Muon-spin-rotation studies of the temperature dependence of the magnetic penetration depth in theYBa2Cu3

Abstract

A systematic muon-spin-rotation (@+SR) study is presented of the temperature dependence of the London penetration depth in sintered powder samples of the YBa2Cu30"system and related compounds.The in-plane penetration depth A, ,b is estimated from the p SR depolarization rate of Bi2Sr2CaCu&08+&, YBa2Cu408, and a series of samples of the YBa2Cu30" family, respectively. It is found that not only the low-temperature value A, ,b(0), but also the temperature behavior A, ,b(T) is specific to each compound.The form of A, ,b( T) can be well characterized by a simple power law. In particular, the YBa2Cu30" family shows a systematic variation of the form of A, ,b ( T) with the oxygen content x which points to a varying coupling strength, whereas A, ,b (0) as a function of x suggests a positive charge transfer into the CuO& planes with increasing oxygen doping. Furthermore, our data is consistent with an empirical ansatz which has been proposed in the framework of a Bose-gas picture of high-temperature superconductivity. As a consequence, the pressure and the isotope coefficients can be extracted from the p+SR depolarization rate and compared to direct measurements of these quantities, showing good agreement. Moreover, in the Bose-gas picture the variation of A. b(T) in the YBa2Cu30" family may be interpreted as a crossover from a dense (high-T, ) to a dilute (low-T, ) system of weakly interacting local pairs.

Anomalous electron-phonon coupling probed on the surface of superconductorZrB12

“…2. The reconstructed data were fitted with the empirical power-law λ −2 (T )/λ −2 (0) = 1 − (T /T c ) n [23]. The fit yields λ −2 (0) = 48.4(2) µm −2 , T c = 6.078(5) K, and n = 3.65(4).…”

Concerning the superconducting gap symmetry in YBa2Cu3O7 − δ, YBa2Cu4O8, and La2 −xSrxCuO4determined from muon spin rotation in mixed states of crystals and powders

“…This functional form with α ≈ 4 has been shown to provide good fits to data for T C ≈ 90-K phase of YBa 2 Cu 3 O 7-δ powders [3,4,49], which we interpret as corresponding to strong fluxon pinning, negligible influence of thermally-activated depinning, and an extremely strong-coupled s-wave pairing. Equation (12) assumes H << H c2 (T), which is applicable for T C -T > 0.2 K. It is worth noting that this result is in excellent agreement with our analysis of single-crystal data in this paper and in previously reported work [25,26].…”

“…Additionally, inhomogeneous disorder produces an observable effect that is abundantly evident in oxygen-deficient YBa 2 Cu 3 O 7-δ (see figures 4 and 5 of [49] which show σ(T) for oxygen content 0.003 ≤ δ ≤ 0.484 and transition temperatures 58.7 K ≤ T C ≤ 92.1 K). Fits using equation (12) to obtain the exponent α (see tables I and II in [49]) are plotted against T C in the inset of figure 2.…”

“…The solid and dashed curves through the data represent fits of the depinning model assuming a two-fluid form for the gap function (fitted parameters in tables 1(a) and 1(b)). Inset: Plot of fitted exponent α in equation (12) versus T C for oxygen-deficient YBa 2 Cu 3 O 7-δ (data taken from [49]). The dashed line denotes the trend.…”

“…Fits using equation (12) to obtain the exponent α (see tables I and II in [49]) are plotted against T C in the inset of figure 2. The observed decrease in α (below the optimal value of α = 4) as oxygen content is decreased and T C is depressed below 90K, and the sharp rise corresponding to the "60-K" oxygen-ordered phase, clearly shows that the exponent α is a good indicator of the effect of disorder on σ(T).…”