Magnetic penetration depth in epitaxial Nd-doped R(NdxBa2−x)Cu3O7 (R=Y and Nd) films

Origin of collapse of J c(θ) peaks at H//c in low temperatures in (RE)BCO thin films with nanorods

“…and the GL parameter κ (=λ ab /ξ ab ) has a weak dependence on temperature, the temperature dependence of 1/l ab 2 directly reflects the temperature dependence of H c . There is a consensus that 1−l ab 2 (0)/l ab 2 (T) is predominantly linear from T 0 (in the range of 1-6 K) up to approximately T c /3 in clean (RE)BCO single crystals and thin films whose λ ab (0) is as low as ∼150 nm and 90T c 93 K [35][36][37][38][39]. The linear T dependence is interpreted to mean that (RE)BCO is a dwave superconductor with line nodes [35,36,38,39].…”

“…There is a consensus that 1−l ab 2 (0)/l ab 2 (T) is predominantly linear from T 0 (in the range of 1-6 K) up to approximately T c /3 in clean (RE)BCO single crystals and thin films whose λ ab (0) is as low as ∼150 nm and 90T c 93 K [35][36][37][38][39]. The linear T dependence is interpreted to mean that (RE)BCO is a dwave superconductor with line nodes [35,36,38,39]. In contrast, dirty (defective) (RE)BCO single crystals and thin films, whose λ ab (0) is as high as 200-340 nm and T c 90 K, have shown that 1−l ab 2 (0)/l ab 2 (T) vary as T 2 over a fairly wide range of temperatures [35,[38][39][40].…”

“…The linear T dependence is interpreted to mean that (RE)BCO is a dwave superconductor with line nodes [35,36,38,39]. In contrast, dirty (defective) (RE)BCO single crystals and thin films, whose λ ab (0) is as high as 200-340 nm and T c 90 K, have shown that 1−l ab 2 (0)/l ab 2 (T) vary as T 2 over a fairly wide range of temperatures [35,[38][39][40]. Because sample A is a high-quality thin film with T c =90.7 K and high self-field J c =3.4 MA cm −2 at 77 K [18], the low temperature upward deviation (T30 K) from equation (4) (figure 5) is attributed to the linear enhancement of H c (T) at low temperatures.…”

“…Considering that the (total) nanorod length l in equation (2) should be slightly shorter than the length of the flux line L, the calculated J c value is in good agreement with the observed value, which also supports the conclusion that small point pins do not contribute to the J c (H//c, T) at low temperatures. Subsequently, I estimate λ ab (77 K) as approximately 270 nm from the high-quality (RE)BCO thin film data, l ab 2 (0)/l ab 2 (77 K)≈0.3 [39]. Assuming that ξ ab (77 K)=4 nm [31], equations (3) and (5) estimate μ 0 H c = 0.22 T and J c = 5.8 MA cm −2 at 77 K, which is much larger than the observed J c =1.02 MA cm −2 at 77 K, 1 T [18].…”