835 research outputs found
Quantum Hall quasielectron operators in conformal field theory
In the conformal field theory (CFT) approach to the quantum Hall effect, the
multi-electron wave functions are expressed as correlation functions in certain
rational CFTs. While this approach has led to a well-understood description of
the fractionally charged quasihole excitations, the quasielectrons have turned
out to be much harder to handle. In particular, forming quasielectron states
requires non-local operators, in sharp contrast to quasiholes that can be
created by local chiral vertex operators. In both cases, the operators are
strongly constrained by general requirements of symmetry, braiding and fusion.
Here we construct a quasielectron operator satisfying these demands and show
that it reproduces known good quasiparticle wave functions, as well as predicts
new ones. In particular we propose explicit wave functions for quasielectron
excitations of the Moore-Read Pfaffian state. Further, this operator allows us
to explicitly express the composite fermion wave functions in the positive Jain
series in hierarchical form, thus settling a longtime controversy. We also
critically discuss the status of the fractional statistics of quasiparticles in
the Abelian hierarchical quantum Hall states, and argue that our construction
of localized quasielectron states sheds new light on their statistics. At the
technical level we introduce a generalized normal ordering, that allows us to
"fuse" an electron operator with the inverse of an hole operator, and also an
alternative approach to the background charge needed to neutralize CFT
correlators. As a result we get a fully holomorphic CFT representation of a
large set of quantum Hall wave functions.Comment: minor changes, publishe
Ferromagnetic coupling of mononuclear Fe centers in a self-assembled metal-organic network on Au(111)
The magnetic state and magnetic coupling of individual atoms in nanoscale
structures relies on a delicate balance between different interactions with the
atomic-scale surrounding. Using scanning tunneling microscopy, we resolve the
self-assembled formation of highly ordered bilayer structures of Fe atoms and
organic linker molecules (T4PT) when deposited on a Au(111) surface. The Fe
atoms are encaged in a three-dimensional coordination motif by three T4PT
molecules in the surface plane and an additional T4PT unit on top. Within this
crystal field, the Fe atoms retain a magnetic ground state with easy-axis
anisotropy, as evidenced by X-ray absorption spectroscopy and X-ray magnetic
circular dichroism. The magnetization curves reveal the existence of
ferromagnetic coupling between the Fe centers
Efficient CSL Model Checking Using Stratification
For continuous-time Markov chains, the model-checking problem with respect to
continuous-time stochastic logic (CSL) has been introduced and shown to be
decidable by Aziz, Sanwal, Singhal and Brayton in 1996. Their proof can be
turned into an approximation algorithm with worse than exponential complexity.
In 2000, Baier, Haverkort, Hermanns and Katoen presented an efficient
polynomial-time approximation algorithm for the sublogic in which only binary
until is allowed. In this paper, we propose such an efficient polynomial-time
approximation algorithm for full CSL. The key to our method is the notion of
stratified CTMCs with respect to the CSL property to be checked. On a
stratified CTMC, the probability to satisfy a CSL path formula can be
approximated by a transient analysis in polynomial time (using uniformization).
We present a measure-preserving, linear-time and -space transformation of any
CTMC into an equivalent, stratified one. This makes the present work the
centerpiece of a broadly applicable full CSL model checker. Recently, the
decision algorithm by Aziz et al. was shown to work only for stratified CTMCs.
As an additional contribution, our measure-preserving transformation can be
used to ensure the decidability for general CTMCs.Comment: 18 pages, preprint for LMCS. An extended abstract appeared in ICALP
201
Quantum Hall quasielectrons - Abelian and non-Abelian
The quasiparticles in Quantum Hall liquids carry fractional charge and obey
fractional quantum statistics. Of particular recent interest are those with
non-Abelian statistics, since their braiding properties could in principle be
used for robust coding of quantum information. There is already a good
theoretical understanding of quasiholes both in Abelian and non-Abelian QH
states. Here we develop conformal field theory methods that allow for an
equally precise description of quasielectrons, and explicitly construct two-
and four-quasielectron excitations of the non-Abelian Moore-Read state.Comment: figure adde
Quasimolecular =3/2 moments in the cluster Mott insulator GaTaSe
Quasimolecular orbitals in cluster Mott insulators provide a route to tailor
exchange interactions, which may yield novel quantum phases of matter. We
demonstrate the cluster Mott character of the lacunar spinel GaTaSe
using resonant inelastic x-ray scattering (RIXS) at the Ta edge.
Electrons are fully delocalized over Ta tetrahedra, forming quasimolecular
=3/2 moments. The modulation of the RIXS intensity as function of
the transferred momentum q allows us to determine the cluster wavefunction,
which depends on competing intracluster hopping terms that mix states with
different character. This mixed wavefunction is decisive for the macroscopic
properties since it affects intercluster hopping and exchange interactions and
furthermore renormalizes the effective spin-orbit coupling constant. The
versatile wavefunction, tunable via intracluster hopping, opens a new
perspective on the large family of lacunar spinels and cluster Mott insulators
in general.Comment: 7 pages, 4 figures, plus supplementary informatio
Endothelial Function Assessed by Digital Volume Plethysmography Predicts the Development and Progression of Type 2 Diabetes Mellitus
Background
Endothelial dysfunction is a consequence of type 2 diabetes mellitus, but it is unclear whether endothelial dysfunction of conductance versus resistance vessels may also precede type 2 diabetes mellitus development.
