arXiv subjects

Moritz B. Heindl

Publications and source records attributed to Moritz B. Heindl.

3 recordsLinked to original sources

arXiv2026

Confinement-induced Ultrafast Conductivity in 2D Perovskites resolved by correlative Terahertz-NIR Spectroscopy

Quantum wells made of two-dimensional organic-inorganic hybrid perovskites (2D-PKs) offer a high degree of flexibility in tailoring optoelectronic properties through carrier confinement and functional interlayers. Compared to their 3D counterparts, 2D-PKs exhibit tunable photoluminescence, excitonic binding at room temperature and enhanced structural stability. However, the dynamics of photo-induced charge carriers and their transport properties are highly intertwined due to the interplay of diverse excitation species, charge carrier cooling, transport, and radiative and non-radiative recombination. In this study, we employ optical-pump terahertz-probe spectroscopy (OPTP) to analyze the local conductivity dynamics of 2D and 3D methylammonium lead iodide (MAPI) perovskites at timescales down to picoseconds. Remarkably, we observe an intensity-dependent, 2D-specific buildup of an ultrafast, few-picosecond decay in local conductivity. By combining OPTP with transient absorption (TA) and picosecond time-resolved photoluminescence (TRPL), we demonstrate the disentanglement of photoconductivity and carrier population. This allows us to attribute the 2D-specific ultrafast THz response to delayed hot-carrier cooling and subsequent exciton formation, which effectively reduces the free-carrier conductivity. This intensity-dependent, ultrafast THz response is a signature of the recently identified hot-carrier bottleneck in 3D MAPI, and this effect manifests itself in a unique form in the 2D material. These results encourage further investigations on the impact of functional organic interlayers and provide insights into designing tunable carrier responses for ultrafast devices via adapted heterostructures and confinement.

cond-mat.mtrl-sci↗

arXiv2024

Strategies to enhance THz harmonic generation combining multilayered, gated, and metamaterial-based architectures

Graphene has unique properties paving the way for groundbreaking future applications. Its large optical nonlinearity and ease of integration in devices notably makes it an ideal candidate to become a key component for all-optical switching and frequency conversion applications. In the terahertz (THz) region, various approaches have been independently demonstrated to optimize the nonlinear effects in graphene, addressing a critical limitation arising from the atomically thin interaction length. Here, we demonstrate sample architectures that combine strategies to enhance THz nonlinearities in graphene-based structures. We achieve this by increasing the interaction length through a multilayered design, controlling carrier density with an electrical gate, and modulating the THz field spatial distribution with a metallic metasurface substrate. Our study specifically investigates third harmonic generation (THG) using a table-top high-field THz source. We measure THG enhancement factors exceeding thirty and propose architectures capable of achieving a two-order-of-magnitude increase. These findings highlight the potential of engineered graphene-based samples in advancing THz frequency conversion technologies for signal processing and wireless communication applications.

physics.optics↗

arXiv2021

Quantum-Probe Field Microscopy of Ultrafast Terahertz Excitations

Rapid evolutions of microscopic fields govern the majority of elementary excitations in condensed matter and drive microelectronic currents at increasing frequencies. Beyond nominal "radio frequencies", however, access to local electric waveforms remains a challenge. Several imaging schemes resolve sub-wavelength fields up to multi-Terahertz (THz) frequencies - including scanning-probe techniques, electro-optic sampling or recent ultrafast electron microscopy. Yet, various constraints on sample geometries, acquisition speed and maximum fields limit applications. Here, we introduce ubiquitous far-field microscopy of ultrafast local electric fields based on drop-cast quantum-dot probes. Our approach, termed Quantum-probe Field Microscopy (QFIM), combines fluorescence imaging of visible photons with phase-resolved sampling of electric fields deeply in the sub-wavelength regime. We capture stroboscopic movies of localized and propagating ultrafast Terahertz excitations with sub-picosecond temporal resolution. The scheme employs field-driven modulations of optical absorption in colloidal quantum-dots via the quantum-confined Stark-effect, accessible via far-field luminescence. The QFIM approach is compatible with strong-field sample excitation and sub-micrometer resolution - introducing a route towards ultrafast field imaging in active nanostructures during operation.

physics.optics↗