TEMPERATURE-DEPENDENCE OF THE 4-EV OPTICAL-TRANSITION IN YBA2CU3O6

With spectroscopic ellipsometry the optical properties of high quality YBa2Cu3O6 thin films deposited by off-axis magnetron sputtering were investigated in situ. The optical transition at 4 eV of these films th at were not exposed to atmospheric condition shows a two limes higher magnitude than reported previously and can be described by a single Lo rentz oscillator in the complete temperature range of 20 degrees C-700 degrees C. The width of the Lorentz oscillator is remarkably small. C ombined with the temperature-independent strength of one electron per unit cell of the 4-eV transition, it is an indication that this optica l transition takes place between a quite isolated occupied and unoccup ied level of the electronic structure.