667 research outputs found
Magnetotransport in Sr3PbO antiperovskite with three-dimensional massive Dirac electrons
Novel topological phenomena are anticipated for three-dimensional (3D) Dirac
electrons. The magnetotransport properties of cubic
antiperovskite, theoretically proposed to be a 3D massive Dirac electron
system, are studied. The measurements of Shubnikov-de Haas oscillations and
Hall resistivity indicate the presence of a low density ( ) of holes with an extremely small cyclotron mass of
0.01-0.06. The magnetoresistance is linear in
magnetic field with the magnitude independent of temperature. These results
are fully consistent with the presence of 3D massive Dirac electrons in . The chemical flexibility of the antiperovskites and our findings
in the family member, , point to their potential as a model
system in which to explore exotic topological phases
Trace element and stable isotope analyses of deep sea fish from the Sulu sea, Philippines
Thirty-five deep sea fishes belonging to 22 species and one unidentified specimen obtained from the Sulu Sea, located in the southwestern area of the Philippines were analyzed in the late 2002, for 23 trace elements using ICP-MS, HGAAS and CV-AAS. Predominant accumulation of strontium (Sr) was observed in all the samples. This stems from the fact that the whole body of fish was homogenized since Sr is known to accumulate in bones and hard tissues. Mercury concentrations in all the 36 samples were below the detection limit. Cadmium concentrations were generally below 1ìg/g dry weight (dw) except in Pterygotrigla spp. (4.29 ìg/g dw) and Sternoptyx pseudodiaphana (2.89 ìg/g dw). Concentrations of Pb were predominantly low with about 90% of the specimens having less than 1 ìg/g dw. In general, concentrations of Sr, Zn, Cu, Se and Cd appeared to increase with increasing depth of occurrence of the species.Manganese, Tl, Pb, Bi, In, Cs and As showed significant positive correlation (p < 0.05) with d15N, suggesting that these elements were biomagnified. To our knowledge, this is the first study reporting Tl biomagnification in fish. Rubidium and Cs showed significant positive correlation with d13C, implying that Rb and Cs would originate from offshore waters as oceanic plankton has high d13C. Comparing results from this study to the dietary standards and guidelines for Hg, Pb, Cu and Zn in fish and shellfish of the Ministry of Agriculture, Fisheries and Food of the United Kingdom,these levels were not high to warrant concern if they were to be consumed by humans. However, 16.7% of the fish samples had high Cr levels when compared with the Hong Kong’s safe limit of 4 ìg/g dw for Cr in sea food. This constitutes a health risk to humans, as Cr is potentially toxic
Majorana-fermion origin of the planar thermal Hall effect in the Kitaev magnet -RuCl
The field-induced quantum disordered state of layered honeycomb magnet
-RuCl is a prime candidate for Kitaev spin liquids hosting Majorana
fermions and non-Abelian anyons. Recent observations of anomalous planar
thermal Hall effect demonstrate a topological edge mode, but whether it
originates from Majorana fermions or bosonic magnons remains controversial.
Here we distinguish these origins from low-temperature measurements of
high-resolution specific heat and thermal Hall conductivity with rotating
in-plane fields. In the honeycomb bond direction, a distinct closure of the
low-energy bulk gap is observed concomitantly with the sign reversal of the
Hall effect. General discussions of topological bands show that this is the
hallmark of an angle-rotation-induced topological transition of fermions,
providing conclusive evidence for the Majorana-fermion origin of the thermal
Hall effect in -RuCl.Comment: 21 pages, 7 figure
Inverse-perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) : a platform for control of Dirac and Weyl fermions
This work was partly supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Nos. 24224010, 15K13523, JP15H05852, JP15K21717, and 17H01140), EPSRC (Grant No. EP/P024564/1), and the Alexander von Humboldt FoundationBulk Dirac electron systems have attracted strong interest for their unique magnetoelectric properties as well as their close relation to topological (crystalline) insulators. Recently, the focus has been shifting toward the role of magnetism in stabilizing Weyl fermions as well as chiral surface states in such materials. While a number of nonmagnetic systems are well known, experimental realizations of magnetic analogs are a key focus of current studies. Here, we report on the physical properties of a large family of inverse perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) in which we are able to not only stabilize 3D Dirac electrons at the Fermi energy but also chemically control their properties. In particular, it is possible to introduce a controllable Dirac gap, change the Fermi velocity, tune the anisotropy of the Dirac dispersion, and—crucially—introduce complex magnetism into the system. This family of compounds therefore opens up unique possibilities for the chemical control and systematic investigation of the fascinating properties of such topological semimetals.Publisher PDFPeer reviewe
Mtss1 promotes cell-cell junction assembly and stability through the small GTPase Rac1
Cell-cell junctions are an integral part of epithelia and are often disrupted in cancer cells during epithelial-to-mesenchymal transition (EMT), which is a main driver of metastatic spread. We show here that Metastasis suppressor-1 (Mtss1; Missing in Metastasis, MIM), a member of the IMD-family of proteins, inhibits cell-cell junction disassembly in wound healing or HGF-induced scatter assays by enhancing cell-cell junction strength. Mtss1 not only makes cells more resistant to cell-cell junction disassembly, but also accelerates the kinetics of adherens junction assembly. Mtss1 drives enhanced junction formation specifically by elevating Rac-GTP. Lastly, we show that Mtss1 depletion reduces recruitment of F-actin at cell-cell junctions. We thus propose that Mtss1 promotes Rac1 activation and actin recruitment driving junction maintenance. We suggest that the observed loss of Mtss1 in cancers may compromise junction stability and thus promote EMT and metastasis
The HERMES Dual-Radiator Ring Imaging Cerenkov Detector
The construction and use of a dual radiator Ring Imaging Cerenkov(RICH)
detector is described. This instrument was developed for the HERMES experiment
at DESY which emphasizes measurements of semi-inclusive deep-inelastic
scattering. It provides particle identification for pions, kaons, and protons
in the momentum range from 2 to 15 GeV, which is essential to these studies.
The instrument uses two radiators, C4F10, a heavy fluorocarbon gas, and a wall
of silica aerogel tiles. The use of aerogel in a RICH detector has only
recently become possible with the development of clear, large homogeneous and
hydrophobic aerogel. A lightweight mirror was constructed using a newly
perfected technique to make resin-coated carbon-fiber surfaces of optical
quality. The photon detector consists of 1934 photomultiplier tubes for each
detector half, held in a soft steel matrix to provide shielding against the
residual field of the main spectrometer magnet.Comment: 25 pages, 23 figure
Charge-neutral fermions and magnetic field-driven instability in insulating YbIr₃Si₇
Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr₃Si₇ reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr₃Si₇ is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures
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