify a tissue with a confidence level of 0.005. Taken together, these results have the potential to stimulate the design of more effective protocols to reduce AFM measurement times and to get rid of curve-fitting, which is a complex and time-consuming issue that requires experienced staff with a strong data-analysis background. Full article
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Open AccessArticle
Mechanism of High-Temperature Superconductivity in Correlated-Electron Systems
Condens. Matter 2019, 4(2), 57; https://doi.org/10.3390/condmat4020057
Received: 25 April 2019 / Revised: 13 June 2019 / Accepted: 15 June 2019 / Published: 19 June 2019
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Abstract
It is very important to elucidate the mechanism of superconductivity for achieving room temperature superconductivity. In the first half of this paper, we give a brief review on mechanisms of superconductivity in many-electron systems. We believe that high-temperature superconductivity may occur in a [...] Read more.
It is very important to elucidate the mechanism of superconductivity for achieving room temperature superconductivity. In the first half of this paper, we give a brief review on mechanisms of superconductivity in many-electron systems. We believe that high-temperature superconductivity may occur in a system with interaction of large-energy scale. Empirically, this is true for superconductors that have been found so far. In the second half of this paper, we discuss cuprate high-temperature superconductors. We argue that superconductivity of high temperature cuprates is induced by the strong on-site Coulomb interaction, that is, the origin of high-temperature superconductivity is the strong electron correlation. We show the results on the ground state of electronic models for high temperature cuprates on the basis of the optimization variational Monte Carlo method. A high-temperature superconducting phase will exist in the strongly correlated region. Full article
(This article belongs to the Special Issue From cuprates to Room Temperature Superconductors)
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Open AccessArticle
Memristive Properties of PANI-Polysterene/PVDF-TrFE Interface
Condens. Matter 2019, 4(2), 56; https://doi.org/10.3390/condmat4020056
Received: 15 April 2019 / Revised: 13 June 2019 / Accepted: 18 June 2019 / Published: 19 June 2019
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Abstract
The article presents the results of an experimental study of the transport of charge carriers through semiconductor PANI-polystyrene/ ferroelectric PVDF-TrFE interface. Current-voltage characteristics of the structure under study have a typical form for memristors and may be explained by the movement of charge [...] Read more.
The article presents the results of an experimental study of the transport of charge carriers through semiconductor PANI-polystyrene/ ferroelectric PVDF-TrFE interface. Current-voltage characteristics of the structure under study have a typical form for memristors and may be explained by the movement of charge carriers in the internal switchable field of the crystal ferroelectric microregions located within a bulk volume of amorphous PVDF-TrFE matrix. This assumption is subject to XRD phase analysis, FTIR spectroscopy, and X-ray EDS microanalysis. A long-term (about 100 h) relaxation is detected for the resistance of the PANI-polysturene/PVDF-TrFE interface after the current-voltage characteristics measurement cycle that is associated with the processes of capture and release traps of charge carriers. Full article
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Open AccessArticle
SAXS Analysis of Magnetic Field Influence on Magnetic Nanoparticle Clusters
Condens. Matter 2019, 4(2), 55; https://doi.org/10.3390/condmat4020055
Received: 9 May 2019 / Revised: 14 June 2019 / Accepted: 16 June 2019 / Published: 18 June 2019
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Abstract
In this work, we investigated the local colloidal structure of ferrofluid, in the presence of the external magnetic field. The nanoparticles studied here are of the core-shell type, with the core formed by manganese ferrite and maghemite shell, and were synthesized by the [...] Read more.
