Ferroelectric Instability Driven Local Atomic Off-Centering and Low Thermal Conductivity in a Topological Crystalline Insulator Sn3Bi0.7Te4

Abstract

The synthesis of new topological quantum materials is necessary as it enables a fascinating platform for studying chemical bonding, crystal structure, and exotic transport phenomena in crystalline solids. The robust charge transport arising from the topologically protected nontrivial electronic states gives rise to intriguing quantum properties. However, quantum technologies at cryogenic temperatures require negligible thermal decoherence, where low thermal conducting components may have a vital role to play. Here, we have synthesized a topological crystalline insulator (TCI) Sn3Bi0.7Te4, which exhibits emergent quantum transport, namely, weak antilocalization and diffusive charge transport like electron–electron interaction, witnessed at low temperatures. Triply degenerate unstable polar optical modes dominated by Sn vibrations cause intrinsic ferroelectric instability in Sn3Bi0.7Te4, as tracked down by piezoresponse force microscopy (PFM). Synchrotron X-ray pair distribution function (X-PDF) analysis and first-principles density functional theory calculations suggest that the stereochemical expression of the 5s2 lone pair of Sn2+ triggers dynamic off-centering of the cation along the ⟨111⟩ crystallographic direction, breaking the symmetry locally. The ferroelectric instability, local lattice distortion, and polarizable soft chemical bonding result in a low lattice thermal conductivity of this TCI at low temperatures (2–300 K).