Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Novel light sources made of 2D materials

28.10.2016

Physicists from the University of Würzburg have designed a light source that emits photon pairs. Two-photon sources are particularly well suited for tap-proof data encryption. The experiment's key ingredients: a semiconductor crystal and some sticky tape.

So-called monolayers are at the heart of the research activities. These "super materials" (as the prestigious science magazine "Nature" puts it) have been surrounded by a virtual hype in the past ten years. This is because they show great promise to revolutionise many areas of physics.


Artistic representation of a two-photon source: The monolayer (below) emits exactly two photons of different frequencies under suitable conditions. They are depicted in red and green.

Picture: Karol Winkler

In physics, the term monolayer refers to solid materials of minimum thickness. Occasionally, it is only a single layer of atoms thick; in crystals it can be three or more layers. Experts also speak of two-dimensional materials. In this form, they frequently exhibit unexpected properties that make them interesting for research. The so-called transition metal dichalcogenides (TMDC) are particularly promising. They behave like semiconductors and can be used to manufacture ultra-small and energy-efficient chips, for example.

Moreover, TMDCs are capable of generating light when supplied with energy. Dr. Christian Schneider, Professor Sven Höfling and their research team from the Chair of Technical Physics of the Julius-Maximilians-Universität Würzburg (JMU) in Bavaria, Germany, have harnessed exactly this effect for their experiments.

Experiments started with sticky tape

First, a monolayer was produced using a simple method. This usually involves a piece of sticky tape to peel a multi-layer film from a TMDC crystal in a first step. Using the same procedure, thinner and thinner layers can be stripped from this film. This process is repeated until the material on the tape is only one layer thick.

The researchers then cooled this monolayer down to a temperature of just above absolute zero and excited it with a laser. This causes the monolayer to emit single protons under specific conditions. "We were now able to show that a specific type of excitement produces not one but exactly two photons," Schneider explains. "The light particles are generated in pairs so to speak."

Such two-photon sources are interesting for the following reason: They can be used to transfer information 100% tap-proof. For this purpose, the light particles are entangled with each other – a quantum mechanical process in which their state is interwoven. The state of the first photon then has a direct impact on that of the second photon, regardless of the distance between the two. This fact can be used to encrypt communication channels.

Monolayers enable novel lasers

In a second study, the JMU scientists demonstrated another application option of the exotic monolayers. For this purpose, they mounted a monolayer between two mirrors and again stimulated it with a laser. The radiation excited the TMDC plate to a level that it began to emit photons itself. These were reflected back to the plate by the mirrors where they excited atoms themselves to create new photons.

"We call this process strong coupling," Schneider explains. The light particles are cloned during this process in a manner of speaking. "Light and matter hybridise, forming new quasi particles in the process: the exciton polaritons," the physicist says. For the first time, it has now been possible to detect these polaritons at room temperature in atomic monolayers.

In the medium run, this will open up interesting new applications. The "cloned" photons have similar properties to laser light. But they are manufactured in completely different ways: Ideally, the production of new light particles is self-sustaining after the initial excitation without requiring any additional energy supply. In a laser in contrast, the light-producing material has to be excited energetically from the outside on a permanent basis. This makes the new light source highly energy-efficient. Moreover, it is excellently suited to study certain quantum effects.

Schneider's ERC project bears fruit

In spring 2016, Christian Schneider received one of the coveted ERC Starting Grants of the European Research Council. The European Union thus funds his work on transition metal dichalcogenides with 1.5 million euros in total. The two studies published in the prestigious science journal "Nature Communication" are the first results of the ERC project.

The publications in Nature Communications

Yu-Ming He, Oliver Iff, Nils Lundt, Vasilij Baumann, Marcelo Davanco, Kartik Srinivasan, Sven Höfling and Christian Schneider: Cascaded emission of single photons from the biexciton in monolayered WSe2; Nature Communications; DOI: 10.1038/ncomms13409

Nils Lundt, Sebastian Klembt, Evgeniia Cherotchenko, Oliver Iff, Anton V. Nalitov, Martin Klaas, Simon Betzold, Christof P. Dietrich, Alexey V. Kavokin, Sven Höfling and Christian Schneider: Room temperature Tamm-Plasmon Exciton-Polaritons with a WSe2 monolayer; Nature Communications; DOI: 10.1038/ncomms13328

Contact

Dr. Christian Schneider, Chair of Technical Physics, JMU, Phone +49 931 31-88021, christian.schneider@physik.uni-wuerzburg.de

Robert Emmerich | Julius-Maximilians-Universität Würzburg
Further information:
http://www.uni-wuerzburg.de

More articles from Physics and Astronomy:

nachricht Structured light and nanomaterials open new ways to tailor light at the nanoscale
23.04.2018 | Academy of Finland

nachricht On the shape of the 'petal' for the dissipation curve
23.04.2018 | Lobachevsky University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Molecules Brilliantly Illuminated

Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.

Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Structured light and nanomaterials open new ways to tailor light at the nanoscale

23.04.2018 | Physics and Astronomy

On the shape of the 'petal' for the dissipation curve

23.04.2018 | Physics and Astronomy

Clean and Efficient – Fraunhofer ISE Presents Hydrogen Technologies at the HANNOVER MESSE 2018

23.04.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>