Controlling the optical spin Hall effect with light

Abstract

The optical spin Hall effect (OSHE) is a transport phenomenon of exciton polaritons in semiconductor microcavities, caused by the polaritonic spin-orbit interaction, that leads to the formation of spin textures. In the semiconductor cavity, the physical basis of the spin orbit coupling is an effective magnetic field caused by the splitting of transverse-electric and transverse-magnetic (TE-TM) modes. The spin textures can be observed in the near field (local spin distribution of polaritons), and as light polarization patterns in the more readily observable far field. For future applications in spinoptronic devices, a simple and robust control mechanism, which establishes a one-to-one correspondence between stationary incident light intensity and far-field polarization pattern, is needed. We present such a control scheme, which is made possible by a specific double-microcavity design.The detection and manipulation of spins is an important part of science, in areas ranging from quantum computing, information, and spintronics 1 , to ubiquitous medical imaging techniques such as Magnetic Resonance Imaging (MRI). Much of the functionality of spin effects rests on the ability to control the spin dynamics through the application of external optical and/or magnetic fields. For example, in MRI spatial gradients of external magnetic fields control the spin precession, and in electron or nuclear spin-based quantum computing logical operations are performed using spatially or time-varying electromagnetic fields (e.g. Ref.1,2 ). Major research efforts have focused on photonic counterparts to magnetic spin systems, including the plasmonic spin Hall effect 3 , and, importantly, wide-ranging investigations of the spin orbit interactions of light 4-8 . All-optical spin systems combine the benefits of magnetic spin systems and their (sometimes relatively simple) spin dynamics with the highly developed technology of optical preparation and detection of polarization states (the optical analogue of spin).A promising semiconductor system is a microcavity containing semiconductor quantum wells, where spin states of exciton-polaritons can be created optically and the TE-TM splitting yields a spin-orbit interaction that can be described by an effective magnetic field. This, in turn, gives rise to a polaritonic spin Hall effect, the so-called optical spin Hall effect (OSHE) 9-14 . Since polaritons with different in-plane wave vectors experience different effective magnetic fields, an isotropic distribution of polaritons on a ring in wave vector space can lead to an anisotropic polarization texture or pattern, both in real (configuration) and wave vector space.Such polarization/spin textures have been found for excitations of linearly and circularly polarized polaritons in Ref.10 and 14 , respectively (structurally similar polarization/spin textures are also present in different physical systems, e.g. 15,16 ). The OSHE in wave vector space corresponds to that seen experimentally in far-field observations, which are particularly important ...

Optically Controlled Orbital Angular Momentum Generation in a Polaritonic Quantum Fluid

“…In semiconductor microcavities, there is also a spin-orbit interaction (SOI), giving rise, for example, to a polaritonic Hall effect, called the optical spin Hall effect [38]. A conceptually simple and robust all-optical control scheme of this effect has been demonstrated in [39]. The question then arises whether the spin-orbit interaction, caused by the splitting of transverse-electric (TE) and transversemagnetic (TM) modes, renders the pure orbital angular momentum control impossible, as orbital and spin angular momentum are not independently conserved.…”

“…For realistic values of the TE-TM splitting, we find the effect of the SOI to be unimportant and, for clarity, omit it in the following discussion (results including the SOI are in the Supplemental Material [40], which includes Refs. [31,39,41]). …”

Optical control of polaritons: from optoelectronic to spinoptronic device concepts

“…The spin-orbit interaction leads to an effective magnetic field that creates an anisotropic polarization texture of polaritons. The OSHE pattern with a linearly polarized ("x"-polarized) light source was recently shown in experiments, 31,32 and is sketched in Fig. 1(c).…”

“…A further increase of the pump intensity will lead to a further rotation of the S1(k) pattern. 31 The data are normalized such that the maximum and minimum values are ±1.…”

“…[25][26][27][28][29][30][31] The OSHE is the formation of polarization/spin pattern of exciton-polaritons in an optically pumped semiconductor microcavity. The effect arises from the transverse-electric and transverse magnetic (TE-TM) splitting, which yields a polariton spin-orbit interaction.…”