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Condens. Matter, Volume 5, Issue 2 (June 2020) – 14 articles

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Open AccessArticle
Superfluid Properties of Superconductors with Disorder at the Nanoscale: A Random Impedance Model
Condens. Matter 2020, 5(2), 36; https://doi.org/10.3390/condmat5020036 - 14 May 2020
Viewed by 341
Abstract
Some two-dimensional superconductors like, e.g., LaAlO 3 /SrTiO 3 heterostructures or thin films of transition metal dichalcogenides, display peculiar properties that can be understood in terms of electron inhomogeneity at the nanoscale. In this framework, unusual features of the metal-superconductor transition have been [...] Read more.
Some two-dimensional superconductors like, e.g., LaAlO 3 /SrTiO 3 heterostructures or thin films of transition metal dichalcogenides, display peculiar properties that can be understood in terms of electron inhomogeneity at the nanoscale. In this framework, unusual features of the metal-superconductor transition have been interpreted as due to percolative effects within a network of superconducting regions embedded in a metallic matrix. In this work we use a mean-field-like effective medium approach to investigate the superconducting phase below the critical temperature T c at which the resistivity vanishes. Specifically, we consider the finite frequency impedance of the system to extract the dissipative part of the conductance and the superfluid stiffness in the superconducting state. Intriguing effects arise from the metallic character of the embedding matrix: upon decreasing the temperature below T c proximity effects may rapidly increase the superfluid stiffness. Then, a rather fragile superconducting state, living on a filamentary network just below T c , can be substantially consolidated by additional superconducting regions induced by proximity effect in the interstitial metallic regions. This mean-field prediction should call for further theoretical analyses and trigger experimental investigations of the superconducting properties of the above systems. Full article
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Open AccessArticle
Static Kinks in Chains of Interacting Atoms
Condens. Matter 2020, 5(2), 35; https://doi.org/10.3390/condmat5020035 (registering DOI) - 13 May 2020
Viewed by 235
Abstract
We theoretically analyse the equation of topological solitons in a chain of particles interacting via a repulsive power-law potential and confined by a periodic lattice. Starting from the discrete model, we perform a gradient expansion and obtain the kink equation in the continuum [...] Read more.
We theoretically analyse the equation of topological solitons in a chain of particles interacting via a repulsive power-law potential and confined by a periodic lattice. Starting from the discrete model, we perform a gradient expansion and obtain the kink equation in the continuum limit for a power-law exponent n 1 . The power-law interaction modifies the sine-Gordon equation, giving rise to a rescaling of the coefficient multiplying the second derivative (the kink width) and to an additional integral term. We argue that the integral term does not affect the local properties of the kink, but it governs the behaviour at the asymptotics. The kink behaviour at the center is dominated by a sine-Gordon equation and its width tends to increase with the power law exponent. When the interaction is the Coulomb repulsion, in particular, the kink width depends logarithmically on the chain size. We define an appropriate thermodynamic limit and compare our results with existing studies performed for infinite chains. Our formalism allows one to systematically take into account the finite-size effects and also slowly varying external potentials, such as for instance the curvature in an ion trap. Full article
(This article belongs to the Special Issue Many Body Quantum Chaos)
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Open AccessArticle
Evaluation of Bunch Length by Measuring Coherent Synchrotron Radiation with a Narrow-Band Detector at LEBRA
Condens. Matter 2020, 5(2), 34; https://doi.org/10.3390/condmat5020034 - 09 May 2020
Viewed by 202
Abstract
This study presents a novel technology to measure electron bunch length with a high time resolution by measuring coherent synchrotron radiation using a narrow-band detector at Laboratory for Electron Beam Research and Application (LEBRA)—an S-band linear accelerator facility for free-electron lasers. The form [...] Read more.
This study presents a novel technology to measure electron bunch length with a high time resolution by measuring coherent synchrotron radiation using a narrow-band detector at Laboratory for Electron Beam Research and Application (LEBRA)—an S-band linear accelerator facility for free-electron lasers. The form factor was observed to decrease exponentially with charge—in concordance with the relationship between the intensity of the coherent synchrotron radiation and the magnitude of electron bunch charge—in the region in which the effect of electron bunch charge on bunch length is negligible. The calculated root-mean-square bunch length was observed to agree well with the value determined from the spectral shape obtained. The aforementioned results are expected to be useful in real-time observation of small changes in electron bunches in advanced accelerators. Full article
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Open AccessArticle
Proximity Array Device: A Novel Photon Detector Working in Long Wavelengths
Condens. Matter 2020, 5(2), 33; https://doi.org/10.3390/condmat5020033 - 01 May 2020
Viewed by 243
Abstract
We present here an innovative photon detector based on the proximity junction array device (PAD) working at long wavelengths. We show that the vortex dynamics in PAD undergoes a transition from a Mott insulator to a vortex metal state by application of an [...] Read more.
