Fluctuation conductivity in Y-Ba-Cu-O films with artificially produced defects

The fluctuation-induced conductivity (paraconductivity) measured in YBa₂Cu₃O₇₋d (YBCO) films grown on 10° miscut SrTiO₃ (001) substrates is analyzed using various theoretical models describing weak fluctuations in high-Tc superconductors and considering both Aslamazov-Larkin and Maki-Thompson fluctuation contributions in the clean limit approach. The analysis reveals a highly anisotropic pair-breaking caused by structural defects produced. This result is in favor of an idea that pseudogap in high-Tc oxydes is mainly governed by the fluctuating pairing

Pseudogap and Local Pairs in High-Tc Superconductors

The temperature (T) dependence of pseudogap (PG) Δ*(T) is calculated for Bi2201 within the local pair (LP) model [1, 2]. The model is based on analysis of the excess conductivity derived from resistivity experiments in hightemperature superconductors (HTSs) and supposes the local pairs, which are formed in HTSs at T well above Tc, to generate a pseudogap. To confirm the conclusion, Δ*(T) is compared with the temperature dependence of the loss of the spectral weight W(EF)(T) measured by ARPES for the same Bi2201 sample [3]. A good agreement between Δ*(T) and W(EF)(T) is found, confirming the local pairs to be one of the most likely cause for the PG formation.Температурну залежність псевдощілини Δ*(T) розраховано для Bi2201 в межах моделю локальних пар [1, 2]. Цей модель засновано на аналізі надлишкової провідности, яка одержується з експериментів щодо питомого опору у високотемпературних надпровідниках (ВТНП), і припускає наявність локальних пар, що мають утворюватися у ВТНП за температур T, набагато більш високих, ніж Tc, формуючи псевдощілину. Для підтвердження цього висновку Δ*(T) порівнюється з температурною залежністю втрати спектральної ваги W(EF)(T), що вимірюється ARPES в тому ж самому зразку Bi2201 [3]. Одержано хороший збіг Δ*(T) і W(EF)(T), який підтверджує, що локальні пари є однією з найбільш ймовірних причин утворення псевдощілини.Температурная зависимость псевдощели Δ*(T) рассчитана для Bi2201 в рамках модели локальных пар [1, 2]. Эта модель основана на анализе избыточной проводимости, которая получается из экспериментов по удельному сопротивлению в высокотемпературных сверхпроводниках (ВТСП), и подразумевает наличие локальных пар, которые должны образовываться в ВТСП при температурах T, намного более высоких, чем Tc, формируя псевдощель. Для подтверждения этого вывода Δ*(T) сравнивается с температурной зависимостью потерь спектрального веса W(EF)(T), измеряемого ARPES в том же самом образце Bi2201 [3]. Получено хорошее совпадение Δ*(T) и W(EF)(T), подтверждающее, что локальные пары являются одной из наиболее вероятных причин образования псевдощели

Fluctuation conductivity due to the preformed local pairs

We investigated the properties of a system where the itinerant electrons coexist and interact with the preformed local pairs. Using the nonperturbative continuous unitary transformation technique we show that Andreev-type scattering between these charge carriers gives rise to the enhanced diamagnetic response and is accompanied by appearance of the Drude peak inside the pseudogap regime ω ≤ 2Δpg . Both effects are caused by the short-range superconducting correlations above the transition temperature Tc. In fact, the residual diamagnetism has been detected by the torque magnetometry in the lanthanum and bismuth cuprate superconductors at temperatures up to ~1.5 T c. In this work we show how the superconducting correlations can be observed in the ac and dc conductivity. Remove selecte

Possibility of local pair existence in optimally doped SmFeAsO₁₋х in pseudogap regime

We report the analysis of pseudogap Δ* derived from resistivity experiments in FeAs-based superconductor SmFeAsO₀.₈₅, having a critical temperature Tc=55 K. Rather specific dependence Δ*(T) with two representative temperatures followed by a minimum at about 120 K was observed. Below Ts ≈ 147 K, corresponding to the structural transition in SmFeAsO, Δ*(T) decreases linearly down to the temperature TAFM ≈ 133 K. This last peculiarity can likely be attributed to the antiferromagnetic (AFM) ordering of Fe spins. It is believed that the found behavior can be explained in terms of Machida, Nokura, and Matsubara theory developed for the AFM superconductors

c-Axis tunneling in YBa2Cu3O7-\delta/PrBa2Cu3O7-\delta superlattices

In this work we report c-axis conductance measurements done on a superlattice based on a stack of 2 layers YBa2Cu3O{7-\delta} and 7 layers PrBa2Cu3O{7-\delta} (2:7). We find that these quasi-2D structures show no clear superconducting coupling along the c-axis. Instead, we observe tunneling with a gap of \Delta_c=5.0\pm 0.5 meV for the direction perpendicular to the superconducting planes. The conductance spectrum show well defined quasi-periodic structures which are attributed to the superlattice structure. From this data we deduce a low temperature c-axis coherence length of \xi_c=0.24\pm 0.03 nm.Comment: 15 pages, 5 figures. To appear in Phys.Rev.

