Specific temperature dependence of pseudogap in YBa2Cu3O7−δ nanolayers

Abstract

The pseudogap (PG) derived from the analysis of the excess conductivity σ ′ (T ) in superlattices and double-layer films of YBa2Cu3O 7−δ − PrBa2Cu3O 7−δ (YBCO-PrBCO), prepared by pulsed laser deposition, is studied for the first time. The σ ′ (T ) analysis has been performed within the local-pair (LP) model based on the assumption of the paired fermion (LPs) formation in the cuprate highTc superconductors (cuprates) below the representative temperature T * ≫ Tc resulting in the PG opening. Within the model, the temperature dependencies of the PG, ∆ * (T ), for the samples with different number of the PrBCO layers (NP r ) were analyzed in the whole temperature range from T * down to Tc. Near Tc, σ ′ (T ) was found to be perfectly described by the Aslamasov-Larkin (AL) and Hikami-Larkin (HL) [Maki-Thompson (MT) term] fluctuation theories, suggesting the presence of superconducting fluctuations in a relatively large (up to 15 K) temperature range above Tc. All sample parameters were found to change with increase of NP r , finally resulting in the appearance of the pronounced maximum of ∆ * (T ) at high temperatures. The result is most likely due to increasing influence of the intrinsic magnetism of PrBCO (µP r ≈ 4 µB) and suggests the possibility to search in that way the change of interplay between the superconductivity and magnetism in cuprates.

Fluctuation conductivity and possible pseudogap state in FeAs-based superconductor EuFeAsO0.85F0.15

“…Recently the similar ∆ * (T ) dependence was observed in YBCO-PrBCO superlattices and YBCP-PrBCO sandwiches [79] as well as in HoBa 2 Cu 3 O 7−δ slightly doped single crystals [57] suggesting the generality of the interaction mechanism for the superconductors in which the AF ordering may coexist with superconductivity.…”

Effect of electron irradiation on the fluctuation conductivity in YBa2Cu3O7−δ single crystals

“…As the temperature is lowered below a certain characteristic value T*, a deviation of ρ ab (Т) from the linear dependence occurs, which indicates the appearance of some excess conductivity, which, as noted above, is due to a transition to a pseudogap regime [5][6][7]. The "rounding" of the ρ ab (T) curves below a certain characteristic temperature T* is due to the appearance of excess conductivity, the temperature dependence of which can be obtained from the formula: where σ 0 = ρ 0 −1 = (А + ВТ) −1 is the conductivity, determined by interpolating the linear portion of the measurements observed in the high-temperature region to the zero temperature, and σ = ρ −1 is the experimentally measured value of the conductivity at Т < T*.…”

“…According to contemporary concepts (see, for example, [5][6][7]), such a behavior of the ρ ab (Т) dependences can be caused by the transition to the so-called pseudogap state, characteristic for the "underdoped" compositions of HTSC compounds. A certain role in this is played by the presence of structural and kinematic anisotropy in the system [38][39][40][41][42].…”

“…As it is established [1,4], the large penetration depth, the short coherence length and the layered structure contribute to the appearance of an anomalously wide region of excess conductivity (Δσ) in HTSC compounds in the ρ ab (T) dependences (in the basal plane). Far from the critical temperature (T c ) at Т с ≤ Т < Т* (where T* is the temperature that the deviation from the linear in the ρ ab (T) dependence commences), Δσ is determined by the so-called pseudogap anomaly (PG) [5][6][7], which was previously studied in detail [8]. Near Т с , Δσ is caused due to the formation of fluctuation superconducting pairs [9,10].…”

Diffusion of the superconducting transition in HTSC

“…It is well known [1][2][3][4], that in high-temperature superconductors (HTSC), the superconducting transition has a significant width in comparison to the classic superconducting transitions widths observed in pure metals. The broadening of the superconducting transition in HTSC is primarily associated with the inhomogeneous distribution of the labile oxygen concentration [5], which leads to phases with different oxygen deficiency in the sample, that is with different critical temperatures (T c ).…”