Projects - Area B
Charge Transfer investigates how charges move between molecules and 2D materials and how this affects excitonic behavior at their interface. Ground-state charge transfer reshapes the chemical and optical properties of the system, while photoexcitation creates charge-transfer excitons across the interface. Area B aims to understand and control these processes and explore a rare quantum state: the excitonic insulator. Research focuses on (i) charge-transfer mechanisms, (ii) charge-transfer excitons, and (iii) excitonic insulators, novel ground states driven by strong interactions and molecular charge control.
Principal Investigator: Prof. Dr. Kirill Bolotin
Located at: Freie Universität Berlin
Project B01 explores how charge transfer and excitons interact in electrically tuned mol2Dmat systems. Using optical spectroscopy, it probes how electric fields and molecular structure affect exciton behavior. The project aims to control exciton energies down to zero, enabling the study of exotic states like excitonic insulators and paving the way for novel optoelectronic devices.
Experimental methods: nanofabrication, optical spectroscopy, electronic transport
Principal Investigator: Dr. Sebastian Heeg
Located at: Humboldt-Universität zu Berlin
Project B02 investigates charge transfer in mol2Dmat heterostructures with high spatial resolution using tip-enhanced Raman and photoluminescence spectroscopy. It bridges the gap between nanoscale and microscale techniques to study how defects, strain, and inhomogeneity influence charge-transfer excitons. The project develops novel approaches to map exciton diffusion and distinguishes between localized and mobile excitonic states.
Experimental methods: tip-enhanced Raman spectroscopy (TERS), tip-enhanced photoluminescence (TEPL)
Principal Investigator: Prof. Dr. Katharina Franke
Located at: Freie Universität Berlin
Project B03 uses scanning tunneling microscopy (STM) to study molecular structures on charge-density-wave materials like TiSe2 and Ta2NiSe5. It investigates whether bandgap changes and charge-density waves are due to exciton formation or structural causes by analyzing how these features vary with molecular coverage.
Experimental methods: scanning tunneling microscopy (STM), atomic force microscopy (AFM)
Principal Investigator: Prof. Dr. Martin Weinelt
Located at: Freie Universität Berlin
Project B04 investigates excitons in mol2Dmat heterostructures using time-resolved ARPES to identify signatures of exciton condensation into an excitonic insulator. It focuses on molecule/TiSe₂ and molecule/Ta₂NiSe₅ systems to distinguish between excitonic insulator and pure charge-density-wave phase, and on molecule/WS₂ to study energy level alignment, charge-transfer exciton formation, and their ultrafast dynamics.
Experimental methods: time- and angle-resolved photoemission spectroscopy (tr-ARPES)
Principal Investigatorr: Prof. Dr. Norbert Koch
Located at: Humboldt-Universität zu Berlin
Project B05 examines charge transfer and electronic energy level alignment in complex mol2Dmat heterostructures using ARPES and XPS. By preparing bilayers with molecules on both sides, it quantifies how energy levels, intermolecular interactions, and defects affect charge transfer and excitations. The project aims to control charge flow to enable tunable electronic and optical properties.
Experimental methods: sample preparation, angle-resolved photoemission spectroscopy (ARPES), X-ray photoelectron spectroscopy (XPS)
Principal Investigator: Prof. Dr. Felix von Oppen
Located at: Freie Universität Berlin
Project B06 studies how excitonic insulators in 2D materials, like TiSe2, interact with molecular donors and acceptors—from single molecules to disordered arrays. It explores how these adsorbates affect exciton stability and scattering, aiming to identify clear experimental signatures of excitonic insulator states.
Theoretical methods: Mean field theory, Keldysh method (tunneling Hamiltonian), Bogoliubov-de-Gennes formalism, Green-function techniques