  Topological Kondo insulators have been attracting great attention from the
condensed-matter physics community due to their fascinating topological and
strongly correlated properties. Here, we report angle-dependent c-axis
magnetoresistance (MR) oscillations in a Kondo insulator, SmB6 single crystal,
in a magnetic field of up to 13 T rotated in the ab-plane. Four-fold symmetric
MR oscillations are first observed above 8 K, which result from the four-fold
(C4) degeneracy of the bulk Fermi surface of SmB6. With decreasing temperature
down to 2.3 K, the C4 symmetry of the MR oscillations gradually weakens and C2
symmetry appears. This demonstrates a crossover from three-dimensional bulk
states to two-dimensional surface states and implies the possible emergence of
topological nematic states. Our experimental observations shed new light on the
metallic surface states and nematic states in the Kondo insulator SmB6.
