Anomalous Nernst Effect in Dirac Semimetal Cd3As2

Dirac and Weyl semimetals display a host of novel properties. In Cd$_3$As$_2$, the Dirac nodes lead to a protection mechanism that strongly suppresses backscattering in zero magnetic field, resulting in ultrahigh mobility ($\sim$ 10$^7$ cm$^2$ V$^{-1}$ s$^{-1}$). In applied magnetic field, an anomalous Nernst effect is predicted to arise from the Berry curvature associated with the Weyl nodes. We report observation of a large anomalous Nernst effect in Cd$_3$As$_2$. Both the anomalous Nernst signal and transport relaxation time $\tau_{tr}$ begin to increase rapidly at $\sim$ 50 K. This suggests a close relation between the protection mechanism and the anomalous Nernst effect. In a field, the quantum oscillations of bulk states display a beating effect, suggesting that the Dirac nodes split into Weyl states, allowing the Berry curvature to be observed as an anomalous Nernst effect.Comment: 13 pages, 7 figure

Evidence for massive bulk Dirac Fermions in Pb1−x_{1-x}Snx_xSe from Nernst and thermopower experiments

The lead chalcogenides (Pb,Sn)Te and (Pb,Sn)Se are the first examples of topological crystalline insulators (TCI) predicted \cite{Fu,Hsieh} (and confirmed \cite{Hasan,Story,Takahashi}) to display topological surface Dirac states (SDS) that are protected by mirror symmetry. A starting premise \cite{Hsieh} is that the SDS arise from bulk states describable as massive Dirac states \cite{Wallis,Svane}, but this assumption is untested. Here we show that the thermoelectric response of the bulk states display features specific to the Dirac spectrum. We show that, in the quantum limit, the lowest Landau Level (LL) is singly spin-degenerate, whereas higher levels are doubly degenerate. The abrupt change in spin degeneracy leads to a large step-decrease in the thermopower $S_{xx}$. In the lowest LL, $S_{xx}$ displays a striking linear increase vs. magnetic field. In addition, the Nernst signal undergoes an anomalous sign change when the bulk gap inverts at 180 K.Comment: 16 pages, 8 figure

Correlation of Crystal Quality and Extreme Magnetoresistance of WTe2_2

High quality single crystals of WTe$_2$ were grown using a Te flux followed by a cleaning step involving self-vapor transport. The method is reproducible and yields consistently higher quality single crystals than are typically obtained via halide assisted vapor transport methods. Magnetoresistance (MR)values at 9 Tesla and 2 Kelvin as high as 1.75 million \%, nearly an order of magnitude higher than previously reported for this material, were obtained on crystals with residual resistivity ratio (RRR) of approximately 1250. The MR follows a near B$^2$ law (B = 1.95(1)) and, assuming a semiclassical model, the average carrier mobility for the highest quality crystal was found to be ~167,000 cm$^2$/Vs at 2 K. A correlation of RRR, MR ratio and average carrier mobility ($\mu_{avg}$) is found with the cooling rate during the flux growth.Comment: 7 pages, 3 figures, 1 tabl

Conserved and unique transcriptional features of pharyngeal arches in the skate (Leucoraja erinacea) and evolution of the jaw