In this work, we investigated the local colloidal structure of ferrofluid, in the presence of the external magnetic field. The nanoparticles studied here are of the core-shell type, with the core formed by manganese ferrite and maghemite shell, and were synthesized by the coprecipitation method in alkaline medium. Measures of Small Angle X-ray Scattering (SAXS) performed in the Brazilian Synchrotron Light Laboratory (LNLS) were used for the study of the local colloidal structure of ferrofluid, so it was possible to study two levels of structure, cluster and isolated particles, in the regimes with and without applied magnetic field. In the methodology used here there is a combination of the information obtained in the system with and without magnetic field application. In this way, it is possible to undertake a better investigation of the colloidal dispersion. The theoretical formalism used: (i) the unification equation proposed by Beaucage G.; (ii) the analysis of the radial distribution function p ( r ) and (iii) theoretical calculation of the radius of gyration as a function of the moment of inertia of the spherical of n-nanoparticles. Full article
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Open AccessArticle
Evaluating Superconductors through Current Induced Depairing
Condens. Matter 2019, 4(2), 54; https://doi.org/10.3390/condmat4020054
Received: 22 May 2019 / Revised: 13 June 2019 / Accepted: 15 June 2019 / Published: 17 June 2019
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Abstract
The phenomenon of superconductivity occurs in the phase space of three principal parameters: temperature T, magnetic field B, and current density j. The critical temperature Tc is one of the first parameters that is measured and in a certain way defines [...] Read more.
The phenomenon of superconductivity occurs in the phase space of three principal parameters: temperature T, magnetic field B, and current density j. The critical temperature T c is one of the first parameters that is measured and in a certain way defines the superconductor. From the practical applications point of view, of equal importance is the upper critical magnetic field B c 2 and conventional critical current density j c (above which the system begins to show resistance without entering the normal state). However, a seldom-measured parameter, the depairing current density j d , holds the same fundamental importance as T c and B c 2 , in that it defines a boundary between the superconducting and normal states. A study of j d sheds unique light on other important characteristics of the superconducting state such as the superfluid density and the nature of the normal state below T c , information that can play a key role in better understanding newly-discovered superconducting materials. From a measurement perspective, the extremely high values of j d make it difficult to measure, which is the reason why it is seldom measured. Here, we will review the fundamentals of current-induced depairing and the fast-pulsed current technique that facilitates its measurement and discuss the results of its application to the topological-insulator/chalcogenide interfacial superconducting system. Full article
(This article belongs to the Special Issue From cuprates to Room Temperature Superconductors)
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Open AccessArticle
Understanding Phase Stability of Metallic 1T-MoS2 Anodes for Sodium-Ion Batteries
Condens. Matter 2019, 4(2), 53; https://doi.org/10.3390/condmat4020053
Received: 24 April 2019 / Revised: 2 June 2019 / Accepted: 3 June 2019 / Published: 10 June 2019
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Abstract
We discuss metallic 1T-MoS2 as an anode material for sodium-ion batteries (SIBs). In situ Raman is used to investigate the stability of metallic MoS2 during the charging and discharging processes. Parallel first-principles computations are used to gain insight into the experimental [...] Read more.
We discuss metallic 1T-MoS2 as an anode material for sodium-ion batteries (SIBs). In situ Raman is used to investigate the stability of metallic MoS2 during the charging and discharging processes. Parallel first-principles computations are used to gain insight into the experimental observations, including the measured conductivities and the high capacity of the anode. Full article
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Open AccessArticle
Scaling between Superfluid Density and Tc in Overdoped La2−xSrxCuO4 Films
Condens. Matter 2019, 4(2), 52; https://doi.org/10.3390/condmat4020052
Received: 19 April 2019 / Revised: 3 June 2019 / Accepted: 4 June 2019 / Published: 6 June 2019
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Abstract
We used an electronic phase separation approach to interpret the scaling between the low-temperature superfluid density average ρsc(0) and the superconducting critical temperature Tc on overdoped La2xSrxCuO4 films. Guided by the [...] Read more.
