Anisotropic irreversibility of the Abrikosov and Josephson flux dynamics inYBa2−xSrx

Abstract

Very detailed magnetic irreversibility data for fields applied along the c axis or the ab plane of a pure and untwinned YBa 2 Cu 3 O 7Ϫ␦ single crystal and Sr-doped and heavily twinned YBa 2Ϫx Sr x Cu 3 O 7Ϫ␦ (xϭ0.25, 0.37, and 0.5͒ single crystals are reported. The irreversibility lines T irr (H) of the pure single crystal show a considerable planar anisotropy but follow the same power-law regime, for both field orientations, arising within the conventional flux-creep theories in the whole field range. Very differently, however, the T irr (H) lines of the doped superconductors exhibit besides large anisotropies, several different regimes. In fields lower than 8 kOe the T irr (H) data of the doped samples display the de Almeida-Thouless ͑AT͒ and Gabay-Toulouse ͑GT͒-like power-law behaviors, the signature of a frustrated superconductor. For higher-field values, and in particular for Hʈc, flux dynamics seems to be conventional. However, for Hʈab and field values above 30 kOe, the flux dynamics displays sharp directional properties along the twinning planes ͑TP's͒ for rotations about the c axis. This behavior is cusplike, comparable to that caused by columnar defects, which characterizes a Bose-flux-glass phase. We appoint the superconducting granularity and frustration as responsible for the AT and GT behaviors below 8 kOe and the strong anisotropic pinning for H parallel to the TP's as the cause of the Bose-glass features. On the other hand, the isotropic pinning for large angular displacements or for any angle in fields below 30 kOe is the most probable cause of the vortex-glass features.

Unconventional superconducting granularity of theY1−xPrxBa2Cu3Barros1, Pureur2, Schaf3 et al. 2006Phys. Rev. BSelf Cite335310View full textAdd to dashboardCite

“…This coherence transition is very sensitive to an applied magnetic field and therefore can thoroughly decide if a given sample is a weak linked aggregate of superconducting grains or a homogeneous superconducting medium. 25,[30][31][32] While our polycrystalline sample displays a clear coherence transition between T c 2 and the point of zero resistance, the resistivity of the single crystal falls to zero at once. This strongly excludes the occurrence of a grain coupling process in the single crystal.…”

“…Therefore it exhibits the physics of the superconducting grain couplings that are strongly affected by the applied field and largely dominated by frustration. 25,30,31 It is hardly imaginable that a thermal softening 33 can lead to such specific and exclusive power law behaviors.…”

AFM as an alternative for Young’s modulus determination in ceramic materials in elastic deformation regime

“…The YBa [13,14]. Y 2 O 3 , CaCO 3 , Ba 2 CO 3 , SrCO 3 and CuO powders were thoroughly mixed in the proportions 1:3.5:0.5:10 of Y, Ba, Sr and Cu respectively for YBa(Sr)CuO samples, and in proportions 0.95:0.05:4:10 of Y, Ca, Ba, Cu for Y(Ca)BaCuO samples.…”

Фазовые переходы и эволюция вихревой структуры в двухуровневом высокотемпературном гранулярном сверхпроводнике YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=- под действием температуры и магнитного поля

“…Заметим, что если в части изучения первого во-проса выполнено достаточно большое количество ра-бот [23][24][25][26][27][28][29][30][31][32][33][34][37][38][39][42][43][44][45][46][47][48][49][50][51], то исследованиям второго во-проса посвящено ограниченное число эксперименталь-ных и теоретических исследований. Более того, ес-ли большинство исследований предшественников осно-вывалось на изучении и анализе магнитосопротивле-ния ρ(H ext ) T =const , то в настоящей работе использовал-ся сравнительно редко применяемый метод измерения и последующего анализа температурных зависимостей электросопротивления во внешнем магнитном поле ρ(T ) Hext=const , тем более связанных с измерениями при росте и понижении температуры (подобным приведен-ным на рис.…”

“…Традиционно исследования влияния температуры и магнитного поля на электрофизические свойства ВТСП проводятся по трем различным алгоритмам: a) измерения магнитосопротивления при постоянной температуре (см., например, [13,[22][23][24][25]); б) снятие вольтамперных характеристик в магнит-ном поле при постоянной температуре (см., напри-мер, [26][27][28][29][30]); в) изучение температурных зависимостей электросо-противления во внешнем магнитном поле (см., напри-мер, [31][32][33][34]). …”