Detection of an interface-specific coherent phonon mode – Publication by B5 (Höfer/Mette), A1 (Stolz) and A5 (Volz) in Advanced Materials Interfaces

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Gerson Mette, former project B5, and co-workers succeeded in exciting and detecting an interface-specific coherent phonon signal at the buried GaP/Si(001) heterointerface

An important goal of the collaborative research centre SFB 1083 “Structure and Dynamics of Internal Interfaces” has been the advancement of the spectroscopy of buried interfaces. In this respect, the investigation of interface-specific phonons has proven to be most challenging. With the detection of a 2-THz difference-combination mode between a GaP-like and a Si phonon, Mette and coworkers could recently observe such an interface-specific vibrational excitation.

The key to their success was a new laser experiment that we started setting up in 2019. With intense excitation pulses, which are at the same time short enough for coherent phonon spectroscopy and widely tunable, Mette et al. could launch the phonons by resonantly exciting an electronic interface transition. The work has been conducted in collaboration with Kunie Ishioka from the National Institute for Materials Science (NIMS) in Tsukuba, Japan. The samples were grown and characterized by Wolfgang Stolz, former project A1, and Kerstin Volz, project A5, in Marburg.

Publication

G. Mette, K. Ishioka, S. Youngkin, W. Stolz, K. Volz, U. Höfer
Interface‐specific excitation of coherent phonons at the buried GaP/Si(001) heterointerface
Adv. Mater. Interfaces (2025) 2400573 DOI:10.1002/admi.202400573

Contact

Prof. Dr. Ulrich Höfer
Philipps-Universität Marburg
SFB 1083 project B5 and B6
Tel.: 06421 28-24215
EMAIL

Ultrafast switching of trions in 2D materials by terahertz photons – Publication by B9 (Malic) in Nature Photonics

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In a joint study including the experimental group of  Alexey Chernikov (TU Dresden), Manfred Helm and Stephan Winnerl (Helmholtz Zentrum Dresden-Rossendorf) as well as the theoretical group of Ermin Malic (Philipps-Universität Marburg),the ultrafast switching of trions in 2D materials were investigated by terahertz photons.

External control of optical excitations is crucial for manipulating light–matter coupling and is highly desirable for photonic technologies. Excitons in monolayer semiconductors emerged as a unique nanoscale platform in this context, offering strong light–matter coupling, spin–valley locking and exceptional tunability. Importantly, they allow electrical switching of their optical response due to efficient interactions of excitonic emitters with free charge carriers, forming new quasiparticles known as trions and Fermi polarons. Due to major limitations of how fast the light emission of these states can be tuned, the majority of applications are restricted to an essentially static regime.

Here, the groups of Ermin Malic, Alexey Chernikov as well as Manfred Helm and Stephan Winnerl demonstrate switching of excitonic light emitters in monolayer semiconductors on ultrafast picosecond time scales by applying short pulses in the terahertz spectral range following optical injection. The process is based on a rapid conversion of trions to excitons by absorption of terahertz photons inducing photodetachment. The required resonance conditions as well as the demonstration of the tunability of the process with delay time and terahertz pulse power were achieved by monitoring time-resolved emission dynamics in optical-pump/terahertz-push experiments.

The results introduce a versatile experimental tool for fundamental research of light-emitting excitations of composite Bose–Fermi mixtures and open up pathways towards technological developments of new types of nanophotonic device based on atomically thin materials.

Publication

T. Venanzi, M. Cuccu, R. Perea-Causin, X. Sun, S. Brem, D. Erkensten, T. Taniguchi, K. Watanabe, Ermin Malic, M. Helm, S. Winnerl, A. Chernikov
Ultrafast switching of trions in 2D materials by terahertz photons
Nat. Photon. (2024) DOI:10.1038/s41566-024-01512-0

Contact

Prof. Dr. Ermin Malic
Philipps-Universität Marburg
SFB 1083 project B9
Tel.: 06421 28-22640
EMAIL

The International Conference on Internal Interfaces, ICII-24, was held in Marburg

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SFB 1083 organized the third International Conference on Internal Interfaces (ICII-24) in Marburg with many national and international speakers.

The meeting brought together more than 100 scientists from across the world in the new library building of the Philipps-Universität Marburg. From those, over 25 national and international speakers were invited to present their most recent progress in interface-research. Oral and poster sessions set the framework for intensive discussions on the newest developments in a fast-changing research field.

Thanks to the generous donations of Dock Chemicals and Scienta Omicron, the SFB awarded poster prizes for the best posters presented during conference. The first price was awarded to Klaus Zollner from the University of Regensburg (poster title: “Proximity-induced spin interactions in twisted van der Waals heterostructures”). The second price was shared between Dr. Sabine Wenzel (poster title: “Selective on-surface synthesis of isokekulene through strong molecule-metal interaction”) and Dr. Roberto Rosati (poster title: “Engineering the charge-transfer excitons in 2D lateral heterostructures”) both from Marburg. The committee congratulates all three award winners.

The attractive setting for the event provided by the Philipps-Universität Marburg and the city contributed to making it a memorable meeting.

For more details please check out the meeting’s homepage.