Geometric dependence of Nb-Bi2{_2}Te3{_3}-Nb topological Josephson junction transport parameters

Superconductor-topological insulator-superconductor Josephson junctions have been fabricated in order to study the width dependence of the critical current, normal state resistance and flux periodicity of the critical current modulation in an external field. Previous literature reports suggest anomalous scaling in topological junctions due to the presence of Majorana bound states. However, for most realised devices, one would expect that trivial $2\pi$-periodic Andreev levels dominate transport. We also observe anomalous scaling behaviour of junction parameters, but the scaling can be well explained by mere geometric effects, such as the parallel bulk conductivity shunt and flux focusing

Magnetoresistance from time-reversal symmetry breaking in topological materials

Magnetotransport measurements are a popular way of characterizing the electronic structure of topological materials and often the resulting datasets cannot be described by the well-known Drude model due to large, non-parabolic contributions. In this work, we focus on the effects of magnetic fields on topological materials through a Zeeman term included in the model Hamiltonian. To this end, we re-evaluate the simplifications made in the derivations of the Drude model and pinpoint the scattering time and Fermi velocity as Zeeman-term dependent factors in the conductivity tensor. The driving mechanisms here are the aligment of spins along the magnetic field direction, which allows for backscattering, and a significant change to the Fermi velocity by the opening of a hybridization gap. After considering 2D and 3D Dirac states, as well as 2D Rashba surface states and the quasi-2D bulk states of 3D topological insulators, we find that the 2D Dirac states on the surfaces of 3D topological insulators produce magnetoresistance, that is significant enough to be noticable in experiments. As this magnetoresistance effect is strongly dependent on the spin-orbit energy, it can be used as a telltale sign of a Fermi energy located close to the Dirac point

Ruptured abdominal aortic aneurysms: Factors influencing postoperative mortality and long-term survival

Objective:To update mortality rates and long-term survival of patients admitted to the hospital with ruptured abdominal aortic aneurysm (AAA) and to study prognostic factors associated with mortality.Design:Retrospective follow-up.Materials:309 patients (274 men, 35 women, average age 71) admitted to the hospital between January 1980 and January 1994 who were surgically treated for ruptured AAA were studied.Methods:To identify the preoperative (9), intraoperative (23) and postoperative (49) variables associated with mortality logistic regression analysis (mortality within 48 h) and Cox regression analysis (mortality between 48 h and 30 days) were performed.Results:Hospital mortality improved from 1980 to 1994. Compared with the normal population adjusted for age and sex the long-term mortality rate was increased (standardised mortality ratio 2.1; 95% confidence interval 1.7–2.5). Increased age, peroperative hypotension and need for a bifurcated graft were associated with significantly increased mortality. Co-morbidity was not a predictive variable. Overall hospital mortality was 25%.Conclusion:Surgical repair of ruptured AAA should be considered even in patients with co-morbidity. Elderly patients with severe preoperative hypotension have a very high mortality rate and surgery may not be justified in these cases. Long-term survival is also worse in older patients

Carrier freeze-out induced metal-insulator transition in oxygen deficient SrTiO3 films

We report the optical, electrical transport, and magnetotransport properties of high quality oxygen deficient SrTiO3 (STO) single crystal film fabricated by pulsed laser deposition and reduced in the vacuum chamber. The oxygen vacancy distribution in the thin film is expected to be uniform. By comparing the electrical properties with oxygen deficient bulk STO, it was found that the oxygen vacancies in bulk STO is far from uniform over the whole material. The metal-insulator transition (MIT) observed in the oxygen deficient STO film was found to be induced by the carrier freeze-out effect. The low temperature frozen state can be re-excited by an electric field, Joule heating, and surprisingly also a large magnetic field.Comment: 5 pages, 5 figure

The effect of bone marrow aspiration strategy on the yield and quality of human mesenchymal stem cells

Introduction Large inter-donor differences exist in human mesenchymal stem cell (hMSC) yield and the response of these cells to osteogenic stimuli. The source of these differences may be clinical differences in stem cell characteristics between individuals or the aspiration procedure itself

Nonlinear Insulator in Complex Oxides

The insulating state is one of the most basic electronic phases in condensed matter. This state is characterised by an energy gap for electronic excitations that makes an insulator electrically inert at low energy. However, for complex oxides, the very concept of an insulator must be re-examined. Complex oxides behave differently from conventional insulators such as SiO2, on which the entire semiconductor industry is based, because of the presence of multiple defect levels within their band gap. As the semiconductor industry is moving to such oxides for high-dielectric (high-k) materials, we need to truly understand the insulating properties of these oxides under various electric field excitations. Here we report a new class of material called nonlinear insulators that exhibits a reversible electric-field-induced metal-insulator transition. We demonstrate this behaviour for an insulating LaAlO3 thin film in a metal/LaAlO3/Nb-SrTiO3 heterostructure. Reproducible transitions were observed between a low-resistance metallic state and a high-resistance non-metallic state when applying suitable voltages. Our experimental results exclude the possibility that diffusion of the metal electrodes or oxygen vacancies into the LaAlO3 layer is occurring. Instead, the phenomenon is attributed to the formation of a quasi-conduction band (QCB) in the defect states of LaAlO3 that forms a continuum state with the conduction band of the Nb-SrTiO3. Once this continuum (metallic) state is formed, the state remains stable even when the voltage bias is turned off. An opposing voltage is required to deplete the charges from the defect states. Our ability to manipulate and control these defect states and, thus, the nonlinear insulating properties of complex oxides will open up a new path to develop novel devices.Comment: 23 pages, 4 figure

Definitiestudie afwegingskader : naar een klimaatbestendig Nederland : definitiestudie Fase 1, kaders voor afweging

Onzekerheid over (omvang en tempo van) de gevolgen van klimaatverandering vormt een essentieel punt bij beslissingen over de ruimtelijke inrichting. De mate waarin en de snelheid waarmee veranderingen optreden zijn niet precies bekend. Een afwegingskader geeft de overheid en de planontwikkelaar instrumenten in handen om de risico’s, de kansen, de kosten en de baten van klimaatadaptatie op verschillende onderscheiden thema’s inzichtelijk te maken. Afwegen: hoe doe je dat. Daarvoor wordt in drie stappen een kader voor gegeven