Super-resolution lightwave tomography of electronic bands in quantum materials – Publication by B4

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The researchers developed a method, which was published in Science, to reconstruct the band structure of quantum materials with very high precision

A light flash (yellow) induces the movement of electrons in the band structure (red curve) resulting in the formation of localized electronic interference combs (peaks). The emitted radiation (red) enables the analysis of the electronic band structure. © Markus Borsch, University of Michigan, USA. Reprinted with permission from AAAS.

Stacking of two-dimensional (2D) materials yield promising properties for the development of new devices with outstanding functionality. However, detailed knowledge of the electronic structure is necessary to tailor their properties. Within the cooperation of Prof. Huber (Uni Regensburg), Prof. Kira (Uni Michigan) and Prof. Koch (Uni Marburg, project B4), a new method was developed enabling the reconstruction of the band structure of 2D materials.

The quantum material WSe2 was simultaneously excited by two laser pulses in the visible range and in the THz spectral range. The resonant excitation of the weak optical pulse and simultaneous irradiation with a strong THz pulse result in harmonic sideband generation (HSG) in the transmitted spectrum. Due to the wave-particle dualism of electrons, electronic interference combs evolve in momentum space (cf. Figure on the left). By analyzing multiple sideband spectra at different THz frequencies and intensities, it is possible to reconstruct the band structure with super-resolution.

This concept offers an all-optical and practical approach for a three-dimensional tomography of the electronic structure of small quantum materials as shown for WSe2. This work is a great extend to the research in the SFB as it provides the possibility to examine the electronic band structure of 2D materials, such as TMDCs, even under ambient conditions.

Publication

M. Borsch, C.P. Schmid, L. Weigl, S. Schlauderer, N. Hofmann, C. Lange, J.T. Steiner, S.W. Koch, R. Huber, M. Kira
Super-resolution lightwave tomography of electronic bands in quantum materials
Science 370 (2020) 1204 DOI:10.1126/science.abe2112

Contact

Prof. Dr. Stephan W. Koch
Philipps-Universität Marburg
Department of Physics, Theoretical Semiconductor Physics
Renthof 5, 35032 Marburg
Tel.: 06421 28-21336
EMAIL

Lars Bannow and Benedikt P. Klein awarded the dissertation prize of Philipps-Universität Marburg

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Congratulation to Dr. Lars Bannow and Dr. Benedikt P. Klein, PhD-students of the GRK 1782 (SW Koch) and the SFB project A4 (Gottfried), respectively, for being awarded a prize by Philipps-Universität Marburg for their excellent dissertations presented in 2019.

Lars Bannow, GRK 1782 (SW Koch) Foto: Paul Ndimande

In the thesis of Dr. Bannow with the title “Optical and Electronic Properties of Semiconductor Materials”, he investigates optical and electronic properties of novel semiconductor materials such as Ga(AsBi), In(AsBi) and the methylammonium (MA) perovskite MAPbI3. Using a combination of density functional theory calculation and semiconductor Bloch equations, a precise prediction of opto-electronic properties was possible at a minimum of experimental data. The examined materials are promising options for the fabrication of more efficient laser diodes and more economic solar cells.

Benedikt Klein, A4 (Gottfried)

In his thesis “The Surface Chemical Bond of Non-alternant Aromatic Molecules on Metal Surfaces”, Dr. Klein explores interfaces between model organic semiconductors and metals. He compares π-electron systems with alternant and non-alternant topologies and finds that the non-alternant topology leads to much stronger interfacial interactions. These studies pave the way to novel organic semiconductors with tailored properties and provide important insight into the bonding of non-alternant defect structures in graphene with metals.

See the news release of the Philipps-Universität Marburg for details of the event.

Directional ultrafast charge transfer in a TMDC heterostructure – Publication by B5 (Höfer/Mette)

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In a new publication in Nanoscale Horizons, Zimmermann and coworkers introduce time-resolved SHG imaging microscopy as a new experimental method for investigating ultrafast charge-transfer processes in heterostructures of transition metal dichalcogenides.

Time- and polarization-resolved SHG microscopy in combination with pump-photon energy dependent measurements reveals ultrafast interlayer hole transfer from WSe2 to MoSe2 and vice versa. Copyright by CC BY 3.0.

Heterostructures of transition metal dichalcogenides (TMD) feature a type-II band alignment which can separate photoexcited electrons and holes into different layers through ultrafast charge transfer. While this charge transfer is essential for potential applications, the underlying mechanisms still remain elusive. Main drawbacks of previous experiments are insufficient time-resolution of the employed microscopy setups and deficiencies of linear optical spectroscopies to address individual layers of the heterostructure selectively.In their new approach, Zimmermann and coworkers have combined the advantages of time-resolved optical second-harmonic generation (SHG) with an optical microscopy setup. On the one hand, their method allows for pump-probe experiments in µm small structures with a superior time-resolution. On the other hand, the tensorial nature of the second-order nonlinear susceptibility allows them to distinguish the response from differently oriented layers to elucidate directional interlayer charge transfer as demonstrated for a rotationally mismatched WSe2/MoSe2 heterostructure. As their results show, the new approach is particularly suited to perform systematic investigations of the charge transfer in dependence of the rotational layer mismatch in TMD heterostructures.

Publication

J. E. Zimmermann, Y. D. Kim, J. C. Hone, U. Höfer, G. Mette
Directional ultrafast charge transfer in a WSe2/MoSe2 heterostructure selectively probed by time-resolved SHG imaging microscopy
Nanoscale Horizons 5 (2020) 1603 DOI: 10.1039/d0nh00396d

Contact

Dr. Gerson Mette
Philipps-Universität Marburg
SFB 1083 subproject B5
https://internal-interfaces.de/projects/B5
Tel.: +49 6421 28-24123
EMAIL