Fig. 1: ARPES characterization with polarized photons.
a The 2-Fe (red square) and 1-Fe (blue square) Brillouin zones (BZs), and the sketch of Fermi surfaces (blue and red ellipses) of monolayer FeSe/STO26. The green lines are the two cuts for the ARPES in Figs. 1–4. b Experimental geometry for linear polarization-dependent ARPES, where p (s) indicates the electric field of incident photon is parallel (perpendicular) to the emission plane defined by the analyzer slit. c, d Schematic diagram of band structure and orbital characters of monolayer FeSe/STO at Γ and M points, respectively, as determined by this ARPES study and in agreement with refs. 26,27. Here we use the same coordinate system as in b to define the d orbitals, i.e., x and y along the nearest Fe–Fe directions. Photoemission maps along cut #1, with 24 eV photons in p polarization (e) and s polarization (f). The solid and dashed curves indicate principal and replica bands with ~90 meV intervals, respectively. The white arrow indicates the other set of replica band at ~60 meV below the principal band. The yellow arrow indicates the Fermi momentum of the δ1 band, where a superconducting gap is opened.
