Affiliation: | a Institute for Physical Researches, National Academy of Sciences, Ashtarak-2, Gitavan IFI 378410, Armenia b Graduate School of ISEE, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan c Applied Superconductivity Center, University of Wisconsin–Madison, Madison WI 53706, USA d Department of Physics of Semiconductors & Microelectronics, Yerevan State University, 1 Alex Manukyan str., Yerevan 375049, Armenia e Kyushu Institute of Technology, 680-4, Kawazu, Iizuka 820-8502, Japan |
Abstract: | Owing to a pick-up coil's flat design, relatively low MHz-range operation frequency, and six orders relative resolution a flat coil-based tunnel diode oscillator has advantages, compared to all other methods. They become crucial in studies with thin high-Tc superconductivity (HTSC) materials (with small signals), especially at the start of the Cooper pairs’ formation. Due to this the superconductivity precursor ‘paramagnetic’ effect was detected recently in YBaCuO films at N/S transition. It precedes Meissner ejection and specifies details of the shape of the transition curve. We discuss the influence of the currents on this effect, and the relationship between the quality of the material and the shape of the effect. A new imaging device has also been created based on this test method (using a focused He–Ne laser beam as a probing signal), capable of imaging the properties of HTSC films with 3 μm spatial resolution. The method is based on detection of the inductance and Q-factor value changes of a single-layer flat coil, placed at the face of the sample. This leads to frequency and/or amplitude changes of the stable oscillator. The test device enabled 2D-mapping of the grain structure of a bridge-shaped YBaCuO film. Basically, the method is capable of imaging 2D-current distribution in thin HTS with sub-μm spatial-resolution, using non-bolometric response. However, the achieved resolution 3 μm of a bolometric nature (in a given device with 3.5 mm-size coil) by no means is limited by the abilities of the method, but mainly, it depends on how narrowly it is possible to focus the probing beam, while the own resolution of a present flat coil-based technique is better than 0.1 μm, and can be improved essentially by reducing the coil size. |