Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Physics of low-dimensional systems

Physics of Low Dimensional Systems

 

 

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Welcome to our group website!

 

The main topic of our experimental research is the physics of low-dimensional solid-state systems. We focus on investigating 1D-systems (carbon nanotubes, confined carbyne), 2D-structures (graphene, transition-metal dichalcogenides), and their heterostructures by confocal and tip-enhanced Raman spectroscopy. We want to understand the physics that governs the behavior of these materials, achieve active control over their optical properties, and use them to explore advanced concepts like molecular optomechanics.

 

Follow us in Twitter: @SHeegLab

 

News & Highlights

 

  • March 17 to March 22, 2024: We take part in the DPG Frühjahrstagung 2024 in the campus of the Technische Universität zu Berlin. Pietro, Johannes and Pablo contribute to the Condensed Matter section of the 87th Spring Meeting of the German Physics Society with talks about surface-sensitive plasmonic membranes, higher order Raman modes of confined carbyne and strain engineering of 2D semiconductors.

  

  • March 16, 2024: Our friend Rafael Battistella Nadas, PhD candidate at the Universidade de Minas Gerais, Belo Horizonte, Brazil and member of the team of FabNS visits our lab.

 

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  • January 29, 2024: Official inauguration of our lab after the installation of the Porto system. We celebrated with friends and colleagues and toasted to the exciting physics to come.

 

  • January 20 to January 28, 2024: The FabNS installation team visits our lab to set up our new Porto Tip-enhanced Raman Spectroscopy system. During the installation and training we had the chance to meet and learn from Cassiano, Vitor and Mário.

 

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  • January 6, 2024: PLD in the media. Our acquisition of the Porto TERS system from the Brazilian startup FabNS received considerable media coverage in Brazil in the last weeks. Our colleagues from FabNS were first interviewed for Jornal da Band, a Brazilian TV newscast, when they shipped our new Porto system to Germany. Sebastian was then interviewed for a similar news clip for Jornal Nacional in TV Glovo, the second largest TV network in the world. Our PLD-FabNS partnership was highlighted by the Brazilian embassy in Germany as an example of German-Brazilian scientific and technological cooperation. News coverage of the first Porto shipment also included printed journals as O Tempo or Diário do Comércio.

 

 

  • December 13, 2023: We celebrate our Christmas dinner with former colleagues, friends and family. Happy holidays!

 

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In this work lead by our colleagues in the group of Kirill Bolotin at the Freie Universität Berlin we use our previously presented electrostatic straining technique to identify the valley character of the many excitonic species present in suspended TMDs at cryogenic temperatures. Our strain approach allow us to brighten otherwise dark momentum-indirect excitons with wavefunctions residing in the K, Q, and Γ valleys. We report the first experimental observation of ΓQ excitons and the largest energy tuning range for single photon emitters in WSe2. Overall, we demonstrate the possibilities of our combined optical and straining technique to probe and manipulate momentum direct and momentum-indirect excitons in suspended 2D semiconductors.

 

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  • November 23, 2023: Our new Tip-Enhanced Raman Spectroscopy system arrives from Belo Horizonte, Brazil. The PORTO scanning near-field optical microscope is the core prodcut of FabNS, a Brazilian startup of which we are proud to be the first customer.  
     
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  • November 15, 2023: Welcome back, Pietro! Dr. Pietro Marabotti joins us as a Postdoctoral researcher. He was recently awarded with an Einstein International PostDoctoral Fellowship with his project Probing nonlinearities in carbyne with undetected photons at nanoscale. Pietro obtained his PhD in Energy and Nuclear Science and Technology in the group of Prof. Carlo Casari at the Politecnico di Milano, where he studied the optical and vibrational properties of linear carbons chains.

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  • November 14, 2023: Pietro is awarded a fourth prize at the Spitzenforschung competition organized by Humboldt Innovation and the Industrieforschung Stiftung with his pitch on a novel near-field optical microscope with entangled photons. Congratulations!

 

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News item at the HU website (in German): https://www.hu-berlin.de/de/pr/nachrichten/november-2023/nr-231116

 

  • October 19, 2023: We attended the official inauguration of the Center for the Science of Materials Berlin (CSMB) in the IRIS Research Building on Humboldt-Universität's Science Campus in Adlershof, Berlin. We were delighted to celebrate with colleagues and friends the beginning of a new and surely very succesful scientific institution in Berlin.

 

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  • August 8, 2023: Welcome  Kaan! Kaan Yapıcı from Istanbul Technical University joins us this Autumn as a Erasmus+ intern to work on 2D Materials fabrication and characterization of plasmonic structures.

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Pietro worked with us as a visiting PhD student in Autumn 2022. After obtaining his PhD in Energy and Nuclear Science and Technology at the Politecnico di Milano in Italy, Dr. Marabotti is coming back to Berlin.

Pietro will set up a near-field scanning optical microscope that performs infrared spectroscopy using entangled photons pairs at nanoscale resolution. He will study how structural non-linearities like defects, kinks or bends affect the optical and electronic properties of confined carbyne and explore its potential for nanoscale light transduction.


Welcome back!

 

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  • March 18 to March 24, 2023: We will be taking part in the 35th International Winterschool on Electronic Properties of Novel Materials (IWEPNM) in Kirchberg am Tirol, Austria. This winter schools gives a broad overview over the physics and chemistry of carbon nanostructures, two-dimensional materials and topological systems through a series of invited talks and contributed poster presentations. We are very excited to meet many friends, colleagues and collaborators there and to engage in many fruitful discussions!

 

 

It is often challenging or impossible to perform Raman spectroscopy of surfaces or thin films since their Raman signatures are very weak or obscured by the much stronger bulk Raman signal. In this work we overcome this problem by placing a thin nanoporous gold membrane on the surface of interest. The pores act as plasmonic slot antennas and enhanced the Raman signals of the surface underneath, while the membrane itself suppresses the bulk Raman signal. We improve the surface-to-bulk Raman signal ratio by three orders of magnitude show that the Raman enhancement occurs in the top few nanometers only.

 

Is this approach actually useful? Yes! We use our plasmonic membranes to study the surface of a thin film of LaNiO3, a conductive complex oxide that is an important electrode material for perovskite type heterostructures. We find a clear Raman mode splitting that is indicative of structural changes in the surface layer of the LaNiO3 film. This splitting is absent in the Raman spectra without our nanoporous membrane and has, to the best of our knowledge, not been reported before. Collaboration with between HU Berlin, Université Le Mans, and several groups from ETH Zürich.

 

Lala, Giorgia, Sebastian, and our collaborator Roman Wyss are working on making our nanoporous gold membranes generally available. Get in touch if you are interested in performing surface-sensitive Raman spectroscopy on your surface of interest!

 

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