Condensed Matter

1 pages, 510 KiB

Open AccessCorrection

Correction: Benedek et al. Measuring the Electron–Phonon Interaction in Two-Dimensional Superconductors with He-Atom Scattering. Condens. Matter 2020, 5, 79

by Giorgio Benedek, Joseph R. Manson, Salvador Miret-Artés, Adrian Ruckhofer, Wolfgang E. Ernst, Anton Tamtögl and Jan Peter Toennies

Condens. Matter 2021, 6(4), 54; https://doi.org/10.3390/condmat6040054 - 16 Dec 2021

Cited by 1 | Viewed by 1635

Abstract

In the original publication [...] Full article

10 pages, 2470 KiB

Open AccessArticle

Weak Ferromagnetism in a One-Orbital Double-Exchange Model with Ising Spins for Cerium Oxides

by Cengiz Şen

Condens. Matter 2021, 6(4), 53; https://doi.org/10.3390/condmat6040053 - 16 Dec 2021

Viewed by 2291

Abstract

Cerium oxides (ceria) are materials that exhibit weak, room-temperature ferromagnetism without d-electrons. The latter are usually responsible for magnetism in a variety of other oxide compounds, but the underlying mechanism for such a magnetic response in ceria without the d-electrons ( [...] Read more.

Cerium oxides (ceria) are materials that exhibit weak, room-temperature ferromagnetism without d-electrons. The latter are usually responsible for magnetism in a variety of other oxide compounds, but the underlying mechanism for such a magnetic response in ceria without the d-electrons (

d^{0}

-magnetism) is still under debate. A possible explanation is Zener double-exchange, where itinerant electrons polarize the localized spins via Hund-coupling as they hop from site to site. Here, we report magnetization and spin-spin correlation results using various values of the Hund-coupling in a one-orbital double-exchange model with Ising spins. In the real material with formula CeO

_{2 - x}

, the oxygen-deficient sites are denoted by x. These sites are related to the density of tetravalent cerium spins (the Ising spin background in our model), which we denoted as and set at

N = 0.50

in our simulations. Our results at this value of localized spin concentration show ferromagnetic tendencies at low carrier densities (

n = 0.25

). However, ferromagnetism is lost at intermediate carrier concentrations (

n = 0.50)

due to charge localization at high temperatures, as evident from density of states calculations and Monte Carlo snapshots. To our knowledge, our study based on a realistic Zener-type double exchange mechanism is a first in the study of magnetism in cerium oxides. Our results are also consistent with previous studies using similar Hamiltonians in the context of diluted magnetic semiconductors, where Heisenberg spins were used. Full article

(This article belongs to the Section Magnetism)

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14 pages, 495 KiB

Open AccessArticle

Evolution of Charge-Lattice Dynamics across the Kuramoto Synchronization Phase Diagram of Quantum Tunneling Polarons in Cuprate Superconductors

by Victor Velasco, Marcello B. Silva Neto, Andrea Perali, Sandro Wimberger, Alan R. Bishop and Steven D. Conradson

Condens. Matter 2021, 6(4), 52; https://doi.org/10.3390/condmat6040052 - 16 Dec 2021

Cited by 6 | Viewed by 2920

Abstract

Because of its sensitivity to the instantaneous structure factor, S(Q,t = 0), Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for probing the dynamic structure of condensed matter systems in which the charge and lattice dynamics are coupled. When applied to [...] Read more.

Because of its sensitivity to the instantaneous structure factor, S(Q,t = 0), Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for probing the dynamic structure of condensed matter systems in which the charge and lattice dynamics are coupled. When applied to hole-doped cuprate superconductors, EXAFS has revealed the presence of internal quantum tunneling polarons (IQTPs). An IQTP arises in EXAFS as a two-site distribution for certain Cu–O pairs, which is also duplicated in inelastic scattering but not observed in standard diffraction measurements. The Cu–Sr pair distribution has been found to be highly anharmonic and strongly correlated to both the IQTPs and to superconductivity, as, for example, in

