Robust Surface States and Coherence Phenomena in Magnetically Alloyed SmB_{6}

Samarium hexaboride is a candidate for the topological Kondo insulator state, in which Kondo coherence is predicted to give rise to an insulating gap spanned by topological surface states. Here we investigate the surface and bulk electronic properties of magnetically alloyed Sm_{1-x}M_{x}B_{6} (M=Ce, Eu), using angle-resolved photoemission spectroscopy and complementary characterization techniques. Remarkably, topologically nontrivial bulk and surface band structures are found to persist in highly modified samples with up to 30% Sm substitution and with an antiferromagnetic ground state in the case of Eu doping. The results are interpreted in terms of a hierarchy of energy scales, in which surface state emergence is linked to the formation of a direct Kondo gap, while low-temperature transport trends depend on the indirect gap.

Low Energy Band Structure and Symmetries of UTe_{2} from Angle-Resolved Photoemission Spectroscopy

The compound UTe_{2} has recently been shown to realize spin triplet superconductivity from a nonmagnetic normal state. This has sparked intense research activity, including theoretical analyses that suggest the superconducting order parameter to be topologically nontrivial. However, the underlying electronic band structure is a critical factor for these analyses, and remains poorly understood. Here, we present high resolution angle-resolved photoemission measurements covering multiple planes in the 3D Brillouin zone of UTe_{2}, revealing distinct Fermi-level features from two orthogonal quasi-one-dimensional light electron bands and one heavy band. The electronic symmetries are evaluated in comparison with numerical simulations, and the resulting picture is discussed as a platform for unconventional many-body order.

Orbital-selective Kondo lattice and enigmatic f electrons emerging from inside the antiferromagnetic phase of a heavy fermion

Novel electronic phenomena frequently form in heavy-fermions because of the mutual localized and itinerant nature of f-electrons. On the magnetically ordered side of the heavy-fermion phase diagram, f-moments are expected to be localized and decoupled from the Fermi surface. It remains ambiguous whether Kondo lattice can develop inside the magnetically ordered phase. Using spectroscopic imaging with scanning tunneling microscope, complemented by neutron scattering, x-ray absorption spectroscopy, and dynamical mean field theory, we probe the electronic states in antiferromagnetic USb₂. We visualize a large gap in the antiferromagnetic phase within which Kondo hybridization develops below ~80 K. Our calculations indicate the antiferromagnetism and Kondo lattice to reside predominantly on different f-orbitals, promoting orbital selectivity as a new conception into how these phenomena coexist in heavy-fermions. Finally, at 45 K, we find a novel first order-like transition through abrupt emergence of nontrivial 5f-electronic states that may resemble the "hidden-order" phase of URu₂Si₂.

High temperature singlet-based magnetism from Hund's rule correlations

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. The antiferromagnetic dipnictide USb₂ has been of recent interest due to the discovery of rich proximate phase diagrams and unusual quantum coherence phenomena. Here, linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb₂ and isostructural UBi₂. Of these two materials, only USb₂ is found to enable strong Hund’s rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. Theoretical analysis reveals that these and other anomalous properties of the material may be understood by attributing it as the first known high temperature realization of a singlet ground state magnet, in which magnetism occurs through a process that resembles exciton condensation.

Electrons in uranium-based materials are often on the border between localised and itinerant behaviour, which can lead to unusual magnetic behaviour. Here the authors combine experiment and theory to show that USb₂ may be an unusually high temperature example of a singlet-ground-state magnet.

Disorder enabled band structure engineering of a topological insulator surface

Three-dimensional topological insulators are bulk insulators with Z₂ topological electronic order that gives rise to conducting light-like surface states. These surface electrons are exceptionally resistant to localization by non-magnetic disorder, and have been adopted as the basis for a wide range of proposals to achieve new quasiparticle species and device functionality. Recent studies have yielded a surprise by showing that in spite of resisting localization, topological insulator surface electrons can be reshaped by defects into distinctive resonance states. Here we use numerical simulations and scanning tunnelling microscopy data to show that these resonance states have significance well beyond the localized regime usually associated with impurity bands. At native densities in the model Bi₂X₃ (X=Bi, Te) compounds, defect resonance states are predicted to generate a new quantum basis for an emergent electron gas that supports diffusive electrical transport.

The surface electrons in a topological insulator are resistant to localization by nonmagnetic disorder, but are affected by lattice disorder. Here, the authors show that resonance states near lattice defects on the surface have significance beyond the localized regime usually associated with impurity bands.

