  High-quality single-crystal inorganic halide perovskites have begun to
attract interest for future quantum devices applications. In this work, we
focus on the quantum transport properties of single-crystal epitaxial halide
perovskites and present low-temperature quantum magnetotransport measurements
on thin film devices of single-crystal cesium tin bromide (CsSnBr$_{3}$) at low
temperature. We demonstrate that the system exhibits two-dimensional (2D) Mott
variable range hopping (VRH) transport with a giant negative magnetoresistance.
This large negative magnetoresistance can be described by the
Nguyen-Spivak-Shkovskii (NSS) model which describes the quantum interference of
different directed hopping paths of charge carriers. Based on this model, we
extract the temperature-dependent hopping length of charge carriers in
epitaxial CsSnBr$_{3}$, estimate their localization length, and find a lower
bound for their phase coherence length of ~ 100 nm at low temperatures. These
new observations add to a growing body of experimental evidence that
demonstrate that epitaxial halide perovskites are emerging as a new material
class for the study of low-dimensional quantum coherent transport phenomena.
