The research team demonstrates a control mechanism for quantum material

When a control voltage is applied to graphene, the frequency conversion of the current can be controlled. Credits: Junix, Dresden, CC-BY

How can large amounts of data be transferred or processed as quickly as possible? One of the keys to this could be graphene. The ultrathin material is only one atomic layer thick, and the electrons it contains have very special properties due to quantum effects. It could therefore be very suitable for use in high performance electronic components. Up to this point, however, there was a lack of knowledge on how to properly control certain properties of graphene. A new study by a team of scientists from Bielefeld and Berlin, along with researchers from other research institutes in Germany and Spain, is changing that. The team’s findings were published in the journal Scientific progress.

Consisting of carbon atoms, graphene is a material only one atom thick, where the atoms are arranged in a hexagonal lattice. This arrangement of atoms results in a unique property of graphene: the electrons in this material move as if they had no mass. This “fat-free” behavior of electrons leads to a very high electrical conductivity in graphene and, most importantly, this property is maintained at room temperature and under ambient conditions. Graphene is therefore potentially very interesting for the modern application of electronics.

It has recently been discovered that the high electronic conductivity and “massless” behavior of its electrons allows graphene to change the frequency components of the electric currents passing through it. This property largely depends on the strength of this current. In modern electronics, such nonlinearity contains one of the most basic functions for switching and processing electrical signals. Graphene is unique in that its nonlinearity is by far the strongest of all electronic materials. Moreover, it works very well at extremely high electronic frequencies, extending into the technologically important terahertz (THz) range where most conventional electronic materials fail.

In their new study, a team of researchers from Germany and Spain showed that graphene nonlinearity can be controlled very effectively by applying a relatively low electrical voltage to the material. For this, the researchers produced a transistor-like device, where a control voltage can be applied to a group of electrical contacts on graphene. The THz ultrafrequency signals were then transmitted using the device: the transmission and subsequent transformation of these signals were analyzed in relation to the applied voltage. The researchers found that graphene becomes almost perfectly transparent at a certain voltage – its normally strong nonlinear response almost disappears. By slightly increasing or decreasing the voltage from this critical value, graphene can be converted to a highly nonlinear material, which significantly alters the strength and frequency components of the transmitted and assigned THz electronic signals.

“This is a significant step forward towards the application of graphene in the application of electrical signal processing and signal modulation,” says prof. Dmitry Turchinovich, a physicist from the University of Bielefeld and one of the leaders of this study. “We’ve shown before that graphene is by far the most nonlinear functional material we know of. We also understand the physics behind nonlinearity, known today as the thermodynamic picture of ultrafast electron transfer in graphene. But so far we didn’t know how to control this nonlinearity. there was a lack of a link regarding the use of graphene in everyday technologies. ”

“By applying control voltage to graphene, we were able to change the number of electrons in the material that can move freely when an electrical signal is applied to it,” explains Dr. Hassan A. Hafez, member of professor dr. Turchinovich’s laboratory in Bielefeld and one of the leading authors of the study. “On the one hand, the more electrons can move in response to an applied electric field, the stronger the currents, which should amplify the nonlinearity. But on the other hand, the more free electrons available, the stronger the interaction between them, and this suppresses the nonlinearity. Here we have shown – both experimentally and theoretically – that the application of a relatively weak external voltage of only a few volts can create optimal conditions for the strongest THz-nonlinearity in graphene. “

“With this work, we have achieved an important milestone on the way to the use of graphene as an extremely efficient nonlinear functional quantum material in devices such as THz frequency converters, mixers and modulators,” says Professor Dr. Michael Gensch from the Institute of Optics. Sensor systems of the German Aviation Center (DLR) and the Technical University of Berlin, which is the second leader of this study. “This is extremely relevant because graphene is perfectly compatible with existing electronic half-frequency ultrafrequency technology such as CMOS or Bi-CMOS. Therefore, it is now possible to imagine hybrid devices in which the initial electrical signal is generated at lower frequencies using existing semiconductor technology but then they can very efficiently convert to much higher frequencies THz in graphene, all in a completely controlled and predictable way. “

Researchers from the University of Bielefeld, the Institute for Optical Sensor Systems DLR, the Technical University of Berlin, the Helmholtz Center Dresden-Rossendorf and the Max Planck Institute for Polymer Research in Germany, as well as the Catalan Institute for Nanoscience and Nanotechnology (ICN2) and the Institute for Photonic Sciences ) in Spain participated in this study.

Kagome graphene promises exciting properties

More information:
Sergey Kovalev et al. Electrical adaptability of terahertz nonlinearity in graphene, Scientific progress (2021). DOI: 10.1126 / sciadv.abf9809

Provided by the University of Bielefeld

Citation: Research team demonstrates quantum material control mechanism (2021, April 8) retrieved April 8, 2021 from

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