Development of High Tc SQUID Magnetometer

点击翻译按钮获取中文摘要

In this project, we have developed superconducting quantum interference device (SQUID) using high Tc superconductors. In order tomake dc SQUID,high quality YBaCuO superconducting thin films are deposited on SrTiO3 bicrystal substrate with laser ablation method. The so-called bicrystal junction fabricated in this way shows characteristics expected from RSJ model, and enables stable SQUID operation at T=77K.For the improvement of the SQUID characteristics, we have investigated quantitatively the effect of large thermal noise at T=77K on the characteristics. It is shown that the value of inductance available at T=77K is limited below L<150pH due to large thermal noise. It is important to take into account this limitation for the design of the SQUID.Moreover, we have studied dependencies of the SQUID characteristics on SQUID parameters. From theoretical and experimental studies, we show the design rule for the development of high performance SQUID.This design rule has been used in many laboratories.In order to realize SQUID magnetometer, we have also studied the so-called magnetic coupling circuit. It is important to realeze both high performance SQUID and efficient coupling circuit. We should use inductance ranging from 50pH to 150 pH in order to satisfy these requirement. The magnetometer designed in this way shows good performance at T=77K