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Temperature-dependent resistivity of single-crystal and thin film . The insulator-metal transition occurs in both samples near , with similar hysteresis curves. A fit to the resistivity in the insulating phase gives an activation energy (bandgap) of for both samples.
Schematic band diagram of . In the insulating phase, a bandgap is formed between the valence band and the conduction band. A second empty conduction band has the same symmetry as the valence band, which is split by a Peiers distortion and by Hubbard energy. Photoexcitation at high photodoping energies is dominated by transitions. The time-dependent optical response of single-crystal and thin-film after photoexcitation with pulses is shown in the lower part of the figure.
Fluence dependence of the photoinduced phase transition in the thin films for various pump photon energies above the bandgap. A threshold of is found for all photon energies, with a region of superlinear growth and saturation.
(a) Fluence dependence of the photoinduced phase transition in the thin films for various pump photon energies below the bandgap. (b) Threshold for the photoinduced phase transition for various wavelengths in bulk and thin films.
Measurement of the IR absorption coefficient for thin films. The absorption coefficient for single-crystal samples exhibits lower absorption at photon energies below the bandgap.
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