Thermal decoherence of a nonequilibrium polariton fluid

Exciton-polaritons constitute a unique realization of a quantum fluid interacting with its environment. Using Selenide based microcavities, we exploit this feature to warm up a polariton condensate in a controlled way and monitor its spatial coherence. We determine directly the amount of heat picked up by the condensate by measuring the phonon-polariton scattering rate and comparing it with the loss rate. We find that upon increasing the heating rate, the spatial coherence length decreases markedly, while localized phase structures vanish, in good agreement with a stochastic mean field theory. From the thermodynamical point-of-view, this regime is unique as it involves a nonequilibrium quantum fluid with no well-defined temperature, but which is nevertheless able to pick up heat with dramatic effects on the order parameter.Comment: 6 pages, 4 figure

Polariton lasing in high-quality Selenide-based micropillars in the strong coupling regime

We have designed and fabricated all-epitaxial ZnSe-based optical micropillars exhibiting the strong coupling regime between the excitonic transition and the confined optical cavity modes. At cryogenic temperatures, under non-resonant pulsed optical excitation, we demonstrate single transverse mode polariton lasing operation in the micropillars. Owing to the high quality factors of these microstructures, the lasing threshold remains low even in micropillars of the smallest diameter. We show that this feature can be traced back to a sidewall roughness grain size below 3 nm, and to suppressed in-plane polariton escape.Comment: 5 pages, 3 figure

Exciton-polaritons gas as a nonequilibrium coolant

Using angle-resolved Raman spectroscopy, we show that a resonantly excited ground-state exciton-polariton fluid behaves like a nonequilibrium coolant for its host solid-state semiconductor microcavity. With this optical technique, we obtain a detailed measurement of the thermal fluxes generated by the pumped polaritons. We thus find a maximum cooling power for a cryostat temperature of $50$K and below where optical cooling is usually suppressed, and we identify the participation of an ultrafast cooling mechanism. We also show that the nonequilibrium character of polaritons constitutes an unexpected resource: each scattering event can remove more heat from the solid than would be normally allowed using a thermal fluid with normal internal equilibration.Comment: 5 pages, 3 figures + supplemental materia

Analytik von und mit ionischen Flüssigkeiten

Es wurde die Anwendbarkeit analytischer Methoden für die Charakterisierung ionischer Flüssigkeiten untersucht. Mittels massenspektrometrischer Messungen konnten Abhängigkeiten der Clusterbildung verdünnter ionischer Flüssigkeiten von verschiedenen Parametern festgestellt werden. Cyclovoltammetrische Untersuchungen am Zweiphasensystem lieferten Aussagen zur Polarität ionischer Flüssigkeiten und der Clusterbildung in verdünnter Lösung. Ebenfalls aus massenspektrometrischen Untersuchungen konnten Aussagen über das Vorliegen ionischer Flüssigkeiten in der Gasphase getroffen werden

Band gap bowing of binary alloys: Experimental results compared to theoretical tight-binding supercell calculations for CdZnSe

Compound semiconductor alloys of the type ABC find widespread applications as their electronic bulk band gap varies continuously with x, and therefore a tayloring of the energy gap is possible by variation of the concentration. We model the electronic properties of such semiconductor alloys by a multiband tight-binding model on a finite ensemble of supercells and determine the band gap of the alloy. This treatment allows for an intrinsic reproduction of band bowing effects as a function of the concentration x and is exact in the alloy-induced disorder. In the present paper, we concentrate on bulk CdZnSe as a well-defined model system and give a careful analysis on the proper choice of the basis set and supercell size, as well as on the necessary number of realizations. The results are compared to experimental results obtained from ellipsometric measurements of CdZnSe layers prepared by molecular beam epitaxy (MBE) and photoluminescence (PL) measurements on catalytically grown CdZnSe nanowires reported in the literature.Comment: 7 pages, 6 figure