Modular soft x-ray spectrometer for applications in energy sciences and quantum materials

Over the past decade, the advances in grating-based soft X-ray spectrometers have revolutionized the soft X-ray spectroscopies in materials research. However, these novel spectrometers are mostly dedicated designs, which cannot be easily adopted for applications with diverging demands. Here we present a versatile spectrometer design concept based on the Hettrick-Underwood optical scheme that uses modular mechanical components. The spectrometer's optics chamber can be used with gratings operated in either inside or outside orders, and the detector assembly can be reconfigured accordingly. The spectrometer can be designed to have high spectral resolution, exceeding 10 000 resolving power when using small source (∼1μm) and detector pixels (∼5μm) with high line density gratings (∼3000 lines/mm), or high throughput at moderate resolution. We report two such spectrometers with slightly different design goals and optical parameters in this paper. We show that the spectrometer with high throughput and large energy window is particularly useful for studying the sustainable energy materials. We demonstrate that the extensive resonant inelastic X-ray scattering (RIXS) map of battery cathode material LiNi_1/3Co_1/3Mn_1/3O₂ can be produced in few hours using such a spectrometer. Unlike analyzing only a handful of RIXS spectra taken at selected excitation photon energies across the elemental absorption edges to determine various spectral features like the localized dd excitations and non-resonant fluorescence emissions, these features can be easily identified in the RIXS maps. Studying such RIXS maps could reveal novel transition metal redox in battery compounds that are sometimes hard to be unambiguously identified in X-ray absorption and emission spectra. We propose that this modular spectrometer design can serve as the platform for further customization to meet specific scientific demands.

Selective interlayer ferromagnetic coupling between the Cu spins in YBa2Cu3O7-x grown on top of La0.7Ca0.3MnO3

Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa2Cu3O7-x (YBCO) superconductor when it is grown on top of ferromagnetic La0.7Ca0.3MnO3 (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO2 but not with La0.7Ca0.3O interfacial termination. Such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO2 plane at the La0.7Ca0.3O and MnO2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems.

Perceived challenges and priorities in co-morbidity management of older patients with Type 2 diabetes

AIMS

To explore older patients' perceived impact of chronic co-morbid conditions on Type 2 diabetes self-management.

METHODS

We used purposive sampling to select 32 mentally alert community-dwelling adults, aged 60 years or older, diagnosed with Type 2 diabetes and at least one other chronic health condition to participate in focus groups. We summarized the discussions following each focus group and identified codes to describe the overarching themes.

RESULTS

We conducted eight 90-min focus groups, each consisting of two to six patients. Three themes emerged. (i) Diabetes complications as a motivator: managing co-morbid conditions made health an important focal point in the lives of older patients. Most patients acknowledged the positive effect complications had on their diabetes self-management by motivating them to pay greater attention to their diabetes to diminish the progression of these complications. (ii) Prioritizing health conditions: patients reported prioritizing health conditions and selectively attending to the management of those conditions based on perceived severity or importance. Further, many patients perceived some conditions as more serious than others and admitted to prioritizing another health condition over their diabetes. (iii) Emotional impact of co-morbidity management: patients described feeling frustrated, confused, and overwhelmed in response to conflicting treatment recommendations, particularly for diet, physical activity and medication regimens.

CONCLUSIONS

Complications and co-morbidities may have differential impacts on the diabetes self-management of older patients. Addressing the perceived impact of co-morbidity on diabetes self-management may improve patients' outcomes; however, the most effective method of utilizing this information in clinical practice needs to be examined.

Single-Dirac-cone topological surface states in the TlBiSe(2) class of topological semiconductors

We investigate several strong spin-orbit coupling ternary chalcogenides related to the (Pb,Sn)Te series of compounds. Our first-principles calculations predict the low-temperature rhombohedral ordered phase in TlBiTe₂, TlBiSe₂, and TlSbX₂ (X=Te, Se, S) to be topologically nontrivial. We identify the specific surface termination that realizes the single Dirac cone through first-principles surface state computations. This termination minimizes effects of dangling bonds, making it favorable for photoemission experiments. In addition, our analysis predicts that thin films of these materials could harbor novel 2D quantum spin Hall states, and support odd-parity topological superconductivity.

Half-Heusler ternary compounds as new multifunctional experimental platforms for topological quantum phenomena

Recent discovery of spin-polarized single-Dirac-cone insulators, whose variants can host magnetism and superconductivity, has generated widespread research activity in condensed-matter and materials-physics communities. Some of the most interesting topological phenomena, however, require topological insulators to be placed in multiply connected, highly constrained geometries with magnets and superconductors, all of which thus require a large number of functional variants with materials design flexibility as well as electronic, magnetic and superconducting tunability. Given the optimum materials, topological properties open up new vistas in spintronics, quantum computing and fundamental physics. We have extended the search for topological insulators from the binary Bi-based series to the ternary thermoelectric Heusler compounds. Here we show that, although a large majority of the well-known Heuslers such as TiNiSn and LuNiBi are rather topologically trivial, the distorted LnPtSb-type (such as LnPtBi or LnPdBi, Ln = f(n) lanthanides) compounds belonging to the half-Heusler subclass harbour Z(2) = -1 topological insulator parent states, where Z(2) is the band purity product index. Our results suggest that half-Heuslers provide a new platform for deriving a host of topologically exotic compounds and their nanoscale or thin-film device versions through the inherent flexibility of their lattice parameter, spin-orbit strength and magnetic moment tunability paving the way for the realization of multifunctional topological devices.

