Technology reported in new study has nanoelectronics applications

A research team led by a physicist from the University of California, Riverside has identified a new magnetized state in a monolayer of tungsten ditelluride, or WTe2, a new quantum material. Called a magnetized or ferromagnetic quantum spin Hall insulator, this one-atom-thick material has an insulating interior but a conductive edge, which has important implications for controlling the flow of electrons in nanodevices.

In a typical conductor, electric current flows uniformly throughout. Insulators, on the other hand, do not easily conduct electricity. Ordinarily, monolayer WTe2 is a special insulator with a conductive edge; magnetizing it gives it more unusual properties.

“We stacked the single layer WTe2 with a ferromagnetic insulator of several thicknesses of atomic layers — of Cr2Ge2You6or simply CGT – and found that the WTe2 had developed ferromagnetism with a conductive edge,” said Jing Shi, a distinguished professor of physics and astronomy at UCR, who led the study. “The edge flow of electrons is unidirectional and can be made to change direction with the help of an external magnetic field. »

Shi explained that when only the edge conducts electricity, the size of the inside of the material is irrelevant, making it possible to reduce the size of electronic devices that use such materials – in fact, almost as small as the edge. driver. Since devices using this material would consume less power and dissipate less energy, they could be made more energy efficient. Batteries using this technology, for example, would last longer.

The results of the study appear in Nature Communication.

Currently, the technology only works at very low temperatures; CGT is ferromagnetic at around 60 K (or -350 F). The goal of future research would be to operate the technology at higher temperatures, enabling many nanoelectronic applications such as non-volatile memory chips used in computers and cell phones.

According to Shi, the conducting edge in ideal quantum spin Hall insulators comprises two narrow channels side by side, similar to a two-lane highway with cars traveling in opposite directions. Electrons flowing in one channel cannot cross the other channel, Shi said, unless impurities are introduced. Conductive edge in WTe monolayer2 was first visualized in an earlier study by co-author Yongtao Cui, an associate professor of physics and astronomy at UCR and a colleague of Shi.

“It’s two channels per edge,” Shi said. “If you eliminate a channel, you end up with current only flowing in one direction, leaving you with what’s called a quantum anomalous Hall insulator, yet another special quantum material. Such an insulator has only one highway lane, to use the highway. analogy. This insulator transports electrons in a fully spin-polarized manner. »

On the other hand, the magnetized WTe2 that Shi and his colleagues experimented with is called a ferromagnetic quantum spin Hall insulator, which has a conducting edge with partially spin-polarized electrons.

“In both channels of ferromagnetic quantum spin Hall insulators, we have an unequal number of electrons flowing in opposite directions, giving a net current, which we can control with an external magnet,” Shi said.

According to Shi, quantum materials such as WTe2 are the future of nanoelectronics.

“The CHIPS Act will encourage researchers to come up with new materials with properties superior to those of current silicon materials,” he said.

Shi was joined in the study by Cui and Xi Chen at UCR as well as the following researchers in their labs: Mina Rashetnia, Mark Lohmann and Youming Xu. The first author, Junxue Li, was a postdoctoral researcher in Shi’s lab when the research was done. The other co-authors of the article are Jahyun Koo and Binghai Yan from the Weizmann Institute of Science in Israel; Xiao Zhang and Shuang Jia from Peking University in China; and Kenji Watanabe and Takashi Taniguchi of the National Institute of Materials Science in Japan.

Shi was supported in the research by grants from the Department of Energy and the National Science Foundation.

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