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The Wiedemann-Franz law and its discontents Kamran Behnia

Thursday, May 31, 2018 - 11:15 to 12:30 Auditorium

In the middle of nineteenth century, Wiedemann and Franz discovered a correlation between thermal and electrical conductivities of various metals. Since then, a law bearing their name has become one of the oldest laws of the solid-state physics. It survived the quantum revolution, which linked it to a ratio of fundamental constants. The equality between this Sommerfeld ratio and the Lorenz number (the ratio of thermal conductivity divided by temperature to electric conductivity) in the zero-temperature limit was enshrined as a canonical signature of a Fermi liquid. The subject of this talk is the experimental research on the validity of (and the deviations from) the Wiedemann-Franz law in uncommon metals. After reviewing different unsuccessful assaults in the past three decades, we will focus on ongoing research and the information brought by verifying this correlation. Two distinct contexts will be discussed. The first is strong electron-electron scattering and possible hydrodynamic signatures in the transport of charge and entropy. The second subject is anomalous transverse transport arising from the Berry curvature of Bloch waves. In both cases, the zero-temperature validity is accompanied by a finite-temperature deviation, a controversial source of information on mobile electrons in solids.