Quantum Transport in Magnetic Topological Insulator Thin Films

The experimental observation of the long-sought quantum anomalous Hall effect was recently reported in magnetically doped topological insulator thin films [Chang et al., Science 340, 167 (2013)]. An intriguing observation is a rapid decrease from the quantized plateau in the Hall conductance, accompanied by a peak in the longitudinal conductance as a function of the gate voltage. Here, we present a quantum transport theory with an effective model for magnetic topological insulator thin films. The good agreement between theory and experiment reveals that the measured transport originates from a topologically nontrivial conduction band which, near its band edge, has concentrated Berry curvature and a local maximum in group velocity. The indispensable roles of the broken structure inversion and particle-hole symmetries are also revealed. The results are instructive for future experiments and transport studies based on first-principles calculations.Comment: 5 pages, 4 figure

Rigid vortices in MgB2

Magnetic relaxation of high-pressure synthesized MgB$_2$ bulks with different thickness is investigated. It is found that the superconducting dia-magnetic moment depends on time in a logarithmic way; the flux-creep activation energy decreases linearly with the current density (as expected by Kim-Anderson model); and the activation energy increases linearly with the thickness of sample when it is thinner than about 1 mm. These features suggest that the vortices in the MgB$_2$ are rather rigid, and the pinning and creep can be well described by Kim-Anderson model.Comment: Typo corrected & reference adde

Covert Laparoscopic Cholecystectomy: A New Minimally Invasive Technique

To further improve our developed transumbilical endoscopic surgery (TUES), we developed a completely covert laparoscopic cholecystectomy (LC). Twelve cases of LC were recruited for this new approach. First, a 10-mm trocar was placed above the umbilicus for inserting the laparoscope. Two 5-mm trocars were then placed near the right and left ends of the superior margin of the suprapubic hair. After the 5-mm 30° laparoscope was shifted to the left suprapubic trocar, the harmonic scalper, electric hook, and grasper were inserted either through the 10-mm umbilical trocar or through the right suprapubic trocar. All gallbladders were successfully removed without intraoperative complications. The mean operating time was 28.5±5.7min (range 20-45min). All patients felt well after surgery and did not need postoperative analgesia. They resumed free oral intake 6h after the procedure. All patients were satisfied with the appearance of the incisions, which were completely hidden in the umbilicus and suprapubic hair. The approach we developed has overcome both external instrument interference around the umbilicus and the loss of triangulation in the operative field. It is relatively simpler than a typical TUES and offers better cosmetic results