Evidence for Helical Hinge Zero Modes in an Fe-Based Superconductor.

Combining topology and superconductivity provides a powerful tool for investigating fundamental physics as well as a route to fault-tolerant quantum computing. There is mounting evidence that the Fe-based superconductor FeTe0.55Se0.45 (FTS) may also be topologically nontrivial. Should the superconducting order be s±, then FTS could be a higher order topological superconductor with helical hinge zero modes (HHZMs). To test the presence of these modes, we have fabricated normal-metal/superconductor junctions on different surfaces via 2D atomic crystal heterostructures. As expected, junctions in contact with the hinge reveal a sharp zero bias anomaly that is absent when tunneling purely into the c-axis. Additionally, the shape and suppression with temperature are consistent with highly coherent modes along the hinge and are incongruous with other origins of zero bias anomalies. Additional measurements with soft-point contacts in bulk samples with various Fe interstitial contents demonstrate the intrinsic nature of the observed mode. Thus, we provide evidence that FTS is indeed a higher order topological superconductor.

The impact of cognitive training in substance use disorder: the effect of working memory training on impulse control in methamphetamine users.

OBJECTIVES: Impulsivity is a vulnerability trait for poor self-regulation in substance use disorder (SUD). Working memory (WM) training improves impulsivity and self-regulation in psychiatric disorders. Here we test WM training in methamphetamine use disorder (MUD). METHODS: There are 15 MUD patients receiving inpatient treatment as usual (TAU) and 20 who additionally completed WM cognitive training (CT) and 25 healthy controls (HC). MANCOVA repeated measures analyses examined changes in impulsivity and self-regulation at baseline and after 4 weeks. RESULTS: Post hoc t tests confirmed that at baseline, feelings of self-control were significantly lower in the MUD (t = 2.001, p = 0.05) and depression was higher (t = 4.980, p = 0.001), as was BIS total impulsivity (t = 5.370, p = 0.001) compared to the HC group. Total self-regulation score was higher in HC than MUD patients (t = 5.370, p = 0.001). CT had a 35% learning rate (R 2 = 0.3523, p < 0.05). Compared to follow-up TAU, follow-up CT group had higher self-reported mood scores (t = 2.784, p = 0.01) and higher compared to CT baseline (t = 2.386, p = 0.036). Feelings of self-control were higher in CT than TAU at follow-up (t = 2.736, p = 0.012) and also compared to CT baseline (t = 3.390, p = 0.006), lack of planning significantly improved in CT between baseline and follow-up (t = 2.219, p = 0.048), as did total impulsivity scores (t = 2.085, p = 0.048). Measures of self-regulation were improved in the CT group compared to TAU at follow-up, in total score (t = 2.442, p = 0.038), receiving score (t = 2.314, p = 0.029) and searching score (t = 2.362, p = 0.027). Implementing self-regulation was higher in the CT group compared to TAU (t = 2.373, p = 0.026). CONCLUSIONS: WM training may improve control of impulsivity and self-regulation in people with MUD.

Psychological intervention with working memory training increases basal ganglia volume: A VBM study of inpatient treatment for methamphetamine use.

BACKGROUND: Protracted methamphetamine (MA) use is associated with decreased control over drug craving and altered brain volume in the frontostriatal network. However, the nature of volumetric changes following a course of psychological intervention for MA use is not yet known. METHODS: 66 males (41 MA patients, 25 healthy controls, HC) between the ages of 18-50 were recruited, the MA patients from new admissions to an in-patient drug rehabilitation centre and the HC via public advertisement, both in Cape Town, South Africa. 17 MA patients received 4 weeks of treatment as usual (TAU), and 24 MA patients completed TAU plus daily 30-minute cognitive training (CT) using an N-back working memory task. Magnetic resonance imaging (MRI) at baseline and 4-week follow-up was acquired and voxel-based morphometry (VBM) was used for analysis. RESULTS: TAU was associated with larger bilateral striatum (caudate/putamen) volume, whereas CT was associated with more widespread increases of the bilateral basal ganglia (incorporating the amygdala and hippocampus) and reduced bilateral cerebellum volume coinciding with improvements in impulsivity scores. CONCLUSIONS: While psychological intervention is associated with larger volume in mesolimbic reward regions, the utilisation of additional working memory training as an adjunct to treatment may further normalize frontostriatal structure and function.

Sn-doped Bi1.1Sb0.9Te2S bulk crystal topological insulator with excellent properties.

A long-standing issue in topological insulator research has been to find a bulk single crystal material that provides a high-quality platform for characterizing topological surface states without interference from bulk electronic states. This material would ideally be a bulk insulator, have a surface state Dirac point energy well isolated from the bulk valence and conduction bands, display quantum oscillations from the surface state electrons and be growable as large, high-quality bulk single crystals. Here we show that this material obstacle is overcome by bulk crystals of lightly Sn-doped Bi1.1Sb0.9Te2S grown by the vertical Bridgman method. We characterize Sn-BSTS via angle-resolved photoemission spectroscopy, scanning tunnelling microscopy, transport studies, X-ray diffraction and Raman scattering. We present this material as a high-quality topological insulator that can be reliably grown as bulk single crystals and thus studied by many researchers interested in topological surface states.

