Entropic Origin of Pseudogap Physics and a Mott-Slater Transition in Cuprates

We propose a new approach to understand the origin of the pseudogap in the cuprates, in terms of bosonic entropy. The near-simultaneous softening of a large number of different $q$-bosons yields an extended range of short-range order, wherein the growth of magnetic correlations with decreasing temperature $T$ is anomalously slow. These entropic effects cause the spectral weight associated with the Van Hove singularity (VHS) to shift rapidly and nearly linearly toward half filling at higher $T$, consistent with a picture of the VHS driving the pseudogap transition at a temperature $\sim T^*$. As a byproduct, we develop an order-parameter classification scheme that predicts supertransitions between families of order parameters. As one example, we find that by tuning the hopping parameters, it is possible to drive the cuprates across a {\it transition between Mott and Slater physics}, where a spin-frustrated state emerges at the crossover.Comment: 24 pgs, 15 figs + Supp. Material [6pgs, 3 figs]. Major revision of arXiv:1505.0477

Characterization of Thin Film Materials using SCAN meta-GGA, an Accurate Nonempirical Density Functional

We discuss self-consistently obtained ground-state electronic properties of monolayers of graphene and a number of beyond graphene compounds, including films of transition-metal dichalcogenides (TMDs), using the recently proposed strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) to the density functional theory. The SCAN meta-GGA results are compared with those based on the local density approximation (LDA) as well as the generalized gradient approximation (GGA). As expected, the GGA yields expanded lattices and softened bonds in relation to the LDA, but the SCAN meta-GGA systematically improves the agreement with experiment. Our study suggests the efficacy of the SCAN functional for accurate modeling of electronic structures of layered materials in high-throughput calculations more generally

Ab-initio Molecular Dynamics study of electronic and optical properties of silicon quantum wires: Orientational Effects

We analyze the influence of spatial orientation on the optical response of hydrogenated silicon quantum wires. The results are relevant for the interpretation of the optical properties of light emitting porous silicon. We study (111)-oriented wires and compare the present results with those previously obtained within the same theoretical framework for (001)-oriented wires [F. Buda {\it et al.}, {\it Phys. Rev. Lett.} {\bf 69}, 1272, (1992)]. In analogy with the (001)-oriented wires and at variance with crystalline bulk silicon, we find that the (111)-oriented wires exhibit a direct gap at ${\bf k}=0$ whose value is largely enhanced with respect to that found in bulk silicon because of quantum confinement effects. The imaginary part of the dielectric function, for the external field polarized in the direction of the axis of the wires, shows features that, while being qualitatively similar to those observed for the (001) wires, are not present in the bulk. The main conclusion which emerges from the present study is that, if wires a few nanometers large are present in the porous material, they are optically active independently of their specific orientation.Comment: 14 pages (plus 6 figures), Revte

Modeling and characterization of InAs∕GaAs quantum dot lasers grown using metal organic chemical vapor deposition

We report on the lasing characteristics of three- and five-stack InAs∕GaAsquantum dot(QD) lasers grown by metal organic chemical vapor deposition. By increasing the number of stacked dot layers to 5, lasing was achieved from the ground state at 1135nm for device lengths as short as 1.5mm (no reflectivity coatings). The unamplified spontaneous emission and Z ratio as a function of injection current were also investigated. While the five-stack QD lasers behaved as expected with Z ratios of ≈2 prior to lasing, the three-stack QD lasers, which lased from the excited state, exhibited Z-ratio values as high as 4. A simple model was developed and indicated that high Z ratios can be generated by three nonradiative recombination pathways: (i) high monomolecular recombination within the wetting layer, (ii) Auger recombination involving carriers within the QDs (“unmixed” Auger), and (iii) Auger recombination involving both the QD and wetting layer states (“mixed” Auger), which dominate once the excited and wetting layer states become populated.We also acknowledge the financial support of the Australian Research Council

Health Care Resource Utilization Costs Related to Anaemia Management in Chronic Kidney Disease Non-Dialysed Patients: A Retrospective Clinical and Administrative Database Analysis

