Observation of Nonlinear Spin-Charge Conversion in the Thin Film of Nominally Centrosymmetric Dirac Semimetal SrIrO_{3} at Room Temperature.

Spin-charge conversion via spin-orbit interaction is one of the core concepts in the current spintronics research. The efficiency of the interconversion between charge and spin current is estimated based on Berry curvature of Bloch wave function in the linear-response regime. Beyond the linear regime, nonlinear spin-charge conversion in the higher-order electric field terms has recently been demonstrated in noncentrosymmetric materials with nontrivial spin texture in the momentum space. Here, we report the observation of the nonlinear charge-spin conversion in a nominally centrosymmetric oxide material SrIrO_{3} by breaking inversion symmetry at the interface. A large second-order magnetoelectric coefficient is observed at room temperature because of the antisymmetric spin-orbit interaction at the interface of Dirac semimetallic bands, which is subject to the symmetry constraint of the substrates. Our study suggests that nonlinear spin-charge conversion can be induced in many materials with strong spin-orbit interaction at the interface by breaking the local inversion symmetry to give rise to spin splitting in otherwise spin degenerate systems.

Using the technology acceptance model to explore health provider and administrator perceptions of the usefulness and ease of using technology in palliative care.

BACKGROUND: Studies have shown that telehealth applications in palliative care are feasible, can improve quality of care, and reduce costs but few studies have focused on user acceptance of current technology applications in palliative care. Furthermore, the perspectives of health administrators have not been explored in palliative care and yet they are often heavily involved, alongside providers, in the coordination and use of health technologies. The study aim was to explore both health care provider and administrator perceptions regarding the usefulness and ease of using technology in palliative care. METHODS: The Technology Acceptance Model (TAM) was used as the guiding theoretical framework to provide insight into two key determinants that influence user acceptance of technology (perceived usefulness and ease of use). Semi-structured interviews (n = 18) with health providers and administrators with experience coordinating or using technology in palliative care explored the usefulness of technologies in palliative care and recommendations to support adoption. Interview data were analyzed using inductive thematic analysis to identify common, meaningful themes. RESULTS: Four themes were identified; themes related to perceived usefulness were: enabling remote connection and information-sharing platform. Themes surrounding ease of use included: integration with existing IT systems and user-friendly with ready access to technical support. Telehealth can enable remote connection between patients and providers to help address insufficiencies in the current palliative care environment. Telehealth, as an information sharing platform, could support the coordination and collaboration of interdisciplinary providers caring for patients with palliative needs. However, health technologies need to passively integrate with existing IT systems to enhance providers' workflow and productivity. User-friendliness with ready access to technical support was considered especially important in palliative care as patients often experience diminished function. CONCLUSION: Participants' perspectives of technology acceptance in palliative care were largely dependent on their potential to help address major challenges in the field without imposing significant burden on providers and patients.

Exploring how virtual primary care visits affect patient burden of treatment.

BACKGROUND: There is growing emphasis on the role of digital solutions in supporting chronic disease management. This has the potential to increase the burden patients experience in managing their health by offloading care from the health system to patients. This paper explores the effects of virtual visits on patient burden using an explicit framework measuring both the work patients do to care for their health and the challenges they experience that exacerbate burden. METHODS: This mixed methods study evaluates a large pilot implementation of virtual visits (video, audio, and asynchronous messaging with providers) in primary care in Ontario, Canada. Participants were recruited using convenience sampling from patients using a virtual visit platform to complete a semi-structured interview or a survey including a free-text response. We conducted 17 interviews and reviewed 427 free text responses related to explore patients' perceived value and burden of these visits. We used qualitative analyses to map patients' feedback on their experience to the framework on patient burden. MAIN FINDINGS: Virtual visits appear to reduce the work patients must do to manage their care by 1) improving access, convenience, and time needed for medical appointments, and 2) making it easier to access information and support for chronic disease management. Virtual visits also alleviate patients' perceived burden by improving continuity of care, experience of care, and providing some cost savings. CONCLUSIONS: Virtual visits reduced overall patient burden of treatment by decreasing the required patient effort of managing medical appointments and monitoring their health, and by minimizing challenges experienced when accessing care. For regions that want to improve patient experience of care, virtual visits are likely to be of benefit. There is need for further research on the generalizability of the findings herein, particularly for high-needs populations under-represented such as those of low socioeconomic status and those in rural and remote locations.

