Thema der Dissertation:
Engineering of excitonic landscapes
Engineering of excitonic landscapes
Abstract: Transition-metal dichalcogenides (TMDs), prototypical two-dimensional semiconductors, exhibit strongly reduced Coulomb screening, which gives rise to large exciton binding energies and enables a rich variety of many-body excitonic states. This calls for development of experimental techniques for the direct control of band structure and symmetry in 2D materials, with the aim of studying currently debated many-body states and inducing new states that are normally inaccessible.
In my defense talk, I will present several approaches for studying and manipulating excitonic complexes in TMDs. First, I will discuss a method for applying biaxial strain at low temperatures, which enables direct tuning of the band structure and allows control over the energy hierarchy of excitons. Using this approach, we revealed previously inaccessible optically dark excitons and achieved controlled hybridization of excitons originating from distinct valleys in momentum space. Second, I will show how uniaxial strain can break discrete rotational symmetry and lift degeneracies in exciton states, effectively creating a pseudomagnetic field exceeding 40 T. Under this strain-induced field, we observed analogs of Larmor precession and Zeeman splitting, and identified the bosonic nature of charged excitons through pseudomagnetic g-factor measurements.
Third, I will present the use of high-resolution electron-beam lithography to engineer excitonic bands with single-photon emission characteristics that remain stable up to room temperature. Finally, I will discuss ultrafast photocurrent measurements and terahertz emission spectroscopy, which reveal femtosecond exciton formation and transport dynamics, including interlayer exciton formation as well as shift currents and Rabi oscillations between interlayer and intralayer excitons in homobilayers.
Together, these results establish new routes for controlling and probing the fundamental properties of excitons, including their valley structure, binding energy, symmetry, and ultrafast dynamics, and provide a foundation for accessing excitonic states beyond the limits of conventional optical experiments.
In my defense talk, I will present several approaches for studying and manipulating excitonic complexes in TMDs. First, I will discuss a method for applying biaxial strain at low temperatures, which enables direct tuning of the band structure and allows control over the energy hierarchy of excitons. Using this approach, we revealed previously inaccessible optically dark excitons and achieved controlled hybridization of excitons originating from distinct valleys in momentum space. Second, I will show how uniaxial strain can break discrete rotational symmetry and lift degeneracies in exciton states, effectively creating a pseudomagnetic field exceeding 40 T. Under this strain-induced field, we observed analogs of Larmor precession and Zeeman splitting, and identified the bosonic nature of charged excitons through pseudomagnetic g-factor measurements.
Third, I will present the use of high-resolution electron-beam lithography to engineer excitonic bands with single-photon emission characteristics that remain stable up to room temperature. Finally, I will discuss ultrafast photocurrent measurements and terahertz emission spectroscopy, which reveal femtosecond exciton formation and transport dynamics, including interlayer exciton formation as well as shift currents and Rabi oscillations between interlayer and intralayer excitons in homobilayers.
Together, these results establish new routes for controlling and probing the fundamental properties of excitons, including their valley structure, binding energy, symmetry, and ultrafast dynamics, and provide a foundation for accessing excitonic states beyond the limits of conventional optical experiments.
Zeit & Ort
14.08.2026 | 15:00
Hörsaal A (1.3.14)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)