arXiv subjects

Henry Mittenzwey

Publications and source records attributed to Henry Mittenzwey.

7 recordsLinked to original sources

arXiv2026

Many-Body Rashba Spin-Orbit Interaction and Exciton Spin Relaxation in Atomically Thin Semiconductor Structures

We propose a pair spin-orbit interaction (PSOI) mechanism by establishing a mesoscopic many-particle Rashba Hamiltonian. In lowest order, this Hamiltonian self-consistently describes exciton spin relaxation in monolayer transition metal dichalcogenides (TMDC) due to local electric fields caused by spatial asymmetries in the dielectric environment. For a monolayer MoSe$_2$ on a SiO$_2$ substrate above 77$\,$K showing a bright-dark splitting in the meV range, the local electric field causes fast intravalley spin relaxation on a sub-picosecond timescale, whereas it is negligible for other TMDCs with larger bright-dark splitting.

cond-mat.mes-hall↗

arXiv2026

Excitonic Theory of the Ultrafast Optical Response of 2D-Quantum-Confined Semiconductors at Elevated Densities

An excitonic approach to the ultrafast optical response of confined semiconductors at elevated densities below the Mott transition is presented. The theory is valid from the coherent regime, where coherent excitonic transitions and biexcitons dominate, to the incoherent regime, where excitonic occupations dominate. Numerical simulations of the $1s$ exciton dynamics during intense circularly polarized pump pulses in two different Coulomb-interaction regimes are performed for two-dimensional semiconductors: Moderate Coulomb interaction is compared with dominating Coulomb interaction with respect to the light-matter interaction strength. The different many-body contributions are disentangled and it is found, that excitonic Rabi oscillations in the Coulomb-dominated regime are considerably less strong. By also comparing circular and linear excitation in a MoSe$_2$ monolayer, it is found, that linear excitation creates a regime, where excitonic Rabi oscillations are almost completely suppressed.

cond-mat.mes-hall↗

arXiv2026

Coulomb Interaction in Atomically Thin Semiconductors and Density-Independent Exciton-Scattering Processes

In quantum-kinetic approaches to the dynamics of Coulomb-bound many-body correlations such as excitons, trions, biexcitons or higher-order correlations, a detailed knowledge of the many-body Coulomb Hamiltonian serving as a starting point is important. In this manuscript, the second-quantized description of the Coulomb interaction between Bloch electrons in a Heisenberg-equation-of-motion approach in atomically thin semiconductors is derived and reviewed. Emphasis is put on a discussion of Umklapp processes and the dielectric screening including all local-field effects. A link between \textit{ab initio} methods of screening and few-band models in effective-mass approximations for the quantum kinetics is established and all important Coulomb scattering processes contributing to the exciton energy landscape and density-independent exciton scattering are discussed.

cond-mat.mes-hall↗

arXiv2026

Theory of In-Plane-Magnetic-Field-Dependent Excitonic Spectra in Atomically Thin Semiconductors

The linear absorption spectrum of excitons in TMDC monolayers under the influence of an in-plane magnetic field is theoretically studied. We demonstrate that in-plane magnetic fields induce a hybridization between spin-bright and spin-dark exciton transitions, resulting in a brightening of spin-dark excitons. We analytically investigate spectral features including resonance energy shifts, broadening and amplitudes ratios. In particular, for a MoSe$_2$ monolayer with radiatively-limited linewidth, we find a complex interplay of dark-bright splitting and linewidth difference of both involved spin-bright and spin-dark excitons.

cond-mat.mes-hall↗

arXiv2025

Dissecting intervalley coupling mechanisms in monolayer transition metal dichalcogenides

Monolayer (1L) transition metal dichalcogenides (TMDs) provide a unique opportunity to control the valley degree of freedom of optically excited charge carriers due to the spin-valley locking effect. Despite extensive studies of the valley-contrasting physics, stimulated by perspective valleytronic applications, a unified picture of competing intervalley coupling processes in 1L-TMDs is lacking. Here, we apply broadband helicity-resolved transient absorption to explore exciton valley polarization dynamics in 1L-WSe${}_2$. By combining experimental results with microscopic simulations, we dissect individual intervalley coupling mechanisms and reveal the crucial role of phonon-assisted scattering in the fast decay of the A exciton circular dichroism and the formation of the dichroism of opposite polarity for the B exciton. We further provide a consistent description of the valley depolarization driven by the combined action of Coulomb scattering processes and indicate the presence of efficient single spin-flip mechanisms. Our study brings us closer to a complete understanding of exciton dynamics in TMDs.

cond-mat.mes-hall↗

arXiv2024

Ultrafast Optical Control of Rashba Interactions in a TMDC Heterostructure

We investigate spin relaxation dynamics of interlayer excitons in a MoSe2/MoS2 heterostructure induced by the Rashba effect. In such a system, Rashba interactions arise from an out-of-plane electric field due to photo-generated interlayer excitons inducing a phonon-assisted intravalley spin relaxation. We develop a theoretical description based on a microscopic approach to quantify the magnitude of Rashba interactions and test these predictions via time-resolved Kerr rotation measurements. In agreement with the calculations, we find that the Rashba-induced intravalley spin mixing becomes the dominating spin relaxation channel above T = 50 K. Our work identifies a previously unexplored spin-depolarization channel in heterostructures which can be used for ultrafast spin manipulation.

cond-mat.mes-hall↗

arXiv2023

Time-domain observation of interlayer exciton formation and thermalization in a MoSe$_2$/WSe$_2$ heterostructure

Vertical heterostructures (HS) of transition metal dichalcogenides (TMDs) host interlayer excitons (ILX), with electrons and holes residing in different layers. With respect to their intralayer counterparts, ILX feature much longer lifetimes and diffusion lengths, paving the way to excitonic optoelectronic devices operating at room temperature. While the recombination dynamics of ILX has been intensively studied, the formation process and its underlying physical mechanisms are still largely unexplored. Here we use ultrafast transient absorption spectroscopy with a white-light probe, spanning both intralayer and interlayer exciton resonances, to simultaneously capture and time-resolve interlayer charge transfer and ILX formation dynamics in a MoSe$_2$/WSe$_2$ HS. We find that the ILX formation timescale is nearly an order of magnitude (~1 ps) longer than the interlayer charge transfer time (~100 fs). Microscopic calculations attribute the relative delay to an interplay between a phonon-assisted interlayer exciton cascade and subsequent cooling processes, and excitonic wave-function overlap. Our results provide an explanation to the efficient photocurrent generation observed in optoelectronic devices based on TMD HS, as the ILX have an opportunity to dissociate during their thermalization process.

cond-mat.mtrl-sci↗