First 2-D Form of Tungsten Ditelluride Undergo Ferroelectric Switching

Recently, researchers of University of Washington discover that the 2-D form of tungsten ditelluride can undergo ferroelectric switching. When two monolayers of WTe2 are stacked into a bilayer, a spontaneous electrical polarization appears, one layer becoming positively charged and the other negatively charged. This polarization can be flipped by applying an electric field. The research result has been published by Nature.

The single monolayer of tungsten ditelluride can be prepared and separated from the 3-D crystalline form of tungsten ditelluride. Tungsten ditelluride is known as the first 2-D material which exists the phenomenon of ferroelectric switching. Before that, scientist have only observed the ferroelectric switching in electrical insulators. However, WTe2 isn't an electrical insulator; it is actually a metal, albeit not a very good one.

“Finding ferroelectric switching in this 2-D material was a complete surprise,” said senior author David Cobden, a UW professor of physics. “We weren't looking for it, but we saw odd behavior, and after making a hypothesis about its nature we designed some experiments that confirmed it nicely.” The materials which own ferroelectric property have a potential value of application to memory storage, capacitors, sensors and so on.

“Think of ferroelectrics as nature’s switch,” said Cobden. “The polarized state of the ferroelectric material means that you have an uneven distribution of charges within the material -- and when the ferroelectric switching occurs, the charges move collectively, rather as they would in an artificial electronic switch based on transistors.”

According to Cobden, the ferroelectric switching of tungsten ditelluride can remain stable at room temperature and won’t degrade over time which is different for many traditional 3-D ferroelectric materials. Compared with other ferroelectric compounds, these properties enable tungsten ditelluride to transform into a smaller material which can be widely applied. 

Ferroelectric switching is the second important finding for the monolayer of tungsten ditelluride made by Cobden and his team. In a 2017 paper published on Nature Physics, the team has reported that this material is also a topological insulator and the first 2-D material with this special property. Cobden and his colleagues plan to continue studying the secret of tungsten ditelluride and expect for a more exciting discovery.

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