  Superconductivity with exotic properties has often been discovered in
materials with a layered (two-dimensional) crystal structure. The low
dimensionality affects the electronic structure of materials, which could
realize a high transition temperature (Tc) and/or unconventional pairing
mechanisms. Here, we report the superconductivity in a layered tin arsenide
NaSn2As2. The crystal structure consists of (Sn2As2)2- bilayers, which is bound
by van-der-Waals forces, separated by Na+ ions. Measurements of electrical
resistivity and specific heat confirm the bulk nature of superconductivity of
NaSn2As2 with Tc of 1.3 K. Our results propose that the SnAs layers will be a
basic structure providing another universality class of a layered
superconducting family, and it provides a new platform for the physics and
chemistry of low-dimensional superconductors with lone pair electrons.
