Polarization Bistability and Resultant Spin Rings in Semiconductor Microcavities

Abstract

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 high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on spin dependent Gross-Pitaevskii equations 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. Nonlinear interactions in optical systems result in a variety of important phenomena such as frequency conversion, parametric oscillation, bistability, pattern formation and self-organization. In this context hybrid lightmatter particles, polaritons, which form due to strong exciton-photon coupling in semiconductor microcavities (MCs), attract much attention [1]. In this case strong nonlinear interactions due to the excitonic component of polaritons lead to stimulated polariton-polariton scattering and optical parametric oscillation [2,3], bistability [4,5] and superfluidity [6,7]. Bose-Einstein condensation of polariton quasi-particles has also been reported [8]. It is notable that compared to weakly coupled light/matter microcavity systems, polariton nonlinear interactions are several orders of magnitude stronger [1].A further distinguishing feature of polariton systems arises from their spin properties. In particular, polaritons with parallel spins repel, whereas polaritons with opposite spins attract. Such interactions provide blueshifts and redshifts respectively of the energies of coherent polariton modes. This anisotropy in spin properties results in polarization bistability and multistability predicted recently [9]. Polariton polarization bistability has also been predicted to lead to the formation of spatial spin rings of high degree of circular polarization (DCP) [11]. These non-linear spin properties and spatial patterns may lead to novel optical/spin-based devices such as fast optical modulators, spin switches [11,12] and polariton logic elements (polariton neurons) [10], operating at high picosecond speeds and very low pump powers.In the present work we investigate bistability of spin-up and spin-down polariton fields as a function of the intensity and polarization of an external pump beam. As a result of spin dependent polariton-polariton interactions [9] we are able to switch abruptly the internal polariton DCP by 40-50% by tuning the pump power. Despite strong photonic disorder we demonstrate the formation of spatial ring patterns of high DCP, a result of the bistable threshold-like behavior of the DCP for spatially nonuniform excitation [11]. The pump power behavior and the similar bistability thresholds for spin-up and spindown coherent po...

Blowup dynamics of coherently driven polariton condensates: Experiment

“…Optical multistability in cavity-polariton systems attracts much attention as it enables one to implement controllable ultrafast all-optical switches of microcavities on the time scale of several picoseconds [1][2][3][4][5][6][7][8][9][10][11]. Cavity polaritons are composite bosons formed by strongly coupled excitons and cavity photons [12].…”

“…In general, the one-mode approximation can be inappropriate to describe system dynamics; in such cases, the manymode Gross-Pitaevskii equations were solved numerically in a number of works. Nevertheless, it was usually accepted that under plane-wave excitation at normal incidence, the threshold for the transition to the upper state corresponds to the right turning point of the S-shaped curve where its lower steady-state branch terminates [1][2][3][4][5][6][7][8]15]. Provided the polariton decay rate γ is much smaller than D, the critical cavity-field intensity in the turning point amounts to |ψ| 2 ≈ D/3V , where V is the polariton-polariton interaction constant [2].…”

Determination of operating parameters for a GaAs-based polariton laser

“…[3][4][5][6] In the last years, Bose-Einstein condensation (BEC) of exciton-polaritons, which is a prerequisite for a polariton laser device, was reported for different material systems such as CdTe, 7 ZnO, 8 GaN, 9 and GaAs. 10 On the road towards a polariton laser, systematic studies need to be done in order to determine the optimal operating parameters.…”

Transient optical parametric oscillations in resonantly pumped multistable cavity polariton condensates

“…The latter enables thermalization of nonresonantly pumped polaritons and formation of Bose-Einstein condensates in high-Q cavities [6]. Under resonant pumping, the polariton-polariton interaction leads to a variety of nonlinear collective effects such as parametric scattering [7][8][9][10][11][12], bi-and multistability [12][13][14][15][16][17][18][19], pattern formation [20], self-organization [21][22][23], and bright polariton solitons [24]. All these phenomena imply strong redistributions of the intracavity field that occur at certain threshold characteristics of excitation.…”