{YSr}_{2} {Cu}_{2.75} {Mo}_{0.25} O_{7.54}

(T_{c} = 84

K). In order to describe such nontrivial, anharmonic charge-lattice dynamics, we have proposed a model Hamiltonian for a prototype six-atom cluster, in which two Cu-apical-O IQTPs are charge-transfer bridged through Cu atoms by an O atom in the

{CuO}_{2}

plane and are anharmonically coupled via a Sr atom. By applying an exact diagonalization procedure to this cluster, we have verified that our model indeed produces an intricate interplay between charge and lattice dynamics. Then, by using the Kuramoto model for the synchronization of coupled quantum oscillators, we have found a first-order phase transition for the IQTPs into a synchronized, phase-locked phase. Most importantly, we have shown that this transition results specifically from the anharmonicity. Finally, we have provided a phase diagram showing the onset of the phase-locking of IQTPs as a function of the charge-lattice and anharmonic couplings in our model. We have found that the charge, initially confined to the apical oxygens, is partially pumped into the

{CuO}_{2}

plane in the synchronized phase, which suggests a possible connection between the synchronized dynamic structure and high-temperature superconductivity (HTSC) in doped cuprates. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-Linear Phenomena in Superfluids and Superconductors VI)

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25 pages, 6858 KiB

Open AccessArticle

X-ray Micro-Tomography as a Method to Distinguish and Characterize Natural and Cultivated Pearls

by Luisa Vigorelli, Elisabetta Croce, Debora Angelici, Raffaella Navone, Sabrina Grassini, Laura Guidorzi, Alessandro Re and Alessandro Lo Giudice

Condens. Matter 2021, 6(4), 51; https://doi.org/10.3390/condmat6040051 - 13 Dec 2021

Cited by 6 | Viewed by 5416

Abstract

Digital radiography and computed tomography are two fundamental diagnostic techniques in different fields of research, including cultural heritage studies and gemmology. The application of these physical methods of investigation has gained considerable importance as they are non-invasive techniques. The presented work has been [...] Read more.

Digital radiography and computed tomography are two fundamental diagnostic techniques in different fields of research, including cultural heritage studies and gemmology. The application of these physical methods of investigation has gained considerable importance as they are non-invasive techniques. The presented work has been mainly focused on micro-tomographic analysis. The project is concerned with the study of natural and cultivated pearls in order to develop an investigation methodology for the analysis, distinction and characterization of different types of pearls, some of them belonging to different precious jewels from private collections. The investigations, carried out on a total of 22 heterogeneous types of pearls, allowed us to establish their origin (natural or cultivated) or to confirm/deny if a hypothesis was already expressed, and as well to highlight the cultivation methodology used case by case. Furthermore, it was possible to ascertain how large and varied the market for cultured pearls is nowadays and how difficult is, in some particular cases, to ascertain their attribution to a certain origin. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2021)

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24 pages, 3334 KiB

Open AccessReview

Extremely Overdoped Superconducting Cuprates via High Pressure Oxygenation Methods

by Linda Sederholm, Steven D. Conradson, Theodore H. Geballe, Chang-Qing Jin, Andrea Gauzzi, Edmondo Gilioli, Maarit Karppinen and Gianguido Baldinozzi

Condens. Matter 2021, 6(4), 50; https://doi.org/10.3390/condmat6040050 - 1 Dec 2021

Cited by 6 | Viewed by 3860

Abstract

Within the cuprate constellation, one fixed star has been the superconducting dome in the quantum phase diagram of transition temperature vs. the excess charge on the Cu in the CuO₂-planes, p, resulting from O-doping or cation substitution. However, a more [...] Read more.

