Direct observation of intrinsic Josephson junction characteristics in electron-dopedSm2−xCexCuO4−δ

Abstract

We have investigated the current-voltage $(CV)$ characteristics of the intrinsic Josephson junctions (IJJs) in the electron-doped high-${T}_{c}$ superconductor ${\mathrm{Sm}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}\mathrm{Cu}{\mathrm{O}}_{4\ensuremath{-}\ensuremath{\delta}}$ by using a small mesa structure fabricated on a single crystal surface. It is found that multiple resistive branches, i.e., typical IJJ characteristics, are observed in the $CV$ characteristics when the junction area of a mesa is $10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{2}$ or less. It is also found that a typical Josephson critical current density ${J}_{c}$ is $7.5\phantom{\rule{0.3em}{0ex}}\mathrm{kA}∕{\mathrm{cm}}^{2}$ at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for ${T}_{c}=20.7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The Josephson penetration depth is experimentally estimated to be $1.0--1.6\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ from the size dependence of ${J}_{c}$. Both ${J}_{c}$ and ${T}_{c}$ are found to decrease with the carrier doping level, as is found for hole-doped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ in the heavily overdoped region. These results are discussed in relation to the current locking in terms of the coupled Josephson junction stack model.