Glasslike thermal conductivity and narrow insulating gap of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>EuTiO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>
Alexandre Jaoui, Shan Jiang, Xiaokang Li, Y. Tomioka, Isao Inoue, Johannes Engelmayer, Rohit Sharma, Lara Pätzold, T. Lorenz, Benoît Fauqué, Kamran Behnia
Abstract
Crystals and glasses differ by the amplitude and the temperature dependence of their thermal conductivity. However, there are crystals known to display glasslike thermal conductivity. Here, we show that ${\mathrm{EuTiO}}_{3}$, a quantum paraelectric known to order antiferromagnetically at 5.5 K, is one such system. The temperature dependence of resistivity and Seebeck coefficient yield an insulating band gap of $\ensuremath{\sim}0.22$ eV. Thermal conductivity is drastically reduced. Its amplitude and temperature dependence are akin to what is seen in amorphous silica. Comparison with nonmagnetic perovskite solids, ${\mathrm{SrTiO}}_{3}$, ${\mathrm{KTaO}}_{3}$, and ${\mathrm{EuCoO}}_{3}$, shows that what impedes heat transport are $4f$ spins at ${\mathrm{Eu}}^{2+}$ sites, which couple to phonons well above the ordering temperature. Thus, in this case, superexchange and valence fluctuations, not magnetic frustration, are the drivers of the glasslike thermal conductivity.