3,484 research outputs found
On the Origin of the Checkerboard Pattern in Scanning Tunneling Microscopy Maps of Underdoped Cuprate Superconductors
The checkerboard pattern in the differential conductance maps on underdoped
cuprates appears when the STM is placed above the O-sites in the outermost
CuO-plane. In this position the interference between tunneling
paths through the apical ions above the neighboring Cu-sites leads to an
asymmetric weighting of final states in the two antinodal regions of
-space. The form of the asymmetry in the differential
conductance spectra in the checkerboard pattern favors asymmetry in the
localization length rather than a nematic displacement as the underlying
origin.Comment: 8 pages, 5 figures, final versio
Elastic fracture toughness for ductile metal pipes with circumferential surface cracks
Surface cracks have long been recognized as a major cause for potential failures of metal pipes. In fracture analysis, the widely used method is based on linear elastic fracture mechanics. However, for ductile metal pipes, it has been known that the existence of plasticity results in easing of stress concentration at the crack front. This will ultimately increase the total fracture toughness. Therefore, when using linear elastic fracture mechanics to predict fracture failure of ductile metal pipes, the plastic portion of fracture toughness should be excluded. Otherwise, the value of fracture toughness will be overestimated, resulting in an under-estimated probability of failure. This paper intends to derive a model of elastic fracture toughness for steel pipes with a circumferential crack. The derived elastic fracture toughness is a function of crack geometry and material properties of the cracked pipe. The significance of the derived model is that the well-established linear elastic fracture mechanics can be used for ductile materials in predicting the fracture failur
Localization and Mobility Gap in Topological Anderson Insulator
It has been proposed that disorder may lead to a new type of topological
insulator, called topological Anderson insulator (TAI). Here we examine the
physical origin of this phenomenon. We calculate the topological invariants and
density of states of disordered model in a super-cell of 2-dimensional
HgTe/CdTe quantum well. The topologically non-trivial phase is triggered by a
band touching as the disorder strength increases. The TAI is protected by a
mobility gap, in contrast to the band gap in conventional quantum spin Hall
systems. The mobility gap in the TAI consists of a cluster of non-trivial
subgaps separated by almost flat and localized bands.Comment: 8 pages, 7 figure
Andreev and Single Particle Tunneling Spectroscopies in Underdoped Cuprates
We study tunneling spectroscopy between a normal metal and underdoped cuprate
superconductor modeled by a phenomenological theory in which the pseudogap is a
precursor to the undoped Mott insulator. In the transparent tunneling limit,
the spectra show a small energy gap associated with Andreev reflection. In the
Giaever limit, the spectra show a large energy gap associated with single
particle tunneling. Our theory semi-quantitatively describes the two gap
behavior observed in tunneling experiments.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Lett. minor changes of
reference
Observation of electric current induced by optically injected spin current
A normally incident light of linear polarization injects a pure spin current
in a strip of 2-dimensional electron gas with spin-orbit coupling. We report
observation of an electric current with a butterfly-like pattern induced by
such a light shed on the vicinity of a crossbar shaped InGaAs/InAlAs quantum
well. Its light polarization dependence is the same as that of the spin
current. We attribute the observed electric current to be converted from the
optically injected spin current caused by scatterings near the crossing. Our
observation provides a realistic technique to detect spin currents, and opens a
new route to study the spin-related science and engineering in semiconductors.Comment: 15 pages, 4 figure
Ediacaran Macro Body Fossils
This paper, Ediacaran Macro Body Fossils, reports a new discovery of well preserved three dimensional macro body fossils of the Ediacaran Period in central YunNan province in the People's Republic of China. These body fossils will enable more detailed and in-depth exploration of the evolution of multi-cellular macro organisms on this planet, whereas in the past, researches could only rely on cast or imprint fossils
Why a local moment induces an antiferromagnetic ordering: An RVB picture
Based on a Gutzwiller projected BCS wavefunction, it is shown that a local
S=1/2 moment is present around a vacancy site (zinc impurity) in a form of
staggered magnetic moments, which is a direct consequence of the short-ranged
resonating-valence-bond (RVB) pairing in the spin background.Comment: 4 pages, 3 figure
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