The research team demonstrates a control mechanism for quantum material.
How can large amounts of data be transferred or processed as quickly as possible? One key to this could be graphs. The ultra-thin 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 well suited for use in high-performance electronic components. Up to this point, however, there was a lack of knowledge about how to properly control certain properties of graphs.
A new study by a team of scientists from Bielefeld and Berlin together with researchers from other research institutes in Germany and Spain changes this. The team's results were published in the journal Science Advances.
Graphene is made up of carbon atoms and is a material only one atom thick, in which the atoms are arranged in a hexagonal lattice. This arrangement of atoms leads to the unique property of graphene: the electrons in this material move as if they had no mass. This "massless" behavior of electrons leads to a very high electrical conductivity in graphene, and above all this property is retained at room temperature and under ambient conditions. Graphene is therefore possibly very interesting for modern electronic applications.
It was recently discovered that the high electronic conductivity and “massless” behavior of its electrons allow graphene to change the frequency components of the electrical currents flowing through it. This property strongly depends on how strong this current is. In modern electronics, such non-linearity includes one of the most basic functions for switching and processing electrical signals. What makes graphene unique is that its nonlinearity is by far the strongest of any electronic material. In addition, it is very suitable for exceptionally high electronic frequencies and extends into the technologically important terahertz range (THz) in which most conventional electronic materials fail.
In their new study, the research team from Germany and Spain showed that the nonlinearity of graphene can be controlled very efficiently by applying comparatively low electrical voltages to the material. To do this, the researchers made a device that resembled a transistor, in which a control voltage could be applied to graphene through a set of electrical contacts. Then, ultra-high frequency THz signals were transmitted using the device: the transmission and subsequent transformation of these signals were then analyzed with respect to the applied voltage.
The researchers found that at a certain voltage, graphene becomes almost perfectly transparent – 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 non-linear material, thereby significantly changing the strength and frequency components of the transmitted and transmitted THz electronic signals.
"This is a significant step forward towards the implementation of graphs in electrical signal processing and signal modulation applications," says Prof. Dmitry Turchinovich, physicist at Bielefeld University and one of the leaders of this study. “We had previously shown that graphene is by far the most nonlinear functional material we know. We also understand the physics behind the nonlinearity now known as the thermodynamic picture of ultrafast electron transport in graphs. So far, however, we didn't know how to control this nonlinearity, which was the missing link in terms of using graphs in everyday technology. "
“By applying the control voltage to graphene, we were able to change the number of electrons in the material that can move freely when the electrical signal is applied to the graph,” explains Dr. Hassan A. Hafez, member of Professor Dr. Turchinovich Laboratory in Bielefeld and one of the main authors of the study.
“On the one hand, the more electrons can move in response to the applied electric field, the stronger the currents, which should improve the non-linearity. On the other hand, the more free electrons are available, the stronger the interaction between them, and this suppresses the non-linearity. Here we have shown both experimentally and theoretically that the optimal conditions for the strongest THz nonlinearity in graphs can be created by applying a relatively weak external voltage of only a few volts. "
"With this work we have reached an important milestone on the way to using graphene as an extremely efficient non-linear functional quantum material in devices such as THz frequency converters, mixers and modulators," says Professor Dr. Michael Gensch from the Institute of Optical Sensor Systems at the German Aerospace Center (DLR) and the Technical University of Berlin, the other head of this study.
“This is extremely relevant because graphene is perfectly compatible with existing ultra-high frequency electronic semiconductor technology such as CMOS or Bi-CMOS. It is therefore now possible to envision hybrid devices where the initial electrical signal is generated at a lower frequency using existing semiconductor technology, but then can be very efficiently upconverted in graphs to much higher THz frequencies, all of which are fully controllable and predictable way. ”
Source: Bielefeld University