We have investigated quantum transport phenomena in various superconducting
and magnetic materials in order to explore the possibilities of novel quantum
devices. Figure 1 shows the aluminum quantum disk (2 mm in diameter)
with the 200 nm wide electrodes. At very low temperatures, re-entrant superconducting
transition is observed after a significant resistance enhancement when
magnetic field is applied perpendicular to the sample. Figure 2 shows
resistance of a magnetic organic compound l-(BETS)2FexGa1-xCl4 (x=0.45)
under magnetic field along the c axis. A striking insulator-superconductor
transition is observed at low temperatures. In this phenomenon, nano-scale
magnetic interaction between the Fe moments and the electrons on the BETS
organic molecules plays a crucial role.
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