Regensburg 2004 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 2: Elektrische und optische Eigenschaften II

DF 2.1: Hauptvortrag

Montag, 8. März 2004, 14:30–15:10, H11

Charge induced insulator-metal transition and resistive memory in doped perovskites — •J. Georg Bednorz — IBM Research Laboratory, Säumerstrasse 4, CH-8803 Rüschlikon, Switzerland

Certain doped perovskites exhibit a charge induced insulator-metal transition with a resistive memory effect. When exposed to an electrical field, the resistivity of the doped perovskite is reduced by several orders of magnitude. Consecutive electrical current pulses (typically 100 ns) of opposite polarity switch the resistance of the perovskite reversibly between a higher-resistance and a lower-resistance state. These two different states persist after removal of the applied electrical bias. Since these compounds show long retention times they are interesting candidates for non-volatile memory applications.

Bulk single crystals of doped SrTiO₃ are a model system for this class of materials to study the drastic resistivity changes under applied electrical field and the memory effect. Optical changes in the crystal that are observed during this transformation indicate a gradual transformation of the bulk through injection of charges. Large birefringence of the crystal is observed in the conducting state during current flow. This is shown to be caused by mechanical stress due to sample heating. A rather homogeneous pattern, however, suggests a uniform current distribution. Charge transfer processes possibly mediate the conduction process as indicated by optical absorption spectroscopy on doped crystals. Electron spin resonance measurements give a hint at the presence of different valence states in the insulating and conducting state.