From antiferromagnetic and hidden order to Pauli paramagnetism in UM 2Si2 compounds with 5f electron duality.

Using inelastic X-ray scattering beyond the dipole limit and hard X-ray photoelectron spectroscopy we establish the dual nature of the U [Formula: see text] electrons in U[Formula: see text] (M = Pd, Ni, Ru, Fe), regardless of their degree of delocalization. We have observed that the compounds have in common a local atomic-like state that is well described by the U [Formula: see text] configuration with the [Formula: see text] and [Formula: see text] quasi-doublet symmetry. The amount of the U 5[Formula: see text] configuration, however, varies considerably across the U[Formula: see text] series, indicating an increase of U 5f itineracy in going from M = Pd to Ni to Ru and to the Fe compound. The identified electronic states explain the formation of the very large ordered magnetic moments in [Formula: see text] and [Formula: see text], the availability of orbital degrees of freedom needed for the hidden order in [Formula: see text] to occur, as well as the appearance of Pauli paramagnetism in [Formula: see text] A unified and systematic picture of the U[Formula: see text] compounds may now be drawn, thereby providing suggestions for additional experiments to induce hidden order and/or superconductivity in U compounds with the tetragonal body-centered [Formula: see text] structure.

Induced Topological Superconductivity in a BiSbTeSe2-Based Josephson Junction.

A 4 π -periodic supercurrent through a Josephson junction can be a consequence of the presence of Majorana bound states. A systematic study of the radio frequency response for several temperatures and frequencies yields a concrete protocol for examining the 4 π -periodic contribution to the supercurrent. This work also reports the observation of a 4 π -periodic contribution to the supercurrent in BiSbTeSe 2 -based Josephson junctions. As a response to irradiation by radio frequency waves, the junctions showed an absence of the first Shapiro step. At high irradiation power, a qualitative correspondence to a model including a 4 π -periodic component to the supercurrent is found.

Electrochemical Scanning Tunneling Microscopy Study of Bismuth Chalcogenide Single Crystals.

We use electrochemical scanning tunneling microscopy (EC-STM) to image single-crystal surfaces of the layered bismuth chalcogenide Sn0.01Bi1.99Te2Se in situ under electrochemical control for the first time. The Bi chalcogenides are of interest for their thermoelectric properties and as model topological insulators (TIs). We show that oxidative dissolution takes place via the progressive nucleation of pits in the initially smooth surface terraces rather than at their edges. Nanometer-resolution EC-STM images show that the pit depth is generally equal to the thickness of a complete chalcogenide quintuple layer. The preferential redeposition of dissolved components at step and defect edges on application of a more negative potential after oxidation is observed. Our work demonstrates the ability to control and characterize the surface morphology of single-crystal TIs in an electrochemical environment.

Zeeman-Effect-Induced 0-π Transitions in Ballistic Dirac Semimetal Josephson Junctions.

One of the consequences of Cooper pairs having a finite momentum in the interlayer of a Josephson junction is π-junction behavior. The finite momentum can either be due to an exchange field in ferromagnetic Josephson junctions, or due to the Zeeman effect. Here, we report the observation of Zeeman-effect-induced 0-π transitions in Bi_{1-x}Sb_{x}, three-dimensional Dirac semimetal-based Josephson junctions. The large in-plane g factor allows tuning of the Josephson junctions from 0 to π regimes. This is revealed by measuring a π phase shift in the current-phase relation measured with an asymmetric superconducting quantum interference device (SQUID). Additionally, we directly measure a nonsinusoidal current-phase relation in the asymmetric SQUID, consistent with models for ballistic Josephson transport.

Electrochemical Modification and Characterization of Topological Insulator Single Crystals.

