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Berry curvature (BC) governs topological phases of matter and generates anomalous transport. When a magnetic field is applied, phonons can acquire BC indirectly through spin-lattice coupling, leading to a linear phonon Hall effect. Here, we show that polar lattice distortion directly couples to a phonon BC dipole, which causes a switchable non-linear phonon Hall effect. In a SnS monolayer, the in-plane ferroelectricity induces a phonon BC and leads to the phononic version of the non-volatile BC memory effect. As a new type of ferroelectricity-phonon coupling, the phonon Rashba effect emerges and opens a mass-gap in tilted Weyl phonon modes, resulting in a large phonon BC dipole. Furthermore, our ab initio non-equilibrium molecular dynamics simulations reveal that non-linear phonon Hall transport occurs in a controllable manner via ferroelectric switching. The ferroelectricity-driven phonon BC and corresponding non-linear phonon transports provide a novel scheme for constructing topological phononic transport/memory devices., Comment: 12pages, 4 figures

Defect engineering is one of the key technologies in materials science, enriching the modern semiconductor industry and providing good test-beds for solid-state physics. While homogenous doping prevails in conventional defect engineering, various artificial defect distributions have been predicted to induce desired physical properties in host materials, especially associated with symmetry breakings. Here, we show layer-by-layer defect-gradients in two-dimensional PtSe

The heavy fermion state with Kondo-hybridization (KH), usually manifested in f-electron systems with lanthanide or actinide elements, was recently discovered in several 3d transition metal compounds without f-electrons. However, KH has not yet been observed in 4d/5d transition metal compounds, since more extended 4d/5d orbitals do not usually form flat bands that supply localized electrons appropriate for Kondo pairing. Here, we report a doping- and temperature-dependent angle-resolved photoemission study on 4d Ca2-xSrxRuO4, which shows the signature of KH. We observed a spectral weight transfer in the γ-band, reminiscent of an orbital-selective Mott phase (OSMP). The Mott localized γ-band induces the KH with an itinerant β-band, resulting in spectral weight suppression around the Fermi level. Our work is the first to demonstrate the evolution of the OSMP with possible KH among 4d electrons, and thereby expands the material boundary of Kondo physics to 4d multi-orbital systems.

The spin-orbit entangled (SOE) ${J}_{\mathrm{eff}}$ state has been a fertile ground to study quantum phenomena. Contrary to the conventional weakly correlated ${J}_{\mathrm{eff}}=1/2$ state of $4d$ and $5d$ transition metal compounds, the ground state of $\mathrm{Cu}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ hosts a ${J}_{\mathrm{eff}}=1/2$ state with a strong correlation of Coulomb $U$. Here, we report that, surprisingly, ${\mathrm{Cu}}^{2+}$ ions of $\mathrm{Cu}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ overcome the otherwise usually strong Jahn-Teller distortion and instead stabilize the SOE state, although the cuprate has relatively small spin-orbit coupling. From the x-ray absorption spectroscopy and high-pressure x-ray diffraction studies, we obtained definite evidence of the ${J}_{\mathrm{eff}}=1/2$ state with a cubic lattice at ambient pressure. We also found the pressure-induced structural transition to a compressed tetragonal lattice consisting of the spin-only $S=1/2$ state for pressure ${P}_{c}g8\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$. This phase transition from the Mott insulating ${J}_{\mathrm{eff}}=1/2$ to the $S=1/2$ states is a unique phenomenon. Our study offers an example of the SOE ${J}_{\mathrm{eff}}$ state under strong electron correlation and its pressure-induced transition to the $S=1/2$ state.

A van Hove singularity (VHS) often significantly amplifies the electronic instability of a crystalline solid, including correlation-induced phenomena such as Hund's metallicity. We perform a systematic study on the interplay between Hund's coupling and electronic structures with a VHS focusing on Hund's metallicity. We construct a simplified tight-binding model targeting cubic perovskite materials and test the effects of the VHS utilizing dynamical mean-field theory with an exact diagonalization solver. The quasiparticle weight and the low-frequency power exponent of the self-energy provide a quantitative estimation of metallicity over the phase diagram. We find the VHS to substantially enhance Hund's metallicity. The results here suggest a range of parameters through which a VHS can bring great synergy with Hund's coupling., Comment: 7 pages, 6 figures

Rotation of MO6 (M = transition metal) octahedra is a key determinant of the physical properties of perovskite materials. Therefore, tuning physical properties, one of the most important goals in condensed matter research, may be accomplished by controlling octahedral rotation (OR). In this study, it is demonstrated that OR can be driven by an electric field in Sr2RuO4. Rotated octahedra in the surface layer of Sr2RuO4 are restored to the unrotated bulk structure upon dosing the surface with K. Theoretical investigation shows that OR in Sr2RuO4 originates from the surface electric field, which can be tuned via the screening effect of the overlaid K layer. This work establishes not only that variation in the OR angle can be induced by an electric field, but also provides a way to control OR, which is an important step toward in situ control of the physical properties of perovskite oxides.

