Magnetic field dependence of micromachined Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions with a submicron loop

Two-stacked intrinsic Josephson junctions (IJJs) on a Bi2Sr2CaCu2O8+delta(Bi-2212) whisker with a submicron hole are micromachined by a 3D focused ion beam (FIB) etching method. The junction area, the number of elementary junctions, and the loop area of the SQUIDs are 3, 20, and 0.42 mum(2), respectively. The SQUIDs show typical I-V characteristics of IJJs with a critical current I-C of 12 muA at 4.2 K. The modulation parameter beta(L)(=2I(C)L/Phi(0)) is 6.4, and the inductance L of the SQUID is 1120 pH. That includes the inductances of the elementary junction around a SQUID loop. In a strong magnetic field, the Fraunhofer pattern is obtained and well fitted to the calculated value from the junction size, DeltaB=Phi(0)/tW; t is the interlayer distance, and W is the junction width. In a low magnetic field, approximately 10% of the I-C modulation corresponding to the value of beta(L) is observed. Eighty G of the modulation period approximately agrees with the value calculated from the SQUID. (C) 2002 American Institute of Physics.