We used an electronic phase separation approach to interpret the scaling between the low-temperature superfluid density average ρ sc ( 0 ) and the superconducting critical temperature T c on overdoped La 2 x Sr x CuO 4 films. Guided by the observed nematic and incommensurate charge ordering (CO), we performed simulations with a free energy that reproduces charge domains with wavelength λ C O and provides a scale to local superconducting interactions. Under these conditions a complex order parameter with amplitude Δ d ( r i ) and phase θ ( r i ) may develop at a domain i. We assumed that these domains are coupled by Josephson energy E J ( r i j ) , proportional to the local superfluid density ρ sc ( r i j ) . Long-range order occured when the average E J ( T c ) is k B T c . The linear ρ s c ( 0 ) vs. T c relation was satisfied whenever CO was present, even with almost vanishing charge amplitudes. Full article
(This article belongs to the Special Issue From cuprates to Room Temperature Superconductors)
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Open AccessReview
Fermi-Bose Mixtures and BCS-BEC Crossover in High-Tc Superconductors
Condens. Matter 2019, 4(2), 51; https://doi.org/10.3390/condmat4020051
Received: 13 May 2019 / Revised: 31 May 2019 / Accepted: 31 May 2019 / Published: 3 June 2019
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Abstract
In this review article we consider theoretically and give experimental support to the models of the Fermi-Bose mixtures and the BCS-BEC (Bardeen Cooper Schrieffer–Bose Einstein) crossover compared with the strong-coupling approach, which can serve as the cornerstones on the way from high-temperature to [...] Read more.
In this review article we consider theoretically and give experimental support to the models of the Fermi-Bose mixtures and the BCS-BEC (Bardeen Cooper Schrieffer–Bose Einstein) crossover compared with the strong-coupling approach, which can serve as the cornerstones on the way from high-temperature to room-temperature superconductivity in pressurized metallic hydrides. We discuss some key theoretical ideas and mechanisms proposed for unconventional superconductors (cuprates, pnictides, chalcogenides, bismuthates, diborides, heavy-fermions, organics, bilayer graphene, twisted graphene, oxide hetero-structures), superfluids and balanced or imbalanced ultracold Fermi gases in magnetic traps. We build a bridge between unconventional superconductors and recently discovered pressurized hydrides superconductors H3S and LaH10 with the critical temperature close to room temperature. We discuss systems with a line of nodal Dirac points close to the Fermi surface and superconducting shape resonances, and hyperbolic superconducting networks which are very important for the development of novel topological superconductors, for the energetics, for the applications in nano-electronics and quantum computations. Full article
(This article belongs to the Special Issue From cuprates to Room Temperature Superconductors)
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Open AccessEditorial
Surface Plasmon Resonance (SPR) to Magneto-Optic SPR
Condens. Matter 2019, 4(2), 50; https://doi.org/10.3390/condmat4020050
Received: 19 May 2019 / Accepted: 22 May 2019 / Published: 27 May 2019
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Abstract
In this editorial, a brief background of the surface plasmon resonance (SPR) principle is discussed, followed by several aspects of magneto-optic SPR (MOSPR) and sensing schemes from the viewpoint of fundamental studies and potential technological applications. New sensitivity metrics are introduced that would [...] Read more.
In this editorial, a brief background of the surface plasmon resonance (SPR) principle is discussed, followed by several aspects of magneto-optic SPR (MOSPR) and sensing schemes from the viewpoint of fundamental studies and potential technological applications. New sensitivity metrics are introduced that would allow researchers to compare the performance of SPR and MOSPR-based sensors. Merits of MOSPR over SPR based sensors and challenges faced by MOSPR sensors in terms of their practical use and portability are also considered. The editorial ends with potential new configurations and future prospects. This work is considered highly significant to device engineers, graduate and undergraduate students, and researchers of all levels involved in developing new classes of bio-devices for sensing, imaging, environmental monitoring, toxic gas detection, and surveying applications to name a few. Full article
(This article belongs to the Special Issue Magnetoplamonics Material and Devices)
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Open AccessArticle
Improved Transition Metal Dichalcogenides-Based Surface Plasmon Resonance Biosensors
Condens. Matter 2019, 4(2), 49; https://doi.org/10.3390/condmat4020049
Received: 13 April 2019 / Revised: 10 May 2019 / Accepted: 21 May 2019 / Published: 22 May 2019
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Abstract
Surface plasmon resonance (SPR) biosensors based on transition metal dichalcogenides (TMDC) materials have shown improved performance in terms of sensitivity, detection accuracy (DA), and quality factor (QF) over conventional biosensors. In this paper, we propose a five-layers model containing black phosphorus (BP) and [...] Read more.
