  After the discovery of nematic topological superconductivity in CuxBi2Se3,
carrier-doped topological insulators are established as a fertile ground for
topological superconductors. The superconductor Cu1.5(PbSe)5(Bi2Se3)6 (CPSBS)
contains Bi2Se3 blocks as a constitutional unit, but its superconducting gap
appears to have nodes [S. Sasaki et al., Phys. Rev. B 90, 220504 (2014)], which
is in contrast to the fully-opened gap in CuxBi2Se3 and the relation between
the two superconductors remained an open question. Here we report our
observation of clear two-fold symmetry in the in-plane magnetic-field-direction
dependencies of the upper critical field and of the specific heat of CPSBS,
where the direction of the maxima, which is different from that in CuxBi2Se3,
indicates that the gap nodes are located in the mirror plane of the crystal
lattice. This means that the topological nematic state with
mirror-symmetry-protected nodes is realized in CPSBS.
