Excess conductivity and the pseudogap state in Hf-doped YBa₂Cu₃O7−δ ceramics

Abstract

The electrical conductivity of hafnium (Hf)-doped YBa2Cu3O[Formula: see text] ceramics is investigated. Hf doping has been revealed to lead to an increase of the number of effective scattering centers for the normal charge carriers. In a broad temperature range, the excess conductivity of the investigated samples obeys an exponential temperature dependence, while near [Formula: see text] it is satisfactorily described by the Aslamazov–Larkin model. Meanwhile, Hf doping has been shown to lead to a notable broadening of the temperature range for the manifestation of the pseudogap anomaly in the [Formula: see text]-plane.

Effect of Hafnium Impurities on the Magnetoresistance of $$\hbox {YBa}_{2}\hbox {Cu}_{3}\hbox {O}_{7-\delta }$$ YBa 2 Cu 3 O 7 - δ

“…The inset shows the resistive transition to the superconducting state at different magnetic fields ranging from H = 0-12 T. As it can be observed, when the temperature is lowered below 300 K, the ρ(T ) decreases almost linearly down to a characteristic temperature T * ≈ 141 K. Below this temperature begins a systematic downward deviation of the experimental points from the linear dependence indicating the appearance of excess conductivity σ , as it was mentioned above. This behavior in ρ ab (T ) dependence at temperatures T >> T c is due to the manifestation of the "pseudogap anomalies" (PG) (refer to [17]). Notably, the application of the magnetic field, within the experimental error limits, is not affecting the behavior of the curves ρ(T ) above the SCS transition and results in a significant broadening of the superconducting transition, in comparison with the sufficiently sharp ( T c ≈ 1.5 K) transition, that was observed at H = 0.…”

“…This is a technologically important issue as YBa 2 Cu 3 O 7−δ is relatively simple to synthesize and has a high critical temperature that exceeds the liquid nitrogen temperature [16][17][18]. Secondly, this compound has one of the highest-among the HTSC materials-critical currents [5,9].…”

“…Secondly, this compound has one of the highest-among the HTSC materials-critical currents [5,9]. Thirdly, the presence of intergrain boundaries hinder the diffusion processes of the labile components, contributing to the stability of the oxygen subsystem during long-term operation and aging [17,19,20]. Finally, the introduction of Hf and Zr impurities leads to substitutional impurities, which contribute to the formation of additional pinning centers.…”

Modification by high pressure of fluctuation paraconductivity of underdoped HoBa2Cu3O7-δ single crystals

“…In spite of 30 years of intense experimental and theoretical studies, the microscopic nature of high T c superconductivity is still unclear [6,7]. The layered structure of HTSC compounds [8,9], along with a short coherence length [10,11] and a large depth of penetration [12], contributes to the emergence of a wide temperature section of excess conductivity [13,14]. It is established that near the critical temperature T c , the excess conductivity is conditioned by the fluctuation pairing of carriers fluctuation conductivity (FC) [15], and at higher temperatures T ) T c , by the so-called pseudo-gap anomaly (PG) [16,17].…”