Three-dimensional disordered conductors in a strong magnetic field: surface states and quantum Hall plateaus

We study localization in layered, three-dimensional conductors in strong magnetic fields. We demonstrate the existence of three phases - insulator, metal and quantized Hall conductor - in the two-dimensional parameter space obtained by varying the Fermi energy and the interlayer coupling strength. Transport in the quantized Hall conductor occurs via extended surface states. These surface states constitute a subsystem at a novel critical point, which we describe using a new, directed network model.Comment: 4 pages (PostScript) replaced due to compression error, slightly shortened version to appear in PR

How people know their risk preference

People differ in their willingness to take risks. Recent work found that revealed preference tasks (e.g., laboratory lotteries)—a dominant class of measures—are outperformed by survey-based stated preferences, which are more stable and predict real-world risk taking across different domains. How can stated preferences, often criticised as inconsequential “cheap talk,” be more valid and predictive than controlled, incentivized lotteries? In our multimethod study, over 3,000 respondents from population samples answered a single widely used and predictive risk-preference question. Respondents then explained the reasoning behind their answer. They tended to recount diagnostic behaviours and experiences, focusing on voluntary, consequential acts and experiences from which they seemed to infer their risk preference. We found that third-party readers of respondents’ brief memories and explanations reached similar inferences about respondents’ preferences, indicating the intersubjective validity of this information. Our results help unpack the self perception behind stated risk preferences that permits people to draw upon their own understanding of what constitutes diagnostic behaviours and experiences, as revealed in high-stakes situations in the real world

Extreme magnesium isotope fractionation at outcrop scale records the mechanism and rate at which reaction fronts advance

Isotopic fractionation of cationic species during diffusive transport provides novel means of constraining the style and timing of metamorphic transformations. Here we document a major (~1‰) decrease in the Mg isotopic composition of the reaction front of an exhumed contact between rocks of subducted crust and serpentinite, in the Syros mélange zone. This isotopic perturbation extends over a notable length-scale (~1 m), implicating diffusion of Mg through an intergranular fluid network over a period of ~100 kyr. These novel observations confirm models of diffusion-controlled growth of reaction zones formed between rocks of contrasting compositions, such as found at the slab-mantle interface in subduction zones. The results also demonstrate that diffusive processes can result in exotic stable isotope compositions of major elements with implications for mantle xenoliths and complex intrusions

Point-Contact Conductances from Density Correlations

We formulate and prove an exact relation which expresses the moments of the two-point conductance for an open disordered electron system in terms of certain density correlators of the corresponding closed system. As an application of the relation, we demonstrate that the typical two-point conductance for the Chalker-Coddington model at criticality transforms like a two-point function in conformal field theory.Comment: 4 pages, 2 figure