Imaging the Evolution of <i>d</i> States at a Strontium Titanate Surface

Abstract

Oxide electronics is a promising alternative to the conventional silicon-based semiconductor technology, owing to the rich functionalities of oxide thin films and heterostructures. In contrast to the silicon surface, however, the electronic structure of the SrTiO₃ surface, the most important substrate for oxide thin films growth, is not yet completely understood. Here we report on the electronic states of a reconstructed (001) surface of SrTiO₃ determined in real space, with scanning tunneling microscopy/spectroscopy and density functional theory calculations. We found a remarkable energy dependence of the spectroscopic image: Theoretical analysis reveals that symmetry breaking at the surface lifts the degeneracy in the <i>t</i>_2<i>g</i> state (<i>d</i>_<i>xy</i>, <i>d</i>_<i>yz</i>, and <i>d</i>_<i>zx</i>) of Ti 3<i>d</i> orbitals, whose anisotropic spatial distribution leads to a sharp transition in the spectroscopic image as a function of energy. The knowledge obtained here could be used to gain further insights into emergent phenomena at the surfaces and interfaces with SrTiO₃