Han Zheng

In correlated electron materials, electrons often self-organize and form a variety of patterns with potential ordering of charges, spins, and orbitals, which are believed to be closely connected to many novel properties of these materials including superconductivity, metal-insulator transitions, and the CMR effect. How these real-space patterns affect the conductivity and other properties of materials is one of the major challenges of modern condensed matter physics. Moreover, although the presence of static stripes is indisputable, the existence of fluctuating stripes in such compounds is a subject of great debate. Here we present the electronic excitations of La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ probed by angle-resolved photoemission, from which we demonstrate that a novel type of ordering, termed bi-stripes, can exhibit either static or fluctuating order as a function of temperature. We found that the static bi-stripe order is especially damaging to electrical conductivity, completely localizing the electrons in the bi-stripe regions, while the fluctuating stripes can coexist with mobile carriers. This physics drives a novel phase transition with colossal conductivity changes as a function of temperature. Our finding suggests that quantum stripes can give rise to electronic properties significantly different from their static counterparts. Inducing transition between them can turn on remarkable electronic phenomena, enriching our understanding of correlated electron systems as well as opening a window for potential applications in electronic devices.

© 2015, Springer Science+Business Media New York. Background and Aims: Nonalcoholic fatty liver disease and obstructive sleep apnea are growing in prevalence in the USA. Existing data on the relationship between OSA and NAFLD are conflicting and limited by the use of various histologic definitions of nonalcoholic steatohepatitis. Using a robust definition of NASH in a large, well-characterized cohort, we sought to evaluate whether OSA was associated with NASH and advanced fibrosis. Methods: Two hundred and thirteen subjects undergoing weight loss surgery were queried for OSA and then underwent liver biopsy. NASH was defined, as recommended by the American Association for the Study of Liver Disease, by the presence of all of the following: >5 % macrovesicular steatosis, lobular inflammation, and hepatocyte ballooning. NAFLD activity score was also determined for each subject. Results: Subjects with OSA had significantly higher alanine and aspartate aminotransferase levels than subjects without OSA. OSA was associated with the presence of NASH, and this remained significant after adjusting for age, gender, race, and diabetes mellitus. Steatosis grade, lobular inflammation grade, NAS score, and fibrosis stage were all significantly associated with the presence of OSA and remained so after adjustment. Conclusions: OSA is associated with elevated aminotransferase levels, the presence of NASH, and advanced NASH histology. Further studies are needed to evaluate the impact of OSA treatment on NASH.