  Through a thorough magneto-transport study of antiferromagnetic topological
insulator MnBi2Te4 (MBT) thick films, a positive linear magnetoresistance (LMR)
with a two-dimensional (2D) character is found in high perpendicular magnetic
fields and temperatures up to at least 260 K. The nonlinear Hall effect further
reveals the existence of high-mobility surface states in addition to the bulk
states in MBT. We ascribe the 2D LMR to the high-mobility surface states of
MBT, thus unveiling a transport signature of surface states in thick MBT films.
A suppression of LMR near the Neel temperature of MBT is also noticed, which
might suggest the gap opening of surface states due to the
paramagnetic-antiferromagnetic phase transition of MBT. Besides these, the
failure of the disorder and quantum LMR model in explaining the observed LMR
indicates new physics must be invoked to understand this phenomenon.
