arXiv subjects

Sebastian Klembt

Publications and source records attributed to Sebastian Klembt.

At least 19 recordsLinked to original sources

arXiv2026

Encapsulated macroscopic WS$_2$ monolayers enable room-temperature exciton-polariton lattices

Large-area, optically homogeneous monolayer semiconductors are a critical prerequisite for scalable room-temperature polaritonics and for realizing polariton lattices extending across many unit cells. Yet, the small size, optical inhomogeneity, and device-to-device variability of conventional exfoliated flakes have remained major obstacles. Here, we overcome these limitations using 1-dodecanol-encapsulated WS$_2$ monolayers that combine millimeter-scale coverage with remarkably uniform optical properties over lateral distances approaching $300\,$$\mu \mathrm{m}$. Integrated into a tunable open microcavity, these monolayers exhibit robust room-temperature exciton-photon strong coupling, evidenced by a pronounced anti-crossing and a Rabi splitting of $\hbar \Omega_{\mathrm{R}} \approx 31\,\mathrm{meV}$. Leveraging the exceptional uniformity of this platform, we realize a two-dimensional polaritonic kagome lattice and directly resolve its characteristic band structure. Angle-resolved spectroscopy reveals Dirac dispersive bands together with a weakly dispersive flat-band-like branch within the $s$-band, in good agreement with a linear non-interacting model. Complementary momentum- and real-space imaging further identifies the associated bond-centered and site-centered mode profiles. These results establish large-area WS$_2$ monolayers in open microcavities as a scalable platform for engineering polariton band structures and exploring synthetic quantum materials under ambient conditions.

cond-mat.mes-hall↗

arXiv2026

Lattice quantum electrodynamics of a molecular emitter in a topological gap

Engineering the photonic environment using lattices of coupled resonators, which we refer to as lattice quantum electrodynamics (QED), provides a route to control both the spontaneous emission of individual quantum emitters and the photon-mediated interactions between them. Here we introduce an optical lattice QED platform based on individual dibenzoterrylene (DBT) molecules embedded in anthracene crystals and coupled to lattices of open optical microcavities. This hybrid architecture benefits from narrow-linewidth molecular emitters, site-resolved optical access, engineered coupled-resonator bands, and compatibility with established molecular frequency-tuning techniques. As a proof-of-principle demonstration, we observe emitter-photon bound states formed when the optical transition of a single molecule is tuned to the band gap of a Su-Schrieffer-Heeger (SSH) cavity lattice. These in-gap states display directional localization and photon emission on a single sublattice, inherited from the vacancy-induced topological edge modes of the underlying SSH lattice. Our results establish open-cavity lattices coupled to DBT molecules as a versatile architecture for engineering many-emitter quantum optical systems with controllable photon-mediated interactions.

quant-ph↗

arXiv2026

Wide-angle emission in cylindrical moir\'e lattices enabled by rolling origami

Twisted photonic lattices that form moir\'e superlattices have attracted significant attention owing to their unique properties, such as strong field confinement and high-quality factors, in which the localized optical modes can serve as efficient light sources. However, in conventional moir\'e lattices, the emission direction of confined modes is typically fixed, and achieving a broad range of emission angles through simple modulation remains a significant challenge. Here, we design and fabricate single-layer moir\'e photonic lattices into cylindrical geometries using a nanomembrane origami technique. This approach enables wide-angle localized-mode emission while maintaining stable single-mode operation and excellent spectral uniformity. The moir\'e supercells support localized flat-band modes under various effective twist angles, resulting in the observation of periodic localized-mode emission over a wide range of azimuthal angles. Our research provides an approach for developing moir\'e light sources on curved surfaces, offering significant potential in applications that demand spatial light control, including three dimensional imaging, light detection and ranging, and topological states manipulation.

