arXiv subjects

Amir Kleiner

Publications and source records attributed to Amir Kleiner.

4 recordsLinked to original sources

arXiv2025

Photoemission tomography of excitons in 2D systems: momentum-space signatures of correlated electron-hole wave functions

The momentum-space signatures of excitons can be experimentally accessed through time-resolved (pump-probe) photoelectron spectroscopy. In this work, we develop a computational framework for exciton photoemission orbital tomography (exPOT) in periodic systems, enabling the simulation and interpretation of experimental observables within many-body perturbation theory. By connecting the GW +Bethe-Salpeter equation (BSE) approach to photoemission tomography, our formalism captures exciton photoemission in periodic systems, explicitly incorporating photoemission matrix element effects induced by the light-matter interaction via the probe pulse. The correlated nature of electrons and holes introduces distinct consequences for excitonic photoemission. Using the prototypical two-dimensional material hexagonal boron nitride, we demonstrate these effects, including a dependence of the photoemission angular distribution on the pump pulse polarization. Moreover, our framework extends to excitons with finite center-of-mass momentum, making it well-suited to studying momentum-dark excitons. This provides valuable insights into the microscopic nature of excitonic phenomena in quantum materials.

cond-mat.mtrl-sci↗

arXiv2025

Strain-induced exciton mobility in layered WS2 from first principles

Exciton mobility in two-dimensional semiconductors is a key ingredient in materials-based design of optoelectronic functionalities. Monolayer transition metal dichalcogenides (TMDs) set a good test case, with tightly bound excitons and designable flexibility that offer an ideal platform for realizing strain effects on exciton energy transfer. Here, we present an ab initio study to construct strain-induced exciton energy profiles and model exciton dynamics on top of these potential surfaces. We focus on inhomogeneously-strained monolayer WS$_2$, combining excitonic band structures derived from many-body perturbation theory for a large variety of strain profiles and calculate the change in mobility characteristics using a semiclassical ballistic transport model. We connect a wealth of strain patterns to exciton drift, diffusion, and confinement. Our results point to strain-induced regimes of super-ballistic propagation and an anomalous effective diffusion, governed entirely by the strain landscape. Our results provide structure-specific understanding of ballistic strain-tunable exciton behavior, offering design principles for engineering exciton dynamics in two-dimensional materials.

cond-mat.mtrl-sci↗

arXiv2024

Designable exciton mixing through layer alignment in WS$_2$-graphene heterostructures

Optical properties of heterostructures composed of layered 2D materials, such as transition metal dichalcogenides (TMDs) and graphene, are broadly explored. Of particular interest are light-induced energy transfer mechanisms in these materials and their structural roots. Here, we use state-of-the-art first-principles calculations to study the excitonic composition and the absorption properties of WS$_2$-graphene heterostructures as a function of interlayer alignment and the local strain resulting from it. We find that Brillouin zone mismatch and the associated energy level alignment between the graphene Dirac cone and the TMD bands dictate an interplay between interlayer and intralayer excitons, mixing together in the many-body representation upon the strain-induced symmetry breaking in the interacting layers. Examining the representative cases of the 0$^\circ$ and 30$^\circ$ interlayer twist angles, we find that this exciton mixing strongly varies as a function of the relative alignment. We quantify the effect of these structural modifications on exciton charge separation between the layers and the associated graphene-induced homogeneous broadening of the absorption resonances. Our findings provide guidelines for controllable optical excitations upon interface design and shed light on the importance of many-body effects in the understanding of optical phenomena in complex heterostructures.

cond-mat.mtrl-sci↗

arXiv2023

Reduced absorption due to defect-localized interlayer excitons in transition metal dichalcogenide-graphene heterostructures

Associating the presence of atomic vacancies to excited-state transport phenomena in two dimensional semiconductors is of emerging interest, and demands detailed understanding of the involved exciton transitions. Here we study the effect of such defects on the electronic and optical properties of WS$_2$-graphene and MoS$_2$-graphene van der Waals heterobilayers by employing many-body perturbation theory. We find that the combination of chalcogen defects and graphene adsorption onto the transition metal dichalcogenide layer can radically alter the optical properties of the heterobilayer, due to a combination of dielectric screening, the impact of the missing chalcogen atoms in the intralayer and interlayer optical transitions, and the different nature of each layer. By analyzing the intrinsic radiative rates of the most stable subgap excitonic features, we find that while the presence of defects introduces low-lying optical transitions, resulting in excitons with larger oscillator strength, it also decreases the optical response associated to the pristine-like transition-metal dichalcogenide intralayer excitons. Our findings relate excitonic features with interface design for defect engineering in photovoltaic and transport applications.

cond-mat.mes-hall↗