http://news.mynavi.jp/news/2016/11/22/263/
The topological was not because by a special complex crystal structure , but by the nature of crystals centered on bismuth.
The University of Tokyo Graduate School of Science PhD course Doctoral course Mr. Shun Ito,
Associate professor Iwawaru Matsuda Institute for Physical Properties, The University of Tokyo,
Ochanomizu University Faculty Research Institute Professor Koji Kobayashi
These are the achievements.
By reading the article, by observing the band structure by photoelectron spectroscopy, they measure the topological nature.
The bismuth thin film may be used at that time.
There was no condition to prepare the bismuth thin film in the short article.
Regardless of the film forming method, it is possible to produce a crystal thin film of a similar polycrystalline type.
Depending on the film formation conditions and the firing temperature, such a polycrystalline type thin film was known that insulation property changes.
Why it is important for insulation to change ?
It was because we tried to use bismuth based insulating thin film as a capacitor of memory.
Naturally, insulation is a key factor in performance.
Bismuth-containing ferroelectrics are not only insulative but also have the property of retaining dielectricity even when normal voltage is applied.
I was studying that Bismuth films 20 years ago.
Since SBT (SrBi2Ta2O9) is a typical bismuth ferroelectric, that can be much potential to make memory device.
But SBT films can not be memory device because of its leakage current.
Thinking now,
There is probably a topological nature and leak current will flow.
In fact, the firing temperature and the topological leakage current are related.
We observed the existence of pyrochlore fine crystals was created by baking at low temperature.
At those days, I thought that pyrochlore fine crystals in the films may flow current.
Now, I think that pyrochlore fine crystals reducing around the insulating crystal to semi-metal bismuth.
That semi-metal bismuth is exist. We observed by XPS measurement that the peak shift of Bismuth.
In near future, the bismuth contained in pyrochlore fine crystals will close up.
The condition of bismuth in Pyrochlore and the insulated crystal around those fine crystals is very depend on baking temperature and the topological factor is also depend on temperature.
The mechanism the Pyrochlore crystal reduce the around insulator crystals is related to red-ox tendency of those elements, I think.