Anisotropic Transport at the LaAlO₃/SrTiO₃ Interface Explained by Microscopic Imaging of Channel-Flow over SrTiO₃ Domains

Abstract

Oxide interfaces, including the LaAlO3/SrTiO3 interface, have been a subject of intense interest for over a decade due to their rich physics and potential as low-dimensional nanoelectronic systems. The field has reached the stage where efforts are invested in developing devices. It is critical now to understand the functionalities and limitations of such devices. Recent scanning probe measurements of the LaAlO3/SrTiO3 interface have revealed locally enhanced current flow and accumulation of charge along channels related to SrTiO3 structural domains. These observations raised a key question regarding the role these modulations play in the macroscopic properties of devices. Here we show that the microscopic picture, mapped by scanning superconducting quantum interference device, accounts for a substantial part of the macroscopically measured transport anisotropy. We compared local flux data with transport values, measured simultaneously, over various SrTiO3 domain configurations. We show a clear relation between maps of local current density over specific domain configurations and the measured anisotropy for the same device. The domains divert the direction of current flow, resulting in a direction-dependent resistance. We also show that the modulation can be significant and that in some cases up to 95% of the current is modulated over the channels. The orientation and distribution of the SrTiO3 structural domains change between different cooldowns of the same device or when electric fields are applied, affecting the device behavior. Our results, highlight the importance of substrate physics, and in particular, the role of structural domains, in controlling electronic properties of LaAlO3/SrTiO3 devices. Furthermore, these results point to new research directions, exploiting the STO domains’ ability to divert or even carry current.

Imaging and tuning polarity at SrTiO3 domain walls

“…S3); (c) we compare V map with maps of the current flow obtained by scanning superconducting quantum interference device (SQUID). The configuration of the modulated current streaks over STO domains 20,25,26 is similar to the V map recorded simultaneously (Supplementary Information Fig. S4).…”

“…The domain wall polarization is highly anisotropic and Fig. 1c shows that below 40 K the ratio between two perpendicular measuring directions decays to values below unity 20,26 .…”

Low-Temperature Dielectric Anisotropy Driven by an Antiferroelectric Mode in SrTiO3

“…[4,5] The most obvious manifestation of tetragonality is the anisotropy of the dielectric constant [6,7], which is responsible for the observed birefringence [8]. Recently, ferroelastic domain formation was shown [9][10][11] to strongly influence other electronic phenomena in SrTiO 3 , e.g., superconductivity [12] or two-dimensional electron gases [13][14][15]. The ability of controlling the electronic degrees of freedom by altering the ferroelastic domain structure provides, in principle, a tantalizing opportunity for new device concepts.…”

Anisotropic multicarrier transport at the (111) LaAlO3/SrTiO3 interface

“…The difference was largest at low temperatures, but still appreciable at room temperature. Frenkel et al observed a weak anisotropy 35 associated with the channeling of currents along microstructural channels that changed on warming above the cubic to orthorhombic transition that occurs in STO at ∼ 105 K. Gopinadhan et al observed a weak anisotropy in the mobility of (110) samples at low temperatures 9 . In contrast to these previous observations, the anisotropy in the electrical characteristics of our (111) samples does not exist at room temperature or liquid nitrogen temperatures, and is reproducible even after repeated warming to room temperature.…”