Figure 1

(a) Apart from the in-plane ferromagnetic splitting [3] with some reduction from the neutron observation, FS is compared with bulk LT based on NMR [5] to isolate valence components and with the homogeneous single-valence theory [2]. The Na concentration within the probe depth of ARPES in $x=0.8$ is easily measured via the Na-$2p$ signal by comparison with a reference $x=0.35$, which shows that the zero-Na termination theory [2] is incorrect. (d) Using $x=0.5$ as a benchmark, the effective doping is found to lie within a 10% accuracy level. This degree of bulk representation $\mathrm{ARPES}\mathrm{\text{gap}}\sim \mathrm{\text{optical gap}}/2$, $T_{\mathrm{MIT}}\sim \mathrm{\text{bulk}}\mathrm{\text{−}}{T}_{\mathrm{MIT}}$) results from the nearly-half-terminated $\pm 10\%$ top layer and the bulklike hexagonal surface symmetry [3].Reuse & Permissions