Room Temperature Spin-to-Charge Conversion in Amorphous Topological Insulating Gd-Alloyed Bi (x) Se1-x /CoFeB Bilayers

Disordered topological insulator (TI) films have gainedintenseinterest by benefiting from both the TI's exotic transportproperties and the advantage of mass production by sputtering. Here,we report on the clear evidence of spin-charge conversion (SCC) inamorphous Gd-alloyed Bi (x) Se1-x (BSG)/CoFeB bilayers fabricated by sputtering, whichcould be related to the amorphous TI surface states. Two methods havebeen employed to study SCC in BSG (t (BSG) = 6-16 nm)/CoFeB(5 nm) bilayers with different BSG thicknesses.First, spin pumping is used to generate a spin current in CoFeB anddetect SCC by the inverse Edelstein effect (IEE). The maximum SCCefficiency (SCE) is measured to be as large as 0.035 nm (IEE length & lambda; (IEE)) in a 6 nm thick BSG sample, whichshows a strong decay when t (BSG) increasesdue to the increase of BSG surface roughness. The second method isTHz time-domain spectroscopy, which reveals a small t (BSG) dependence of SCE, validating the occurrence of apure interface state-related SCC. Furthermore, our angle-resolvedphotoemission spectroscopy data show dispersive two-dimensional surfacestates that cross the bulk gap until the Fermi level, strengtheningthe possibility of SCC due to the amorphous TI states. Our studiesprovide a new experimental direction toward the search for topologicalsystems in amorphous solids.