Superconducting quantum interference phenomenon in   Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystals
  The operational dc-SQUID based on intrinsic Josephson junctions in Bi$_2$Sr$_2$CaCu2O$_{8+\delta}$ high-$T_c$ superconductor is fabricated and studied. The novel in-plane loop layout and the developed in-situ endpoint detection method allowed an accurate control of the number of junctions in the SQUID. A clear periodic modulation of the superconducting current as a function of magnetic flux through the SQUID loop is observed. This is an unambiguous evidence for the quantum interference phenomenon in Bi$_2$Sr$_2$CaCu2O$_{8+\delta}$ single crystals. 
M. Sandberg and V. M. Krasnov