Article
Materials Science, Multidisciplinary
K. Katsumata
Summary: This article discusses the origin of the spin-crossover phenomenon in LaCoO3, based on the realization of the D-5 electronic state in an intermediate crystal field. By calculating the splitting of the D-5 state in a predominantly cubic crystal field with trigonal distortion, the author obtained rigorous results that accord with existing experimental measurements.
Article
Materials Science, Multidisciplinary
T. Watanabe, R. Okada, K. Tomiyasu
Summary: Ultrasound velocity measurements reveal two types of symmetry-resolved elastic anomaly in the pseudocubic spin-crossover cobaltite LaCoO3 and the lightly Ni-substituted La(Co0.99Ni0.01)O-3. The temperature dependence of the bulk modulus indicates isostructural lattice instability arising from orbital fluctuations, while the temperature dependence of the shear moduli exhibits elasticity crossover arising from spin crossover. The study also shows that the isostructural lattice instability in LaCoO3 is suppressed with Ni substitution, suggesting the suppression of orbital fluctuations.
Article
Materials Science, Multidisciplinary
Xu-jing Li, Bao-Tian Wang, Wen Yin
Summary: The discussions on the origins of the magnetic and insulating properties in LaCoO3 films have been ongoing. This study investigates the energy of different spin configurations using first principle calculations, considering various distortions in the films. The results show that the spin state transition can be controlled by rhombohedral distortion and octahedral rotations. The octahedral rotations can induce breathing or Jahn-Teller distortions, leading to a change in the electronic structure from metal to semiconductor. These findings highlight the importance of octahedral rotations in controlling the electronic structure and spin states in LaCoO3 films.
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
(2022)
Article
Materials Science, Ceramics
Ashish Shukla, Arun Kumar, Kedar Pathak
Summary: A solid solution polycrystalline powder sample of LaMnO3 - LaFeO3 - LaCoO3 was synthesized via mixed-oxide method in a 1:1:1 ratio by mass. It exhibits a blend of orthorhombic and cubic crystal structure and shows ferromagnetic nature from 50 K to 300 K.
CERAMICS INTERNATIONAL
(2023)
Article
Physics, Multidisciplinary
D. Takegami, A. Tanaka, S. Agrestini, Z. Hu, J. Weinen, M. Rotter, C. Schuessler-Langeheine, T. Willers, T. C. Koethe, T. Lorenz, Y. F. Liao, K. D. Tsuei, H. -j. Lin, C. T. Chen, L. H. Tjeng
Summary: The electronic structure of LaCoO3 in the gradual spin-state and insulator-to-metal transitions was investigated using bulk-sensitive hard x-ray photoelectron and soft x-ray absorption spectroscopies. The temperature variation was found to cause strong variations in the spectra. Although the energy gap is reduced with increasing temperature, LaCoO3 is classified as a bad metal even in the metallic phase due to the small intensity near the Fermi level. By considering incoherent sums of low-spin and high-spin Co3+ spectra, the spectra were successfully explained. Moreover, it was discovered that the energy parameters for the two Co sites are significantly different, indicating the highly inhomogeneous nature of paramagnetic LaCoO3 with spin-state-specific local lattice relaxations. This provides a natural explanation for the debated temperature dependence of the activation energy for the transitions.
Article
Chemistry, Multidisciplinary
Shanquan Chen, Jhong-Yi Chang, Qinghua Zhang, Qiuyue Li, Ting Lin, Fanqi Meng, Haoliang Huang, Yangyang Si, Shengwei Zeng, Xinmao Yin, My Ngoc Duong, Yalin Lu, Lang Chen, Er-Jia Guo, Hanghui Chen, Chun-Fu Chang, Chang-Yang Kuo, Zuhuang Chen
Summary: The spin state of Co ions in epitaxial LaCoO3 thin films under tensile strain has been determined to have mixed high-spin and low-spin states, while it is practically a low-spin state under compressive strain. The identification of this spin state ratio explains the origin of ferromagnetism in LaCoO3 films. This study highlights the importance of spin state degrees of freedom and thin-film strain engineering in creating new physical properties that do not exist in bulk materials.
