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Condens. Matter, Volume 5, Issue 3 (September 2020) – 12 articles

Cover Story (view full-size image): By reviewing experiments that probed the surface and bulk of hole-doped cuprate high-temperature superconductors (HTSs), Alex Müller in a series of papers suggested that the symmetry of the superconducting order parameter in these materials changes “from purely d at the surface to more s inside”. In this study, we present evidence that the mixed order parameter symmetry is realized in Sr0.9La0.1CuO2, i.e., in a superconductor belonging to the family of electron-doped cuprate HTSs. View this paper
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Article
Carbon Deposition on Hematite (α-Fe2O3) Nanocubes by Annealing in the Air: Morphology Study with Grazing Incidence Small Angle X-ray Scattering (GISAXS)
Condens. Matter 2020, 5(3), 54; https://doi.org/10.3390/condmat5030054 - 17 Sep 2020
Viewed by 635
Abstract
GISAXS has been used to study morphology change of α-Fe2O3 nanocubes after annealing processes. A submonolayer of the nanocubes was deposited on a Si(100) substrate. While an annealing at 400 °C in vacuum does not change a GISAXS pattern from [...] Read more.
GISAXS has been used to study morphology change of α-Fe2O3 nanocubes after annealing processes. A submonolayer of the nanocubes was deposited on a Si(100) substrate. While an annealing at 400 °C in vacuum does not change a GISAXS pattern from as-prepared nanocubes submonolayer, subsequent annealing in air at the same temperature altered the GISAXS pattern significantly. SEM images showed that the air-annealed nanocubes were coated with thin layers which were identified as amorphous carbon layers based on Raman measurements. GISAXS simulations from morphologies of nanocube with 38 nm side-length and core-shell (nanocube-core and 7 nm thick carbon-shell) reproduced measured patterns from the vacuum- and the air-annealed nanocubes, respectively. The current study provides new approach for in-situ characterization of carbon deposition on a uniform shape nanoparticle through monitoring of deposited carbon thickness. Full article
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Article
Evolution of Spin-Orbital Entanglement with Increasing Ising Spin-Orbit Coupling
Condens. Matter 2020, 5(3), 53; https://doi.org/10.3390/condmat5030053 - 26 Aug 2020
Viewed by 863
Abstract
Several realistic spin-orbital models for transition metal oxides go beyond the classical expectations and could be understood only by employing the quantum entanglement. Experiments on these materials confirm that spin-orbital entanglement has measurable consequences. Here, we capture the essential features of spin-orbital entanglement [...] Read more.
Several realistic spin-orbital models for transition metal oxides go beyond the classical expectations and could be understood only by employing the quantum entanglement. Experiments on these materials confirm that spin-orbital entanglement has measurable consequences. Here, we capture the essential features of spin-orbital entanglement in complex quantum matter utilizing 1D spin-orbital model which accommodates SU(2)⊗SU(2) symmetric Kugel-Khomskii superexchange as well as the Ising on-site spin-orbit coupling. Building on the results obtained for full and effective models in the regime of strong spin-orbit coupling, we address the question whether the entanglement found on superexchange bonds always increases when the Ising spin-orbit coupling is added. We show that (i) quantum entanglement is amplified by strong spin-orbit coupling and, surprisingly, (ii) almost classical disentangled states are possible. We complete the latter case by analyzing how the entanglement existing for intermediate values of spin-orbit coupling can disappear for higher values of this coupling. Full article
(This article belongs to the Special Issue Quantum Complex Matter 2020)
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Article
Controlling Electrical Conduction through Noble Metal Thin Films by Surface Plasmon Resonance
Condens. Matter 2020, 5(3), 52; https://doi.org/10.3390/condmat5030052 - 26 Aug 2020
Cited by 2 | Viewed by 795
Abstract
We have conducted in situ measurements of the surface plasmons and electrical resistivity of noble metal thin films. We present results for the electrical resistivity of these materials as functions of the angle of incidence for p-polarized light of wavelength λ = [...] Read more.
We have conducted in situ measurements of the surface plasmons and electrical resistivity of noble metal thin films. We present results for the electrical resistivity of these materials as functions of the angle of incidence for p-polarized light of wavelength λ = 632 nm in the Kretschmann configuration optical system. We observe a significantly lower resistivity (higher conductivity) under resonance conditions for the surface plasmon polaritons. The resistivity data are supported by COMSOL simulations of the evanescent fields associated with the surface plasmons. We discuss the resistivity data in terms of the theoretical models, which suggest that the electrical conductivity of the transition metals is sensitive to Umklapp electron-electron scattering and attractive interactions between free electrons because of the screening of the d-band electrons by the s-band electrons. Full article
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Article
Spiral Thermal Waves Generated by Self-Propelled Camphor Boats
Condens. Matter 2020, 5(3), 51; https://doi.org/10.3390/condmat5030051 - 06 Aug 2020
Viewed by 846
Abstract
Spiral thermal surface waves arising from self-propulsion of the camphor-driven objects are reported. Spiral thermal waves were registered for dissolution and evaporation-guided self-propulsion. Soluto-capillarity is accompanied by thermo-capillarity under self-propulsion of camphor boats. The jump in the surface tension due to the soluto-capillarity [...] Read more.
