233 research outputs found
Enhanced adic formalism and perverse t-structures for higher Artin stacks
In this sequel of arXiv:1211.5294 and arXiv:1211.5948, we develop an adic
formalism for \'etale cohomology of Artin stacks and prove several desired
properties including the base change theorem. In addition, we define perverse
t-structures on Artin stacks for general perversity, extending Gabber's work on
schemes. Our results generalize results of Laszlo and Olsson on adic formalism
and middle perversity. We continue to work in the world of -categories
in the sense of Lurie, by enhancing all the derived categories, functors, and
natural transformations to the level of -categories.Comment: 53 pages. v2: reformulatio
Weak Localization and Antilocalization in Topological Materials with Impurity Spin-Orbit Interactions
Topological materials have attracted considerable experimental and
theoretical attention. They exhibit strong spin-orbit coupling both in the band
structure (intrinsic) and in the impurity potentials (extrinsic), although the
latter is often neglected. Here we discuss weak localization and
antilocalization of massless Dirac fermions in topological insulators and
massive Dirac fermions in Weyl semimetal thin films taking into account both
intrinsic and extrinsic spin-orbit interactions. The physics is governed by the
complex interplay of the chiral spin texture, quasiparticle mass, and scalar
and spin-orbit scattering. We demonstrate that terms linear in the extrinsic
spin-orbit scattering are generally present in the Bloch and momentum
relaxation times in all topological materials, and the correction to the
diffusion constant is linear in the strength of the extrinsic spin-orbit. In
TIs, which have zero quasiparticle mass, the terms linear in the impurity
spin-orbit coupling lead to an observable density dependence in the weak
antilocalization correction. They produce substantial qualitative modifications
to the magnetoconductivity, differing greatly from the conventional HLN formula
traditionally used in experimental fits, which predicts a crossover from weak
localization to antilocalization as a function of the extrinsic spin-orbit
strength. In contrast, our analysis reveals that topological insulators always
exhibit weak antilocalization. In WSM thin films having intermediate to large
values of the quasiparticle mass extrinsic spin-orbit scattering strongly
affects the boundary of the weak localization to antilocalization transition.
We produce a complete phase diagram for this transition as a function of the
mass and spin-orbit scattering strength. We discuss implications for
experiments and provide a brief comparison with transition metal
dichalcogenides.Comment: arXiv admin note: text overlap with arXiv:1705.0761
Misplaced Trust: Measuring the Interference of Machine Learning in Human Decision-Making
ML decision-aid systems are increasingly common on the web, but their
successful integration relies on people trusting them appropriately: they
should use the system to fill in gaps in their ability, but recognize signals
that the system might be incorrect. We measured how people's trust in ML
recommendations differs by expertise and with more system information through a
task-based study of 175 adults. We used two tasks that are difficult for
humans: comparing large crowd sizes and identifying similar-looking animals.
Our results provide three key insights: (1) People trust incorrect ML
recommendations for tasks that they perform correctly the majority of the time,
even if they have high prior knowledge about ML or are given information
indicating the system is not confident in its prediction; (2) Four different
types of system information all increased people's trust in recommendations;
and (3) Math and logic skills may be as important as ML for decision-makers
working with ML recommendations.Comment: 10 page
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