  Topological superconductors (TSCs) are of significant current interest
because they offer promising platforms for finding Majorana fermions. Here we
report a new superconductor synthesized by intercalating Cu into a
naturally-formed topological insulator (TI) heterostructure consisting of
Bi2Se3 TI units separated by nontopological PbSe units. For the first time in a
TI-based superconductor, the specific-heat behavior of this material suggests
the occurrence of unconventional superconductivity with gap nodes. The
existence of gap nodes in a strongly spin-orbit coupled superconductor would
give rise to spin-split Andreev bound states that are the hallmark of
topological superconductivity. Hence, this new superconductor emerges as an
intriguing candidate TSC.
