Ullrich Scherf

In Bose-Einstein condensates, spin-orbit coupling (SOC) produces supersolidity. It is a peculiar state of matter, which, in addition to the superfluid behavior, shows periodic density modulation typical for crystals. Here, we report the fabrication of an original type of optical microcavity, allowing the achievement of room-temperature supersolidity for a quantum fluid of light. The microcavity is filled with a nematic liquid crystal (LC) and two layers of the organic polymer methyl-substituted ladder-type poly( p -phenylene) (MeLPPP) hosting exciton resonances. We demonstrate exciton-polariton condensation in the two distinct degenerate minima of the dispersion created by the LC-induced Rashba-Dresselhaus SOC. The condensate real-space distribution shows density stripes located randomly from one condensate realization to another despite the presence of a random disorder potential. This demonstrates the immunity of stripes against disorder and the spontaneous breaking of translational invariance. We also report the random appearance of vortices, another feature of superfluids.

We report on the experimental observation of stimulated cooling in the non-equilibrium Bose--Einstein condensate (BEC) of weakly interacting exciton-polaritons from approximately room temperature down to 20K. Our results indicate that the temperature of the weakly interacting Bose gas is universally set by the density-dependent chemical potential, revealing a defining property of non-equilibrium BECs. We demonstrate that the stimulated nature of the cooling process directly governs the emergence of quantum coherence of the condensate and shapes the dissipative properties of the excited states.

A methyl‐substituted ladder meta ‐phenylene macrocycle ( MeLMMP ) and its corresponding ladder polymer ( MeLPMP ), a meta ‐analogue of the well‐known ladder‐type poly( para ‐phenylene), LPPP , were synthesized and comprehensively investigated. Both compounds exhibit limited conjugation due to the meta ‐linked phenylene units, resulting in absorption and emission features shaped by cross‐conjugation. Despite having a longer chain, MeLPMP and MeLMMP exhibit nearly identical electronic and photophysical behavior, suggesting that the number of repeat units has minimal influence. MeLPMP exhibits enhanced vibronic resolution compared to MeLMMP due to a broadening of the optical bands of the macrocycle caused by the presence of a mixture of stereoisomers formed during the non‐stereoselective ladderization step. A small amount of fluorenone‐type keto defects produces a weak emission near 500 nm, more evident in the macrocycle, and introduces radiationless decay pathways that compete with fluorescence. This decay pathway, together with the weak π,π* conjugation in these angular compounds, lowers the fluorescence quantum yield when compared with the linear MeLPPP , while promoting singlet–triplet conversion and phosphorescence. The data indicate the presence of three chromophoric populations: pristine oligo( meta ‐phenylene) units; units quenched by nearby keto defects; and intramolecular charge‐transfer complexes (ICTCs) formed between oligo( meta ‐phenylene) units and keto defects. These findings clarify the photophysics of meta ‐phenylene ladder systems, showing that the MeLMMP macrocycle can act as a structural and electronic model for related ladder polymers.

All-optical logic has the potential to overcome the operation speed barrier that has persisted in electronic circuits for two decades. However, the development of scalable architectures has been prevented so far by the lack of materials with sufficiently strong nonlinear interactions needed to realize compact and efficient ultrafast all-optical switches with optical gain. Microcavities with embedded organic material in the strong light-matter interaction regime have recently enabled all-optical transistors operating at room temperature with picosecond switching times. However, the vertical cavity geometry, which is predominantly used in polaritonics, is not suitable for complex circuits with on-chip coupled transistors. Here, by leveraging state-of-the-art silicon photonics technology, we have achieved exciton-polariton condensation at ambient conditions in fully integrated high-index contrast sub-wavelength grating microcavities filled with a π-conjugated polymer as optically active material. We demonstrate ultrafast all-optical transistor action by coupling two resonators and utilizing seeded polariton condensation. With a device area as small as 2 × 2 µm ² , we realize picosecond switching and amplification up to 60x, with extinction ratio up to 8:1. This compact ultrafast transistor device with in-plane integration is a key component for a scalable platform for all-optical logic circuits that could operate two orders of magnitude faster than electronic counterparts.

