# Definition A strong topological insulator is a 3D [[Time-Reversal Symmetric Topological Insulator|time-reversal symmetric topological insulator]] characterized by a $Z_2$ [[Z2 Topological Invariant|topological invariant]] of $Z_2 = (1; \nu_1 \nu_2 \nu_3)$ where $\nu_i$ can be $0$ or $1$. # Examples Examples include Bi$_2$Te$_3$ ([[Bi2Te3]]), Bi$_2$Se$_3$ ([[Bi2Se3]]), Sb$_2$Te$_3$ ([[Sb2Te3]]), and many others. They are very well studied systems.