Surface plasmon resonance (SPR) biosensors based on transition metal dichalcogenides (TMDC) materials have shown improved performance in terms of sensitivity, detection accuracy (DA), and quality factor (QF) over conventional biosensors. In this paper, we propose a five-layers model containing black phosphorus (BP) and TMDC (Ag/BP/WS2) in Kretschmann configuration. Using TM-polarized light at 633 nm, we numerically demonstrate the highest sensitivity (375°/RIU), DA (0.9210), and QF (65.78 1/RIU) reported so far over similar materials. Refractive index (RI) of the coupling prism has also played an essential role in enhancing the performance of these biosensors. The research on TMDC materials is still new, and these materials bring about opportunities to develop a new class of biosensor. Full article
(This article belongs to the Special Issue Magnetoplamonics Material and Devices)
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Open AccessArticle
On Quantum Extensions of Hydrodynamic Lattice Gas Automata
Condens. Matter 2019, 4(2), 48; https://doi.org/10.3390/condmat4020048
Received: 11 April 2019 / Revised: 3 May 2019 / Accepted: 3 May 2019 / Published: 11 May 2019
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Abstract
We consider quantum extensions of classical hydrodynamic lattice gas models. We find that the existence of local conserved quantities strongly constrains such extensions. We find the only extensions that retain local conserved quantities correspond to changing the local encoding of a subset of [...] Read more.
We consider quantum extensions of classical hydrodynamic lattice gas models. We find that the existence of local conserved quantities strongly constrains such extensions. We find the only extensions that retain local conserved quantities correspond to changing the local encoding of a subset of the bits. These models maintain separability of the state throughout the evolution and are thus efficiently classically simulable. We then consider evolution of these models in the case where any of the bits can be encoded and measured in one of two local bases. In the case that either encoding is allowed, the models are efficiently classically simulable. In the case that both encoding and measurement is allowed in either basis, we argue that efficient classical simulation is unlikely. In particular, for classical models that are computationally universal such quantum extensions can encode Simon’s algorithm, thus presenting an obstacle to efficient classical simulation. Full article
(This article belongs to the Special Issue Quantum Cellular Automata and Quantum Walks)
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Open AccessReview
Time Reversal Symmetry Breaking Superconductors: Sr2RuO4 and Beyond
Condens. Matter 2019, 4(2), 47; https://doi.org/10.3390/condmat4020047
Received: 9 March 2019 / Revised: 23 April 2019 / Accepted: 6 May 2019 / Published: 9 May 2019
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Abstract
Recent work done on the time reversal symmetry (TRS) breaking superconductors is reviewed in this paper. The special attention is paid to Sr2RuO4 believed to be spin triplet chiral p-wave superconductor which break TRS and is expected to posses non-trivial [...] Read more.
Recent work done on the time reversal symmetry (TRS) breaking superconductors is reviewed in this paper. The special attention is paid to Sr 2 RuO 4 believed to be spin triplet chiral p-wave superconductor which break TRS and is expected to posses non-trivial topological properties. The family of TRS breaking superconductors is growing relatively fast, with many of its newly discovered members being non-centrosymmetric. However not only Sr 2 RuO 4 but also many other superconductors which possess center of inversion also break TRS. The TRS is often identified by means of the muon spin relaxation ( μ SR) and the Kerr effect. Both methods effectively measure the appearance of the spontaneous bulk magnetic field below superconducting transition temperature. This compound provides an example of the material whose many band, multi-condensate modeling has enjoyed a number of successes, but the full understanding has not been achieved yet. We discuss in some details the properties of the material. Among them is the Kerr effect and by understanding has resulted in the discovery of the novel mechanism of the phenomenon. The mechanism is universal and thus applicable to all systems with multi-orbital character of states at the Fermi energy. Full article
(This article belongs to the Special Issue From cuprates to Room Temperature Superconductors)
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Open AccessReview
Orbital Symmetry and Orbital Excitations in High-Tc Superconductors
Condens. Matter 2019, 4(2), 46; https://doi.org/10.3390/condmat4020046
Received: 12 March 2019 / Revised: 29 April 2019 / Accepted: 2 May 2019 / Published: 6 May 2019
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Abstract
We discuss a few possibilities of high-Tc superconductivity with more than one orbital symmetry contributing to the pairing. First, we show that the high energies of orbital excitations in various cuprates suggest a simplified model with a single orbital of x [...] Read more.
