An optimized scheme for detecting magneto-optic effects in ultrathin films with Sagnac interferometry.

Sagnac interferometry is advantageous in measuring time-reversal-symmetry breaking effects in ferromagnetic and antiferromagnetic materials as it suppresses time-reversal symmetric birefringent effects that are ubiquitous and often overwhelming in optical detection systems. When its sensitivity is limited only by the amplifier noise in the photo-detector, one needs to optimize the optical power that returns to the detector. We demonstrate an experimental scheme that maximizes the returning optical power in a Sagnac interferometry when detecting the magneto-optic effect in ultrathin films. In this scheme, the optical beam bearing the Faraday effect on a thin film is reflected at a second surface coated with a highly reflective gold film. The gold film increases the returned optical power by a factor of 4-5. For a normal-incidence Sagnac interferometer, this scheme yields an increase in the signal-to-noise ratio by the same factor. For an oblique-incidence Sagnac interferometer, this scheme should yield an increase in the signal-to-noise ratio by a factor of 20-25. For illustration, this scheme is used to measure magnetization curves and Kerr rotation images of 4.5-unit-cell thick SrRuO3(001) grown on SrTiO3(001).

Gut microbiota-associated bile acid deconjugation accelerates hepatic steatosis in ob/ob mice.

AIM: Nonalcoholic hepatic fat accumulation has been hypothesized to be associated with alterations in gut microbiota composition, although mechanistic explanations for this link are largely insufficient. The aim of this study was to elucidate the microbiota-driven mechanisms involved in the development of nonalcoholic hepatic steatosis. METHODS AND RESULTS: Ob/ob mice and their wild-type lean control mice were fed an AIN-93G diet for 12 weeks. Faecal microbiota composition, faecal bile acid (BA) profile and intestinal and hepatic markers of BA metabolism were analysed. Ob/ob mice had significantly less faecal taurine-conjugated BAs compared to their lean controls. The proportions of butyrate-producing bacteria were lower in ob/ob mice compared to those in lean mice. Intestinal expression of farnesoid X receptor (FXR) mRNA was significantly higher, whereas hepatic expression of cholesterol-7α-hydroxylase 1 (CYP7A1) and small heterodimer partner (SHP) were significantly lower in ob/ob mice compared to those in control mice. CONCLUSION: Microbiota-associated BAs deconjugation may induce nonalcoholic fatty liver disease (NAFLD) by activating intestinal FXR signalling and blocking hepatic FXR-SHP pathway, thereby accelerating fat synthesis. SIGNIFICANCE AND IMPACT OF THE STUDY: We provided evidences that changes in the gut microbiota and their metabolites can alter the profile of BAs, thereby providing a mechanism by which an altered microbiota profile contributes to the development of NAFLD.