Bad Metal Behavior in SrRuO3

A new class of materials known as so-called "bad metals" show transport properties not understandable using conventional transport theory. Their resistivities at high temperatures imply electron mean free paths less than an inter-atomic distance, and their infrared conductivity is not in agreement with conventional Drude theory. We are using SrRuO₃ as a model system to study this phenomenon.

DC conductivity measurements on SrRuO₃ films reveal some anomalous behavior. The resistance at high temperatures continues to rise linearly with temperature beyond the point where conventional theories are no longer applicable Measurements of the frequency dependent conductivity by infrared reflectivity and terahertz time-domain spectroscopy, show an analytic structure fundamentally different from that predicted by the standard theory of metals. The low temperature resistance incrased like T², as expected from electron-electron scattering. Residual resistivities achieved are comparable to the best single crystal values.

Introducing disorder by means of electron irradiation also has an unusual effect, violating Matthiessen's rule. We observe quantum oscillations in the electrical resistivity verses field of a high-quality thin film of SrRuO₃. Our study demonstrates the existence of long-lived fermion quasiparticles at low temperatures, and strongly suggests that the ground state of SrRuO₃ is a Fermi liquid, even though conductivity measurements at higher temperatures show anomalous metallic behavior.

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