We discuss a few possibilities of high- T c superconductivity with more than one orbital symmetry contributing to the pairing. First, we show that the high energies of orbital excitations in various cuprates suggest a simplified model with a single orbital of x 2 y 2 symmetry doped by holes. Next, several routes towards involving both e g orbital symmetries for doped holes are discussed: (i) some give superconductivity in a CuO 2 monolayer on Bi2212 superconductors, Sr 2 CuO 4 δ , Ba 2 CuO 4 δ , while (ii) others as nickelate heterostructures or Eu 2 x Sr x NiO 4 , could in principle realize it as well. At low electron filling of Ru ions, spin-orbital entangled states of t 2 g symmetry contribute in Sr 2 RuO 4 . Finally, electrons with both t 2 g and e g orbital symmetries contribute to the superconducting properties and nematicity of Fe-based superconductors, pnictides or FeSe. Some of them provide examples of orbital-selective Cooper pairing. Full article
(This article belongs to the Special Issue From cuprates to Room Temperature Superconductors)
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Open AccessArticle
High Precision Test of the Pauli Exclusion Principle for Electrons
Condens. Matter 2019, 4(2), 45; https://doi.org/10.3390/condmat4020045
Received: 6 March 2019 / Revised: 8 April 2019 / Accepted: 23 April 2019 / Published: 2 May 2019
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Abstract
The VIP-2 experiment aims to perform high precision tests of the Pauli Exclusion Principle for electrons. The method consists in circulating a continuous current in a copper strip, searching for the X radiation emission due to a prohibited transition (from the 2p level [...] Read more.
The VIP-2 experiment aims to perform high precision tests of the Pauli Exclusion Principle for electrons. The method consists in circulating a continuous current in a copper strip, searching for the X radiation emission due to a prohibited transition (from the 2p level to the 1s level of copper when this is already occupied by two electrons). VIP already set the best limit on the PEP violation probability for electrons 1 2 β 2 < 4.7 × 10 29 , the goal of the upgraded VIP-2 (VIolation of the Pauli Exclusion Principle-2) experiment is to improve this result of two orders of magnitude at least. The experimental apparatus and the results of the analysis of a first set of collected data will be presented. Full article
(This article belongs to the Special Issue High Precision X-Ray Measurements)
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Open AccessArticle
Electrostatic Interaction of Point Charges in Three-Layer Structures: The Classical Model
Condens. Matter 2019, 4(2), 44; https://doi.org/10.3390/condmat4020044
Received: 4 April 2019 / Revised: 27 April 2019 / Accepted: 29 April 2019 / Published: 2 May 2019
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Abstract
Electrostatic interaction energy W between two point charges in a three-layer plane system was calculated on the basis of the Green’s function method in the classical model of constant dielectric permittivities for all media involved. A regular method for the calculation of W [...] Read more.
Electrostatic interaction energy W between two point charges in a three-layer plane system was calculated on the basis of the Green’s function method in the classical model of constant dielectric permittivities for all media involved. A regular method for the calculation of W ( Z , Z , R ) , where Z and Z are the charge coordinates normal to the interfaces, and R the lateral (along the interfaces) distance between the charges, was proposed. The method consists in substituting the evaluation of integrals of rapidly oscillating functions over the semi-infinite interval by constructing an analytical series of inverse radical functions to a required accuracy. Simple finite-term analytical approximations of the dependence W ( Z , Z , R ) were proposed. Two especially important particular cases of charge configurations were analyzed in more detail: (i) both charges are in the same medium and Z = Z ; and (ii) the charges are located at different interfaces across the slab. It was demonstrated that the W dependence on the charge–charge distance S = R 2 + Z Z 2 differs from the classical Coulombic one W S 1 . This phenomenon occurs due to the appearance of polarization charges at both interfaces, which ascribes a many-body character to the problem from the outset. The results obtained testify, in particular, that the electron–hole interaction in heterostructures leading to the exciton formation is different in the intra-slab and across-slab charge configurations, which is usually overlooked in specific calculations related to the subject concerned. Our consideration clearly demonstrates the origin, the character, and the consequences of the actual difference. The often used Rytova–Keldysh approximation was analyzed. The cause of its relative success was explained, and the applicability limits were determined. Full article
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Open AccessArticle
Superconducting Properties of 3D Low-Density TI-Bipolaron Gas in Magnetic Field
Condens. Matter 2019, 4(2), 43; https://doi.org/10.3390/condmat4020043
Received: 27 December 2018 / Revised: 22 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
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Abstract
Consideration is given to thermodynamical properties of a three-dimensional Bose-condensate of translation-invariant bipolarons (TI-bipolarons) in magnetic field. The critical temperature of transition, critical magnetic fields, energy, heat capacity and the transition heat of TI-bipolaron gas are calculated. Such values as maximum magnetic field, [...] Read more.
