Spin polarization in photoemission from the cuprate superconductor Bi2Sr2CaCu2O8+δ

Photoelectrons produced from the excitation of spin-degenerate states in solids can have a sizable spin polarization, which is related to the phase of interfering channels in the photoemission matrix elements. Such spin polarization can be measured by spin-resolved photoemission spectroscopy to gain information about the transitions and the Wigner time delay of the process. Incorporating strongly correlated electron systems into this paradigm could yield a novel means of extracting phase information crucial to understanding the mechanism of their emergent behavior. In this work, we present, as a case study, experimental measurements of the cuprate superconductor Bi2Sr2CaCu2O8+δ by spin-resolved photoemission while maintaining full angular and energy resolution. A spin polarization of at least 10% is observed, which is related to the phase of the photoelectron wave function.