physics.optics↗

arXiv2025

Probing Local Topology in a Disordered Higher-Order Topological Insulator

Higher-order topology is prized for its ability to realize lower-dimensional boundary states which are stable beyond fine-tuning. However, disorder presents a failure mechanism that can destroy topological in-gap states. Here, we investigate a disordered two-dimensional polariton lattice and employ the spectral localizer framework to define a real-space topological index rooted in crystalline spatial symmetries. This framework enables direct real-space mapping of topology beyond conventional momentum-space classifications, confirming the presence of corner and edge modes in this generalized Su-Schrieffer-Heeger model. Furthermore, it can directly quantify topological protection of a state. We leverage the versatility of our platform to experimentally realize normally distributed, random disorder and find that the corner states persist until the spectral gap closes. Experimentally, this corresponds to a disorder strength of approximately one quarter of the spectral gap. The spectral localizer accurately identifies the disorder strength at which the bandgap closes, establishing the framework as a predictive tool for every finite size system. Our results broaden the design principles for higher-order topological insulators and open the way towards imple menting disorder-resilient devices for robust lasing, light-routing, and quantum computation.

physics.optics↗

arXiv2025

Direct experimental access to the bulk band inversion in a topological metamaterial

Topological phases in exciton-polaritons and other metamaterial platforms have attracted significant attention due to their flexibility as Hamiltonian simulators. In previous works, signatures of topology have mainly been investigated from the perspective of edge states - strongly localised modes with exponentially decaying intensity into the bulk. While these edge states have become the hallmark of topological systems as they can facilitate non-reciprocal transport in potential applications, the topology is fundamentally encoded in the bulk band structure. In particular, the momentum-dependence of the eigenstates, i.e., the wave functions, determines the topology, usually reflected in a bulk band inversion. We present a band inversion in the paradigmatic Su-Schrieffer-Heeger (SSH) model, characterised by a reversal of the sublattice symmetry, quantified by the expectation value $\langle \sigma_\mathrm{x} \rangle$, when going from the centre of the Brillouin zone to the zone boundary. Here, we show direct experimental access to this bulk band inversion in SSH exciton-polariton chains, using two-dimensional momentum-space ($k$-space) mapping - without the need for real-space imaging. This technique enables the direct observation of the momentum-dependent inversion of the sublattice symmetry in the bulk bands, providing a unique perspective on topological phases beyond conventional edge state measurements. Our approach establishes effective momentum-resolved sublattice phase measurements as a powerful tool for accessing the wave function and bulk topology in photonic and polaritonic systems and beyond.

physics.optics↗

arXiv2025

Electrical Control of Excitons in Bare-MoSe2 and MoSe2/NbSe2 Heterostructure

Monolayer transition metal dichalcogenides (TMDCs) are promising materials for next-generation optoelectronic devices, owing to their strong excitonic responses and atomic thickness. Controlling their light emission electrically is a crucial step towards realizing practical nanoscale optoelectronic devices such as light-emitting diodes and optical modulators. However, photoluminescence (PL) quenching in van der Waals TMDC/metal heterostructures, caused by ultrafast interlayer charge or energy transfer, impedes such electrical modulation. Here, we investigate monolayer-MoSe2/bulk-NbSe2 heterostructures and demonstrate that a vertical electric field can effectively recover the PL intensity up to ~ 80% of bare-MoSe2. Furthermore, our analysis reveals that the room temperature PL intensity can be tuned by nearly three orders of magnitude in bare-MoSe2 and by about one order of magnitude in MoSe2/NbSe2 heterostructures. First-principles calculations incorporating spin-orbit coupling reveal that the perpendicular electric fields drive a transition from a direct to an indirect bandgap, fundamentally altering the optical response in the heterostructure. Unlike bare-MoSe2, the heterostructure exhibits a pronounced thermal dependence of the enhancement factor, implying that exciton lifetime dominates over interfacial transfer processes. Our findings demonstrate reversible, electric-field-driven PL control at a TMDC/metal interface, providing a pathway to electrically tunable light emission and improved contact engineering in two-dimensional optoelectronic devices.

physics.app-ph↗

arXiv2025

Observation of Kardar-Parisi-Zhang universal scaling in two dimensions

Equilibrium and nonequilibrium states of matter can exhibit fundamentally different behavior. A key example is the Kardar-Parisi-Zhang universality class in two spatial dimensions (2D KPZ), where microscopic deviations from equilibrium give rise to macroscopic scaling laws without equilibrium counterparts. While extensively studied theoretically, direct experimental evidence of 2D KPZ scaling has remained limited to interface growth so far. Here, we report the observation of universal scaling consistent with the KPZ universality class in 2D exciton-polariton condensates -- quantum fluids of light that are inherently driven and dissipative, thus breaking equilibrium conditions. Using momentum-resolved photoluminescence spectroscopy as well as space- and time-resolved interferometry, we probe the phase correlations across microscopically different systems, varying drive conditions in two distinct lattice geometries. Our analysis reveals correlation dynamics and scaling exponents in excellent agreement with 2D KPZ predictions. These results establish exciton-polariton condensates as a robust experimental platform for exploring 2D nonequilibrium universality quantitatively, and open new avenues for investigating the emergence of coherence in interacting quantum systems far from equilibrium.

