Quantum oscillations with angular dependence in PdTe2single crystals.

The layered transition-metal dichalcogenide PdTe2has been discovered to possess bulk Dirac points as well as topological surface states. By measuring the magnetization (up to 7 T) and magnetic torque (up to 35 T) in single crystalline PdTe2, we observe distinct de Haas-van Alphen (dHvA) oscillations. Eight frequencies are identified withH||c, with two low frequencies (Fα= 8 T andFß= 117 T) dominating the spectrum. The effective masses obtained by fitting the Lifshitz-Kosevich (LK) equation to the data aremα*=0.059m0andmß*=0.067m0wherem0is the free electron mass. The corresponding Landau fan diagrams allow the determination of the Berry phase for these oscillations resulting in values of ∼0.67πfor the 3D α band (hole-type) (down to the 1st Landau level) and ∼0.23π-0.73πfor the 3D ß band (electron-type) (down to the 3rd Landau level). By investigating the angular dependence of the dHvA oscillations, we find that the frequencies and the corresponding Berry phase (ΦB) vary with the field direction, with a ΦB∼ 0 whenHis 10°-30° away from theabplane for both α and ß bands. The multiple band nature of PdTe2is further confirmed from Hall effect measurements.

Effect of doping on the intersubband absorption in Si- and Ge-doped GaN/AlN heterostructures.

In this paper, we study band-to-band and intersubband (ISB) characteristics of Si- and Ge-doped GaN/AlN heterostructures (planar and nanowires) structurally designed to absorb in the short-wavelength infrared region, particularly at 1.55 µm. Regarding the band-to-band properties, we discuss the variation of the screening of the internal electric field by free carriers, as a function of the doping density and well/nanodisk size. We observe that nanowire heterostructures consistently present longer photoluminescence decay times than their planar counterparts, which supports the existence of an in-plane piezoelectric field associated to the shear component of the strain tensor in the nanowire geometry. Regarding the ISB characteristics, we report absorption covering 1.45-1.75 µm using Ge-doped quantum wells, with comparable performance to Si-doped planar heterostructures. We also report similar ISB absorption in Si- and Ge-doped nanowire heterostructures indicating that the choice of dopant is not an intrinsic barrier for observing ISB phenomena. The spectral shift of the ISB absorption as a function of the doping concentration due to many body effects confirms that Si and Ge efficiently dope GaN/AlN nanowire heterostructures.

Effect of doping on the far-infrared intersubband transitions in nonpolar m-plane GaN/AlGaN heterostructures.

This paper assesses the effects of Si doping on the properties of nonpolar m-plane GaN/AlGaN quantum wells (QWs) designed for intersubband (ISB) absorption in the far-infrared spectral range. For doping levels up to 3 × 10(12) cm(-2), structural analysis reveals uniform QWs with abrupt interfaces and no epitaxially induced defects. Cathodoluminescence spectroscopy confirms the homogeneity of the multiple QWs along the growth direction. Increasing the doping density in the QWs from 1 × 10(11) cm(-2) to 3 × 10(12) cm(-2) induces a broadening of the photoluminescence as well as a reduction of the exciton localization energy in the alloy. Also, enhancement of the ISB absorption is observed, along with a blue shift and widening of the absorption peak. The magnitude of the ISB absorption saturates for doping levels around 1 × 10(12) cm(-2), and the blue shift and broadening increase less than theoretically predicted for the samples with higher doping levels. This is explained by the presence of free carriers in the excited electron level due to the increase of the Fermi level energy.

PdTe: a strongly coupled superconductor.

We report the electrical transport, magnetic, and thermodynamic properties of polycrystalline PdTe which exhibits superconductivity below 4.5 K. Using the measured values for the lower (H(c1)) and upper (H(c2)) critical fields, and the specific heat C(p), we estimate the thermodynamic critical field H(c)(0), coherence length ξ(0), penetration depth λ(0), and the Ginzburg-Landau parameter κ. Compared with band structure calculations, the density of states at the Fermi level is enhanced due to electron-phonon coupling with λ(ep) = 1.4. Furthermore, the large values of ΔC(p)/γ(n)T(c) and 2Δ(0)/k(B)T(c) suggest that PdTe is a strongly coupled superconductor.

Quantum criticality and incipient phase separation in the thermodynamic properties of the Hubbard model.

Transport measurements on the cuprates suggest the presence of a quantum critical point (QCP) hiding underneath the superconducting dome near optimal hole doping. We provide numerical evidence in support of this scenario via a dynamical cluster quantum Monte Carlo study of the extended two-dimensional Hubbard model. Single-particle quantities, such as the spectral function, the quasi-particle weight and the entropy, display a crossover between two distinct ground states: a Fermi liquid at low filling and a non-Fermi liquid with a pseudo-gap at high filling. Both states are found to cross over to a marginal Fermi-liquid state at higher temperatures. For finite next-nearest-neighbour hopping t', we find a classical critical point at temperature T(c). This classical critical point is found to be associated with a phase-separation transition between a compressible Mott gas and an incompressible Mott liquid corresponding to the Fermi liquid and the pseudo-gap state, respectively. Since the critical temperature T(c) extrapolates to zero as t' vanishes, we conclude that a QCP connects the Fermi liquid to the pseudo-gap region, and that the marginal Fermi-liquid behaviour in its vicinity is the analogue of the supercritical region in the liquid-gas transition.