Within the cuprate constellation, one fixed star has been the superconducting dome in the quantum phase diagram of transition temperature vs. the excess charge on the Cu in the CuO₂-planes, p, resulting from O-doping or cation substitution. However, a more extensive search of the literature shows that the loss of the superconductivity in favor of a normal Fermi liquid on the overdoped side should not be assumed. Many experimental results from cuprates prepared by high-pressure oxygenation show T_c converging to a fixed value or continuing to slowly increase past the upper limit of the dome of p = 0.26–0.27, up to the maximum amounts of excess oxygen corresponding to p values of 0.3 to > 0.6. These reports have been met with disinterest or disregard. Our review shows that dome-breaking trends for T_c are, in fact, the result of careful, accurate experimental work on a large number of compounds. This behavior most likely mandates a revision of the theoretical basis for high-temperature superconductivity. That excess O atoms located in specific, metastable sites in the crystal, attainable only with extreme O chemical activity under HPO conditions, cause such a radical extension of the superconductivity points to a much more substantial role for the lattice in terms of internal chemistry and bonding. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-Linear Phenomena in Superfluids and Superconductors VI)

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12 pages, 709 KiB

Open AccessArticle

Reliability of the Ginzburg–Landau Theory in the BCS-BEC Crossover by Including Gaussian Fluctuations for 3D Attractive Fermions

by Filippo Pascucci, Andrea Perali and Luca Salasnich

Condens. Matter 2021, 6(4), 49; https://doi.org/10.3390/condmat6040049 - 1 Dec 2021

Cited by 2 | Viewed by 2816

Abstract

We calculate the parameters of the Ginzburg–Landau (GL) equation of a three-dimensional attractive Fermi gas around the superfluid critical temperature. We compare different levels of approximation throughout the Bardeen–Cooper–Schrieffer (BCS) to the Bose–Einstein Condensate (BEC) regime. We show that the inclusion of Gaussian [...] Read more.

We calculate the parameters of the Ginzburg–Landau (GL) equation of a three-dimensional attractive Fermi gas around the superfluid critical temperature. We compare different levels of approximation throughout the Bardeen–Cooper–Schrieffer (BCS) to the Bose–Einstein Condensate (BEC) regime. We show that the inclusion of Gaussian fluctuations strongly modifies the values of the Ginzburg–Landau parameters approaching the BEC regime of the crossover. We investigate the reliability of the Ginzburg–Landau theory, with fluctuations, studying the behavior of the coherence length and of the critical rotational frequencies throughout the BCS-BEC crossover. The effect of the Gaussian fluctuations gives qualitative correct trends of the considered physical quantities from the BCS regime up to the unitary limit of the BCS-BEC crossover. Approaching the BEC regime, the Ginzburg–Landau equation with the inclusion of Gaussian fluctuations turns out to be unreliable. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-Linear Phenomena in Superfluids and Superconductors VI)

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7 pages, 1927 KiB

Open AccessArticle

Out-of-Plane Sulfur Distortions in the Bi₄O₄S₃ Superconductor

by Sharon S. Philip, Anushika Athauda, Yosuke Goto, Yoshikazu Mizuguchi and Despina Louca

Condens. Matter 2021, 6(4), 48; https://doi.org/10.3390/condmat6040048 - 26 Nov 2021

Viewed by 2590

Abstract

The local atomic structure of the non-magnetic layered superconductor Bi

_{4}

O

_{4}

S

_{3}

was investigated using neutron diffraction and pair density function (PDF) analysis. Although on average, the crystal structure is well ordered, evidence for local, out–of–plane sulfur distortions is provided, [...] Read more.

The local atomic structure of the non-magnetic layered superconductor Bi

_{4}

O

_{4}

S

_{3}

was investigated using neutron diffraction and pair density function (PDF) analysis. Although on average, the crystal structure is well ordered, evidence for local, out–of–plane sulfur distortions is provided, which may act as a conduit for charge transfer from the SO

_{4}

blocks into the superconducting BiS

_{2}

planes. In contrast with LaO

_{1 - x}

F

_{x}

BiS

_{2}

, no sulfur distortions were detected in the planes, which indicates that charge density wave fluctuations are not supported in Bi

_{4}

O

_{4}

S

_{3}

. Full article

(This article belongs to the Special Issue Quantum Complex Matter from Charge Density Waves to Superstripes)

