Dissipation-induced Superconducting Transition in one-dimensional arrays of Josephson Junction

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The superconductor-to-insulator (SI) transition in small Josephson junction arrays is a typical example of the quantum phase transition. The aim of this research was to clarify the role of dissipation in the transition in one-dimensional array of Josephson junctions. In order to investigate the effects of quantum fluctuations and dissipation in Josephson junction array, we have fabricated one-dimensional arrays of Al small Josephson junctions, each of which was shunted by Cr shunt resistance, and measured the I/V characteristics at low temperatures. Our conclusions are as follows.1. We have observed the SI transition in 1d arrays of Josephson junction caused by dissipation as well as by quantum fluctuation. Namely, arrays with large E_J/E_C or with small R_S showed the Josephson-like I-V characteristics and the zero-bias resistance decreased at the lowest temperature. On the other hand, those with small E_J/E_C and large R_S showed the Coulomb blockade in the I-V characteristics and the resistance increased. Here, E_J, E_C, and R_S are the Josephson energy, the single electron charging energy and the shunting resistance, respectively.2. Based on the observation, we have determined the phase diagram of the system at T= 0 K in the parameter space of E_J/E_C and R_S.3. The S-I transition takes place at R_S nearly equals to the quantum resistance R_Q when E_J/E_C <<1, which supports the theories of dissipative phase transition in this system.4. The critical value of E_J/E_C for the case R_Q/R_S =0 was much smaller than the theoretical prediction, for which we have no definite answer yet.5. We have also observed the insulators-to-superconductor transition when we increase the width of the array from one-dimensional chain to two-dimensional one.