Hall effect studies in YBCO films

The longitudinal, rhoxx(T), transverse, rhoxy(T), and Hall, rhoH(T) resistivities have been measured for YBa₂Cu₃Ox (YBCO) films, showing positive resistivity buckling and those with usual linear rhoxx(T) dependence. In the former case unexpected peak on rhoxy(T) and unusual rhoH(T) dependence with double sign change just above transition temperature Tc have been revealed. The data are analyzed using recent theory for the sign of the Hall conductivity in strongly correlated systems

Моделювання руйнування p-n-переходу електромагнітними імпульсами

У рамках теорії існування густини та методів молекулярної динаміки у статті розглядається процес руйнування кремнієвого p-n-переходу під дією електромагнітного імпульсу (термічний ефект). Зі збільшенням амплітуди електромагнітного імпульсу виникає нелінійність рухливості квазічастинок і відбуваються процеси ударної іонізації, що приводять до утворення різноманітних дефектів у кристалічній решітці напівпровідника. Показано еволюцію виникнення точкових дефектів у напівпровіднику шляхом термічної деформації, а також подальше збільшення їх концентрації. Показано, що первинне проходження електромагнітного імпульсу породжує дефекти в бездефектному кристалі. Подальший термічний вплив імпульсу приводить до збільшення відхилення атомів та накопичення дефектів і руйнування структури. З підвищенням температури p-n-перехід втрачає свої випрямляючі властивості і спостерігається миттєве збільшення величини зворотного струму за рахунок виникнення струму іонізації, який збігається за напрямком зі струмом насичення. Виявлено, що термічна деформація суттєво спотворює профіль p-n-переходу. Встановлено, що руйнування напівпровідникової структури відбувається в бездефектній частині кристала. У напівпровідниках, легованих Li або Sr, час руйнування p-n-переходу збільшується за рахунок заселення рухливими іонами Li або Sr утвореними вакансіями кремнію під час теплової дії імпульсу. Отримані результати можуть бути корисними при розробці напівпровідникових структур, стійких до зовнішнього впливу електромагнітного імпульсу.Within the framework of the density functional theory and methods of molecular dynamics, the process of destruction of a silicon p-n junction at the influence of an electromagnetic pulse (thermal effect) is considered. With an increase in the amplitude of the electromagnetic pulse, a nonlinearity of the mobility of quasiparticles arises and impact ionization processes occur, leading to the formation of various defects in the crystal lattice of the semiconductor. The evolution of the occurrence of point defects in a semiconductor by thermal deformation, as well as a further increase in their concentration, is shown. It is demonstrated that the primary passage of an electromagnetic pulse generates defects in a defect-free crystal. Further thermal impact of the pulse leads to an increase in the deviation of atoms, leading to the accumulation of defects and the destruction of the structure. With an increase in temperature, the p-n junction loses its rectifying properties and an instantaneous increase in the magnitude of the reverse current is observed due to the occurrence of an ionization current, which coincides in direction with the saturation current. It is revealed that thermal deformation significantly distorts the p-n junction profile. It was found that the destruction of the semiconductor structure occurs in the defect-free part of the crystal, and the defects stimulate destruction. In semiconductors doped with Li or Sr, the destruction time of the p-n junction increases due to the occupation of mobile Li or Sr ions by the formed silicon vacancies during the thermal action of the pulse. The results obtained can be useful in the development of semiconductor structures resistant to external influences of an electromagnetic pulse

Impact of temperature and pressure on phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-δsingle crystals

Here, we study the impact of high hydrostatic pressure (up to 11 kbar) on the conductivity in the basal ab plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals. Conversely to YBa2Cu3O7-δ single crystals, it was found that high pressure leads to phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals. The mechanisms of the influence of praseodymium and high hydrostatic pressure on the two-step resistive transition to the superconducting state are discussed. © 2022 Author(s)

Self-diffusion in perovskite and perovskite related oxides: Insights from modelling

Perovskite and perovskite related oxides are important materials with applications ranging from solid oxide fuel cells, electronics, batteries and high temperature superconductors. The investigation of physical properties at the atomic scale such as self-diffusion is important to further improve and/or miniaturize electronic or energy related devices. In the present review we examine the oxygen self-diffusion and defect processes in perovskite and perovskite related oxides. This contribution is not meant to be an exhaustive review of the literature but rather aims to highlight the important mechanisms and ways to tune self-diffusion in this important class of energy materials. © 2020 by the authors

Influence of electron irradiation on fluctuation conductivity and pseudogap in YBa2Cu3O7-δsingle crystals

The effect of electron irradiation with the energy of 2.5 MeV on the temperature dependences of the resistivity ρ(T) of an optimally doped YBa2Cu3O7-δ single crystal has been studied. The temperature dependences of both fluctuation conductivity σ′ (T) and the pseudogap Δ*(T) on irradiation dose φ have been calculated within the local pair model. Here we show that with an increase in φ, the value of ρ(300 K) increases linearly, while Tc decreases linearly. Concurrently, the value of ρ(100 K) increases nonlinearly, demonstrating a feature for φ3 = 4.3·1018 e/cm2, which is also observed in the number of other dose-dependent parameters. Regardless of the irradiation dose, in the temperature range from Tc up to T01, σ′(T) obeys the classical fluctuation theories of Aslamazov-Larkin (3D-AL) and Maki-Thompson (2D-MT), demonstrating 3D-2D crossover with increasing temperature. The crossover temperature T0 makes it possible to determine the coherence length along the c axis, ζc(0), which increases by ∼3 times under irradiation. Furthermore, the range of superconducting fluctuations above Tc also noticeably increases. At φ1 = 0, the dependence Δ*(T) typical for single crystals containing pronounced twin boundaries is observed with a maximum at Tpair ∼120 K and a distinct minimum at T = T01. It was determined for the first time that at φ3 = 4.3·1018 e/cm2 the shape of Δ*(T) changes strongly and becomes the same as in optimally doped YBa2Cu3O7-δ single crystals with a very low pseudogap opening temperature T∗ and noticeably reduced Tpair, while at Tc(φ) there are no singularities. With an increase in the irradiation dose up to φ4 = 8.81018 e/cm2, the shape of Δ*(T) is restored and becomes the same as in well-structured YBa2Cu3O7-δ films and untwined single crystals. Moreover, in this case, Tpair and T∗ increase noticeably. © 2022 Author(s)