Electronic structure of ${\mathrm{LaO}}_{1-x}{\mathrm{F}}_x{\mathrm{BiSe}}_2$ $(x=0.18)$ revealed by photoelectron spectromicroscopy

We report an electronic structure study on ${\mathrm{LaO}}_{1-x}{\mathrm{F}}_x{\mathrm{BiSe}}_2$ $(x=0.18)$ by means of photoelectron spectromicroscopy. The Fermi surfaces and band dispersions are basically consistent with the band-structure calculations on ${\mathrm{BiS}}_2$-based materials, indicating that the electron correlation effects may be irrelevant to describe physics of the new ${\mathrm{BiSe}}_2$ system. In ${\mathrm{LaO}}_{1-x}{\mathrm{F}}_x{\mathrm{BiSe}}_2$ $(x=0.18)$, the area of the Fermi pockets is estimated to be $0.16\pm 0.02$ per Bi, consistent with the amount of F substitution. Although the spectromicroscopy technique avoids the effect of microscale inhomogeneity for angle-resolved photoemission spectroscopy (ARPES), the ARPES spectral features are rather broad in the momentum space, indicating the likely effect of local disorder in the ${\mathrm{BiSe}}_2$ layer.

Figure 1

(a) Overview image of photoelectron spectromicroscopy on ${\mathrm{LaO}}_{0.82}{\mathrm{F}}_{0.18}{\mathrm{BiSe}}_2$. The photoemission intensity is integrated from 0.5 to –3.5 eV relative to $E_F$. The solid box indicates the region selected for the fine image. (b) Fine image of photoelectron spectromicroscopy on ${\mathrm{LaO}}_{0.82}{\mathrm{F}}_{0.18}{\mathrm{BiSe}}_2$. The photoemission intensity is integrated from 0.5 to –3.5 eV relative to $E_F$. (c) Photoemission spectra taken at points A, B, and C in Fig. 1. (d) Fine image of photoelectron spectromicroscopy on ${\mathrm{LaO}}_{0.82}{\mathrm{F}}_{0.18}{\mathrm{BiSe}}_2$. The photoemission intensity is integrated from–1.0 to –2.0 eV relative to $E_F$.

Figure 2

(a) Fermi surface map at $h\nu =$ 27 eV of ${\mathrm{LaO}}_{0.82}{\mathrm{F}}_{0.18}{\mathrm{BiSe}}_2$. The dotted box indicates the region in which the ARPES data were taken. The map is obtained by tetragonal symmetrization. The image in the dotted box was rotated by ${90}^{\circ }$, ${180}^{\circ }$, and ${270}^{\circ }$ around $\Gamma$, and the ARPES intensity was averaged when the rotated boxes overlap. (b) Relationship between $k_x$ and $k_z$ at $h\nu =$ 27 eV. (c) Fermi pockets around the $X$ point. The open circles indicate peaks in MDCs that correspond to $E_F$ crossing points.

Figure 3

(a) Second derivative plot for the wide energy range along cut 1 of Fig. 2. (b) Second derivative plot for the wide range along cut 2 of Fig. 2. (c) Second derivative plot for the near $E_F$ range along cut 1. (d) MDCs for the near $E_F$ range along cut 1. (e) Second derivative plot for the near $E_F$ range along cut 2. (f) MDCs for the near $E_F$ range along cut 2. The open circles indicate peaks in MDCs that correspond to band dispersions. $k_x$ is the momentum relative to the $X$ point.

Figure 4

(a) Comparison between the band dispersions along cut 1 estimated for ${\mathrm{LaO}}_{0.82}{\mathrm{F}}_{0.18}{\mathrm{BiSe}}_2$ compared with the band dispersions reported for ${\mathrm{NdO}}_{0.5}{\mathrm{F}}_{0.5}{\mathrm{BiS}}_2$ [26]. (b) Comparison between the band dispersions along cut 2 estimated for ${\mathrm{LaO}}_{0.82}{\mathrm{F}}_{0.18}{\mathrm{BiSe}}_2$ compared with the band dispersions reported for ${\mathrm{NdO}}_{0.5}{\mathrm{F}}_{0.5}{\mathrm{BiS}}_2$ [26]. $k_x$ is the momentum relative to the $X$ point. (c) EDC at the $X$ point and Gaussian fit.