What is it about?

Temperature and doping dependence of resistivity in high-Tc cuprates has been a central challenge for understanding for several decades, and it has only recently been shown that, at least in the ultra-high temperature regime, one can understand it by disentangling it via the Nernst-Einstein relation to the diffusion constant and the charge susceptibility (compressibility). It was further realized that besides the diffusion constant, which incorporates particle speed and scattering rates, the charge susceptibility, a simpler thermodynamic quantity, also plays an important role. Our understanding of the resistivity would be improved by knowing the diffusion constant in the more interesting regimes, e.g., for temperatures closer to Tc. However, both the diffusion constant and charge susceptibility are not reliably measured, and their behavior in real materials is not clear. In this publication, the Nernst-Einstein relation for heat and charge conductivity, previous measurements, and findings from numerical simulations were used to determine the behavior of the diffusion constant and, in turn, the charge susceptibility. The results revealed unexpectedly short mean free paths, values below the so-called Planckian bound, and charge susceptibility with a significant dependence on temperature and doping. This indicates that understanding the resistivity in high-Tc cuprates will only be possible by simultaneously considering, besides scattering mechanisms, also the thermodynamic quantities.

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Why is it important?

Provides estimates of electronic diffusion and charge susceptibility and give a new insight into the behavior of electrons in cuprates.


I hope this work will stimulate further work to determine the behaviour of charge susceptibility in real materials, as that could considerably help our understanding.

Jure Kokalj
Faculty of Civil and Geodetic Engineering, University of Ljubljana, Slovenia

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This page is a summary of: Electronic diffusion in a normal state of high-Tc cuprate YBa 2 Cu 3 O 6+x, Proceedings of the National Academy of Sciences, March 2024, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2322670121.
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