We investigate the roles of spin-orbit coupling and the Van Hove singularity in the dynamical properties of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, which become prominent at zero and very low temperature, by means of density functional theory plus dynamical mean-field theory with an exact diagonalization solver. We examine the crossover between a Fermi liquid and a Hund's metal for a wide range of temperatures and Hund's coupling. In the absence of doping, we confirm that the Fermi liquid persists at zero temperature even with nonzero Hund's coupling. The freezing-moment mechanism suggests that thermal fluctuations lead to a suppression of the Fermi liquid phase and promote Hund's metallicity with incoherence. We show that the Van Hove singularity is an additional key ingredient to drive the suppression at very low temperature by observing a doping dependence of the freezing or long-lived paramagnetic moments. The role of spin-orbit coupling is marked by an amplified Van Vleck contribution of spin susceptibility, significantly promoting Hund's metallicity. Together with the known doping dependence of Hund's metallicity, the additional Van Hove singularity doping dependence found here may allow for the control of the Hund's metallicity of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}({t}_{2g}^{4})$ by a fine tuning of the doping or possibly even strain.

Spin-orbit coupling (SOC) is essential in understanding the properties of $5d$ transition metal compounds, whose SOC value is large and almost comparable to other key parameters. Over the past few years, there have been numerous studies on the SOC-driven effects of the electronic bands, magnetism, and spin-orbit entanglement for those materials with a large SOC. However, how the SOC affects the lattice dynamics is less studied and remains an unsolved problem. We therefore measured the phonon spectra of $5d$ pyrochlore ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$ over the full Brillouin zone to address the question by using inelastic x-ray scattering. Our main finding is a visible mode dependence in the phonon spectra, measured across the metal-insulator transition at 227 K. We examined the SOC strength dependence of the lattice dynamics and its spin-phonon (SP) coupling, with first-principles calculations. Our experimental data taken at 100 K are in good agreement with the theoretical results obtained with the optimized $U=2.0\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ with SOC. By scaling the SOC strength and the $U$ value in the density-functional theory calculations, we demonstrate that SOC is more relevant than $U$ in explaining the observed mode-dependent phonon energy shifts with temperature. Furthermore, the temperature dependence of the phonon energy can be effectively described by scaling SOC. Our work provides clear evidence of SOC producing a non-negligible and essential effect on the lattice dynamics of ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$ and its SP coupling.

5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd2Os2O7. Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii–Moriya and exchange interactions play a significant role in the spin-wave dispersions. The Raman data also reveal complex spin–charge–lattice coupling and indicate that the metal–insulator transition in Cd2Os2O7 is Lifshitz-type. Our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets. Pyrochlore 5d transition metal oxides are expected to have interesting forms of magnetic order but are hard to study with conventional probes. Here the authors show that Raman scattering can be used to measure magnetic excitations in Cd2Os2O7 and that it exhibits complex spin-charge-lattice coupling.

We investigate ultrafast dynamics from photoinduced reflectivity of ${\mathrm{Sr}}_{2}{\mathrm{RhO}}_{4}$ by using femtosecond near-infrared pulses. We observe a clear temperature dependent anomaly in its electronic dynamics which slows down below ${T}_{\mathrm{S}}\ensuremath{\sim}160$ K. In addition, coherent oscillations of the 5.3 THz ${A}_{1g}$ phonon exhibit a ${90}^{\ensuremath{\circ}}$ shift in its initial phase across ${T}_{\mathrm{S}}$, indicating a structural change in octahedral rotation distortions. We propose that octahedral structure in ${\mathrm{Sr}}_{2}{\mathrm{RhO}}_{4}$ evolves around ${T}_{\mathrm{S}}$, and it can influence the nonequilibrium dynamics of photo-induced carriers as well as realtime phonon responses.

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 Y2Ir2O7 using optical spectroscopy. Three infrared-active phonons soften below the Néel temperature of TN ≈ 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.

