196,180 research outputs found
Nonlinear c-axis transport in Bi2Sr2CaCu2O8+delta from two-barrier tunneling
No full textMotivated by the peculiar features observed through intrinsic tunneling spectroscopy of Bi2Sr2CaCu2O8+delta mesas in the normal state, we have extended the normal-state two-barrier model for the c-axis transport [M. Giura , Phys. Rev. B 68, 134505 (2003)] to the analysis of dI/dV curves. We have found that the purely normal-state model reproduces all the following experimental features: (a) the parabolic V dependence of dI/dV in the high-T region (above the conventional pseudogap temperature), (b) the emergence and the nearly voltage-independent position of the "humps" from this parabolic behavior by lowering the temperature, and (c) the crossing of the absolute dI/dV curves at a characteristic voltage V-x. Our findings indicate that conventional tunneling can be at the origin of most of the uncommon features of the c-axis transport in Bi2Sr2CaCu2O8+delta. We have compared our calculations to experimental data taken in severely underdoped and slightly underdoped Bi2Sr2CaCu2O8+delta small mesas. We have found good agreement between the data and the calculations, without any shift of the calculated dI/dV on the vertical scale. In particular, in the normal state (above T-*) simple tunneling reproduces the experimentaldI/dV quantitatively. Below T-* quantitative discrepancies are limited to a simple rescaling of the voltage in the theoretical curves by a factor similar to 2. The need for such modifications remains an open question, that might be connected to a change of the charge of a fraction of the carriers across the pseudogap opening
Experimental study of the resistivity tensor in BSCCO crystals by means of multi-terminal measurements
No full textWe present measurements of the in-plane (ρab) and out-of-plane (ρc) resistivity in BSCCO single crystals. The resistivities are measured simultaneously on the same sample by means of a multi-terminal technique. Results are presented in the normal state and in the superconducting state, both in presence and in absence of an applied magnetic field. We underline the main differences with standard four probe measurements, showing in which cases the new method is strictly needed to avoid erroneous results. The technique is also able to test the locality of the dynamic: we present an accurate experimental analysis of the temperature and magnetic field ranges where the dynamic is local or non local. We finally show that above Tc this method gives results reliable enough to allow for a detailed study of the excess conductivity. We find that the data do not follow simple Aslamazov-Larkin laws in temperature ranges wider 1K, and that an accurate description of the data over a wide temperature range must include the effects of a short-wavelength cutoff in the fluctuational spectrum
Experimental study of conductivity in Bi2Sr2CaCu2O8+x crystals by means of multiterminal measurements
No full textResistivity measurements have been demonstrated to be a powerful tool for the investigation of vortex dynamics. Multiterminal measurements have been widely used to analyze the correlation of Vortices across the planes (pseudo-Giaever experiment). We present a large set of measurements in different configurations for various magnetic field strengths and orientations, both in the normal state and in the mixed state. We will discuss a large class of experimental features relating them to the correlation between the CuO planes. (C) 2000 Elsevier Science B.V. All rights reserved
Anisotropic properties of the fluctuational conductivity in YBCO
No full textWe report on resistive transitions in YBCO films as a function of strength and orientation of the applied magnetic field. Angular behaviour is found to be markedly different in the upper and lower part of the transition. At high dissipation level, an angular scaling behaviour is observed, following the anisotropic Lawrence-Doniach expression for the upper critical field. The scaling breaks down at the midpoint of the transition. No scaling is observed at lower temperatures, even if different angular scaling functions are used. The results are very well interpreted in terms of superconducting fluctuations above rho/rho(n)=0.5 and pinning phenomena below
IV measurements in Bi:2212 film in magnetic fields: scaling behavior
No full textEds. L. Zhou, H.W.Weber, E.W.Colling
Interlayer tunnel and thermal activation in c-axis transport in Bi2Sr2CaCu2O8+d
No full textWe present a phenomenological model for the electrical transport in double-layered cuprates, based on the existence of two energy
barriers along the c-axis. The model is applied to measurements of the dc resistivity in Bi2Sr2CaCu2O8+d single crystals. We find that the
model gives a comprehensive description of the out-of-plane normal resistivity qc at various doping d. Once the normal state has been
determined, it is possible to obtain the fraction g(T, d) of the carriers that, below the pseudogap temperature T *, do not participate to the
c-axis conductivity. We find that all the curves g(T, d) collapse onto a single universal curve g[T/T *(d)]
Tunnel and thermal c-axis transport in BSCCO in the normal and pseudogap states
No full textWe consider the problem of c-axis transport in double-layered cuprates, in
particular with reference to Bi2Sr2 CaCu2O8+δ compounds. We exploit the
effect of the two barriers on the thermal and tunnel transport. The resulting
model is able to describe accurately the normal state c-axis resistivity in
Bi2Sr2 CaCu2 O8+δ , from the underdoped side up to the strongly overdoped.
We extend the model, without introducing additional parameters, in order to
allow for the decrease of the barrier when an external voltage bias is applied.
The extended model is found to describe properly the c -axis resistivity for
small voltage bias above the pseudogap temperature T ∗, the c -axis resistivity
for large voltage bias even below Tc , and the differential d I /d V curves taken in mesa structures
GLASSY BEHAVIOR IN RESISTIVE MEASUREMENTS IN BI2SR2CACU2OX
No full textWe present a large set of measurements of resistance as a function of magnetic field at fixed temperatures, and as a function of temperature at fixed magnetic field, in epitaxial highly-oriented Bi:2212 films. A new model of the glassy dynamics of the flux lines is developed, where the leading dissipative term is the phase slippage of the flux lines over a disordered network of highly-damped Josephson junctions, with an activation process given by a Vogel-Fulcher equation. The glass-to-liquid temperature obtained by the fits reproduces the irreversibility line reported in the literature. The proposed phenomenological model is able to fit all the data from low temperatures up to T(c), for the accessible magnetic field range
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