Intrinsic Josephson junctions formed inside ultra-thin BSCCO single crystals

Abstract

Ultra-thin pieces of Bi2Sr2CaCu2O8+δ single crystals (d<100 nm) can be isolated by cleaving pre-etched mesas off the main crystal using a flip-chip technique. Further thinning of the pieces by Ar-ion milling down to a few nanometres reveals the superconductor–insulator transition in the samples. In a refined technique, a precise control of the etching depth from both sides of the crystal makes it possible to form stacks of intrinsic Josephson junctions (IJJs) inside these ultra-thin single crystals. The stacks can be tailor-made to any small height (0–9 nm) thus assuring any low number of IJJs in the stacks (N = 0–6). Several features can be seen in the current–voltage (I–V) characteristics of these stacks, and therefore dI/dV (V) curves contain several peaks that behave differently with N. While the high-bias peaks shift in the normalized voltage V/N, the low-lying peaks at V/N≈32.4 ± 0.8 mV are N-independent. These peaks are reproducibly found in stacks of various lateral dimensions (0.5–11 µm2, N = 1...5) in a wide temperature range (T<0.8Tc). We briefly discuss possible reasons for the small values of the peak voltage.