  We propose SnBi2Te4 to be a novel candidate material exhibiting temperature
(T) mediated transitions between rich topological phases. From a combined
theoretical and experimental studies, we find that SnBi2Te4 goes from a low-T
topological semimetallic phase to a high-T (room temperature) topological
insulating phase via an intermediate topological metallic phase. Single
crystals of SnBi2Te4 are characterized by various experimental probes including
Synchrotron based X-ray diffraction, magnetoresistance, Hall effect, Seebeck
coefficient, magnetization and angle-resolved photoemission spectroscopy
(ARPES). 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, as confirmed by our density
functional theory calculations. Simulated surface states at 15 K agree fairly
well with our ARPES data and are found to be robust with varying T. This
indirectly supports the experimentally observed paramagnetic singularity in the
entire T-range. The proposed coexistence of rich topological phases is a rare
occurrence, yet paves a fertile ground to tune various topological phases in a
material driven by structural distortion.
