318 research outputs found
Topological Defects Coupling Smectic Modulations to Intra-unit-cell Nematicity in Cuprate
We study the coexisting smectic modulations and intra-unit-cell nematicity in
the pseudogap states of underdoped Bi2Sr2CaCu2O8+{\delta}. By visualizing their
spatial components separately, we identified 2\pi topological defects
throughout the phase-fluctuating smectic states. Imaging the locations of large
numbers of these topological defects simultaneously with the fluctuations in
the intra-unit-cell nematicity revealed strong empirical evidence for a
coupling between them. From these observations, we propose a Ginzburg-Landau
functional describing this coupling and demonstrate how it can explain the
coexistence of the smectic and intra-unit-cell broken symmetries and also
correctly predict their interplay at the atomic scale. This theoretical
perspective can lead to unraveling the complexities of the phase diagram of
cuprate high-critical-temperature superconductors
One-Component Order Parameter in URuSi Uncovered by Resonant Ultrasound Spectroscopy and Machine Learning
The unusual correlated state that emerges in URuSi below T =
17.5 K is known as "hidden order" because even basic characteristics of the
order parameter, such as its dimensionality (whether it has one component or
two), are "hidden". We use resonant ultrasound spectroscopy to measure the
symmetry-resolved elastic anomalies across T. We observe no anomalies in
the shear elastic moduli, providing strong thermodynamic evidence for a
one-component order parameter. We develop a machine learning framework that
reaches this conclusion directly from the raw data, even in a crystal that is
too small for traditional resonant ultrasound. Our result rules out a broad
class of theories of hidden order based on two-component order parameters, and
constrains the nature of the fluctuations from which unconventional
superconductivity emerges at lower temperature. Our machine learning framework
is a powerful new tool for classifying the ubiquitous competing orders in
correlated electron systems
Commensurate period Charge Density Modulations throughout the Pseudogap Regime
Theories based upon strong real space (r-space) electron electron
interactions have long predicted that unidirectional charge density modulations
(CDM) with four unit cell (4) periodicity should occur in the hole doped
cuprate Mott insulator (MI). Experimentally, however, increasing the hole
density p is reported to cause the conventionally defined wavevector of
the CDM to evolve continuously as if driven primarily by momentum space
(k-space) effects. Here we introduce phase resolved electronic structure
visualization for determination of the cuprate CDM wavevector. Remarkably, this
new technique reveals a virtually doping independent locking of the local CDM
wavevector at throughout the underdoped phase diagram of the
canonical cuprate . These observations have significant
fundamental consequences because they are orthogonal to a k-space (Fermi
surface) based picture of the cuprate CDM but are consistent with strong
coupling r-space based theories. Our findings imply that it is the latter that
provide the intrinsic organizational principle for the cuprate CDM state
Quantum limit transport and destruction of the Weyl nodes in TaAs
Weyl fermions are a new ingredient for correlated states of electronic
matter. A key difficulty has been that real materials also contain non-Weyl
quasiparticles, and disentangling the experimental signatures has proven
challenging. We use magnetic fields up to 95 tesla to drive the Weyl semimetal
TaAs far into its quantum limit (QL), where only the purely chiral 0th Landau
levels (LLs) of the Weyl fermions are occupied. We find the electrical
resistivity to be nearly independent of magnetic field up to 50 tesla: unusual
for conventional metals but consistent with the chiral anomaly for Weyl
fermions. Above 50 tesla we observe a two-order-of-magnitude increase in
resistivity, indicating that a gap opens in the chiral LLs. Above 80 tesla we
observe strong ultrasonic attenuation below 2 kelvin, suggesting a
mesoscopically-textured state of matter. These results point the way to
inducing new correlated states of matter in the QL of Weyl semimetals
Impact of dietary manganese on experimental colitis in mice
Diet plays a significant role in the pathogenesis of inflammatory bowel disease (IBD). A recent epidemiological study has shown an inverse relationship between nutritional manganese (Mn) status and IBD patients. Mn is an essential micronutrient required for normal cell function and physiological processes. To date, the roles of Mn in intestinal homeostasis remain unknown and the contribution of Mn to IBD has yet to be explored. Here, we provide evidence that Mn is critical for the maintenance of the intestinal barrier and that Mn deficiency exacerbates dextran sulfate sodium (DSS)â induced colitis in mice. Specifically, when treated with DSS, Mnâ deficient mice showed increased morbidity, weight loss, and colon injury, with a concomitant increase in inflammatory cytokine levels and oxidative and DNA damage. Even without DSS treatment, dietary Mn deficiency alone increased intestinal permeability by impairing intestinal tight junctions. In contrast, mice fed a Mnâ supplemented diet showed slightly increased tolerance to DSSâ induced experimental colitis, as judged by the colon length. Despite the wellâ appreciated roles of intestinal microbiota in driving inflammation in IBD, the gut microbiome composition was not altered by changes in dietary Mn. We conclude that Mn is necessary for proper maintenance of the intestinal barrier and provides protection against DSSâ induced colon injury.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154377/1/fsb220201_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154377/2/fsb220201-sup-0002-TableS3.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154377/3/fsb220201-sup-0005-TableS6.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154377/4/fsb220201.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154377/5/fsb220201-sup-0003-TableS4.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154377/6/fsb220201-sup-0004-TableS5.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154377/7/fsb220201-sup-0001-TableS1-S2.pd
Dirac Spectrum in Piecewise Constant One-Dimensional Potentials
We study the electronic states of graphene in piecewise constant potentials
using the continuum Dirac equation appropriate at low energies, and a transfer
matrix method. For superlattice potentials, we identify patterns of induced
Dirac points which are present throughout the band structure, and verify for
the special case of a particle-hole symmetric potential their presence at zero
energy. We also consider the cases of a single trench and a p-n junction
embedded in neutral graphene, which are shown to support confined states. An
analysis of conductance across these structures demonstrates that these
confined states create quantum interference effects which evidence their
presence.Comment: 10 pages, 12 figures, additional references adde
Inter edge Tunneling in Quantum Hall Line Junctions
We propose a scenario to understand the puzzling features of the recent
experiment by Kang and coworkers on tunneling between laterally coupled quantum
Hall liquids by modeling the system as a pair of coupled chiral Luttinger
liquid with a point contact tunneling center. We show that for filling factors
the effects of the Coulomb interactions move the system deep into
strong tunneling regime, by reducing the magnitude of the Luttinger parameter
, leading to the appearance of a zero-bias differential conductance peak of
magnitude at zero temperature. The abrupt appearance of the zero
bias peak as the filling factor is increased past a value ,
and its gradual disappearance thereafter can be understood as a crossover
controlled by the main energy scales of this system: the bias voltage , the
crossover scale , and the temperature . The low height of the zero bias
peak observed in the experiment, and its broad finite width,
can be understood naturally within this picture. Also, the abrupt reappearance
of the zero-bias peak for can be explained as an effect caused
by spin reversed electrons, \textit{i. e.} if the 2DEG is assumed to have a
small polarization near . We also predict that as the temperature is
lowered should decrease, and the width of zero-bias peak should become
wider. This picture also predicts the existence of similar zero bias peak in
the spin tunneling conductance near for .Comment: 17 pages, 8 figure
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