Spiral thermal surface waves arising from self-propulsion of the camphor-driven objects are reported. Spiral thermal waves were registered for dissolution and evaporation-guided self-propulsion. Soluto-capillarity is accompanied by thermo-capillarity under self-propulsion of camphor boats. The jump in the surface tension due to the soluto-capillarity is much larger than that due to the thermo-capillarity. The spiral patterns inherent for the surface thermal waves are imposed by the self-rotational motion of camphor grains. The observed thermal effect is related to the adsorption of camphor molecules at the water/vapor interface. The observed spirals are shaped as Archimedean ones. Full article
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Article
Suppression of the s-Wave Order Parameter Near the Surface of the Infinite-Layer Electron-Doped Cuprate Superconductor Sr0.9La0.1CuO2
Condens. Matter 2020, 5(3), 50; https://doi.org/10.3390/condmat5030050 - 03 Aug 2020
Cited by 2 | Viewed by 756
Abstract
The temperature dependencies of the in-plane (λab) and out-of-plane (λc) components of the magnetic field penetration depth were investigated near the surface and in the bulk of the electron-doped superconductor Sr0.9La0.1CuO2 by means of magnetization measurements. The measured λab(T) and λc(T) were analyzed in terms of a two-gap model with mixed s+d-wave symmetry of the order parameter. λab(T) is well described by an almost pure anisotropic d-wave symmetry component (96%), mainly reflecting the surface properties of the sample. In contrast, λc(T) exhibits a mixed s+d-wave order parameter with a substantial s-wave component of more than 50%. The comparison of λab2(T) measured near the surface with that determined in the bulk by means of the muon-spin rotation/relaxation technique demonstrates that the suppression of the s-wave component of the order parameter near the surface is associated with a reduction of the superfluid density by more than a factor of two. Full article
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Article
Phenomenon of Electromagnetic Field Resonance in Metal and Dielectric Gratings and Its Possible Practical Applications
Condens. Matter 2020, 5(3), 49; https://doi.org/10.3390/condmat5030049 - 24 Jul 2020
Cited by 1 | Viewed by 678
Abstract
Calculations of the field distribution in the structure of the dielectric substrate/buffer layer/volume phase grating/analyzed medium were performed. It is shown that in the presence of a buffer layer with a low refractive index in the dielectric waveguide leads to a shift of [...] Read more.
Calculations of the field distribution in the structure of the dielectric substrate/buffer layer/volume phase grating/analyzed medium were performed. It is shown that in the presence of a buffer layer with a low refractive index in the dielectric waveguide leads to a shift of the maximum field at the waveguide resonance into analyzed medium. As a result, the spectral and angular sensitivity of the corresponding sensor increases. Based on the waveguide equation, analytical expressions are obtained that connect the spectral and angular sensitivity of the sensor to the sensitivity of the propagation constant change due to the refractive index change of the analyzed medium. The conditions for the excitation of the resonance of surface plasmon–polariton waves in the structure with a metal or dielectric grating on a metal substrate are also given. The fields that occur at resonance for silver and gold gratings are calculated. Full article
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Article
C-2p Spin-Polarizations along with Two Mechanisms in Extended Carbon Multilayers: Insight from First Principles
Condens. Matter 2020, 5(3), 48; https://doi.org/10.3390/condmat5030048 - 22 Jul 2020
Viewed by 824
Abstract
From density functional theory investigations helped with crystal chemistry rationale, single-atom C, embedded in layered hexagonal CC’n (n = 6, 12 and 18) networks, is stable in a magnetic state with M(C) = 2 μB. The examined compositions, all [...] Read more.
From density functional theory investigations helped with crystal chemistry rationale, single-atom C, embedded in layered hexagonal CC’n (n = 6, 12 and 18) networks, is stable in a magnetic state with M(C) = 2 μB. The examined compositions, all inscribed within the P6/mmm space group are characterized as increasingly cohesive with n, figuring mono-, bi- and tri-layered honeycomb-like C’6 networks respectively. The spin projected total density of states shows a closely half-metallic behavior with a gap at minority spins (↓) and metallic majority spins (↑). Such results together with the large C-C intersite separation and the integer 2 μB magnetization, let us propose an intra-band mechanism of magnetic moment onset on carbon 2p states. Support is provided from complementary calculations assuming a C2C’12 structure with planar 2C with d(C-C) = 2.46 Å resulting into a lowering of the magnetization down to the 0.985 μB/C atom and a ferromagnetic order arising from interband spin polarization on C where one nonbonding spin polarizes whereas the other is involved with the bonding with the other carbon. Illustration of proofs is provided with the magnetic charge density projected onto the different atoms, showing its prevalence around C, contrary to the C’n (C’6 layers), as well as electron localization function ELF. Full article
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Article
Broadband Anisotropic Optical Properties of the Terahertz Generator HMQ-TMS Organic Crystal
Condens. Matter 2020, 5(3), 47; https://doi.org/10.3390/condmat5030047 - 14 Jul 2020
Cited by 5 | Viewed by 903
Abstract
HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, [...] Read more.
HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet. Here, from polarized reflectance and transmittance measurements along the x 1 and x 3 axes of a HMQ-TMS single-crystal, we extract both the refraction index n and the extinction coefficient k between 50 and 35,000 cm 1 . We further measure the THz radiation generated by optical rectification at different infrared (IR) wavelengths and along the two x 1 and x 3 axes. These data highlight the remarkable anisotropic linear and nonlinear optical behavior of HMQ-TMS crystals, expanding the knowledge of its properties and applications from the THz to the UV region. Full article
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Article
A Lattice Litany for Transition Metal Oxides
Condens. Matter 2020, 5(3), 46; https://doi.org/10.3390/condmat5030046 - 13 Jul 2020
Cited by 1 | Viewed by 908
Abstract
In this tribute to K Alex Müller, I describe how his early insights have influenced future decades of research on perovskite ferroelectrics and more broadly transition metal oxides (TMOs) and related quantum materials. I use his influence on my own research journey to [...] Read more.
In this tribute to K Alex Müller, I describe how his early insights have influenced future decades of research on perovskite ferroelectrics and more broadly transition metal oxides (TMOs) and related quantum materials. I use his influence on my own research journey to discuss impacts in three areas: structural phase transitions, precursor structure, and quantum paraelectricity. I emphasize materials functionality in ground, metastable, and excited states arising from competitions among lattice, charge, and spin degrees of freedom, which results in highly tunable landscapes and complex networks of multiscale configurations controlling macroscopic functions. I discuss competitions between short- and long-range forces as particularly important in TMOs (and related materials classes) because of their localized and directional metal orbitals and the polarizable oxygen ions. I emphasize crucial consequences of elasticity and metal–oxygen charge transfer. Full article
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Article
Jumping Sundogs, Cat’s Eye and Ferrofluids
Condens. Matter 2020, 5(3), 45; https://doi.org/10.3390/condmat5030045 - 08 Jul 2020
Viewed by 1686
Abstract
We have explored some features of the complex fluids present in Earth’s atmosphere by the observation of some optical phenomena and compared them to the optical phenomena observed in gems and magnetic materials. The main feature of a complex fluid is that it [...] Read more.
We have explored some features of the complex fluids present in Earth’s atmosphere by the observation of some optical phenomena and compared them to the optical phenomena observed in gems and magnetic materials. The main feature of a complex fluid is that it contains polyatomic structures such as polymer molecules or colloidal grains. This paper includes some setups using tabletop experiments, which are intended to show concretely the principles discussed, giving a sense of how well the idealizations treated apply to the atmospheric systems. We have explored sundogs, light pillars, and the halo formation, which involve the existence of a certain structure in the atmospheric medium, resembling the structures observed in some types of gems and ferrofluids. Full article
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Creative
Meetings with a Remarkable Man, Alex Müller—The Professor of SrTiO3
Condens. Matter 2020, 5(3), 44; https://doi.org/10.3390/condmat5030044 - 02 Jul 2020
Cited by 1 | Viewed by 814
Abstract
After my bachelor degree in chemistry with physics and mathematics (in Dutch kandidaatsexamen) at the University of Amsterdam, I chose to study for my master degree (in Dutch doctoraal) a physical chemistry direction [...] Full article
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Creative
The Crucial Things in Science Often Happen Quite Unexpectedly—Das Entscheidende in der Wissenschaft geschieht oft ganz unerwartet (K. Alex Müller)
Condens. Matter 2020, 5(3), 43; https://doi.org/10.3390/condmat5030043 - 01 Jul 2020
Cited by 1 | Viewed by 766
Abstract
We analyzed the publication output of one of the 1987 Nobel Prize awardees, K. Alex Müller, using bibliometric methods. The time-dependent number of publications and citations and the network with respect to the coauthors and their affiliations was studied. Specifically, the citation history [...] Read more.
We analyzed the publication output of one of the 1987 Nobel Prize awardees, K. Alex Müller, using bibliometric methods. The time-dependent number of publications and citations and the network with respect to the coauthors and their affiliations was studied. Specifically, the citation history of the Nobel Prize awarded 1986 article on “Possible high-temperature superconductivity in the Ba-La-Cu-O system” has been evaluated in terms of the overall number of articles on superconductivity and the corresponding citations of other most frequently referenced articles. Thereby, a publication with “delayed recognition” was identified. Full article
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