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Proposed optical terahertz graphene transistor

Posted By Graphene Council, Monday, March 9, 2020
Researchers at the Center for Theoretical Physics of Complex Systems (PCS), within the Institute for Basic Science (IBS, South Korea) have proposed a transistor made of graphene and a two-dimensional superconductor that amplifies terahertz (THz) signals.

This research was conducted in collaboration with colleagues from the Micro/Nano Fabrication Laboratory Microsystem and Terahertz Research Center (China), the A. V. Rzhanov Institute of Semiconductor Physics (Russia), and Loughborough University (UK) and was published in Physical Review Letters ("Optical Transistor for Amplification of Radiation in a Broadband Terahertz Domain").

The growing interest in the THz frequency range can be easily explained by its various potential applications. This region of the electromagnetic spectrum, between radio waves and infrared light, is suited for extremely high-resolution images, non-invasive tumor detection, biosecurity, telecommunications, and encryption-decryption procedures, among others.

However, practically, finding a powerful source of rays in this frequency range is so challenging, that researchers commonly refer to this problem as the “Terahertz gap.”

In this work, the researchers proposed a novel strategy to amplify THz radiation from weak and non-uniform signals, which are common in, for instance, biological samples.

The device consists of a graphene sheet positioned in the vicinity of a two-dimensional superconductor and is connected to a power source, which provides enough energy to excite the electrons of the superconductor.

The THz signal amplification is explained by the collective oscillatory behavior of electrons in both of the two materials plus the quantum capacity of graphene.

“This work demonstrates the application-oriented perspectives of systems characterized purely by quantum effects. Light-matter interaction in these hybrid systems not only represent fundamental interest, but it can become a basis for future devices, such as terahertz logic gates, which are currently in high demand,” explains Ivan Savenko, the leader of the Light-Matter Interaction in Nanostructures (LUMIN) team at PCS IBS.

Tags:  A. V. Rzhanov Institute of Semiconductor Physics  Center for Theoretical Physics of Complex Systems  Graphene  Institute for Basic Science  Ivan Savenko  Loughborough University  Micro/Nano Fabrication Laboratory Microsystem  Physical Review Letters  Terahertz Research Center  transistor 

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Unconventional phenomena triggered by acoustic waves in 2D materials

Posted By Graphene Council, Tuesday, July 30, 2019
Researchers at the Center for Theoretical Physics of Complex Systems (PCS), within the Institute for Basic Science (IBS, South Korea), and colleagues have reported a novel phenomenon, called Valley Acoustoelectric Effect, which takes place in 2D materials, similar to graphene. This research is published in Physical Review Letters and brings new insights to the study of valleytronics.

In acoustoelectronics, surface acoustic waves (SAWs) are employed to generate electric currents. In this study, the team of theoretical physicists modelled the propagation of SAWs in emerging 2D materials, such as single-layer molybdenum disulfide (MoS2). SAWs drag MoS2 electrons (and holes), creating an electric current with conventional and unconventional components. The latter consists of two contributions: a warping-based current and a Hall current. The first is direction-dependent, is related to the so-called valleys -- electrons' local energy minima -- and resembles one of the mechanisms that explains photovoltaic effects of 2D materials exposed to light. The second is due to a specific effect (Berry phase) that affects the velocity of these electrons travelling as a group and resulting in intriguing phenomena, such as anomalous and quantum Hall effects.

The team analyzed the properties of the acoustoelectric current, suggesting a way to run and measure the conventional, warping, and Hall currents independently. This allows the simultaneous use of both optical and acoustic techniques to control the propagation of charge carriers in novel 2D materials, creating new logical devices.

The researchers are interested in controlling the physical properties of these ultra-thin systems, in particular those electrons that are free to move in two dimensions, but tightly confined in the third. By curbing the parameters of the electrons, in particular their momentum, spin, and valley, it will be possible to explore technologies beyond silicon electronics. For example, MoS2 has two district valleys, which could be potentially used in the future for bit storage and processing, making it an ideal material to delve into valleytronics.

"Our theory opens a way to manipulate valley transport by acoustic methods, expanding the applicability of valleytronic effects on acoustoelectronic devices," explains Ivan Savenko, leader of the Light-Matter Interaction in Nanostructures Team at PCS.

Tags:  2D materials  Center for Theoretical Physics of Complex Systems  Electronics  Graphene  Institute for Basic Science  Ivan Savenko 

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