We present low temperature transport measurements in one dimensional Josephson junctions rhombi chains. We have measured the current phase relation of a chain of 8 rhombi. The junctions are either in the classical phase regime with the Josephson energy much larger than the charging energy, $E_{ J}\gg E_{ C}$, or in the quantum phase regime where $E_{ J}/E_{ C}\approx 2$. In the strong Josephson coupling regime ($E_{ J}\gg E_{ C} \gg k_{ B}T$) we observe a sawtooth-like supercurrent as a function of the phase difference over the chain. The period of the supercurrent oscillations changes abruptly from one flux quantum $\Phi_{ 0}$ to half the flux quantum $\Phi_{ 0}/2$ as the rhombi are tuned in the vicinity of full frustration. The main observed features can be understood from the complex energy ground state of the chain. For $E_{ J}/E_{ C}\approx 2$ we do observe a dramatic suppression and rounding of the switching current dependence which we found to be consistent with the model developed by Matveev et al.(Phys. Rev. Lett. { \bf 89}, 096802(2002)) for long Josephson junctions chains.
Categories: cond-mat.mes-hall cond-mat.supr-con