We compare electrochemically modified or thiol-functionalized single-crystal samples of the topological insulator (TI) Bi2Te0.9Se2.1 to freshly cleaved/air-exposed control samples and use X-ray photoelectron spectroscopy (XPS) to investigate the extent of any surface oxidation. XPS spectra for a TI sample maintained at an appropriate potential for 2 h demonstrate the feasibility of protecting the TI surface from oxidation while working in an electrochemical environment. Deliberate electrochemical oxidation, in contrast, generates prominent Bi, Te, and Se peaks associated with oxidation. However, this change is reversible, as further XPS spectra following electrochemical reduction are similar to those measured for an in situ cleaved sample. XPS also shows that adsorption of pentanedithiol (PDT) protects the TI surface from oxidation. Cyclic voltammetry shows that PDT adsorption suppresses electrochemical oxidation and reduction, while electrochemical impedance spectroscopy shows that it increases the charge transfer resistance significantly. Our work demonstrates the ability to control and characterize the surface chemistry of single-crystal TIs in an electrochemical environment for the first time.

Quantum critical behavior in Ce(Fe0.76Ru0.24)2Ge2.

Systems with embedded magnetic ions that exhibit a competition between magnetic order and disorder down to absolute zero can display unusual low-temperature behaviors of the resistivity, susceptibility, and specific heat. Moreover, the dynamic response of such a system can display hyperscaling behavior in which the relaxation back to equilibrium when an amount of energy E is given to the system at temperature T only depends on the ratio E/T. Ce(Fe0.755Ru0.245)2Ge2 is a system that displays these behaviors. We show that these complex behaviors are rooted in a fragmentation of the magnetic lattice upon cooling caused by a distribution of local Kondo screening temperatures, and that the hyperscaling behavior can be attributed to the flipping of the total magnetic moment of magnetic clusters that spontaneously form and order upon cooling. We present our arguments based on the review of two-decades worth of neutron scattering and transport data on this system, augmented with new polarized and unpolarized neutron scattering experiments.

4π-periodic Andreev bound states in a Dirac semimetal.

Although signatures of superconductivity in Dirac semimetals have been reported, for instance by applying pressure or using point contacts, our understanding of the topological aspects of Dirac semimetal superconductivity is still developing. Here, we utilize nanoscale phase-sensitive junction technology to induce superconductivity in the Dirac semimetal Bi1-xSbx. Our radiofrequency irradiation experiments then reveal a significant contribution of 4π-periodic Andreev bound states to the supercurrent in Nb-Bi0.97Sb0.03-Nb Josephson junctions. The conditions for a substantial 4π contribution to the supercurrent are favourable because of the Dirac cone's very broad transmission resonances and a measurement frequency faster than the quasiparticle poisoning rate. In addition, we show that a magnetic field applied in the plane of the junction allows tuning of the Josephson junctions from 0 to π regimes. Our results open the technologically appealing avenue of employing the topological bulk properties of Dirac semimetals for topological superconductivity research and topological quantum computer development.

Familial Risk of Appendicitis: A Nationwide Population Study.

OBJECTIVE: To investigate the familial risk of appendicitis in the general population. STUDY DESIGN: A nationwide, cross-sectional study consisting of 24 349 599 Taiwan National Health Insurance beneficiaries in 2015 was conducted. Among them, 788 042 individuals had at least 1 first-degree relative with appendicitis. The familial relative risks (RRs) of appendicitis and familial transmission were estimated. RESULTS: The overall RR (95% CI) of appendicitis in individuals with any affected first-degree relatives was 1.67 (1.64-1.71) compared with the general population. The RRs for individuals with an affected twin, sibling, offspring, and parent were 3.40 (2.66-4.35), 1.98 (1.92-2.04), 1.55 (1.51-1.59), and 1.54 (1.50-1.58), respectively. The RRs for individuals with 1, 2, 3 or more affected first-degree relatives were 1.65 (1.62-1.68), 2.63 (2.37-2.91), and 6.70 (4.22-10.63), respectively. Furthermore, there was an age-dependent trend of the RRs, with the greatest RR in the youngest group. The estimated familial transmission (genetic plus shared environmental contribution to the total phenotypic variance of appendicitis) was 23.2%. CONCLUSION: Individuals with a family history of appendicitis have an increased risk of appendicitis. This risk is age-dependent and related to the genetic distance and numbers of affected relatives.

