Condensed Matter

14 pages, 1835 KiB

Open AccessEditor’s ChoiceArticle

Magnetic and Electronic Inhomogeneity in Sm_1−xEu_xB₆

by M. Victoria Ale Crivillero, Priscila F. S. Rosa, Zachary Fisk, Jens Müller, Pedro Schlottmann and Steffen Wirth

Condens. Matter 2024, 9(4), 55; https://doi.org/10.3390/condmat9040055 - 13 Dec 2024

Cited by 1 | Viewed by 1347

Abstract

While SmB₆ attracts attention as a possible topological Kondo insulator, EuB₆ is known to host magnetic polarons that give rise to large magnetoresistive effects above its ferromagnetic order transition. Here, we investigate single crystals of Sm_1−xEu_xB₆ [...] Read more.

While SmB₆ attracts attention as a possible topological Kondo insulator, EuB₆ is known to host magnetic polarons that give rise to large magnetoresistive effects above its ferromagnetic order transition. Here, we investigate single crystals of Sm_1−xEu_xB₆ by magnetic and magnetotransport measurements to explore a possible interplay of these two intriguing phenomena, with a focus on the Eu-rich substitutions. Sm_0.01Eu_0.99B₆ exhibits generally similar behavior as EuB₆. Interestingly, Sm_0.05Eu_0.95B₆ combines a global antiferromagnetic order with local polaron formation. A pronounced hysteresis is found in the magnetoresistance of Sm_0.1Eu_0.9B₆ at low temperature (

T =

1.9 K) and applied magnetic fields between 2.3 and 3.6 T. The latter is in agreement with a phenomenological model that predicts the stabilization of ferromagnetic polarons with an increasing magnetic field within materials with a global antiferromagnetic order. Full article

(This article belongs to the Special Issue Superstripes Physics, 3rd Edition)

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12 pages, 1360 KiB

Open AccessEditor’s ChoiceArticle

Enhancing Spectroscopic Experiment Calibration through Differentiable Programming

by Fabrizio Napolitano

Condens. Matter 2024, 9(2), 26; https://doi.org/10.3390/condmat9020026 - 5 Jun 2024

Cited by 1 | Viewed by 1339

Abstract

In this work, we present an innovative calibration technique leveraging differentiable programming to enhance energy resolution and reduce the energy scale systematic uncertainty in X-ray spectroscopic experiments. This approach is demonstrated using synthetic data and is applicable in general to various spectroscopic measurements. [...] Read more.

In this work, we present an innovative calibration technique leveraging differentiable programming to enhance energy resolution and reduce the energy scale systematic uncertainty in X-ray spectroscopic experiments. This approach is demonstrated using synthetic data and is applicable in general to various spectroscopic measurements. This method extends the scope of differentiable programming for calibration, employing Kernel Density Estimation (KDE) to achieve a target Probability Density Function (PDF) for a fully differentiable model of the calibration. To assess the effectiveness of the calibration, we conduct a toy simulation replicating the entire detector response chain and compare it with a standard calibration. This ensures a robust and reliable calibration methodology, holding promise for improving energy resolution and providing a more versatile and efficient approach without the need for extensive fine-tuning. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2023)

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16 pages, 329 KiB

Open AccessEditor’s ChoiceArticle

The Effective Potential of Scalar Pseudo-Quantum Electrodynamics in (2 + 1)D

by Leandro O. Nascimento, Carlos A. P. C. Junior and José R. Santos

Condens. Matter 2024, 9(2), 25; https://doi.org/10.3390/condmat9020025 - 30 May 2024

Viewed by 1729

Abstract

The description of the electron–electron interactions in two-dimensional materials has a dimensional mismatch, where electrons live in (2 + 1)D while photons propagate in (3 + 1)D. In order to define an action in (2 + 1)D, one may perform a dimensional reduction [...] Read more.

The description of the electron–electron interactions in two-dimensional materials has a dimensional mismatch, where electrons live in (2 + 1)D while photons propagate in (3 + 1)D. In order to define an action in (2 + 1)D, one may perform a dimensional reduction of quantum electrodynamics in (3 + 1)D (QED4) into pseudo-quantum electrodynamics (PQED). The main difference between this model and QED4 is the presence of a pseudo-differential operator in the Maxwell term. However, besides the Coulomb repulsion, electrons in a material are subjected to several microscopic interactions, which are inherent in a many-body system. These are expected to reduce the range of the Coulomb potential, leading to a short-range interaction. Here, we consider the coupling to a scalar field in PQED for explaining such a mechanism, which resembles the spontaneous symmetry breaking (SSB) in Abelian gauge theories. In order to do so, we consider two cases: (i) by coupling the quantum electrodynamics to a Higgs field in (3 + 1)D and, thereafter, performing the dimensional reduction; and (ii) by coupling a Higgs field to the gauge field in PQED and, subsequently, calculating its effective potential. In case (i), we obtain a model describing electrons interacting through the Yukawa potential and, in case (ii), we show that SSB does not occur at one-loop approximation. The relevance of the model for describing electronic interactions in two-dimensional materials is also addressed. Full article

