Narrow Results

In this article, we perform a self-consistent calculation for the self-energy, based on the pairing mechanism for the two-dimensional phenomenological model below half filling. The non-Fermi versus Fermi liquid behavior is analyzed and the self-energies are compared. We also investigate the doping dependence of the pseudogap in the underdoped regime of the phase diagram of cuprates superconductors. Comparing the obtained results with experimental data, it is found that Δ_pg scales with characteristic temperature T*.

The in-plane resistivity ρ_ab(T) are measured for Bi₂Sr₂CaCu₂O₈ superconducting thin films successfully deposited by in situ magnetron RF-sputtering on vicinal (100) SrTiO₃ substrates. Oriented film with c-axis inclined with respect to the basal plane by a tilt angle α≈4° was obtained. The oxygen content of the film was changed from the maximally overdoped state to strongly underdoped nonsuperconducting states. It was found that for underdoped and overdoped regions ρ_ab(T) deviates from the high T-linear behavior at characteristic temperatures T* and T**.

The influence of praseodymium doping on the electrical resistivity in the ab-plane of Y_1-zPr_zBa₂Cu₃O_7-δ single crystals, is investigated. It is determined that as the concentration of praseodymium (0.0 ≤ z ≤ 0.5) is rising there occurs a significant shift of the temperature regions, corresponding to the metal–insulator transitions, as well as to the regime of the implementation of the pseudogap anomaly. The part of the curves related to the metal–insulator transition are well described by means of an asymptotic dependence that corresponds to the implementation of a quantum critical regime in the system, the so-called law of the "one third".

The electrical conductivity of hafnium (Hf)-doped YBa₂Cu₃O${}_{7-\delta }$ 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 $T_c$ 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 $ab$-plane.

Within the framework of the fermion-spin theory, the charge transport in the doped Mott insulators on a honeycomb lattice is studied by taking into account the pseudogap effect. It is shown that the conductivity spectrum in the low-doped regime is separated by the pseudogap into a low-energy non-Drude peak followed by a broad mid-infrared band. However, the decrease of the pseudogap with the increase of doping leads to a shift of the position of the mid-infrared band towards the low-energy non-Drude peak, and then the low-energy Drude behavior recovers in the high-doped regime. The combined results of both the doped honeycomb-lattice and square-lattice Mott insulators indicate that the two-component conductivity induced by the pseudogap is a universal feature in the doped Mott insulators.

There is a long-standing issue that the optical conductivity in normal-state of cuprate superconductors deviates the conventional Drude type marked by ${\omega }^{-2}$ dependence, exhibiting two main components from underdoping to overdoping, a narrow band peaked around zero energy and a broadband centered in the mid-infrared region called mid-infrared band. Within the renormalized t-J model and self-consistent mean field theory, we discuss the doping and energy dependence of optical conductivity in cuprate superconductors. Our results show that the appearance of the pseudogap in normal state is responsible for anomalous optical conductivity, giving rise to the mid-infrared band. In particular, in analogy to the doping dependence of pseudogap, optical conductivity is also strongly doping dependent. By increasing the doping concentration, the spectral weight of the optical conductivity suppressed strongly in underdoped region increases quickly, and the peak position of the mid-infrared band moves towards to the lower energy region, then incorporates into the narrow band centered in zero energy in the heavily overdoped region.

By considering the pseudogap effect, the doping and energy dependences of thermal conductivity in cuprate superconductors are studied. Our results show that the thermal conductivity as a function of energy exhibits a characteristic peak from underdoping to overdoping due to the presence of the pseudogap in pseudogap phase of cuprate superconductors. The thermal conductivity is strongly doping dependent. On the one hand, with increasing doping concentration, the weight of thermal conductivity increases quickly, especially the residual thermal conductivity which is in qualitative agreement with the experimental data. On the other hand, the characteristic energy corresponding to the position of the characteristic peak decreases monotonically upon increasing doping concentration, and it scales with the doping dependence of pseudogap. In particular, we have studied the doping dependence of the ratio of quasiparticle velocities normal and tangential to the Fermi surface at the nodes $v_F/v_2$. It is shown that $v_F/v_2$ increases with the increase of doping concentration. Moreover, we explain that both the residual thermal conductivity and $v_F/v_2$ increase rapidly upon the increase in doping concentration in heavily overdoped cuprate superconductors.

Temperature dependences of the electrical resistance along the c-axis of ${\mathrm{\text{YBa}}}_2{\mathrm{\text{Cu}}}_3{\mathrm{\text{O}}}_{7-\delta }$ single crystals are investigated before and after irradiation with electrons at 0.5–2.5 MeV energies. The irradiation was done at $T\lesssim 10$ K and the irradiation dose was varied from $1.4\times 10^{18}{\mathrm{\text{cm}}}^{-2}$ to $8.8\times 10^{18}{\mathrm{\text{cm}}}^{-2}$. An enhancement of the charge carriers localization with increase of the irradiation dose has been revealed. A crossover from the pseudogap (PG) regime to the variable-range hopping conductivity has been observed.

The effect of room-temperature annealing on the basal-plane conductivity of YBCO single crystals is investigated after their irradiation with fast electrons. It is revealed that the excess conductivity $\mathrm{\Delta }\sigma (T)$ of the samples obeys an exponential temperature dependence in a broad temperature range $T_f<T<T^{\ast }$. Here, $T_f$ is the crossover temperature from the pseudogap to the fluctuation conductivity regime. The description of the excess conductivity with the expression $\mathrm{\Delta }\sigma \propto T/T^{\ast }exp({\mathrm{\Delta }}^{\ast }/T)$ can be interpreted in terms of the mean-field theory where $T^{\ast }$ corresponds to the mean-field transition temperature to the pseudogap state and the dependence $\mathrm{\Delta }\sigma (T)$ is described within the framework of the BCS-BEC crossover theory.