When the intracell hopping is smaller than the intercell hopping, one of these materials is the solution to the SSH model. Notable examples of these materials belong to symmetry classes A, AII (“A two”), and BDI (“BD one”) of (15[1])the Altland–Zirbauer classification. A 2D one of these materials is the non-trivial solution to the time-reversal symmetric Kane–Mele model, which is described by elements of Z-sub-2. Since strong spin-orbit coupling is required for these materials, they can be realized as mercury (*) telluride quantum (10[1])wells or bismuth chalcogenides. (10[1]-5[1])The Hall conductance is an invariant for many of these materials, (10[1])which have (10[1])symmetry-protected, gapless (10[1])edge states but have a bandgap in their bulk. For 10 points, name (-5[1])this recently-discovered class of materials whose interiors do not conduct electricity, (10[1])but whose surfaces do. ■END■ (10[2]0[1])