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7 pages, 3307 KiB

Open AccessArticle

Silicon Drift Detectors’ Spectroscopic Response during the SIDDHARTA-2 Kaonic Helium Run at the DAΦNE Collider

by Marco Miliucci, Massimiliano Bazzi, Damir Bosnar, Mario Bragadireanu, Marco Carminati, Michael Cargnelli, Alberto Clozza, Catalina Curceanu, Griseld Deda, Luca De Paolis, Raffaele Del Grande, Carlo Fiorini, Carlo Guaraldo, Mihail Iliescu, Masahiko Iwasaki, Pietro King, Paolo Levi Sandri, Johann Marton, Paweł Moskal, Fabrizio Napolitano, Szymon Niedźwiecki, Kristian Piscicchia, Alessandro Scordo, Francesco Sgaramella, Hexi Shi, Michał Silarski, Diana Sirghi, Florin Sirghi, Magdalena Skurzok, Antonio Spallone, Marlene Tüchler, Oton Vazquez Doce and Johann Zmeskal Show full author list Hide full author list

Condens. Matter 2021, 6(4), 47; https://doi.org/10.3390/condmat6040047 - 25 Nov 2021

Cited by 11 | Viewed by 2878

Abstract

A large-area silicon drift detectors (SDDs) system has been developed by the SIDDHARTA-2 collaboration for high precision light kaonic atom X-ray spectroscopy at the DA

Φ

NE collider of Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Frascati. The SDDs’ geometry and electric field [...] Read more.

A large-area silicon drift detectors (SDDs) system has been developed by the SIDDHARTA-2 collaboration for high precision light kaonic atom X-ray spectroscopy at the DA

Φ

NE collider of Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali di Frascati. The SDDs’ geometry and electric field configuration, combined with their read-out electronics, make these devices suitable for performing high precision light kaonic atom spectroscopy measurements in the background of the DA

Φ

NE collider. This work presents the spectroscopic response of the SDDs system during the first exotic atoms run of SIDDHARTA-2 with kaonic helium, a preliminary to the kaonic deuterium data taking campaign. The SIDDHARTA-2 spectroscopic system has good energy resolution and a 2 μs timing window which rejects the asynchronous events, scaling the background by a factor of

10^{- 5}

. The results obtained for the first exotic atoms run of SIDDHARTA-2 prove this system to be ready to perform the challenging kaonic deuterium measurement. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2021)

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28 pages, 556 KiB

Open AccessArticle

How to Calculate Condensed Matter Electronic Structure Based on Multi-Electron Atom Semi-Classical Model

by Levan Chkhartishvili

Condens. Matter 2021, 6(4), 46; https://doi.org/10.3390/condmat6040046 - 25 Nov 2021

Viewed by 2635

Abstract

Atoms are proved to be semi-classical electronic systems in the sense of closeness of their exact quantum electron energy spectrum with that calculated within semi-classical approximation. Introduced semi-classical model of atom represents the wave functions of bounded in atom electrons in form of [...] Read more.

Atoms are proved to be semi-classical electronic systems in the sense of closeness of their exact quantum electron energy spectrum with that calculated within semi-classical approximation. Introduced semi-classical model of atom represents the wave functions of bounded in atom electrons in form of hydrogen-like atomic orbitals with explicitly defined effective charge numbers. The hydrogen-like electron orbitals of constituting condensed matter atoms are used to calculate the matrix elements of the secular equation determining the condensed matter electronic structure in the linear-combination-of-atomic-orbitals (LCAO) approach. Preliminary test calculations are conducted for boron B atom and diboron B₂ molecule electron systems. Full article

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11 pages, 1700 KiB

Open AccessArticle

Nanoscale Phase Separation of Incommensurate and Quasi-Commensurate Spin Stripes in Low Temperature Spin Glass of La_2−xSr_xNiO₄

by Gaetano Campi, Antonio Bianconi and Alessandro Ricci

Condens. Matter 2021, 6(4), 45; https://doi.org/10.3390/condmat6040045 - 23 Nov 2021

Cited by 4 | Viewed by 2824

Abstract

While spin striped phases in La_2−xSr_xNiO_4+y for 0.25 < x < 0.33 are the archetypal case of a 1D spin density wave (SDW) phase in doped antiferromagnetic strongly correlated perovskites, few information is available on the SDW spatial [...] Read more.

