Universal Structural Influence on the 2D Electron Gas at SrTiO₃ Surfaces

Abstract

The 2-dimensional electron gas (2DEG) found at the surface of SrTiO 3 and related interfaces has attracted significant attention as a promising basis for oxide electronics. In order to utilize its full potential, the response of this 2DEG to structural changes and surface modification must be understood in detail. Here, a study of the detailed electronic structure evolution of the 2DEG as a function of sample temperature and surface step density is presented. By comparing the experimental results with ab initio calculations, it is shown that local structure relaxations cause a metal-insulator transition of the system around 135 K. This study presents a new and simple way of tuning the 2DEG via surface vicinality and identifies how the operation of prospective devices will respond to changes in temperature.

Slow Magnetic Relaxation of Dy Adatoms with In-Plane Magnetic Anisotropy on a Two-Dimensional Electron Gas

“…Moreover, whereas bulk STO has a large band gap of 3.25 eV, 40 its surface can host a high-mobility two-dimensional electron gas (2DEG). 41 − 45 The density of carriers within this surface can be controlled either via the application of a gate voltage 46 or through exposure to intense ultraviolet radiation. 43 , 47 , 48 Both methods can be effective in controlling the scattering rate between the conduction electrons of the substrate and the localized magnetic moments of the lanthanide atom, thus offering a potential way to control the reversal of the rare-earth spins.…”

“…This is a paradigmatic example of a quantum paraelectric material, where paraelectricity down to temperatures in the mK range is the result of the competition between ferroelectricity, quantum fluctuations, and structural distortions. − Paraelectricity in STO is intimately coupled with the giant piezoelectric effect observed at cryogenic temperatures. , These properties make STO a rich playground to study the effect of electric-field-induced changes of the local crystalline environment on the magnetic properties of the lanthanide atoms. Moreover, whereas bulk STO has a large band gap of 3.25 eV, its surface can host a high-mobility two-dimensional electron gas (2DEG). − The density of carriers within this surface can be controlled either via the application of a gate voltage or through exposure to intense ultraviolet radiation. ,, Both methods can be effective in controlling the scattering rate between the conduction electrons of the substrate and the localized magnetic moments of the lanthanide atom, thus offering a potential way to control the reversal of the rare-earth spins.…”

Disclosing the response of the surface electronic structure in SrTiO3 (001) to strain

“…Favorably, the finding of the low-dimensional electronic state (LDES) on a surface of the STO wafer [13][14][15] grants us with an unadulterated playground for studying this marvel using very susceptible methods such as scanning tunneling spectroscopy (STM) 16 and angle-resolved photoemission spectroscopy (ARPES). [13][14][15]17 A recent study reports that a relatively standard annealing temperature of 550 C in an oxygen-rich atmosphere leads to a Sr-rich surface, 18 consequently favoring the formation of 2DEG at the surface, similar to findings related to SrO-terminated STO films. 19 STO used as a substrate undergoes extreme annealing procedures during the film growth, which must also be considered.…”

“…15 Matrix element effects, i.e., modulations of the spectral intensity caused by the dependence of the ARPES data on photon energy and experimental geometry, 30 are known to greatly impact the observation of the 2DEG on STO. 14,15,18 In particular, the bottom of the d yz band and the outer d xy band are easily seen around Γ 00 , while the bottom of the d xy,xz bands are very clear around Γ 10 . 15 Thus, the measurements were performed around both the Γ 00 and Γ 10 points, which allowed us to identify all the features in the spectra necessary for the reliable analysis of the data.…”

“…However, STO films grown on STO 20 or NdGaO 3 (110) 21 show a tendency to end with Sr-rich surfaces. One of the important features of the LDES is a relatively large splitting between d xy and d xz =d yz bands, 15,18 suggesting that deviations from the cubic (or slightly tetragonal when at low temperatures) structure occurs at the surface region. The enhancement of the electron mobility of over 300% observed in La-doped STO films under uniaxial stress 22 confirmed that the strain could be effectively used for altering the STO bulk properties.…”