(This article belongs to the Special Issue PQED: 30 Years of Reduced Quantum Electrodynamics)

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11 pages, 543 KiB

Open AccessEditor’s ChoiceArticle

A Theoretical Study of Doping Evolution of Phonons in High-Temperature Cuprate Superconductors

by Saheli Sarkar

Condens. Matter 2024, 9(1), 13; https://doi.org/10.3390/condmat9010013 - 6 Feb 2024

Cited by 1 | Viewed by 2476

Abstract

Hole-doped high-temperature copper oxide-based superconductors (cuprates) exhibit complex phase diagrams where electronic orders like a charge density wave (CDW) and superconductivity (SC) appear at low temperatures. The origins of these electronic orders are still open questions due to their complex interplay and correlated [...] Read more.

Hole-doped high-temperature copper oxide-based superconductors (cuprates) exhibit complex phase diagrams where electronic orders like a charge density wave (CDW) and superconductivity (SC) appear at low temperatures. The origins of these electronic orders are still open questions due to their complex interplay and correlated nature. These electronic orders can modify the phonons in the system, which has also been experimentally found in several cuprates as a softening in the phonon frequency at the CDW vector. Recent experiments have revealed that the softening in phonons in cuprates due to CDW shows intriguing behavior with increasing hole doping. Hole doping can also change the underlying Fermi surface. Therefore, it is an interesting question whether the doping-induced change in the Fermi surface can affect the softening of phonons, which in turn can reveal the nature of the electronic orders present in the system. In this work, we investigate this question by studying the softening of phonons in the presence of CDW and SC within a perturbative approach developed in an earlier work. We compare the results obtained within the working model to some experiments. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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13 pages, 674 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Shrinking Fermi Liquid Scenario for Strange-Metal Behavior from Overdamped Optical Phonons

by Giovanni Mirarchi, Marco Grilli, Götz Seibold and Sergio Caprara

Condens. Matter 2024, 9(1), 14; https://doi.org/10.3390/condmat9010014 - 6 Feb 2024

Cited by 2 | Viewed by 1911

Abstract

We discuss how the interaction of electrons with an overdamped optical phonon can give rise to a strange-metal behavior over extended temperature and frequency ranges. Although the mode has a finite frequency, an increasing damping shifts spectral weight to progressively lower energies so [...] Read more.

We discuss how the interaction of electrons with an overdamped optical phonon can give rise to a strange-metal behavior over extended temperature and frequency ranges. Although the mode has a finite frequency, an increasing damping shifts spectral weight to progressively lower energies so that despite the ultimate Fermi liquid character of the system at the lowest temperatures and frequencies, the transport and optical properties of the electron system mimic a marginal Fermi liquid behavior. Within this shrinking Fermi liquid scenario, we extensively investigate the electron self-energy in all frequency and temperature ranges, emphasizing similarities and differences with respect to the marginal Fermi liquid scenario. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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8 pages, 252 KiB

Open AccessEditor’s ChoiceArticle

On the Importance of Future, Precise, X-ray Measurements in Kaonic Atoms

by Sławomir Wycech and Kristian Piscicchia

Condens. Matter 2024, 9(1), 4; https://doi.org/10.3390/condmat9010004 - 11 Jan 2024

Cited by 1 | Viewed by 2052

Abstract

Progress in the construction of precise X-ray detectors allows measurements of energies and widths of “upper levels” in K⁻ mesic atoms. These can be used to determine sub-threshold Kaon-nucleon amplitudes, which are important in investigations of nuclear states of these mesons. The [...] Read more.