We investigate the ultrafast dynamics of ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$, a prototype material showing a Lifshitz-type transition as a function of temperature. In the paramagnetic metallic state, the photoreflectivity shows a subpicosecond relaxation, followed by a featureless small offset. In the antiferromagnetic state slightly below ${T}_{N}$, however, the photoreflectivity resurges over hundreds of picoseconds, which goes beyond the usual realm of the effective-temperature model. Our observations are consistent with the Lifshitz phase transition of ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$ driven by the evolution of the local magnetic moment.

Based on first-principles density-functional theory (DFT) calculations, we report that the transition-metal bis-dithiolene, M3C12S12 (M = Mn and Fe), complexes can be a two-dimensional (2D) ferromagnetic insulator with nontrivial Chern number. Among various synthetic pathways leading to metal bis-dithiolenes, the simplest choice of ligand, Benzene-hexathiol, connecting metal cations to form a Kagome lattice is studied following the experimental report of time-reversal symmetric isostructural compound Ni3C12S12. We show sulfur and carbon-based ligands play the key role in making the complexes topologically nontrivial. An unusual topological quantum phase transition induced by the on-site Coulomb interaction brings a nearly flat band with a nonzero Chern number as the highest occupied band. With this analysis we explain the electronic structure of the class M3C12S12 and predict the existence of nearly flat band with nonzero Chern number and it can be a fractional Chern insulator candidate with carrier doping.

Based on first-principles calculations and symmetry analysis, we propose that a transition-metal rutile oxide, in particular ${\ensuremath{\beta}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{PtO}}_{2}$, can host a three-dimensional topological Dirac semimetal phase. We find that ${\ensuremath{\beta}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{PtO}}_{2}$ possesses an inner nodal chain structure when spin-orbit coupling is neglected. Incorporating spin-orbit coupling gaps the nodal chain while preserving a single pair of three-dimensional Dirac points protected by a screw rotation symmetry. These Dirac points are created by a band inversion of two $d$ bands, which is a realization of a Dirac semimetal phase in a correlated electron system. Moreover, a mirror plane in the momentum space carries a nontrivial mirror Chern number ${n}_{M}=\ensuremath{-}2$, which distinguishes ${\ensuremath{\beta}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{PtO}}_{2}$ from the Dirac semimetals known so far, such as ${\mathrm{Na}}_{3}\mathrm{Bi}$ and ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$. If we apply a perturbation that breaks the rotation symmetry and preserves the mirror symmetry, the Dirac points are gapped, and the system becomes a topological crystalline insulator.

The electronic structure of ${\mathrm{SrRuO}}_{3}$ thin film with a thickness from 1 to 50 unit cell (u.c.) is investigated via the resonant inelastic x-ray scattering (RIXS) technique at the O $K$ edge to unravel the intriguing interplay of orbital and charge degrees of freedom. We found that the orbital-selective quantum confinement effect (QCE) induces the splitting of Ru $4d$ orbitals. At the same time, we observed a clear suppression of the electron-hole continuum across the metal-to-insulator transition occurring in the 4-u.c. sample. From these two clear observations we conclude that the QCE gives rise to a Mott insulating phase in ultrathin ${\mathrm{SrRuO}}_{3}$ films. Our interpretation of the RIXS spectra is supported by the configuration interaction calculations of ${\mathrm{RuO}}_{6}$ clusters.

We present results indicating that Chern insulator states can be achieved in the recently synthesized pristine chromium triiodide (${\mathrm{CrI}}_{3}$) by either electron or hole doping. Our first-principles density-functional-theory calculations confirmed that monolayer ${\mathrm{CrI}}_{3}$ show nontrivial Chern number $C$ in both the valence and conduction bands. By introducing on-site Coulomb interaction or epitaxial strain, the doped ${\mathrm{CrI}}_{3}$ exhibit a series of topological quantum phase transitions between multiple Chern insulator phases as well as semimetal-to-insulator transitions. We show that the covalency of Cr $d$-I $p$ bands controlled by the on-site Coulomb interaction $U$ and strain is one of the key ingredients determining the topological phase and semimetal-insulator phase boundary.

