ARPES intensity maps of 3 (a), 6 (b), and 9 (c) QL of Bi₂Se₃ thin films grown on 2H–NbSe₂ superconductors. (d) d I / d V spectra demonstrating that the superconducting gap on the Bi₂Se₃ thin films is at the indicated thickness. (e) and (f) Spin-resolved ARPES data for a 4-QL Bi₂Se₃ thin film on a NbSe₂ substrate. Panels (a)–(d) are reproduced from Ref. [70], while panels (e) and (f) are from Ref. [120].