The Ability to Electrically Tune the Dimensionality of mesoscopic LAO/STO Channels

In this study Michelle Tomczyk and her colleagues studied the effect of electrostatic gating on the  magnetotransport properties of quasi-1D and quasi-2D nanostructures formed at the interface of the LaALO3(LAO)/SrTiO3 (STO).  

Recently, LAO/STO LaALO3(LAO)/SrTiO3 (STO) has became one of the most studied complex-oxide heterostructure due to its ability to confine electrons in two dimensional layer at the interface. Many of these studies include modifying the carrier density at the interface by applying a back-gate voltage. There are several techniques to fabricate LAO/STO devices. In this work, authors used conductive atomic force microscope (c-AFM) lithography in which the conduction is controlled by surface protons that are distributed on the LAO surface. They have created two conducting channel with varying witdhs as 10 and 200nm on a  LAO/STO heterostructures grown by pulsed-laser deposition. They designed the the devices in a way that two conducting channels connected in series with two leads and voltage probes. By using silver epoxy on the bottom of the STO substrate they created contacts for a back gate voltage. They investigated changes in the magnetotransport properties on the channels with different widths by varying back gate voltage and applied magnetic field. Initially they measured the conductance for both narrow and wide channels and demonstarted the hysteresis of both channels with back gating. Saturation of the conductance at higher gate voltages was also shown.

They were able to demonstrate dimensional crossover from 2d to 1D behavior with their magnetoconductance measurements. They have observed a negative quadratic Kohler magnetoconductance on the wide channel with positive and zero back-gate bias. No quadratic contribution detected in the narrow channel. They quantify the effect of back gate voltage on magnetoconductance by fitting the high field conductance to a second order polynomial. They have investigated relationship between quadratic coefficient and  back gate voltage and magnetoconductance. They observed overlaps in the narrow range of conductance for the 10nm channel. The universality of the relationship between the magnitude of the conductance and the orbital magnetoconductance behavior was revealed. Subtracting the high-field quadratic fit from the magnetoconductance results in a sharp peak near zero-field. These peaks were associated with weak anti-localizations (WAL) which are the superimposed on the quadratic magnetoconductance. They have showed that WAL peak remains similar for both channels over a wide range of conductance values while the high-field behavior changes with the size of the channels.

They attributed the independence of the size of the WAL feature over a broad range of back-gate voltage and conductance to underlying spin-orbit coupling being one-dimensional. They conclude that the suppression of orbital magnetoconductance under negative gate-bias at the conductance quantum and the striking resemblance of the magnetoconductance provide evidence for a gate-tunable dimensional crossover between 2D transport and quasi 1D- transport.

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