Evidence for a bulk complex order parameter in Y _0.9 Ca _0.1 Ba ₂ Cu ₃ O ₇ _−δ thin films

Abstract

We have measured the penetration depth of overdoped Y0.9Ca0.1Ba2Cu3O7-delta\n(Ca-YBCO) thin films using two different methods. The change of the penetration\ndepth as a function of temperature has been measured using the parallel plate\nresonator (PPR), while its absolute value was obtained from a quasi-optical\ntransmission measurements. Both sets of measurements are compatible with an\norder parameter of the form: Delta*dx2-y2+i*delta*dxy, with Delta=14.5 +- 1.5\nmeV and delta=1.8 meV, indicating a finite gap at low temperature. Below 15 K\nthe drop of the scattering rate of uncondensed carriers becomes steeper in\ncontrast to a flattening observed for optimally doped YBCO films. This decrease\nsupports our results on the penetration depth temperature dependence. The\nfindings are in agreement with tunneling measurements on similar Ca-YBCO thin\nfilms.\n