Temperature dependence of the superconducting gap anisotropy in Bi2_{2}Sr2_{2}Ca1_{1}Cu2_{2}O8+x_{8+x}

We present the first detailed data of the momentum-resolved, temperature dependence of the superconducting gap of $Bi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+x}$, complemented by similar data on the intensity of the photoemission superconducting condensate spectral area. The gap anisotropy between the $\Gamma-\bar{M}$ and $\Gamma-X$ directions increases markedly with increasing temperature, contrary to what happens for conventional anisotropic-gap superconductors such as lead. Specifically, the size of the superconducting gap along the $\Gamma-X$ direction decreases to values indistinguishable from zero at temperatures for which the gap retains virtually full value along the $\Gamma-\bar{M}$ direction.Comment: APS_REVTEX. 19 pages, including 8 figures, available upon request. UW-Madison preprin

Localization Effects in Bi2Sr2Ca(Cu,Co)2O8+y High Temperature Superconductors

Doping Bi2Sr2Ca1Cu2O8+y with Co causes a superconductor-insulator transition. We study correlations between changes in the electrical resistivity RHOab(T) and the electronic bandstructure using identical single crystalline samples. For undoped samples the resistivity is linear in temperature and has a vanishing residual resistivity. In angle resolved photoemission these samples show dispersing band-like states. Co-doping decreases TC and causes and increase in the residual resistivity. Above a threshold Co-concentration the resistivity is metallic (drab/dT >0) at room temperature, turns insulating below a characteristic temperature Tmin and becomes super- conducting at even lower temperature. These changes in the resistivity correlate with the disappearance of the dispersing band-like states in angle resolved photoemission. We show that Anderson localization caused by the impurity potential of the doped Co-atoms provides a consistent explanation of all experimental features. Therefore the TC reduction in 3d-metal doped high- temperature superconductors is not caused by Abrikosov Gor'kov pair- breaking but by spatial localization of the carriers. The observed suppression of TC indicates that the system is in the homogenous limit of the superconductor-insulator transition. The coexistance of insulating (dRHOab/dT <0) normal state behavior and super- conductivity indicates that the superconducting ground state is formed out of spatially almost localized carriers.Comment: Postscript file 11 pages plus 4 figures available on reques

Observation of a van Hove Singularity in Bi2Sr2Ca1Cu2O8+xBi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+x} with Angle Resolved Photoemission

We have performed high energy resolution angle-resolved photoemission studies of the normal state band structure of oxygen overdoped $Bi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+x}$. We find that there is an extended saddle point singularity in the density of states along $\Gamma-\bar{M}-Z$ direction. The data also indicate that there is an asymmetry in the Fermi surface for both the $\Gamma-\bar{M}-Z$ and perpendicular directions.Comment: APS_Revtex. 28 pages, including 16 figures, available upon request. UW-Madison preprint#

Anomalous Normal-State Properties of High-Tc_c Superconductors -- Intrinsic Properties of Strongly Correlated Electron Systems?

A systematic study of optical and transport properties of the Hubbard model, based on Metzner and Vollhardt's dynamical mean-field approximation, is reviewed. This model shows interesting anomalous properties that are, in our opinion, ubiquitous to single-band strongly correlated systems (for all spatial dimensions greater than one), and also compare qualitatively with many anomalous transport features of the high-T$_c$ cuprates. This anomalous behavior of the normal-state properties is traced to a ``collective single-band Kondo effect,'' in which a quasiparticle resonance forms at the Fermi level as the temperature is lowered, ultimately yielding a strongly renormalized Fermi liquid at zero temperature.Comment: 27 pages, latex, 13 figures, Invited for publication in Advances in Physic

Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni2_2MnGa

Magnetic shape memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic and structural order. To study these correlations we use time resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300~fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320~fs, which is comparable to the quenching of the structural modulation.Comment: 5 pages, 3 figures. Supplementary materials 5 pages, 5 figure

Structural and magnetic dynamics of a laser induced phase transition in FeRh

We use time-resolved x-ray diffraction and magnetic optical Kerr effect to study the laser induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (\tau_1 ~ 30ps). This is significantly faster than the magnetic response (\tau_2 ~ 60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases co-exist on short time-scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented.Comment: 5 pages, 3 figures - changed to reflect version accepted for PR

