Evolution of electronic structure from insulator to superconductor in ${\text{Bi}}_2{\text{Sr}}_{2-x}{\text{La}}_x\left(\text{Ca},\text{Y}\right){\text{Cu}}_2{\text{O}}_{8+\delta }$

La-doped and Y-doped ${\text{Bi}}_2{\text{Sr}}_2{\text{CaCu}}_2{\text{O}}_{8+\delta }$ compounds ${\text{Bi}}_2{\text{Sr}}_{2-x}{\text{La}}_x\left(\text{Ca},\text{Y}\right){\text{Cu}}_2{\text{O}}_{8+\delta }$, which range from the insulator to the deeply underdoped superconductor, have been studied by angle-resolved photoemission spectroscopy. We have observed that the lower Hubbard band (LHB) of the parent insulator is gradually shifted upward with doping without significantly changing the band dispersions, which implies a downward shift of the chemical potential with hole doping. This behavior is analogous to ${\text{Bi}}_2{\text{Sr}}_{2-x}{\text{La}}_x{\text{CuO}}_{6+\delta }$ and ${\text{Ca}}_{2-x}{\text{Na}}_x{\text{CuO}}_2{\text{Cl}}_2$ but is different from ${\text{La}}_{2-x}{\text{Sr}}_x{\text{CuO}}_4$, where the LHB stays well below the chemical potential and does not move while its intensity quickly diminishes in the underdoped region.

Figure 1

(Color online) ARPES spectra of lightly doped Bi2212 along the (0,0)-$\left(\pi ,\pi \right)$ nodal direction in the second BZ. [(a)–(d)]: EDCs. A bold line for each doping indicates the spectrum where the dispersive feature comes closest to $E_{\text{F}}$. [(e)–(h)]: intensity plot of the spectra in the $E\text{−}k$ plane. The features denoted by $SS$ are diffraction replica of the MB due to the Bi-O plane superstructure.

Figure 2

(Color online) ARPES spectra of lightly doped Bi2212 along the underlying Fermi surface in the second BZ. [(a)–(d)]: EDCs. The peak position determined by the second derivatives are shown by vertical bars. [(e)–(h)]: second derivatives of the EDCs in the $E\text{−}k$ plane.

Figure 3

(Color online) Energy positions of the EDC peaks at $\sim \left(\pi /2,\pi /2\right)$ and $\sim \left(\pi ,0\right)$ in Bi2212, LSCO[14]), and Bi2201[5] as functions of doping levels.

Figure 4

(Color online) Doping evolution of the electronic structure along the nodal direction near $E_{\text{F}}$. [(a)–(d)]: blow up of Fig. 1 near $E_{\text{F}}$. Vertical bars indicate the position of the LHB. (e): position of the LHB and the “QP” band obtained from MDCs. The plots have been shifted vertically so that the chemical potential $\mu$ shifts the average of the shift in the LHB at $\sim \left(\pi /2,\pi /2\right)$ and $\sim \left(\pi ,0\right)$ in Fig. 3 for each doping. The chemical potential $\mu$ is also displayed. (f): doping dependence of Fermi momentum $k_{\text{F}}$ positions in Bi2212, LSCO[14]), Bi2201[5], and Na-CCOC[8].