Figure 1

Angle-resolved photoemission results of $\mathrm{NCO}\mathrm{\text{−}}{\mathrm{H}}_2\mathrm{O}$. (a) Fermi surfaces obtained by LDA calculations [14] and the momentum space measured by ARPES. (b) Procedure for subtracting background from raw EDCs. Red curve is the background spectrum (see the text). Upper and lower spectra show raw data and analyzed spectra, respectively. (c) EDCs at 30 K after subtracting the background as illustrated in (b). Both blue and red diamonds are superimposed on the slow dispersions of the $a_{1g}$ band for line 2 and line 6, respectively. Light blue diamonds indicate dispersive $e_g^{\prime }$ band on line 2. (d) Second derivative of ARPES intensity $I(k,\omega )$ with respect to momentum $k$. Number on the panels corresponds to the measured regions indicated in (a). Markers in the panel 2 and 6 are obtained by MDC fitting, which also represent those in (c). White arrows on each panel indicate the Fermi momenta $k_F$, where the $a_{1g}$ band crosses the $E_F$. (e) MDCs and their fitting results along line 2. Black and red curves are MDCs and Lorenztian fitting functions while the markers show the peak positions obtained by fitting. (f) The momentum dependencies of $v_{F_{\mathrm{AR}}}$ (blue circle), $v_{F_{\mathrm{cal}}}$ (red circle) and $m_{\mathrm{AR}}/m_{\mathrm{cal}}$ (black diamond) along the FS contour are plotted as the function of $\varphi$ (FS angle relative to $\Gamma \mathrm{\text{−}}K$ direction).Reuse & Permissions

Figure 2

Intensity images at the momentum space ranging from $E_F$ and up to 50 meV binding energy (steps of 10 meV), obtained by integrating spectral weight with an energy window of $\pm 2\mathrm{meV}$.Reuse & Permissions

Figure 3

(a) Fermi surface of $\mathrm{NCO}\mathrm{\text{−}}{\mathrm{H}}_2\mathrm{O}$ ($\mathrm{HeI}\alpha$) with virtual FSs estimated from the cobalt valencies as reported by Takada et al. [1, 19]. Hexagons depicted by solid and broken light blue lines indicate the FS corresponding to the Co valence of $+3.42$ [${\mathrm{Na}}_{0.343}({\mathrm{H}}_3\mathrm{O}{)}_{0.237}{\mathrm{CoO}}_2·1.19{\mathrm{H}}_2\mathrm{O}$] and $+3.65$ (${\mathrm{Na}}_{0.35}{\mathrm{CoO}}_2·1.3{\mathrm{H}}_2\mathrm{O}$), respectively. Markers show the peak positions obtained from MDC at $E_F$. (b) FS measured using $\mathrm{HeII}\alpha$ (40.8 eV). The momentum space measured by $\mathrm{HeII}\alpha$ is also superimposed in (a) by a rectangle (broken line). Light blue points indicate the peak positions in the same manner as in (a).Reuse & Permissions