Ramp Josephson junctions based on NdBa2Cu3O7-δ electrodes and PrBa2Cu3O7-δ barriers
We report on smooth high quality c-axis oriented
NdBa2Cu3O7-δ (NBCO) superconducting thin films
grown on (001) SrTiO3 substrates using pulsed laser deposition.
The transition temperature of these NBCO films was around 89.5 K
and the root-mean-square (RMS) surface roughness was 0.75 nm for
150 nm thick films.
Insulating layers of
grown in-situ on top of the NBCO
superconducting films, result in superconductor/insulator
multilayers of about 400 nm in total thickness and an RMS surface
roughness of 2.4 nm.
Smooth ramps with angles of about 20° are patterned in the
multilayers using a photoresist reflow process and Ar+-ion
A study of the conduction mechanism in
PrBa2Cu3O7-δ with different Ga doping levels has
been done. We found that the conductivity was governed by variable
range hopping conductivity at higher temperatures
(>200 K). At lower temperatures (<200 K) the
conductivity can be described by Glazman & Matveev theory for
hopping through a few number of localized states.
A Ga-doped PrBa2Cu3O7-δ insulting barrier around
20 nm thick and NBCO counter electrode are deposited on the ramp
forming a Josephson junction. Current-voltage curves of the
obtained ramp Josephson junctions were studied at 4.2 K. Multiple
Shapiro steps were observed when the junctions were irradiated at
a frequency of 9.7 GHz, despite the fact that they have a large
excess current. The amplitudes of these steps oscillate with
microwave power in agreement with the resistively shunted
Josephson junction (RSJ) model.
ramp Josephson junction
pulsed laser deposition