quant-ph↗

arXiv2025

Artificial Gauge Fields and Dimensions in a Polariton Hofstadter Ladder

Artificial gauge fields allow uncharged particles to mimic the behavior of charged particles subjected to magnetic fields, providing a powerful platform for exploring topological physics. Neutral particles, like photons, are typically unaffected by real magnetic fields. However, it is possible to introduce artificial gauge fields that control the effective dynamics of these neutral particles. Topological exciton-polariton lasers have attracted considerable interest, in part due to the wide range of tunable system parameters, but often require strong magnetic fields to realise propagating topological edge states. Here we show, that by using an artificial gauge field the topological Hall effect in a micron-scale micropillar chain is experimentally realised, exploiting the circular polarisation of polaritons as an artificial dimension. By careful rotational alignment of elliptical micropillars, we introduce an effective plaquette phase that induces strictly polarisation-dependent edge-state propagation, demonstrating non-reciprocal transport of the polariton pseudospins. Our results demonstrate that the dimensionality limitation of topological interface states as well as requirements for strong external magnetic fields in coupled topological laser arrays can be overcome by utilizing polarisation effects and careful engineering of the potential landscape. Our results open new ways towards the implementation of topological polariton lattices and related optically active devices with additional artificial dimension.

physics.optics↗

arXiv2025

Hybrid confinement techniques for polariton simulators

Exciton-polariton III-V semiconductor microcavities provide a robust platform for emulating complex Hamiltonians, enabling topological photonics and quantum simulation for advanced photonic functionalities. Here, we introduce two novel fabrication techniques - etch-and-oversputter and deposit-and-oversputter - that overcome limitations of traditional photonic confinement. Both use structured, locally elongated semiconductor cavities to create deep, highly controllable potentials, while leveraging high-quality GaAs-based materials, which achieve excellent Q-factors. A sputtered all-dielectric top mirror introduces an innovative hybrid approach, simplifying fabrication while maintaining quality compared to deep ion etching. Utilizing a Kagome lattice as a benchmark, we show high-quality optical band structures previously inaccessible with deep etching. Furthermore, we study a two-dimensional breathing Kagome lattice and demonstrate polariton lasing from a zero-dimensional corner mode, confirming precise control over couplings and tight polariton localization. These methods enable fabrication of intricate lattices, including higher-order topological insulators, or on-chip quantum regimes utilizing the polariton blockade mechanism due to tight photonic confinement.

physics.optics↗

arXiv2024

Enwrapped Perylene Bisimide Enables Room Temperature Polariton Lasing and Photonic Lattices

Perylene bisimides (PBIs) are organic dyes with photoluminescence quantum yields (PLQY) close to unity in solution and great thermal and photo-chemical stability. These features alongside the tunability of their solid-state packing arrangement via chemical functionalization make this material class an excellent candidate for exciton-polariton lasing at room temperature. Polariton lasing is well understood in III-V semiconductors at cryogenic temperatures, however, the search for emitter materials for robust and versatile room temperature applications is ongoing. While e.g. perovskites and several organic materials have been identified to support polariton lasing, many of these materials lack tunability and long-term stability under ambient conditions. Here, we fabricate optical microcavities using a strongly enwrapped PBI chromophore with prevailing monomer-like absorption and emission properties in the solid state. Voluminous bay-substituents prevent stacking induced PLQY-quenching, thereby enabling polariton lasing at room temperature. Additionally, photonic confinement in single hemispheric resonators is demonstrated leading to localized polaritonic modes with discrete energies, as well as optical lattices revealing distinct polaritonic band-structures. Due to the possibility of tunable properties by the precise control of the solid-state packing arrangement of PBI emitters, our results pave the way for polarization-dependent light-matter coupling, including topological photonic effects within oriented crystalline thin-film microcavity structures.