Large Variation of Dirac Semimetal State in Perovskite CaIrO_{3} with Pressure-Tuning of Electron Correlation.

The impact of electron correlation on the Dirac semimetal state is investigated for perovskite CaIrO_{3} in terms of the magnetotransport properties under varying pressures. The reduction of electron correlation with a pressure of 1 GPa enhances the Fermi velocity as much as 40%, but it reduces the mobility by an order of magnitude by detuning the Dirac node from the Fermi energy. Moreover, the giant magnetoresistance at the quantum limit due to the one-dimensional confinement of Dirac electrons is critically suppressed under pressure. These results indicate that the electron correlation is a crucial knob for controlling the transport of a correlated Dirac semimetal.

Spectral dynamics of shift current in ferroelectric semiconductor SbSI.

Photoexcitation in solids brings about transitions of electrons/holes between different electronic bands. If the solid lacks an inversion symmetry, these electronic transitions support spontaneous photocurrent due to the geometric phase of the constituting electronic bands: the Berry connection. This photocurrent, termed shift current, is expected to emerge on the timescale of primary photoexcitation process. We observe ultrafast evolution of the shift current in a prototypical ferroelectric semiconductor antimony sulfur iodide (SbSI) by detecting emitted terahertz electromagnetic waves. By sweeping the excitation photon energy across the bandgap, ultrafast electron dynamics as a source of terahertz emission abruptly changes its nature, reflecting a contribution of Berry connection on interband optical transition. The shift excitation carries a net charge flow and is followed by a swing over of the electron cloud on a subpicosecond timescale. Understanding these substantive characters of the shift current with the help of first-principles calculation will pave the way for its application to ultrafast sensors and solar cells.

Strong-correlation induced high-mobility electrons in Dirac semimetal of perovskite oxide.

Electrons in conventional metals become less mobile under the influence of electron correlation. Contrary to this empirical knowledge, we report here that electrons with the highest mobility ever found in known bulk oxide semiconductors emerge in the strong-correlation regime of the Dirac semimetal of perovskite CaIrO3. The transport measurements reveal that the high mobility exceeding 60,000 cm2V-1s-1 originates from the proximity of the Fermi energy to the Dirac node (ΔE < 10 meV). The calculation based on the density functional theory and the dynamical mean field theory reveals that the energy difference becomes smaller as the system approaches the Mott transition, highlighting a crucial role of correlation effects cooperating with the spin-orbit coupling. The correlation-induced self-tuning of Dirac node enables the quantum limit at a modest magnetic field with a giant magnetoresistance, thus providing an ideal platform to study the novel phenomena of correlated Dirac electron.

Tensile-Strain-Dependent Spin States in Epitaxial LaCoO_{3} Thin Films.

The spin states of Co^{3+} ions in perovskite-type LaCoO_{3}, governed by the complex interplay between the electron-lattice interactions and the strong electron correlations, still remain controversial due to the lack of experimental techniques which can directly detect them. In this Letter, we revealed the tensile-strain dependence of spin states, i.e., the ratio of the high- and low-spin states, in epitaxial thin films and a bulk crystal of LaCoO_{3} via resonant inelastic soft x-ray scattering. A tensile strain as small as 1.0% was found to realize different spin states from that in the bulk.

Optical Magnetoelectric Resonance in a Polar Magnet (Fe,Zn)_{2}Mo_{3}O_{8} with Axion-Type Coupling.

We report the polarization rotation of terahertz light resonant with the magnetoelectric (ME) spin excitation in the multiferroic (Fe,Zn)_{2}Mo_{3}O_{8}. This resonance reflects the frequency dispersion of the diagonal ME susceptibility (axion term), with which we quantitatively reproduce the thermal and magnetic-field evolution of the observed polarization rotation spectra. The application of the sum rule on the extrapolated dc value of the spectral weight of the ME oscillator provides insight into the dc linear ME effect. The present finding highlights a novel optical functionality of spin excitations in multiferroics that originates from diagonal ME coupling.

Diversity of solitons in a generalized nonlinear Schrödinger equation with self-steepening and higher-order dispersive and nonlinear terms.

