Anomalous thermal diffusivity in underdoped YBa2Cu3O6+x [Physics]
The thermal diffusivity in the
ab plane of underdoped YBCO crystals is measured by means of a local optical technique in the temperature range of 25–300 K.
The phase delay between a point heat source and a set of detection points around it allows for high-resolution measurement
of the thermal diffusivity and its in-plane anisotropy. Although the magnitude of the diffusivity may suggest that it originates
from phonons, its anisotropy is comparable with reported values of the electrical resistivity anisotropy. Furthermore, the
anisotropy drops sharply below the charge order transition, again similar to the electrical resistivity anisotropy. Both of
these observations suggest that the thermal diffusivity has pronounced electronic as well as phononic character. At the same
time, the small electrical and thermal conductivities at high temperatures imply that neither well-defined electron nor phonon
quasiparticles are present in this material. We interpret our results through a strongly interacting incoherent electron–phonon
“soup” picture characterized by a diffusion constant
vB is the soup velocity, and scattering of both electrons and phonons saturates a quantum thermal relaxation time
Publisher URL: http://feedproxy.google.com/~r/Pnas-RssFeedOfEarlyEditionArticles/~3/xmE5DHLftJw/1703416114.short
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