Dial It Down: The Effect of Strongly Interacting Adsorbates on the BiAg2 Rashba Surface State

Organic semiconductors interfaced with spin-orbit coupled materials offer a rich playground for fundamental studies of controlling spin dynamics in spintronic devices. The adsorbate-surface interactions at such interfaces play a key role in determining the valence electronic and spin structure and consequently, the device physics as well. Here we present the adsorption and electronic structure of the strong organic electron acceptor 2,7-dinitropyrene-4,5,9,10-tetrone (NO2-PyT, C16H4N2O8) on the Rashba spin-orbit coupled surface alloy BiAg2/Ag(111). We show that the strong adsorbate-surface alloy interaction leads to weakening of the electronic coupling between the surface alloy atoms and quench the spin-orbit coupled surface state in BiAg2/Ag(111). Our findings demonstrate an important challenge associated with using molecular adsorbates to tailor the spin polarization in BiAg2/Ag(111), and our work provides guidelines to consider while designing interfacial systems to engineer the spin polarization in Rashba surface alloys.