Discovery of the Griffiths phase in the itinerant magnetic semiconductor Fe1-xCoxS2.

Critical points that can be suppressed to zero temperature are interesting because quantum fluctuations have been shown to dramatically alter electron gas properties. Here, the metal formed by Co doping the paramagnetic insulator FeS2, Fe1-xCoxS2 is demonstrated to order ferromagnetically at x > xc = 0.01+/-0.005, where we observe unusual transport, magnetic, and thermodynamic properties. We show that this magnetic semiconductor undergoes a percolative magnetic transition with distinct similarities to the Griffiths phase, including singular behavior at xc and zero temperature.

Undiagnosed phaeochromocytoma mimicking severe preeclampsia in a pregnant woman at term.

We report an unusual case of phaeochromocytoma in pregnancy. The patient presented with severe hypertension, visual disturbances, proteinuria, glycosuria and pulmonary oedema at 38 weeks' gestation. The initial diagnosis was severe preeclampsia, but rapid deterioration of the fetus necessitated an emergency caesarean section under general anaesthesia, following which the maternal condition deteriorated rapidly. Differential diagnoses included pulmonary embolus, cardiomyopathy, amniotic fluid embolus and ischaemic/embolic cerebrovascular accident. Despite aggressive maximal treatment, mother and baby died 36 h later. Post mortem examination of the mother revealed a 5.5-cm tumour of the right adrenal gland confirmed histologically as a phaeochromocytoma. We examine the diagnostic dilemmas of this case and consider the treatment and management options when faced with a critically ill mother and the need to deliver her fetus by emergency caesarean section. We also question the clinical priorities during management of a sudden deterioration in both maternal and fetal health.

Interaction of Ising-Bloch fronts with Dirichlet boundaries.

We study the Ising-Bloch bifurcation in two systems, the complex Ginzburg Landau equation (CGLE) and a FitzHugh Nagumo (FN) model in the presence of spatial inhomogeneity introduced by Dirichlet boundary conditions. It is seen that the interaction of fronts with boundaries is similar in both systems, establishing the generality of the Ising-Bloch bifurcation. We derive reduced dynamical equations for the FN model that explain front dynamics close to the boundary. We find that front dynamics in a highly nonadiabatic (slow front) limit is controlled by fixed points of the reduced dynamical equations, that occur close to the boundary.

Comparison of four subarachnoid solutions in a needle-through-needle technique for elective caesarean section.

We have used both spinal and extradural anaesthesia with a 26-gauge, long spinal needle through a 16-gauge Tuohy needle for elective Caesarean section. Four different subarachnoid solutions of bupivacaine were compared: 0.5% heavy bupivacaine alone, or with adrenaline, fentanyl or adrenaline and fentanyl. The incidence of complications and time of regression of the sensory block were analysed. The technique is recommended because it allows rapid onset of anaesthesia and the advantages of an extradural catheter. The subarachnoid solution of choice was 0.5% heavy bupivacaine 12.5 mg with fentanyl 10 micrograms.

Regional anaesthesia and cough effectiveness. A study in patients undergoing caesarean section.

We report the results of a study of the effects of spinal and epidural anaesthesia for Caesarean section on commonly used indicators of a patient's ability to cough effectively. Both spinal and epidural anaesthesia, after the achievement of a block adequate for surgery, were associated with statistically significant decreases (p less than 0.05) in all the respiratory variables recorded: forced vital capacity, forced expiratory volume in one second, peak expiratory flow rate and maximum expiratory pressure. We conclude that although the observed changes are unlikely to impair the normal patient's ability to cough effectively in these circumstances, there may be clinically significant impairment in the presence of an inadvertently high block or in a patient with pre-existing pulmonary disease.

An evaluation of the Level 1 blood warmer series.

The Level 1 blood warmer series comprises three infusion sets and two blood warmers of different power outputs. All systems were found to be extremely efficient, with the larger 500 series capable of warming the equivalent of 80 units of blood an hour almost to body temperature.

alpha 1 Antitrypsin (PI) allotypes in rheumatoid arthritis.

alpha 1 Antitrypsin (PI) phenotypes were defined in 144 patients with rheumatoid arthritis (RA) and in 223 normal controls. The frequencies of the rare F, S, and Z variants were similar in RA and control groups. No relationships were found between PI allotypes and rheumatoid disease severity or autoantibody titre. The PI M1M2 phenotype was increased in frequency in the RA group, and phenotype frequencies in DR4 positive and negative disease were similar. These results support the suggestion that genes on the 14th chromosome which are linked to PI predispose to RA.