Abstract
Using atomic force microscope (AFM) as a lithography tool, we ploughed (a) constant thickness nanoconstriction (∼492 nm) and (b) variable thickness bridges (∼25 to 50 nm) on YBa2Cu3O7−x thin films. We measured I-V characteristics and observed Shapiro steps, giving positive evidence of Josephson effect in these nanobridges. Further the linear temperature dependence of the critical current (Ic) and the well defined Fraunhofer-type pattern of Ic versus the applied magnetic field, rules out any flux flow behavior and firmly establishes Josephson effect in the constant thickness nanoconstriction type junction. The temperature dependence of Ic is again linear in the variable thickness bridge. However the magnetic field dependence of Ic did not show Fraunhofer-type pattern, possibly due to averaging effects. We believe that the observed low field dependence of Ic in these nanobridges allows one to tune the Josephson energy by small applied fields, making these nanojunctions useful for quantum applications like qubits.
Published Version
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