2D Quantum Materials
In this research theme we aim to understand and control atomic-scale quantum systems (AQS) in scalable and robust solid-state 2D material platforms. The extreme confinement of AQS equips them with resilient quantum properties that can be exploited in emerging quantum technology applications. We engineer and probe atomic and molecular quantum systems in 2D frameworks by leveraging recent breakthrough developments in the synthetic control of 2D materials and our advanced scanning probe toolbox. This allows us to explore the electronic, magnetic and optical properties, and excitation dynamics of single and coupled AQS at their native length and time scales.
Defects in 2D Transition Metal Dichalcogenide (TMD) Semiconductors
TMDs are a prototypical class of 2D semiconductors, which are heavily investigated for next-generation nanoelectronics and photonics applications. TMDs are unique in their facile synthesis, chemical diversity, inertness, and processability.
Together with our synthesis collaborators, we aim to design functional atomic quantum systems such as point defects by chemical design principles. We employ scanning probe methods to investigate the discrete electronic and spin spectrum associated with single and coupled defects/dopants in TMDs. Moreover, we explore their use as quantum emitters, single photon sources that can encode information about the emitter's spin state. Such quantum emitters are a central building block in quantum communication and sensing schemes.
2D Materials Hetero- and Device-Structures
The smooth interface formed between layered van der Waals (vdW) materials offers fundamentally new prospects for heteromaterial integration in devices where lattice matching requirements pose a huge constraint on material compability. In addition, electrostatic gating is highly effective at these reduced dimensions such that the charge carrier concentration can be tuned uniformly over a large range.
In this research project, we aim at two goals: (i) Develop gate-tunable devices to control the charge and spin state of atomic and molecular systems on or embedded in 2D materials, and (ii) establish ultrathin insulating decoupling layers such as hBN as a substrate platform to increase excitation lifetimes and quench incoherent decay channels.
Scanning Tunneling Electron Induced Light Emission
In recent years, STM-induced luminescence (STML), tip-enhanced Raman spectroscopy (TERS) and nano photo luminescence (PL) have demonstrated that optical spectroscopy can be pushed to sub-molecular resolution. The strong enhancement of the light field under the metallic scanning probe tip leads to a massive enhancement of the spatial resolution, beating the diffraction limit of light by more than two orders of magnitude.
Here we employ STML, nano-PL and photon correlation statistics to study optical properties and charge transfer processes of atomic and molecular quantum emitters. We use high numeric aperture parabolic mirrors to efficiently detect emitted photons from the STM junction and guide them to our sensitive detectors and spectrometers.
Ultrafast Lightwave-Driven Scanning Probe Microscopy
Ultrafast lightwave-driven tunneling constitutes a new research frontier that combines the sub-picosecond time resolution of ultrafast pump-probe spectroscopy with the atomic spatial resolution of a scanning tunneling microscope – a unique tool to study ultrafast light-matter interaction at the space-time limit.
In our lab, we are developing a variant of time-resolved STM that makes use of ultrashort Terahertz (THz) pulses, the so-called THz-STM. Phase-stable, single-cycle THz pulses are generated in a nonlinear crystal by optical rectification of a femtosecond laser pulse. When guided into the STM, a THz pulse acts as an ultrashort transient bias that triggers electron tunneling at a well-defined point in time. By using pump-probe schemes, we can follow the propagation of single charge, spin, vibrational or excitonic excitations with orders of magnitude faster time resolution as compared to conventional STM. This allows us to explore the ultrafast dynamics of fundamental quantum excitations in low-dimensional materials at their intrinsic length and time scales.
This work is supported by an European Research Council (ERC) Starting Grant under the European Union’s Horizon 2020 research and innovation program (Grant agreement No. 948243).