A switchable two-dimensional electron gas based on ferroelectric Ca:SrTiO$_3$

TL;DR

This paper presents a novel ferroelectric 2DEG in Ca:SrTiO3 that can be non-volatilely switched via electric fields, enabling potential applications in spintronics with stable, controllable electronic properties.

Contribution

The study introduces a ferroelectric 2DEG with non-volatile electrostatic switching, demonstrated through Ca doping in SrTiO3, and explores its hysteretic transport behavior linked to ferroelectricity.

Findings

Ferroelectric phase transition observed at 25 K.

Hysteretic dependence of carrier density on electric field.

Potential for ferromagnet-free spintronic devices.

Abstract

Two-dimensional electron gases (2DEGs) can form at the surface of oxides and semiconductors or in carefully designed quantum wells and interfaces. Depending on the shape of the confining potential, 2DEGs may experience a finite electric field, which gives rise to relativistic effects such as the Rashba spin-orbit coupling. Although the amplitude of this electric field can be modulated by an external gate voltage, which in turn tunes the 2DEG carrier density, sheet resistance and other related properties, this modulation is volatile. Here, we report the design of a ''ferroelectric'' 2DEG whose transport properties can be electrostatically switched in a non-volatile way. We generate a 2DEG by depositing a thin Al layer onto a SrTiO$_3$ single crystal in which 1 percent of Sr is substituted by Ca to make it ferroelectric. Signatures of the ferroelectric phase transition at 25 K are visible in the Raman response and in the temperature dependences of the carrier density and sheet resistance that shows a hysteretic dependence on electric field as a consequence of ferroelectricity. We suggest that this behavior may be extended to other oxide 2DEGs, leading to novel types of ferromagnet-free spintronic architectures.