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 NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

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: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>