8,282 research outputs found
Observation of Landau quantization and standing waves in HfSiS
Recently, HfSiS was found to be a new type of Dirac semimetal with a line of
Dirac nodes in the band structure. Meanwhile, Rashba-split surface states are
also pronounced in this compound. Here we report a systematic study of HfSiS by
scanning tunneling microscopy/spectroscopy at low temperature and high magnetic
field. The Rashba-split surface states are characterized by measuring Landau
quantization and standing waves, which reveal a quasi-linear dispersive band
structure. First-principles calculations based on density-functional theory are
conducted and compared with the experimental results. Based on these
investigations, the properties of the Rashba-split surface states and their
interplay with defects and collective modes are discussed.Comment: 6 pages, 5 figure
Dirac Line-nodes and Effect of Spin-orbit Coupling in Non-symmorphic Critical Semimetal MSiS (M=Hf, Zr)
Topological Dirac semimetals (TDSs) represent a new state of quantum matter
recently discovered that offers a platform for realizing many exotic physical
phenomena. A TDS is characterized by the linear touching of bulk (conduction
and valance) bands at discrete points in the momentum space (i.e. 3D Dirac
points), such as in Na3Bi and Cd3As2. More recently, new types of Dirac
semimetals with robust Dirac line-nodes (with non-trivial topology or near the
critical point between topological phase transitions) have been proposed that
extends the bulk linear touching from discrete points to 1D lines. In this
work, using angle-resolved photoemission spectroscopy (ARPES), we explored the
electronic structure of the non-symmorphic crystals MSiS (M=Hf, Zr).
Remarkably, by mapping out the band structure in the full 3D Brillouin Zone
(BZ), we observed two sets of Dirac line-nodes in parallel with the kz-axis and
their dispersions. Interestingly, along directions other than the line-nodes in
the 3D BZ, the bulk degeneracy is lifted by spin-orbit coupling (SOC) in both
compounds with larger magnitude in HfSiS. Our work not only experimentally
confirms a new Dirac line-node semimetal family protected by non-symmorphic
symmetry, but also helps understanding and further exploring the exotic
properties as well as practical applications of the MSiS family of compounds.Comment: 5 figure
Postprocessing for quantum random number generators: entropy evaluation and randomness extraction
Quantum random-number generators (QRNGs) can offer a means to generate
information-theoretically provable random numbers, in principle. In practice,
unfortunately, the quantum randomness is inevitably mixed with classical
randomness due to classical noises. To distill this quantum randomness, one
needs to quantify the randomness of the source and apply a randomness
extractor. Here, we propose a generic framework for evaluating quantum
randomness of real-life QRNGs by min-entropy, and apply it to two different
existing quantum random-number systems in the literature. Moreover, we provide
a guideline of QRNG data postprocessing for which we implement two
information-theoretically provable randomness extractors: Toeplitz-hashing
extractor and Trevisan's extractor.Comment: 13 pages, 2 figure
Mott physics, sign structure, ground state wavefunction, and high-Tc superconductivity
In this article I give a pedagogical illustration of why the essential
problem of high-Tc superconductivity in the cuprates is about how an
antiferromagnetically ordered state can be turned into a short-range state by
doping. I will start with half-filling where the antiferromagnetic ground state
is accurately described by the Liang-Doucot-Anderson (LDA) wavefunction. Here
the effect of the Fermi statistics becomes completely irrelevant due to the no
double occupancy constraint. Upon doping, the statistical signs reemerge,
albeit much reduced as compared to the original Fermi statistical signs. By
precisely incorporating this altered statistical sign structure at finite
doping, the LDA ground state can be recast into a short-range antiferromagnetic
state. Superconducting phase coherence arises after the spin correlations
become short-ranged, and the superconducting phase transition is controlled by
spin excitations. I will stress that the pseudogap phenomenon naturally emerges
as a crossover between the antiferromagnetic and superconducting phases. As a
characteristic of non Fermi liquid, the mutual statistical interaction between
the spin and charge degrees of freedom will reach a maximum in a
high-temperature "strange metal phase" of the doped Mott insulator.Comment: 12 pages, 12 figure
Merger Dynamics of the Pair of Galaxy Clusters -- A399 and A401
Convincing evidence of a past interaction between two rich clusters A399 and
A401 was recently found by the X-ray imaging observations. In this paper we
examine the structure and dynamics of this pair of galaxy clusters. A
mixture-modeling algorithm has been applied to obtain a robust partition into
two clusters, which allows us to discuss the virial mass and velocity
distribution for each cluster. Assuming that these two clusters follow a linear
orbit and they have once experienced a close encounter, we model the binary
cluster as a two-body system. As a result, four gravitationally bound solutions
are obtained. The recent X-ray observations seem to favor a scenario in which
the two clusters with a true separation of Mpc are currently
expanding at 583 km/s along the direction with a projection angle of 67.5
degree, and they will reach a maximum extent of Mpc in about
Gyr.Comment: 11 pages, including 6 EPS figures and 4 tables, uses chjaa.cls,