physics.optics↗

arXiv2024

Exciton diffusion in two-dimensional chiral perovskites

Two-dimensional (2D) organic-inorganic hybrid perovskites emerged as a versatile platform for light-emitting and photovol-taic applications due to their unique structural design and chemical flexibility. Their properties depend heavily on both the choice of the inorganic lead halide framework and the surrounding organic layers. Recently, the introduction of chiral cations into 2D perovskites has attracted major interest due to their potential for introducing chirality and tuning the chiro-optical response. Importantly, the optical properties in these materials are dominated by tightly bound excitons that also serve as primary carriers for the energy transport. The mobility of photoinjected excitons is thus important from the perspectives of fundamental material properties and optoelectronic applications, yet remains an open question. Here, we demonstrate exciton propagation in a 2D chiral perovskite methylbenzylammonium lead iodide (MBA2PbI4) using transient photoluminescence microscopy and reveal density-dependent transport over more than 100 nanometers at room temperature with diffusion coeffi-cients as high as 2 cm2/s. We observe two distinct regimes of initially rapid diffusive propagation and subsequent localiza-tion. Moreover, perovskites with enantiomer pure cations are found to exhibit faster exciton diffusion compared to the race-mic mixture, correlated with the impact of the material composition on disorder. Altogether, the observations of efficient exciton diffusion at room temperature highlight the potential of 2D chiral perovskites to merge chiro-optical properties with strong light-matter interaction and efficient energy transport.

cond-mat.mtrl-sci↗

arXiv2024

Anomalous dispersion via dissipative coupling in a quantum well exciton-polariton microcavity

Although energy level repulsion is typically observed in interacting quantum systems, non-Hermitian physics predicts the effect of level attraction, which occurs when significant energy dissipation is present. Here, we show a manifestation of dissipative coupling in a high-quality AlGaAs-based polariton microcavity, where two polariton branches attract, resulting in an anomalous, inverted dispersion of the lower branch in momentum dispersion. Using angle-resolved photoluminescence measurements we observe the evolution of the level attraction with exciton-photon detuning, leading to changes in anomalous dispersion shape within a single sample. The dissipative coupling is explained by the interaction with an indirect exciton, acting as a highly dissipative channel in our system, and the observed dispersions are well captured within a phenomenological model. Our results present a new mechanism of dissipative coupling in light-matter systems and offer a tunable and well-controlled AlGaAs-based platform for engineering the non-Hermitian and negative mass effects in polariton systems.

cond-mat.mes-hall↗

arXiv2024

Optical properties and dynamics of direct and spatially and momentum indirect excitons in AlGaAs/AlAs quantum wells

We present an experimental study on optical properties and dynamics of direct and spatially and momentum indirect excitons in AlGaAs/AlAs quantum wells near the crossover between $\varGamma-$ and $X$-valley confined electron states. The time-integrated photoluminescence experiment at $T=$4.8 K revealed three simultaneously observed optical transitions resulting from (a) a direct exciton recombination, involving an electron and a hole states both located in the $\varGamma$-valley in the quantum well layer, and (b) two spatially and momentum indirect excitons, comprising of the confined electron states in the $X$-valley in the AlAs barrier with different effective masses and quantum well holes in the $\varGamma$-valley. This interpretation has been based on the optical pumping density-dependent, temperature-dependent and spatially-resolved photoluminescence measurements, which provided the characterization of the structure, crucial in potential system's applications. Additionally, the time-resolved photoluminescence experiments unveiled complex carrier relaxation dynamics in the investigated quantum well system, which is strongly governed by a non-radiative carrier recombination - the characteristics further critical in potential system's use. This solid state platform hosting both direct and indirect excitons in a highly tunable monolithic system can benefit and underline the operation principles of novel electronic and photonic devices.

cond-mat.mes-hall↗

arXiv2024

Dynamic Phase Enabled Topological Mode Steering in Composite Su-Schrieffer-Heeger Waveguide Arrays

Topological boundary states localize at interfaces whenever the interface implies a change of the associated topological invariant encoded in the geometric phase. The generically present dynamic phase, however, which is energy and time dependent, has been known to be non-universal, and hence not to intertwine with any topological geometric phase. Using the example of topological zero modes in composite Su-Schrieffer-Heeger (c-SSH) waveguide arrays with a central defect, we report on the selective excitation and transition of topological boundary mode based on dynamic phase-steered interferences. Our work thus provides a new knob for the control and manipulation of topological states in composite photonic devices, indicating promising applications where topological modes and their bandwidth can be jointly controlled by the dynamic phase, geometric phase, and wavelength in on-chip topological devices.