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hirschberger, C., Sleight, V. A., Criswell, K. E., Clark, S. J., & Gillis, J. A. Conserved and unique transcriptional features of pharyngeal arches in the skate (Leucoraja erinacea) and evolution of the jaw. Molecular Biology and Evolution, (2021): msab123, https://doi.org/10.1093/molbev/msab123The origin of the jaw is a long-standing problem in vertebrate evolutionary biology. Classical hypotheses of serial homology propose that the upper and lower jaw evolved through modifications of dorsal and ventral gill arch skeletal elements, respectively. If the jaw and gill arches are derived members of a primitive branchial series, we predict that they would share common developmental patterning mechanisms. Using candidate and RNAseq/differential gene expression analyses, we find broad conservation of dorsoventral patterning mechanisms within the developing mandibular, hyoid and gill arches of a cartilaginous fish, the skate (Leucoraja erinacea). Shared features include expression of genes encoding members of the ventralising BMP and endothelin signalling pathways and their effectors, the joint markers nkx3.2 and gdf5 and pro-chondrogenic transcription factor barx1, and the dorsal territory marker pou3f3. Additionally, we find that mesenchymal expression of eya1/six1 is an ancestral feature of the mandibular arch of jawed vertebrates, while differences in notch signalling distinguish the mandibular and gill arches in skate. Comparative transcriptomic analyses of mandibular and gill arch tissues reveal additional genes differentially expressed along the dorsoventral axis of the pharyngeal arches, including scamp5 as a novel marker of the dorsal mandibular arch, as well as distinct transcriptional features of mandibular and gill arch muscle progenitors and developing gill buds. Taken together, our findings reveal conserved patterning mechanisms in the pharyngeal arches of jawed vertebrates, consistent with serial homology of their skeletal derivatives, as well as unique transcriptional features that may underpin distinct jaw and gill arch morphologies.This work was supported by a Biotechnology and Biological Sciences Research Council Doctoral Training Partnership studentship to CH, by a Wolfson College Junior Research Fellowship and MBL Whitman Early Career Fellowship to VAS, and by a Royal Society University Research Fellowship (UF130182 and URF\R\191007), Royal Society Research Grant (RG140377) and University of Cambridge Sir Isaac Newton Trust Grant (14.23z) to JAG

The magnetic phase diagram of underdoped YBa2Cu3Oy inferred from torque magnetization and thermal conductivity

Strong evidence for charge-density correlation in the underdoped phase of the cuprate YBa2Cu3Oy was obtained by nuclear magnetic resonance (NMR) and resonant x-ray scatter- ing. The fluctuations were found to be enhanced in strong magnetic fields. Recently, 3D (three dimensional) charge-density wave (CDW) formation with long-range order (LRO) was observed by x-ray diffraction in H >15 T. To elucidate how the CDW transition impacts the pair condensate, we have used torque magnetization to 45 T and thermal conductivity $\kappa_{xx}$ to construct the magnetic phase diagram in untwinned crystals with hole density p = 0.11. We show that the 3D CDW transitions appear as sharp features in the susceptibility and $\kappa_{xx}$ at the fields HK and Hp, which define phase boundaries in agreement with spectroscopic techniques. From measurements of the melting field Hm(T) of the vortex solid, we obtain evidence for two vortex solid states below 8 K. At 0.5 K, the pair condensate appears to adjust to the 3D CDW by a sharp transition at 24 T between two vortex solids with very different shear moduli. At even higher H (42 T) the second vortex solid melts to a vortex liquid which survives to fields well above 45 T. de Haas-van Alphen oscillations appear at fields 24-28 T, below the lower bound for the upper critical field Hc2.Comment: 7 pages, 8 figures; New version of previous posting, reporting torque measurements to 45 Tesla and final magnetic phase diagra

Liver Transplantation for Advanced Liver Disease with Alpha-1antitrypsin Deficiency

ALPHA-1-antitrypsin deficiency associated with chronic obstructive airway disease was recognized in 1963 by Laurell and Ericksson.1 In 1969, Sharp2 described the first cases of alpha-1-antitrypsin-deficiency disease in children with cirrhosis. Since then, this inborn error has been recognized as one of the more common factors in cirrhosis of infancy and childhood,3 including “neonatal hepatitis.”4 Alpha-1-antitrypsin is a glycoprotein that accounts for a major portion of the alpha-1 globulin fraction of the serum.5 It is responsible for approximately 90 per cent of the antitrypsin activity6 of the serum, and it also inhibits several other plasma enzymes, including plasmin,7 elastase,8 collagenase,9 and. © 1980, Massachusetts Medical Society. All rights reserved