Charge-spin correlation in van der Waals antiferromagenet NiPS3

Strong charge-spin coupling is found in a layered transition-metal trichalcogenide NiPS3, a van derWaals antiferromagnet, from our study of the electronic structure using several experimental and theoretical tools: spectroscopic ellipsometry, x-ray absorption and photoemission spectroscopy, and density-functional calculations. NiPS3 displays an anomalous shift in the optical spectral weight at the magnetic ordering temperature, reflecting a strong coupling between the electronic and magnetic structures. X-ray absorption, photoemission and optical spectra support a self-doped ground state in NiPS3. Our work demonstrates that layered transition-metal trichalcogenide magnets are a useful candidate for the study of correlated-electron physics in two-dimensional magnetic material.Comment: 6 pages, 3 figur

Unconventional spin-phonon coupling via the Dzyaloshinskii???Moriya interaction

Spin-phonon coupling (SPC) plays a critical role in numerous intriguing phenomena of transition metal oxides (TMOs). In 3d and 4d TMOs, the coupling between spin and lattice degrees of freedom is known to originate from the exchange interaction. On the other hand, the origin of SPC in 5d TMOs remains to be elucidated. To address this issue, we measured the phonon spectra of the 5d pyrochlore iridate Y 2 Ir 2 O 7 using optical spectroscopy. Three infrared-active phonons soften below the N??el temperature of T N ??? 170 K, indicating the existence of strong SPC. Simulations using density functional theory showed that the coupling is closely related to the Ir???O???Ir bond angle. A tight-binding model analysis reveals that this SPC is mainly mediated by the Dzyaloshinskii???Moriya interaction rather than the usual exchange interaction. We suggest that such unconventional SPC may be realized in other 5d TMOs with non-collinear magnetic order

Tuning orbital-selective phase transitions in a two-dimensional Hund's correlated system

Hund's rule coupling ($\textit{J}$) has attracted much attention recently for its role in the description of the novel quantum phases of multi orbital materials. Depending on the orbital occupancy, $\textit{J}$ can lead to various intriguing phases. However, experimental confirmation of the orbital occupancy dependency has been difficult as controlling the orbital degrees of freedom normally accompanies chemical inhomogeneities. Here, we demonstrate a method to investigate the role of orbital occupancy in $\textit{J}$ related phenomena without inducing inhomogeneities. By growing SrRuO$_3$ monolayers on various substrates with symmetry-preserving interlayers, we gradually tune the crystal field splitting and thus the orbital degeneracy of the Ru \textit{t_2_g$}$ orbitals. It effectively varies the orbital occupancies of two-dimensional (2D) ruthenates. Via in-situ angle-resolved photoemission spectroscopy, we observe a progressive metal-insulator transition (MIT). It is found that the MIT occurs with orbital differentiation: concurrent opening of a band insulating gap in the $\textit{d$_x_y} band and a Mott gap in the \textit{d_x$$_z$$_/$$_y$$_z} bands. Our study provides an effective experimental method for investigation of orbital-selective phenomena in multi-orbital materials

Sharp contrast in the electrical and optical properties of vanadium Wadsley (VmO2m+1, m > 1) epitaxial films selectively stabilized on (111)-oriented Y-stabilized ZrO2

Four oxidation states (V2+, V3+, V4+, and V5+) in vanadium oxides and the conversion between them have attracted attention for application to batteries and electronics. Compared to single-valence counterparts, however, there have been few reports on the fundamental properties of mixed-valence vanadium oxide films, as their complexity and closeness in thermodynamic phase diagrams hinder the formation of pure phases in film. Here, using an epitaxial growth technique with precise control of oxygen partial pressure (20-100 mTorr) on (111)-oriented Y-stabilized ZrO2, we selectively stabilize pure phases of VO2(B) (m = infinity), V6O13 (m = 6), and V2O5 (m = 2), so-called Wadsley phases (VmO2m+1, m > 1) in which V4+ and/or V5+ can coexist. Fractional increase of V4+ changes the electrical ground state, insulating VO2 (B) and V2O5, metallic V6O13 transition into insulators below 150 K. While VO2 (B) and V(6)O(13 )exhibit strong spectral weights at low photon energy in the room-temperature extinction coefficients, the band-edge absorption shifts toward higher photon energy for smaller m, opening an indirect band gap of 2.6 eV in V2O5 . The sharp contrast of electrical and optical properties between vanadium Wadsley phases highlights the importance of precisely controlling the oxidation state of vanadium. ©2019 American Physical Societ

Infrared Transparent and Electromagnetic Shielding Correlated Metals via Lattice-Orbital-Charge Coupling