Article
Chemistry, Multidisciplinary
Hannah Kurz, Konstantin Schoetz, Ilias Papadopoulos, Frank W. Heinemann, Harald Maid, Dirk M. Guldi, Anna Koehler, Gerald Hoerner, Birgit Weber
Summary: The study presents a family of planar nickel(II) complexes with sensitive CISSS tracked by fluorescence detection. These complexes fluoresce in noncoordinating solvents but are fluorescence-silent in the presence of axial ligands. FD-CISSS shows higher sensitivity compared to absorption-based CISSS.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
(2021)
Article
Physics, Multidisciplinary
Wenjin Zhao, Elliott Runburg, Zaiyao Fei, Joshua Mutch, Paul Malinowski, Bosong Sun, Xiong Huang, Dmytro Pesin, Yong-Tao Cui, Xiaodong Xu, Jiun-Haw Chu, David H. Cobden
Summary: Evidence of quantum spin Hall effect (QSHE) has been observed in experimental systems, with edge conductance approaching quantized values at zero magnetic field. However, a fundamental feature of QSHE, spin-momentum locking, has not been demonstrated until now. Recent research on monolayer WTe2 material suggests that the suppression of edge conductance in applied magnetic fields implies spin orientation along a specific axis fixed relative to the crystal structure. This finding supports the idea of simple spin textures with a single, momentum-independent spin axis inherited by the edge modes.
Article
Materials Science, Multidisciplinary
Parrydeep Kaur Sachdeva, Shuchi Gupta, Chandan Bera
Summary: In this work, the strain-coupled spin-valleytronic properties of monoclinic monochalcogenide tellurene monolayers in two stable phases (β-Te and β'-Te) were explored using first-principles calculations. The results show that β-Te and β'-Te exhibit high Rashba spin splittings and spin-valley oscillations under strain, which make them promising for device applications in low-power quantum electronics and other fields.
Article
Materials Science, Multidisciplinary
Ryuji Okazaki, Keisuke Tomiyasu
Summary: In this study, we measured the electrical resistivity and thermopower of electron-doped perovskite cobaltites. We found that the electron-doped samples exhibit insulating behavior, but the thermopower shows relatively large positive values. This study also highlights the electron-hole asymmetry in the thermopower and the impact of a spin-state blockade on thermoelectric transport.
Article
Physics, Applied
Yuan Cao, Linfeng Gao, Zhenhai Lai, Cheng Wang, Yingfang Yao, Xi Zhu, Zhigang Zou
Summary: In this study, the introduction of Mn substitution to LaCoO3 resulted in lattice expansion and reduced crystalline field splitting energy, leading to an increase in effective magnetic moment which triggered the transfer of Co3+ from low to higher spin states. This enhanced the hybridization of Co e(g) and O 2p states across the Fermi level, transitioning LaCoO3 from a semiconductor to a half-metal with 25% Mn substitution, benefiting spin-oriented electronic transport and promoting the OER. This method opens up new possibilities for constructing spin pathways in catalysts.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Fluids & Plasmas
Dries Sels, Anatoli Polkovnikov
Summary: We investigate a one-dimensional XXZ spin chain in a disordered magnetic field, utilizing the sensitivity of eigenstates and the low-frequency asymptotes of the spectral function to understand the system's behavior. We identify a region of maximal chaos with exponentially enhanced susceptibility, separating the many-body localized phase from the diffusive ergodic phase. This region exhibits slow transport characteristics, which we argue highly constrains any possible localization transition in the thermodynamic limit, suggesting an absence of the localized phase.
Article
Chemistry, Physical
J. J. Lu, R. Liu, F. F. Yue, X. W. Zhao, G. C. Hu, X. B. Yuan, J. F. Ren
Summary: Through first-principles calculations, we have discovered a two-dimensional MXene material, Y3N2O2, with spontaneous valley polarization (VP) that induces intrinsic anomalous valley Hall effect (AVHE). The VP can be linearly modulated, providing an effective control route for valley signals. By adjusting spin-orbit coupling, we have enhanced the VP in the proposed monolayer La3N2O2 to 100.4 meV, enabling easy achievement of AVHE. This work not only offers compelling AVHE material candidates but also presents a novel mindset for finding suitable valleytronic devices.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2023)
Article
Multidisciplinary Sciences
Junxue Li, Mina Rashetnia, Mark Lohmann, Jahyun Koo, Youming Xu, Xiao Zhang, Kenji Watanabe, Takashi Taniguchi, Shuang Jia, Xi Chen, Binghai Yan, Yong-Tao Cui, Jing Shi
Summary: Van der Waals heterostructures allow for integration of different materials with distinct properties, leading to novel physical phenomena. In this study, Li et al combine a quantum spin hall insulator, WTe2, with an insulating ferromagnet, Cr2Ge2Te6, resulting in induced magnetism in the WTe2 layer and anomalous Hall and Nernst effects. The proximity-induced ferromagnetic order in WTe2 manifests in various transport phenomena, and spin-polarized edge states are revealed in the magnetized quantum spin hall insulator.
