Fluctuations in Planar Magnetotransport Due to Tilted Dirac Cones in Topological Materials.

Fluctuations in planar magnetotransport are ubiquitous in topological HgTe structures, in both tensile (topological insulator) and compressively strained layers (Weyl semimetal phase). We show that the common reason for the fluctuations is the presence of tilted Dirac cones combined with the formation of charge puddles. The origin of the tilted Dirac cones is the mix of the Zeeman term due to the in-plane magnetic field and quadratic contributions to the dispersion relation. We develop a network model that mimics the transport of tilted Dirac fermions in the landscape of charge puddles. The model captures the essential features of the experimental data. It should be relevant for the interpretation of planar magnetotransport in a variety of topological and small band gap materials.

Macroscopic Quantum Tunneling of a Topological Ferromagnet.

The recent advent of topological states of matter spawned many significant discoveries. The quantum anomalous Hall (QAH) effect is a prime example due to its potential for applications in quantum metrology, as well as its influence on fundamental research into the underlying topological and magnetic states and into axion electrodynamics. Here, electronic transport studies on a (V,Bi,Sb)2 Te3 ferromagnetic topological insulator nanostructure in the QAH regime are presented. This allows access to the dynamics of an individual ferromagnetic domain. The domain size is estimated to be in the 50-100 nm range. Telegraph noise resulting from the magnetization fluctuations of this domain is observed in the Hall signal. Careful analysis of the influence of temperature and external magnetic field on the domain switching statistics provides evidence for quantum tunneling (QT) of magnetization in a macrospin state. This ferromagnetic macrospin is not only the largest magnetic object in which QT is observed, but also the first observation of the effect in a topological state of matter.

Finite Field Transport Response of a Dilute Magnetic Topological Insulator-Based Josephson Junction.

Hybrid samples combining superconductors with magnetic topological insulators are a promising platform for exploring exotic new transport physics. We examine a Josephson junction of such a system based on the dilute magnetic topological insulator (Hg,Mn)Te and the type II superconductor MoRe. In the zero and very low field limits, to the best of our knowledge, the device shows, for the first time, an induced supercurrent through a magnetically doped semiconductor, in this case, a topological insulator. At higher fields, a rich and hysteretic magnetoresistance is revealed. Careful analysis shows that the explanation of this behavior can be found in magnetic flux focusing stemming from the Meissner effect in the superconductor, without invoking any role of proximity-induced superconductivity. The phenomena is important because it will ubiquitously coexist with any exotic new physics that may be present in this class of devices.

Quantum anomalous Hall edge channels survive up to the Curie temperature.

Achieving metrological precision of quantum anomalous Hall resistance quantization at zero magnetic field so far remains limited to temperatures of the order of 20 mK, while the Curie temperature in the involved material is as high as 20 K. The reason for this discrepancy remains one of the biggest open questions surrounding the effect, and is the focus of this article. Here we show, through a careful analysis of the non-local voltages on a multi-terminal Corbino geometry, that the chiral edge channels continue to exist without applied magnetic field up to the Curie temperature of bulk ferromagnetism of the magnetic topological insulator, and that thermally activated bulk conductance is responsible for this quantization breakdown. Our results offer important insights on the nature of the topological protection of these edge channels, provide an encouraging sign for potential applications, and establish the multi-terminal Corbino geometry as a powerful tool for the study of edge channel transport in topological materials.

Absence of evidence for chiral Majorana modes in quantum anomalous Hall-superconductor devices.

A quantum anomalous Hall (QAH) insulator coupled to an s-wave superconductor is predicted to harbor chiral Majorana modes. A recent experiment interprets the half-quantized two-terminal conductance plateau as evidence for these modes in a millimeter-size QAH-niobium hybrid device. However, non-Majorana mechanisms can also generate similar signatures, especially in disordered samples. Here, we studied similar hybrid devices with a well-controlled and transparent interface between the superconductor and the QAH insulator. When the devices are in the QAH state with well-aligned magnetization, the two-terminal conductance is always half-quantized. Our experiment provides a comprehensive understanding of the superconducting proximity effect observed in QAH-superconductor hybrid devices and shows that the half-quantized conductance plateau is unlikely to be induced by chiral Majorana fermions in samples with a highly transparent interface.

Mechanochemical ablation for symptomatic great saphenous vein reflux: A two-year follow-up.

