Polariton Chimeras: Bose-Einstein Condensates with Intrinsic Chaoticity and Spontaneous Long-Range Ordering.

The system of cavity polaritons driven by a plane electromagnetic wave is found to undergo the spontaneous breaking of spatial symmetry, which results in a lifted phase locking with respect to the driving field and, consequently, in the possibility of internal ordering. In particular, periodic spin and intensity patterns arise in polariton wires; they exhibit strong long-range order and can serve as media for signal transmission. Such patterns have the properties of dynamical chimeras: they are formed spontaneously in perfectly homogeneous media and can be partially chaotic. The reported new mechanism of chimera formation requires neither time-delayed feedback loops nor nonlocal interactions.

Effects of spin-dependent interactions on polarization of bright polariton solitons.

We report on the spin properties of bright polariton solitons supported by an external pump to compensate losses. We observe robust circularly polarized solitons when a circularly polarized pump is applied, a result attributed to phase synchronization between nondegenerate TE and TM polarized polariton modes at high momenta. For the case of a linearly polarized pump, either σ+ or σ- circularly polarized bright solitons can be switched on in a controlled way by a σ+ or σ- writing beam, respectively. This feature arises directly from the widely differing interaction strengths between co- and cross-circularly polarized polaritons. In the case of orthogonally linearly polarized pump and writing beams, the soliton emission on average is found to be unpolarized, suggesting strong spatial evolution of the soliton polarization. The observed results are in agreement with theory, which predicts stable circularly polarized solitons and unstable linearly polarized solitons.

Exciton-polariton gap solitons in two-dimensional lattices.

We report on the two-dimensional gap-soliton nature of exciton-polariton macroscopic coherent phases (PMCP) in a square lattice with a tunable amplitude. The resonantly excited PMCP forms close to the negative mass M point of the lattice band structure with energy within the lattice band gap and its wave function localized within a few lattice periods. The PMCPs are well described as gap solitons resulting from the interplay between repulsive polariton-polariton interactions and effective attractive forces due to the negative mass. The solitonic nature accounts for the reduction of the PMCP coherence length and optical excitation threshold with increasing lattice amplitude.

Polarization bistability and resultant spin rings in semiconductor microcavities.

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with a high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on effective semiclassical equations of motion provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.

Kinetics of stimulated polariton scattering in planar microcavities: evidence for a dynamically self-organized optical parametric oscillator.

Strong temporal hysteresis effects in the population kinetics of pumped and scattered lower polaritons (LPs) have been observed in a planar semiconductor microcavity under a nanosecond-long pulsed resonant excitation (by frequency and angle) near the inflection point of the LPs' dispersion. The hysteresis loops have a complicated shape due to the interplay of two instabilities. The self-instability (bistability) of the nonlinear pumped LP is accompanied by a strong parametric instability which causes an explosive growth of the scattered LPs' population over a wide range of wave vectors. Finally, after a 30-500 ps period, a three-mode scattering pattern forms, thereby demonstrating a dynamically self-organized regime of the optical parametric oscillator. Stability is maintained by the presence of numerous weak "above-condensate" modes; the whole system therefore appears to be highly correlated.

Polarization multistability of cavity polaritons.

New effects of polarization multistability and polarization hysteresis in a coherently driven polariton system in a semiconductor microcavity are predicted and theoretically analyzed. The multistability arises due to polarization-dependent polariton-polariton interactions and can be revealed in polarization resolved photoluminescence experiments. The pumping power required to observe this effect is 4 orders of magnitude lower than the characteristic pumping power in conventional bistable optical systems.

[5-hydroxytryptamine and 5-methoxytryptamine increase tolerance to global cerebral ischemia].

In the global cerebral ischemia, 5-hydroxytryptamine (serotonin, 5-HT) and 5-methoxytryptamine (5-MT) produce a significant neuroprotector effect closely correlated with their hypothermic action. This expands the spectrum of cerebral functions controlled by 5-HT. At the same time, melatonin and 2-iodmelatonin, which are chemically (but not pharmacologically) close to 5-HT and 5-MT, do not exhibit such protective effects. Probably, an important role in the interaction with 5-HT receptors belongs to the NH2 group of the indole ring.

[Neuroprotective effect of antipsychotic drugs (neuroleptics) in global brain ischemia].

Most of typical and atypical neuroleptics belonging to various chemical groups produce a significant, dose-dependent increase in the brain tolerance to global ischemia. This activity of neuroleptics is related to their structure and exhibits no correlation with their antipsychotic properties. Therefore, the ability to increase the brain tolerance to global ischemia is an independent property of neuroleptics. The neuroprotective effect is also not correlated with their affinity to serotonin 5-HT2A and dopamine D2 receptors, but is closely related to the development of deep hypothermia. Thermoneutral conditions prevent both effects. Tolerant strategy plays the main role in the development of the neuroprotective effect of neuroleptics.

[Influence of the selective ligands of dopamine and 5-hydroxytryptamine receptors on the tolerance to global cerebral ischemia].

Selective dopamine (D) receptor agonists either slightly improve (D2 and D3) or do not affect (D1 and D4) the tolerance of the brain to global ischemia. As for D and 5-HT (hydroxytryptamine) antagonists, only D1 antagonist SCH 23390 and 5-HT2 antagonist ketanserin produce a small neuroprotective effect, while D2, D4, 5-HT(2B) and 5-HT(2C) antagonists are not active. Simultaneous injection of D2 (raclopride), D3 (GR 103691), and D4 (L 745870) receptor blockers also does not protect the brain. These results are not at variance with a widespread hypothesis that the accumulation of extracellular 5-HT and especially D in the brain causes the neuron damage. The effect of ketanserine is not increased by D2 or D4 blockers, but the introduction of D3 blocker GR 103691 (+88%) and especially the simultaneous injection of D2,3,4 antagonists improve the effect of ketanserine (+134%). The neuroprotective effect of the last combination is not lower but even exceeds that of some neuroleptics. This fact shows the possibility to increase the tolerance to cerebral ischemia by simultaneously blocking D and 5-HT-receptors.