We present here an innovative photon detector based on the proximity junction array device (PAD) working at long wavelengths. We show that the vortex dynamics in PAD undergoes a transition from a Mott insulator to a vortex metal state by application of an external magnetic field. The PAD also evidences a Josephson I-V characteristic with the external field dependent tunneling current. At high applied currents, we observe a dissipative regime in which the vortex dynamics is dominated by the quasi-particle contribution from the normal metal. The PAD has a relatively high photo-response even at frequencies below the expected characteristic frequency while, its superconducting properties such as the order parameter and the Josephson characteristic frequency can be modulated via external fields to widen the detection band. This device represents a promising and reliable candidate for new high-sensitivity long-wavelength detectors. Full article
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Open AccessFeature PaperCommunication
Polaronic States and Superconductivity in WO3-x
Condens. Matter 2020, 5(2), 32; https://doi.org/10.3390/condmat5020032 - 01 May 2020
Viewed by 212
Abstract
Superconducting domain boundaries were found in WO3-x and doped WO3. The charge carriers in WO3-type materials were identified by Schirmer and Salje as bipolarons. Several previous attempts to determine the electronic properties of polarons in WO3 failed [...] Read more.
Superconducting domain boundaries were found in WO3-x and doped WO3. The charge carriers in WO3-type materials were identified by Schirmer and Salje as bipolarons. Several previous attempts to determine the electronic properties of polarons in WO3 failed until Bousque et al. (2020) reported a full first principle calculation of free polarons in WO3. They confirmed the model of Schirmer and Salje that each single polaron is centred around one tungsten position with surplus charges smeared over the adjacent eight tungsten positions. Small additional charges are distributed further apart. Further calculations to clarify the coupling mechanism between polaron to form bipolarons are not yet available. These calculations would help to identify the carrier distribution in Magneli clusters, which were shown recently to contain high carrier concentrations and may indicate totally localized superconductivity in non-percolating clusters. Full article
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Open AccessArticle
Effect of Inter-Well Interactions on Non-Linear Beam Splitters for Matter-Wave Interferometers
Condens. Matter 2020, 5(2), 31; https://doi.org/10.3390/condmat5020031 - 21 Apr 2020
Viewed by 239
Abstract
We study the non-linear beam splitter in matter-wave interferometers using ultracold quantum gases in a double-well configuration in presence of non-local interactions inducing inter-well density-density coupling, as they can be realized, e.g., with dipolar gases. We explore this effect after considering different input [...] Read more.
We study the non-linear beam splitter in matter-wave interferometers using ultracold quantum gases in a double-well configuration in presence of non-local interactions inducing inter-well density-density coupling, as they can be realized, e.g., with dipolar gases. We explore this effect after considering different input states, in the form of either coherent, or Twin-Fock, or NOON states. We first review the non-interacting limit and the case in which only the local interaction is present, including the study of sensitivity near the self-trapping threshold. Then, we consider the two-mode model in the presence of inter-well interactions and consider the scaling of the sensitivity as a function of the non-local coupling strength. Our analysis clearly shows that non-local interactions can compensate the degradation of the sensitivity induced by local interactions, so that they may be used to restore optimal sensitivity. Full article
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Open AccessReview
Translational-Invariant Bipolarons and Superconductivity
Condens. Matter 2020, 5(2), 30; https://doi.org/10.3390/condmat5020030 - 21 Apr 2020
Viewed by 265
Abstract
A translation-invariant (TI) bipolaron theory of superconductivity based, like Bardeen–Cooper–Schrieffer theory, on Fröhlich Hamiltonian is presented. Here the role of Cooper pairs belongs to TI bipolarons which are pairs of spatially delocalized electrons whose correlation length of a coupled state is small. The [...] Read more.
