Ramp Josephson junctions based on NdBa2Cu3O7-δ electrodes and PrBa2Cu3O7-δ barriers
Licentiate thesis, 2006

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 PrBa2Cu3O7-δ/SrTiO3/PrBa2Cu3O7-δ 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 milling. 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.


high temperature

superconducting device

ramp Josephson junction


pulsed laser deposition

thin film


Mikael Sjöstrand

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

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Materials Engineering

Other Engineering and Technologies

Physical Sciences

Electrical Engineering, Electronic Engineering, Information Engineering

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 55

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