Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTemperature range of superconducting fluctuations above T_c in YBa_2Cu_3O_{7-delta} single crystals
138
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Microwave absorption measurements in magnetic fields from zero up to 16 T were used to determine the temperature range of superconducting fluctuations above the superconducting critical temperature T_c in YBa_2Cu_3O_{7-delta}. Measurements were performed on deeply underdoped, slightly underdoped, and overdoped single crystals. The temperature range of the superconducting fluctuations above T_c is determined by an experimental method which is free from arbitrary assumptions about subtracting the nonsuperconducting contributions to the total measured signal, and/or theoretical models to extract the unknown parameters. The superconducting fluctuations are detected in the ab-plane, and c-axis conductivity, by identifying the onset temperature T. Within the sensitivity of the method, this fluctuation regime is found only within a fairly narrow region above T_c. Its width increases from 7 K in the overdoped sample (T_c = 89 K), to at most 23 K in the deeply underdoped sample (T_c = 57 K), so that T falls well below the pseudogap temperature T*. Implications of these findings are discussed in the context of other experimental probes of superconducting fluctuations in the cuprates.
rate research
Read More
We report on isofield curves of $sqrt{-M}$ vs. T, where M is the reversible magnetization, of YBa_2Cu_3O_{6.95}, YBa_2Cu_3O_{6.65}, and Bi_2Sr_2CaCu_2O_{8+x} with the magnetic field, H, applied parallel to the c-axis of the samples (and also parallel to the ab- planes for YBaCuO). For temperatures close to the critical temperature, T_c, the quantity sqrt{-M} is proportional to the order parameter amplitude |psi|. Curves of sqrt{-M} vs. T allowed to study the asymptotic behavior of the form (T_a-T)^m of |psi| near T_c, as a function of field. Results for the studied samples produced values of T_a(H) lying above T_c, suggesting that the magnetic field gradually allows to probe a region of temperatures where phase correlations persist above T_c. The study performed here in YBaCuO samples allowed to study how phase correlations evolve with doping in the pseudo-gap region of YBaCuO. sqrt{-M} vs. T curves for all samples show a rather large amplitude fluctuation with no phase correlation extending well above T_a(H) which is interpreted in terms of a Gaussian Ginzburg-Landau approach with a {total-energy} cutoff in the fluctuation spectrum. Resulting values for the exponent m found for all samples, 0.5 < m < 0.7, are interpreted as due to phase fluctuations of the d-wave pairing symmetry of the order parameter in the ab- planes.
We have obtained isofield curves for the square root of the average kinetic energy density of the superconducting state for three single crystals of underdoped YBa_2Cu_3O_{7-x}, an optimally doped single crystal of Bi_2Sr_2CaCu_2O_{8+delta}, and Nb. These curves, determined from isofield magnetization versus temperature measurements and the virial theorem of superconductivity, probe the order parameter amplitude near the upper critical field. The striking differences between the Nb and the high-T_c curves clearly indicate for the latter cases the presence of a unique superconducting condensate below and above T_c.
We study dynamic fluctuation effects of $YBa_2Cu_3O_{7-delta}$ thin films in zero field around $T_c$ by doing frequency-dependent microwave conductivity measurements at different powers. The length scales probed in the experiments are varied systematically allowing us to analyze data which are not affected by the finite thickness of the films, and to observe single-parameter scaling. DC current-voltage characteristics have also been measured to independently probe fluctuations in the same samples. The combination of DC and microwave measurements allows us to precisely determine critical parameters. Our results give a dynamical scaling exponent $z=1.55pm0.15$, which is consistent with model E-dynamics.
We have studied the normal-to-superconducting phase transition in optimally-doped YBa$_2$Cu$_3$O$_{7-delta}$ in zero external magnetic field using a variety of different samples and techniques. Using DC transport measurements, we find that the dynamical critical exponent $z=1.54pm0.14$, and the static critical exponent $ u=0.66pm0.10$ for both films (when finite-thickness effects are included in the data analysis) and single crystals (where finite-thickness effects are unimportant). We also measured thin films at different microwave frequencies and at different powers, which allowed us to systematically probe different length scales to avoid finite-thickness effects. DC transport measurements were also performed on the films used in the microwave experiments to provide a further consistency check. These microwave and DC measurements yielded a value of z consistent with the other results, $z=1.55pm0.15$. The neglect of finite-thickness, finite-current, and finite-frequency effects may account for the wide ranges of values for $ u$ and $z$ previously reported in the literature.
We report here the results of scanning tunneling spectroscopic experiments performed on hole doped NdBa$_2$Cu$_3$O$_{7-delta}$ single crystals of $T_c$ values of 76 K, 93.5 K and 95.5 K. The energy gaps are observed to be increasing with decreasing $T_c$ values. The coherence peaks are asymmetric with the peaks at the filled states being larger than those at the empty ones. The asymmetry increases with decreasing $T_c$. The observed asymmetry and its $T_c$ dependence can be explained by considering the Mott insulating nature of the material at the undoped state.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