NATURE COMMUNICATIONS
(2022)
Article
Materials Science, Multidisciplinary
Zhaopeng Guo, Dayu Yan, Haohao Sheng, Simin Nie, Youguo Shi, Zhijun Wang
Summary: The research predicts that monolayer Ta2Pd3Te5 can act as a QSH insulator based on first-principles calculations, with nontrivial topology. It is also found that the QSH state in Ta2M3Te5 (M = Pd, Ni) can be tuned by external strain, as confirmed through experimental and computational analysis.
Article
Physics, Multidisciplinary
Andrii Sotnikov, Kyo-Hoon Ahn, Jan Kunes
Article
Physics, Multidisciplinary
J. Ebad-Allah, S. Rojewski, M. Voest, G. Eickerling, W. Scherer, E. Uykur, Raman Sankar, L. Varrassi, C. Franchini, K. -H. Ahn, J. Kunes, C. A. Kuntscher
Summary: The anisotropic optical response of the layered, nodal-line semimetal ZrSiS under different pressures was investigated, showing strong pressure-induced effects on the out-of-plane optical conductivity spectrum. These effects cannot be explained by structural phase transitions or electronic correlations, and are related to the excitonic insulator phase proposed in ZrSiS.
PHYSICAL REVIEW LETTERS
(2021)
Article
Chemistry, Physical
Lorenzo Tesi, Dominik Bloos, Martin Hrton, Adam Benes, Mario Hentschel, Michal Kern, Alisa Leavesley, Rainer Hillenbrand, Vlastimil Krapek, Tomas Sikola, Joris van Slageren
Summary: A new resonator composed of an array of diabolo antennas with a back-reflecting mirror is designed and fabricated to enhance THz magnetic fields in a microscopic volume. Simulations and THz EPR measurements show a 30-fold signal increase for thin film samples, reaching a theoretical value of 7500 for samples confined to the active region of the antennas. These findings open the door to understanding fundamental processes in nanoscale samples, such as junctions in spintronic devices or biological membranes.
Article
Physics, Multidisciplinary
D. Takegami, C-Y Kuo, K. Kasebayashi, J-G Kim, C. F. Chang, C. E. Liu, C. N. Wu, D. Kasinathan, S. G. Altendorf, K. Hoefer, F. Meneghin, A. Marino, Y. F. Liao, K. D. Tsuei, C. T. Chen, K-T Ko, A. Guenther, S. G. Ebbinghaus, J. W. Seo, D. H. Lee, G. Ryu, A. C. Komarek, S. Sugano, Y. Shimakawa, A. Tanaka, T. Mizokawa, J. Kunes, L. H. Tjeng, A. Hariki
Summary: We present a comprehensive study of CaCu3Ru4O12 using bulk sensitive hard and soft x-ray spectroscopy combined with local-density approximation + dynamical mean-field theory (DMFT) calculations. Correlation effects on both the Cu and Ru ions can be observed. Based on the analysis of Cu 2p corelevel spectra, we infer the presence of magnetic Cu2+ ions hybridized with itinerant electrons. The photon energy dependence of the valence band allows us to optimize the DMFT calculations, indicating that CaCu3Ru4O12 can be classified as a Kondo system with a Kondo temperature in the range of 500-1000 K.
Article
Physics, Multidisciplinary
Keisuke Higashi, Mathias Winder, Jan Kunes, Atsushi Hariki
Summary: By studying the core-level spectra, the optimal model parameters for the ground state of NdNiO2 were determined, showing that self-doping from the Nd 5d states prevents the opening of a Mott-Hubbard gap. However, the current calculations for LaNiO2 cannot explain the difference in spectra compared to NdNiO2.
Article
Multidisciplinary Sciences
M. C. Rahn, K. Kummer, A. Hariki, K-H Ahn, J. Kunes, A. Amorese, J. D. Denlinger, D-H Lu, M. Hashimoto, E. Rienks, M. Valvidares, F. Haslbeck, D. D. Byler, K. J. McClellan, E. D. Bauer, J. X. Zhu, C. H. Booth, A. D. Christianson, J. M. Lawrence, F. Ronning, M. Janoschek
Summary: Resonant inelastic X-ray scattering (RIXS) was used in this study to investigate CePd3 and clarify the hybridization process between local high-energy degrees of freedom and the underlying metallic state at low temperature, highlighting its impact on the properties of correlated metals.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Multidisciplinary
M. Kvapil, T. Sikola, V Krapek
Summary: We theoretically demonstrate the capability of a simple device composed of a metal layer and subwavelength slits to transform far-field optical power to near-field power with high conversion efficiency. Different slit arrangements result in different field distributions and have important implications for the spatial resolution of photoluminescence.
