Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNernst Effect in NdBa_2[Cu_{1-y}Ni_y]_3O_{7-delta}
283
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In NdBa_2[Cu_{1-y}Ni_y]_3O_{7-delta}, magnetic Ni-impurities suppress Tc but at the same time the pseudogap is strongly enhanced. This unique feature makes it an ideal system to study possible relations between the anomalous Nernst effect, superconductivity and the pseudogap. We present Nernst effect measurements on a series of optimally doped (O_7) and underdoped (O_{6.8}) samples with Ni contents ranging from y=0 to 0.12. In all samples an onset of the Nernst signal is found at T^ u > Tc. For the optimally doped samples T^ u and Tc decrease simultaneously with increasing Ni content. The underdoped samples show a different behavior, i.e. the onset of the Nernst signal is hardly affected by increasing the Ni content from y=0 to 0.03. Irrespective of the oxygen content, T^ u clearly does not track the enhanced pseudogap temperature T*.
rate research
Read More
We report the first Nernst effect measurement on the new iron-based superconductor LaO$_{1-x}$F$_{x}$FeAs $(x=0.1)$. In the normal state, the Nernst signal is negative and very small. Below $T_{c}$ a large positive peak caused by vortex motion is observed. The flux flowing regime is quite large compared to conventional type-II superconductors. However, a clear deviation of the Nernst signal from normal state background and an anomalous depression of off-diagonal thermoelectric current in the normal state between $T_{c}$ and 50 K are observed. We propose that this anomaly in the normal state Nernst effect could correlate with the SDW fluctuations.
We present a study of the Nernst effect in amorphous 2D superconductor InO$_x$, whose low carrier density implies low phase rigidity and strong superconducting phase fluctuations. Instead of presenting the abrupt jump expected at a BCS transition, the Nernst signal evolves continuously through the superconducting transition as previously observed in underdoped cuprates. This contrasts with the case of Nb$_{0.15}$Si$_{0.85}$, where the Nernst signal due to vortices below T$_{c}$ and by Gaussian fluctuations above are clearly distinct. The behavior of the ghost critical field in InO$_x$ points to a correlation length which does not diverge at $T_c$, a temperature below which the amplitude fluctuations freeze, but phase fluctuations survive.
We have studied the oxygen-isotope effect on the superconducting transition temperature $T_{c}$ in overdoped Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-delta}$ with $x$ = 0.10, 0.20, and 0.25. We find the oxygen-isotope exponent $alpha_{O}$ to be small ($sim$0.02) for $x$ = 0.10 but substantial ($sim$0.1) for $x$ = 0.20 and 0.25. The doping level above which $alpha_{O}$ increases sharply coincides with a quantum critical point where the normal-state pseudogap starts to diminish. The present isotope-effect experiments provide direct and quantitative constraints on the pairing mechanism of high-temperature superconductivity in cuprates.
The intragrain pinning in high-$T_c$ superconductor compounds Y$_{1-x}$RE$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-delta}$ with low concentration of RE (La, Ce, Pr) was investigated. Magnetic and transport measurements reveal that the pinning is maximal for the concentration of heterovalent RE such that the average distance between the impurity ions in the plane of rare-earth elements close to the diameter of Abrikosov vortices in YBCO.
I-V characteristics of polycrystalline Y(1-x)CaxBa2Cu3O(7-{delta}) samples (x=0.025 and 0.20) have been measured at different temperatures and magnetic fields in the range 0.1 T-6.9 T. The scaling behavior has been established for both samples at all magnetic fields. The dynamic exponent z displays some morphology dependence with higher value for small grain size sample Y0.8Ca0.2Ba2Cu3O(7-{delta}). The static exponent { u} has been determined from {rho} vs. T dependence at given magnetic field. The critical exponents are field independent with one only exception ({ u} - for Y0.975Ca0.025Ba2Cu3O(7-{delta}) sample). This is connected with the special interrelation between the vortex correlation length, {xi}, and intervortex spacing {alpha} ({xi} leq {alpha}) at all magnetic fields above Tg for this sample and its better pinning.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
