Characteristics of two-stacked intrinsic Josephson junctions with a submicron loop on a Bi 2Sr 2CaCu 2O 8+ δ (Bi-2212) single crystal whisker

Abstract

We report on serial dc superconducting quantum interference devices (dc SQUIDs) arrays of two-stacked intrinsic Josephson junctions (IJJs) on a Bi 2Sr 2CaCu 2O 8+ δ (Bi-2212) whisker with a submicron hole fabricated by a 3-D 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 μm 2, respectively. The SQUIDs show typical I– V characteristics of IJJs with a critical current I C of 12 A at 4.2 K. The modulation parameter β L(=2 I C L/ Φ 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; Δ B= Φ 0/ tW; t is the interlayer distance; and W is the junction width. In a low magnetic field, modulation depth of approximately 10% of the I C corresponding to the value of β L is observed. The modulation period of 80 G approximately agrees with the value calculated from the SQUID.