Unconventional electronic phase transition in SnBi2Te4: role of anomalous thermal expansion

Abstract We propose SnBi 2 Te 4 to be a novel topological quantum material exhibiting temperature ( T ) mediated transitions between rich electronic phases. Our combined theoretical and experimental results suggest that SnBi 2 Te 4 goes from a low- T semimetallic phase to a high- T (room temperature) insulating phase via an intermediate metallic phase. Single crystals of SnBi 2 Te 4 are characterized by various experimental probes including synchrotron based x-ray diffraction, magnetoresistance, Hall effect, Seebeck coefficient and magnetization. X-ray diffraction data confirms an anomalous thermal expansion of the unit cell volume below ∼100 K, which significantly affects the bulk band structure and hence the transport properties. Simulated surface states are found to be topologically robust with varying T . This indirectly supports the experimentally observed paramagnetic singularity in the entire T -range. The proposed coexistence of such rich phases is a rare occurrence, yet it facilitates a fertile ground to tune them in a material driven by structural changes.