Find here the scientific production related to PoLLoC.

1 2 3
Gabriele Rainò

Superfluorescence from Binary Perovskite

Lead-halide perovskite APbX3 (A=Cs or organic cation; X=Cl, Br, I) quantum dots (QDs) are subject of intense research due to their exceptional properties as both classical 1 and quantum light sources. Here we present perovskite-type (ABO3) binary nanocrystal superlattices, created via the shape-directed co-assembly of steric-stabilized, highly luminescent cubic CsPbBr 3 nanocrystals (which occupy the B and/or O lattice sites), assembled in combination with spherical Fe 3O4 or NaGdF4 nanocrystals (A sites). These ABO3 superlattices, as well as the binary NaCl and AlB 2 superlattice structures that we demonstrated, exhibit a high degree of orientational ordering of the CsPbBr 3 nanocubes which preserve their high oscillator strength and long exciton coherence time in the assembly. Such superlattices exhibit superfluorescence—a collective emission that results in a burst of photons with ultrafast radiative decay (22 picoseconds) that could be tailored, by structural engineering of the nanoparticle assembly, for use in ultrabright (quantum) light sources. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures.

En savoir plus
Tan Nguyen, Claudine Katan, Jacky Even


Perovskite nanocrystals (NCs) are among the most fashionable names nowadays in the field of colloidal synthesis owing to their superior photoluminescence quantum yield and blinking-free properties, which make them promising materials for both classical and quantum light sources. Their brightness and sub-nanosecond radiative decay originates from the inherent correlation effects. The many-body Coulomb interaction has generally been studied for semiconductor quantum dots. Perovskites, as a consequence of the unique properties of their dielectric functions, possess enhanced Coulomb interaction between the charge carriers. This leads to large binding energies of multi-exciton systems such as trion and biexciton in these NCs or the sizable splitting in the fine structure of single exciton states. Considering each NC as an artificial atom under the envelope function approximation, this problem of correlation effects can be approached at first by using second-order many-body techniques. This offers an elegant and efficient method that provides qualitative results for the trion and biexciton binding energies. In going beyond the second-order description, configuration interaction can be employed to include the correlation energies between the various charge carriers in a more holistic manner.

En savoir plus
Mateusz Krol, Helgi Sigurdsson, Katarzyna Rechcinska, ..., Pavlos G. Lagoudakis, Barbara Pietka, Jacek Szczytko

Observation of second-order meron polarization textures in optical microcavities

Multicomponent Bose–Einstein condensates, quantum Hall systems, and chiral magnetic materials display twists and knots in the continuous symmetries of their order parameters known as skyrmions. Originally discovered as solutions to the nonlinear sigma model in quantum field theory, these vectorial excitations are quantified by a topological winding number dictating their interactions and global properties of the host system. Here, we report the experimental observation of a stable individual second-order meron and antimeron appearing in an electromagnetic field. We realize these complex textures by confining light into a liquid-crystal-filled cavity that, through its anisotropic refractive index, provides an adjustable artificial photonic gauge field that couples the cavity photon motion to its polarization, resulting in the formation of these fundamental vectorial vortex states of light. Our observations could help bring topologically robust room-temperature optical vector textures into the field of photonic information processing and storage.

En savoir plus
P. Kokhanchik, H. Sigurdsson, B. Pietka, J. Szczytko, P. G. Lagoudakis

Photonic Berry curvature in double liquid crystal microcavities with broken inversion symmetry

We investigate a photonic device consisting of two coupled optical cavities possessing Rashba-Dresselhaus spin-orbit coupling, TE-TM splitting, and linear polarization splitting that opens a tunable energy gap at the diabolic points of the photon dispersion; giving rise to an actively addressable local Berry curvature. The proposed architecture stems from recent advancements in the design of artificial photonic gauge fields in liquid crystal cavities [K. Rechcinska et al., Science 366, 727 (2019)]. Our study opens perspectives for topological photonics, room-temperature spinoptronics, and studies on the quantum geometrical structure of photonic bands in extreme settings.

Exporter la référence : Phys. Rev. B 103, L081406 (2021)
En savoir plus
L. Pickup, J. D. Töpfer, H. Sigurdsson, P. G. Lagoudakis

Polariton spin jets through optical control

We demonstrate spin-polarized jets in extended systems of ballistic exciton-polariton condensates in semiconductor microcavities using optical nonresonant excitation geometries. The structure of the spin jets is determined by the spatially patterned degree of circular polarization of the nonresonant excitation laser. The presence of the laser excitation, strong particle interactions, and spin relaxation leads to a tunable spin-dependent potential landscape for polaritons, with the appearance of intricate polarization patterns due to coherent matter-wave interference. Our work realizes polarization-structured coherent light sources in the absence of gauge fields.

Exporter la référence : Phys. Rev. B 103, 155302 (2021)
En savoir plus
Tamsin Cookson, Kirill Kalinin, Helgi Sigurdsson, Julian D. Töpfer, Sergey Alyatkin, Matteo Silva, Wolfgang Langbein, Natalia G. Berloff, Pavlos G. Lagoudakis

Geometric frustration in polygons of polariton condensates creating vortices of varying topological charge

Vorticity is a key ingredient to a broad variety of fluid phenomena, and its quantised version is considered to be the hallmark of superfluidity. Circulating flows that correspond to vortices of a large topological charge, termed giant vortices, are notoriously difficult to realise and even when externally imprinted, they are unstable, breaking into many vortices of a single charge. In spite of many theoretical proposals on the formation and stabilisation of giant vortices in ultra-cold atomic Bose-Einstein condensates and other superfluid systems, their experimental realisation remains elusive. Polariton condensates stand out from other superfluid systems due to their particularly strong interparticle interactions combined with their non-equilibrium nature, and as such provide an alternative testbed for the study of vortices. Here, we nonresonantly excite an odd number of polariton condensates at the vertices of a regular polygon and we observe the formation of a stable discrete vortex state with a large topological charge as a consequence of antibonding frustration between nearest neighbouring condensates.

