Interlayer thermal transport and glasslike behavior in crystalline <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>CsCu</mml:mi> <mml:mn>4</mml:mn> </mml:msub> <mml:msub> <mml:mi>Se</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math>

Abstract

Understanding lattice dynamics and thermal transport in crystalline compounds with intrinsically low lattice thermal conductivity (${\ensuremath{\kappa}}_{L}$) is crucial in condensed matter physics. In this work, we investigate the lattice thermal conductivity of ${\mathrm{CsCu}}_{4}{\mathrm{Se}}_{3}$ by coupling first-principles anharmonic lattice dynamics with a unified theory of thermal transport. Our results reveal that the vibrational properties of ${\mathrm{CsCu}}_{4}{\mathrm{Se}}_{3}$ are characterized by strong anharmonicity and wavelike phonon tunneling. At room temperature, the predicted intralayer thermal conductivity is an exceptionally low 0.39 ${\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, markedly lower than the interlayer value of 0.69 ${\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, strikingly challenging the conventional understanding of thermal transport in layered materials. This anomalous phenomenon can be traced back to the substantial coherence contribution along the $z$ axis, driven by the coupling of distinct vibrational eigenstates, which enables efficient thermal transport across layers. Furthermore, the coherence-driven conductivity dominates the total thermal conductivity along the $z$ axis, leading to an anomalous, wide-temperature-range (100--700 K) glasslike thermal transport. We attribute the nonmonotonic temperature dependence of coherence thermal conductivity to the combined effects of anharmonic scattering rates, frequency difference, and phonon renormalization. Our work not only uncovers the microscopic mechanism underlying effective interlayer thermal transport in ${\mathrm{CsCu}}_{4}{\mathrm{Se}}_{3}$ but also elucidates the nonmonotonic temperature dependence of thermal conductivity, offering valuable insights into the anomalous heat transport in layered compounds.

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