Interplay of Fermi surface topology and electron correlation is the quintessential ingredient underlying spontaneous symmetry breaking in itinerant electronic systems. In one-dimensional (1D) systems at half-filling, the inherent Fermi surface nesting makes the translationally invariant metallic state unstable, which is known as Peierls instability. Extending the scope of Peierls instability to two (2D) or three dimensions (3D), however, is not straightforward, since the Fermi surface in higher dimensions is generally not nested. In this work, we show that a perfectly nested Fermi surface can be realized in a class of 2D perovskite oxides, giving rise to 2D Peierls instability. Here the central role is played by the zone boundary Dirac line node (DLN) protected by two orthogonal glide mirrors induced by the rotation of oxygen octahedra. Especially, at a critical angle of the octahedron rotation, the zone-boundary DLN flattens, leading to logarithmically diverging susceptibility. We propose the 2D Peierls instability driven by dispersionless DLN as a principle mechanism for spontaneous symmetry breaking in various layered perovskite oxides including the antiferromagnetism of Sr$_2$IrO$_4$. As a clear signature of the 2D Peierls instability, we predict that the magnetic domain wall in Sr$_2$IrO$_4$ hosts localized soliton modes., 26+31 pages, 6+8 figures

The carrier effective mass plays a crucial role in modern electronic, optical, and catalytic devices and is fundamentally related to key properties of solids such as the mobility and density of states. Here we demonstrate a method to deterministically engineer the effective mass using spatial confinement in metallic quantum wells of the transition metal oxide ${\mathrm{IrO}}_{2}$. Using a combination of in situ angle-resolved photoemission spectroscopy measurements in conjunction with precise synthesis by oxide molecular-beam epitaxy, we show that the low-energy electronic subbands in ultrathin films of rutile ${\mathrm{IrO}}_{2}$ have their effective masses enhanced by up to a factor of 6 with respect to the bulk. The origin of this strikingly large mass enhancement is the confinement-induced quantization of the highly nonparabolic, three-dimensional electronic structure of ${\mathrm{IrO}}_{2}$ in the ultrathin limit. This mechanism lies in contrast to that observed in other transition metal oxides, in which mass enhancement tends to result from complex electron-electron interactions and is difficult to control. Our results demonstrate a general route towards the deterministic enhancement and engineering of carrier effective masses in spatially confined systems, based on an understanding of the three-dimensional bulk electronic structure.

The prototypical correlated metal ${\mathrm{Sr}}_{2}{\mathrm{RhO}}_{4}$ 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 $\mathrm{\ensuremath{\Gamma}}X$. 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.

We utilize near-infrared femtosecond pulses to investigate coherent phonon oscillations of Ca2RuO4. The coherent Ag phonon mode of the lowest frequency changes abruptly not only its amplitude but also the oscillation-phase as the spin order develops. In addition, the phonon mode shows a redshift entering the magnetically ordered state, which indicates a spin-phonon coupling in the system. Density functional theory calculations reveal that the Ag oscillations result in octahedral tilting distortions, which are exactly in sync with the lattice deformation driven by the magnetic ordering. We suggest that the structural distortions by the spin-phonon coupling can induce the unusual oscillation-phase shift between impulsive and displacive type oscillations., 6 pages, 4 figures, 1 table

The original proposal to achieve superconductivity by starting from a quantum spin-liquid (QSL) and doping it with charge carriers, as proposed by Anderson in 1987, has yet to be realized. Here we propose an alternative strategy: use a QSL as a substrate for heterostructure growth of metallic films to design exotic superconductors. By spatially separating the two key ingredients of superconductivity, i.e., charge carriers (metal) and pairing interaction (QSL), the proposed setup naturally lands on the parameter regime conducive to a controlled theoretical prediction. Moreover, the proposed setup allows us to "customize" electron-electron interaction imprinted on the metallic layer. The QSL material of our choice is quantum spin ice well-known for its emergent gauge-field description of spin frustration. Assuming the metallic layer forms an isotropic single Fermi pocket, we predict that the coupling between the emergent gauge-field and the electrons of the metallic layer will drive topological odd-parity pairing. We further present guiding principles for materializing the suitable heterostructure using ab initio calculations and describe the band structure we predict for the case of Y$_2$Sn$_{2-x}$Sb$_x$O$_7$ grown on the (111) surface of Pr$_2$Zr$_2$O$_7$. Using this microscopic information, we predict topological odd-parity superconductivity at a few Kelvin in this heterostructure, which is comparable to the $T_c$ of the only other confirmed odd-parity superconductor Sr$_2$RuO$_4$., Comment: 13 papers, 3 figures + 30 pages of supplemental material

