Thermal Depinning of Abrikosov Vortices in a Nb Polycrystalline Bulk Absorber for Gamma-Ray Superconducting Detector

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• 作者：M.P. Lisitskiy ; A.P. Volodin ; A. Bruno ; C. Van Haesendonck
• 关键词：Abrikosov vortices ; Pinning ; Gamma-ray superconducting detector ; Magnetic force microscopy
• 刊名：Physics Procedia
• 出版年：2012
• 出版时间：2012
• 年：2012
• 卷：36
• 期：Complete
• 页码：405-410
• 全文大小：377 K

文摘

The threshold temperature at which the thermal depinning of Abrikosov vortices starts to be pronounced, defines the upper temperature limit for secure operation of a gamma-ray superconducting detector based on Abrikosov vortices. Indeed, because of the flux creep phenomenon, unwanted spontaneous vortex jumps can take place concurrently with those resulting from the gamma-ray photon absorption, resulting in the appearance of dark counts. Low temperature magnetic force microscopy (MFM) was applied for the evaluation of the threshold temperature for a 0.3 mm thick Nb polycrystalline bulk absorber with dimensions of 5¡Á5 mmp>2p>, which was chosen for the fabrication of Josephson tunnel junctions serving as vortex sensor element of the gamma-ray detector. Vortices were generated by cooling the sample to 4.3 K in a small magnetic field. A field of 0.1 mT was chosen in order to produce more than two vortices within the 7¡Á7 ¦Ìmp>2p> scan area, but with sufficiently large inter-vortex spacing such that vortex-vortex interactions would be negligible. The threshold temperature associated with the thermal depinning of a single vortex was found to be 6.3 ¡À 0.2 K, whereas the threshold temperature associated with the thermal depinning of half of vortices was found to be 7.2 ¡À 0.2 K.