705 research outputs found
Odd-Even Crossover in a non-Abelian Interferometer
We compute the backscattered current in a double point-contact geometry of a
Quantum Hall system at filling fraction as a function of bias voltage
in the weak backscattering regime. We assume that the system is in the
universality class of either the Pfaffian or anti-Pfaffian state. When the
number of charge quasiparticles in the interferometer is odd, there is no
interference pattern. However, the coupling between a charge
quasiparticle and the edge causes it to be absorbed by the edge at low
energies. Consequently, an interference pattern appears at low bias voltages
and temperatures, as if there were an even number of quasiparticles in the
interferometer. We relate this problem to that of a semi-infinite Ising model
with a boundary magnetic field. Using the methods of perturbed boundary
conformal field theory, we give an exact expression for this crossover of the
interferometer as a function of bias voltage. Finally, we comment on the
possible relevance of our results to recent interference experiments.Comment: Two figures added, along with a brief explanation of them. Abstract
slightly edited, and one reference adde
The non-Abelian Interferometer
We consider the tunneling current through a double point-contact Fabry-Perot
interferometer such as used in recent experimental studies of the fractional
quantum Hall plateau at filling fraction nu=5/2. We compare the predictions of
several different models of the state of the electrons at this plateau: the
Moore-Read, anti-Pfaffian, SU(2)_2 NAF, K=8 strong pairing, and (3,3,1) states.
All of these predict the existence of charge e/4 quasiparticles, but the first
three are non-Abelian while the last two are Abelian. We give explicit formulas
for the scaling of charge e/2 and charge e/4 quasiparticle contributions to the
current as a function of temperature, gate voltage and distance between the two
point contacts for all three models. Based on these, we analyze several
possible explanations of two phenomena reported for recent experiments by
Willett et al., namely halving of the period of the observed resistance
oscillations with rising temperature and alternation between the same two
observed periods at low temperatures as the area of the interference loop is
varied with a side gate. We conclude that the most likely explanation is that
the observed alternation is due to switching between even and odd numbers of
charge e/4 quasiparticles enclosed within the loop as a function of side gate
voltage, which is a clear signature of the presence of non-Abelian anyons.
However, there are important features of the data which do not have a simple
explanation within this picture. We suggest further experiments which could
help rule out some possible scenarios. We make the corresponding predictions
for future tunneling and interference experiments at the other observed second
Landau level fractional quantum Hall states.Comment: 15 pages, 1 figure; v2: additional discussions and references added;
v3: clarifications and references updated; Appendix C has been removed and
incorporated in arXiv:0909.1056; this paper has been given the more clear,
accurate, and informative title "Interferometric signature of non-Abelian
anyons" in PRB by its editor
Exotic resonant level models in non-Abelian quantum Hall states coupled to quantum dots
In this paper we study the coupling between a quantum dot and the edge of a
non-Abelian fractional quantum Hall state. We assume the dot is small enough
that its level spacing is large compared to both the temperature and the
coupling to the spatially proximate bulk non-Abelian fractional quantum Hall
state. We focus on the physics of level degeneracy with electron number on the
dot. The physics of such a resonant level is governed by a -channel Kondo
model when the quantum Hall state is a Read-Rezayi state at filling fraction
or its particle-hole conjugate at . The
-channel Kondo model is channel symmetric even without fine tuning any
couplings in the former state; in the latter, it is generically channel
asymmetric. The two limits exhibit non-Fermi liquid and Fermi liquid
properties, respectively, and therefore may be distinguished. By exploiting the
mapping between the resonant level model and the multichannel Kondo model, we
discuss the thermodynamic and transport properties of the system. In the
special case of , our results provide a novel venue to distinguish between
the Pfaffian and anti-Pfaffian states at filling fraction . We present
numerical estimates for realizing this scenario in experiment.Comment: 18 pages, 2 figures. Clarified final discussio
Microstructure of a spark-plasma-sintered Fe2VAl-type Heusler alloy for thermoelectric application
The influence of microstructure on thermoelectricity is increasingly
recognized. Approaches for microstructural engineering can hence be exploited
to enhance thermoelectric performance, particularly through manipulating
crystalline defects, their structure, and composition. Here, we focus on a
full-Heusler Fe2VAl-based compound that is one of the most promising
thermoelectric materials containing only Earth-abundant, non-toxic elements. A
Fe2VTa0.05Al0.95 cast alloy was atomized under a nitrogen-rich atmosphere to
induce nitride precipitation. Nanometer- to micrometer-scale microstructural
investigations by advanced scanning electron microscopy and atom probe
tomography (APT) are performed on the powder first and then on the material
consolidated by spark-plasma sintering for an increasing time. APT reveals an
unexpected pick-up of additional impurities from atomization, namely W and Mo.
