Edge modes and their conductance in narrow nanoribbons of 2D materials in a topological phase

•The subbands in MoS2, MoSe2, WS2, and WSe2 nanoribbons in a 1T′ phase are analyzed.•The energy dispersion of the topologically protected edge states is obtained.•The gap between the electron and hole edge states increases with the normal field in all materials.•The topological phase transition in a nanoribbon is clarified.•The electric field-induced conductance modulation is the largest in 1T′ MoS2 nanoribbons.