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Prevalence of various Upper Extremity Disorders in Patients with Carpal Tunnel Syndrome versus Patients without Carpal Tunnel Syndrome

Background and Purpose: Increasingly larger numbers of patients present with repetitive strain injuries of the upper extremities, especially carpal tunnel syndrome (CTS). A large number of these patients appear to have more than one upper extremity condition. The purpose of this study was to determine the probability that a patient diagnosed with carpal tunnel syndrome will also be diagnosed with other upper extremity and/or cervical spine disorders. Subjects: A group of 188 subjects diagnosed with carpal tunnel syndrome and a group of 203 subjects without carpal tunnel syndrome were selected through a chart review of patients at Loma Linda University Medical Center. Subjects were Caucasian or African-American, between the ages of 24 and 75 years. Methods: Patients were selected for the carpal tunnel syndrome group based on both clinical diagnosis and validation through electrodiagnosis. A group of subjects who had not been diagnosed with carpal tunnel syndrome, the control group, was selected by a chart review of patients seen by the same surgeons as the carpal tunnel group. The prevalence of different upper extremity disorders and other conditions was compared in the two groups. Results: Of the 188 subjects in the carpal tunnel group, 25 (13.3%) were also diagnosed with at least one ulnar nerve disorder, compared to none of the 203 subjects in the control group. Thirty-four subjects (20.2%) were diagnosed with at least one nerve disorder other than carpal tunnel syndrome in the carpal tunnel syndrome group, compared to 12 (5.9%) in the control group. Also, 21 subjects (11.2%) in the carpal tunnel syndrome group were diagnosed with trigger finger while only one (0.5%) had the same diagnosis in the control group. Seven subjects (3.7%) were diagnosed with ganglion cysts, and 30 subjects (16.0%) were diagnosed with at least one other upper extremity disorder that involved muscle, tendon, or joint capsule in the carpal tunnel group while one (0.5%) and two (1.0%) subjects respectively had these diagnoses in the control group. Discussion and Conclusion: As often seen in physical therapy clinics, when a patient has been diagnosed with carpal tunnel syndrome, there is a good chance that other upper extremity disorders have or will be diagnosed in the same patient. These conditions may or may not be related to carpal tunnel syndrome. An apparent predisposition of some patients to upper extremity disorders has been observed before and appears to be the case in this study. Clinicians should consider screening their patients for all these disorders, when only one of them may be readily apparent. Key Words: Carpal tunnel syndrome, Upper extremity disorders, Repetitive strain injury

Modulating spin transfer torque switching dynamics with two orthogonal spin-polarizers by varying the cell aspect ratio

We study in-plane magnetic tunnel junctions with additional perpendicular polarizer for subnanosecond-current-induced switching memories. The spin-transfer-torque switching dynamics was studied as a function of the cell aspect ratio both experimentally and by numerical simulations using the macrospin model. We show that the anisotropy field plays a significant role in the dynamics, along with the relative amplitude of the two spin-torque contributions. This was confirmed by micromagnetic simulations. Real-time measurements of the reversal were performed with samples of low and high aspect ratio. For low aspect ratios, a precessional motion of the magnetization was observed and the effect of temperature on the precession coherence was studied. For high aspect ratios, we observed magnetization reversals in less than 1 ns for high enough current densities, the final state being controlled by the current direction in the magnetic tunnel junction cell.Comment: 6 pages, 7 figure

Chirality-induced asymmetric magnetic nucleation in Pt/Co/AlOx ultrathin microstructures

The nucleation of reversed magnetic domains in Pt/Co/AlO$_{x}$ microstructures with perpendicular anisotropy was studied experimentally in the presence of an in-plane magnetic field. For large enough in-plane field, nucleation was observed preferentially at an edge of the sample normal to this field. The position at which nucleation takes place was observed to depend in a chiral way on the initial magnetization and applied field directions. An explanation of these results is proposed, based on the existence of a sizable Dzyaloshinskii-Moriya interaction in this sample. Another consequence of this interaction is that the energy of domain walls can become negative for in-plane fields smaller than the effective anisotropy field.Comment: Published version, Physical Review Letters 113, 047203 (2014