Enhancement of persistent photoconductivity by uv excitation in GdBa2Cu3O6.3

Disentangling Photodoping, Photoconductivity, and Photosuperconductivity in the Cuprates

The normal-state conductivity and superconducting critical temperature of oxygen-deficient YBa_{2}Cu_{3}O_{7-δ} can be persistently enhanced by illumination. Strongly debated for years, the origin of those effects-termed persistent photoconductivity and photosuperconductivity (PPS)-has remained an unsolved critical problem, whose comprehension may provide key insights to harness the origin of high-temperature superconductivity itself. Here, we make essential steps toward understanding PPS. While the models proposed so far assume that it is caused by a carrier-density increase (photodoping) observed concomitantly, our experiments contradict such conventional belief: we demonstrate that it is instead linked to a photo-induced decrease of the electronic scattering rate. Furthermore, we find that the latter effect and photodoping are completely disconnected and originate from different microscopic mechanisms, since they present different wavelength and oxygen-content dependences as well as strikingly different relaxation dynamics. Besides helping disentangle photodoping, persistent photoconductivity, and PPS, our results provide new evidence for the intimate relation between critical temperature and scattering rate, a key ingredient in modern theories on high-temperature superconductivity.

Interfacially controlled transient photoinduced superconductivity

We report on a large transient photoinduced enhancement of the superconducting critical temperature (DeltaTc = 23 K) in epitaxial YBa2Cu3O(6.7)/La(0.7)Ca(0.3)MnO3 bilayers upon visible light illumination. The effect relaxes with a characteristic time of 100 s at low temperatures, which is 4 orders of magnitude faster than the persistent photoconductivity or persistent photoinduced superconductivity previously found in single high-Tc superconducting films. This result is discussed in terms of light induced charge transfer through the interface similar to what happens in semiconductor junctions.