Quantum mechanical tunneling of electrons across ultrathin insulating oxide barriers has been studied extensively for decades due to its great potential in electronic device applications. In the few-nanometer-thick epitaxial oxide films, atomic-scale structural imperfections, such as the ubiquitously existed one-unit-cell-high terrace edges, can dramatically affect the tunneling probability and device performance. However, the underlying physics has not been investigated adequately. Here, taking ultrathin BaTiO3 films as a model system, we report an intrinsic tunneling conductance enhancement near the terrace edges. Scanning probe microscopy results demonstrate the existence of highly-conductive regions (tens of nanometers-wide) near the terrace edges. First-principles calculations suggest that the terrace edge geometry can trigger an electronic reconstruction, which reduces the effective tunneling barrier width locally. Furthermore, such tunneling conductance enhancement can be discovered in other transition-metal-oxides and controlled by surface termination engineering. The controllable electronic reconstruction could facilitate the implementation of oxide electronic devices and discovery of exotic low-dimensional quantum phases., 53 pages, 4 figures, and supporting information

We found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE=Y and La). According to our analysis of high-resolution X-ray and neutron diffraction experiments, the Cu-network of CuRE2Ge2O8 (RE=Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b-axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg = 2 eV. Taken together, our observations make CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering.

We performed angle-resolved photoemission experiments on Au(111) surface with circularly polarized light. Data were taken with photon energies in the range between 20 and 100 eV in order to investigate the photon energy dependent behavior in the circular dichroism (CD). While the magnitude of the normalized CD value varies with a maximum value of about 70%, the sign of CD does not change for the photon energy within the range, inconsistent with the prediction based on the density-functional theory (DFT) calculation. Our calculation of the CD using DFT initial state and free electron final state shows a better consistency with experimental results than an earlier study using the inverse low-energy electron diffraction state as the final state. We briefly discuss the dominating factor that determines the CD from Au(111) states.

Recently, $\alpha$-$\textrm{RuCl}_3$ has attracted much attention as a possible material realization of the honeycomb Kitaev model, which may stabilize a quantum-spin-liquid state. Compared to extensive studies on its magnetic properties, there is still a lack of understanding on its electronic structure, which is strongly related with its Kitaev physics. Here, the electronic structure of $\alpha$-$\textrm{RuCl}_3$ is investigated by photoemission (PE) and inverse photoemission (IPE) spectroscopies. The band gap, directly measured from PE/IPE spectra, is found to be 1.9 eV, much larger than previous estimations. The LDA calculations show that the on-site Coulomb interaction $\textit{U}$ can open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between $\textit{U}$ and SOC plays an essential role in the physics of $\alpha$-$\textrm{RuCl}_3$. There exist some spectral features in PE/IPE spectra which cannot be explained by the LDA calculations. To explain such discrepancies, we perform the configuration-interaction calculations for a ${\textrm{RuCl}}_6^{3-}$ cluster. The experimental data and calculations demonstrate that the 4$\textit{d}$ compound $\alpha$-$\textrm{RuCl}_3$ is a $J_{\textrm{eff}}$ = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters, required in verifying the proposed Kitaev physics in $\alpha$-$\textrm{RuCl}_3$., Comment: 22 pages, 4 figures

We investigated the electronic structure of $[{(\mathrm{SrIr}{\mathrm{O}}_{3})}_{m},(\mathrm{SrTi}{\mathrm{O}}_{3})](m=\phantom{\rule{0.16em}{0ex}}1,\phantom{\rule{0.16em}{0ex}}2,\mathrm{and}\phantom{\rule{0.16em}{0ex}}\ensuremath{\infty})$ superlattice (SL) thin films with optical spectroscopy and first principles calculations. Our optical results confirmed the existence of the ${J}_{\mathrm{eff}}=1/2$ states in SL samples, similar to the bulk Ruddlesden-Popper series $\mathrm{S}{{\mathrm{r}}_{n}}_{+1}\mathrm{I}{\mathrm{r}}_{n}{\mathrm{O}}_{3n+1}$ iridates. Apart from this similarity, in the SL samples, we observed red shifts of the characteristic optical excitations in the ${J}_{\mathrm{eff}}=1/2$ state and an enhancement of the low-energy spectral weight, which implies a reduction in the effective electron correlation for bands near the Fermi energy. The density functional theory plus Coulomb interactions $(\mathrm{DFT}+U)$ calculations suggested that the $\mathrm{SrTi}{\mathrm{O}}_{3}$ layer intervened between $\mathrm{SrIr}{\mathrm{O}}_{3}$ layers in the SLs activated additional hopping channels between the Ir ions, thus increasing the bandwidth and reducing the effective strength of the correlations. This paper demonstrates that fabrication of iridium-based heterostructures can be used to finely tune electronic structures via alteration of their local orbital environments.