Methods and Results
In a populationābased cohort of 15 010 individuals from the GHS (Gutenberg Health Study) (aged 35ā74 years at enrollment in 2007ā2012), we identified 1610 cases of incident preādiabetes mellitus and 386 cases of incident type 2 diabetes mellitus by hemoglobin A1c (HbA1c) and/or medical history between 2012 and 2017. Endothelial function of conductance and resistance vessels was measured by flowāmediated dilation and digital volume plethysmographyāderived reactive hyperemia index, respectively. Multivariable regression modeling was used to estimate Ī² coefficients of HbA1c levels at followāup and relative risks of incident (preā)diabetes mellitus. Reactive hyperemia index was independently associated with HbA1c after multivariable adjustment for baseline HbA1c, sex, age, socioeconomic status, arterial hypertension, waist/height ratio, packāyears of smoking, nonāhighādensity lipoprotein/highādensity lipoprotein ratio, physical activity, family history of myocardial infarction/stroke, prevalent cardiovascular disease, medication use, and Cāreactive protein (Ī²=ā0.020; P=0.0029). The adjusted relative risk per SD decline in reactive hyperemia index was 1.08 (95% CI, 1.02ā1.15; P=0.012) for incident preādiabetes mellitus and 1.16 (95% CI, 1.01ā1.34; P=0.041) for incident type 2 diabetes mellitus. Flowāmediated dilation independently increased the relative risk for developing preādiabetes mellitus by 8% (95% CI, 1.02ā1.14; P=0.012), but it was not independently associated with incident type 2 diabetes mellitus (relative risk, 1.01; 95% CI, 0.86ā1.19; P=0.92) and with HbA1c (Ī²=ā0.003; P=0.59).
Conclusions
Endothelial dysfunction of resistance rather than conductance vessels may precede the development of (preā)diabetes mellitus. Assessment of endothelial function by digital volume plethysmography may help to identify subjects at risk for development of type 2 diabetes mellitus
Sigref ā A Symbolic Bisimulation Tool Box
We present a uniform signature-based approach to compute the most popular bisimulations. Our approach is implemented symbolically using BDDs, which enables the handling of very large transition systems. Signatures for the bisimulations are built up from a few generic building blocks, which naturally correspond to efficient BDD operations. Thus, the definition of an appropriate signature is the key for a rapid development of algorithms for other types of bisimulation.
We provide experimental evidence of the viability of this approach by presenting computational results for many bisimulations on real-world instances. The experiments show cases where our framework can handle state spaces efficiently that are far too large to handle for any tool that requires an explicit state space description.
This work was partly supported by the German Research Council (DFG) as part of the Transregional Collaborative Research Center āAutomatic Verification and Analysis of Complex Systemsā (SFB/TR 14 AVACS). See www.avacs.org for more information
RIXS interferometry and the role of disorder in the quantum magnet BaTiIrO
Motivated by several claims of spin-orbit driven spin-liquid physics in
hexagonal BaTiIrO hosting Ir2O9 dimers, we report on
resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge for different x.
We demonstrate that magnetism in BaTiIrO is governed by an
unconventional realization of strong disorder, where cation disorder affects
the character of the local moments. RIXS interferometry, studying the RIXS
intensity over a broad range of transferred momentum q, is ideally suited to
assign different excitations to different Ir sites. We find pronounced Ir-Ti
site mixing. Both ions are distributed over two crystallographically
inequivalent sites, giving rise to a coexistence of quasimolecular singlet
states on Ir2O9 dimers and spin-orbit entangled j=1/2 moments of 5d
Ir ions. RIXS reveals different kinds of strong magnetic couplings for
different bonding geometries, highlighting the role of cation disorder for the
suppression of long-range magnetic order in this family of compounds.Comment: 12 pages, 9 figure
Recommended from our members
RIXS interferometry and the role of disorder in the quantum magnet Ba3 Ti3-x Irx O9
Motivated by several claims of spin-orbit-driven spin-liquid physics in hexagonal Ba3Ti3-xIrxO9 hosting Ir2O9 dimers, we report on resonant inelastic x-ray scattering (RIXS) at the Ir L3 edge for different x. We demonstrate that magnetism in Ba3Ti3-xIrxO9 is governed by an unconventional realization of strong disorder, where cation disorder affects the character of the local moments. RIXS interferometry, studying the RIXS intensity over a broad range of transferred momentum q, is ideally suited to assign different excitations to different Ir sites. We find pronounced Ir-Ti site mixing. Both ions are distributed over two crystallographically inequivalent sites, giving rise to a coexistence of quasimolecular singlet states on Ir2O9 dimers and spin-orbit-entangled j=1/2 moments of 5d5Ir4+ ions. RIXS reveals different kinds of strong magnetic couplings for different bonding geometries, highlighting the role of cation disorder for the suppression of long-range magnetic order in this family of compounds
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