ACTA PHYSICA POLONICA A
(2022)
Article
Chemistry, Physical
Petr Liska, Tomas Musalek, Tomas Samoril, Matous Kratochvil, Radovan Matula, Michal Horak, Matej Nedved, Jakub Urban, Jakub Planer, Katarina Rovenska, Petr Dvorak, Miroslav Kolibal, Vlastimil Krapek, Radek Kalousek, Tomas Sikola
Summary: We investigated the optical properties of CsPbBr3 polycrystalline thin film at a single grain level. A sample composed of isolated nanocrystals was prepared, and their structural, chemical, and optical properties were examined using correlative microscopy. Our results showed that the stoichiometry of the CsPbBr3 nanocrystals was uniform and independent of their morphology. The photoluminescence peak emission wavelength slightly depended on the dimensions of the nanocrystals, with a small blue shift detectable only by high-resolution photoluminescence mapping.
JOURNAL OF PHYSICAL CHEMISTRY C
(2023)
Article
Chemistry, Physical
Michal Horak, Vojtech Calkovsky, Jindrich Mach, Vlastimil Krapek, Tomas Sikola
Summary: In this work, the relationship between the shape and size of gallium nanoparticles and their optical properties is experimentally demonstrated. Lens-shaped gallium nanoparticles with a diameter between 10 and 200 nm were directly grown on a silicon nitride membrane. It is proven that these particles support localized surface plasmon resonances, and their dipole mode can be tuned through their size from the ultraviolet to near-infrared spectral region. The measurements are supported by numerical simulations using realistic particle shapes and sizes.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2023)
Article
Nanoscience & Nanotechnology
Michal Horak, Andrea Konecna, Tomas Sikola, Vlastimil Krapek
Summary: Electron energy loss spectroscopy (EELS) is commonly used to study localized surface plasmon modes of plasmonic antennas, but it has limited spectral resolution and difficulty in resolving closely spaced modes. In this study, we address this issue by analyzing the plasmon modes of a dimer plasmonic antenna composed of two gold discs. We propose metrics based on spectral and spatial sensitivity to resolve the modes and validate them through electrodynamic simulations. Experimental data demonstrate the capability of these metrics to resolve and identify the modes, except for the transverse bonding and antibonding modes. Overall, the spatio-spectral metrics enhance the information extracted from EELS for plasmonic antennas.
Article
Materials Science, Multidisciplinary
Pavel Gallina, Michal Kvapil, Jirf Liska, Andrea Konecna, Vlastimil Krapek, Radek Kalousek, Jakub Zlamal, Tomas Sikola
Summary: In this paper, the scattering cross-section spectra of Au antennas on a SiO2 layer on a Si substrate in the IR region are analyzed. A classical model of coupled oscillators is used to determine the resonant energies, damping rates, and coupling strengths of four phonon polariton modes in the SiO2 layer coupled to a localized surface plasmon mode in a Au antenna. The calculated Hopfield mixing coefficients show the contribution of the individual uncoupled modes to the hybrid modes of the coupled system.
Article
Nanoscience & Nanotechnology
Petr Dvorak, Pavel Klok, Michal Kvapil, Martin Hrton, Petr Bouchal, Jan Krpensky, Vlastimil Krapek, Tomas Sikola
Summary: In this study, we demonstrate the formation of the near field with non-trivial phase distribution using surface plasmon interference devices and perform experimental quantitative imaging of that phase with near-field phase microscopy. The phase distribution can be controlled by the polarization of the external illumination and the area of the device assigned to the object wave. Comparison with numerical and analytical models confirms the origin of the near-field phase and verifies the predictive power of the models. Additionally, we show that it is possible to generate near-field plane waves with different propagation directions on a single device.
Article
Materials Science, Multidisciplinary
Atsushi Hariki, Kyo-Hoon Ahn, Jan Kunes
Summary: The computational study of PbCoO3 at ambient and elevated pressure using DFT+U and DFT+DMFT methods reveals the unsaturated Pb 6s - O 2p bonds as the driving force behind the complex physics of PbCoO3. Geometrical analysis of structural distortions and discussions on internal doping effects triggering phase transitions are provided.
Article
Materials Science, Multidisciplinary
A. Niyazi, D. Geffroy, J. Kunes
Summary: In this study, we explored the dynamical mean-field properties of antiferromagnetic magnons in a one-, two-, and three-orbital Hubbard model under intermediate coupling strength. The effects of anisotropy introduced by external magnetic field or single-ion anisotropy were investigated, with a continuous tuning between easy-axis and easy-plane models. It was found that ordered states and magnetic excitations are sensitive to even small breaking of SU(2) symmetry of the model, in line with spin-wave theory and general symmetry considerations.
Article
Materials Science, Multidisciplinary
Mathias Winder, Atsushi Hariki, Jan Kunes