physics.optics↗

arXiv2024

Topological Optical Waveguiding of Exciton-Polariton Condensates

One-dimensional models with topological non-trivial band structures are a simple and effective way to study novel and exciting concepts in topological photonics. In this work we are studying the propagation of light-matter quasi-particles, so called exciton-polaritons, in waveguide arrays. Specifically, we are investigating topological states at the interface between dimer chains, characterized by a non-zero winding number. In order to exercise precise control over the polariton propagation, we study non-resonant laser excitation as well as resonant excitation in transmission geometry. The results highlight a new platform for the study of quantum fluids of light and non-linear optical propagation effects in coupled semiconductor waveguides.

physics.optics↗

arXiv2024

An electrically pumped topological polariton laser

With a seminal work of Raghu and Haldane in 2008, concepts of topology have been successfully introduced in a wide range of optical systems, emulating specific lattice Hamiltonians. Certainly, one of the most promising routes to an application of topological photonics in an actual device are topological lasers, where efficient and highly coherent lasing from a topologically non-trivial mode is achieved. While some attempts have been made to excite such structures electrically, the majority of published fundamental experiments use a form of laser excitation. In this paper, we use a lattice of vertical resonator polariton micropillars to form an exponentially localized topological Su-Schrieffer-Heeger defect. Upon electrical excitation of the p-i-n doped structure, the system unequivocally shows polariton lasing from the topological defect using a carefully placed gold contact. Despite the presence of doping and electrical contacts, the polariton band structure clearly preserves its topological properties. At high excitation power the Mott density is exceeded leading to highly efficient lasing in the weak coupling regime. This work is an important step towards applied topological lasers using vertical resonator microcavity structures.

physics.optics↗

arXiv2024

Coupling Dynamics and Linear Polarization Phenomena in Codirectional Polariton Waveguide Couplers

In this work, we explore the potential of spin-based integrated devices using polariton waveguides that form codirectional couplers. For suitable coupler parameters, a transfer of condensates between the arms of the coupler, occurs leading to the observation of Josephson-like oscillations. The ability to tune the periodicity of these oscillations opens the way to the design of polaritonic circuits in which the directionality of the signal towards the output terminals can be controlled. We also investigate the response of the devices to linearly polarized excitation, delving into the dynamics of linear polarization at the output terminals of long couplers, providing valuable insights into the potential applications of spin-based polariton devices, including polariton switches and logic gates with efficient operation. Our results are supported by numerical simulations based on generalized Gross-Pitaevskii equation describing the dynamics of coherent polaritons in spatially non-uniform system. We show, how the coupling and the controllable spin degree of freedom in polariton couplers opens avenues for innovative optical architectures and functionalities.

cond-mat.mes-hall↗

arXiv2024

Dirac Cones and Room Temperature Polariton Lasing Evidenced in an Organic Honeycomb Lattice

Artificial one- and two-dimensional lattices have emerged as a powerful platform for the emulation of lattice Hamiltonians, the fundamental study of collective many-body effects, and phenomena arising from non-trivial topology. Exciton-polaritons, bosonic part-light and part-matter quasiparticles, combine pronounced nonlinearities with the possibility of on-chip implementation. In this context, organic semiconductors embedded in microcavities have proven to be versatile candidates to study nonlinear many-body physics and bosonic condensation, and in contrast to most inorganic systems, they allow the use at ambient conditions since they host ultra-stable Frenkel excitons. We implement a well-controlled, high-quality optical lattice that accommodates light-matter quasiparticles. The realized polariton graphene presents with excellent cavity quality factors, showing distinct signatures of Dirac cone and flatband dispersions as well as polariton lasing at room temperature. This is realized by filling coupled dielectric microcavities with the fluorescent protein mCherry. We demonstrate the emergence of a coherent polariton condensate at ambient conditions, taking advantage of coupling conditions as precise and controllable as in state-of-the-art inorganic semiconductor-based systems, without the limitations of e.g. lattice matching in epitaxial growth. This progress allows straightforward extension to more complex systems, such as the study of topological phenomena in two-dimensional lattices including topological lasers and non-Hermitian optics.

physics.optics↗