Risk of Appendicitis among Children with Different Piped Water Supply: A Nationwide Population-Based Study.

Appendicitis is a common surgical condition for children. However, environmental effects, such as piped water supply, on pediatric appendicitis risk remain unclear. This longitudinal, nationwide, cohort study aimed to compare the risk of appendicitis among children with different levels of piped water supply. Using data from Taiwan Water Resource Agency and National Health Insurance Research Database, we identified 119,128 children born in 1996⁻2010 from areas of the lowest piped water supply (prevalence 51.21% to 63.06%) as the study cohort; additional 119,128 children of the same period in areas of the highest piped water supply (prevalence 98.97% to 99.63%) were selected as the controls. Both cohorts were propensity-score matched by baseline variables. We calculated the hazard ratios (HRs) and 95% confidence intervals (CIs) of appendicitis in the study cohort compared to the controls by Cox proportional hazards regression. The study cohort had a raised overall incidence rates of appendicitis compared to the control cohort (12.8 vs. 8.7 per 10,000 person-years). After covariate adjustment, the risk of appendicitis was significantly increased in the study cohort (adjusted HR = 1.46, 95% CI: 1.35, 1.58, p < 0.001). Subgroup and sensitivity analyses showed consistent results that children with low piped water supply had a higher risk of appendicitis than those with high piped water supply. This study demonstrated that children with low piped water supply were at an increased risk of appendicitis. Enhancement of piped water availability in areas lacking adequate, secure, and sanitized water supply may protect children against appendicitis.

Increased risk of autoimmune diseases in dengue patients: A population-based cohort study.

OBJECTIVE: To investigate the risk of autoimmune diseases in dengue patients. METHODS: We conducted a population-based cohort study by the Taiwan National Health Insurance Research Database, including a total of 12,506 newly diagnosed dengue patients and 112,554 control subjects between 2000 and 2010, matched by gender, age, income, urbanization, and comorbidities. Both cohorts were followed for a 3-year period to examine the incidence of autoimmune diseases. A Cox proportional hazards regression analysis was applied to calculate the risk of autoimmune diseases between both groups. RESULTS: The dengue group showed an overall increased risk for 21 autoimmune diseases, with an adjusted hazard ratio (aHR) of 1.88 (95% confidence interval [CI], 1.49-2.37, p < 0.001). Compared with the control group, the dengue group had higher risks of Reiter's syndrome (aHR 14.03, 95 % CI 1.63-120.58), multiple sclerosis (aHR 11.57, 95 % CI 1.8-74.4), myasthenia gravis (aHR 5.35, 95 % CI 1.43-20.02), autoimmune encephalomyelitis (aHR 3.8, 95% CI 1.85-7.8), systemic vasculitis (aHR 3.7, 95 % CI 1.11-12.28), systemic lupus erythematosus (aHR 3.5, 95% CI 1.85-6.63), and primary adrenocortical insufficiency (aHR 2.05, 95% CI 1.25-3.35). CONCLUSION: Dengue patients were associated with an increased risk of autoimmune diseases.

Risk of stroke in patients with dengue fever: a population-based cohort study.

