Superconducting fluctuation diamagnetism aboveTcinYBa1

W. C. Lee

¹

,

R. A. Klemm

²

,

D. C. Johnston

³

Abstract

Magnetic susceptibility data are presented for the title compounds. All show negative curvature below ~~2T C . Data for grain-aligned YBa2Cu3C>7 are in excellent agreement with a new calculation of the superconducting fluctuation diamagnetism. We infer j-wave pairing and Ginzburg-Landau coherence lengths %ab (0) -13.6 ± 0.8 A and £ c (0) -1.23 ± 0.19 A. Both of the order-parameter bands are found to be essential in the fit. Part of the above negative curvature is inferred to arise from the normal-state background.PACS numbers: 74.20. De, 74.40.+k, 74.65.+n, 74.70.Vy Low-frequency 1 " 6 and microwave 7 conductivity data above T c -92 K as well as heat-capacity 8 data near T c for YBa2Cu3C>7 (Y 1:2:3) indicate that superconducting fluctuations are strong at temperatures T in the vicinity of T c and above, and that the superconductivity is three dimensional. In these measurements, a strong Tdependent background is present and must be subtracted, subject to strong assumptions about the background, in order to extract the fluctuation contributions, leading to ambiguities in the derived microscopic parameters. On the other hand, these fluctuations are also observable as a diamagnetic contribution to the magnetic susceptibility x(T) above r c , 1>9 ' 10 which is otherwise nearly independent of !T. 9 ' 10 Herein, we report #(70 data for a batch of Y 1:2:3 which we believe closely approximate the intrinsic #(70. The data increase monotonically with T up to at least 400 K, and exhibit negative curvature below -200 K. We present the results of a new calculation of the angular dependence of the superconducting fluctuation diamagnetism (SFD) and compare the predictions with our %(T) data for a highly oriented powder with Hllc and H-Lc. This comparison shows that the data are consistent with s-wave pairing and strong SFD up to at least 126 K, and provides quantitative estimates of the r-0 coherence lengths and the effective mass anisotropy. We infer that the background #(70 exhibits negative curvature above T c . Powder #(70 data are also reported for La1.sSro.2CuO3.96 (LaSr 2:1:4) and Bi 2 -*Pb JC Sr2CaCu208+ < 5 (2:2:1:2) for x-0 and x-0.2 which show that the strong SFD is a universal property of the copper-oxide-based materials.Polycrystalline YI^C^OT-^ was prepared from predried Ames Laboratory Y 2 0 3 , 99.999% CuO and 99.9% BaC0 3 at 940 °C for 90 d in air with ten intermediate grindings, followed by heating in O2 at 640 °C for 1 d and oven cooling. From x-ray diffraction analysis, the batch was single phase with y -0. Magnetization M data were obtained in a magnetic field H using a quantum design SQUID magnetometer. The small (corresponding to ==3 ppm Fe/Cu) ferromagnetic im-purity contribution to M was determined from M(H) isotherms and is corrected below. Meissner effect MlH measurements in 77-50 G gave 48% of -1/4TT at 10 K with a zero-field-cooled value in the same H of 127%, both uncorrected for demagnetization factors. The Meissner effect attained 10% and 50% of its maximum value at 91.4 and 88.1 K, respectively. ...

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

“…This compound is stoichiometric, which minimizes the randomness of dopant atom distribution and then the corresponding disorder and inhomogeneities. 1 These data will be then used to check if the existing GL approaches with fluctuations of vortices and of Cooper pairs 3,7,8,9,23,24,25 explain, at quantitatively and consistently above and below T C , the diamagnetism measured in homogeneous cuprate superconductors.…”

Superconducting fluctuations in the reversible magnetization of the iron-pnictideBa1−xKxFe2As

“…Superconducting fluctuations are important in the vicinity of the transition temperature T c and have been extensively studied in all kinds of superconductors [17,18,19]. In the case of layered systems, fluctuation superconductivity is enhanced, and there are robust theories predicting the behavior of many measurable quantities with temperature and magnetic field, in or out of the critical region [17,20,21,22,23,24,25,26].…”

“…In the case of layered systems, fluctuation superconductivity is enhanced, and there are robust theories predicting the behavior of many measurable quantities with temperature and magnetic field, in or out of the critical region [17,20,21,22,23,24,25,26]. Comparison of experimental results with these theories helps to understand the nature of the fluctuations, its dimensionality [18,23,27,28,29] and give additional insight about the pairing mechanism symmetry of the studied system [24,30].…”

Experimental observation of two-dimensional fluctuation magnetization in the vicinity ofTcfor low values of the magnetic field in deoxygenatedYBa2Cu3Salem‐Sugui1, Alvarenga2, Vieira3 et al. 2006Phys. Rev. B140110View full textAdd to dashboardCite

“…Superconducting diamagnetic fluctuations above and below T c have been the issue of extensive investigations since the discovery of the high-T c materials. These materials due to their high value of T c , low coherence lengths and layered structure (anisotropy), display a much larger fluctuations effects than the low T c superconductors [1,2]. For high-T c materials the δT region around T c where critical fluctuations occur can be of the order of 1 K [1].…”

“…These materials due to their high value of T c , low coherence lengths and layered structure (anisotropy), display a much larger fluctuations effects than the low T c superconductors [1,2]. For high-T c materials the δT region around T c where critical fluctuations occur can be of the order of 1 K [1]. From the theoretical point of view diamagnetic fluctuations in layered materials were previously treated in detail by Klemm et al, [3] and by Gerhardts [4].…”