  Topologically non-trivial electronic structures can give rise to a range of
unusual physical phenomena, and the interplay of band topology with other
effects such as electronic correlations and magnetism requires further
exploration. The rare earth monopnictides $X$(Sb,Bi) ($X$ = lanthanide) are a
large family of semimetals where these different effects may be tuned by the
substitution of rare-earth elements. Here we observe anomalous behavior in the
quantum oscillations of one member of this family, antiferromagnetic SmSb. The
analysis of Shubnikov-de Haas (SdH) oscillations provides evidence for a
non-zero Berry phase, indicating a non-trivial topology of the $\alpha$-band.
Furthermore, striking differences are found between the temperature dependence
of the amplitudes of de Haas-van Alphen effect oscillations, which are well
fitted by the Lifshitz-Kosevich (LK) formula across the measured temperature
range, and those from SdH measurements which show a significant disagreement
with LK behavior at low temperatures. Our findings of unusual quantum
oscillations in an antiferromagnetic, mixed valence semimetal with a possible
non-trivial band topology can provide an opportunity for studying the interplay
between topology, electronic correlations and magnetism.