Explaining the role of sex on disability: a population-based study

PURPOSE

There is no clear consensus about how sex influences prevalent disability and through what mechanisms. We investigated whether sex had a direct independent effect on disability or whether sex had an interactive effect on the relationship between chronic diseases/conditions and disability, and whether these effects differed in middle-aged versus older adults.

DESIGN AND METHODS

We used baseline data from two nationally representative health interview surveys, the Health and Retirement Study (HRS) and the Study of Asset and Health Dynamics Among the Oldest Old (AHEAD), and disability and covariate measures that were nearly identical in both surveys. Logistic regression models tested the contributions of diseases, impairments, and demographic and social characteristics on difficulties with prevalent activities of daily living (ADLs), mobility, and strength.

RESULTS

Models demonstrated no direct sex effect for ADL disability in either age group after adjusting for key covariates. However, sex did exert an indirect effect on ADL disability in older adults via musculoskeletal conditions and depressive symptoms. In contrast, female sex remained strongly associated with mobility and strength disability in both age groups, net of covariates. Major interactions were also significant, including a female sex/body mass index (BMI) interaction for mobility difficulty and several sex-disease interactions for strength disability in the middle-aged group.

IMPLICATIONS

The effect of sex on ADL difficulty is largely explained by social and health-related covariates in middle-aged and older adults. In contrast, the independent association of female sex with decreased strength and mobility in both groups cannot be explained by our models' social or health-related variables. In addition, the positive association of BMI with mobility difficulty is significantly worse for women than for men.

The impact of education and heart attack on smoking cessation among middle-aged adults

Considerable evidence supports the premise that higher levels of education lead to enhanced health, including protective health behaviors. This paper focuses on how education affects one health behavior known to lead to enhanced health: the cessation of smoking. In particular, the authors examine the extent to which education influences the decision by middle-aged adults to quit smoking following a heart attack, a potentially life-threatening health event. We first hypothesize that middle-aged adults with more formal education will stop smoking more readily than people with less formal education following the experience of a heart attack. Second, we ask what other factors might underlie and explain that hypothesized effect. Using longitudinal data, the authors track changes in individual smoking behaviors after a heart attack among preretirement-age Americans. We control for documented correlates of smoking and heart attack plus other factors associated with education, heart attack, and smoking that may also influence whether a person quits smoking. In addition to confirming evidence on the education-health association as well as the documented connection between heart attack and smoking cessation, this study provides a surprising twist on those links: Our results show that the move to quit smoking following the experience of a heart attack among middle-aged adults is significantly and dramatically moderated by their level of educational attainment.

The role of ethnicity in the disability and work experience of preretirement-age Americans

Using the 1992 HRS, this study examines the effects of social and demographic risk factors, including ethnicity, as well as health and job characteristics on disability and work status among 8,701 preretirement-age Americans with work history. Analytic results indicated that non-Anglo ethnicity was not a significant predictor of disability status but that being African American was a strong significant predictor of being a past versus current worker. The primary predictors of disability and work status were health behaviors, effects of health conditions, job characteristics, and workplace adaptations, factors that lend themselves to policy manipulation.

The relationship between retirement life cycle changes and older men's labor force participation rates

This study probes the utility of older men's labor force participation rates (LFPRs) as indicators of the work-to-retirement transition. Specific attention is directed at how shifts in the retirement life cycle are related to LFPRs. Based on Current Population Survey data for the 1970s, a life table modeling approach showed that LFPRs are relatively weak indicators of the work-to-retirement transition. This was demonstrated by the relative stability in older men's age profiles of LFPRs despite significant changes in the timing and "organization" of the work-to-retirement transition. The 1970s evidenced a contraction of the main career and the expansion of both post-retirement work activity and retirement, yet none of these changes substantially altered the age profiles of older men's labor force participation rates.

Funding and policies affecting geriatric rehabilitation

Policy makers and practitioners are increasingly acknowledging the need to shift health care expenditures toward cost-effective strategies that reduce disability and dependency in older persons. That need is driven by current research on disability and population aging, disability interventions, and the inadequacy of the existing service delivery system for chronic care needs. How disability and dependency should be reduced most effectively and efficiently is a critical yet unanswered policy question.

Health policy and ethnic diversity in older Americans. Dissonance or harmony?

The rapid growth and diversity of the older population have long-term implications for health care policies in the United States. Current policies designed for a homogeneous population are increasingly obsolete. To ameliorate obstacles that handicap many ethnic minority elders and to provide equal access to adequate and acceptable health care, several factors need to be considered. Enhanced data collection and analytic techniques are needed. The effects of race or ethnicity must be separated from other biologic, environmental, socioeconomic, cultural, and temporal factors on health status and behavior. Health care professionals and organizations serving minority elders must continue to expand their advocacy efforts to articulate the findings and their concerns to policymakers. Policymakers must understand and acknowledge the implications of an increasingly diverse society and determine what will constitute adequate, accessible, and acceptable health care within continuing fiscal constrains. Program planning, implementation, and evaluation methods must be revised to meet future health care needs effectively and efficiently.