Topological Foundations era
Michael Berry's 1984 introduction of the geometric (Berry) phase showed how adiabatic evolution endows quantum states with a topological phase, laying groundwork for topology-based classifications of solids. David J. Thouless, with Kohmoto, Nightingale, and den Nijs, derived the TKNN formula in 1982, showing the integer quantum Hall conductance equals a Chern-number of the band structure. Haldane's 1988 lattice model demonstrated a quantum Hall effect without net magnetic field, illustrating that topology of bands can yield robust edge states. Robert Laughlin's 1981 explanation of the fractional quantum Hall effect highlighted topological order and the emergence of fractionally charged excitations as evidence of global band topology.