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arXiv · 1908.03810

Soft phonons and ultralow lattice thermal conductivity in the Dirac semimetal Cd3As2

Shengying Yue·Hamid T. Chorsi·Manik Goyal·Timo Schumann·Runqing Yang·Tashi Xu·Bowen Deng·Susanne Stemmer·Jon A. Schuller·Bolin Liao
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Abstract

Recently, Cd3As2 has attracted intensive research interest as an archetypical Dirac semimetal, hosting three-dimensional linear-dispersive electronic bands near the Fermi level. Previous studies have shown that single-crystalline Cd3As2 has an anomalously low lattice thermal conductivity, ranging from 0.3 W/mK to 0.7 W/mK at 300 K, which has been attributed to point defects. In this work, we combine first-principles lattice dynamics calculations and temperature-dependent high-resolution Raman spectroscopy of high-quality single-crystal thin films grown by molecular beam epitaxy to reveal the existence of a group of soft optical phonon modes at the Brillouin zone center of Cd3As2. These soft phonon modes significantly increase the scattering phase space of heat-carrying acoustic phonons and are the origin of the low lattice thermal conductivity of Cd3As2. Furthermore, we show that the interplay between the phonon-phonon Umklapp scattering rates and the soft optical phonon frequency explains the unusual non-monotonic temperature dependence of the lattice thermal conductivity of Cd3As2. Our results further suggest that the soft phonon modes are potentially induced by a Kohn anomaly associated with the Dirac nodes, in analogy to similar, nonetheless weaker, effects in graphene and Weyl semimetals.

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Shengying Yue, Hamid T. Chorsi, Manik Goyal, Timo Schumann, Runqing Yang, Tashi Xu, Bowen Deng, Susanne Stemmer, Jon A. Schuller, Bolin Liao. 2019-08-10. Soft phonons and ultralow lattice thermal conductivity in the Dirac semimetal Cd3As2. https://doi.org/10.1103/physrevresearch.1.033101

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