A translation-invariant (TI) bipolaron theory of superconductivity based, like Bardeen–Cooper–Schrieffer theory, on Fröhlich Hamiltonian is presented. Here the role of Cooper pairs belongs to TI bipolarons which are pairs of spatially delocalized electrons whose correlation length of a coupled state is small. The presence of Fermi surface leads to the stabilization of such states in its vicinity and a possibility of their Bose–Einstein condensation (BEC). The theory provides a natural explanation of the existence of a pseudogap phase preceding the superconductivity and enables one to estimate the temperature of a transition T * from a normal state to a pseudogap one. It is shown that the temperature of BEC of TI bipolarons determines the temperature of a superconducting transition T c which depends not on the bipolaron effective mass but on the ordinary mass of a band electron. This removes restrictions on the upper limit of T c for a strong electron-phonon interaction. A natural explanation is provided for the angular dependence of the superconducting gap which is determined by the angular dependence of the phonon spectrum. It is demonstrated that a lot of experiments on thermodynamic and transport characteristics, Josephson tunneling and angle-resolved photoemission spectroscopy (ARPES) of high-temperature superconductors does not contradict the concept of a TI bipolaron mechanism of superconductivity in these materials. Possible ways of enhancing T c and producing new room-temperature superconductors are discussed on the basis of the theory suggested. Full article
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Open AccessArticle
Nanostructured TiC Layer is Highly Suitable Surface for Adhesion, Proliferation and Spreading of Cells
Condens. Matter 2020, 5(2), 29; https://doi.org/10.3390/condmat5020029 - 10 Apr 2020
Viewed by 279
Abstract
Cell culture is usually performed in 2D polymer surfaces; however, several studies are conducted with the aim to screen functional coating molecules to find substrates more suitable for cell adhesion and proliferation. The aim of this manuscript is to compare the cell adhesion [...] Read more.
Cell culture is usually performed in 2D polymer surfaces; however, several studies are conducted with the aim to screen functional coating molecules to find substrates more suitable for cell adhesion and proliferation. The aim of this manuscript is to compare the cell adhesion and cytoskeleton organization of different cell types on different surfaces. Human primary fibroblasts, chondrocytes and osteoblasts isolated from patients undergoing surgery were seeded on polystyrene, poly-d-lysine-coated glass and titanium carbide slides and left to grow for several days. Then their cytoskeleton was analyzed, both by staining cells with phalloidin, which highlights actin fibers, and using Atomic Force Microscopy. We also monitored the production of Fibroblast Growth Factor-2, Bone Morphogenetic Protein-2 and Osteocalcin, using ELISA, and we highlighted production of Collagen type I in fibroblasts and osteoblasts and Collagen type II in chondrocytes by immunofluorescences. Fibroblasts, chondrocytes and osteoblasts showed both an improved proliferative activity and a good adhesion ability when cultured on titanium carbide slides, compared to polystyrene and poly-d-lysine-coated glass. In conclusion, we propose titanium carbide as a suitable surface to cultivate cells such as fibroblasts, chondrocytes and osteoblasts, allowing the preservation of their differentiated state and good adhesion properties. Full article
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Open AccessArticle
Infrared Synchrotron Radiation and Its Application to the Analysis of Cultural Heritage
Condens. Matter 2020, 5(2), 28; https://doi.org/10.3390/condmat5020028 - 09 Apr 2020
Viewed by 168
Abstract
Infrared synchrotron radiation (IR-SR) is a broad-band light source. Its brilliance is the main advantage for microspectroscopy experiments, when the limited size of the sample often prevents the use of conventional thermal radiation sources. Cultural heritage materials are delicate and valuable; therefore, nondestructive [...] Read more.
Infrared synchrotron radiation (IR-SR) is a broad-band light source. Its brilliance is the main advantage for microspectroscopy experiments, when the limited size of the sample often prevents the use of conventional thermal radiation sources. Cultural heritage materials are delicate and valuable; therefore, nondestructive experiments are usually preferred. Nevertheless, sometimes, small pieces can be acquired in the process of preservation and conservation. These samples are analyzed by various experimental techniques and give information about the original material and current condition. In this paper, four attempts to analyze cultural heritage materials are introduced. All these experiments are performed at the microspectroscopy station of IR beamline BL43IR in SPring-8. Full article
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Open AccessReview
Superconductivity in La2O2M4S6 -Type Bi-based Compounds: A Review on Element Substitution Effects
Condens. Matter 2020, 5(2), 27; https://doi.org/10.3390/condmat5020027 - 06 Apr 2020
Viewed by 270
Abstract
Since 2012, layered compounds containing Bi-Ch (Ch: S and Se) layers have been extensively studied in the field of superconductivity. The most-studied system is BiS2-based superconductors with two-layer-type conducting layers. Recently, superconductivity was observed in La2O [...] Read more.
Since 2012, layered compounds containing Bi-Ch (Ch: S and Se) layers have been extensively studied in the field of superconductivity. The most-studied system is BiS2-based superconductors with two-layer-type conducting layers. Recently, superconductivity was observed in La2O2M2S6 (M = metals), which contains four-layer-type conducting layers. The four-layer-type Bi-based superconductors are new systems in the family of Bi-based superconductors; we can expect further development of Bi-based layered superconductors. In this review article, we summarize the progress of synthesis, structural analysis, investigations on superconducting properties, and material design of the four-layer-type Bi-based superconductors. In-plane chemical pressure is the factor essential for the emergence of bulk superconductivity in the system. The highest Tc of 4.1 K was observed in Rare Earth elements (RE) substituted La2-xRExO2Bi3Ag0.6Sn0.4S6. Full article
(This article belongs to the Special Issue Layered Superconductors II)
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Open AccessArticle
Classical and Quantum Signatures of Quantum Phase Transitions in a (Pseudo) Relativistic Many-Body System
Condens. Matter 2020, 5(2), 26; https://doi.org/10.3390/condmat5020026 - 04 Apr 2020
Viewed by 380
Abstract
We identify a (pseudo) relativistic spin-dependent analogue of the celebrated quantum phase transition driven by the formation of a bright soliton in attractive one-dimensional bosonic gases. In this new scenario, due to the simultaneous existence of the linear dispersion and the bosonic nature [...] Read more.
