Tuning Shiba states hybridization on proximitized superconducting surface

Magnetic atoms on a superconductor induce in-gap Shiba states that can be hybridized to create a topological superconducting phase when placed in one-dimensional chains, with Majorana zero modes (MZMs) localized at their ends. Here we study magnetic Gd adatoms deposited on the surface of epitaxially grown Bi(110) thin films on a superconducting Nb(110) surface using a dilution refrigerator scanning tunneling microscope (STM). Our spectroscopic measurements show a hard superconducting gap of 1.5 meV on Bi surface and the presence of Shiba states near Gd atoms. By manipulating Gd atoms with the STM tip, we find the Shiba states start hybridizing once two Gd atoms are closer than Fermi wavelength of Bi(110) surface states (~ 20 Å), which indicates the critical role of RKKY interaction mediated by Bi electrons. Through systematically changing the configurations of two Gd atoms, we show the hybridization can be dramatically strengthened as the distance between Gd atoms decreases. Our work provides a promising platform for realizing MZMs because it allows fine control over Shiba states hybridization.