We investigated the electronic structure of $\mathrm{Ir}{\mathrm{O}}_{2}$ to address the controversy regarding spin-orbit coupling (SOC) effects in metallic $5d$ transition-metal oxides. Two issues have come to the forefront: (1) SOC effects on electronic structure and physical properties of $\mathrm{Ir}{\mathrm{O}}_{2}$ and (2) the possible formation of a novel ground state in this material, the ${J}_{\mathrm{eff}}=1/2$ state. To better understand the SOC mechanism, we grew epitaxial $\mathrm{Ir}{\mathrm{O}}_{2}$ films whose $dc$ resistivity values were comparable with those of a single crystal. We obtained polarization-dependent optical and x-ray absorption spectra (XAS) and compared these results with those acquired using the generalized gradient approximation (GGA) and $\mathrm{GGA}+\mathrm{SOC}$ calculations. From the optical spectra, peak structures were identified at 0.4 and 2.0 eV, which could only be explained using the $\mathrm{GGA}+\mathrm{SOC}$ calculation. This suggests that SOC plays an important role in the electronic structure of $\mathrm{Ir}{\mathrm{O}}_{2}$. From the polarization-dependent $\mathrm{O}\phantom{\rule{0.16em}{0ex}}1s$ XAS spectra, we observed that the empty state near the Fermi level lacks involvement of an Ir ${d}_{xy}$ orbital. Despite the importance of SOC in $\mathrm{Ir}{\mathrm{O}}_{2}$, the ${J}_{\mathrm{eff}}=1/2$ state does not form in metallic $\mathrm{Ir}{\mathrm{O}}_{2}$.

Hypercholesterolemia is a main feature of nephrotic syndrome (NS) and is, in part, caused by acquired low-density lipoprotein (LDL) receptor deficiency. The LDL receptor deficiency in NS is accompanied by normal hepatic LDL receptor messenger RNA (mRNA) abundance. Expression of LDL receptor, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, and several other cholesterol-regulatory factors is regulated by sterol regulatory element binding protein 2 (SREBP-2). This study tested the hypothesis that nephrotic hypercholesterolemia may be associated with dysregulation of hepatic tissue SREBP-2 abundance or activity. Protein and mRNA abundance of SREBP-2, LDL receptor, and HMG-CoA reductase was determined in the livers of rats with chronic puromycin-induced NS and of control rats. The nephrotic group showed heavy proteinuria, hypoalbuminemia, severe hypercholesterolemia, and normal liver tissue total and free cholesterol concentrations. Despite severe hypercholesterolemia, the inactive microsomal and the active nuclear SREBP-2 levels were unchanged in the liver of the nephrotic animals. This was associated with a marked reduction in LDL receptor protein abundance. In confirmation of our earlier studies, LDL receptor and HMG-CoA reductase mRNA levels were unchanged in nephrotic animals. Hepatic SREBP-2 abundance and activity in hypercholesterolemic nephrotic rats were similar to those found in the normocholesterolemic control animals, representing a maladaptive response. This paradox may be, in part, due to acquired LDL receptor deficiency that helps sustain SREBP-2 expression/activity and maintain hypercholesterolemia by limiting hepatic cholesterol uptake. This is because SREBP-2 expression and activity are, in part, regulated by intracellular as opposed to plasma cholesterol.

Objective: Obesity is associated with oxidative stress and inflammation. We hypothesized that the pro-inflammatory state in obesity may result in spontaneous activation and, hence, increased generation of reactive oxygen species (ROS) and integrin expression in the circulating leukocytes. Methods: Flow cytometry was used to determine integrin expression (immunostaining) as well as superoxide and hydrogen peroxide productions (fluorescent probes) in the peripheral blood and splenic leukocyte of 24-week-old male obese normotensive and not-as-yet diabetic Zucker rats (n = 6) and their lean counterparts (n = 6). Results: Obese rats had hyperlipidemia and normal arterial pressure, plasma glucose, and creatinine concentrations. Nevertheless, obese rats exhibited increased hydrogen peroxide production by circulating and splenic CD4+ and CD8+ T lymphocytes and by splenic macrophages. This was accompanied by up-regulations of CD11a expression in the peripheral blood and splenic CD4+ T cells, CD11b in circulating macrophages, and CD11a and CD18 in circulating granulocytes. Conclusion: The study revealed direct evidence of spontaneous leukocyte activation and increased ROS generation by T lymphocytes and monocytes in the peripheral blood of obese Zucker rats before the development of diabetes or hypertension. These findings illustrate the link between obesity, oxidative stress, and inflammation.

