1,231 research outputs found
Dirac parameters and topological phase diagram of Pb1-xSnxSe from magneto-spectroscopy
Pb1-xSnxSe hosts 3D massive Dirac fermions across the entire composition
range for which the crystal structure is cubic. In this work, we present a
comprehensive experimental mapping of the 3D band structure parameters of
Pb1-xSnxSe as a function of composition and temperature. We cover a parameter
space spanning the band inversion that yields its topological crystalline
insulator phase. A non-closure of the energy gap is evidenced in the vicinity
of this phase transition. Using magnetooptical Landau level spectroscopy, we
determine the energy gap, Dirac velocity, anisotropy factor and topological
character of Pb1-xSnxSe epilayers grown by molecular beam epitaxy on BaF2
(111). Our results are evidence that Pb1-xSnxSe is a model system to study
topological phases and the nature of the phase transition.Comment: Submitte
Molecular Imaging in Synthetic Biology, and Synthetic Biology in Molecular Imaging
Biomedical synthetic biology is an emerging field in which cells are engineered at the genetic level to carry out novel functions with relevance to biomedical and industrial applications. This approach promises new treatments, imaging tools, and diagnostics for diseases ranging from gastrointestinal inflammatory syndromes to cancer, diabetes, and neurodegeneration. As these cellular technologies undergo pre-clinical and clinical development, it is becoming essential to monitor their location and function in vivo, necessitating appropriate molecular imaging strategies, and therefore, we have created an interest group within the World Molecular Imaging Society focusing on synthetic biology and reporter gene technologies. Here, we highlight recent advances in biomedical synthetic biology, including bacterial therapy, immunotherapy, and regenerative medicine. We then discuss emerging molecular imaging approaches to facilitate in vivo applications, focusing on reporter genes for noninvasive modalities such as magnetic resonance, ultrasound, photoacoustic imaging, bioluminescence, and radionuclear imaging. Because reporter genes can be incorporated directly into engineered genetic circuits, they are particularly well suited to imaging synthetic biological constructs, and developing them provides opportunities for creative molecular and genetic engineering
Massive and massless Dirac fermions in Pb1-xSnxTe topological crystalline insulator probed by magneto-optical absorption
Dirac fermions in condensed matter physics hold great promise for novel
fundamental physics, quantum devices and data storage applications. IV-VI
semiconductors, in the inverted regime, have been recently shown to exhibit
massless topological surface Dirac fermions protected by crystalline symmetry,
as well as massive bulk Dirac fermions. Under a strong magnetic field (B), both
surface and bulk states are quantized into Landau levels that disperse as
B^1/2, and are thus difficult to distinguish. In this work, magneto-optical
absorption is used to probe the Landau levels of high mobility Bi-doped
Pb0.54Sn0.46Te topological crystalline insulator (111)-oriented films. The high
mobility achieved in these thin film structures allows us to probe and
distinguish the Landau levels of both surface and bulk Dirac fermions and
extract valuable quantitative information about their physical properties. This
work paves the way for future magnetooptical and electronic transport
experiments aimed at manipulating the band topology of such materials.Comment: supplementary material included, to appear in Scientific Report
Antiferromagnetic phase of the gapless semiconductor V3Al
Discovering new antiferromagnetic compounds is at the forefront of developing
future spintronic devices without fringing magnetic fields. The
antiferromagnetic gapless semiconducting D03 phase of V3Al was successfully
synthesized via arc-melting and annealing. The antiferromagnetic properties
were established through synchrotron measurements of the atom-specific magnetic
moments, where the magnetic dichroism reveals large and oppositely-oriented
moments on individual V atoms. Density functional theory calculations confirmed
the stability of a type G antiferromagnetism involving only two-third of the V
atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray
diffraction and transport measurements also support the antiferromagnetism.
This archetypal gapless semiconductor may be considered as a cornerstone for
future spintronic devices containing antiferromagnetic elements.Comment: Accepted to Physics Review B on 02/23/1
Overlap properties of geometric expanders
The {\em overlap number} of a finite -uniform hypergraph is
defined as the largest constant such that no matter how we map
the vertices of into , there is a point covered by at least a
-fraction of the simplices induced by the images of its hyperedges.
