Efficient stray-light suppression for resonance fluorescence in quantum dot-micropillars using self-aligned metal apertures

Within this work we propose and demonstrate a technological approach to efficiently suppress excitation laser stray-light in resonance fluorescence experiments on quantum dot-micropillars. To ensure efficient stray-light suppression, their fabrication process includes a planarization step and the subsequent covering with a titanium mask to fabricate self-aligned apertures at the micropillar positions. These apertures aim at limiting laser straylight in side-excitation vertical-detection configuration, while enabling detection of the optical signal through the top facet of the micropillars. Beneficial effects of these apertures are proven and quantitatively evaluated within a statistical study in which we determine and compare the stray-light suppression of 48 micropillars with and without metal apertures. Actual resonance fluorescence experiments on single quantum dots coupled to the cavity mode prove the relevance of the proposed approach and demonstrate that it will foster further studies on cavity quantum electrodynamics phenomena under coherent optical excitation.PostprintPeer reviewe

The Effects of Ligand Substituents on the Character of Zn-Coordination in Zeolitic Imidazolate Frameworks

Due to their favorable properties and high porosity, zeolitic imidazolate frameworks (ZIFs) have recently received much limelight for key technologies such as energy storage, optoelectronics, sensorics, and catalysis. Despite the widespread interest in these materials, fundamental questions regarding the zinc coordination environment remain poorly understood. By focusing on zinc(II)2-methylimidazolate (ZIF-8) and its tetrahedrally coordinated analogs with Br-, Cl-, and H-substitution in the 2-ring position, we aim to clarify how variations in the local environment of Zn impact the charge distribution and the electronic properties of these materials. Our results from density-functional theory confirm the presence of a Zn coordinative bond with a large polarization that is quantitatively affected by different substituents on the organic ligand. Moreover, our findings suggest that the variations induced by the functionalization in the Zn coordination have a negligible effect on the electronic structure of the considered compounds. On the other hand, halogen terminations of the ligands lead to distinct electronic contributions in the vicinity of the frontier region which ultimately reduce the band-gap size by a few hundred meV. Experimental results obtained from X-ray absorption spectroscopy (Zn $K$-edge) confirm the trends predicted by theory and, together with them, contribute to a better understanding of the structure-property relationships that are needed to tailor ZIFs for target applications

An Amorphous Teflate Doped Aluminium Chlorofluoride: A Solid Lewis‐Superacid for the Dehydrofluorination of Fluoroalkanes

An anion-doped aluminium chlorofluoride AlCl0.1F2.8(OTeF5)0.1 (ACF-teflate) was synthesized. The material contains pentafluoroorthotellurate (teflate) groups, which mimic fluoride ions electronically, but are sterically more demanding. They are embedded into the amorphous structure. The latter was studied by PDF analysis, EXAFS data and MAS NMR spectroscopy. The mesoporous powder is a Lewis superacid, and ATR-IR spectra of adsorbed CD3CN reveal a blue-shift of the adsorption band by 73 cm−1, which is larger than the shift for SbF5. Remarkably, ACF-teflate catalyzes dehydrofluorination reactions of monofluoroalkanes to yield olefins in C6D6. In these cases, no Friedel-Crafts products were formed.German Research Foundation http://dx.doi.org/10.13039/501100001659Diamond Light Source http://dx.doi.org/10.13039/100011889German Research Foundation http://dx.doi.org/10.13039/501100001659Peer Reviewe

An Amorphous Teflate Doped Aluminium Chlorofluoride: A Solid Lewis‐Superacid for the Dehydrofluorination of Fluoroalkanes