Sum-rule constraints on the surface state conductance of topological insulators.

We report the Drude oscillator strength D and the magnitude of the bulk band gap E_{g} of the epitaxially grown, topological insulator (Bi,Sb)_{2}Te_{3}. The magnitude of E_{g}, in conjunction with the model independent f-sum rule, allows us to establish an upper bound for the magnitude of D expected in a typical Dirac-like system composed of linear bands. The experimentally observed D is found to be at or below this theoretical upper bound, demonstrating the effectiveness of alloying in eliminating bulk charge carriers. Moreover, direct comparison of the measured D to magnetoresistance measurements of the same sample supports assignment of the observed low-energy conduction to topological surface states.

Hybridization and superconducting gaps in the heavy-fermion superconductor PuCoGa5 probed via the dynamics of photoinduced quasiparticles.

We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa5. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature Tc=18.5 K, which speaks against phonon-mediated superconductivity. Upon lowering the temperature, we observe an order-of-magnitude increase of the quasiparticle relaxation time in agreement with the phonon bottleneck scenario--evidence for a hybridization gap in the electronic density of states. The modification of photoinduced reflectance in the superconducting state is consistent with the heavy character of the quasiparticles that participate in Cooper pairing.

Towards a two-dimensional superconducting state of La(2-x)Sr(x)CuO4 in a moderate external magnetic field.

We report a novel aspect of the competition and coexistence between magnetism and superconductivity in the high-T(c) cuprate La(2-x)Sr(x)CuO4 (La214). With a modest magnetic field applied H parallel c axis, we monitored the infrared signature of pair tunneling between the CuO2 planes and discovered the complete suppression of interlayer coupling in a series of underdoped La214 single crystals. We find that the in-plane superconducting properties remain intact, in spite of enhanced magnetism in the planes.

Sum rules and interlayer infrared response of the high temperature YBa2Cu3Oy superconductor in an external magnetic field.

We present infrared magneto-optical measurements of the c-axis conductivity of YBa2Cu3Oy in both the underdoped (y=6.67 and 6.75) and optimally doped (y=6.95) regimes. We show that modest c-axis magnetic fields radically modify the condensate formation and restore conventional BCS-like energetics. Additionally, we demonstrate the pivotal role of interplane coherence in the anomalous high-energy contribution to the superfluid density.

Coupling between an optical phonon and the Kondo effect.

We explore the ultrafast optical response of Yb14MnSb11, providing further evidence that this compound is the first d-electron, ferromagnetic, underscreened Kondo lattice. These results also provide the first demonstration of coupling between an optical phonon mode and the Kondo effect.

Impurity band conduction in a high temperature ferromagnetic semiconductor.

The band structure of a prototypical dilute magnetic semiconductor (DMS), Ga1-xMnxAs, is studied across the phase diagram via infrared and optical spectroscopy. We prove that the Fermi energy (EF) resides in a Mn-induced impurity band (IB). Specifically the changes in the frequency dependent optical conductivity [sigma1(omega)] with carrier density are only consistent with EF lying in an IB. Furthermore, the large effective mass (m*) of the carriers inferred from our analysis of sigma1(omega) supports this conclusion. Our findings demonstrate that the metal to insulator transition in this DMS is qualitatively different from other III-V semiconductors doped with nonmagnetic impurities. We also provide insights into the anomalous transport properties of Ga1-xMnxAs.

Optical study of interactions in a d-electron Kondo lattice with ferromagnetism.

We report on a comprehensive optical, transport, and thermodynamic study of the Zintl compound Yb(14)MnSb(11), demonstrating that it is the first ferromagnetic Kondo lattice compound in the underscreened limit. We propose a scenario whereby the combination of Kondo and Jahn-Teller effects provides a consistent explanation of both transport and optical data.

Brain blood flow in the nitroglycerin (GTN) model of migraine: measurement using positron emission tomography and transcranial Doppler.

Nitroglycerin has been widely used as a model of experimental migraine. Studies combining measurement of flow velocity using transcranial Doppler (TCD) concurrently with measures of cerebral blood flow (CBF) are uncommon. We report the results of a study combining TCD and positron emission tomography (PET). Healthy volunteers with no personal or family history of migraine underwent measurement of CBF using H215O PET, and velocity using TCD. Measurements were done at baseline, and following i.v. nitroglycerin at 0.125, 0.25 and 0.5 micro g/kg per min. Subcutaneous sumatriptan (6 mg) was injected, with CBF and velocity measured 15, 30, and 60 min later. Nitroglycerin was terminated and measurements obtained 30 min later. Six male and six female subjects were studied. Nitroglycerin increased global CBF while flow velocities decreased. Sumatriptan did not have a significant effect on these values. Regions of increased flow included the anterior cingulate, while regions of decreased flow included the occipital cortex. Our data suggest that nitroglycerin induces regional changes in CBF that are similar to changes reported in spontaneous migraine, but produces distinctly different effects on global CBF and velocity.

Age-heterogamy and Canadian union.