In~\cite{Gro2}, motivated by the search for an analogue of the notion of graph
expansion for higher dimensional simplicial complexes, it was asked whether or
not there exists a sequence of arbitrarily large
-uniform hypergraphs with bounded degree, for which . Using both random methods and explicit constructions, we answer this
question positively by constructing infinite families of -uniform
hypergraphs with bounded degree such that their overlap numbers are bounded
from below by a positive constant . We also show that, for every ,
the best value of the constant that can be achieved by such a
construction is asymptotically equal to the limit of the overlap numbers of the
complete -uniform hypergraphs with vertices, as
. For the proof of the latter statement, we establish the
following geometric partitioning result of independent interest. For any
and any , there exists satisfying the
following condition. For any , for any point and
for any finite Borel measure on with respect to which
every hyperplane has measure , there is a partition into measurable parts of equal measure such that all but
at most an -fraction of the -tuples
have the property that either all simplices with
one vertex in each contain or none of these simplices contain
A Pair of Disjoint 3-GDDs of type g^t u^1
Pairwise disjoint 3-GDDs can be used to construct some optimal
constant-weight codes. We study the existence of a pair of disjoint 3-GDDs of
type and establish that its necessary conditions are also sufficient.Comment: Designs, Codes and Cryptography (to appear
Miniband engineering and topological phase transitions in topological - normal insulator superlattices
Periodic stacking of topologically trivial and non-trivial layers with
opposite symmetry of the valence and conduction bands induces topological
interface states that, in the strong coupling limit, hybridize both across the
topological and normal insulator layers. Using band structure engineering, such
superlattices can be effectively realized using the IV-VI lead tin
chalcogenides. This leads to emergent minibands with a tunable topology as
demonstrated both by theory and experiments. The topological minibands are
proven by magneto-optical spectroscopy, revealing Landau level transitions both
at the center and edges of the artificial superlattice mini Brillouin zone.
Their topological character is identified by the topological phase transitions
within the minibands observed as a function of temperature. The critical
temperature of this transition as well as the miniband gap and miniband width
can be precisely controlled by the layer thicknesses and compositions. This
witnesses the generation of a new fully tunable quasi-3D topological state that
provides a template for realization of magnetic Weyl semimetals and other
strongly interacting topological phases.Comment: 21 pages, 8 figure
First Passage Distributions in a Collective Model of Anomalous Diffusion with Tunable Exponent
We consider a model system in which anomalous diffusion is generated by
superposition of underlying linear modes with a broad range of relaxation
times. In the language of Gaussian polymers, our model corresponds to Rouse
(Fourier) modes whose friction coefficients scale as wavenumber to the power
. A single (tagged) monomer then executes subdiffusion over a broad range
of time scales, and its mean square displacement increases as with
. To demonstrate non-trivial aspects of the model, we numerically
study the absorption of the tagged particle in one dimension near an absorbing
boundary or in the interval between two such boundaries. We obtain absorption
probability densities as a function of time, as well as the position-dependent
distribution for unabsorbed particles, at several values of . Each of
these properties has features characterized by exponents that depend on
. Characteristic distributions found for different values of
have similar qualitative features, but are not simply related quantitatively.
Comparison of the motion of translocation coordinate of a polymer moving
through a pore in a membrane with the diffusing tagged monomer with identical
also reveals quantitative differences.Comment: LaTeX, 10 pages, 8 eps figure
Reduction of quantum noise in optical interferometers using squeezed light
We study the photon counting noise in optical interferometers used for
gravitational wave detection. In order to reduce quantum noise a squeezed
vacuum state is injected into the usually unused input port. Here, we
specifically investigate the so called `dark port case', when the beam splitter
is oriented close to 90{\deg} to the incoming laser beam, such that nearly all
photons go to one output port of the interferometer, and only a small fraction
of photons is seen in the other port (`dark port'). For this case it had been
suggested that signal amplification is possible without concurrent noise
amplification [R.Barak and Y.Ben-Aryeh, J.Opt.Soc.Am.B25(361)2008]. We show
that by injection of a squeezed vacuum state into the second input port,
counting noise is reduced for large values of the squeezing factor, however the
signal is not amplified. Signal strength only depends on the intensity of the
laser beam.Comment: 8 pages, 1 figur
Patient-Led Research Collaborative: embedding patients in the Long COVID narrative
A large subset of patients with coronavirus disease 2019 (COVID-19) are experiencing symptoms well beyond the claimed 2-week recovery period for mild cases. These long-term sequelae have come to be known as Long COVID. Originating out of a dedicated online support group, a team of patients formed the Patient-Led Research Collaborative and conducted the first research on Long COVID experience and symptoms. This article discusses the history and value of patient-centric and patient-led research; the formation of Patient-Led Research Collaborative as well as key findings to date; and calls for the following: the acknowledgement of Long COVID as an illness, an accurate estimate of the prevalence of Long COVID, publicly available basic symptom management, care, and research to not be limited to those with positive polymerase chain reaction and antibody tests, and aggressive research and investigation into the pathophysiology of symptoms
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