An anion‐doped aluminium chlorofluoride AlCl0.1F2.8(OTeF5)0.1 (ACF‐teflate) was synthesized. The material contains pentafluoroorthotellurate (teflate) groups, which mimic fluoride ions electronically, but are sterically more demanding. They are embedded into the amorphous structure. The latter was studied by PDF analysis, EXAFS data and MAS NMR spectroscopy. The mesoporous powder is a Lewis superacid, and ATR‐IR spectra of adsorbed CD3CN reveal a blue‐shift of the adsorption band by 73 cm−1, which is larger than the shift for SbF5. Remarkably, ACF‐teflate catalyzes dehydrofluorination reactions of monofluoroalkanes to yield olefins in C6D6. In these cases, no Friedel‐Crafts products were formed

Exciton-polaritons in flatland : controlling flatband properties in a Lieb lattice

Funding: T.H.H., J.B., P.G., J.M., M.E., C.S., S.H., and S.K. acknowledge financial support by the German Research Foundation (DFG) under Germany’s Excellence Strategy–EXC2147 “ct.qmat” (project id 390858490). S.K., J.B., U.P., and O.A.E. acknowledge support by the German Research Foundation (DFG) within project KL2431/2-1. S.H. is furthermore grateful for support within the EPSRC Hybrid Polaritonics Grant (Grant No. EP/M025330/1). T.H.H. and S.H. acknowledge funding by the doctoral training program Elitenetzwerk Bayern Graduate School “Topological insulators.” T.H.H. acknowledges support by the German Academic Scholarship Foundation.In recent years, novel two-dimensional materials such as graphene, bismuthene, and transition-metal dichalcogenides have attracted considerable interest due to their unique physical properties. However, certain lattice geometries, such as the Lieb lattice, do not exist as atomic monolayers. Fortunately, a range of physical effects can be transferred to the realms of photonics by creating artificial photonic lattices emulating these two-dimensional materials. Here, exciton-polaritons in semiconductor microcavities offer an exciting opportunity to study a part-light, part-matter quantum fluid of light in a complex lattice potential. In this Rapid Communication, we study exciton-polaritons in a two-dimensional Lieb lattice of buried optical traps. The S and Pxy photonic orbitals of such a Lieb lattice give rise to the formation of two flatbands which are of greatest interest for the distortion-free storage of compact localized states. By using a well controlled etch-and-overgrowth technique, we manage to control the trapping as well as the site couplings with great precision. This allows us to spectroscopically monitor the flatness of the flatbands across the full Brillouin zone. Furthermore, we demonstrate experimentally that these flatbands can be directly populated by condensation under nonresonant laser excitation. Finally, using this advanced device approach we demonstrate resonant and deterministic excitation of flatband modes in transmission geometry. Our findings establish the exciton-polariton systems as a highly controllable, optical many-body system to study flatband effects and for distortion-free storage of compact localized states.Publisher PDFPeer reviewe

Coherent topological polariton laser

Funding: The Würzburg group acknowledges support from the DFG through the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter “ct.qmat” (EXC 2147, project‐id 39085490) and the doctoral training program “Elitenetzwerk Bayern". S.H. acknowledges support by the EPSRC ”Hybrid Polaritonics” Grant (EP/M025330/1). M.S., I.V. and I.G.S acknowledge the support by the Institute for Basic Science in Korea (Project No.~IBS-R024-D1). T.H. acknowledges support by the German Academic Scholarship Foundation.Topological concepts have been applied to a wide range of fields in order to successfully describe the emergence of robust edge modes that are unaffected by scattering or disorder. In photonics, indications of lasing from topologically protected modes with improved overall laser characteristics were observed. Here, we study exciton-polariton microcavity traps that are arranged in a one-dimensional Su-Schrieffer-Heeger lattice and form a topological defect mode from which we unequivocally observe highly coherent polariton lasing. Additionally, we confirm the excitonic contribution to the polariton lasing by applying an external magnetic field. These systematic experimental findings of robust lasing and high temporal coherence are meticulously reproduced by a combination of a generalized Gross-Pitaevskii model and a Lindblad master equation model. Thus, by using the comparatively simple SSH geometry, we are able to describe and control the exciton-polariton topological lasing, allowing for a deeper understanding of topological effects on microlasers.PostprintPeer reviewe