While spin striped phases in La_2−xSr_xNiO_4+y for 0.25 < x < 0.33 are the archetypal case of a 1D spin density wave (SDW) phase in doped antiferromagnetic strongly correlated perovskites, few information is available on the SDW spatial organization. In this context, we have measured the spatial variation of the wave vector of the SDW reflection profile by scanning micro X-ray diffractions with a coherent beam. We obtained evidence of a SDW order–disorder transition by lowering a high temperature phase (T > 50 K) to a low temperature phase (T < 50 K). We have identified quasi-commensurate spin stripe puddles in the ordered phase at 50 < T < 70 K, while the low temperature spin glassy phase presents a nanoscale phase separation of T = 30 K, with the coexistence of quasi-commensurate and incommensurate spin stripe puddles assigned to the interplay of quantum frustration and strong electronic correlations. Full article

(This article belongs to the Special Issue Quantum Complex Matter from Charge Density Waves to Superstripes)

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14 pages, 2851 KiB

Open AccessArticle

Majorana Zero Modes in Ferromagnetic Wires without Spin-Orbit Coupling

by Giorgos Livanas, Nikolaos Vanas and Georgios Varelogiannis

Condens. Matter 2021, 6(4), 44; https://doi.org/10.3390/condmat6040044 - 22 Nov 2021

Cited by 3 | Viewed by 2899

Abstract

We present a novel controllable platform for engineering Majorana zero modes. The platform consists of a ferromagnetic metallic wire placed among conventional superconductors, which are in proximity to ferromagnetic insulators. We demonstrate that Majorana zero modes emerge localised at the edges of the [...] Read more.

We present a novel controllable platform for engineering Majorana zero modes. The platform consists of a ferromagnetic metallic wire placed among conventional superconductors, which are in proximity to ferromagnetic insulators. We demonstrate that Majorana zero modes emerge localised at the edges of the ferromagnetic wire, due to the interplay of the applied supercurrents and the induced by proximity exchange fields with conventional superconductivity. Our mechanism does not rely on the pairing of helical fermions by combining conventional superconductivity with spin-orbit coupling, but rather exploits the misalignment between the magnetization of the ferromagnetic insulators and that of the ferromagnetic wire. Full article

(This article belongs to the Special Issue Feature Special Issue for Global Summit on Condensed Matter Physics)

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10 pages, 522 KiB

Open AccessArticle

Study of Multi-Pixel Scintillator Detector Configurations for Measuring Polarized Gamma Radiation

by Ana Marija Kožuljević, Damir Bosnar, Zdenka Kuncic, Mihael Makek, Siddharth Parashari and Petar Žugec

Condens. Matter 2021, 6(4), 43; https://doi.org/10.3390/condmat6040043 - 16 Nov 2021

Cited by 13 | Viewed by 3090

Abstract

When a positron annihilates, two gamma photons are created with orthogonal polarizations. It is possible to use coincidence measurements where both photons undergo Compton scattering to estimate their initial relative polarization orientation. This information is of great interest in gamma imaging systems, such [...] Read more.

When a positron annihilates, two gamma photons are created with orthogonal polarizations. It is possible to use coincidence measurements where both photons undergo Compton scattering to estimate their initial relative polarization orientation. This information is of great interest in gamma imaging systems, such as Positron Emission Tomography, where it may be used as an additional tool to distinguish true coincidence events from scatter and random background. The successful utilization of this principle critically depends on the detector’s angular and energy resolution, which determine its polarimetric performance. In this study, we use Monte Carlo simulations based on the Geant4 toolkit to model two multi-pixel detector configurations identified as prospective for the measurement of gamma-ray polarization in PET. One is based on 2 mm × 2 mm × 20 mm LYSO scintillators and the other is based on 3 mm × 3 mm × 20 mm GAGG scintillators. Each configuration has a pair of modules, each consisting of 64 crystals set up in a single 8 × 8 matrix, where both the recoil electron and the Compton-scattered photon are absorbed. We simulate positron annihilation by generating two back-to-back gamma photons of 511 keV with orthogonal polarizations. The Compton scattering is successfully identified and the modulation of the azimuthal angle difference is clearly observed. The configuration based on GAGG crystals demonstrates slightly better polarimetric performance than the one based on LYSO crystals, reflected in the more pronounced azimuthal modulation. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2021)

