Direct observation of the transition from the conventional superconducting state to the pi state in a controllable Josephson junction.
We measure the full supercurrent-phase relation of a controllable pi junction around the transition from the conventional 0 state to the pi state. We show that around the transition the Josephson supercurrent-phase relation changes from I(sc) approximately I(c)sin((phi) to I(sc) approximately I(c)sin((2phi). This implies that, around the transition, two minima in the junction free energy exist, one at phi=0 and one at phi=pi, whereas only one minimum exists at the 0 state (at phi=0) and at the pi state (at phi=pi). Theoretical calculations based on the quasiclassical theory are in good agreement with the observed behavior.
Baselmans
J J A
JJ
Department of Applied Physics and Materials Science Center, University of Groningen, Nijenborg 4, 9747 AG Groningen, The Netherlands.
Heikkilä
T T
TT
van Wees
B J
BJ
Klapwijk
T M
TM