  2D topological insulators promise novel approaches towards electronic,
spintronic, and quantum device applications. This is owing to unique features
of their electronic band structure, in which bulk-boundary correspondences
enforces the existence of 1D spin-momentum locked metallic edge states - both
helical and chiral - surrounding an electrically insulating bulk. Forty years
since the first discoveries of topological phases in condensed matter, the
abstract concept of band topology has sprung into realization with several
materials now available in which sizable bulk energy gaps - up to a few hundred
meV - promise to enable topology for applications even at room-temperature.
Further, the possibility of combining 2D TIs in heterostructures with
functional materials such as multiferroics, ferromagnets, and superconductors,
vastly extends the range of applicability beyond their intrinsic properties.
While 2D TIs remain a unique testbed for questions of fundamental condensed
matter physics, proposals seek to control the topologically protected bulk or
boundary states electrically, or even induce topological phase transitions to
engender switching functionality. Induction of superconducting pairing in 2D
TIs strives to realize non-Abelian quasiparticles, promising avenues towards
fault-tolerant topological quantum computing. This roadmap aims to present a
status update of the field, reviewing recent advances and remaining challenges
in theoretical understanding, materials synthesis, physical characterization
and, ultimately, device perspectives.