Exciton-polariton flows in cross-dimensional junctions

The Wurzburg group acknowledges the financial support by the state of Bavaria and the DFG within the project Schn1376-3.1.We study the nonequilibrium exciton-polariton condensation in 1D to 0D and 1D to quasi-2D junctions by means of non-resonant spectroscopy. The shape of our potential landscape allows to probe the resonant transmission of a propagating condensate between a quasi-1D waveguide and cylindrically symmetric states. We observe a distinct mode selection by varying the position of the non-resonant pump laser. Moreover, we study the the case of propagation from a localized trapped condensate state into a waveguide channel. Here, the choice of the position of the injection laser allows us to tune the output in the waveguide. Our measurements are supported by an accurate Ginzburg-Landau modeling of the system shining light on the underlying mechanisms.PostprintPeer reviewe

Spatio-temporal coherence in vertically emitting GaAs-based electrically driven polariton lasers

Authors gratefully acknowledge the financial support by the state of Bavaria, the DFG within the projects Schn1376-3.1 as well as KL3124/2-1 and the Wurzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter - ct.qmat. S.H. is grateful for funding received within the EPSRC Hybrid Polaritonics programme grant (EP/M025330/1).We report on the implementation of a GaAs-based, vertically emitting electrically pumped polariton laser operated at cryogenic temperatures. The structure consists of a high quality factor AlGaAs/AlAs microcavity (Q=15 000) with two stacks of four GaAs quantum wells and features a Rabi splitting of 11 meV. Polariton lasing manifests by a clear threshold in the input–output characteristics of our device with a sharp drop in the emission linewidth and a continuous blueshift of 0.7 meV above threshold with increasing injection current. We measure spatial and temporal coherence of our device in the condensed phase by utilizing interference spectroscopy. Our results clearly demonstrate that electrically driven polariton lasers have promise as monolithic polaritonic sources of coherent light.PostprintPeer reviewe

Optical probing of the Coulomb interactions of an electrically pumped polariton condensate

The authors would like to thank the State of Bavaria for financial support. SM and TL were supported by the NAP Start-Up grant M4081630 and MOE AcRF Tier 1 grant 2016-T1-001-084.We report on optical probing of the Coulomb interactions in an electrically driven exciton-polariton laser. By positioning a weak non-resonant Gaussian continuous wave-beam with a diameter of 2 μm inside an electrical condensate excited in a 20 μm diameter micropillar, we study a repulsion effect which is characteristic of the part-excitonic nature of the microcavity system in strong coupling. It manifests itself in a modified real space distribution of the emission pattern. Furthermore, polariton repulsion results in a continuous blueshift of the emission with increased power of the probe beam. A Gross-Pitaevskii equation approach based on modeling the electrical and optical potentials explains our experimental data.PostprintPeer reviewe

Room temperature organic exciton-polariton condensate in a lattice

Funding: The Würzburg group acknowledges financial support from the state of Bavaria. We also thank the Würzburg–Dresden Cluster of Excellence ct.qmat for financial support.Interacting Bosons in artificial lattices have emerged as a modern platform to explore collective manybody phenomena and exotic phases of matter as well as to enable advanced on-chip simulators. On chip, exciton–polaritons emerged as a promising system to implement and study bosonic non-linear systems in lattices, demanding cryogenic temperatures. We discuss an experiment conducted on a polaritonic lattice at ambient conditions: We utilize fluorescent proteins providing ultra-stable Frenkel excitons. Their soft nature allows for mechanically shaping them in the photonic lattice. We demonstrate controlled loading of the coherent condensate in distinct orbital lattice modes of different symmetries. Finally, we explore the self-localization of the condensate in a gap-state, driven by the interplay of effective interaction and negative effective mass in our lattice. We believe that this work establishes organic polaritons as a serious contender to the well-established GaAs platform for a wide range of applications relying on coherent Bosons in lattices.Publisher PDFPeer reviewe