Mott physics and band topology in materials with strong spin-orbit interaction

Recent theory and experiment have revealed that strong spin-orbit coupling can have dramatic qualitative effects on the band structure of weakly interacting solids. Indeed, it leads to a distinct phase of matter, the topological band insulator. In this paper, we consider the combined effects of spin-orbit coupling and strong electron correlation, and show that the former has both quantitative and qualitative effects upon the correlation-driven Mott transition. As a specific example we take Ir-based pyrochlores, where the subsystem of Ir 5d electrons is known to undergo a Mott transition. At weak electron-electron interaction, we predict that Ir electrons are in a metallic phase at weak spin-orbit interaction, and in a topological band insulator phase at strong spin-orbit interaction. Very generally, we show that with increasing strength of the electron-electron interaction, the effective spin-orbit coupling is enhanced, increasing the domain of the topological band insulator. Furthermore, in our model, we argue that with increasing interactions, the topological band insulator is transformed into a "topological Mott insulator" phase, which is characterized by gapless surface spin-only excitations. The full phase diagram also includes a narrow region of gapless Mott insulator with a spinon Fermi surface, and a magnetically ordered state at still larger electron-electron interaction.Comment: 10+ pages including 3+ pages of Supplementary Informatio

Imaging Coulomb Islands in a Quantum Hall Interferometer

In the Quantum Hall regime, near integer filling factors, electrons should only be transmitted through spatially-separated edge states. However, in mesoscopic systems, electronic transmission turns out to be more complex, giving rise to a large spectrum of magnetoresistance oscillations. To explain these observations, recent models put forward that, as edge states come close to each other, electrons can hop between counterpropagating edge channels, or tunnel through Coulomb islands. Here, we use scanning gate microscopy to demonstrate the presence of quantum Hall Coulomb islands, and reveal the spatial structure of transport inside a quantum Hall interferometer. Electron islands locations are found by modulating the tunneling between edge states and confined electron orbits. Tuning the magnetic field, we unveil a continuous evolution of active electron islands. This allows to decrypt the complexity of high magnetic field magnetoresistance oscillations, and opens the way to further local scale manipulations of quantum Hall localized states

Non-Equilibrium Edge Channel Spectroscopy in the Integer Quantum Hall Regime

Heat transport has large potentialities to unveil new physics in mesoscopic systems. A striking illustration is the integer quantum Hall regime, where the robustness of Hall currents limits information accessible from charge transport. Consequently, the gapless edge excitations are incompletely understood. The effective edge states theory describes them as prototypal one-dimensional chiral fermions - a simple picture that explains a large body of observations and calls for quantum information experiments with quantum point contacts in the role of beam splitters. However, it is in ostensible disagreement with the prevailing theoretical framework that predicts, in most situations, additional gapless edge modes. Here, we present a setup which gives access to the energy distribution, and consequently to the energy current, in an edge channel brought out-of-equilibrium. This provides a stringent test of whether the additional states capture part of the injected energy. Our results show it is not the case and thereby demonstrate regarding energy transport, the quantum optics analogy of quantum point contacts and beam splitters. Beyond the quantum Hall regime, this novel spectroscopy technique opens a new window for heat transport and out-of-equilibrium experiments.Comment: 13 pages including supplementary information, Nature Physics in prin

Position dependent mismatch discrimination on DNA microarrays – experiments and model

<p>Abstract</p> <p>Background</p> <p>The propensity of oligonucleotide strands to form stable duplexes with complementary sequences is fundamental to a variety of biological and biotechnological processes as various as microRNA signalling, microarray hybridization and PCR. Yet our understanding of oligonucleotide hybridization, in particular in presence of surfaces, is rather limited. Here we use oligonucleotide microarrays made in-house by optically controlled DNA synthesis to produce probe sets comprising all possible single base mismatches and base bulges for each of 20 sequence motifs under study.</p> <p>Results</p> <p>We observe that mismatch discrimination is mostly determined by the defect position (relative to the duplex ends) as well as by the sequence context. We investigate the thermodynamics of the oligonucleotide duplexes on the basis of double-ended molecular zipper. Theoretical predictions of defect positional influence as well as long range sequence influence agree well with the experimental results.</p> <p>Conclusion</p> <p>Molecular zipping at thermodynamic equilibrium explains the binding affinity of mismatched DNA duplexes on microarrays well. The position dependent nearest neighbor model (PDNN) can be inferred from it. Quantitative understanding of microarray experiments from first principles is in reach.</p

