Disentangling photodoping, photoconductivity and photosuperconductivity in the cuprates

Persistent photoconductivity (PPC) and persistent photo-superconductivity (PPS) describe both the enhancement of the conductivity and the increase of the superconducting transition temperature (Tc) of cuprate superconductors upon visible and UV light illumination. The debate on the microscopic origin of those effects has not been settled, but the existing models assume a link between them and the concomitant carrier-density enhancement (photodoping). Here we present experiments that show that, contrary to conventional wisdom, the enhancement of Tc correlates instead with a reduction of the impurity scattering rate. Since this decrease in scattering rate and the photoinduced increase in carrier density exhibit different wavelength and oxygen-content dependence, as well as contrasting relaxation dynamics we conclude a decoupling of these two parameters. Besides shedding light on the entanglement of PPS and PPC, our results provide new evidence on the intimate relationship between carrier mobility and critical temperature which promises to provide new insights into the mechanism at the heart of high Tc superconductivity.