Progress in the construction of precise X-ray detectors allows measurements of energies and widths of “upper levels” in K⁻ mesic atoms. These can be used to determine sub-threshold Kaon-nucleon amplitudes, which are important in investigations of nuclear states of these mesons. The special case of the 2P state in Kaonic Helium is discussed and used to check the properties of the K⁻ proton quasi-bound state. Similar attempts in other elements indicate a need for new, precise measurements. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2023)

11 pages, 1505 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Different Methods for Evaluating Quantitative X-ray Fluorescence Data in Copper-Based Artefacts

by Eleni Konstantakopoulou, Annalaura Casanova Municchia, Loredana Luvidi and Marco Ferretti

Condens. Matter 2024, 9(1), 5; https://doi.org/10.3390/condmat9010005 - 11 Jan 2024

Cited by 6 | Viewed by 3616

Abstract

Handheld X-ray Fluorescence devices (HH-XRF) have given archaeologists and conservators the opportunity to study a wide range of materials encountered in their work with great accessibility and flexibility. The investigation of copper-based artefacts is a frequent application of these instruments in the field [...] Read more.

Handheld X-ray Fluorescence devices (HH-XRF) have given archaeologists and conservators the opportunity to study a wide range of materials encountered in their work with great accessibility and flexibility. The investigation of copper-based artefacts is a frequent application of these instruments in the field of cultural heritage as it gives direct and rapid quantitative results that can provide very important information about them, such as their fabrication technology. This paper discusses the comparison of quantitative results, obtained by a commercial handheld XRF device “Bruker Tracer 5g” on certified standards, compositionally significant in copper-based alloys of interest in the field of cultural heritage. The measured elemental concentrations were derived using three different calibrations, which were examined for their accuracy. Two of them were based on the empirical coefficients approach, performed by the built-in calibration/software (copper alloy calibrations provided by Bruker manufacturer and the Bruker EasyCal software), while the third one was performed off-line by processing the spectra with an independent fundamental parameters (FP) software (PyMca version 5.9.2., a X-ray fluorescence analysis software developed at the European Synchrotron Radiation Facility). The results highlight that although HH-XRF devices simplify data collection, for optimal quantitative results, the correct choice of analysis conditions and calibration method still requires a detailed understanding of the principles of X-ray spectrometry. Full article

(This article belongs to the Special Issue High Precision X-ray Measurements 2023)

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14 pages, 510 KiB

Open AccessEditor’s ChoiceArticle

Topological Gauge Theory of Josephson Junction Arrays: The Discovery of Superinsulation

by Maria Cristina Diamantini

Condens. Matter 2023, 8(4), 97; https://doi.org/10.3390/condmat8040097 - 16 Nov 2023

Viewed by 2144

Abstract

We review the topological gauge theory description of Josephson junction arrays (JJA), fabricated systems which exhibit the superconductor-to-insulator transition (SIT). This description revealed the topological nature of the phases around the SIT and led to the discovery of a new state of matter, [...] Read more.

We review the topological gauge theory description of Josephson junction arrays (JJA), fabricated systems which exhibit the superconductor-to-insulator transition (SIT). This description revealed the topological nature of the phases around the SIT and led to the discovery of a new state of matter, the superinsulator, characterized by infinite resistance, even at finite temperatures, due to linear confinement of electric charges. This discovery is particularly relevant for the physics of superconducting films with emergent granularity, which are modeled with JJAs and share the same phase diagram. Full article

(This article belongs to the Special Issue Selected Papers from the 8th International Conference on Superconductivity and Magnetism (ICSM2023))

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9 pages, 1663 KiB

Open AccessEditor’s ChoiceArticle

The Superconducting Dome in Artificial High-T_c Superlattices Tuned at the Fano–Feshbach Resonance by Quantum Design

by Gennady Logvenov, Nicolas Bonmassar, Georg Christiani, Gaetano Campi, Antonio Valletta and Antonio Bianconi

Condens. Matter 2023, 8(3), 78; https://doi.org/10.3390/condmat8030078 - 6 Sep 2023

Cited by 7 | Viewed by 2662

Abstract

While the search for new high-temperature superconductors had been driven by the empirical “trials and errors” method for decades, we now report the synthesis of Artificial High-T_c Superlattices (AHTS) designed by quantum mechanics theory at the nanoscale. This discovery paves the [...] Read more.

