Three dimensional phase diagram of superfluidity controlled voltage nonlinearity in superconductors

Abstract

We have studied current-voltage (IV) characteristics of (i) underdoped and (ii) electron doped high temperature superconductors (HTS) around the superconducting phase transition. Over a wide range of temperature below the critical temperature a nonlinear current-voltage behavior has been observed both in the undoped and electron doped sample. Following the dependence of the pinning potential on the current sweeping rates (CSR) several moderate values of CSR have been used for the measurement of IV at a constant temperature T. An exponent related to the superfluid density varies with CSR mostly at the range of the lower temperature. Variation of the nonlinear voltage with respect to the sweeping rate is found to be a function of both the applied current and temperature. On the basis of the variation we propose that the three dimensional phase diagram identifies the potential regions of nonlinearity. A collinear arrangement of maxima loops by the driving current is possible in a narrrow range of T.