Boundary line of the transition into the pseudogap state in thulium cuprates

Ragimov

et al. 2011

A new superconducting ceramic material CdBa2Cu3O7−δ is obtained. It is found that the superconducting transition (at 86 K) is retained when yttrium is fully replaced by cadmium in the Y-Ba-Cu-O system. X-ray diffraction studies show that the crystalline structure is unchanged and the identified peaks coincide when Y is replaced by Cd in YBa2Cu3O7−δ. Besides a stable superconducting transition, a phase transition near 275 K was seen in the temperature dependence of the specific resistivity which shifted toward lower temperatures (252 K) and then disappeared completely over repeated measurement cycles. The thermal conductivity k of YBa2Cu3O7−δ and CdBa2Cu3O7−δ was found to vary little with temperature up to the superconducting transition. Substituting Cd for Y in the initial HTSC material led to a substantial increase in the lattice thermal conductivity. Measurements of the thermal emf showed that it is positive in YBa2Cu3O7−δ and negative in CdBa2Cu3O7−δ.

Preparation of CdBa2Cu3O7−δ superconducting ceramic and a study of its electrical properties

Ragimov

et al. 2011

Pseudogap in CdBa2Cu3O7−δ HTSC material

Ragimov

Селим-заде

2013

Long-lived minima are detected at Tmin1 = 275 K and Tmin2 = 252 K in the ρ(T) curve of polycrystalline CdBa2Cu3O7−δ, which has a superconducting transition at 86.8 K. It is shown that the excess conductivity Δσ(T) near Tmin obeys the classical Aslamazov-Larkin fluctuation theory. This suggests that fluctuation Cooper pairs may develop in CdBa2Cu3O7−δ at T ≫ Tc. The experimental data are used to calculate the coherence length ξc(0), the 2D-3D crossover temperature T0, and the interplanar pairing constants. The magnitude and temperature dependence of the pseudogap for a sample without the minima are found to be typical of cuprate HTSC materials.

A study of the pseudogap state in Bi2Sr2CaCu2Ox and Bi2Sr2ZnCu2Oy HTSC materials

Mamedova

Raqimov

et al. 2016

We examine the effect of replacing calcium by zinc has on the transport properties of the BiSrCaCuO-2221 system. It is shown that the critical temperatures Tc of the Bi2Sr2CaCu2Ox(B1) and Bi2Sr2ZnCu2Oy(B2) samples are close (81 K and 80.72 K). However, the resistivity ρ of the Bi2Sr2ZnCu2Oy sample increases considerably, and the ratio ρB2/ρB1 ≈ 10 at 100 K. We use the local pair model to analyze the mechanism behind the formation of excess conductivity in Bi2Sr2CaCu2Ox and Bi2Sr2ZnCu2Oy(B2), with consideration of the Aslamazov-Larkin theory near Tc. We determined the temperature T0 of the transition from the 2D fluctuation area to the 3D region (i.e., the 2D-3D crossover temperature). We calculated the coherence length of the fluctuation Cooper pairs along the c axis, ξc(0). It is shown that substituting Zn for Ca reduces ξc(0) by almost 1.5 times (4.8 Å and 3.3 Å, respectively), and also leads to a narrowing of both the pseudogap region and the superconducting fluctuation area near Tc. We determined the temperature dependence of the pseudogap Δ*T and Δ*(Tc). The increase of ρ, its specific temperature dependence and the significant decrease of T* in sample B2, all point to the destruction of local pairs at all high temperatures, i.e., to the suppression of the pseudogap by Zn doping.