1,118 research outputs found
Determining topological order from a local ground state correlation function
Topological insulators are physically distinguishable from normal insulators
only near edges and defects, while in the bulk there is no clear signature to
their topological order. In this work we show that the Z index of topological
insulators and the Z index of the integer quantum Hall effect manifest
themselves locally. We do so by providing an algorithm for determining these
indices from a local equal time ground-state correlation function at any
convenient boundary conditions. Our procedure is unaffected by the presence of
disorder and can be naturally generalized to include weak interactions. The
locality of these topological indices implies bulk-edge correspondence theorem.Comment: 7 pages, 3 figures. Major changes: the paper was divided into
sections, the locality of the order in 3D topological insulators is also
discusse
Does Marijuana Use Impair Human Capital Formation?
In this paper we examine the relationship between marijuana use and human capital formation by examining performance on standardized tests among a nationally representative sample of youths from the National Education Longitudinal Survey. We find that much of the negative association between cross-sectional measures of marijuana use and cognitive ability appears to be attenuated by individual differences in school attachment and general deviance. However, difference-in-difference estimates examining changes in test scores across 10th and 12th grade reveal that marijuana use remains statistically associated with a 15% reduction in performance on standardized math tests.
A New RING Tossed into an Old HAT
p300 and CBP are multi-domain histone acetyltransferases (HATs) that regulate gene expression and are mutated in human diseases including cancer. Delvecchio and colleagues report the structure of the p300 catalytic core, revealing the presence of a previously unknown RING domain that regulates the enzyme’s activity
Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy
Deep level defects in n-type unintentionally doped a-plane MgxZn1−xO, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of MgxZn1−xO were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of Ec − 1.4 eV, 2.1 eV, 2.6 V, and Ev + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at Ec − 2.1 eV, Ev + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at Ev + 0.3 eV and Ec − 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the Ev + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the Ec − 1.4 eV and Ec − 2.6 eV levels in Mg alloyed samples
Stability conditions and Stokes factors
Let A be the category of modules over a complex, finite-dimensional algebra.
We show that the space of stability conditions on A parametrises an
isomonodromic family of irregular connections on P^1 with values in the Hall
algebra of A. The residues of these connections are given by the holomorphic
generating function for counting invariants in A constructed by D. Joyce.Comment: Very minor changes. Final version. To appear in Inventione
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Unusual Formation of Point-Defect Complexes in the Ultrawide-Band-Gap Semiconductor β-Ga2 O3
Understanding the unique properties of ultra-wide band gap semiconductors requires detailed information about the exact nature of point defects and their role in determining the properties. Here, we report the first direct microscopic observation of an unusual formation of point defect complexes within the atomic-scale structure of β-Ga2O3 using high resolution scanning transmission electron microscopy (STEM). Each complex involves one cation interstitial atom paired with two cation vacancies. These divacancy-interstitial complexes correlate directly with structures obtained by density functional theory, which predicts them to be compensating acceptors in β-Ga2O3. This prediction is confirmed by a comparison between STEM data and deep level optical spectroscopy results, which reveals that these complexes correspond to a deep trap within the band gap, and that the development of the complexes is facilitated by Sn doping through increased vacancy concentration. These findings provide new insight on this emerging material's unique response to the incorporation of impurities that can critically influence their properties
Topological States and Adiabatic Pumping in Quasicrystals
The unrelated discoveries of quasicrystals and topological insulators have in
turn challenged prevailing paradigms in condensed-matter physics. We find a
surprising connection between quasicrystals and topological phases of matter:
(i) quasicrystals exhibit nontrivial topological properties and (ii) these
properties are attributed to dimensions higher than that of the quasicrystal.
Specifically, we show, both theoretically and experimentally, that
one-dimensional quasicrystals are assigned two-dimensional Chern numbers and,
respectively, exhibit topologically protected boundary states equivalent to the
edge states of a two-dimensional quantum Hall system.We harness the topological
nature of these states to adiabatically pump light across the quasicrystal. We
generalize our results to higher-dimensional systems and other topological
indices. Hence, quasicrystals offer a new platform for the study of topological
phases while their topology may better explain their surface properties.Comment: 10 pages, 5 figures, 4 appendice
Hamiltonian submanifolds of regular polytopes
We investigate polyhedral -manifolds as subcomplexes of the boundary
complex of a regular polytope. We call such a subcomplex {\it -Hamiltonian}
if it contains the full -skeleton of the polytope. Since the case of the
cube is well known and since the case of a simplex was also previously studied
(these are so-called {\it super-neighborly triangulations}) we focus on the
case of the cross polytope and the sporadic regular 4-polytopes. By our results
the existence of 1-Hamiltonian surfaces is now decided for all regular
polytopes.
Furthermore we investigate 2-Hamiltonian 4-manifolds in the -dimensional
cross polytope. These are the "regular cases" satisfying equality in Sparla's
inequality. In particular, we present a new example with 16 vertices which is
highly symmetric with an automorphism group of order 128. Topologically it is
homeomorphic to a connected sum of 7 copies of . By this
example all regular cases of vertices with or, equivalently, all
cases of regular -polytopes with are now decided.Comment: 26 pages, 4 figure
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