26 research outputs found
Hall effect in the vicinity of quantum critical point in Tm1-xYbxB12
The angular, temperature and magnetic field dependences of Hall resistance
roH for the rare-earth dodecaboride solid solutions Tm1-xYbxB12 have been
studied in a wide vicinity of the quantum critical point (QCP) xC~0.3. The
measurements performed in the temperature range 1.9-300 K on high quality
single crystals allowed to find out for the first time in these fcc compounds
both an appearance of the second harmonic contribution in ro2H at QCP and its
enhancement under the Tm to ytterbium substitution and/or with increase of
external magnetic field. When the Yb concentration x increases a negative
maximum of a significant amplitude was shown to appear on the temperature
dependences of Hall coefficient RH(T) for the Tm1-xYbxB12 compounds. Moreover,
a complicated activation type behavior of the Hall coefficient is observed at
intermediate temperatures for x>0.5 with activation energies Eg~200K and
Ea~55-75K in combination with the sign inversion of RH(T) at low temperatures
in the coherent regime. The density of states renormalization effects are
analyzed within the variation of Yb concentration and the features of the
charge transport in various regimes (charge gap formation, intra-gap manybody
resonance and coherent regime) are discussed in detail in Tm1-xYbxB12 solid
solutions.Comment: 38 pages including 10 figures, 70 reference
The Guarguaraz Complex and the Neoproterozoic-Cambrian evolution of southwestern Gondwana: Geochemical signatures and geochronological constraints
The Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage, associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which are interpreted as Ordovician dismembered ophiolites. Two kinds of dikes are recognized, a group associated with the metasediments and the other ophiolite-related. Both have N-MORB signatures, with εNd between +3.5 and +8.2, indicating a depleted source, and Grenville model ages between 0.99 and 1.62 Ga. A whole-rock Sm-Nd isochron yielded an age of 655 ± 76 Ma for these mafic rocks, which is compatible with cianobacteria and acritarchae recognized in the clastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)-Cambrian age of deposition. The Guarguaraz metasedimentary-ophiolitic complex represents, therefore, a remnant of an oceanic basin developed to the west of the Grenville-aged Cuyania terrane during the Neoproterozoic. The southernmost extension of these metasedimentary sequences in Cordón del Portillo might represent part of this platform and not fragments of the Chilenia terrane. An extensional event related to the fragmentation of Rodinia is represented by the mafic and ultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor and slices of the Cuyania terrane (Las Yaretas Gneisses) in tectonic contact with the Neoproterozoic metasediments, marking the Devonian western border of Gondwana. © 2009 Elsevier Ltd. All rights reserved.Fil: López de Azarevich, Vanina L.. Universidad Nacional de Salta; ArgentinaFil: Escayola, Monica Patricia. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Salta; ArgentinaFil: Azarevich, Miguel Basilio. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Salta; Argentina. Universidad Nacional de Salta; ArgentinaFil: Pimentel, Márcio M.. Universidade do BrasÃlia; BrasilFil: Tassinari, Colombo. Universidade de Sao Paulo; Brasi
The Guarguaraz Complex and the Neoproterozoic-Cambrian evolution of southwestern Gondwana: Geochemical signatures and geochronological constraints
The Guarguaraz Complex, in western Argentina, comprises a metasedimentary assemblage, associated with mafic sills and ultramafic bodies intruded by basaltic dikes, which are interpreted as Ordovician dismembered ophiolites. Two kinds of dikes are recognized, a group associated with the metasediments and the other ophiolite-related. Both have N-MORB signatures, with epsilon(Nd) between +3.5 and +8.2, indicating a depleted source, and Grenville model ages between 0.99 and 1.62 Ga. A whole-rock Sm-Nd isochron yielded an age of 655 +/- 76 Ma for these mafic rocks, which is compatible with cianobacteria and acritarchae recognized in the clastic metasedimentary platform sequences, that indicate a Neoproterozoic (Vendian)-Cambrian age of deposition. The Guarguaraz metasedimentary-ophiolitic complex represents, therefore, a remnant of an oceanic basin developed to the west of the Grenville-aged Cuyania terrane during the Neoproterozoic. The southernmost extension of these metasedimentary sequences in Cordon del Portillo might represent part of this platform and not fragments of the Chilenia terrane. An extensional event related to the fragmentation of Rodinia is represented by the mafic and ultramafic rocks. The Devonian docking of Chilenia emplaced remnants of ocean floor and slices of the Cuyania terrane (Las Yaretas Gneisses) in tectonic contact with the Neoproterozoic metasediments, marking the Devonian western border of Gondwana. (C) 2009 Elsevier Ltd. All rights reserved
Evidence of electronic phase separation in the strongly correlated semiconductor YbB12
The studies of high-quality single-domain crystals of YbB12 were carried out
by the precise x-ray diffraction technique in combination with the low
temperature polarized THz - infrared spectroscopy and accurate magnetotransport
measurements. It has been shown for the first time that this archetypal
strongly correlated system with a metal-insulator transition to a mysterious
dielectric ground state with a metal Fermi surface (Science 362, 65-69 (2018)
and ibid 362, 32-33 (2018)) is actually a heterogeneous compound in the regime
of electronic phase separation. Changes in the configuration of the discovered
dynamic charge stripes are investigated upon cooling, as a result, a conclusion
is drawn in favor of a crossover between different patterns of the filamentary
electronic structure penetrating the semiconducting matrix of YbB12. We argue
that the discovery of stripes in YbB12 is fundamental, elucidating the nature
of exotic dielectric state in Kondo insulators.Comment: 12 pages including 4 figure