Spin and Valley Dynamics in 2D van der Waals Materials

• Applicant: Privatdozent Dr. Jens Hübner
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391378795

• Final Report Year: 2023

Final Report Abstract

Transition metal dichalcogenides (TMDs) have emerged as a promising candidate for applications in the opto-electronics due to their unique optical properties. The combination of the existence of a spin and a valley-pseudospin and valley specific optical selection rules provides the optimal basis for the utilization of the electron and hole characteristics in (quantum) information processing. For this application, the spin- and carrier dynamics are fundamental. In the course of this, both, the fabrication and investigation of TMDs were optimized and complementary new methods were established. In the context of the exfoliation of TMDs, new high-quality MoSe2, MoTe2, WSe2 and MoS2 monolayers have already been fabricated. Here, in addition, wet-chemical synthesis of TMDs was established as an additional up-scalable fabrication method. Optimized and competitive colloidal samples were fabricated based on the application of highly sensitive, laterally resolved photoluminescence (PL) measurements. Further optimizations of the different fabrication techniques enabled the fabrication of laterally confined, nearly zero-dimensional, colloidal samples. The spin and carrier dynamics of these highly developed TMD structures were investigated using different spectroscopic approaches, including time resolved photoluminescence spectroscopy, spin noise spectroscopy and the establishment of temperature-dependent pump-probe spectroscopy. The latter allowed a comprehensive insight in the competing recombination dynamics in TMDs, in the regime of the low-energetic A and B exciton as well as in the high-energetic C and D exciton. These, up-to-now sparsely investigated C and D excitons, show an increased influence in spatially confined TMD structures. In conclusion, the cooperation of all contributing partners yielded a profound understanding of the promising material system of the TMDs as well as the establishment of new and optimized fabrication and investigation methods.

Publications

• Room Temperature Micro-Photoluminescence Studies of Colloidal WS2 Nanosheets. The Journal of Physical Chemistry C, 125(34), 18841-18848.
  Frauendorf, André Philipp; Niebur, André; Harms, Lena; Shree, Shivangi; Urbaszek, Bernhard; Oestreich, Michael; Hübner, Jens & Lauth, Jannika
  
• How to Make Nanosheets Glow: An Innovative Route to Photoluminescent Colloidal 2D TMDCs. Proceedings of the nanoGe Spring Meeting 2022. Fundació Scito.
  Niebur, André; Frauendorf, André P.; Oestreich, Michael; Hübner, Jens & Lauth, Jannika
  
• “Advanced Optical Spectroscopy of Colloidal Transition Metal Dichalcogenides” NanoDay of the Laboratory for Nano and Quantum Engineering, Hannover, Germany, 22.09.2022
  André P. Frauendorf; A. Niebur; J. Lauth; M. Oestreich & Jens Hübner
  
• “Optical Spectroscopy of Colloidal Transition Metal Dichalcogenides” DFG Spring Meeting 2022 Regensburg, Germany, 04.09.- 09.09.2022
  André P. Frauendorf; A. Niebur; Jens Hübner; J. Lauth & M. Oestreich
  
• “Optical Spectroscopy of Colloidal Transition Metal Dichalcogenides” Humboldt meets Leibniz - Emerging Topics in Optics and Photonics, Hannover, Germany, 12.-14.06.2022
  André P. Frauendorf; A. Niebur; J. Lauth; M. Oestreich & Jens Hübner
  
• Untangling the intertwined: metallic to semiconducting phase transition of colloidal MoS2 nanoplatelets and nanosheets. Nanoscale, 15(12), 5679-5688.
  Niebur, André; Söll, Aljoscha; Haizmann, Philipp; Strolka, Onno; Rudolph, Dominik; Tran, Kevin; Renz, Franz; Frauendorf, André Philipp; Hübner, Jens; Peisert, Heiko; Scheele, Marcus & Lauth, Jannika
  
• “Low temperature transient absorption spectroscopy: Unraveling the ultra-fast carrier dynamics in TMDs” NanoDay of the Laboratory for Nano and Quantum Engineering, Hannover, Germany, 20.09.2023
  André P. Frauendorf; A. Niebur; D. Rudolph; J. Lauth; M. Oestreich & Jens Hübner
  
• “Temperature-dependent transient absorption spectroscopy: Revealing the ultra-fast carrier dynamics in transition metal dichalcogenides” International Winterschool on New Developments in Solid State Physics, Mauterndorf, Austria, 12.-17.02.2023
  André P. Frauendorf; A. Niebur; J. Lauth; M. Oestreich & Jens Hübner