Visualizing Poiseuille flow of hydrodynamic electrons.

Hydrodynamics, which generally describes the flow of a fluid, is expected to hold even for fundamental particles such as electrons when inter-particle interactions dominate1. Although various aspects of electron hydrodynamics have been revealed in recent experiments2-11, the fundamental spatial structure of hydrodynamic electrons-the Poiseuille flow profile-has remained elusive. Here we provide direct imaging of the Poiseuille flow of an electronic fluid, as well as a visualization of its evolution from ballistic flow. Using a scanning carbon nanotube single-electron transistor12, we image the Hall voltage of electronic flow through channels of high-mobility graphene. We find that the profile of the Hall field across the channel is a key physical quantity for distinguishing ballistic from hydrodynamic flow. We image the transition from flat, ballistic field profiles at low temperatures into parabolic field profiles at elevated temperatures, which is the hallmark of Poiseuille flow. The curvature of the imaged profiles is qualitatively reproduced by Boltzmann calculations, which allow us to create a 'phase diagram' that characterizes the electron flow regimes. Our results provide direct confirmation of Poiseuille flow in the solid state, and enable exploration of the rich physics of interacting electrons in real space.

Geometric Stiffness in Interlayer Exciton Condensates.

Recent experiments have confirmed the presence of interlayer excitons in the ground state of transition metal dichalcogenide bilayers. The interlayer excitons are expected to show remarkable transport properties when they undergo Bose condensation. In this Letter, we demonstrate that quantum geometry of Bloch wave functions plays an important role in the phase stiffness of the interlayer exciton condensate. Notably, we identify a geometric contribution that amplifies the stiffness, leading to the formation of a robust condensate with an increased Berezinskii-Kosterlitz-Thouless temperature. Our results have direct implications for the ongoing experimental efforts on interlayer excitons in materials that have nontrivial quantum geometry. We provide estimates for the geometric contribution in transition metal dichalcogenide bilayers through a realistic continuum model with gated Coulomb interaction, and find that the substantially increased stiffness may allow an interlayer exciton condensate to be realized at amenable experimental conditions.

A Class of Magnetic Topological Material Candidates with Hypervalent Bi Chains.

The link between crystal and electronic structure is crucial for understanding structure-property relations in solid-state chemistry. In particular, it has been instrumental in understanding topological materials, where electrons behave differently than they would in conventional solids. Herein, we identify 1D Bi chains as a structural motif of interest for topological materials. We focus on Sm3ZrBi5, a new quasi-one-dimensional (1D) compound in the Ln3MPn5 (Ln = lanthanide; M = metal; Pn = pnictide) family that crystallizes in the P63/mcm space group. Density functional theory calculations indicate a complex, topologically nontrivial electronic structure that changes significantly in the presence of spin-orbit coupling. Magnetic measurements show a quasi-1D antiferromagnetic structure with two magnetic transitions at 11.7 and 10.7 K that are invariant to applied field up to 9 T, indicating magnetically frustrated spins. Heat capacity, electrical, and thermoelectric measurements support this claim and suggest complex scattering behavior in Sm3ZrBi5. This work highlights 1D chains as an unexplored structural motif for identifying topological materials, as well as the potential for rich physical phenomena in the Ln3MPn5 family.

Delocalization Transition of a Disordered Axion Insulator.

The axion insulator is a higher-order topological insulator protected by inversion symmetry. We show that, under quenched disorder respecting inversion symmetry on average, the topology of the axion insulator stays robust, and an intermediate metallic phase in which states are delocalized is unavoidable at the transition from an axion insulator to a trivial insulator. We derive this conclusion from general arguments, from classical percolation theory, and from the numerical study of a 3D quantum network model simulating a disordered axion insulator through a layer construction. We find the localization length critical exponent near the delocalization transition to be ν=1.42±0.12. We further show that this delocalization transition is stable even to weak breaking of the average inversion symmetry, up to a critical strength. We also quantitatively map our quantum network model to an effective Hamiltonian and we find its low-energy k·p expansion.

Splitting the Hinge Mode of Higher-Order Topological Insulators.

