Persistent Photoconductivity in YBa2Cu3Ox and Other High-Temperature Superconductors

Wilhelm Markovitsch

The persistent photoconductivity (PPC) in high-temperature superconductors has
some very special features. The effect is primarily observed in oxygen-deficient 1-2-3 superconductors such as YBa2Cu3Ox, but there are also reports of similar effects in some other compounds. The illumination of these substances leads to significant changes of the electronic properties. The electrical conductivity can be enhanced up to a factor of about 3 and the Hall effect shows that not only the free carrier concentration but also the carrier mobility is modified. Most intriguing is the persistence of the photo-induced effects in YBa2Cu3Ox up to temperatures slightly below room temperature. Below approx. 250 K, PPC relaxation is practically unobservable. Even at higher temperatures the relaxation is extremely slow, taking hours or even days at room temperature. The photo-excitation, commonly called “photodoping”, is not only able to persistently change the doping level in these substances, but also their crystal
structure: the lattice parameters are modified and also the electronic anisotropy is affected by the photo-excitation. Raman and infrared measurements give evidence for re-arrangements of the oxygen ions within the so-called copper-oxide chains in the crystal unit cell. There is a long-standing discussion whether these structural changes are just a side effect of photodoping or are important to stabilise the photo-induced electronic state, or are the actual origin of the persistent photo-induced phenomena in the high-temperature superconductors.

Electronic Properties of Materials
No. of pages
Publication date
Austrian Fields of Science 2012
Physics, Astronomy
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