Temperature-dependent Fermi surface of the misfit cobaltite ${\left[{\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{O}}_4\right]}_{0.51}{\mathrm{CoO}}_2$: A comparison with ${\left[{\mathrm{Bi}}_2{\mathrm{Ba}}_2{\mathrm{O}}_4\right]}_{0.50}{\mathrm{CoO}}_2$

Angle-resolved photoemission spectroscopy has been performed to investigate the Fermi surface (FS) and the electronic structure of misfit cobaltites, by comparing ${\left[{\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{O}}_4\right]}_p{\mathrm{CoO}}_2$ with $\left[{\mathrm{Bi}}_2{\mathrm{Ba}}_2{\mathrm{O}}_4\right]{}_{0.50}{\mathrm{CoO}}_2$. In $\left[{\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{O}}_4\right]{}_{0.51}{\mathrm{CoO}}_2$, we observed a suppression of spectral weight near the Fermi energy. Nevertheless, the FS can be mapped out by measuring the photoelectron intensity distribution. The FS size changes with temperature. Additionally, results show that the electronic band structure at a higher binding energy was changed by changing the sample temperature. Our results provide insight into the characteristics of the pseudogap state in the misfit-layered cobaltites. The unusual properties are probably related to the local deformations of the incommensurate structure.

Figure 1

(a) Temperature dependence of the in-plane resistivity of BSCO and BBCO. Inset: X-ray $(0,0,l)$ diffraction patterns measured using Cu $\mathit{K}\alpha$ radiation. (b) Core-level photoemission spectra $(h\nu =680$ eV) of the BSCO.

Figure 2

(a) Photoemission spectra $(h\nu =100$ eV) of BBCO and BSCO at various temperatures. Spectra are integrated over the area of a circle with a radius of $k=0.65$ ${\AA }^{-1}$ around the $\mathrm{\Gamma }$ point. (b) Enlarged view of the rectangular area in (a) for BSCO.

Figure 3

(a) Plots of ARPES intensity of BBCO as a function of $k_{\mathrm{x}}$ and $k_{\mathrm{y}}$. Data were taken at 20 K and integrated over the energy range of $\pm 15$ meV with respect to $E_{\mathrm{F}}$. The dashed line corresponds to the BZ of the ${\mathrm{CoO}}_2$. (b) Plots of ARPES intensity as a function of binding energy and wave vector. Measurements are performed along the high-symmetry line $\mathrm{\Gamma }M$. (c) Intensity profiles along the $\mathrm{\Gamma }M$ and $\mathrm{\Gamma }K$ directions.

Figure 4

(a) Plots of ARPES intensity measured at 20 K along the $\mathrm{\Gamma }M$ direction in BSCO. (b) Intensity map integrated over the energy range of $\pm 15$ meV with respect to $E_{\mathrm{F}}$. The dashed and dotted lines respectively present the BZ of the ${\mathrm{CoO}}_2$ and the RS sublattices. (c) Intensity profiles along the $\mathrm{\Gamma }M$ and $\mathrm{\Gamma }K$ directions.

Figure 5

(a) The ARPES intensity map around $E_{\mathrm{F}}$ of BSCO measured at 300 K. Intensity profiles along the $\mathrm{\Gamma }M$ direction (b) at 300 K and (c) at 20 K at three different binding energies.

Figure 6

Energy distribution curves along the $\mathrm{\Gamma }M$ direction of BSCO measured (a) at 300 K and (b) at 20 K. The blue and black dashed bars are guides to the eyes to trace the peak positions. Second derivatives of ARPES spectra (c) at 300 K and (d) at 20 K.

Figure 7

Second derivatives of ARPES spectra along the $\mathrm{\Gamma }M$ direction of BBCO (a) at 300 K and (b) at 20 K.

Figure 8

Oxygen $1s$ core-level photoemission spectra of BSCO $(h\nu =680$ eV). Inset: Cobalt $2p_{1/2}$ and $2p_{3/2}$ spectra $(h\nu =1080$ eV).