Polymers of higher rylene dyes remain largely unexplored despite their promising photophysical properties, due to the synthetic challenges and poor solubility, in contrast to their well-studied lower homologs, perylene and naphthalene derivatives. In this study, we report the first synthesis of terrylene-based regioregular and regioirregular homopolymers, namely rr-Polyterrylene and ri-Polyterrylene, respectively. Selective bromination of our previously synthesized 7,8-bis(hexadecyloxy)terrylene (TER-C16) furnished the corresponding dibromoterrylene. Then, Ni(0)-mediated Yamamoto homocoupling reaction produced the first soluble terrylene-based homopolymers. Both polymers achieved high solubility, high thermal stability, alongside very high molecular weight. Owing to these properties, the polymers were successfully deployed in organic field-effect transistors (OFETs), achieving p-type mobility 27 times higher than the monomeric unit TER-C16. Moreover, the photoresponsive OFETs from rr-Polyterrylene demonstrated 116-times improved photodetection ability compared to TER-C16 with specific detectivity (D*) of 4.3 × 10¹⁰ Jones in the deep red region, which is the highest among terrylenes and their derivatives. This work introduced the synthesis of dibromoterrylene, a versatile synthetic intermediate with significant potential for constructing diverse polymers. The strategic functionalization of terrylene molecules revealed a novel synthetic approach, enabling innovative polymer construction and facilitating significant advances in organic electronics, specifically OFETs and organic phototransistors (OPTs).

A central challenge for advancing polariton‐based circuits is the controlled and scalable coupling of individual condensates. Existing approaches based on etched or epitaxially grown microcavities are fabrication‐intensive and restrict in‐plane coupling. To overcome these limitations, we introduce a lithographically defined silicon‐based platform of high‐contrast grating (HCG) microcavities with a ladder‐type π‐conjugated polymer. In this system, doublet cavities exhibit mode hybridization into bonding and antibonding states, where coupling is mediated across shared HCG mirrors. Extending the design to arrays, N ‐coupled condensates exhibit systematic red‐shifts of the condensate energy, due to delocalization, and a progressive threshold reduction, consistent with extended binding modes. Our experimental results are quantitatively supported by transition‐matrix multi‐scattering simulations, together with tight‐binding modelling. First‐order coherence measurements using Michelson interferometry confirm the existence of spatially extended condensates with exponentially decaying temporal coherence. Altogether, these results establish a scalable route toward integrated polariton devices and quantum photonic networks.

Exciton-polariton microcavity arrays have emerged as a promising semiconductor-based platform for analog simulations of model Hamiltonians and topological effects. To study a variety of Hamiltonians and investigate their properties, it is essential to have highly configurable and easily engineerable structures with low disorder. Here, we demonstrate in situ tunable, room-temperature polariton condensation in individual states of a Su-Schrieffer-Heeger topological lattice by using an open-cavity configuration with an organic polymer layer. Changing the cavity length in combination with vibron-mediated relaxation in the polymer allows us to achieve selective polariton condensation into different states of the band structure, unveiled by nonlinear emission, linewidth narrowing, energy blue shift, and extended macroscopic coherence. Furthermore, we engineer the bandgap and the edge state localization by adjusting the interaction between adjacent lattice sites. Our results demonstrate the versatility and accuracy of the platform for the investigation of quantum fluids in complex potential landscapes and topological effects at room temperature.

Since its first synthesis by Clar in 1948, terrylene has garnered significant research interest due to its extended π-conjugated system and exceptional optoelectronic properties. Its peri-substituted diimide derivatives, i.e. terrylenediimides (TDIs), have demonstrated extensive applications in organic field-effect transistors (OFETs), bulk heterojunction (BHJ) organic solar cells, and bioimaging. Despite this potential, the widespread adoption of terrylene-based materials remains limited due to their innate synthetic challenges and poor solubility. To address these challenges, herein, we report a novel, cost-effective route to synthesize bay-substituted terrylenes via a Grignard–Kumada cross-coupling reaction sequence followed by a dehydrohalogenation step. The incorporation of three different alkyloxy chains (–OC₈H₁₇, –OC₁₂H₂₅, and –OC₁₆H₃₃) at the bay positions significantly enhances their solubility in common organic solvents. The enhanced solubility enabled the fabrication of solution-processed terrylene-based OFET and organic phototransistor (OPT) devices for the first time, allowing systematic investigation of the effect of alkyloxy chain lengths on the hole mobility and photodetection performance. The fabricated OFETs exhibited p-type semiconducting behavior, with the shortest alkyl chain (–OC₈H₁₇) containing TER-C8 achieving the highest hole mobility compared to the other two analogs (83 times higher mobility than the –OC₁₆H₃₃ containing TER-C16). These terrylene-based devices exhibited exceptional photoresponse characteristics, achieving high-performance metrics including an external quantum efficiency (EQE) and specific detectivity (D*), reaching over 10¹⁰ Jones. Therefore, our works introduced a novel and low-cost synthesis route for highly soluble terrylenes and their first successful implementation in organic field-effect transistors and organic phototransistor devices.