Measuring spin-polarized electronic states of quantum materials: 2H-NbSe2

Probing the energy and spin electron properties of materials by means of photoemission spectroscopy gives insights into the low energy phenomena of matter driven by spin orbit coupling or exchange interaction. The information that can be derived from complete photoelectron spectroscopy experiments, beyond E(k), is contained in the photoemission transition matrix elements that may determine peak intensities. We present here a complete photoemission study of the spin-polarised bands of 2H-, a material that presents a surface spin-texture. Circular dichroism in angular resolved photoemission - CD-ARPES - data are compared with spin-polarised angular-resolved spectra - SARPES - as measured with linearly polarised radiation in a well-characterised experimental chirality, at selected photon energy values. CD-ARPES is due to a matrix element effect - MEE - that strongly depends on photon energy and experimental geometry: we show that it cannot be used to infer intrinsic spin properties in 2H-. On the other hand, SARPES data provide reliable direct information on the spin properties of the electron states. The results on 2H- are discussed and general methodological conclusions are drawn on the best experimental approach to the determination of the spin texture of quantum materials.