We identify a (pseudo) relativistic spin-dependent analogue of the celebrated quantum phase transition driven by the formation of a bright soliton in attractive one-dimensional bosonic gases. In this new scenario, due to the simultaneous existence of the linear dispersion and the bosonic nature of the system, special care must be taken with the choice of energy region where the transition takes place. Still, due to a crucial adiabatic separation of scales, and identified through extensive numerical diagonalization, a suitable effective model describing the transition is found. The corresponding mean-field analysis based on this effective model provides accurate predictions for the location of the quantum phase transition when compared against extensive numerical simulations. Furthermore, we numerically investigate the dynamical exponents characterizing the approach from its finite-size precursors to the sharp quantum phase transition in the thermodynamic limit. Full article
(This article belongs to the Special Issue Many Body Quantum Chaos)
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Open AccessReview
THz Pulsed Imaging in Biomedical Applications
Condens. Matter 2020, 5(2), 25; https://doi.org/10.3390/condmat5020025 - 01 Apr 2020
Cited by 1 | Viewed by 328
Abstract
Recent advances in technology have allowed the production and the coherent detection of sub-ps pulses of terahertz (THz) radiation. Therefore, the potentialities of this technique have been readily recognized for THz spectroscopy and imaging in biomedicine. In particular, THz pulsed imaging (TPI) has [...] Read more.
Recent advances in technology have allowed the production and the coherent detection of sub-ps pulses of terahertz (THz) radiation. Therefore, the potentialities of this technique have been readily recognized for THz spectroscopy and imaging in biomedicine. In particular, THz pulsed imaging (TPI) has rapidly increased its applications in the last decade. In this paper, we present a short review of TPI, discussing its basic principles and performances, and its state-of-the-art applications on biomedical systems. Full article
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Open AccessArticle
Cross-Correlation of THz Pulses from the Electron Storage Ring BESSY II
Condens. Matter 2020, 5(2), 24; https://doi.org/10.3390/condmat5020024 - 27 Mar 2020
Viewed by 264
Abstract
Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. [...] Read more.
Coherent synchrotron radiation from an electron storage ring is observed in the THz spectral range when the bunch length is shortened down to the sub-mm-range. With increasing stored current, the bunch becomes longitudinally unstable and modulates the THz emission in the time domain. These micro-instabilities are investigated at the electron storage ring BESSY II by means of cross-correlation of the THz fields from successive bunches. The investigations allow deriving the longitudinal length scale of the micro bunch fluctuations and show that it grows faster than the current-dependent bunch length. Our findings will help to set the limits for the possible time resolution for pump-probe experiments achieved with coherent THz synchrotron radiation from a storage ring. Full article
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Open AccessCommunication
Ostwald Growth Rate in Controlled Covid-19 Epidemic Spreading as in Arrested Growth in Quantum Complex Matter
Condens. Matter 2020, 5(2), 23; https://doi.org/10.3390/condmat5020023 - 27 Mar 2020
Viewed by 1721
Abstract
Here, we focus on the data analysis of the growth of epidemic spread of Covid-19 in countries where different policies of containment were activated. It is known that the growth of pandemic spread at its threshold is exponential, but it is not known [...] Read more.
Here, we focus on the data analysis of the growth of epidemic spread of Covid-19 in countries where different policies of containment were activated. It is known that the growth of pandemic spread at its threshold is exponential, but it is not known how to quantify the success of different containment policies. We identify that a successful approach gives an arrested phase regime following the Ostwald growth, where, over the course of time, one phase transforms into another metastable phase with a similar free energy as observed in oxygen interstitial diffusion in quantum complex matter and in crystallization of proteins. We introduce the s factor which provides a quantitative measure of the efficiency and speed of the adopted containment policy, which is very helpful not only to monitor the Covid-19 pandemic spread but also for other countries to choose the best containment policy. The results show that a policy based on joint confinement, targeted tests, and tracking positive cases is the most rapid pandemic containment policy; in fact, we found values of 9, 5, and 31 for the success s factor for China, South Korea, and Italy, respectively, where the lowest s factor indicates the best containment policy. Full article
(This article belongs to the Special Issue Quantum Complex Matter 2020)
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