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10 pages, 555 KiB

Open AccessArticle

Uniformly Frustrated XY Model: Strengthening of the Vortex Lattice by Intrinsic Disorder

by Ilaria Maccari, Lara Benfatto and Claudio Castellani

Condens. Matter 2021, 6(4), 42; https://doi.org/10.3390/condmat6040042 - 6 Nov 2021

Cited by 3 | Viewed by 2642

Abstract

In superconducting films, the role of intrinsic disorder is typically to compete with superconductivity by fragmenting the global phase coherence and lowering the superfluid density. Nonetheless, when a transverse magnetic field is applied to the system and an Abrikosov vortex lattice form, the [...] Read more.

In superconducting films, the role of intrinsic disorder is typically to compete with superconductivity by fragmenting the global phase coherence and lowering the superfluid density. Nonetheless, when a transverse magnetic field is applied to the system and an Abrikosov vortex lattice form, the presence of disorder can actually strengthen the superconducting state against thermal fluctuations. By means of Monte Carlo simulations on the uniformly frustrated XY model in two dimensions, we show that while for weak pinning the superconducting critical temperature

T_{c}

increases with the applied field H, for strong enough pinning, the experimental decreasing dependence between

T_{c}

and H is recovered with a resulting more robust vortex lattice. Full article

(This article belongs to the Special Issue Fluctuations and Highly Non-Linear Phenomena in Superfluids and Superconductors VI)

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15 pages, 2319 KiB

Open AccessArticle

Probing Electron Properties in ECR Plasmas Using X-ray Bremsstrahlung and Fluorescence Emission

by Bharat Mishra, Angelo Pidatella, Alessio Galatà, Sandor Biri, Richard Rácz, Eugenia Naselli, Maria Mazzaglia, Giuseppe Torrisi and David Mascali

Condens. Matter 2021, 6(4), 41; https://doi.org/10.3390/condmat6040041 - 5 Nov 2021

Cited by 3 | Viewed by 2460

Abstract

A quantitative analysis of X-ray emission from an electron cyclotron resonance (ECR) plasma was performed to probe the spatial properties of electrons having energy for effective ionisation. A series of measurements were taken by INFN-LNS and ATOMKI, capturing spatially and spectrally resolved X-ray [...] Read more.

A quantitative analysis of X-ray emission from an electron cyclotron resonance (ECR) plasma was performed to probe the spatial properties of electrons having energy for effective ionisation. A series of measurements were taken by INFN-LNS and ATOMKI, capturing spatially and spectrally resolved X-ray maps as well as volumetric emissions from argon plasma. Comparing the former with model generated maps (involving space-resolved phenomenological electron energy distribution function and geometrical efficiency calculated using ray-tracing Monte Carlo (MC) routine) furnished information on structural aspects of the plasma. Similarly, fitting a model composed of bremsstrahlung and fluorescence to the volumetric X-ray spectrum provided valuable insight into the density and temperature of confined and lost electrons. The latter can be fed back to existing electron kinetics models for simulating more relevant energies, consequently improving theoretical X-ray maps and establishing the method as an excellent indirect diagnostic tool for warm electrons, required for both fundamental and applied research in ECR plasmas. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2021)

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9 pages, 2119 KiB

Open AccessReview

Functional Nanoscale Phase Separation and Intertwined Order in Quantum Complex Materials

by Gaetano Campi and Antonio Bianconi

Condens. Matter 2021, 6(4), 40; https://doi.org/10.3390/condmat6040040 - 5 Nov 2021

Cited by 8 | Viewed by 2630

Abstract

Nanoscale phase separation (NPS), characterized by particular types of correlated disorders, plays an important role in the functionality of high-temperature superconductors (HTS). Our results show that multiscale heterogeneity is an essential ingredient of quantum functionality in complex materials. Here, the interactions developing between [...] Read more.

