Influence of oxygen coordination number on the electronic structure of single-layer La-based cuprates

We present an angle-resolved photoemission spectroscopy study of the single-layer T*-type structured cuprate ${\mathrm{SmLa}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ with unique fivefold pyramidal oxygen coordination. Upon varying oxygen content, T*-${\mathrm{SmLa}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ evolved from a Mott-insulating to a metallic state where the Luttinger sum rule breaks down under the assumption of a large holelike Fermi surface. This is in contrast with the known doping evolution of the structural isomer ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ with sixfold octahedral coordination. In addition, quantitatively characterized Fermi surface suggests that the empirical $T_{\mathrm{c}}$ rule for octahedral oxygen-coordination systems does not apply to T*-${\mathrm{SmLa}}_{1-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$. The present results highlight unique properties of the T*-type cuprates possibly rooted in its oxygen coordination, and necessitate thorough investigation with careful evaluation of disorder effects.

Figure 1

Properties of the T*-SLSCO samples. (a) Crystal structure of the T-type (left) and T*-type (right) cuprates. (b) $T_{\mathrm{c}}$ versus Sr concentration for the present ${\mathrm{O}}_2$-annealed T*-SLSCO ($x=0.25$) sample plotted along with previous results on T-LSCO [7] and T*-SLSCO [8]. (c) $c$-axis lattice constant of the as-grown, Ar-annealed, and ${\mathrm{O}}_2$-annealed T*-SLSCO ($x=0.25$) samples. (d) Magnetization of the ${\mathrm{O}}_2$-annealed sample as a function of temperature.

Figure 2

Evolution of the electronic structure of T*-SLSCO by annealing treatment. (a) Constant-energy surface of the Ar-annealed sample. Intensity has been integrated over $\pm 20\mathrm{meV}$ with respect to the indicated energy level. (b) Nodal energy-momentum map of the Ar-annealed sample. The dashed line marks the energy level where the constant-energy surface is mapped. (c)–(f) The same as (a) and (b) for the as-grown and ${\mathrm{O}}_2$-annealed samples. (g) EDCs of the T*-SLSCO samples at the nodal (underlying) $k_{\mathrm{F}}$. EDCs around ($\pi ,\pi$) are overlaid as a background. (h) EDCs after background subtraction. The LHB peak position is marked by vertical bars. The EDC at $E<E_{\mathrm{F}}-0.7\mathrm{eV}$ for the ${\mathrm{O}}_2$-annealed sample is omitted due to possible contributions from other bands. (i) Nodal EDC for T-LSCO at $x=0$ and 0.03 extracted from Ref. [9]. The black shade marks LHB.

Figure 3

Fermi surface geometry. (a), (b) Fermi surface of the ${\mathrm{O}}_2$-annealed T*-SLSCO ($x=0.25$) sample fitted to the tight-binding model. Red dots in (a) represent momentum-distribution-curve (MDC) peak positions gathered into the displayed region according to the $C_4$ and mirror symmetries. Hole concentration $p_{\mathrm{FS}}$ is estimated from the small Fermi surface shaded in (b). See text for detailed descriptions about the small Fermi surface. (c) EDCs from the nodal to the antinodal momentum points indicated in (b). (d) Spectral weight integrated over $E_{\mathrm{F}}\pm 20\mathrm{meV}$ [black shaded region in (c)] and plotted against Fermi surface angle $\phi$ defined in (b). The error bar has been evaluated based on the uncertainty of $E_{\mathrm{F}}$ ($\pm 1\mathrm{meV}$). The arrow marks a steeper change.

Figure 4

Hopping parameter of single-layer cuprates with octahedral or pyramidal oxygen coordination. The value of $-t^{\prime }/t$ versus hole concentration for single-layer hole-doped cuprates as indicated [22, 25, 36, 37, 38, 39]. The assumption of $-t^{″}/t^{\prime }=0.5$ has been applied to all the data.

Figure 5

Tight-binding analysis at deeper binding energies. (a) Energy-momentum map along the nodal direction [indicated by black line in (b)] overlaid with MDC peak positions (red dots). The light blue curve represents the tight-binding-modeled band dispersion with $t=0.31\mathrm{eV}$. (b)$-$(d) Constant-energy maps at indicated energy levels. The photoemission intensity has been integrated within $\pm 20\mathrm{meV}$ for (b) and $\pm 10\mathrm{meV}$ for (c) and (d). Constant energy surfaces modeled by the tight-binding model are plotted as light blue curves.