307 research outputs found
Daday Jenő (1915–1927): „Monographie systématique des Phyllopodes conchostracés” revideált irodalomjegyzéke = Revised list of references to Daday de Deés (1915–1927): Monographie systématique des Phyllopodes conchostracés
Resistive switching in β-SrV6O15
Abstract.: We investigate the pressure and temperature behavior of current-dependent resistivity of β-SrV6O15. We observe a switching between states of different resistivities in the insulating state of β-SrV6O15. In the low pressure phase, the resistive switching appears at temperatures below the semiconductor-insulator transition. In the high pressure phase, under ~1.6GPa, the switching appears in the temperature range of the phase transition. The existence of switching may imply an important role of strontium off-stoichiometry for the electrical transport in β-SrV6O15. No electric-field-induced enhancement of the conductivity is observed. However, the conduction is significantly nonlinear under ~1.6GPa, indicating that the charge order pattern in the high pressure phase is considerably different from that of the low pressure phas
Magnetotransport studies of Superconducting PrFeAsTeO
We report a detailed study of the electrical transport properties of single
crystals of PrFeAsTeO, a recently discovered iron-based
superconductor. Resistivity, Hall effect and magnetoresistance are measured in
a broad temperature range revealing the role of electrons as dominant charge
carriers. The significant temperature dependence of the Hall coefficient and
the violation of Kohler's law indicate multiband effects in this compound. The
upper critical field and the magnetic anisotropy are investigated in fields up
to 16 T, applied parallel and perpendicular to the crystallographic c-axis.
Hydrostatic pressure up to 2 GPa linearly increases the critical temperature
and the resistivity residual ratio. A simple two-band model is used to describe
the transport and magnetic properties of PrFeAsTeO. The
model can successfully explain the strongly temperature dependent negative Hall
coefficient and the high magnetic anisotropy assuming that the mobility of
electrons is higher than that of holes
Beyond the Linearity of Current-Voltage Characteristics in Multiwalled Carbon Nanotubes
We present local and non-local electron transport measurements on individual
multi-wall nanotubes for bias voltage between 0 and about 4 V. Local
current-voltage characteristics are quite linear. In contrast, non-local
measurements are highly non-linear; the differential non-local conductance can
even become negative in the high-bias regime. We discuss the relationship
between these results and transport parameters such as the elastic length, the
number of current carrying shells, and the number of conducting modes.Comment: 5 pages, 5 figure
Magnetic-field-induced transition in BaVS3
The metal-insulator transition (MIT) of BaVS3 is suppressed under pressure
and above the critical pressure of p~2GPa the metallic phase is stabilized. We
present the results of detailed magnetoresistivity measurements carried out at
pressures near the critical value, in magnetic fields up to B=12T. We found
that slightly below the critical pressure the structural tetramerization --
which drives the MIT -- is combined with the onset of magnetic correlations. If
the zero-field transition temperature is suppressed to a sufficiently low value
(T_MI<15K), the system can be driven into the metallic state by application of
magnetic field. The main effect is not the reduction of T_MI with increasing B,
but rather the broadening of the transition due to the applied magnetic field.
We tentatively ascribe this phenomenon to the influence on the magnetic
structure coupled to the bond-order of the tetramers.Comment: 5 pages, 5 figure
The electronic structure and the phases of BaVS3
BaVS3 is a moderately correlated d-electron system with a rich phase diagram.
To construct the corresponding minimal electronic model, one has to decide
which d-states are occupied, and to which extent. The ARPES experiment
presented here shows that the behavior of BaVS3 is governed by the coexistence
of wide-band (A_1g) and narrow-band (twofold degenerate E) d-electrons. We
sketch a lattice fermion model which may serve as a minimal model of BaVS3.
This serves foremost for the understanding of the metal-insulator in pure BaVS3
and its absence in some related compounds. The nature of the low temperature
magnetic order differs for several systems which may be described in terms of
the same electron model. We describe several recent experiments which give
information about magnetic order at high pressures. In particular, we discuss
field-induced insulator-to-metal transition at slightly subcritical pressures,
and an evidence for magnetic order in the high-pressure metallic phase. The
phase diagram of Sr-doped BaVS3 is also discussed. The complexity of the phases
of BaVS3 arises from the fact that it is simultaneously unstable against
several kinds of instabilities.Comment: Presented at the International Conference on Magnetism 2006 (Kyoto),
6 pages, 9 figure
Collective Charge Excitations below the Metal-to-Insulator Transition in BaVS3
The charge response in the barium vanadium sulfide (BaVS3) single crystals is
characterized by dc resistivity and low frequency dielectric spectroscopy. A
broad relaxation mode in MHz range with huge dielectric constant ~= 10^6
emerges at the metal-to-insulator phase transition TMI ~= 67 K, weakens with
lowering temperature and eventually levels off below the magnetic transition
Tchi ~= 30 K. The mean relaxation time is thermally activated in a manner
similar to the dc resistivity. These features are interpreted as signatures of
the collective charge excitations characteristic for the orbital ordering that
gradually develops below TMI and stabilizes at long-range scale below Tchi.Comment: 6 pages, 3 figures, submitted to PR
L4Fe2As2Te1-xO4-yFy (L = Pr, Sm, Gd): a layered oxypnictide superconductor with Tc up to 45 K
The synthesis, structural and physical properties of iron lanthanide
oxypnictide superconductors, L4Fe2As2Te1-xO4 (L = Pr, Sm, Gd), with transition
temperature at ~ 25 K are reported. Single crystals have been grown at high
pressure using cubic anvil technique. The crystal structure consists of layers
of L2O2 tetrahedra separated by alternating layers of chains of Te and of
Fe2As2 tetrahedra: -L2O2-Te-L2O2-Fe2As2-L2O2-Te-L2O2- (space group: I4/mmm, a ~
4.0, c ~ 29.6 {\AA}). Substitution of oxygen by fluorine increases the critical
temperature, e.g. in Gd4Fe2As2Te1-xOyF4-y up to 45 K. Magnetic torque
measurements reveal an anisotropy of the penetration depths of ~31.Comment: 8 figures, 4 table
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