1,560 research outputs found
Terahertz Hall Measurements On Optimally Doped Single Crystal Bi-2212
The infrared Hall angle in optimally doped single crystal was measured from 3.05 to 21.75 meV as a continuous function of
temperature from 25 to 300\,K. In the normal state, the temperature dependence
of the real part of the cotangent of the infrared Hall angle obeys the same
power law as dc measurements. The measured Hall frequency is
significantly larger than the expected value based upon ARPES data analyzed in
terms of the relaxation time approximation. This discrepancy as well as the
temperature dependence of and is well
described by a Fermi liquid theory in which current vertex corrections produced
by electron-magnon scattering are included.Comment: 10 pages, 2 figure
Infrared Hall effect in high Tc superconductors: Evidence for non-Fermi liquid Hall scattering
Infrared (20-120 cm-1 and 900-1100 cm-1) Faraday rotation and circular
dichroism are measured in high Tc superconductors using sensitive polarization
modulation techniques. Optimally doped YBCO thin films are studied at
temperatures down to 15 K and magnetic fields up to 8 T. At 1000 cm-1 the Hall
conductivity varies strongly with temperature in contrast to the longitudinal
conductivity which is nearly independent of temperature. The Hall scattering
rate has a T^2 temperature dependence but, unlike a Fermi liquid, depends only
weakly on frequency. The experiment puts severe constraints on theories of
transport in the normal state of high Tc superconductors.Comment: 8 pages, 3 figure
Navigating Autism: Parent Experiences with Coping and Service Connection
This presentation shares findings from a qualitative study exploring the experiences of parents of youth and young adults with ASD and service providers. Themes from interviews and focus groups are discussed. The presenters explore the implications of the study for providing services to individuals with ASD in relation to research, policy and practice
Mapping Lesion-Related Epilepsy to a Human Brain Network
Importance: It remains unclear why lesions in some locations cause epilepsy while others do not. Identifying the brain regions or networks associated with epilepsy by mapping these lesions could inform prognosis and guide interventions.
Objective: To assess whether lesion locations associated with epilepsy map to specific brain regions and networks.
Design, setting, and participants: This case-control study used lesion location and lesion network mapping to identify the brain regions and networks associated with epilepsy in a discovery data set of patients with poststroke epilepsy and control patients with stroke. Patients with stroke lesions and epilepsy (n = 76) or no epilepsy (n = 625) were included. Generalizability to other lesion types was assessed using 4 independent cohorts as validation data sets. The total numbers of patients across all datasets (both discovery and validation datasets) were 347 with epilepsy and 1126 without. Therapeutic relevance was assessed using deep brain stimulation sites that improve seizure control. Data were analyzed from September 2018 through December 2022. All shared patient data were analyzed and included; no patients were excluded.
Main outcomes and measures: Epilepsy or no epilepsy.
Results: Lesion locations from 76 patients with poststroke epilepsy (39 [51%] male; mean [SD] age, 61.0 [14.6] years; mean [SD] follow-up, 6.7 [2.0] years) and 625 control patients with stroke (366 [59%] male; mean [SD] age, 62.0 [14.1] years; follow-up range, 3-12 months) were included in the discovery data set. Lesions associated with epilepsy occurred in multiple heterogenous locations spanning different lobes and vascular territories. However, these same lesion locations were part of a specific brain network defined by functional connectivity to the basal ganglia and cerebellum. Findings were validated in 4 independent cohorts including 772 patients with brain lesions (271 [35%] with epilepsy; 515 [67%] male; median [IQR] age, 60 [50-70] years; follow-up range, 3-35 years). Lesion connectivity to this brain network was associated with increased risk of epilepsy after stroke (odds ratio [OR], 2.82; 95% CI, 2.02-4.10; P \u3c .001) and across different lesion types (OR, 2.85; 95% CI, 2.23-3.69; P \u3c .001). Deep brain stimulation site connectivity to this same network was associated with improved seizure control (r, 0.63; P \u3c .001) in 30 patients with drug-resistant epilepsy (21 [70%] male; median [IQR] age, 39 [32-46] years; median [IQR] follow-up, 24 [16-30] months).
Conclusions and relevance: The findings in this study indicate that lesion-related epilepsy mapped to a human brain network, which could help identify patients at risk of epilepsy after a brain lesion and guide brain stimulation therapies
The Meissner effect in a strongly underdoped cuprate above its critical temperature
The Meissner effect and the associated perfect "bulk" diamagnetism together
with zero resistance and gap opening are characteristic features of the
superconducting state. In the pseudogap state of cuprates unusual diamagnetic
signals as well as anomalous proximity effects have been detected but a
Meissner effect has never been observed. Here we have probed the local
diamagnetic response in the normal state of an underdoped La1.94Sr0.06CuO4
layer (up to 46 nm thick, critical temperature Tc' < 5 K) which was brought
into close contact with two nearly optimally doped La1.84Sr0.16CuO4 layers (Tc
\approx 32 K). We show that the entire 'barrier' layer of thickness much larger
than the typical c axis coherence lengths of cuprates exhibits a Meissner
effect at temperatures well above Tc' but below Tc. The temperature dependence
of the effective penetration depth and superfluid density in different layers
indicates that superfluidity with long-range phase coherence is induced in the
underdoped layer by the proximity to optimally doped layers; however, this
induced order is very sensitive to thermal excitation.Comment: 7 pages, 7 figures + Erratu
Normal-State Spin Dynamics and Temperature-Dependent Spin Resonance Energy in an Optimally Doped Iron Arsenide Superconductor
The proximity of superconductivity and antiferromagnetism in the phase
diagram of iron arsenides, the apparently weak electron-phonon coupling and the
"resonance peak" in the superconducting spin excitation spectrum have fostered
the hypothesis of magnetically mediated Cooper pairing. However, since most
theories of superconductivity are based on a pairing boson of sufficient
spectral weight in the normal state, detailed knowledge of the spin excitation
spectrum above the superconducting transition temperature Tc is required to
assess the viability of this hypothesis. Using inelastic neutron scattering we
have studied the spin excitations in optimally doped BaFe1.85Co0.15As2 (Tc = 25
K) over a wide range of temperatures and energies. We present the results in
absolute units and find that the normal state spectrum carries a weight
comparable to underdoped cuprates. In contrast to cuprates, however, the
spectrum agrees well with predictions of the theory of nearly antiferromagnetic
metals, without complications arising from a pseudogap or competing
incommensurate spin-modulated phases. We also show that the temperature
evolution of the resonance energy follows the superconducting energy gap, as
expected from conventional Fermi-liquid approaches. Our observations point to a
surprisingly simple theoretical description of the spin dynamics in the iron
arsenides and provide a solid foundation for models of magnetically mediated
superconductivity.Comment: 8 pages, 4 figures, and an animatio
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