Temperature-dependent dielectric function of bulk SrTiO${}_3$: Urbach tail, band edges, and excitonic effects

Abstract

We report the temperature-dependent complex dielectric function of pristine bulk SrTiO${}_3$ between 4.2 and 300 K within the energy range of 0.6-6.5 eV determined by spectroscopic ellipsometry. Fundamental indirect and direct band-gap energies have been extracted and are discussed with regard to existing state-of-the-art theoretical calculations. Furthermore, the dielectric function around the fundamental direct gap is analyzed by considering excitonic states. The excitonic effects, including the Coulomb enhancement of the continuum, are characterized using an extension of the Elliott's formula considering both the real and imaginary parts of the dielectric function. The Urbach tail below the indirect edge shows an unconventional temperature-dependent behavior correlated to the microstructural changes near the structural phase transition around 105 K from the low-temperature tetragonal phase to the cubic phase. The temperature-dependent characterization reveals that the fundamental indirect edge as well as the Urbach tail are affected conspicuously by the structural phase transition while the fundamental direct edge is not. Moreover, the indirect edge follows Varshni's rule only in the cubic phase and the direct edge exhibits an anomalous linear increase with increasing temperature.

arXiv comment12 pages, 7 figures, Phys. Rev. B (Published)

References in corpus (17)

• Physics of thin-film ferroelectric oxides
• Magnetic effects at the interface between nonmagnetic oxides
• Ab initio calculation of excitonic effects in the optical spectra of semiconductors
• Direct imaging of the coexistence of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface
• Coexistence of Magnetic Order and Two-dimensional Superconductivity at LaAlO${}_3$/SrTiO${}_3$ Interfaces
• Unveiling a two-dimensional electron gas with universal subbands at the surface of SrTiO3
• Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface
• Quantum criticality in ferroelectrics
• Electron-phonon interaction and charge carrier mass enhancement in SrTiO3
• Transient excitons at metal surfaces
• Dynamical excitonic effects in metals and semiconductors
• Phonon Calculations in Cubic and Tetragonal Phases of SrTiO3: a Comparative LCAO and Plane Wave Study
• Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity
• Anisotropic optical properties of rhombohedral and tetragonal thin film BiFeO${}_3$ phases
• Derivation of effective spin-orbit Hamiltonians and spin lifetimes, with application to SrTiO${}_3$ heterostructures
• Correlation between surface rumpling and structural phase transformation of SrTiO3
• Depth Dependence of the Structural Phase Transition of SrTiO_3 Studied with β-NMR and Grazing Incidence X-ray Diffraction

Cited by in corpus (3)

• Fully Anharmonic, Non-Perturbative Theory of Vibronically Renormalized Electronic Band Structures
• Simulating terahertz field-induced ferroelectricity in quantum paraelectric SrTiO${}_3$
• Effects of quantum confinement on excited state properties of SrTiO${}_3$ from ab initio many-body perturbation theory