46,703 research outputs found
Observation of anomalous Hanle spin precession lineshapes resulting from interaction with localized states
It has been shown recently that in spin precession experiments, the
interaction of spins with localized states can change the response to a
magnetic field, leading to a modified, effective spin relaxation time and
precession frequency. Here, we show that also the shape of the Hanle curve can
change, so that it cannot be fitted with the solutions of the conventional
Bloch equation. We present experimental data that shows such an effect arising
at low temperatures in epitaxial graphene on silicon carbide with localized
states in the carbon buffer layer. We compare the strength of the effect
between materials with different growth methods, epitaxial growth by
sublimation and by chemical vapor deposition. The presented analysis gives
information about the density of localized states and their coupling to the
graphene states, which is inaccessible by charge transport measurements and can
be applied to any spin transport channel that is coupled to localized states.Comment: 6 pages, 6 figure
Resonant Inelastic X-ray Scattering on Spin-Orbit Coupled Insulating Iridates
We determine how the elementary excitations of iridium-oxide materials, which
are dominated by a strong relativistic spin-orbit coupling, appear in Resonant
Inelastic X-ray Scattering (RIXS). Whereas the RIXS spectral weight at the L2
x-ray edge vanishes, we find it to be strong at the L3-edge. Applying this to
Sr2IrO4, we observe that RIXS, besides being sensitive to local doublet to
quartet transitions, meticulously maps out the strongly dispersive delocalized
excitations of the low-lying spin-orbit doublets.Comment: 4 pages, 3 figure
Morse theory on spaces of braids and Lagrangian dynamics
In the first half of the paper we construct a Morse-type theory on certain
spaces of braid diagrams. We define a topological invariant of closed positive
braids which is correlated with the existence of invariant sets of parabolic
flows defined on discretized braid spaces. Parabolic flows, a type of
one-dimensional lattice dynamics, evolve singular braid diagrams in such a way
as to decrease their topological complexity; algebraic lengths decrease
monotonically. This topological invariant is derived from a Morse-Conley
homotopy index and provides a gloablization of `lap number' techniques used in
scalar parabolic PDEs.
In the second half of the paper we apply this technology to second order
Lagrangians via a discrete formulation of the variational problem. This
culminates in a very general forcing theorem for the existence of infinitely
many braid classes of closed orbits.Comment: Revised version: numerous changes in exposition. Slight modification
of two proofs and one definition; 55 pages, 20 figure
Classical spin systems and the quantum stabilizer formalism: general mappings and applications
We present general mappings between classical spin systems and quantum
physics. More precisely, we show how to express partition functions and
correlation functions of arbitrary classical spin models as inner products
between quantum stabilizer states and product states, thereby generalizing
mappings for some specific models established in [Phys. Rev. Lett. 98, 117207
(2007)]. For Ising- and Potts-type models with and without external magnetic
field, we show how the entanglement features of the corresponding stabilizer
states are related to the interaction pattern of the classical model, while the
choice of product states encodes the details of interaction. These mappings
establish a link between the fields of classical statistical mechanics and
quantum information theory, which we utilize to transfer techniques and methods
developed in one field to gain insight into the other. For example, we use
quantum information techniques to recover well known duality relations and
local symmetries of classical models in a simple way, and provide new classical
simulation methods to simulate certain types of classical spin models. We show
that in this way all inhomogeneous models of q-dimensional spins with pairwise
interaction pattern specified by a graph of bounded tree-width can be simulated
efficiently. Finally, we show relations between classical spin models and
measurement-based quantum computation.Comment: 24 pages, 5 figures, minor corrections, version as accepted in JM
Classical simulation versus universality in measurement based quantum computation
We investigate for which resource states an efficient classical simulation of
measurement based quantum computation is possible. We show that the
Schmidt--rank width, a measure recently introduced to assess universality of
resource states, plays a crucial role in also this context. We relate
Schmidt--rank width to the optimal description of states in terms of tree
tensor networks and show that an efficient classical simulation of measurement
based quantum computation is possible for all states with logarithmically
bounded Schmidt--rank width (with respect to the system size). For graph states
where the Schmidt--rank width scales in this way, we efficiently construct the
optimal tree tensor network descriptions, and provide several examples. We
highlight parallels in the efficient description of complex systems in quantum
information theory and graph theory.Comment: 16 pages, 4 figure
Higher Education and Membership of Voluntary Groups
This research uses the British National Child Development Study to examine the effect of higher education on individual membership of voluntary groups and organizations. Gender differences in the education effects are given emphasis. We apply parametric and nonparametric econometric methods to isolate the influence of confounding variables. There is strong evidence of education endogeneity in the female sample and we observe a negative education effect on women's group membership. Education endogeneity does not cause serious estimation bias in the male sample. Higher education is a significantly positive determinant of men's group membership. Further investigations from a mid-life perspective reveal that the boost of female participation in the workforce and their attitudes towards employment are key factors in the negative association between higher education and women's group membership. Our research provides clues for the divergence in the enrolment in higher education and social participation behavior in Western countries.
A Meta-Analysis of the Effect of Education on Social Capital
To assess the empirical estimates of the effect of education on social trust and social participation - the basic dimensions of individual social capital - a meta-analysis is applied, synthesizing 154 evaluations on social trust, and 286 evaluations on social participation. The publication bias problem is given special emphasis in the meta-analysis. Our statistical synthesis confirms that education is a strong and robust correlate of individual social capital. The meta-analysis provides support for the existence of a relative effect of education on social participation, and of a reciprocity mechanism between the dimensions of social capital. The analysis also suggests that the erosion of social participation during the past decades has coincided with a decrease of the marginal return to education on social capital. Finally, we find differences in the return to education between genders, between US and other nations, and variations for different education attainments.
Differential Cyclic Voltammetry - a Novel Technique for Selective and Simultaneous Detection using Redox Cycling Based Sensors
Redox cycling (RC) is an effect that is used to amplify electrochemical signals. However, traditional techniques such as cyclic voltammetry (CV) do not provide clear insight for a mixture of multiple redox couples while RC is applied. Thus, we have developed a new measurement technique which delivers electrochemical spectra of all reversible redox couples present based on concentrations and standard potentials. This technique has been named differential cyclic voltammetry (DCV). We have fabricated micrometer-sized interdigitated electrode (IDE) sensors to conduct DCV measurements in mixtures of 1mM catechol and 4mM [Ru(NH3)6]Cl3. To simulate the electrochemical behavior of these sensors we have also developed a finite element model (FEM) in Comsol®. The\ud
experimental data corresponds to the calculated spectra obtained from simulations. Additionally, the measured spectra can be used to easily derive standard potentials and concentrations simultaneously and selectively.\u
College Education and social trust. An Evidence-based Study on the Causal Mechanisms
This paper examines the influence of college education on social trust at the individual level. Based on the literature of trust and social trust, we hypothesize that life experience/development since adulthood and perceptions of cultural/social structures are two primary channels in the causal linkage between college education and social trust. In the first part of the empirical study econometric techniques are employed to tackle the omitted-variable problem and substantial evidence is found to confirm the positive effect of college education. In the second part contemporary information is used to examine the hypothetical mechanisms in the causal inference. That life experience is a primary channel via which college education promotes social trust fails to find support in our examination, while individual perceptions of cultural and social structures explain up to 77 percent of the causal effect.
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