Superconducting grains have an illustrious history in dark matter detection. Drukier & Stodolsky [23] proposed superconducting grains for neutrino detectors and this work led Goodman & Witten [31] and Wasserman [73] to propose the development of WIMP detectors.
A superconducting grain detector would consist of numerous micron size superconducting grains in a meta-stable state.When one of these grains is heated by WIMP recoil, it would undergo a phase transition to the normal state. The resultant change in B field would be detected by a SQUID. Most background events, due to radioactivity, would flip multiple grains in the detector. Since the events can also be localized in the detector, this can further enhance background rejection as background events should occur primarily near the outside of the detector. The challenge for superconducting grain detector development is the production of large number of high quality grains. Recently, the Bern group [4] has been able to report significant progress in this direction: they been able to build a superconducting grain detector with several different types of grains (Sn, Al and Zn grains), which they have calibrated with a neutron source.