While the search for new high-temperature superconductors had been driven by the empirical “trials and errors” method for decades, we now report the synthesis of Artificial High-T_c Superlattices (AHTS) designed by quantum mechanics theory at the nanoscale. This discovery paves the way for engineering a new class of high-temperature superconductors, following the predictions of the Bianconi Perali Valletta (BPV) theory recently implemented in 2022 by Mazziotti et al. including Rashba spin-orbit coupling to create nanoscale AHTS composed of quantum wells. The high-T_c superconducting properties within these superlattices are controlled by a conformational parameter of the superlattice geometry, specifically, the ratio L/d which represents the thickness of La₂CuO₄ layers (L) relative to the superlattice period (d). Using molecular beam epitaxy, we have successfully grown numerous AHTS samples. These samples consist of initial layers of stoichiometric La₂CuO₄ units with a thickness L, doped by interface space charge, and intercalated with second layers of non-superconducting metallic material, La_1.55Sr_0.45CuO₄ with thickness denoted as W = d − L. This configuration forms a quantum superlattice with periodicity d. The agreement observed between the experimental dependence T_c (the superconducting transition temperature) versus L/d ratio and the predictions of the BPV theory for AHTS in the form of the superconducting dome validates the hypothesis that the superconducting dome arises from the Fano–Feshbach or shape resonance in multigap superconductivity driven by quantum nanoscale confinement. Full article

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17 pages, 6567 KiB

Open AccessEditor’s ChoiceArticle

Superconducting Stiffness and Coherence Length of FeSe_0.5Te_0.5 Measured in a Zero-Applied Field

by Amotz Peri, Itay Mangel and Amit Keren

Condens. Matter 2023, 8(2), 39; https://doi.org/10.3390/condmat8020039 - 23 Apr 2023

Cited by 2 | Viewed by 3363

Abstract

Superconducting stiffness

ρ_{s}

and coherence length

ξ

are usually determined by measuring the penetration depth

λ

of a magnetic field and the upper critical field

H_{c 2}

of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could [...] Read more.

Superconducting stiffness

ρ_{s}

and coherence length

ξ

are usually determined by measuring the penetration depth

λ

of a magnetic field and the upper critical field

H_{c 2}

of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could lead to erroneous results, since the internal field could be very different from the applied one. To overcome this problem in Fe

_{1 + y}

Se

_{x}

Te

_{1 - x}

with

x \sim 0.5

and

y \sim 0

(FST), we measured both quantities with the Stiffnessometer technique. In this technique, one applies a rotor-free vector potential

A

to a superconducting ring and measures the current density

j

via the ring’s magnetic moment

m

.

ρ_{s}

and

ξ

are determined from London’s equation,

j = - ρ_{s} A

, and its range of validity. This method is particularly accurate at temperatures close to the critical temperature

T_{c}

. We find weaker

ρ_{s}

and longer

ξ

than existing literature reports, and critical exponents which agree better with expectations based on the Ginzburg–Landau theory. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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7 pages, 2421 KiB

Open AccessEditor’s ChoiceProject Report

Effects of Focused Ion Beam Lithography on La_2−xSr_xCuO₄ Single Crystals

by Roberta Caruso, Fernando Camino, Genda Gu, John M. Tranquada, Myung-Geun Han, Yimei Zhu, Anthony T. Bollinger and Ivan Božović

Condens. Matter 2023, 8(2), 35; https://doi.org/10.3390/condmat8020035 - 13 Apr 2023

Cited by 2 | Viewed by 2389

Abstract

Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La_2−xSr_xCuO₄ (LSCO) thin films triggered the [...] Read more.

Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La_2−xSr_xCuO₄ (LSCO) thin films triggered the search for the same phenomenon in bulk LSCO crystals. With this motivation, we have systematically explored FIB patterning of bulk LSCO crystals into micro-devices suitable for longitudinal and transverse resistivity measurements. We found that several detrimental factors can affect the result, ultimately compromising the possibility of effectively using FIB milling to fabricate sub-micrometer LSCO devices, especially in the underdoped regime. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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10 pages, 1003 KiB

Open AccessEditor’s ChoiceArticle

Elucidation of Spin-Correlations, Fermi Surface and Pseudogap in a Copper Oxide Superconductor

by Hiroshi Kamimura, Masaaki Araidai, Kunio Ishida, Shunichi Matsuno, Hideaki Sakata, Kenji Sasaoka, Kenji Shiraishi, Osamu Sugino, Jaw-Shen Tsai and Kazuyoshi Yamada

Condens. Matter 2023, 8(2), 33; https://doi.org/10.3390/condmat8020033 - 4 Apr 2023

Cited by 2 | Viewed by 2682

Abstract

First-principles calculations for underdoped La_2−xSr_xCuO₄ (LSCO) have revealed a Fermi surface consisting of spin-triplet (KS) particles at the antinodal Fermi-pockets and spin-singlet (SS) particles at the nodal Fermi-arcs in the presence of AF local order. By performing [...] Read more.