Accepted by the ChJA
Nuclei Detection Using Mixture Density Networks
Nuclei detection is an important task in the histology domain as it is a main
step toward further analysis such as cell counting, cell segmentation, study of
cell connections, etc. This is a challenging task due to the complex texture of
histology image, variation in shape, and touching cells. To tackle these
hurdles, many approaches have been proposed in the literature where deep
learning methods stand on top in terms of performance. Hence, in this paper, we
propose a novel framework for nuclei detection based on Mixture Density
Networks (MDNs). These networks are suitable to map a single input to several
possible outputs and we utilize this property to detect multiple seeds in a
single image patch. A new modified form of a cost function is proposed for
training and handling patches with missing nuclei. The probability maps of the
nuclei in the individual patches are next combined to generate the final
image-wide result. The experimental results show the state-of-the-art
performance on complex colorectal adenocarcinoma dataset.Comment: 8 pages, 3 figure
GITRL modulates the activities of p38 MAPK and STAT3 to promote Th17 cell differentiation in autoimmune arthritis
published_or_final_versio
Mapping the unconventional orbital texture in topological crystalline insulators
The newly discovered topological crystalline insulators (TCIs) harbor a
complex band structure involving multiple Dirac cones. These materials are
potentially highly tunable by external electric field, temperature or strain
and could find future applications in field-effect transistors, photodetectors,
and nano-mechanical systems. Theoretically, it has been predicted that
different Dirac cones, offset in energy and momentum-space, might harbor vastly
different orbital character, a unique property which if experimentally
realized, would present an ideal platform for accomplishing new spintronic
devices. However, the orbital texture of the Dirac cones, which is of immense
importance in determining a variety of materials properties, still remains
elusive in TCIs. Here, we unveil the orbital texture in a prototypical TCI
PbSnSe. By using Fourier-transform (FT) scanning tunneling
spectroscopy (STS) we measure the interference patterns produced by the
scattering of surface state electrons. We discover that the intensity and
energy dependences of FTs show distinct characteristics, which can directly be
attributed to orbital effects. Our experiments reveal the complex band topology
involving two Lifshitz transitions and establish the orbital nature of the
Dirac bands in this new class of topological materials, which could provide a
different pathway towards future quantum applications
New Family of Robust 2D Topological Insulators in van der Waals Heterostructures
We predict a new family of robust two-dimensional (2D) topological insulators
in van der Waals heterostructures comprising graphene and chalcogenides BiTeX
(X=Cl, Br and I). The layered structures of both constituent materials produce
a naturally smooth interface that is conducive to proximity induced new
topological states. First principles calculations reveal intrinsic
topologically nontrivial bulk energy gaps as large as 70-80 meV, which can be
further enhanced up to 120 meV by compression. The strong spin-orbit coupling
in BiTeX has a significant influence on the graphene Dirac states, resulting in
the topologically nontrivial band structure, which is confirmed by calculated
nontrivial Z2 index and an explicit demonstration of metallic edge states. Such
heterostructures offer an unique Dirac transport system that combines the 2D
Dirac states from graphene and 1D Dirac edge states from the topological
insulator, and it offers new ideas for innovative device designs
Experimental observation of topological Fermi arcs in type-II Weyl semimetal MoTe2
Weyl semimetal is a new quantum state of matter [1-12] hosting the condensed
matter physics counterpart of relativisticWeyl fermion [13] originally
introduced in high energy physics. The Weyl semimetal realized in the TaAs
class features multiple Fermi arcs arising from topological surface states [10,
11, 14-16] and exhibits novel quantum phenomena, e.g., chiral anomaly induced
negative mag-netoresistance [17-19] and possibly emergent supersymmetry [20].
Recently it was proposed theoretically that a new type (type-II) of Weyl
fermion [21], which does not have counterpart in high energy physics due to the
breaking of Lorentz invariance, can emerge as topologically-protected touching
between electron and hole pockets. Here, we report direct spectroscopic
evidence of topological Fermi arcs in the predicted type-II Weyl semimetal
MoTe2 [22-24]. The topological surface states are confirmed by directly
observing the surface states using bulk-and surface-sensitive angle-resolved
photoemission spectroscopy (ARPES), and the quasi-particle interference (QPI)
pattern between the two putative Fermi arcs in scanning tunneling microscopy
(STM). Our work establishes MoTe2 as the first experimental realization of
type-II Weyl semimetal, and opens up new opportunities for probing novel
phenomena such as exotic magneto-transport [21] in type-II Weyl semimetals.Comment: submitted on 01/29/2016. Nature Physics, in press. Spectroscopic
evidence of the Fermi arcs from two complementary surface sensitive probes -
ARPES and STS. A comparison of the calculated band structure for T_d and 1T'
phase to identify the topological Fermi arcs in the T_d phase is also
included in the supplementary informatio
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