Nanoscale phase separation (NPS), characterized by particular types of correlated disorders, plays an important role in the functionality of high-temperature superconductors (HTS). Our results show that multiscale heterogeneity is an essential ingredient of quantum functionality in complex materials. Here, the interactions developing between different structural units cause dynamical spatiotemporal conformations with correlated disorder; thus, visualizing conformational landscapes is fundamental for understanding the physical properties of complex matter and requires advanced methodologies based on high-precision X-ray measurements. We discuss the connections between the dynamical correlated disorder at nanoscale and the functionality in oxygen-doped perovskite superconducting materials. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2021)

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22 pages, 1320 KiB

Open AccessArticle

Connecting Complex Electronic Pattern Formation to Critical Exponents

by Shuo Liu, Erica W. Carlson and Karin A. Dahmen

Condens. Matter 2021, 6(4), 39; https://doi.org/10.3390/condmat6040039 - 4 Nov 2021

Cited by 5 | Viewed by 3165

Abstract

Scanning probes reveal complex, inhomogeneous patterns on the surface of many condensed matter systems. In some cases, the patterns form self-similar, fractal geometric clusters. In this paper, we advance the theory of criticality as it pertains to those geometric clusters (defined as connected [...] Read more.

Scanning probes reveal complex, inhomogeneous patterns on the surface of many condensed matter systems. In some cases, the patterns form self-similar, fractal geometric clusters. In this paper, we advance the theory of criticality as it pertains to those geometric clusters (defined as connected sets of nearest-neighbor aligned spins) in the context of Ising models. We show how data from surface probes can be used to distinguish whether electronic patterns observed at the surface of a material are confined to the surface, or whether the patterns originate in the bulk. Whereas thermodynamic critical exponents are derived from the behavior of Fortuin–Kasteleyn (FK) clusters, critical exponents can be similarly defined for geometric clusters. We find that these geometric critical exponents are not only distinct numerically from the thermodynamic and uncorrelated percolation exponents, but that they separately satisfy scaling relations at the critical fixed points discussed in the text. We furthermore find that the two-dimensional (2D) cross-sections of geometric clusters in the three-dimensional (3D) Ising model display critical scaling behavior at the bulk phase transition temperature. In particular, we show that when considered on a 2D slice of a 3D system, the pair connectivity function familiar from percolation theory displays more robust critical behavior than the spin-spin correlation function, and we calculate the corresponding critical exponent. We discuss the implications of these two distinct length scales in Ising models. We also calculate the pair connectivity exponent in the clean 2D case. These results extend the theory of geometric criticality in the clean Ising universality classes, and facilitate the broad application of geometric cluster analysis techniques to maximize the information that can be extracted from scanning image probe data in condensed matter systems. Full article

(This article belongs to the Special Issue Quantum Complex Matter from Charge Density Waves to Superstripes)

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16 pages, 437 KiB

Open AccessArticle

Charge Carriers Density, Temperature, and Electric Field Dependence of the Charge Carrier Mobility in Disordered Organic Semiconductors in Low Density Region

by Seyfan Kelil Shukri and Lemi Demeyu Deja

Condens. Matter 2021, 6(4), 38; https://doi.org/10.3390/condmat6040038 - 3 Nov 2021

Cited by 2 | Viewed by 4512

Abstract

We investigate the transport properties of charge carriers in disordered organic semiconductors using a model that relates a mobility with charge carriers (not with small polarons) hopping by thermal activation. Considering Miller and Abrahams expression for a hopping rate of a charge carrier [...] Read more.

We investigate the transport properties of charge carriers in disordered organic semiconductors using a model that relates a mobility with charge carriers (not with small polarons) hopping by thermal activation. Considering Miller and Abrahams expression for a hopping rate of a charge carrier between localized states of a Gaussian distributed energies, we employ Monte Carlo simulation methods, and calculate the average mobility of finite charge carriers focusing on a lower density region where the mobility was shown experimentally to be independent of the density. There are Monte Carlo simulation results for density dependence of mobility reported for hopping on regularly spaced states neglecting the role of spatial disorder, which does not fully mimic the hopping of charge carriers on randomly distributed states in disordered system as shown in recent publications. In this work we include the spatial disorder and distinguish the effects of electric field and density which are not separable in the experiment, and investigate the influence of density and electric field on mobility at different temperatures comparing with experimental results and that found in the absence of the spatial disorder. Moreover, we analyze the role of density and localization length on temperature and electric field dependence of mobility. Our results also give additional insight regarding the value of localization length that has been widely used as