En savoir plus
I. Gnusov, H. Sigurdsson, J.D. Töpfer, S. Baryshev, S. Alyatkin, P.G. Lagoudakis

All-Optical Linear-Polarization Engineering in Single and Coupled Exciton-Polariton Condensates

We demonstrate all-optical linear-polarization control in semiconductor microcavities using an excitonpolariton condensate in an elliptically shaped optical trap. The microcavity inherent TE-TM splitting lifts the pseudospin degeneracy of the anisotropic trap ground state. The emerging fine-structure modes are shown to be polarized linearly parallel and perpendicular to the trap major axis. We demonstrate polariton condensation into the excited pseudospin mode with a high degree of linear polarization, which rotates as we rotate the trap. We then extend our study to a system of two coupled linearly polarized condensates and demonstrate rich spin dynamics reflecting spontaneous synchronization and high correlation between the condensate pseudospins as a function of the pump parameters. Our findings open up exciting perspectives in both spinoptronics and studies on extended systems of interacting nonlinear optical elements with anisotropic coupling strength and adjustable fine structure.

Exporter la référence : Phys. Rev. Applied 16, 034014 (2021)
En savoir plus
S. Alyatkin, H. Sigurdsson, A. Askitopoulos, J. D. Töpfer, P. G. Lagoudakis

Quantum fluids of light in all-optical scatterer lattices

One of the recently established paradigms in condensed matter physics is examining a system’s behaviour in artificial potentials, giving insight into phenomena of quantum fluids in hard-to-reach settings. A prominent example is the matter-wave scatterer lattice, where high energy matter waves undergo transmission and reflection through narrow width barriers leading to stringent phase matching conditions with lattice band formation. In contrast to evanescently coupled lattice sites, the realisation of a scatterer lattice for macroscopic matter-wave fluids has remained elusive. Here, we implement a system of exciton-polariton condensates in a non-Hermitian Lieb lattice of scatterer potentials. By fine tuning the lattice parameters, we reveal a nonequilibrium phase transition between distinct regimes of polariton condensation: a scatterer lattice of gain guided polaritons condensing on the lattice potential maxima, and trapped polaritons condensing in the potential minima. Our results pave the way towards unexplored physics of non-Hermitian fluids in non-stationary mixtures of confined and freely expanding waves.

En savoir plus
Anton V. Zasedatelev, Anton V. Baranikov, Denis Sannikov, Darius Urbonas, ..., Thilo Stöferle, Rainer F. Mahrt, Pavlos G. Lagoudakis

Single-photon nonlinearity at room temperature

The recent progress in nanotechnology and single-molecule spectroscopy paves the way for emergent cost-effective organic quantum optical technologies with potential applications in useful devices operating at ambient conditions. We harness a π-conjugated ladder-type polymer strongly coupled to a microcavity forming hybrid light–matter states, so-called exciton-polaritons, to create exciton-polariton condensates with quantum fluid properties. Obeying Bose statistics, exciton-polaritons exhibit an extreme nonlinearity when undergoing bosonic stimulation, which we have managed to trigger at the single-photon level, thereby providing an efficient way for all-optical ultrafast control over the macroscopic condensate wavefunction. Here, we utilize stable excitons dressed with high-energy molecular vibrations, allowing for single-photon nonlinear operation at ambient conditions. This opens new horizons for practical implementations like sub-picosecond switching, amplification and all-optical logic at the fundamental quantum limit.

Exporter la référence : Nature 597, 493–497 (2021)
En savoir plus
Oliviero Cannelli, Nicola Colonna, Michele Puppin, Thomas C. Rossi, Dominik Kinschel, Ludmila M. D. Leroy, ..., Franziska Krieg, Simon C. Boehme, Maksym V. Kovalenko, Majed Chergui*, and Giulia F. Mancini*

Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskite Nanocrystals

The development of next-generation perovskitebased optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr3 perovskites that the Pb−Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work, we demonstrate that the photoinduced lattice changes in the system are due to a specific polaronic distortion, associated with the activation of a longitudinal optical phonon mode at 18 meV by electron−phonon coupling, and we quantify the associated structural changes with atomic-level precision. Key to this achievement is the combination of timeresolved and temperature-dependent studies at Br K and Pb L3 X-ray absorption edges with refined ab initio simulations, which fully account for the screened core-hole final state effects on the X-ray absorption spectra. From the temporal kinetics, we show that carrier recombination reversibly unlocks the structural deformation at both Br and Pb sites. The comparison with the temperaturedependent XAS results rules out thermal effects as the primary source of distortion of the Pb−Br bonding motif during photoexcitation. Our work provides a comprehensive description of the CsPbBr3 perovskites’ photophysics, offering novel insights on the light-induced response of the system and its exceptional optoelectronic properties.

En savoir plus
1 2 3