Local electrostatic imaging of striped domain order in LaAlO3/SrTiO3

Abstract

The emerging field of complex oxide interfaces is generically built on one of the most celebrated substrates--strontium titanate (SrTiO3). This material hosts a range of phenomena, including ferroelasticity, incipient ferroelectricity, and most puzzlingly, contested giant piezoelectricity. Although these properties may markedly influence the oxide interfaces, especially on microscopic length scales, the lack of local probes capable of studying such buried systems has left their effects largely unexplored. Here we use a scanning charge detector--a nanotube single-electron transistor--to non-invasively image the electrostatic landscape and local mechanical response in the prototypical LaAlO3/SrTiO3 system with unprecedented sensitivity. Our measurements reveal that on microscopic scales SrTiO3 exhibits large anomalous piezoelectricity with curious spatial dependence. Through electrostatic imaging we unravel the microscopic origin for this extrinsic piezoelectricity, demonstrating its direct, quantitative connection to the motion of locally ordered tetragonal domains under applied gate voltage. These domains create striped potential modulations that can markedly influence the two-dimensional electron system at the conducting interface. Our results have broad implications to all complex oxide interfaces built on SrTiO3 and demonstrate the importance of microscopic structure to the physics of electrons at the LaAlO3/SrTiO3 interface.

Growth-induced electron mobility enhancement at the LaAlO3/SrTiO3 interface

“…17 More recently, the presence of tetragonal domains in STO (at low temperature) was demonstrated to alter locally the conductance. 18,19 Finally, the control of the LAO surface state was shown to be an efficient lever to enhance the interfacial electron mobility. 8,20,21 In this letter, we perform a systematic study of the effect of the growth temperature (T g ) on the transport properties of the LAO/STO interface.…”

Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO3

“…In terms of the original cubic directions, the twin planes are along (110) p , (101) p , and (011) p . Recent studies have shown that the low-temperature twin structure affects both the interfacial conductivity in LaAlO 3 /SrTiO 3 heterostructures [42,43] and the superconducting transition temperature in STO [44].We measured the magnetic spatial landscape in four EuS/STO-based heterostructures using a scanning superconducting quantum interference device (SQUID) susceptometer in a 4 He cryostat. Unless otherwise indicated, the data in this paper were taken on a thin film (5 nm) of (001) p -oriented EuS grown on a (001) p -oriented STO substrate, but we observed similar effects in samples with (110) p -and (111) p -oriented STO substrates and samples with 3-nm-thick EuS [45].…”

At the interface between electron and hole-doped cuprates

“…We note that lattice tilting is also observed across grain boundaries in oxide systems, for example across a twin grain boundary in tetragonal SrTiO 3 [162] or PbTiO 3 [163]. In both cases the tilting can be described using a simplified version of equation (4.1), since across the domain wall a and c are exchanged and the 'ramp' angle can be defined by arctan (a/c), leading to γ = 2 arctan(c/a) − 90 • .…”

“…A structure like this can be measured quite easily with a technique like nXRD, which has sufficient resolution to measure the local tilt of the lattice. This technique is preferred over a [162] [163]…”

“…Figure 4.9 shows the measured lattice tilt versus the predicted lattice tilt using equation (4.1) for the three materials described above and the LSCO/NCCO system. The measured tilt and the model tilt are determined using the main text and the TEM figures in references [162][163][164]. The two data points for BiFeO 3 correspond to the T /R and the R/T configuration.…”