Direct measurement of the anisotropy of the resistivity in thea-bplane of twin-free, single-crystal, superconductingYBa2Cu

Abstract

We have measured the resistivity tensor in one nearly twin-free crystal and one twin-free crystal of YBa2Cu307 z. The first crystal was grown with a large twin-free region. We removed the twins in the second crystal by applying a uniaxial stress. Using a modified Montgomery technique, we measured the electrical resistivities in all three crystal directions and found them to be linear in temperature above the superconducting transition temperature T, . Our results for p, and pb at room temperature are among the lowest that have been reported in the literature, indicating that our samples are of high quality. The ratio p, /pb is independent of temperature between 150 and 275 K, and its value, 2.2+0.2, indicates that the Cu-0 chains contribute 60% of the current when the electric field is parallel to them, with the rest of the current being contributed by the Cu-0 planes. This result, at zero frequency, is in good agreement with the recent conductivity at infrared frequencies obtained by Schlesinger et al.

Effect of interband transitions on c-axis penetration depth of layered superconductors

“…CITS 23,24 experiments in which the gap is measured separately on the chains and on the plane give added evidence that both gap values are of roughly of the same size. An anisotropy of similar magnitude is also seen in the DC resistivity [25][26][27][28] and optical conductivity 29 .…”

Phenomenology of conduction in incoherent layered crystals

“…In the crystals with maximum T c the onset of superconductivity sometimes can mask the upturn in c so that it may look metallic at all temperatures above T c . 21 This is because, according to Eq. (18), c becomes nonmetallic when ᐉ Ͼ 2 and it may not yet reach this value at temperatures above T c .…”

“…50 Note that the maximum in c in semicoherent crystals is in stark contrast to the minimum in c in incoherent crystals, Eqs. (20), (21), or (34). One can suggest that in some crystals it might be possible to observe the out-of-plane resistivity with two extrema: the minimum at higher temperatures where the crystal is incoherent and the maximum at lower temperature that indicates a crossover to 3D coherence.…”

“…Thus, the experimental data plotted as vs anisotropy would present the "snapshots" of different stages of evolution of a given system along the common trajectory. For example, close to optimal doping, c is metallic in YBa 2 Cu 3 O x , 21 presumably because the minimum in c is hidden by the onset of superconductivity. The decrease of oxygen content shifts the "observable part" of the trajectory so that it crosses the threshold = 2 and the minimum in c becomes evident at T c Ͻ T Ͻ 300 K. This corresponds to YBa 2 Cu 3 O x with x Ϸ 6.88 and 6.78 which exhibit a minimum in c at T Ϸ 150 and 300 K, respectively.…”

The effect of CuO chains on the local density of states in the vortex phase of YBa2Cu3O7

“…Early evidence for the metallicity of the chains came from measurements of the resistivity anisotropy [2], which found ρ a /ρ b ≈ 2 at 100 K, where ρ a and ρ b are the resistivities parallel to the two axes of the CuO 2 planes, and where b is also parallel to the chains. Such an anisotropy is expected if the chains are conducting and carry current in parallel with the planes.…”