Background Several studies have shown comparable early efficacy of mechanochemical ablation to endothermal techniques. The goal of this report was to show if early efficacy is maintained at 24 months. Methods This was a two-year analysis on the efficacy of mechanochemical ablation in patients with symptomatic C2 or more advanced chronic venous disease. Patients with reflux in the great saphenous vein involving the sapheno-femoral junction and no previous venous interventions were included. Demographic information, clinical, and procedural data were collected. The occlusion rate of treated veins was assessed with duplex ultrasound. Patient clinical improvement was assessed by Clinical-Etiology-Anatomy-Pathophysiology (CEAP) class and venous clinical severity score. Results Of the initial 126 patients, there were 65 patients with 24 month follow-up. Of these 65 patients, 70% were female, with a mean age of 70 ± 14 years and an average body mass index (BMI) of BMI of 30.5 ± 6. The mean great saphenous vein diameter in the upper thigh was 7.6 mm and the mean treatment length was 39 cm. Adjunctive treatment of the varicosities was performed in 14% of patients during the procedure. Closure rates were 100% at one week, 98% at three months, 95% at 12 months, and 92% at 24 months. There was one patient with complete and four with partial recanalization ranging from 7 to 12 cm (mean length 9 cm). There was significant improvement in CEAP and venous clinical severity score (P < .001) for all time intervals. Conclusion Early high occlusion rate with mechanochemical ablation is associated with significant clinical improvement which is maintained at 24 months, making it a very good option for the treatment of great saphenous vein incompetence.

Nonepithelial Neoplasms of the Pancreas: Radiologic-Pathologic Correlation, Part 1--Benign Tumors: From the Radiologic Pathology Archives.

Solid and cystic pancreatic neoplasms are being recognized more frequently with increasing utilization and spatial resolution of modern imaging techniques. In addition to the more common primary pancreatic solid (ductal adenocarcinoma) and cystic neoplasms of epithelial origin, nonepithelial neoplasms of the pancreas may appear as well-defined solid or cystic neoplasms. Most of these lesions have characteristic imaging features, such as a well-defined border, which allows differentiation from ductal adenocarcinoma. Solid masses include neurofibroma, ganglioneuroma, leiomyoma, lipoma, and perivascular epithelioid cell tumor (PEComa). Schwannomas and desmoid tumors can be solid or cystic. Cystic tumors include mature cystic teratoma and lymphangioma. Lipoma, PEComa, and mature cystic teratoma can contain fat, and ganglioneuroma and mature cystic teratoma may contain calcification. Although these unusual benign neoplasms are rare, the radiologist should at least consider them in the differential diagnosis of well-defined lesions of the pancreas. The goal of this comprehensive review is to improve understanding of these rare primary pancreatic mesenchymal tumors.

Nonsinusoidal current-phase relationship in Josephson junctions from the 3D topological insulator HgTe.

We use superconducting quantum interference device microscopy to characterize the current-phase relation (CPR) of Josephson junctions from the three-dimensional topological insulator HgTe (3D HgTe). We find clear skewness in the CPRs of HgTe junctions ranging in length from 200 to 600 nm. The skewness indicates that the Josephson current is predominantly carried by Andreev bound states with high transmittance, and the fact that the skewness persists in junctions that are longer than the mean free path suggests that the effect may be related to the helical nature of the Andreev bound states in the surface of HgTe. These experimental results suggest that the topological properties of the normal state can be inherited by the induced superconducting state, and that 3D HgTe is a promising material for realizing the many exciting proposals that require a topological superconductor.

Spin texture of Bi2Se3 thin films in the quantum tunneling limit.

By means of spin- and angle-resolved photoelectron spectroscopy we studied the spin structure of thin films of the topological insulator Bi2Se3 grown on InP(111). For thicknesses below six quintuple layers the spin-polarized metallic topological surface states interact with each other via quantum tunneling and a gap opens. Our measurements show that the resulting surface states can be described by massive Dirac cones which are split in a Rashba-like manner due to the substrate induced inversion asymmetry. The inner and the outer Rashba branches have distinct localization in the top and the bottom part of the film, whereas the band apices are delocalized throughout the entire film. Supported by calculations, our observations help in the understanding of the evolution of the surface states at the topological phase transition and provide the groundwork for the realization of two-dimensional spintronic devices based on topological semiconductors.

Induced superconductivity in the three-dimensional topological insulator HgTe.

A strained and undoped HgTe layer is a three-dimensional topological insulator, in which electronic transport occurs dominantly through its surface states. In this Letter, we present transport measurements on HgTe-based Josephson junctions with Nb as a superconductor. Although the Nb-HgTe interfaces have a low transparency, we observe a strong zero-bias anomaly in the differential resistance measurements. This anomaly originates from proximity-induced superconductivity in the HgTe surface states. In the most transparent junction, we observe periodic oscillations of the differential resistance as a function of an applied magnetic field, which correspond to a Fraunhofer-like pattern. This unambiguously shows that a precursor of the Josephson effect occurs in the topological surface states of HgTe.