Intrinsic Josephson effects inYBa2Cu3O7−δsingle crystals with various oxygen deficiencies

In our experiments, fully oxygenated ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ single crystals were annealed in flowing oxygen at various temperatures and quenched in liquid nitrogen to become oxygen deficient. These single crystals, with transition temperatures ranging from 35 K to 82 K, were then fabricated into mesalike devices along c axis with $a\ensuremath{-}b$ plane dimensions down to 2 $\ensuremath{\mu}\mathrm{m}.$ We measured dc current-voltage $(I\ensuremath{-}V)$ curves, and observed typical intrinsic Josephson effects such as hysteresis, voltage jumps, etc., in all oxygen deficient samples. However, the oxygen contents and $a\ensuremath{-}b$ plane sizes of the samples greatly affected the appearances of the $I\ensuremath{-}V$ characteristics, supplying important information on the intrinsic Josephson effects. Microwave responses were also explored for possible high-frequency applications.