S and D Wave Mixing in High TcT_c Superconductors

For a tight binding model with nearest neighbour attraction and a small orthorhombic distortion, we find a phase diagram for the gap at zero temperature which includes three distinct regions as a function of filling. In the first, the gap is a mixture of mainly $d$-wave with a smaller extended $s$-wave part. This is followed by a region in which there is a rapid increase in the $s$-wave part accompanied by a rapid increase in relative phase between $s$ and $d$ from 0 to $\pi$. Finally, there is a region of dominant $s$ with a mixture of $d$ and zero phase. In the mixed region with a finite phase, the $s$-wave part of the gap can show a sudden increase with decreasing temperature accompanied with a rapid increase in phase which shows many of the characteristics measured in the angular resolved photoemission experiments of Ma {\em et al.} in $\rm Bi_2Sr_2CaCu_2O_8$Comment: 12 pages, RevTeX 3.0, 3 PostScript figures uuencoded and compresse

A Narrative Review of Patient-Reported Outcome Measures and Their Application in Recent Pediatric Surgical Research:Advancing Knowledge and Offering New Perspectives to the Field

Introduction Patient-reported outcome measures (PROMs) can be employed in both research and clinical care to enhance our understanding of outcomes that matter to patients. This narrative review aims to describe PROM use in recent pediatric surgical research, identify and describe psychometrically robust PROMs, providing an overview of those derived from pediatric patient input, and make recommendations for future research. Materials and Methods A search was conducted to identify articles published from 2021 to August 2023 describing the availability and/or use of at least one valid or reliable PROM in children with conditions including anorectal malformations, biliary atresia, congenital diaphragmatic hernia, duodenal atresia, esophageal atresia, abdominal wall defects, Hirschsprung's disease, sacrococcygeal teratoma, and short bowel syndrome. Articles were categorized based on their objectives in applying PROMs. Psychometrically robust PROMs were identified and described. Results Out of the 345 articles identified, 49 met the inclusion criteria. Seventeen focused on esophageal atresia and 14 on Hirschsprung's disease. Twenty-nine PROMs were identified, with 12 deemed psychometrically robust. Seven psychometrically robust PROMs were developed using patient input in the primary item generation. Most PROMs were applied to advance understanding of conditions and/or treatment and fewer were developed or psychometrically evaluated. No PROMs were assessed for their impact or incorporated into an implementation study. Conclusions This review reveals gaps in the application of PROMs in recent pediatric surgical research. Emphasis should be placed on the development and utilization of psychometrically robust PROMs, broadening the scope of covered diseases, conducting impact assessments, and evaluating implementation strategies

A Narrative Review of Patient-Reported Outcome Measures and Their Application in Recent Pediatric Surgical Research:Advancing Knowledge and Offering New Perspectives to the Field

Introduction Patient-reported outcome measures (PROMs) can be employed in both research and clinical care to enhance our understanding of outcomes that matter to patients. This narrative review aims to describe PROM use in recent pediatric surgical research, identify and describe psychometrically robust PROMs, providing an overview of those derived from pediatric patient input, and make recommendations for future research. Materials and Methods A search was conducted to identify articles published from 2021 to August 2023 describing the availability and/or use of at least one valid or reliable PROM in children with conditions including anorectal malformations, biliary atresia, congenital diaphragmatic hernia, duodenal atresia, esophageal atresia, abdominal wall defects, Hirschsprung's disease, sacrococcygeal teratoma, and short bowel syndrome. Articles were categorized based on their objectives in applying PROMs. Psychometrically robust PROMs were identified and described. Results Out of the 345 articles identified, 49 met the inclusion criteria. Seventeen focused on esophageal atresia and 14 on Hirschsprung's disease. Twenty-nine PROMs were identified, with 12 deemed psychometrically robust. Seven psychometrically robust PROMs were developed using patient input in the primary item generation. Most PROMs were applied to advance understanding of conditions and/or treatment and fewer were developed or psychometrically evaluated. No PROMs were assessed for their impact or incorporated into an implementation study. Conclusions This review reveals gaps in the application of PROMs in recent pediatric surgical research. Emphasis should be placed on the development and utilization of psychometrically robust PROMs, broadening the scope of covered diseases, conducting impact assessments, and evaluating implementation strategies

Physical Origin of the Boson Peak Deduced from a Two-Order-Parameter Model of Liquid

We propose that the boson peak originates from the (quasi-) localized vibrational modes associated with long-lived locally favored structures, which are intrinsic to a liquid state and are randomly distributed in a sea of normal-liquid structures. This tells us that the number density of locally favored structures is an important physical factor determining the intensity of the boson peak. In our two-order-parameter model of the liquid-glass transition, the locally favored structures act as impurities disturbing crystallization and thus lead to vitrification. This naturally explains the dependence of the intensity of the boson peak on temperature, pressure, and fragility, and also the close correlation between the boson peak and the first sharp diffraction peak (or prepeak).Comment: 5 pages, 1 figure, An error in the reference (Ref. 7) was correcte