35 research outputs found
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
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
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
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-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 Germanyâs Excellence StrategyâEXC2147 âct.qmatâ (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 âTopological insulators.â 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
Lasing of Moir\'e Trapped MoSe/WSe Interlayer Excitons Coupled to a Nanocavity
Moir\'e trapped interlayer excitons (IXs) in heterobilayer transition metal
dichalcogenides currently attract strong interest due to their potential for
non-classical light generation, coherent spin-photon interfaces and exploring
novel correlated phases of electrons. Here, we report lasing of moir\'e trapped
IXs by integrating a pristine hBN-encapsulated MoSe/WSe heterobilayer
in a high-Q () nanophotonic cavity. We control the detuning between the
IX line and the cavity mode with a magnetic field and measure the dipolar
coupling strength to the cavity mode to be , fully
consistent with the 82 predicted by theory. The emission from
the cavity mode shows clear threshold-like behaviour. We observe a superlinear
power dependence accompanied by a narrowing of the linewidth as the distinct
features of lasing. The onset and prominence of these threshold-like behaviours
are significant at resonance whilst weak off-resonance. Our results show that a
lasing transition can be induced in interacting moir\'e trapped IXs with
macroscopic coherence extending over the lengthscale of the cavity mode. Such
systems raise interesting perspectives for low-power switching and synaptic
nanophotonic devices using 2D materials
Room temperature Tamm-Plasmon exciton-polaritons with a WSe2 monolayer
This work has been supported by the State of Bavaria. A.K. and S.H. acknowledge the partial financial support from the EPSRC Hybrid Polaritonics Programme. C.S. acknowledges financial support by the European Research Council (unLiMIt-2D project).Solid state cavity quantum electrodynamics is a rapidly advancing field which explores the frontiers of light-matter coupling. Metal-based approaches are of particular interest in this field, since they carry the potential to squeeze optical modes to spaces significantly below the diffraction limit. Transition metal dichalcogenides are ideally suited as the active material in cavity quantum electrodynamics as they interact strongly with light at the ultimate monolayer limit. Here, we implement a Tamm-plasmon-polariton structure, and study the coupling to a monolayer of WSe2, hosting highly stable excitons. Exciton-polariton formation at room temperature is manifested in the characteristic energy-momentum dispersion relation studied in photoluminescence, featuring an anti-crossing between the exciton and photon modes with a Rabi-splitting of 23.5 meV. Creating polaritonic quasi-particles in monolithic, compact architectures with atomic monolayers under ambient conditions is a crucial step towards the exploration of non-linearities, macroscopic coherence and advanced spinor physics with novel, low mass bosons.Publisher PDFPeer reviewe
Effects of the linear polarization of polariton condensates in their propagation in codirectional couplers
We report on the linear polarization of polariton condensates in a codirectional coupler that allows evanescent coupling between adjacent waveguides. During the condensate's formation, polaritons usually acquire a randomly oriented polarization, however, our results reveal a preferential orientation of the linear polarization along the waveguide propagation path. Furthermore, we observe polarization-dependent intensity oscillations in the output terminal of the coupler, and we identify the mode beating between the linear-polarized eigenmodes as the origin of these oscillations. Our findings provide an insight into the control of the polarization of polariton condensates, paving the way for the development of spin-based polaritonic architectures where condensates propagate over macroscopic distancesThis work has been partly supported by the Spanish MINECO Grant Nos. MAT2017-83722-R and PID2020-113445GB-I00. A.Y. and I.A.S. were financially supported by the Ministry of Science and Higher Education of the Russian Federation through Megagrant Number 14.Y26.31.0015 and Goszadanie No. 2019-1246. I.A.S. acknowledges also the support from theIcelandic research fund, Grant No. 163082-051. The WuÌrzburgand Jena group acknowledges financial support within the DFGProject Nos. PE 523/18-1 and KL3124/2-1. The WuÌrzburggroup acknowledges financial support by the German ResearchFoundation (DFG) under Germanyâs Excellence StrategyâEXC2147 âct.qmatâ (Project No. 390858490) and is grateful forsupport by the state of Bavari