THz Josephson properties of grain boundary YBaCuO junctions on symmetric, tilted bicrystal sapphire substrates

Abstract

Superconducting Josephson junctions with high characteristic voltages (I c R n larger than 4 mV at 4.2 K) are fabricated by depositing YBa 2 Cu 3 O 7−x on tilted sapphire bicrystal substrates, where the tilting axis is along the grain boundary. The good junction quality and low microwave losses in sapphire gave high frequency response well into the THz region. High quality YBa 2 Cu 3 O 7−x epitaxial films were deposited on tilted sapphire substrates with CeO 2 buffer layers by pulsed laser deposition. YBaCuO films have smaller tilt angles, from 1.0°up to 10.3°, compared to inclination angles of the substrates from 1.5°to 13.6°. X-ray diffraction shows only a single orientation of the films in the a-b plane, as well as an absence of a-axis particles and outgrowths. Critical temperatures as high as T c = 88.5− 89.0 K and ⌬T c ഛ 1.5 K were obtained in all films. The grain boundary in a common high-T c superconducting junction is usually much less straight than in the in-plane rotated bicrystal substrate, depressing Josephson currents. The waviness of the artificial grain boundary in a tilted bicrystal film is three times less than in an in-plane (untilted) bicrystal. Tilted Josephson junctions of widths from 1.5 to 6 µm were tested at temperatures from 0.26 to 77 K. I c R n products as high as 4.5 mV were observed at T = 4.2 K. Shapiro steps were observed at voltages over 3 mV under 300 GHz irradiation. Josephson radiation from the tilted junction was measured at frequencies up to 1.7 THz by a cryogenic bolometer. Suppressing the critical current with a magnetic field can separate Josephson radiation and thermal radiation. A parabolic dependence of the response on bias voltage for thermal radiation corresponds to an increase of junction temperature from 260 mK at zero bias to 3 K at 1 mV bias.

Исследование Свч-Свойств Высокотемпературных Джозефсоновских Контактов На Сапфировой Бикристалической Подложке

“…Однако недостатками этих подложек являются высокие СВЧ-потери и их низкая теплопроводность. В то же время, ВТСП-бикристаллические переходы на сапфиро-вых подложках [6][7][8][9][10] представляются перспективными кандидатами для использования в эталонах напряжения, поскольку сапфир имеет низкое поглощение на СВЧ и хорошие тепловые характеристики. Поэтому создание микросхем на основе сапфировых подложек может при-вести к созданию новых эталонов, что расширит область применения этих приборов в квантовой метрологии и радиоизмерительной технике.…”

Detection of Coherent Terahertz Radiation from a High-Temperature Superconductor Josephson Junction by a Semiconductor Quantum-Dot Detector

“…There have been only a few attempts to measure the coherent radiation emitted by a HTS JJ. A hot electron bolometer and a separate HTS JJ have been used as detectors [10][11][12]. In these experiments, the power of coherent radiation incident on a 0.5 × 0.5 mm 2 area of a bolometer was estimated to be P osc ∼ 10 −13 W, when the source and sensor were placed back to back [10].…”

“…A hot electron bolometer and a separate HTS JJ have been used as detectors [10][11][12]. In these experiments, the power of coherent radiation incident on a 0.5 × 0.5 mm 2 area of a bolometer was estimated to be P osc ∼ 10 −13 W, when the source and sensor were placed back to back [10]. This result, however, has a high level of uncertainty because of an inherent problem with Joule heating affecting detectors and variability related to the samples.…”

Anisotropic distributions of electrical currents in high-T c grain-boundary junctions

“…1b) have been fabri cated [16][17][18][19][20][21][22][23][24][25] with an order of magnitude lower GB meandering and up to a threefold increase of the I c R n values [16][17][18][19]. A complete antiphase correlation between low frequency fluctuations of the resistance R n and the critical current I c has been observed in these junctions, thus showing that both quasiparticles and Cooper pairs flow directly through the same regions of the barrier [24].…”