Graphene Hits Important Quantum Milestone for THz Data Transfer. But Will it Work?

Researchers already use the carbon-based material graphene for many things, including novel applications in materials science and electronics. Now a team based at Bielefeld University in Germany has found another potential use for the versatile material—high-speed data transfer.

Researchers from that university worked alongside other scientists from various institutions in Germany and Spain to explore the quantum effects of graphene and its potential use in high-performance electronic components for data transfer. They found that this potential application is dependent on scientists’ ability to control certain properties of graphene, which is where the new research comes into play.

Specifically, researchers demonstrated that a property of graphene—its nonlinearity—can be efficiently controlled by applying comparatively modest electrical voltages to the material.

This aspect of graphene is important because of its nonlinearity which is by far the strongest of all electronic materials, researchers said. And in modern electronics, such a nonlinearity comprises one of the most basic functionalities for switching and processing, they said.

“This is a significant step forward towards implementation of graphene in electrical signal processing and signal modulation applications,” Dmitry Turchinovich, a physicist at Bielefeld University and one of the lead investigators, said in a press statement.

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Future of Data is Graphene

Indeed, scientists are reaching the end of the road for certain technologies for high-speed data transfer and are seeking new materials for the future of components for the processors responsible for this aspect of our ever more connected world. A material like graphene has the potential to be one of those materials.

The material is especially attractive because it works very well for exceptionally high electronic frequencies, extending into the technologically important terahertz (THz) range where most conventional electronic materials fail, researchers noted.

Prior to their latest work, the team had achieved a new understanding of the physics behind nonlinearity, which is now known as the thermodynamic picture of ultrafast electron transport in graphene, he said. But until now, they did not know how to control this property, “which was the missing link with respect to using graphene in everyday technologies,” Turchinovich said.

Graphene’s nonlinearity is highly dependent on how strong the electric current running through it is. To control the property by applying electrical voltages to the material, researchers manufactured a device resembling a transistor that can apply a control voltage using a set of electrical contacts, they said. Then, they transmitted ultrahigh-frequency THz signals using the device, after which they analyzed the transmission and subsequent transformation of these signals in relation to the voltage applied.

What they discovered is that graphene becomes almost perfectly transparent at a certain voltage, at which point its nonlinear response nearly vanishes, researchers said. Thus, by slightly increasing or lowering the voltage from this critical value, they can transform graphene into a strongly nonlinear material. This significantly alters the strength and the frequency components of the transmitted and remitted THz electronic signals. 

“By applying the control voltage to graphene, we were able to alter the number of electrons in the material that can move freely when the electrical signal is applied to it,” Hassan Hafez, a member of Professor Turchinovich’s lab and another lead in the study, explained in a press statement.

Proving the Concept

On the one hand, the more electrons can move in response to the applied electric field, the stronger the currents are in the material, which should enhance the nonlinearity, he explained. However, on the other hand, the more free electrons are available, the stronger the interaction between them is, which suppresses the nonlinearity, Hafez said.

“Here we demonstrated--both experimentally and theoretically--that by applying a relatively weak external voltage of only a few volts, the optimal conditions for the strongest THz nonlinearity in graphene can be created,” he said.

Researchers published a paper on their work in the journal Science Advances.

This control of the material is an “important milestone” to using the material as a quantum material for use in components for THz data transfer, such as converters, mixers, and modulators, researchers said.

In the future, scientists can potentially design hybrid devices in which the initial electric signal is generated at a lower frequency using existing semiconductor technology but can then very efficiently be up-converted to much higher THz frequencies in graphene in a way that is controlled and predictable; they said.

In addition to researchers from Bielefeld University, others who took part in the work include scientists from the Institute of Optical Sensor Systems of the DLR, the Technical University of Berlin, the Helmholtz Center Dresden-Rossendorf, and the Max Planck Institute for Polymer Research in Germany, the Catalan Institute of Nanoscience and Nanotechnology (ICN2), and the Institute of Photonic Sciences (ICFO) in Spain.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.