Background Renal tubulointerstitial infiltration of activated T cells and macrophages is invariably present and plays a role in elevation of arterial pressure in nearly all animal models of hypertension (HTN). The role, if any, of elevated renal arterial pressure in the pathogenesis of this inflammatory process is uncertain. Also unclear is whether the cellular infiltration is caused by the local activation of immune cells in the kidney or a consequence of leukocyte activation in the systemic circulation. Methods We studied activation of peripheral blood leukocytes and cellular infiltration in the kidneys of Sprague-Dawley rats with abdominal aorta coarctation (banding) above renal arteries, which causes severe HTN proximal but not distal to coarctation. Results Compared with the sham operated controls, the aorta-banded group exhibited tubulointerstitial accumulation of activated T cells, macrophages, angiotensin-II positive cells, leukocyte function–associated antigen–1 integrin expressing cells, increased nitrotyrosine abundance (a measure of oxidative stress), and increased macrophage chemoattractant protein–1 in the kidneys which are not exposed to HTN in this model. These findings were associated with the activation of the circulating leukocytes in the aorta-banded animals. Conclusions Increased baromechanical stress is not a requisite for accumulation of T cells and macrophages in the kidney in the coarctation-induced HTN and possibly in other hypertensive disorders. On the contrary, renal hypoperfusion and the consequent activation of renin-angiotensin system may mediate this process by promoting local induction of chemoattractant and inflammatory cytokines. The observed tubulointerstitial inflammation in this model is associated with leukocyte activation in the systemic circulation.

Hypertension promotes integrin expression and reactive oxygen species generation by circulating leukocytes. Background Compelling evidence has emerged pointing to the role of oxidative stress in the pathogenesis of hypertension (HTN) in experimental animals. Excess production of reactive oxygen species (ROS) in the renal and vascular tissues has been shown to raise arterial pressure via inactivation of nitric oxide and generation of isoprostanes. Accumulation of inflammatory cells in the renal interstitium has been shown to increase ROS generation in the kidneys of hypertensive animals. In addition, considerable evidence has emerged pointing to spontaneous activation of circulating leukocytes in animals and humans with hereditary HTN. This study was designed to explore whether induction of HTN in genetically normal animals can lead to spontaneous activation and ROS production in circulating leukocytes. Methods Integrin expression, superoxide, and hydrogen peroxide production were assessed by flow cytometry in the circulating and splenic leukocytes of Sprague-Dawley rats rendered hypertensive by abdominal aorta banding above the renal arteries, and in sham-operated control rats. Results The hypertensive animals studied 4 weeks after abdominal aorta banding exhibited a significant increase in superoxide and H 2 O 2 production in the circulating granulocyte, and a marked increase in H 2 O 2 production in the blood and splenic helper and cytotoxic T-lymphocytes. This was coupled with a significant up-regulation of CD18 and CD11a in splenic helper T-cells and cytotoxic T cells, and of CD18 in the circulating helper T cells. Conclusion Induction of HTN in genetically normotensive rats causes a spontaneous increase in ROS generation in the circulating and splenic leukocytes. This phenomenon can contribute to systemic oxidative stress, inflammation, cardiovascular and renal complications in hypertensive animals.

Up-regulation of hepatic Acyl CoA: Diacylglycerol acyltransferase-1 (DGAT-1) expression in nephrotic syndrome. Background Nephrotic syndrome is associated with hypercholesterolemia, hypertriglyceridemia, and marked elevations of plasma low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL). Hypertriglyceridemia in nephrotic syndrome is accompanied by increased hepatic fatty acid synthesis, elevated triglyceride secretion, as well as lipoprotein lipase, VLDL-receptor, and hepatic triglyceride lipase deficiencies, which lead to impaired clearance of triglyceride-rich lipoproteins. Acyl CoA: diacylglycerol acyltransferase (DGAT) is a microsomal enzyme that joins acyl CoA to 1, 2-diacylglycerol to form triglyceride. Two distinct DGATs (DGAT-1 and DGAT2) have recently been identified in the liver and other tissues. The present study tested the hypothesis that the reported increase in hepatic triglyceride secretion in nephrotic syndrome may be caused by up-regulation of DGAT. Methods Male Sprague-Dawley rats were rendered nephrotic by two sequential injections of puromycin aminonucleoside (130 mg/kg on day 1 and 60 mg/kg on day 14) and studied on day 30. Placebo-treated rats served as controls. Hepatic DGAT-1 and DGAT-2 mRNA abundance and enzymatic activity were measured. Results The nephrotic group exhibited heavy proteinuria, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia, and marked elevation of VLDL concentration. Hepatic DGAT-1 mRNA, DGAT-1, and total DGAT activity were significantly increased, whereas DGAT-2 mRNA abundance and activity were unchanged in the nephrotic rats compared to the control animals. The functional significance of elevation of DGAT activity was illustrated by the reduction in microsomal free fatty acid concentration in the liver of nephrotic animals. Conclusion Nephrotic syndrome results in up-regulation of hepatic DGAT-1 expression and activity, which can potentially contribute to the associated hypertriglyceridemia by enhancing triglyceride synthesis. Thus, it appears that both depressed catabolism and increased synthetic capacity contribute to hypertriglyceridemia of nephrotic syndrome.

