Dynamics of photodoping and photoconductivity relaxation in oxygen-deficient YBa2Cu3Ox

Spectroscopic Studies of the Persistent In-Plane and Out-of-Plane Photoconductivity in 60 K YBa2Cu3Ox

“…However, their spectra of samples with similar oxygen contents of about 6.5 are only recorded for temperatures of 100 K and above. On the other hand, we have observed this maximum also in conventionally grown, c-axis oriented films [4] at the same temperature. The interpretation within one of the proposed models for PPC [9,10] fails, because, at 1.4 to 1.5 eV, charge-transfer transitions are not expected to occur.…”

“…These results impose the restriction to any theoretical picture of PPC in YBa 2 Cu 3 O x that the process is most likely triggered by electronic transitions between plane-related or chain-related bands. However, in a previous paper we have found evidence for a finite h below the charge-transfer gap, occurring only at low temperatures [4].The above results were derived from in-situ measurements of the in-plane resistivity r ab in YBa 2 Cu 3 O x and GdBa 2 Cu 3 O x thin films during light illumination. We have recently shown that photodoping also affects the out-of-plane resistivity r c using thin films grown on ªtiltedº substrates [5].…”

“…at grain boundaries). However, it is not clear why this contribution vanishes already at 100 K, as reported in [4]. Clearly, more detailed investigations of the spectral efficiencies in the low temperature regime are required to elucidate the nature of this structure.…”

“…2b). This is readily explained by a spurious effect of the PPC relaxation, which becomes very fast near room temperature [7,8]. Since each measurement cycle was started at small photon energies, the sample was pre-photodoped when the excitation energy was switched to 2.05 eV.…”

“…The spectral efficiencies at several temperatures between 70 and 305 K were determined using a similar procedure as in the previous studies [1,2,4]. The photodoping experiments were started with the smallest available photon energy (1.16 eV).…”