Josephson Effects in the Ba-Y-Cu-O Compounds

Abstract

A point-contact Josephson junction between a bulk Ba-Y-Cu-O compound (T c -90 K) and a Nb needle has been made. The I-V characteristics under microwave radiation show Shapiro steps, confirming the Josephson nature of the formed contact. Spin-singlet superconductivity in the Ba-Y-Cu-O system is implied from the voltage of the steps. The temperature dependence of the critical currents suggests that the Josephson junction if formed between Nb and another material with much higher T c . Internal Josephson structure within the bulk ceramics is not found in the Ba-Y-Cu-O system. PACS numbers: 74.50.+r, 74.70.YaRecently a series of high-7V ceramic superconductors have been discovered, 1 triggered initially by the historic finding in the Ba-La-Cu-O system. 2 Among those superconducting oxides, the Ba-Y-Cu-O compound emerged as the first material to show a reproducible T c higher than liquid-nitrogen temperature, a technological, as well as psychological, milestone temperature. As for the origin of the superconductivity in these high-T c superconductors, which are categorized as ceramic superconductors, several exotic mechanisms have been suggested such as interfacial superconductivity, 3 resonatingvalence-bond theory, 4 and also phonon-mediated superconductivity. 5 Experimentally, the superconductivity in these ceramics has been confirmed through resistance measurements and ac and dc diamagnetism measurements. The only known physical mechanism which can produce the large dc diamagnetism is superconductivity. Alongside the zero-resistance state and the Meissner effect, the existence of macroscopic quantum phenomena signifies the central ideas of the superconductivity. The Josephson junction is the celebrated quantumphase-sensitive detector capable of proving the wave nature of superconductive system. For instance, the difference in the macroscopic quantum phases of the electron pairs across the Josephson junction (phase difference <t>) is related to the amount of the supercurrent flowing through the junction, and the rate of change in the phase difference, d<p/dt, is related to the voltage across the junction. The Josephson effect seems to be a universal effect associated with superconductivity, but one might at least innocently ask the following question: "Can BCS electron pairs at one side of the Josephson junction cross to the other side of the junction where non-BCS superconductivity is present (if such superconductivity exists at all), and effortlessly rearrange themselves through a different pairing mechanism?" Assuming such a circumstance, and without clear theoretical guidance, we have set out to construct a point-contact Josephson junction with the Ba-Y-Cu-O compound as at least one of the electrodes.The preparation processes and the crystal phase of the Ba-Y-Cu-O compound are briefly discussed. The Ba-YCu-O samples were prepared from the appropriate mixtures of Y2O3, BaC03, and CuO powders, heated in air and then pressed into disk shape. Such disks were finally sintered in an oxygen-background crucible to adjust...

Recent Developments of High-Tc Electronic Devices with Multilayer Structures and Ramp-Edge Josephson Junctions

“…Observation of Josephson effect is one of indispensable conditions for establishment of superconductivity in a particular material. Following the discovery of HTSs, fabrication of JJs in forms of break junction [13] and point contact [14], as illustrated in Fig. 1, has been tried and physical properties of HTSs such as Josephson coupling and energy gaps were investigated.…”

Josephson effect in high-temperature superconductors and in structures based on them

“…К сожалению, подавляющее большинство анализируемых в этом разделе экспериментальных работ носило скорее демонстрационный, качественный характер и было нацелено лишь на подтверждение факта существования эффекта Джозефсона в ВТСП/НТСП структурах. В ра ботах по точечным контактам (за исключением [142]) отсутствуют за висимости V C (T), а размеры в плане туннельных переходов и SNS сэнд вичей существенно превосходят джозефсоновскую глубину проникнове ния Поэтому в дальнейших обсуждениях (см. раздел 5) мы ограни чимся лишь анализом экспериментальных данных работы [142].…”

“…В ра ботах по точечным контактам (за исключением [142]) отсутствуют за висимости V C (T), а размеры в плане туннельных переходов и SNS сэнд вичей существенно превосходят джозефсоновскую глубину проникнове ния Поэтому в дальнейших обсуждениях (см. раздел 5) мы ограни чимся лишь анализом экспериментальных данных работы [142]. Так же как и в НТСП/ВТСП структурах, на ВАХ ВТСП/ВТСП пе реходов могут наблюдаться ступеньки Шапиро при напряжениях, свя занных с частотой СВЧ сигнала джозефсоновским соотношением (3.1).…”

“…Точечные ВТСП/НТСП переходы [142], а также точечные ВТСП/ /ВТСП контакты и сходные с ними по свойствам межгранульные перехо ды также представляют собой нерегулярные, невоспроизводимые струк туры. Те из них, которые обладают хорошо выраженным избыточным то ком, могут быть приблизительно описаны в рамках либо SNS моде ли с локализованными магнитными центрами в N слое, либо туннельной резонансно перколяционной моделью при таком соотношении парамет ров (5.17), которое обеспечивает практическое сшивание этих моделей.…”

Superconducting Pairing State Based on Atomic Nature

“…The pairs are in spin-triplet state which have both spin and orbital momenta l 1. However, experimental results for a Josephson effect have put severe constraints on the possibility of the p-type pairing by violation of time-reversal invariance [5]. In addition, f-wave pairing has not been observed yet, as far as we know.…”