  Combining angle-resolved photoemission spectroscopy and magneto-transport
measurements, we systematically investigated the possible origin of the extreme
magnetoresistance in Pr/Sm mono-antimonides/bismuthides (PrSb, SmSb, PrBi,
SmBi). Our photoemission measurements reveal that the bulk band inversion and
surface states are absent (present) in Pr/Sm antimonides (bismuthides),
implying that topological surface states are unlikely to play an important role
for the observed extreme magnetoresistance. We found that the electron-hole
compensation is well satisfied in all these compounds and the bulk band
structure exhibits no obvious temperature dependence from 10 K up to 150 K.
Simultaneous fittings of the magnetoresistance and Hall coefficient reveal that
the carrier mobility is dramatically enhanced at low temperature, which
naturally explains the suppression of extreme magnetoresistance at high
temperatures. Our results therefore show that the extreme magnetoresistance in
these compounds can be well accounted for by the two-band model with good
electron-hole compensation. Finally, we found that both PrSb and SmSb exhibit
highly linear bulk bands near the X point and lie close to the transition point
between a topologically trivial and nontrivial phase, which might be relevant
for the observed anomalous quantum oscillations.
