Critical current and scaling laws in evaporated two-phase Cu_2.5Mo₆S₈

We have measured critical currents I_c of an evaporated Cu_xMo₆S₈ (x = 2.5±0.3) film as a function of an external perpendicular field B up to the upper critical field B_c2, at several temperatures (T ≤ 4.2K). Results for the pinning force per unit length F = I_cB do not obey a scaling law. That is, F = K(T)f (b), where K and f are general functions of the temperature T and the reduced field b = B/B_c2, respectively. By comparing data with other evaporated and sputtered Cu_xMo₆S₈ with x ≤ 2, we have separated the pinning force into two parts, each one obeying a scaling law. The recently published phase diagram of Cu_xMo₆S₈, along with our results, suggests that critical current and pinning in this material are controlled by two superconducting phases.