0.1 b

where b is a lattice sites spacing. Full article

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9 pages, 3194 KiB

Open AccessArticle

Confocal Fluorescence Microscopy and Confocal Raman Microspectroscopy of X-ray Irradiated LiF Crystals

by Francesca Bonfigli, Sabina Botti, Angelica Cecilia, Rosa Maria Montereali, Enrico Nichelatti, Valentina Nigro, Massimo Piccinini and Maria Aurora Vincenti

Condens. Matter 2021, 6(4), 37; https://doi.org/10.3390/condmat6040037 - 20 Oct 2021

Cited by 3 | Viewed by 2874

Abstract

Radiation-induced color centers locally produced in lithium fluoride (LiF) are successfully used for radiation detectors. LiF detectors for extreme ultraviolet radiation, soft and hard X-rays, based on photoluminescence from aggregate electronic defects, are currently under development for imaging applications with laboratory radiation sources, [...] Read more.

Radiation-induced color centers locally produced in lithium fluoride (LiF) are successfully used for radiation detectors. LiF detectors for extreme ultraviolet radiation, soft and hard X-rays, based on photoluminescence from aggregate electronic defects, are currently under development for imaging applications with laboratory radiation sources, as well as large-scale facilities. Among the peculiarities of LiF-based detectors, noteworthy ones are their very high intrinsic spatial resolution across a large field of view, wide dynamic range, and versatility. LiF crystals irradiated with a monochromatic 8 keV X-ray beam at KIT synchrotron light source (Karlsruhe, Germany) and with the broadband white beam spectrum of the synchrotron bending magnet have been investigated by optical spectroscopy, laser scanning confocal microscopy in fluorescence mode, and confocal Raman micro-spectroscopy. The 3D reconstruction of the distributions of the color centers induced by the X-rays has been performed with both confocal techniques. The combination of the LiF crystal capability to register volumetric X-ray mapping with the optical sectioning operations of the confocal techniques has allowed performing 3D reconstructions of the X-ray colored volumes and it could provide advanced tools for 3D X-ray detection. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2021)

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14 pages, 1477 KiB

Open AccessArticle

A Parameter Refinement Method for Ptychography Based on Deep Learning Concepts

by Francesco Guzzi, George Kourousias, Alessandra Gianoncelli, Fulvio Billè and Sergio Carrato

Condens. Matter 2021, 6(4), 36; https://doi.org/10.3390/condmat6040036 - 14 Oct 2021

Cited by 11 | Viewed by 3543

Abstract

X-ray ptychography is an advanced computational microscopy technique, which is delivering exceptionally detailed quantitative imaging of biological and nanotechnology specimens, which can be used for high-precision X-ray measurements. However, coarse parametrisation in propagation distance, position errors and partial coherence frequently threaten the experimental [...] Read more.

X-ray ptychography is an advanced computational microscopy technique, which is delivering exceptionally detailed quantitative imaging of biological and nanotechnology specimens, which can be used for high-precision X-ray measurements. However, coarse parametrisation in propagation distance, position errors and partial coherence frequently threaten the experimental viability. In this work, we formally introduce these actors, solving the whole reconstruction as an optimisation problem. A modern deep learning framework was used to autonomously correct the setup incoherences, thus improving the quality of a ptychography reconstruction. Automatic procedures are indeed crucial to reduce the time for a reliable analysis, which has a significant impact on all the fields that use this kind of microscopy. We implemented our algorithm in our software framework, SciComPty, releasing it as open-source. We tested our system on both synthetic datasets, as well as on real data acquired at the TwinMic beamline of the Elettra synchrotron facility. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2021)

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Condens. Matter, Volume 6, Issue 4 (December 2021) – 19 articles

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