Many-body effects on the Rashba-type spin splitting in bulk bismuth tellurohalides

We report on many-body corrections to one-electron energy spectra of bulk bismuth tellurohalides---materials that exhibit a giant Rashba-type spin splitting of the band-gap edge states. We show that the corrections obtained in the one-shot $GW$ approximation noticeably modify the spin-orbit-induced spin splitting evaluated within density functional theory. We demonstrate that taking into account many-body effects is crucial to interpret the available experimental data.