The surface of a higher order topological insulator comprises a two-dimensional topological insulator (TI) with broken inversion symmetry, whose mass is determined by the microscopic details of the surface such as surface potentials and termination. It hosts a helical mode pinned to selected hinges where the surface gap changes its sign. We study the effect of perturbations that break time reversal and particle conservation on this helical mode, such as a Zeeman field and a proximate superconductor. We find that in contrast to the helical modes of inversion symmetric TIs, which are gapped by these couplings, the helical modes at the hinges can remain gapless and spatially split. When this happens, the Zeeman field splits the helical mode into a chiral mode surrounding the magnetized region, and a superconductor results in a helical Majorana mode surrounding the superconducting region. The combination of the two might lead to the gapping of one of the chiral Majorana modes, and leave a single one-dimensional chiral Majorana mode around the superconducting island. We propose that the different topological states can be measured in electrical transport.

Unified Description of the Classical Hall Viscosity.

In the absence of time-reversal symmetry, viscous electron flow hosts a number of interesting phenomena, of which we focus here on the Hall viscosity. Taking a step beyond the hydrodynamic definition of the Hall viscosity, we derive a generalized relation between the Hall viscosity and the transverse electric field using a kinetic equation approach. We explore two different geometries where the Hall viscosity is accessible to measurement. For hydrodynamic flow of electrons in a narrow channel, we find that the viscosity may be measured by a local probe of the transverse electric field near the center of the channel. Ballistic flow, on the other hand, is dominated by boundary effects. In a Corbino geometry, viscous effects arise not from boundary friction but from the circular flow pattern of the Hall current. In this geometry, we introduce a viscous Hall angle that remains well defined throughout the crossover from ballistic to hydrodynamic flow and captures the bulk viscous response of the fluid.

Partial Lattice Defects in Higher-Order Topological Insulators.

Nonzero weak topological indices are thought to be a necessary condition to bind a single helical mode to lattice dislocations. In this work we show that higher-order topological insulators (HOTIs) can, in fact, host a single helical mode along screw or edge dislocations (including step edges) in the absence of weak topological indices. When this occurs, the helical mode is necessarily bound to a dislocation characterized by a fractional Burgers vector, macroscopically detected by the existence of a stacking fault. The robustness of a helical mode on a partial defect is demonstrated by an adiabatic transformation that restores translation symmetry in the stacking fault. We present two examples of HOTIs, one intrinsic and one extrinsic, that show helical modes at partial dislocations. Since partial defects and stacking faults are commonplace in bulk crystals, the existence of such helical modes can measurably affect the expected conductivity in these materials.

Managing opioid use disorder in primary care: PEER simplified guideline.

OBJECTIVE: To use the best available evidence and principles of shared, informed decision making to develop a clinical practice guideline for a simplified approach to managing opioid use disorder (OUD) in primary care. METHODS: Eleven health care and allied health professionals representing various practice settings, professions, and locations created a list of key questions relevant to the management of OUD in primary care. These questions related to the treatment setting, diagnosis, treatment, and management of comorbidities in OUD. The questions were researched by a team with expertise in evidence evaluation using a series of systematic reviews of randomized controlled trials. The Guideline Committee used the systematic reviews to create recommendations. RECOMMENDATIONS: Recommendations outline the role of primary care in treating patients with OUD, as well as pharmacologic and psychotherapy treatments and various prescribing practices (eg, urine drug testing and contracts). Specific recommendations could not be made for management of comorbidities in patients with OUD owing to limited evidence. CONCLUSION: The recommendations will help simplify the complex management of patients with OUD in primary care. They will aid clinicians and patients in making informed decisions regarding their care.

Selection Rules for Quasiparticle Interference with Internal Nonsymmorphic Symmetries.

We study how nonsymmorphic symmetries that commute with lattice translations are reflected in the quasiparticle interference (QPI) maps measured by scanning tunneling microscopy (STM). QPI maps, which result from scattering of Bloch states off impurities, record the interference of incoming and scattered waves as a function of energy and tip's position. Although both the impurity and the tip generically break spatial symmetries, we find that the QPI maps provide universal information on these symmetries. The symmetries impose constraints on the relation between various momentum components of the Bloch functions. These relations result in selection rules on certain momentum transfers in QPI maps. We find that universal information is encoded in the absence of QPI signal, or in the relative intensity of its replications. We show examples for one-dimensional chains and an effective model of the layered compound ZrSiS. We discuss the implications of our theory in the analysis of observed QPI of the Weyl semimetal TaAs. Our theory is particularly relevant for materials in rod and layer space groups, or when a correlated order parameter, such as antiferromagnetism, enlarges the unit cell.