BACKGROUND: Stroke is a severe neurologic complication of dengue fever, described in only a few case reports. The incidence and risk factors for stroke in patients with dengue remain unclear. We conducted a population-based retrospective cohort study to investigate the risk of stroke in patients with dengue. METHODS: Using data from the Taiwan National Health Insurance Research Database, we included a total of 13 787 patients with dengue newly diagnosed between 2000 and 2012. The control cohort consisted of patients who did not have dengue, matched 1:1 by demographic characteristics and stroke-related comorbidities. We calculated the cumulative incidences and hazard ratios (HRs) of stroke in both cohorts using Kaplan-Meier curves and Cox proportional hazards regression. RESULTS: The overall incidence rate of stroke was 5.33 per 1000 person-years in the dengue cohort and 3.72 per 1000 person-years in the control cohort, with an adjusted HR of 1.16 (95% confidence interval [CI] 1.01-1.32). The risk of stroke among patients with dengue was highest in the first 2 months after diagnosis (25.53 per 1000 person-years, adjusted HR 2.49, 95% CI 1.48-4.18). INTERPRETATION: Dengue fever was associated with an increased risk of stroke in the first few months after diagnosis. The effect of dengue on stroke may be acute rather than chronic.

The effect of antibiotic prophylaxis for acute pelvic inflammatory disease after hysterosalpingography: a retrospective cohort study.

AIMS: Concerns about acute pelvic inflammatory disease (PID) after hysterosalpingography (HSG) have been raised since 1980. However, the effectiveness of prophylactic antibiotics remains unclear. This study investigated the effect of antibiotic prophylaxis in women undergoing HSG. METHODS: Women undergoing HSG between 2000 and 2012 were screened from the Taiwan National Health Insurance Research Database for eligibility. The prophylactic cohort included patients using any antibiotics of 1st-generation cephalosporins, doxycycline, clindamycin, and metronidazole, within 7 days before HSG (n = 3257). Patients not using any antibiotics were registered as the non-prophylactic cohort (n = 4662). An unconditional logistic regression model was applied to calculate the odds ratio (OR) and 95% confidence interval (CI) of acute PID after HSG associated with prophylactic antibiotics. RESULTS: The cumulative incidences of acute PID after HSG were 0.46% and 1.42% in the prophylactic and non-prophylactic cohorts, respectively. Prophylactic patients had a significantly reduced estimated relative risk of acute PID compared with non-prophylactic patients (adjusted OR = 0.33, 95% CI = 0.19-0.58; p = .001). Doxycycline users had the lowest adjusted OR of 0.20 (95% CI = 0.04-0.81; p = .02), followed by users of 1st-generation cephalosporins (adjusted OR = 0.35, 95% CI = 0.18-0.68; p = .002). Multivariate sub-group analysis verified this protective effect for almost all sub-groups of prophylactic patients. CONCLUSIONS: Antibiotic prophylaxis is associated with a decreased estimated relative risk of acute PID in HSG patients. Doxycycline and 1st-generation cephalosporins may be effective prophylactic regimens for HSG.

The Association Between Barium Examination and Subsequent Appendicitis: A Nationwide Population-Based Study.

OBJECTIVE: The incidence and association between appendicitis and barium examination (BE) remain unclear. Such potential risk may be omitted. We conducted a longitudinal, nationwide, population-based cohort study to investigate the association between BE and appendicitis risk. METHODS: From the Taiwan National Health Insurance Research Database, a total of 24,885 patients who underwent BE between January 1, 2000 and December 31, 2010 were enrolled in a BE cohort; an additional 98,384 subjects without BE exposure were selected as a non-BE cohort, matched by age, sex, and index date. The cumulative incidences of subsequent appendicitis in the BE and non-BE cohorts were assessed using the Kaplan-Meier curves and log-rank test. Cox proportional hazards regression analyses were employed to calculate the appendicitis risk between the groups. RESULTS: The cumulative incidence of appendicitis was higher in the BE cohort than in the non-BE cohort (P = .001). The overall incidence rates of appendicitis for the BE and non-BE cohorts were 1.19 and 0.80 per 1000 person-years, respectively. After adjustment for sex, age, and comorbidities, the risk of appendicitis was higher in the BE cohort (adjusted hazard ratio = 1.46, 95% confidence interval = 1.23-1.73) compared with the non-BE cohort, especially in the first 2 months (adjusted hazard ratio = 9.72, 95% confidence interval = 4.65-20.3). CONCLUSIONS: BE was associated with an increased, time-dependent appendicitis risk. Clinicians should be aware of this potential risk to avoid delayed diagnoses.

