MESA+ Institute for Nanotechnology

The d-wave pairing symmetry of the high-Tc superconductors

provides the opportunity to realize novel Josephson

quantum-structures, characterized by built-in π-phase shifts.

Such elements are of interest for basic studies and have also been

proposed as new components in superconducting


Using thin-film ramp-type Josephson contacts between a high-Tc

and a low-Tc superconductor, experiments to study the

d-wave-induced π-phase-shift effects in planar Josephson

arrays have been enabled. Based on this, various novel

quantum-structures have been realized, including 1-D and 2-D

arrays of corner junctions and π-rings.

The investigations were first performed on 1-D Josephson arrays

with a zigzag configuration. Apart from demonstrating the

experimental realization of high-quality complex Josephson-arrays

comprising the high-Tc cuprate YBCO, the zigzag Josephson

junctions were shown to be viable structures to resolve

controversial issues regarding the pairing symmetry in the

high-Tc cuprate superconductors. This was further demonstrated

by the order parameter symmetry test experiments performed based

on NCCO/Au/Nb zigzag junctions.

Another interesting aspect of the zigzag junctions is that, under

certain conditions, the lowest-energy ground state of the system

is characterized by a spontaneous generation of a half-integer

magnetic-flux quantum at each corner. The half flux quanta effects

in zigzag junctions have been studied using scanning SQUID


To study the magnetic coupling between the half magnetic-flux

quanta, arrays of electrically isolated π-rings have been

realized. A preferentially antiferromagnetic ordering of

half-integer magnetic-flux quanta was observed for electrically

isolated Josephson structures, when sufficiently closely spaced.

This presents an analogue to the antiferromagnetic Ising-spin

system, and opens a possibility to realize various two-dimensional

Ising antiferromagnetic systems.

Finally, the work described in this thesis will provide a diverse

basis for both fundamental studies and potential applications,

including further investigations on details of the order parameter

symmetry in the high-Tc cuprates, half-integer magnetic-flux

quantum effects, correlation in two-dimensional Ising models, and

to realize the theoretically proposed elements for superconducting

(quantum) electronics such as complementary Josephson circuits and