Doping-dependent band structure of LaAlO${}_3$/SrTiO${}_3$ interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission

Polarization-controlled synchrotron radiation was used to map the electronic structure of buried conducting interfaces of LaAlO${}_3$/SrTiO${}_3$ in a resonant angle-resolved photoemission experiment. A strong polarization dependence of the Fermi surface and band dispersions is demonstrated, highlighting different Ti $3d$ orbitals involved in two-dimensional (2D) conduction. Measurements on samples with different doping levels reveal different band occupancies and Fermi-surface areas. The photoemission results are directly compared with advanced first-principles calculations, carried out for different $3d$-band filling levels connected with the 2D mobile carrier concentrations obtained from transport measurements, with indication of charge localization at the interface.

Figure 1

Band energies of LAO/STO calculated at (a) $Q=0.04$ and (b) $Q=0.1$. The most populated bands are highlighted in color, indicating their character. The corresponding FSs are shown in (c) and (d).

Figure 2

(a) Experimental geometry for polarization-dependent measurements: $\chi$ and $\theta$ allow in-plane $k$-space mapping. ARPES data for the SD samples: (b) FS maps collected for four Brillouin zones with $c$-polarized light at $460.3$ eV, (c) for $s$-polarized, and (d) for $p$-polarized radiation.

Figure 3

(a) ARPES data along the $\Gamma$-X-${\Gamma }^{\prime }$ direction with $s$-polarized light and $h\nu =460.3$ eV collected for a SD sample. (b) Second-derivative plot of data in (a) highlighting the band dispersion; (c) EDCs and (d) MDCs of the data in (a). (e)–(h) The equivalent measurements, but for a LD sample. (b),(f) The calculated $t_{2g}$ parabolic bands. The color scale is the same as that in Fig. 2.

Figure 4

(a) FS collected with $p$-polarized light and $h\nu =460.3$ eV. (b),(c) Second-derivative plots of ARPES data along the $\Gamma$-Y and $\Gamma$-X direction, respectively, for a SD sample with the calculated $t_{2g}$ bands superimposed. (d)–(f) The equivalent measurements for a LD sample. The color scale is the same as in Fig. 2.