We employ reactive molecular-beam epitaxy to synthesize the metastable perovskite SrIrO$_{3}$ and utilize {\it in situ} angle-resolved photoemission to reveal its electronic structure as an exotic narrow-band semimetal. We discover remarkably narrow bands which originate from a confluence of strong spin-orbit interactions, dimensionality, and both in- and out-of-plane IrO$_6$ octahedral rotations. The partial occupation of numerous bands with strongly mixed orbital characters signals the breakdown of the single-band Mott picture that characterizes its insulating two-dimensional counterpart, Sr$_{2}$IrO$_{4}$, illustrating the power of structure-property relations for manipulating the subtle balance between spin-orbit interactions and electron-electron interactions.

We employ molecular beam epitaxy to stabilize ${\mathrm{Ba}}_{2}{\mathrm{IrO}}_{4}$ thin films and utilize in situ angle-resolved photoemission spectroscopy to investigate the evolution of its electronic structure through the N\'eel temperature ${T}_{\mathrm{N}}$. Our measurements indicate that dispersions of the relativistic ${J}_{\mathrm{eff}}=1/2$ and 3/2 bands exhibit an unusual dichotomy in their behavior through the N\'eel transition. Although the charge gap survives into the paramagnetic state, only the ${J}_{\mathrm{eff}}=1/2$ state exhibits a strong temperature dependence and its gap softens with increasing temperature approaching ${T}_{\mathrm{N}}$, while the nearly fully occupied ${J}_{\mathrm{eff}}=3/2$ state which remains nearby in energy exhibits negligible changes with temperature.

The effect of ciprofloxacin, a quinolone antibiotic widely used to treat opportunistic bacterial infections in AIDS patients, was examined in the context of reactivation of latent HIV-1 in chronically infected promonocytic U1 cells. Ciprofloxacin inhibited, in a dose-dependent manner, HIV-1 expression in U1 cells activated with phorbol 12-myristate 13-acetate (PMA). The inhibitory effect of ciprofloxacin was associated with a reduction in the production of tumor necrosis factor alpha, inhibition of activation of transcriptional factor NF-kappaB, and HIV LTR-driven gene expression. Furthermore, ciprofloxacin inhibited TNF-alpha-induced HIV expression in U1 cells. The concentrations of ciprofloxacin that inhibited HIV production are readily achievable in vivo.

Purpose: To determine whether probenecid, an inhibitor of organic anion transport, is able to reverse multidrug resistance (MDR) through modulation of the drug transport function of MDR-associated protein (MRP) and P-glycoprotein (P-gP). Methods: Two MRP-overexpressing cell lines (HL60/AR and H69/AR) and two P-gP-overexpressing cell lines (HL60/Tax and P388/ADR) were cultured with different concentrations of daunorubicin (DNR) or vincristine (VCR) in the presence or absence of various concentrations of probenecid (0.01-10 mM). Drug sensitivity was determined using an MTT assay. DNR accumulation and subcellular distribution were determined by flow cytometry and confocal microscopy respectively. VCR accumulation was determined by scintillation spectrometry. Results: Probenecid, in a concentration-dependent manner, reversed resistance to DNR and VCR in HL60/AR and H69/AR tumor cell lines. This effect of probenecid on MDR was associated with an increased accumulation of DNR and VCR and correction of the altered subcellular distribution of DNR. The concentrations of probenecid that reversed MDR are clinically achievable in vivo. In contrast, probenecid did not reverse MDR in either HL60/Tax or P388/ADR tumor cell lines that overexpress P-gP. Conclusion: These results suggest that probenecid is an effective chemosensitizer of MRP-associated MDR tumor cells and is a potential candidate for clinical use to reverse MDR.