In this article, we show that if the nonlinear Schrödinger (NLS) equation is generalized by simultaneously taking into account higher-order dispersion, a quintic nonlinearity, and self-steepening terms, the resulting equation is interesting as it has exact soliton solutions which may be (depending on the values of the coefficients) stable or unstable, standard or "embedded," fixed or "moving" (i.e., solitons which advance along the retarded-time axis). We investigate the stability of these solitons by means of a modified version of the Vakhitov-Kolokolov criterion, and numerical tests are carried out to corroborate that these solitons respond differently to perturbations. It is shown that this generalized NLS equation can be derived from a Lagrangian density which contains an auxiliary variable, and Noether's theorem is then used to show that the invariance of the action integral under infinitesimal gauge transformations generates a whole family of conserved quantities. Finally, we study if this equation has the Painlevé property.

Ferroelectric-like metallic state in electron doped BaTiO3.

We report that a ferroelectric-like metallic state with reduced anisotropy of polarization is created by the doping of conduction electrons into BaTiO3, on the bases of x-ray/electron diffraction and infrared spectroscopic experiments. The crystal structure is heterogeneous in nanometer-scale, as enabled by the reduced polarization anisotropy. The enhanced infrared intensity of soft phonon along with the resistivity reduction suggests the presence of unusual electron-phonon coupling, which may be responsible for the emergent ferroelectric structure compatible with metallic state.

Magnetic Field-Induced Insulator-Semimetal Transition in a Pyrochlore Nd2Ir2O7.

We investigate magnetotransport properties in a single crystal of pyrochore-type Nd2Ir2O7. The metallic conduction is observed on the antiferromagnetic domain walls of the all-in-all-out-type Ir 5d moment ordered insulating bulk state that can be finely controlled by an external magnetic field along [111]. On the other hand, an applied field along [001] induces the bulk phase transition from insulator to semimetal as a consequence of the field-induced modification of the Nd 4f and Ir 5d moment configurations. A theoretical calculation consistently describing the experimentally observed features suggests a variety of exotic topological states as functions of electron correlation and Ir 5d moment orders, which can be finely tuned by the choice of rare-earth ion and magnetic field, respectively.

Radiating subdispersive fractional optical solitons.

It was recently found [Fujioka et al., Phys. Lett. A 374, 1126 (2010)] that the propagation of solitary waves can be described by a fractional extension of the nonlinear Schrödinger (NLS) equation which involves a temporal fractional derivative (TFD) of order α > 2. In the present paper, we show that there is also another fractional extension of the NLS equation which contains a TFD with α < 2, and in this case, the new equation describes the propagation of radiating solitons. We show that the emission of the radiation (when α < 2) is explained by resonances at various frequencies between the pulses and the linear modes of the system. It is found that the new fractional NLS equation can be derived from a suitable Lagrangian density, and a fractional Noether's theorem can be applied to it, thus predicting the conservation of the Hamiltonian, momentum and energy.

Fractional fluctuation effects on the light scattered by a viscoelastic suspension.

We generalize fluctuating hydrodynamics to study the effect of fractional time derivatives on the light-scattering spectrum of a suspension in a viscoelastic solvent under an external density gradient. Viscoelasticity introduces additional memory effects into the fluctuating hydrodynamic equations, causing the time scales associated with the mesoscopic variables and those of the microscopic events to be no longer well separated. This situation is taken into account by introducing Caputo's fractional time derivative into the description. The structure factor of the suspension is calculated, and we find that its nonequilibrium correction is an odd function of the frequency. It exhibits a shift towards negative frequencies proportional to the magnitude of the imposed gradient. We consider solvents that are described by Maxwell's or power-law rheological equations of state. The fractional structure factor is compared with the nonfractional one, and it is found that the ratio of the former to the latter may be positive and up to two orders of magnitude for both types of viscoelasticity. This prediction of our model calculation suggests that this relative change might be measurable.

Spin-orbital superstructure in strained ferrimagnetic perovskite cobalt oxide.

We have investigated the Co-3d spin-orbital state in a thin film of perovskite LaCoO3 to clarify the origin of strain induced spontaneous magnetization (T(C)=94 K) by means of x-ray diffraction, optical spectroscopy, and magnetization measurements. A lattice distortion with the propagation vector (1/4 -1/4 1/4) and an anomalous activation of optical phonons coupled to Co-3d orbital are observed below 126 K. Combined with the azimuthal angle analysis of superlattice reflection, we propose that the ordering of Co-3d orbital promoted by an epitaxial strain produces a unique ferrimagnetic structure.

Electronic phase transition and an anomalous ordered phase in Ba2Ti13O22 with 3d1 ions on a triangle-based lattice.