Consideration is given to thermodynamical properties of a three-dimensional Bose-condensate of translation-invariant bipolarons (TI-bipolarons) in magnetic field. The critical temperature of transition, critical magnetic fields, energy, heat capacity and the transition heat of TI-bipolaron gas are calculated. Such values as maximum magnetic field, London penetration depth and their temperature dependencies are calculated. The results obtained are used to explain experiments on high-temperature superconductors. Full article
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Open AccessArticle
X-ray Detectors for Kaonic Atoms Research at DAΦNE
Condens. Matter 2019, 4(2), 42; https://doi.org/10.3390/condmat4020042
Received: 19 February 2019 / Revised: 19 April 2019 / Accepted: 21 April 2019 / Published: 25 April 2019
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Abstract
This article presents the kaonic atom studies performed at the INFN National Laboratory of Frascati (Laboratori Nazionali di Frascati dell’INFN, LNF-INFN) since the opening of this field of research at the DAΦNE collider in early 2000. Significant achievements have been obtained [...] Read more.
This article presents the kaonic atom studies performed at the INFN National Laboratory of Frascati (Laboratori Nazionali di Frascati dell’INFN, LNF-INFN) since the opening of this field of research at the DA Φ NE collider in early 2000. Significant achievements have been obtained by the DA Φ NE Exotic Atom Research (DEAR) and Silicon Drift Detector for Hadronic Atom Research by Timing Applications (SIDDHARTA) experiments on kaonic hydrogen, which have required the development of novel X-ray detectors. The 2019 installation of the new SIDDHARTA-2 experiment to measure kaonic deuterium for the first time has been made possible by further technological advances in X-ray detection. Full article
(This article belongs to the Special Issue High Precision X-Ray Measurements)
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Open AccessArticle
Structural Evolution of MoO3 Thin Films Deposited on Copper Substrates upon Annealing: An X-ray Absorption Spectroscopy Study
Condens. Matter 2019, 4(2), 41; https://doi.org/10.3390/condmat4020041
Received: 14 March 2019 / Revised: 13 April 2019 / Accepted: 15 April 2019 / Published: 18 April 2019
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Abstract
Structural changes of MoO3 thin films deposited on thick copper substrates upon annealing at different temperatures were investigated via ex situ X-Ray Absorption Spectroscopy (XAS). From the analysis of the X-ray Absorption Near-Edge Structure (XANES) pre-edge and Extended X-ray Absorption Fine Structure [...] Read more.
Structural changes of MoO3 thin films deposited on thick copper substrates upon annealing at different temperatures were investigated via ex situ X-Ray Absorption Spectroscopy (XAS). From the analysis of the X-ray Absorption Near-Edge Structure (XANES) pre-edge and Extended X-ray Absorption Fine Structure (EXAFS), we show the dynamics of the structural order and of the valence state. As-deposited films were mainly disordered, and ordering phenomena did not occur for annealing temperatures up to 300 °C. At ~350 °C, a dominant α-MoO3 crystalline phase started to emerge, and XAS spectra ruled out the formation of a molybdenum dioxide phase. A further increase of the annealing temperature to ~500 °C resulted in a complex phase transformation with a concurrent reduction of Mo6+ ions to Mo4+. These original results suggest the possibility of using MoO3 as a hard, protective, transparent, and conductive material in different technologies, such as accelerating copper-based devices, to reduce damage at high gradients. Full article
(This article belongs to the Special Issue High Precision X-Ray Measurements)
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Open AccessArticle
Discrete Geometry from Quantum Walks
Condens. Matter 2019, 4(2), 40; https://doi.org/10.3390/condmat4020040
Received: 28 February 2019 / Revised: 7 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
A particular family of Discrete Time Quantum Walks (DTQWs) simulating fermion propagation in 2D curved space-time is revisited. Usual continuous covariant derivatives and spin-connections are generalized into discrete covariant derivatives along the lattice coordinates and discrete connections. The concepts of metrics and 2-beins [...] Read more.
