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Violation of Ohm’s law in a Weyl metal
Shin, Dongwoo,Lee, Yongwoo,Sasaki, M.,Jeong, Yoon Hee,Weickert, Franziska,Betts, Jon B.,Kim, Heon-Jung,Kim, Ki-Seok,Kim, Jeehoon Nature Publishing Group, a division of Macmillan P 2017 Nature materials Vol.16 No.11
Ohm’s law is a fundamental paradigm in the electrical transport of metals. Any transport signatures violating Ohm’s law would give an indisputable fingerprint for a novel metallic state. Here, we uncover the breakdown of Ohm’s law owing to a topological structure of the chiral anomaly in the Weyl metal phase. We observe nonlinear I–V characteristics in Bi<SUB>0.96</SUB>Sb<SUB>0.04</SUB> single crystals in the diffusive limit, which occurs only for a magnetic-field-aligned electric field (E∥B). The Boltzmann transport theory with the charge pumping effect reveals the topological-in-origin nonlinear conductivity, and it leads to a universal scaling function of the longitudinal magnetoconductivity, which completely describes our experimental results. As a hallmark of Weyl metals, the nonlinear conductivity provides a venue for nonlinear electronics, optical applications, and the development of a topological Fermi-liquid theory beyond the Landau Fermi-liquid theory.
Oh, Dong Hoon,Oh, Daeyoung,Son, Hyeon,Webster, Maree J,Weickert, Cyndi S,Kim, Seok Hyeon Springer 2014 JOURNAL OF NEURAL TRANSMISSION Vol.121 No.7
<P>Previous human postmortem studies have shown that expression of glutamate transporters (SLC1A2 and SLC1A3) and gamma-aminobutyric acid-synthesizing enzyme [glutamic acid decarboxylase 1 (GAD1)] are reduced in the dorsolateral prefrontal cortex (dlPFC) in subjects with major depressive disorder (MDD). However, no studies have explored the association between these two molecules and its related biological processes in MDD because of limited postmortem sample availability. Data sharing using the Stanley neuropathology consortium integrative database (SNCID), a web-based tool that integrates datasets from the same postmortem brain samples, allowed us to reanalyze existing postmortem data efficiently. We found two datasets where the mRNA levels of GAD1 and SLC1A2 in subregions of the dlPFC were significantly and marginally lower in subjects with MDD (n = 15) than in controls (n = 15) (p = 0.045 and 0.057, respectively). In addition, there was a positive correlation between these two molecules (n = 30, p < 0.05). Spearman's rank correlation analysis using all available datasets revealed that the expression levels of both GAD1 and SLC1A2 mRNAs were commonly correlated with the expression levels of several neuropathological markers in the dlPFC in all of the SNCID subjects (n = 60, p < 0.001). Most of these markers are known to be involved in the RAF/MEK/ERK signal transduction pathway. This exploratory study provides an initial step for future studies to investigate an association between the reductions in SLC1A2 and GAD1 mRNA expression and their relation to the attenuation of the RAF/MEK/ERK signaling pathway in the dlPFC in MDD. The integration of the existing archival data may shed light on one important aspect of the pathophysiology of MDD.</P>
Uniform Large-Area Free-Standing Silver Nanowire Arrays on Transparent Conducting Substrates
Feng, Yuyi,Kim, Kwang-Dae,Nemitz, Clayton A.,Kim, Paul,Pfadler, Thomas,Gerigk, Melanie,Polarz, Sebastian,Dorman, James A.,Weickert, Jonas,Schmidt-Mende, Lukas The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.8
<P>Arrays of silver nanowires have received increasing attention in a variety of applications such as surface-enhanced Raman scattering (SERS), plasmonic biosensing and electrode for photoelectric devices. However, until now, large scale fabrication of device-suitable silver nanowire arrays on supporting substrates has seen very limited success. Here we show the synthesis of free-standing silver nanowire arrays on indium-tin oxide (ITO) coated glass by pulsed electrodeposition into anodic aluminum oxide (AAO) templates. We use an in situ oxygen plasma cleaning process and a sputtered Ti layer to enhance the adhesion between the template and ITO glass. An ultrathin gold layer (2 nm) is deposited as a nucleation layer for the electrodeposition of silver. An unprecedented high level of uniformity and control of the nanowire diameter, spacing and length has been achieved. The absorption measurements show that the free-standing silver nanowire arrays possess tunable plasmonic resonances.</P>