Abstract
Exciton-polariton systems can sustain macroscopic quantum states (MQSs) under a periodic potential modulation. In this paper, we investigate the structure of these states in acoustic square lattices by probing their wave functions in real and momentum spaces using spectral tomography. We show that the polariton MQSs, when excited by a Gaussian laser beam, self-organize in a concentric structure, consisting of a single, two-dimensional gap-soliton (GS) state surrounded by one dimensional (1D) MQSs with lower energy. The latter form at hyperbolical points of the modulated polariton dispersion. While the size of the GS tends to saturate with increasing particle density, the emission region of the surrounding 1D states increases. The existence of these MQSs in acoustic lattices is quantitatively supported by a theoretical model based on the variational solution of the Gross–Pitaevskii equation. The formation of the 1D states in a ring around the central GS is attributed to the energy gradient in this region, which reduces the overall symmetry of the lattice. The results broaden the experimental understanding of self-localized polariton states, which may prove relevant for functionalities exploiting solitonic objects.
Highlights
In the past two decades, a new type of a two-dimensional half-light half-matter system called microcavity (MC) exciton-polaritons has emerged
The structure and the dynamics of exciton-polariton condensates in moving acoustic square (2D) lattices have been investigated by spectrally-resolved cw- and time-resolved PL spectroscopy, respectively
The tomographic study revealed that the exciton-polariton macroscopic quantum states (MQSs) self-organise in a structure, where three concentric modes coexist under excitation by a laser spot with a Gaussian intensity profile
Summary
In the past two decades, a new type of a two-dimensional half-light half-matter system called microcavity (MC) exciton-polaritons (in the following shortly polaritons) has emerged. In contrast to atomic BEC, polaritons are bosonic quasi-particles, which have a short lifetime of only a few picoseconds. The origin of this lies in their photonic component. Due to their short lifetime, polariton condensates possess an inherently non-equilibrium nature. This may be seen as a disadvantage at first glance. Polaritons are on the forefront of the research in the solid state physics They are rich in fundamental physics and their intriguing potential applications are the reason that has attracted the attention of several research groups around the world. Another important parameter in polariton-based devices and/or functionalities, which needs to be mentioned, is the ability to apply a controllable and, desirably, a tuneable modulation of polaritons as well as to be able to guide
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