A particular family of Discrete Time Quantum Walks (DTQWs) simulating fermion propagation in 2D curved space-time is revisited. Usual continuous covariant derivatives and spin-connections are generalized into discrete covariant derivatives along the lattice coordinates and discrete connections. The concepts of metrics and 2-beins are also extended to the discrete realm. Two slightly different Riemann curvatures are then defined on the space-time lattice as the curvatures of the discrete spin connection. These two curvatures are closely related and one of them tends at the continuous limit towards the usual, continuous Riemann curvature. A simple example is also worked out in full. Full article
(This article belongs to the Special Issue Quantum Cellular Automata and Quantum Walks)
Open AccessArticle
Quantized Alternate Current on Curved Graphene
Condens. Matter 2019, 4(2), 39; https://doi.org/10.3390/condmat4020039
Received: 7 March 2019 / Revised: 3 April 2019 / Accepted: 6 April 2019 / Published: 9 April 2019
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Abstract
Based on the numerical solution of the Quantum Lattice Boltzmann Method in curved space, we predicted the onset of a quantized alternating current on curved graphene sheets. This numerical prediction was verified analytically via a set of semi-classical equations that related the Berry [...] Read more.
Based on the numerical solution of the Quantum Lattice Boltzmann Method in curved space, we predicted the onset of a quantized alternating current on curved graphene sheets. This numerical prediction was verified analytically via a set of semi-classical equations that related the Berry curvature to real space curvature. The proposed quantized oscillating current on curved graphene could form the basis for the implementation of quantum information-processing algorithms. Full article
(This article belongs to the Special Issue Quantum Cellular Automata and Quantum Walks)
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Open AccessArticle
Pyrolitic Graphite Mosaic Crystal Thickness and Mosaicity Optimization for an Extended Source Von Hamos X-ray Spectrometer
Condens. Matter 2019, 4(2), 38; https://doi.org/10.3390/condmat4020038
Received: 28 January 2019 / Revised: 15 March 2019 / Accepted: 29 March 2019 / Published: 3 April 2019
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Abstract
Bragg spectroscopy, one of the best established experimental techniques for high energy resolution X-ray measurements, has always been limited to the measurement of photons produced from well collimated (tens of microns) or point-like sources; recently, the VOXES collaboration at INFN National Laboratories of [...] Read more.
Bragg spectroscopy, one of the best established experimental techniques for high energy resolution X-ray measurements, has always been limited to the measurement of photons produced from well collimated (tens of microns) or point-like sources; recently, the VOXES collaboration at INFN National Laboratories of Frascati developed a prototype of a high resolution and high precision X-ray spectrometer working also with extended isotropic sources. The realized spectrometer makes use of Highly Annealed Pyrolitic Graphite (HAPG) crystals in a “semi”-Von Hamos configuration, in which the position detector is rotated with respect to the standard Von Hamos one, to increase the dynamic energy range, and shows energy resolutions at the level of 0.1% for photon energies up to 10 keV and effective source sizes in the range 400–1200 μ m in the dispersive plane. Such wide effective source dimensions are achieved using a double slit system to produce a virtual point-like source between the emitting target and the crystal. The spectrometer performances in terms of reflection efficiency and peak resolution depend on several parameters, among which a special role is played by the crystal mosaicity and thickness. In this work, we report the measurements of the Cu(K α 1 , 2 ) and the Fe(K α 1 , 2 ) lines performed with different mosaicity and thickness crystals in order to investigate the influence of the parameters on the peak resolution and on the reflection efficiency mentioned above. Full article
(This article belongs to the Special Issue High Precision X-Ray Measurements)
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Open AccessArticle
Ab Initio Study of the Electronic, Vibrational, and Mechanical Properties of the Magnesium Diboride Monolayer
Condens. Matter 2019, 4(2), 37; https://doi.org/10.3390/condmat4020037
Received: 15 March 2019 / Revised: 30 March 2019 / Accepted: 1 April 2019 / Published: 2 April 2019
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Abstract
Magnesium diboride gained significant interest in the materials science community after the discovery of its superconductivity, with an unusually high critical temperature of 39 K. Many aspects of the electronic properties and superconductivity of bulk MgB2 and thin sheets of MgB2 [...] Read more.