Direct bulk-sensitive probe of 5f symmetry in URu2Si2.

The second-order phase transition into a hidden order phase in URu2Si2 goes along with an order parameter that is still a mystery, despite 30 years of research. However, it is understood that the symmetry of the order parameter must be related to the symmetry of the low-lying local electronic [Formula: see text]-states. Here, we present results of a spectroscopic technique, namely core-level nonresonant inelastic X-ray scattering (NIXS). This method allows for the measurement of local high-multipole excitations and is bulk-sensitive. The observed anisotropy of the scattering function unambiguously shows that the 5[Formula: see text] ground-state wave function is composed mainly of the [Formula: see text] with majority [Formula: see text] = [Formula: see text] + [Formula: see text] and/or [Formula: see text] singlet states. The incomplete dichroism indicates the possibility that quantum states of other irreducible representation are mixed into the ground state.

Direct observation of a Fermi liquid-like normal state in an iron-pnictide superconductor.

There are two prerequisites for understanding high-temperature (high-Tc) superconductivity: identifying the pairing interaction and obtaining a correct description of the normal state from which superconductivity emerges. The nature of the normal state of iron-pnictide superconductors, and the role played by correlations arising from partially screened interactions, are still under debate. Here we show that the normal state of carefully annealed electron-doped BaFe(2-x)Co(x)As2 at low temperatures has all the hallmark properties of a local Fermi liquid, with a more incoherent state emerging at elevated temperatures, an identification made possible using bulk-sensitive optical spectroscopy with high frequency and temperature resolution. The frequency dependent scattering rate extracted from the optical conductivity deviates from the expected scaling M2 (ω, T) ∝ (hω)(2) + (pπkBT)(2) with p ≈ 1.47 rather than p = 2, indicative of the presence of residual elastic resonant scattering. Excellent agreement between the experimental results and theoretical modeling allows us to extract the characteristic Fermi liquid scale T0 ≈ 1700 K. Our results show that the electron-doped iron-pnictides should be regarded as weakly correlated Fermi liquids with a weak mass enhancement resulting from residual electron-electron scattering from thermally excited quasi-particles.

Existence, character, and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe(2-x)Co(x)As2.

Low energy electron diffraction (LEED) experiments, LEED simulations, and finite slab density functional calculations are combined to study the cleavage surface of Co doped BaFe(2-x)Co(x)As2 (x = 0.1,0.17). We demonstrate that the energy dependence of the LEED data can only be understood from a terminating 1/2 Ba layer accompanied by distortions of the underlying As-Fe2-As block. As a result, surface-related Fe 3d states are present in the electronic structure, which we identify in angle resolved photoemission spectroscopy (ARPES) experiments. The close proximity of the surface-related states to the bulk bands inevitably leads to broadening of the ARPES signals, which excludes the use of the BaFe(2-x)Co(x)As2 system for accurate determination of self-energies using ARPES.

Visualizing the formation of the Kondo lattice and the hidden order in URu(2)Si(2).

Heavy electronic states originating from the f atomic orbitals underlie a rich variety of quantum phases of matter. We use atomic scale imaging and spectroscopy with the scanning tunneling microscope to examine the novel electronic states that emerge from the uranium f states in URu(2)Si(2). We find that, as the temperature is lowered, partial screening of the f electrons' spins gives rise to a spatially modulated Kondo-Fano resonance that is maximal between the surface U atoms. At T = 17.5 K, URu(2)Si(2) is known to undergo a second-order phase transition from the Kondo lattice state into a phase with a hidden order parameter. From tunneling spectroscopy, we identify a spatially modulated, bias-asymmetric energy gap with a mean-field temperature dependence that develops in the hidden order state. Spectroscopic imaging further reveals a spatial correlation between the hidden order gap and the Kondo resonance, suggesting that the two phenomena involve the same electronic states.