Dimensional Hierarchy of Fermionic Interacting Topological Phases.

We present a dimensional reduction argument to derive the classification reduction of fermionic symmetry protected topological phases in the presence of interactions. The dimensional reduction proceeds by relating the topological character of a d-dimensional system to the number of zero-energy bound states localized at zero-dimensional topological defects present at its surface. This correspondence leads to a general condition for symmetry preserving interactions that render the system topologically trivial, and allows us to explicitly write a quartic interaction to this end. Our reduction shows that all phases with topological invariant smaller than n are topologically distinct, thereby reducing the noninteracting Z classification to Z_{n}.

Prise en charge du trouble de consommation d'opioïdes en première ligne: Lignes directrices simplifiées de PEER.

OBJECTIF: Utiliser les meilleures données probantes et les meilleurs principes de prise de décision partagée et éclairée à notre disposition pour élaborer des lignes directrices de pratique clinique visant une approche simplifiée de prise en charge du trouble de consommation d'opioïdes (TCO) en première ligne. MÉTHODES: Onze professionnels de la santé et professionnels paramédicaux représentant divers milieux de pratique, professions et lieux ont créé une liste de questions pertinentes à la prise en charge du TCO en première ligne. Ces questions étaient liées au contexte thérapeutique, au diagnostic, au traitement et à la prise en charge des comorbidités dans le TCO. Les questions ont été étudiées par une équipe expérimentée dans l'évaluation des données probantes à l'aide d'une série de revues systématiques d'études randomisées et contrôlées. Les recommandations émises par le comité des lignes directrices reposent sur les revues systématiques. RECOMMANDATIONS: Les recommandations font ressortir le rôle des soins primaires dans le traitement des patients aux prises avec un TCO, de même que les traitements pharmacologiques et psychothérapies et les diverses pratiques de prescription (p. ex. test urinaire de dépistage de drogues et contrats). Aucune recommandation précise n'a pu être faite sur la prise en charge des comorbidités chez les patients aux prises avec un TCO, en raison des données probantes limitées. CONCLUSION: Les recommandations contribueront à simplifier la prise en charge des cas complexes de TCO en première ligne. Elles aideront tant les cliniciens que les patients à prendre des décisions éclairées au sujet de leurs soins.

The quantum geometric origin of capacitance in insulators.

In band insulators, without a Fermi surface, adiabatic transport can exist due to the geometry of the ground state wavefunction. Here we show that for systems driven at a small but finite frequency ω, transport likewise depends sensitively on quantum geometry. We make this statement precise by expressing the Kubo formula for conductivity as the variation of the time-dependent polarization with respect to the applied field. We find that at linear order in frequency, the longitudinal conductivity results from an intrinsic capacitance determined by the ratio of the quantum metric and the spectral gap, establishing a fundamental link between the dielectric response and the quantum metric of insulators. We demonstrate that quantum geometry is responsible for the electronic contribution to the dielectric constant in a wide range of insulators, including the free electron gas in a quantizing magnetic field, for which we show the capacitance is quantized. We also study gapped bands of hBN-aligned twisted bilayer graphene and obstructed atomic insulators such as diamond. In the latter, we find its abnormally large refractive index to have a topological origin.

Anderson critical metal phase in trivial states protected by average magnetic crystalline symmetry.

Transitions between distinct obstructed atomic insulators (OAIs) protected by crystalline symmetries, where electrons form molecular orbitals centering away from the atom positions, must go through an intermediate metallic phase. In this work, we find that the intermediate metals will become a scale-invariant critical metal phase (CMP) under certain types of quenched disorder that respect the magnetic crystalline symmetries on average. We explicitly construct models respecting average C2zT, m, and C4zT and show their scale-invariance under chemical potential disorder by the finite-size scaling method. Conventional theories, such as weak anti-localization and topological phase transition, cannot explain the underlying mechanism. A quantitative mapping between lattice and network models shows that the CMP can be understood through a semi-classical percolation problem. Ultimately, we systematically classify all the OAI transitions protected by (magnetic) groups P m , P 2 ' , P 4 ' , and P 6 ' with and without spin-orbit coupling, most of which can support CMP.