Magnesium diboride gained significant interest in the materials science community after the discovery of its superconductivity, with an unusually high critical temperature of 39 K. Many aspects of the electronic properties and superconductivity of bulk MgB 2 and thin sheets of MgB 2 have been determined; however, a single layer of MgB 2 has not yet been fully theoretically investigated. Here, we present a detailed study of the structural, electronic, vibrational, and elastic properties of monolayer MgB 2 , based on ab initio methods. First-principles calculations reveal the importance of reduction of dimensionality on the properties of MgB 2 and thoroughly describe the properties of this novel 2D material. The presence of a negative Poisson ratio, higher density of states at the Fermi level, and a good dynamic stability under strain make the MgB 2 monolayer a prominent material, both for fundamental research and application studies. Full article
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Open AccessArticle
Thermodynamic Stability, Thermoelectric, Elastic and Electronic Structure Properties of ScMN2-Type (M = V, Nb, Ta) Phases Studied by ab initio Calculations
Condens. Matter 2019, 4(2), 36; https://doi.org/10.3390/condmat4020036
Received: 17 February 2019 / Revised: 11 March 2019 / Accepted: 26 March 2019 / Published: 29 March 2019
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Abstract
ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb, but they have up to now not been much studied. However, based on the properties of binary ScN and its [...] Read more.
ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb, but they have up to now not been much studied. However, based on the properties of binary ScN and its alloys, it is reasonable to expect these phases to be of relevance in a range of applications, including thermoelectrics. Here, we have used first-principles calculations to study their thermodynamic stability, elastic, thermoelectric and electronic properties. We have used density functional theory to calculate lattice parameters, the mixing enthalpy of formation and electronic density of states as well as the thermoelectric properties and elastic constants (cij), bulk (B), shear (G) and Young’s (E) modulus, which were compared with available experimental data. Our results indicate that the considered systems are thermodynamically and elastically stable and that all are semiconductors with small band gaps. All three materials display anisotropic thermoelectric properties and indicate the possibility to tune these properties by doping. In particular, ScVN2, featuring the largest band gap exhibits a particularly large and strongly doping-sensitive Seebeck coefficient. Full article
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Open AccessArticle
Observing Dynamical Systems Using Magneto-Controlled Diffraction
Condens. Matter 2019, 4(2), 35; https://doi.org/10.3390/condmat4020035
Received: 26 February 2019 / Revised: 25 March 2019 / Accepted: 26 March 2019 / Published: 28 March 2019
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Abstract
Observing the light passing through a thin layer of ferrofluid, we can see the occurrence of interesting effects, both in the formation patterns within the ferrofluid layer and in the dispersion of light outside that layer. This leads us to ask what the [...] Read more.
Observing the light passing through a thin layer of ferrofluid, we can see the occurrence of interesting effects, both in the formation patterns within the ferrofluid layer and in the dispersion of light outside that layer. This leads us to ask what the explanations associated with these effects are. In this paper, we analyze and explain the occurrence of these luminous patterns using a Ferrolens, commercially known as a Ferrocell. We present details of our experimental apparatus, followed by a discussion of some properties of light polarization and its relation to the formation of magnetic contours produced by a Ferrolens. In addition, we present the observation of a magnetochiral effect in this system. Next, we propose an application of this experiment in dynamical systems. The dynamical system is the direct observation of diffracted lines in Ferrolens, a special case of a Hele-Shaw cell containing a transparent ferrofluid subjected to various light sources. Full article
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