Voluntary Medical Male Circumcision: An Introduction to the Cost, Impact, and Challenges of Accelerated Scaling Up

Catherine Hankins, Steven Forsythe, and Emmanuel Njeuhmeli provide an overview of the “Voluntary Medical Male Circumcision for HIV Prevention: The Cost, Impact, and Challenges of Accelerated Scale-Up in Southern and Eastern Africa” Collection, calling for leadership and vision to help halt the HIV epidemic

Quantum and Classical Ballistic Transport in Constricted Two-Dimensional Electron Gases

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Adiabatic Transport in the Fractional Quantum Hall Effect Regime

Wetensch. publicati

Diagnostic challenges of early Lyme disease: Lessons from a community case series

<p>Abstract</p> <p>Background</p> <p>Lyme disease, the most common vector-borne infection in North America, is increasingly reported. When the characteristic rash, erythema migrans, is not recognized and treated, delayed manifestations of disseminated infection may occur. The accuracy of diagnosis and treatment of early Lyme disease in the community is unknown.</p> <p>Methods</p> <p>A retrospective, consecutive case series of 165 patients presenting for possible early Lyme disease between August 1, 2002 and August 1, 2007 to a community-based Lyme referral practice in Maryland. All patients had acute symptoms of less than or equal to 12 weeks duration. Patients were categorized according to the Centers for Disease Control and Prevention criteria and data were collected on presenting history, physical findings, laboratory serology, prior diagnoses and prior treatments.</p> <p>Results</p> <p>The majority (61%) of patients in this case series were diagnosed with early Lyme disease. Of those diagnosed with early Lyme disease, 13% did not present with erythema migrans; of those not presenting with a rash, 54% had been previously misdiagnosed. Among those with a rash, the diagnosis of erythema migrans was initially missed in 23% of patients whose rash was subsequently confirmed. Of all patients previously misdiagnosed, 41% had received initial antibiotics likely to be ineffective against Lyme disease.</p> <p>Conclusion</p> <p>For community physicians practicing in high-risk geographic areas, the diagnosis of Lyme disease remains a challenge. Failure to recognize erythema migrans or alternatively, viral-like presentations without a rash, can lead to missed or delayed diagnosis of Lyme disease, ineffective antibiotic treatment, and the potential for late manifestations.</p

Volumetry of [11C]-methionine PET uptake and MRI contrast enhancement in patients with recurrent glioblastoma multiforme

We investigated the relationship between three-dimensional volumetric data of the metabolically active tumour volume assessed using [(11)C]-methionine positron emission tomography (MET-PET) and the area of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) enhancement assessed using magnetic resonance imaging (MRI) in patients with recurrent glioblastoma (GBM).MET-PET and contrast-enhanced MRI with Gd-DTPA were performed in 12 uniformly pretreated patients with recurrent GBM. To calculate the volumes in cubic centimetres, a threshold-based volume-of-interest (VOI) analysis of the metabolically active tumour volume (MET uptake indexes of > or = 1.3 and > or = 1.5) and of the area of Gd-DTPA enhancement was performed after coregistration of all images.In all patients, the metabolically active tumour volume as shown using a MET uptake index of > or = 1.3 was larger than the volume of Gd-DTPA enhancement (30.2 + or - 22.4 vs. 13.7 + or - 10.6 cm(3); p = 0.04). Metabolically active tumour volumes as shown using MET uptake indexes of > or =1.3 and > or = 1.5 and the volumes of Gd-DTPA enhancement showed a positive correlation (r = 0.76, p = 0.003, for an index of > or =1.3, and r = 0.74, p = 0.005, for an index of > or =1.5).The present data suggest that in patients with recurrent GBM the metabolically active tumour volume may be substantially underestimated by Gd-DTPA enhancement. The findings support the notion that complementary information derived from MET uptake and Gd-DTPA enhancement may be helpful in developing individualized, patient-tailored therapy strategies in patients with recurrent GBM