Two-Dimensional Topological Insulator State and Topological Phase Transition in Bilayer Graphene

We show that gated bilayer graphene hosts a strong topological insulator (TI) phase in the presence of Rashba spin-orbit (SO) coupling. We find that gated bilayer graphene under preserved time-reversal symmetry is a quantum valley Hall insulator for small Rashba SO coupling $\lambda_{\mathrm{R}}$, and transitions to a strong TI when $\lambda_{\mathrm{R}} > \sqrt{U^2+t_\bot^2}$, where $U$ and $t_\bot$ are respectively the interlayer potential and tunneling energy. Different from a conventional quantum spin Hall state, the edge modes of our strong TI phase exhibit both spin and valley filtering, and thus share the properties of both quantum spin Hall and quantum valley Hall insulators. The strong TI phase remains robust in the presence of weak graphene intrinsic SO coupling.Comment: 5 pages and 4 figure

Topological phases in gated bilayer graphene: Effects of Rashba spin-orbit coupling and exchange field

We present a systematic study on the influence of Rashba spin-orbit coupling, interlayer potential difference and exchange field on the topological properties of bilayer graphene. In the presence of only Rashba spin-orbit coupling and interlayer potential difference, the band gap opening due to broken out-of-plane inversion symmetry offers new possibilities of realizing tunable topological phase transitions by varying an external gate voltage. We find a two-dimensional $Z_2$ topological insulator phase and a quantum valley Hall phase in $AB$-stacked bilayer graphene and obtain their effective low-energy Hamiltonians near the Dirac points. For $AA$ stacking, we do not find any topological insulator phase in the presence of large Rashba spin-orbit coupling. When the exchange field is also turned on, the bilayer system exhibits a rich variety of topological phases including a quantum anomalous Hall phase, and we obtain the phase diagram as a function of the Rashba spin-orbit coupling, interlayer potential difference, and exchange field.Comment: 15 pages, 17figures, and 1 tabl

Anderson Localization from Berry-Curvature Interchange in Quantum Anomalous Hall System

We theoretically investigate the localization mechanism of the quantum anomalous Hall effect (QAHE) in the presence of spin-flip disorders. We show that the QAHE keeps quantized at weak disorders, then enters a Berry-curvature mediated metallic phase at moderate disorders, and finally goes into the Anderson insulating phase at strong disorders. From the phase diagram, we find that at the charge neutrality point although the QAHE is most robust against disorders, the corresponding metallic phase is much easier to be localized into the Anderson insulating phase due to the \textit{interchange} of Berry curvatures carried respectively by the conduction and valence bands. At the end, we provide a phenomenological picture related to the topological charges to better understand the underlying physical origin of the QAHE Anderson localization.Comment: 6 pages, 4 figure

Global time trends in the incidence of esophageal squamous cell carcinoma

Background & Aims: Esophageal squamous cell carcinoma (ESCC) is the dominant histological type of esophageal cancer worldwide (90%). We aimed to provide an update of the global temporal trends in the incidence of ESCC. Methods: Incidence data for ESCC were collected from 30 well-established cancer registries from 20 countries in Europe, Northern America, Australia, or Asia in 1970-2015. Time trends in annual age-standardized incidence rates of ESCC were assessed using joinpoint analysis and log-linear regression. Age-period-cohort analysis was used to estimate the influence of age, calendar-period, and birth-cohort on the observed time trends in incidence. Results: The age-standardized incidence rates of ESCC varied more than 8-fold in men and 7-fold in women across populations. In 2012, the highest rate in men was observed in Japan, Nagasaki (9.7/100 000 person-years) and women in Scotland (2.7/100 000 person-years). In men, the incidence decreased globally during the study period, as well as during the last few years. In women, the incidence increased in Japan (3 regions), the Netherlands, New Zealand, Norway, and Switzerland, while it was stable or decreased in other populations. Among ethnical groups in the United States, black men and women had more pronounced decreases in incidence than other groups. Generally, birth-cohort effects were stronger determinants of incidence trends than calendar-period effects. Conclusions: In men, the global ESCC incidence has decreased over time. In women, the incidence trends vary across populations, and the rates have increased in some countries. Changes in the prevalence of tobacco smoking and alcohol consumption may have contributed to these time trends.The Swedish Research Council (521-2014-2536)The Swedish Cancer Society (CAN 2015/460)Publishe

Smoking cessation and risk of esophageal cancer by histological type : systematic review and meta-analysis

Background Tobacco smoking strongly increases risk of esophageal squamous cell carcinoma and moderately increases risk of esophageal adenocarcinoma. How smoking cessation influences esophageal cancer risk across histological subtypes, time latencies, and geographic regions is not clear. Methods Studies were systematically searched on Medline, Embase, Web of Science, Cochrane Library, and ClinicalTrials.gov. Pooled estimates of risk ratios (RRs) were derived using a random effects model. Cochran’s Q test and I2 statistic were used to detect heterogeneity. Results Among 15 009 studies, 52 fulfilled the inclusion criteria. Using nonsmokers as a reference, risk of esophageal squamous cell carcinoma was lower among former smokers (RR = 2.05, 95% confidence interval [CI] = 1.71 to 2.45) than among current smokers (RR = 4.18, 95% CI = 3.42 to 5.12). Compared with current smokers, a strong risk reduction was evident after five or more years (RR = 0.59, 95% CI = 0.47 to 0.75), and became stronger after 10 or more years (RR = 0.42, 95% CI = 0.34 to 0.51) and 20 or more years (RR = 0.34, 95% CI = 0.25 to 0.47) following smoking cessation. The risk reduction was strong in Western populations, while weak in Asian populations. Using nonsmokers as reference, the risk of esophageal adenocarcinoma was only slightly lower among former smokers (RR = 1.66, 95% CI = 1.48 to 1.85) than among current smokers (RR = 2.34, 95% CI = 2.04 to 2.69). The risk of esophageal adenocarcinoma did not show any clear reduction over time after smoking cessation, with a risk ratio of 0.72 (95% CI = 0.52 to 1.01) 20 or more years after smoking cessation, compared with current smokers. Conclusions Smoking cessation time-dependently decreases risk of esophageal squamous cell carcinoma, particularly in Western populations, while it has limited influence on the risk of esophageal adenocarcinoma.Swedish Cancer SocietySwedish Research CouncilAccepte

Lack of spontaneous ocular neovascularization and attenuated laser-induced choroidal neovascularization in IGF-I overexpression transgenic mice

Robust IGF-I overexpression induces ocular angiogenesis in mice. To investigate the effect of subtle IGF-I overexpression, we examined the ocular phenotype of IGF-II promoter-driven IGF-I transgenic mice. Despite 2.5-fold elevation of IGF-I mRNA in the retina and 29 and 52% increase of IGF-I protein in the retina and aqueous humor, respectively, no ocular abnormality was observed in these transgenics. This was correlated with unaltered VEGF mRNA levels in the transgenic retina. The transgene was also associated with an attenuated laser-induced choroidal neovascularization. Differential expression levels and pattern of IGF-I gene may underlie the different retinal phenotypes in different transgenic lines