478 research outputs found
Thermodynamic evidence for valley-dependent density of states in bulk bismuth
Electron-like carriers in bismuth are described by the Dirac Hamiltonian,
with a band mass becoming a thousandth of the bare electron mass along one
crystalline axis. The existence of three anisotropic valleys offers electrons
an additional degree of freedom, a subject of recent attention. Here, we map
the Landau spectrum by angle-resolved magnetostriction, and quantify the
carrier number in each valley: while the electron valleys keep identical
spectra, they substantially differ in their density of states at the Fermi
level. Thus, the electron fluid does not keep the rotational symmetry of the
lattice at low temperature and high magnetic field, even in the absence of
internal strain. This effect, reminiscent of the Coulomb pseudo-gap in
localized electronic states, affects only electrons in the immediate vicinity
of the Fermi level. It presents the most striking departure from the
non-interacting picture of electrons in bulk bismuth.Comment: 6 pages, 3 Figure
Huge First-Order Metamagnetic Transition in the Paramagnetic Heavy-Fermion System CeTiGe
We report on the observation of large, step-like anomalies in the
magnetization (\,/Ce), in the magnetostriction
(), and in the magnetoresistance in
polycrystals of the paramagnetic heavy-fermion system CeTiGe at a critical
magnetic field 12.5\,T at low temperatures. The size of
these anomalies is much larger than those reported for the prototypical
heavy-fermion metamagnet CeRuSi. Furthermore, hysteresis between
increasing and decreasing field data indicate a real thermodynamic, first-order
type of phase transition, in contrast to the crossover reported for
CeRuSi. Analysis of the resistivity data shows a pronounced decrease of
the electronic quasiparticle mass across . These results establish CeTiGe
as a new metamagnetic Kondo-lattice system, with an exceptionally large,
metamagnetic transition of first-order type at a moderate field.Comment: 5 pages, 4 figure
Quantum Griffiths phase in CePd(1-x)Rh(x) with x ~ 0.8
The magnetic field dependence of the magnetisation () and the temperature
dependence of the ac susceptibility () of CePd(1-x)Rh(x) single
crystals with are analysed within the frame of the
quantum Griffiths phase scenario, which predicts and
with . All vs and
vs data follow the predicted power-law behaviour. The parameter
, extracted from , is very sensitive to the Rh content
and varies systematically with from -0.1 to 0.4. The value of ,
derived from measurements on a \cpr single crystal, seems to be rather
constant, , in a broad range of temperatures between 0.05
and 2 K and fields up to about 10 T. All observed signatures and the
values are thus compatible with the quantum Griffiths scenario.Comment: 4 pages, 3 figure
A interação socio/afetivo/cultural num contexto de ensino e aprendizagem : uma abordagem vigotskiana
O trabalho objetivou analisar, ancorado na teoria de Vigostski, o processo de ensino e aprendizagem durante a construção de conceitos vinculados as disciplinas de Matemática, e Ciências Naturais. A formação de canteiros com plantas medicinais (hortelã, erva cidreira, etc) mediou as ações desenvolvidas com 15 crianças (com necessidade de acompanhamento mais próximo) de uma 6 série do Ciclo I da educação básica. As atividades centradas no referencial vigotskiano consistiram em levar em conta não só aprendizagem apoiada na maturação do aluno, mas naquilo que ainda não está maduro nele e oferecer-lhe possibilidades (mediação) para ultrapassar barreiras decorrentes dessa imaturidade. Concluímos que a formação de conceitos se fundamenta não apenas no processo cognitivo, mas sim, na dimensão cognitiva, interligada na afetiva e, conseqüentemente, na social
Quantum wire junctions breaking time reversal invariance
We explore the possibility to break time reversal invariance at the junction
of quantum wires. The universal features in the bulk of the wires are described
by the anyon Luttinger liquid. A simple necessary and sufficient condition for
the breaking of time reversal invariance is formulated in terms of the
scattering matrix at the junction. The phase diagram of a junction with generic
number of wires is investigated in this framework. We give an explicit
classification of those critical points which can be reached by bosonization
and study the interplay between their stability and symmetry content.Comment: Extended version (Appendices C and D and some references added, typos
corrected) to appear in Phys. Rev.
H - T phase diagram of YbCo2Si2 with H // [100]
We report on the first high-resolution dc-magnetisation () measurements on
a single crystal of \ycs. was measured down to 0.05 K and in fields up to
12 T, with the magnetic field parallel to the crystallographic direction
[100]. Two antiferromagnetic (AFM) phase transitions have been detected in a
field T at K and K, in form of a
sharp cusp and a sudden drop in , respectively. These signatures
suggest that the phase transitions are order at and
order at . The upper transition is suppressed by a critical field
T. The field-dependent magnetisation shows two hysteretic
metamagnetic-like steps at the lowest temperature, followed by a sharp kink,
which separates the AFM region from the paramagnetic one. The magnetic
phase diagram of \ycs has been deduced from the isothermal and isofield curves.
Four AFM regions were identified which are separated by and
order phase-transition lines.Comment: 5 Pages, 3 figure
Personality structure in bottlenose dolphins (Tursiops truncatus).
Comparative studies can help identify selective pressures that contributed to species differences in the number and composition of personality domains. Despite being adapted to an aquatic lifestyle and last sharing a common ancestor with primates some 95 million years ago, bottlenose dolphins (Tursiops truncatus) resemble nonhuman primate species in several behavioral and cognitive traits. For example, like chimpanzees (Pan troglodytes), dolphins live in fission-fusion societies, use tools, and have relatively large brains. To determine the extent to which these and other factors contribute to the evolution of personality structure, we examined personality structure in 134 bottlenose dolphins. Personality was measured in 49 dolphins using a 42-item questionnaire, and in 85 dolphins using a version of the questionnaire that included 7 additional items. We found four domains. Three—openness, sociability, and disagreeableness—resembled personality domains found in nonhuman primates and other species. The fourth, directedness, was a blend of high conscientiousness and low neuroticism, and was unique to dolphins. Unlike other species, dolphins did not appear to have a strong dominance domain. The overlap in personality structure between dolphins and other species suggests that selective pressures, such as those related to group structure, terrestrial lifestyles, morphology, and social learning or tool use are not necessary for particular domains to evolve within a species
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