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

TL;DR

This study used polarization-dependent ARPES to visualize and analyze the orbital-resolved anisotropic electron pockets in Nb-doped SrTiO3, revealing their effective masses, anisotropy, and electron density, which are vital for device applications.

Contribution

First direct orbital-selective visualization of electron pockets in SrTiO3 using polarization-dependent ARPES, providing detailed electronic structure data.

Findings

Electron pocket forms at Gamma point with a bandgap of 3.79 eV

Effective masses identified as 0.63m0 and 8.0m0 in different directions

Electron density estimated at 3.58×10^20 cm^-3

Abstract

SrTiO3 has attracted considerable interest as a wide-band gap 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, remain poorly understood. In this study, polarization-dependent ARPES measurements were performed on Nb 1%-doped SrTiO3 (001), enabling 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 formation of an electron pocket at the Gamma point induced by Nb doping, yielding a direct bandgap of 3.79 eV at Gamma, 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 3.58e20 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.