Despite being a requisite for modern transparent electronics, few metals have a sufficiently high infrared transmittance due to the free electron response. Here, upon alloying the correlated metal SrVO3 with BaVO3, the medium wavelength infrared transmittance at a wavelength of 4 mu m is found to be 50% higher than those for Sn-doped In2O3 (ITO) and La-doped BaSnO3 (BLSO). The room temperature resistivity of the alloy of similar to 100 mu omega cm is 1 order of magnitude lower than those of ITO and BLSO, guaranteeing a profound electromagnetic shielding effectiveness of 22-31 dB at 10 GHz in the X-band. Systematic investigations reveal symmetry breaking of VO6 oxygen octahedra in SrVO3 due to the substitution of Sr2+ with larger Ba2+ ions, localization of electrons in the lower energy V-d(yz) and d(zx) orbitals, and stronger correlation effects. The lattice-orbital-charge-coupled engineering of the electronic band structure in correlated metals offers a new design strategy to create super-broad-band transparent conductors with an enhanced shielding capability.11Nsciescopu

High infrared transparency up to 8-micrometer-wavelength in correlated vanadium Wadsley conductors

Within industrial and military contexts, research on infrared transparent conductors (IR-TCs) has been limited due to the significant suppression of transparency by the free electron response. In this paper, we report that strong correlations between electrons play an important role in the development of a new strategy for fabricating IR-TCs. Metallic VO2(B) and V6O13 persistently exhibit transmittances 45% higher than that of Sn-doped In2O3 for a broad IR wavelength range of up to 8 μm. Based on electronic band structures determined quantitatively using x-ray absorption spectroscopy, x-ray photoemission spectroscopy, and spectroscopic ellipsometry, we propose that the enhancement in the IR-TC is attributed to the redshift of the plasma frequency induced by the correlated electrons. © 2020 Author(s).1

Electronic structure of HxVO2 probed with in-situ spectroscopic ellipsometry

Vanadium dioxide (VO$_{\mathrm{2}})$ undergoes a metal-to-insulator transition (MIT) near 340K. Despite extensive studies on this material, the role of electronelectron correlation and electron-lattice interactions in driving this MIT is still under debate. Recently, it was demonstrated that hydrogen can be reversibly absorbed into VO$_{\mathrm{2}}$ thin film without destroying the lattice framework. This H-doping allows systematic control of the electron density and lattice structure which in turn leads to a insulator (VO$_{\mathrm{2}})$ - metal (H$_{x}$VO$_{\mathrm{2}})$ - insulator (HVO$_{\mathrm{2}})$ phase modulation [Yoon \textit{et al.}, Nat. Mat. \textbf{15}, 1113-1119 (2016)]. To better understand the phase modulation of H$_{x}$VO$_{\mathrm{2}}$, we used \textit{in-situ} spectroscopic ellipsometry to monitor the electronic structure during the hydrogenization process, i.e. we measured the optical conductivity of H$_{x}$VO$_ {\mathrm{2}}$ while varying $x$. Starting in the high temperature rutile metallic phase of VO$_{\mathrm{2}}$, we observed a large change in the electronic structure upon annealing in H gas at 370K: the low energy conductivity is continuously suppressed, consistent with reported DC resistivity data, while the conductivity peaks at high energy show strong changes in energy and spectral weight. The implications of our results for the MIT in H$_{x}$VO$_{\mathrm{2}}$ will be discussed.1

Spin-Orbit Coupling and Interband Transitions in the Optical Conductivity of Sr2RhO4

The prototypical correlated metal Sr2RhO4 was studied using optical and photoemission spectroscopy. At low energies and temperatures, the optical data reveal a complex, multicomponent response that on the surface points to an unconventional metallic state in this material. Via a comparison with photoemission, the anomalous optical response may be attributed to an unexpectedly strong interband transition near 180 meV between spin-orbit coupled bands that are nearly parallel along ΓX. This spin-orbit coupling effect is shown to occur in a number of related metallic ruthenates and explains the previously puzzling optical properties reported for these materials. © 2017 American Physical Society101sciescopu

A Comparison Study of Marginal and Internal Fit Assessment Methods for Fixed Dental Prostheses

Numerous studies have previously evaluated the marginal and internal fit of fixed prostheses; however, few reports have performed an objective comparison of the various methods used for their assessment. The purpose of this study was to compare five marginal and internal fit assessment methods for fixed prostheses. A specially designed sample was used to measure the marginal and internal fit of the prosthesis according to the cross-sectional method (CSM), silicone replica technique (SRT), triple scan method (TSM), micro-computed tomography (MCT), and optical coherence tomography (OCT). The five methods showed significant differences in the four regions that were assessed (p < 0.001). The marginal, axial, angle, and occlusal regions showed low mean values: CSM (23.2 µm), TSM (56.3 µm), MCT (84.3 µm), and MCT (102.6 µm), respectively. The marginal fit for each method was in the range of 23.2–83.4 µm and internal fit (axial, angle, and occlusal) ranged from 44.8–95.9 µm, 84.3–128.6 µm, and 102.6–140.5 µm, respectively. The marginal and internal fit showed significant differences depending on the method. Even if the assessment values of the marginal and internal fit are found to be in the allowable clinical range, the differences in the values according to the method should be considered