Transport characteristics in c-axis La2-xSrxCuO4 (LSCO) single crystals

c-axis micro-bridges of La_2-xSr_xCuO₄ (LSCO) single crystals were fabricated by the focused-ion-beam (FIB) etching method. Small rectangular LSCO pieces were fabricated by cutting and grinding single crystals of underdoped LSCO of x=0.09. The size of LSCO single crystals between electrodes was cut to (5-20)×40 μm² in the ab-plane by using the FIB etching method. The junction resistance exhibited clear two-step structures corresponding to the superconducting transition of two different components of crystal structure. Superconductor-insulator-superconductor (SIS) like-branch structures on I-V curves of the LSCO stacks were observed for the first time. The branch structures show voltage jumps of several tens mV in the range of 2 K to 5 K with temperature dependence. When the temperature is changed from 2 K to 5 K, the critical current around zero bias regions splits into a few small voltage jumps with intervals of several mV in the range of 1 mV to 3 mV.