Toward 1D Transport in 3D Materials: SOC-Induced Charge-Transport Anisotropy in Sm3ZrBi5.

1D charge transport offers great insight into strongly correlated physics, such as Luttinger liquids, electronic instabilities, and superconductivity. Although 1D charge transport is observed in nanomaterials and quantum wires, examples in bulk crystalline solids remain elusive. In this work, it is demonstrated that spin-orbit coupling (SOC) can act as a mechanism to induce quasi-1D charge transport in the Ln3MPn5 (Ln = lanthanide; M = transition metal; Pn = Pnictide) family. From three example compounds, La3ZrSb5, La3ZrBi5, and Sm3ZrBi5, density functional theory calculations with SOC included show a quasi-1D Fermi surface in the bismuthide compounds, but an anisotropic 3D Fermi surface in the antimonide structure. By performing anisotropic charge transport measurements on La3ZrSb5, La3ZrBi5, and Sm3ZrBi5, it is demonstrated that SOC starkly affects their anisotropic resistivity ratios (ARR) at low temperatures, with an ARR of ≈4 in the antimonide compared to ≈9.5 and ≈22 (≈32 after magnetic ordering) in La3ZrBi5 and Sm3ZrBi5, respectively. This report demonstrates the utility of spin-orbit coupling to induce quasi-low-dimensional Fermi surfaces in anisotropic crystal structures, and provides a template for examining other systems.

Infrared plasmons propagate through a hyperbolic nodal metal.

Metals are canonical plasmonic media at infrared and optical wavelengths, allowing one to guide and manipulate light at the nanoscale. A special form of optical waveguiding is afforded by highly anisotropic crystals revealing the opposite signs of the dielectric functions along orthogonal directions. These media are classified as hyperbolic and include crystalline insulators, semiconductors, and artificial metamaterials. Layered anisotropic metals are also anticipated to support hyperbolic waveguiding. However, this behavior remains elusive, primarily because interband losses arrest the propagation of infrared modes. Here, we report on the observation of propagating hyperbolic waves in a prototypical layered nodal-line semimetal ZrSiSe. The observed waveguiding originates from polaritonic hybridization between near-infrared light and nodal-line plasmons. Unique nodal electronic structures simultaneously suppress interband loss and boost the plasmonic response, ultimately enabling the propagation of infrared modes through the bulk of the crystal.

Face-to-Face Clinical Practice Under COVID-19 Pandemic: How Psychotherapists Describe Their Experiences.

Driven by the theory-building around the role of the non-verbal components to communication, we aimed to understand how therapists experience the therapeutic process using a facial mask. The empirical evidence of the power of non-verbal communication to engage therapists and clients in therapeutic work, develop a positive and collaborative relationship between them, and display empathy is quite large. A mixed-methods approach was adopted, drawing from the therapists' participation in an online survey. A sample of 137 psychotherapists with different therapy orientations and years of clinical practice participated in the study. Therapists conducted face-to-face therapy wearing face masks with existing and/or new clients. We performed an exploratory analysis, using descriptive statistics, to explore the psychotherapists' evaluations regarding perceived impact of face masks on different therapy quality dimensions. In a complementary rationale, we analyzed the therapists' perspectives on their experience wearing face masks using the thematic analysis methodology. Results show that among 137 psychotherapists, 114 were attending both existing and new clients, whereas only 13 were seeing exclusively existing clients and 10 were working exclusively with new clients. Despite no major differences were found between conditions regarding the perceived impact of face masks on different therapy quality dimensions and strategies adopted, the qualitative analysis allowed us to expand the quantitative results and deepen understanding of psychotherapists' experience. Based on general and typical patterns, we propose two distinct models to describe the therapist's experiences narrative when working with existing or new clients wearing face masks. Based on the results, we propose some recommendations to clinical practice in similar conditions.

Pseudo field effects in type II Weyl semimetals: new probes for over titled cones.