The microstructure is then correlated with local and global measurements of the
thermoelectric properties. At grain boundaries, segregation and precipitation
locally reduce the electrical resistivity, as evidenced by in-situ four-point
probe measurements. The final microstructure contains a hierarchy of structural
defects, including individual point defects, dislocations, grain boundaries,
and precipitates, that allow for a strong decrease in thermal conductivity. In
combination, these effects provide an appreciable increase in thermoelectric
performance
The role of the cytoskeleton in capacitaftive calcium entry in myenteric glia
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73680/1/j.1365-2982.2003.00406.x.pd
Quasi-Particle Tunneling in Anti-Pfaffian Quantum Hall State
We study tunneling phenomena at the edge of the anti-Pfaffian quantum Hall
state at the filling factor . The edge current in a single
point-contact is considered. We focus on nonlinear behavior of two-terminal
conductance with the increase in negative split-gate voltage. Expecting the
appearance of the intermediate conductance plateau we calculate the value of
its conductance by using the renormalization group (RG) analysis. Further, we
show that non-perturbative quasi-particle tunneling is effectively described as
perturbative electron tunneling by the instanton method. The two-terminals
conductance is written as a function of the gate voltage. The obtained results
enable us to distinguish the anti-Pfaffian state from the Pfaffian state
experimentally.Comment: 5 pages, 4 figure
Social interaction, noise and antibiotic-mediated switches in the intestinal microbiota
The intestinal microbiota plays important roles in digestion and resistance
against entero-pathogens. As with other ecosystems, its species composition is
resilient against small disturbances but strong perturbations such as
antibiotics can affect the consortium dramatically. Antibiotic cessation does
not necessarily restore pre-treatment conditions and disturbed microbiota are
often susceptible to pathogen invasion. Here we propose a mathematical model to
explain how antibiotic-mediated switches in the microbiota composition can
result from simple social interactions between antibiotic-tolerant and
antibiotic-sensitive bacterial groups. We build a two-species (e.g. two
functional-groups) model and identify regions of domination by
antibiotic-sensitive or antibiotic-tolerant bacteria, as well as a region of
multistability where domination by either group is possible. Using a new
framework that we derived from statistical physics, we calculate the duration
of each microbiota composition state. This is shown to depend on the balance
between random fluctuations in the bacterial densities and the strength of
microbial interactions. The singular value decomposition of recent metagenomic
data confirms our assumption of grouping microbes as antibiotic-tolerant or
antibiotic-sensitive in response to a single antibiotic. Our methodology can be
extended to multiple bacterial groups and thus it provides an ecological
formalism to help interpret the present surge in microbiome data.Comment: 20 pages, 5 figures accepted for publication in Plos Comp Bio.
Supplementary video and information availabl
CEO Education and the Ability to Raise Capital
Research Question/Issue: Using a unique handâcollected dataset, this study examines the role of Chief Executive Officer (CEO) educational attainments in relation to newly public firms.
Research Findings/Insights: We find that Initial Public Offering (IPO) firms led by CEOs with superior educational credentials â in terms of level and quality â are associated with lower levels of IPO underpricing. This association is mainly driven by CEOs that hold advanced degrees. Notably, a differenceâinâdifference approach based on two quasiânatural experiments indicates that the impact of CEO education on IPO underpricing is more pronounced within environments characterized by lower information transparency. The baseline results also hold in the longer term, thereby confirming the value of signaling prestigious academic awards at the time of the IPO.
Theoretical/Academic Implications: Using human capital, institutional and upper echelon theories, we hypothesize and demonstrate that CEO educational attainments do not unambiguously affect investorsâ perceptions of a firm's future prospects. Instead, their influence depends on the quality of CEO education as well as on the degree of uncertainty regarding the firm's future performance, and the level of information asymmetry between issuers and prospective investors. To our knowledge, this is the first study that provides a comprehensive treatment of the role of CEO education in the IPO context.
Practitioner/Policy Implications: Our evidence on the importance of CEO education, and especially that CEOs with varying levels and quality of educational training might differentially affect newly listed firms, is useful to providers of financial capital and boards of directors interested in assessing the viability of new ventures. The implication of our study for IPO investors is that it is worth paying more to take an equity position in firms run by betterâeducated CEOs
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