First-principles calculations for underdoped La_2−xSr_xCuO₄ (LSCO) have revealed a Fermi surface consisting of spin-triplet (KS) particles at the antinodal Fermi-pockets and spin-singlet (SS) particles at the nodal Fermi-arcs in the presence of AF local order. By performing a unique method of calculating the electronic-spin state of overdoped LSCO and by measurement of the spin-correlation length by neutron inelastic scattering, the origin of the phase-diagram, including the pseudogap phase in the high temperature superconductor, Sr-doped copper-oxide LSCO, has been elucidated. We have theoretically solved the long-term problem as to why the angle-resolved photoemission spectroscopy (ARPES) has not been able to observe Fermi pockets in the Fermi surface of LSCO. As a result, we show that the pseudogap region is bounded below the characteristic temperature T*(x) and above the superconducting transition temperature T_c(x) in the T vs. x phase diagram, where both the AF order and the KS particles in the Fermi pockets vanish at T*(x), whilst KS particles contribute to d-wave superconductivity below T_c. We also show that the relationship T*(x_c) = T_c(x_c) holds at x_c = 0.30, which is consistent with ARPES experiments. At T*(x), a phase transition occurs from the pseudogap phase to an unusual metallic phase in which only the SS particles exist. Full article

(This article belongs to the Special Issue Spin Dynamics in Magnetic Materials: Spin Resistivity, Spin Waves, Spin-Orbit Coupling, Phase Transition)

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19 pages, 3452 KiB

Open AccessEditor’s ChoiceArticle

Investigating the Individual Performances of Coupled Superconducting Transmon Qubits

by Halima Giovanna Ahmad, Caleb Jordan, Roald van den Boogaart, Daan Waardenburg, Christos Zachariadis, Pasquale Mastrovito, Asen Lyubenov Georgiev, Domenico Montemurro, Giovanni Piero Pepe, Marten Arthers, Alessandro Bruno, Francesco Tafuri, Oleg Mukhanov, Marco Arzeo and Davide Massarotti

Condens. Matter 2023, 8(1), 29; https://doi.org/10.3390/condmat8010029 - 21 Mar 2023

Cited by 5 | Viewed by 4196

Abstract

The strong requirement for high-performing quantum computing led to intensive research on novel quantum platforms in the last decades. The circuital nature of Josephson-based quantum superconducting systems powerfully supports massive circuital freedom, which allowed for the implementation of a wide range of qubit [...] Read more.

The strong requirement for high-performing quantum computing led to intensive research on novel quantum platforms in the last decades. The circuital nature of Josephson-based quantum superconducting systems powerfully supports massive circuital freedom, which allowed for the implementation of a wide range of qubit designs, and an easy interface with the quantum processing unit. However, this unavoidably introduces a coupling with the environment, and thus to extra decoherence sources. Moreover, at the time of writing, control and readout protocols mainly use analogue microwave electronics, which limit the otherwise reasonable scalability in superconducting quantum circuits. Within the future perspective to improve scalability by integrating novel control energy-efficient superconducting electronics at the quantum stage in a multi-chip module, we report on an all-microwave characterization of a planar two-transmon qubits device, which involves state-of-the-art control pulses optimization. We demonstrate that the single-qubit average gate fidelity is mainly limited by the gate pulse duration and the quality of the optimization, and thus does not preclude the integration in novel hybrid quantum-classical superconducting devices. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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10 pages, 2725 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Experimental and Theoretical Investigation of High-Resolution X-ray Absorption Spectroscopy (HR-XAS) at the Cu K-Edge for Cu₂ZnSnSe₄

by Wei Xu, Yujun Zhang, Kenji Ishii, Hiroki Wadati, Yingcai Zhu, Zhiying Guo, Qianshun Diao, Zhen Hong, Haijiao Han and Lidong Zhao

Condens. Matter 2023, 8(1), 8; https://doi.org/10.3390/condmat8010008 - 13 Jan 2023

Viewed by 3040

Abstract

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu₂ZnSnSe₄ (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The [...] Read more.

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu₂ZnSnSe₄ (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The defect chemistry and atomic ordering in this particular compound also triggers interests in understanding its crystallographic structure as well as defects. Hereby, high energy resolution X-ray absorption spectroscopy is employed to investigate the electronic and geometric structural complexity in pristine and cobalt-doped Cu₂ZnSnSe₄. The occupational atomic sites of Cu are found to be mixed with the Zn atoms, forming Cu_Zn anti-defects, which serve as a knob to tune local electronic structures. With proper doping, the band structure can be manipulated to improve the optical and thermoelectric properties of the CZTSe compounds. Full article

(This article belongs to the Special Issue Superstripes Physics)

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