Emergent topological mirror insulator in t2g-orbital systems

The electronic band structure of iron pnictides exhibits four Dirac cones, which are due to crystal symmetry and orbital bonding orientation. This hallmark signature presents the pnictide family as an ideal candidate in the search for quasi-two-dimensional topological crystalline insulators. In this report, we explore interaction-induced topological phases which cannot be described by conventional local order parameters. Based on a model Hamiltonian our symmetry analysis shows that sponta- neous novel topological phases may be realized in compounds with tetragonal crystal field symmetry, where the electrons occupy the two degenerate t2g energy levels at low temperature. We identify two stable topological phases in the ground state, which emerge from spontaneous orbital current order. These currents are driven by electronic correlations caused by inter-orbital Coulomb interactions. The first topological phase is an anomalous orbital Hall phase, characterized by a nonzero Chern number, while the second topological phase has a vanishing Chern number, though with an extra Z2-like invariant that preserves parity. More specifically, the interaction-induced novel phase of the quasi-two-dimensional topological crystalline insulator is protected by mirror reflection symmetries and therefore may be realized in pnictides

Towards understanding the electronic structure of Fe-doped CeO2 nanoparticles with X-ray spectroscopy

[[abstract]]This study reports on the electronic structure of Fe-doped CeO2 nanoparticles (NPs), determined by coupled X-ray absorption spectroscopy and X-ray emission spectroscopy. A comparison of the local electronic structure around the Ce site with that around the Fe site indicates that the Fe substitutes for the Ce. The oxygen K-edge spectra that originated from the hybridization between cerium 4f and oxygen 2p states are sensitive to the oxidation state and depend strongly on the concentration of Fe doping. The Ce M4,5-edges and the Fe L2,3-edges reveal the variations of the charge states of Ce and Fe upon doping, respectively. The band gap is further obtained from the combined absorption–emission spectrum and decreased upon Fe doping, implying Fe doping introduces vacancies. The oxygen vacancies are induced by Fe doping and the spectrum reveals the charge transfer between Fe and Ce. Fe3+ doping has two major effects on the formation of ferromagnetism in CeO2 nanoparticles. The first, at an Fe content of below 5%, is that the formation of Fe3+–Vo–Ce3+ introduces oxygen deficiencies favoring ferromagnetism. The other, at an Fe content of over 5%, is the formation of Fe3+–Vo–Fe3+, which favors antiferromagnetism, reducing the Ms. The defect structures Fe3+–Vo–Ce3+ and Fe3+–Vo–Fe3+ are crucial to the magnetism in these NPs and the change in Ms can be described as the effect of competitive interactions of magnetic polarons and paired ions.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

Experiences with a simple laparoscopic gastric tube construction

BACKGROUND: Minimally invasive esophagectomy (MIE) is a complex operation, and the detailed optimal surgical procedure has not been well described. Our aim was to evaluate use of a simple method of laparoscopic gastric tube construction as minimally invasive surgery for patients with esophageal cancer. METHODS: We performed a retrospective review of 26 consecutive patients who underwent MIE for esophageal cancer in the Koo Foundation Sun Yat-Sen Cancer Center between September 2009 and August 2011. Perioperative data and postoperative complications were statistically analyzed. RESULTS: The patient group consisted of 22 men and 4 women. MIE was performed successfully in all patients. The mean operative time was 430.4 ± 60.6 minutes, and the mean estimated operative blood loss was 135.0 ± 97.8 mL. There were no cases of conversion to open surgery during the procedure. The postoperative complication rate was 53.8%, and there was no surgical mortality. CONCLUSIONS: We recommend this novel method of total laparoscopic staplized formation of gastric tube to facilitate gastric pull-up