TRANSITIONS IN DISORDERED SUSPENSIONS OF SUPERCONDUCTING GRANULES UNDER EXTERNAL MAGNETIC FIELD

)Weperform simulations of transitionsin three-dimensional suspensionsof superconducting granules, placed completely at random in a sample,when an external magnetic field is slowly increased. The results showthat these transitions induce order in the system. This eVect appears asadvantageous in applications for Superheated Superconducting Gran-ule detectors.c 1998 Elsevier Science Ltd. All rights reservedKeywords: A. superconductors, A. disordered systems, D. phasetransitionsIn a disordered suspension of superconducting gran-ules placed into an external magnetic field, the interac-tions produce a broad distribution of magnetic fieldson the surface of the granules.As a consequence, tran-sitions induced,for example, by increasing theexternalapplied field or by external radiation, should occur forvery diVerent values of the applied field or the energyof the radiation than if the granules were isolated, andalso diVerent for diVerent granulesof the same sample.On the other hand, and due to the long-range natureof the diamagnetic interaction, each transition occur-ing in the system changes the surface field values forthe whole system, and therefore these disorder eVectscan completely change as succesive transitions occur.These eVects are relevant in the analysis of systemslike Superheated Superconducting Granule [SSG] de-tectors, which are being studied for the detection ofneutrinos, dark matter, and other particules [1–3]. Inthese detectors, superconducting granules are main-tained in a metastable state by an external field, andwhen incident radiation with enough energy scattersover a granule, the normal phase can nucleate and thetransition of the granule can be detected. Interpreta-tion of experimental results are here hampered by thespreading of the transition fields of the sample, whichcan be typically around 20% [4–7].