We found that Ba(2)Ti(13)O(22) with Ti(3+) (3d(1)) ions on a triangle-based lattice exhibits a phase transition at T(c)~200 K, below which the increase of electrical resistivity and decrease of magnetic susceptibility were observed. Transmission electron microscopy and optical reflectivity measurements indicate that the low-temperature phase of the present compound shares characteristics in common with a charge-density-wave state with remnant carriers, although a commensurate wave vector of the modulation and a linear temperature dependence of the magnetic susceptibility below T(c) suggest an exotic ordered state.

Variation of charge dynamics in the course of metal-insulator transition for pyrochlore-type Nd2Ir2O7.

We have spectroscopically investigated the thermally and doping-induced metal-insulator transitions for pyrochlore-type Nd2Ir2O7 as well as its Rh-doped analogs Nd2(Ir(1-x)Rh(x))(2)O(7), where the spin-orbit interaction as well as the electron correlation is effectively tuned by the doping level (x). The charge dynamics dramatically changes on an energy scale of 1 eV in the course of thermally and doping-induced metal-insulator transitions, while the insulating ground state shows a small but well-defined charge gap of 45 meV. Anomalous doping variation of the low-energy (<0.3 eV) optical-conductivity spectra at the ground state can be interpreted in terms of the phase changes among the narrow-gap Mott insulator, Weyl semimetal, and correlated metal.

Symmetry breaking in linearly coupled Korteweg-de Vries systems.

We consider solitons in a system of linearly coupled Korteweg-de Vries (KdV) equations, which model two-layer settings in various physical media. We demonstrate that traveling symmetric solitons with identical components are stable at velocities lower than a certain threshold value. Above the threshold, which is found exactly, the symmetric modes are unstable against spontaneous symmetry breaking, which gives rise to stable asymmetric solitons. The shape of the asymmetric solitons is found by means of a variational approximation and in the numerical form. Simulations of the evolution of an unstable symmetric soliton sometimes produce its breakup into two different asymmetric modes. Collisions between moving stable solitons, symmetric and asymmetric ones, are studied numerically, featuring noteworthy features. In particular, collisions between asymmetric solitons with identical polarities are always elastic, while in the case of opposite polarities the collision leads to a switch of the polarities of both solitons. Three-soliton collisions are studied too, featuring quite complex interaction scenarios.

Chaotic solitons in the quadratic-cubic nonlinear Schrödinger equation under nonlinearity management.

We analyze the response of rational and regular (hyperbolic-secant) soliton solutions of an extended nonlinear Schrödinger equation (NLSE) which includes an additional self-defocusing quadratic term, to periodic modulations of the coefficient in front of this term. Using the variational approximation (VA) with rational and hyperbolic trial functions, we transform this NLSE into Hamiltonian dynamical systems which give rise to chaotic solutions. The presence of chaos in the variational solutions is corroborated by calculating their power spectra and the correlation dimension of the Poincaré maps. This chaotic behavior (predicted by the VA) is not observed in the direct numerical solutions of the NLSE when rational initial conditions are used. The solitary-wave solutions generated by these initial conditions gradually decay under the action of the nonlinearity management. On the contrary, the solutions of the NLSE with exponentially localized initial conditions are robust solitary-waves with oscillations consistent with a chaotic or a complex quasiperiodic behavior.

Displacement-type ferroelectricity with off-center magnetic ions in perovskite Sr(1-x)Ba(x)MnO3.

We report a ferroelectric transition driven by the off-centering of magnetic Mn(4+) ions in antiferromagnetic Mott insulators Sr(1-x)Ba(x)MnO(3) with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ferroelectricity shows up for x ≥ 0.45. The observed polarization is comparable to that for a prototypical ferroelectric BaTiO(3). We further demonstrate that the magnetic order suppresses the ferroelectric lattice dilation by ∼70% and increases the soft-phonon energy by ∼50%, indicating the largest magnetoelectric effects yet attained.

Dynamical disorder of pi-molecular structures induced by proton dynamics in an organic ferroelectric compound.

We have investigated the optical response resulting from the proton-pi-electron-molecular-skeleton coupled dynamics in an organic ferroelectric 55DMBP-Hia. Upon the ferroelectric-to-paraelectric transition, almost all of the vibrational modes below 500 cm;{-1} are anomalously blurred and amalgamated into the high-frequency tail of the polarization-relaxation mode. This indicates that the constituent molecular shape is no more well defined around T_{C} due to the dynamical disorder of the pi-conjugated structure originating from proton delocalization on the intermolecular bifurcated hydrogen bond.