Orbital-resolved anisotropic electron pockets in electron-doped SrTiO3 observed by ARPES

Abstract

SrTiO3 (STO) has attracted considerable interest as a wide-bandgap semiconductor for advanced high-k capacitors and photocatalytic applications. Although previous angle-resolved photoemission spectroscopy (ARPES) studies have characterized the valence band structure originating from O 2p orbitals, the conduction band arising from Ti 3d orbitals upon electron doping, which is called electron pockets, remains poorly understood. In this study, polarization-dependent ARPES measurements were performed on Nb 1%-doped SrTiO3 (001), enabling the direct, orbital-selective visualization of the electron pockets. From the measured band dispersion, we quantitatively determined their effective masses, anisotropy, and electron density. Our results revealed the formation of an electron pocket at the Γ point induced by Nb doping, yielding a direct bandgap energy of 3.79 eV, consistent with previous optical measurements. Furthermore, the effective masses of m1 = 0.63m0 (short-axis direction) and m2 = 8.0m0 (long-axis direction) were identified, where m0 is the free electron mass, and the Fermi surface has been shown to be ellipsoidal. The electron density derived from these dispersions was found to be 3.58 × 1020 cm−3. These findings provide a comprehensive picture of the conduction-band electronic structure that will be crucial in the design of STO-based functional devices.