The Influence of the Second Harmonic in the Current-Phase Relation on   the Voltage-Current Characteristic of high TC DC SQUID
  A theory for the voltage-current characteristic in high TC DC SQUIDs, which accounts for a second harmonic in the junction current-phase relation, is developed. The comparison with experiment is performed. It is shown that if the second harmonic is prevailed, the theory can explain the large deviations of the experimental voltage modulation from theoretical predictions and computer simulations based on conventional sinusoidal current-phase relation. 
Ya. S. Greenberg, I. L. Novikov, V. Schultze, and H.-G. Meyer