This study provides a much-needed exploration of the determinants of age-discrepant unions in Canada. What little research has been conducted in this area of sociology of the family is now outdated. Further, the growing number of Canadians living in nonmarital cohabitation warrants their inclusion in any consideration of contemporary, heterosexual unions, and we have done so here. Utilizing multinomial logit modeling techniques, we analyze data drawn from the 1995 Canadian General Social Survey. We find that cohabitations and remarriages are more likely to be age-discrepant than marriages, and that as age at union formation increases, so does the likelihood that the union will be age-heterogamous. Although we hypothesized a positive relationship between education and the chances of age-heterogamous unions because the availability of eligible mates may decrease with education, we actually find an inverse association for women: a one-level increase in education decreases a woman's odds of entering an age-discrepant union by about 4 percent. We speculate that for women, greater education (economic position) may increase age-homogamy because they may be more economically attractive and thus more able to select a partner of their own age.

Successful treatment by meropenem of Campylobacter jejuni meningitis in a chronic alcoholic following neurosurgery.

Meningitis caused by Campylobacter jejuni is rare, we describe a case following neurosurgery for intra-cranial haematoma in a chronic alcoholic patient. Conventional culture of CSF and blood was supplemented by polymerase chain reaction (PCR) detection of Campylobacter jejuni.

Surgical management of catheter tip thrombus: surgical therapy for right atrial thrombus and fungal endocarditis (Candida tropicalis) complicating paediatric sickle-cell disease.

The use of indwelling central catheters for long-term administration of hyperalimentation, chemotherapy or other intravenous therapies is increasing. This unusual presentation of a catheter-induced right atrial thrombus was complicated by fungal infection. We present a case of a paediatric sickle-cell patient who underwent surgical removal of a right atrial thrombus secondary to fungal (Candida tropicalis) endocarditis from an indwelling catheter. Successful thrombus removal utilizing cardiopulmonary bypass and subsequent discharge underscores the importance of surgical therapy in treating this important complication.

Drug use evaluation of antibiotics in a pediatric teaching hospital.

OBJECTIVE: To determine the incidence and type of antibiotic use variances at our institution. DESIGN: Inpatient bacterial culture and susceptibility results were reviewed for 1 week per month. Medication administration records were evaluated to determine whether antibiotic selection was appropriate, given the susceptibility of the organism. Process indicators included use of the least costly antibiotic, as well as appropriate dose, interval, and route of administration. The complete medical record was reviewed for all patients if management did not appear to meet criteria. SETTING: A 225-bed, tertiary-care children's teaching hospital. RESULTS: Thirty-five (8.2%) of 428 patients reviewed over 12 months had a total of 49 variances: failure to treat (3), treatment of contaminant/colonizer (2), use of more costly agent (10), failure to revise therapy (8), inappropriate route (2), inappropriate empiric antibiotic (4), incorrect dose (3), unnecessary multiple antibiotics (6), inappropriate drug (8), and prolonged prophylaxis (3). CONCLUSIONS: Thirty-five patients with 10 types of variances were identified during the study. Follow-up monitoring will assess the impact of educational efforts on the incidence of variances. Specific problem antibiotics have been identified for further audits.

Within-patient correlation between the antihypertensive effects of atenolol, lisinopril and nifedipine.

OBJECTIVE: To investigate whether there are definable subgroups of patients with essential hypertension who respond specifically to particular antihypertensive drugs. DESIGN: Randomized cross-over comparison of the antihypertensive effect of 50 mg atenolol per day, 10 mg lisinopril per day and 20 mg nifedipine retard twice a day. Ambulatory blood pressure monitoring was used to assess the blood pressure level both for recruitment and at the end of each treatment period. The treatment periods lasted 4 weeks and were preceded by 4 weeks of placebo. PATIENTS: Seventy-two untreated hypertensive patients with a mean age of 52 (SD 8.4) years were recruited from six general practices and from the hospital outpatient clinic. Sixty-eight patients completed the trial. MAIN OUTCOME MEASURES: To assess the within-patient correlations among the blood pressure responses to each drug and explore the possible role of simple characteristics, such as the initial blood pressure, plasma renin concentration and age, in identifying the responders to a particular drug. RESULTS: Systolic/diastolic blood pressure fell significantly with each agent (P < 0.001): atenolol reduced it by 16.3 +/- 13.3/9.9 +/- 8.8, lisinopril by 14.8 +/- 15.0/9.4 +/- 9.1 and nifedipine by 11.6 +/- 12.3/6.7 +/- 8.3 mmHg. There was a low degree of correlation between the changes in blood pressure with the three drugs in individual patients. With each drug there was a small percentage (8.9-14.7%) of non-responders. The initial level of systolic blood pressure was weakly correlated with the antihypertensive effect of nifedipine (r = 0.47, P < 0.001) and plasma renin concentration was related to the effect of atenolol (r = 0.32, P < 0.01). Age did not predict the blood pressure response to any agent. CONCLUSIONS: The low level of the correlation between the blood pressure changes with the three drugs suggests that different mechanisms may be involved in the aetiology of essential hypertension. Plasma renin concentration and the initial level of systolic blood pressure contribute only weakly to the identification of responders to the three drugs.