Quasiparticle evolution on a high-Tc superconductor surface decorated with sub-monolayer magnetic atoms

Unconventional superconductivity has been a fertile research field for both its basic science and application values. Among the most exciting endeavors is the investigation of electronic states inside and around superconducting vortices, where elusive new quasiparticles (Majorana bound states) or competing orders (superconducting pair density waves) thrive. So far, direct investigation of pinned vortices in momentum space is scarce, mainly due to the inherent difficulty of performing perform photoemission experiments under a macroscopic magnetic field. Here, by combining molecular beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES), we study the evolution of electronic structures of the high-Tc cuprate Bi2Sr2CaCu2O8 when a monolayer of iron is deposited on the surface. We discuss the nature of the surface chemical environment and charge transfer, and report on the low energy quasiparticle evolution in energy-momentum space during this process. We discuss the general scope of using surface magnetic ion decoration as a versatile method to induce time-reversal symmetry breaking for in-situ photoemission experiments, and its specific impact on the pairing symmetry in high-Tc cuprates.