We study the effects of pseudo-magnetic fields on Weyl semimetals with over-tilted Weyl cones, or type II cones. We compare the phenomenology of the resulting pseudo-Landau levels in the type II Weyl semimetal to the known case of type I cones. We predict that due to the nature of the chiral Landau level resulting from a magnetic field, a pseudo-magnetic field, or their combination, the optical conductivity can be utilized to detect a type II phase and deduce the direction of the tilt. Finally, we discuss ways to engineer homogeneous and inhomogeneous type II semimetals via generalizations of known layered constructions in order to create controlled pseudo-magnetic fields and over-tilted cones.

Experimental characterization of fragile topology in an acoustic metamaterial.

Symmetries crucially underlie the classification of topological phases of matter. Most materials, both natural as well as architectured, possess crystalline symmetries. Recent theoretical works unveiled that these crystalline symmetries can stabilize fragile Bloch bands that challenge our very notion of topology: Although answering to the most basic definition of topology, one can trivialize these bands through the addition of trivial Bloch bands. Here, we fully characterize the symmetry properties of the response of an acoustic metamaterial to establish the fragile nature of the low-lying Bloch bands. Additionally, we present a spectral signature in the form of spectral flow under twisted boundary conditions.

Mapping nursing training in Brazil: challenges for actions in complex and globalized scenarios. / Mapeando a formação do enfermeiro no Brasil: desafios para atuação em cenários complexos e globalizados.

The article discusses the professional formation of nurses, implications of the increase in the number of Higher Education Institutions and their distribution in Brazil. It considers the results of the Nursing Profile Survey in Brazil, carried out with 35,916 nursing professionals, in 2013. The analysis that characterizes the trajectory of undergraduate nursing in this article is structured in three dimensions: the increase in the number of undergraduate and postgraduate nursing education institutions; the boom in nursing schools and the public vs. private relationship; and the territorial distribution of the registered nurse in Brazil. The increase in the number of Nursing Education Institutions implies an exponential formation, with a predominance of private schools in undergraduate and postgraduate courses. The courses seek to align themselves with changes in health and society, but it is crucial to equalize the territorial asymmetries between the undergraduate and graduate training institutions, the overconcentration and care gaps resulting from the insufficiency of nurses per inhabitant, as well as to qualify the nurses for the exercise of their professional activities in the face of global changes.

O artigo discorre sobre a formação profissional do enfermeiro, implicações da expansão das Instituições de Ensino Superior e a distribuição dessas no Brasil. Considera os resultados da Pesquisa Perfil da Enfermagem no Brasil, realizada com 35.916 profissionais de Enfermagem, em 2013. A análise que caracteriza a trajetória da graduação em enfermagem neste artigo, estrutura-se em três dimensões: a expansão da formação do enfermeiro na graduação e pós-graduação; o boom de escolas de enfermagem e a relação público x privado; e, a distribuição territorial do profissional enfermeiro no Brasil. O crescimento de Instituições de Ensino em Enfermagem implica em uma formação exponencial, com predomínio de escolas privadas na graduação e na pós-graduação; os cursos buscam alinhar-se às mudanças na saúde e sociedade, mas urge equalizar as assimetrias territoriais entre as instituições formadoras na graduação e pós-graduação, a superconcentração e vazios assistenciais decorrentes da insuficiência de enfermeiros por habitantes, bem como qualificar o enfermeiro para o exercício profissional ante as transformações globais.

Resolving the topological classification of bismuth with topological defects.

The growing diversity of topological classes leads to ambiguity between classes that share similar boundary phenomenology. This is the status of bulk bismuth. Recent studies have classified it as either a strong or a higher-order topological insulator, both of which host helical modes on their boundaries. We resolve the topological classification of bismuth by spectroscopically mapping the response of its boundary modes to a screw-dislocation. We find that the one-dimensional mode, on step-edges, extends over a wide energy range and does not open a gap near the screw-dislocations. This signifies that this mode binds to the screw-dislocation, as expected for a material with nonzero weak indices. We argue that the small energy gap, at the time reversal invariant momentum L, positions bismuth within the critical region of a topological phase transition between a higher-order topological insulator and a strong topological insulator with nonzero weak indices.