A Ferroelectric on the Edge
A 2D electron gas sandwiched between a metal and a metal oxide exhibits “impossible” ferroelectric-like behavior.
The material strontium titanate, or STO for short, is a jack-of-all-trades: depending on how it is doped, it behaves as an insulator, a metal, a superconductor, or a ferroelectric. Moreover, when undoped (insulating) STO is layered with other materials, it can host a thin conductive interface, called a two-dimensional electron gas (2DEG). Julien Bréhin, from the French National Center for Scientific Research (CNRS) in Paris, and his colleagues have now induced a 2DEG using a ferroelectric form of STO. Surprisingly, the thin conductor exhibits a kind of ferroelectric memory effect in the way that it switches between two different resistance states.
As previous work has shown, doping STO with small amounts of calcium can transform it into a ferroelectric, which is a material that can retain a permanent electric polarization—like the permanent magnetization in a ferromagnet. Earlier research also demonstrated that depositing aluminum on pure STO can induce a 2DEG at the interface between the two materials.
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