Inducing optical spin-orbit coupling: The coupling of the spin-orbit interactions in solid-state systems can give rise to a wide range of exotic electronic transport effects. But solid-state systems tend to be somewhat limited in their flexibility because the spin-orbit coupling is fixed. By contrast, optical systems have recently been shown to mimic complex solid-state systems, with flexibility in design providing the ability to control and manipulate the system properties. Using a liquid crystal–filled photonic cavity, Rechcińska et al. emulated an artificial Rashba-Dresselhaus spin-orbit coupling in a photonic system and showed control of an artificial Zeeman splitting. The results illustrate a powerful approach of engineering synthetic Hamiltonians with photons for the simulation of nontrivial condensed matter and quantum phenomena. Science , this issue p. 727

Microcrystalline Ga1−xMnxN samples with Mn content up to x=0.005 were grown by an ammonothermal method and were studied using various techniques. X-ray diffraction showed characteristic diffraction lines for hexagonal GaN phase mixed with a small contribution (<5%) from the Mn3N2 phase. Raman spectra exhibited characteristic peaks of pure GaN and modes that could be associated with Mn-induced lattice disorder. Electron spin resonance and magnetization measurements were consistent with the dominant Mn2+(d5) configuration of spin S=5/2 which is responsible for the observed paramagnetic behavior of the GaMnN material.

We have studied density-dependent time-resolved photoluminescence from a 80 Å $\mathrm{InGaAs}/\mathrm{GaAs}$ single quantum well excited by picosecond pulses. We succeed in giving evidence for the transition from an exciton-dominated population to an unbound electron-hole pair population as the pair density increases. For pair densities below this excitonic Mott transition we observe a spectrally separate emission from free electron-hole pairs in addition to excitonic luminescence, thereby proving the coexistence of both species. Exciton binding energy and band gap remain unchanged even near the upper bound of this coexistence region. Above the Mott density we observe a purely exponential high energy tail of the photoluminescence and a redshift of the band gap with pair density. The transition occurs gradually between $1\times {10}^{10}$ and $1\times {10}^{11}{\mathrm{cm}}^{-2}$ at the carrier temperatures of our experiment.

The $s,p-d$ exchange interaction of p-type ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}\hspace{0.5em}\mathrm{}(x<\mathrm{}0.05\mathrm{})\mathrm{}$ epilayers is investigated by means of magnetoabsorption. The observed ferromagnetic-type splitting of fundamental absorption edge is explained by antiferromagnetic $p-d$ exchange interaction, taking into account the Moss-Burstein effect, resulting from high hole concentration.

We present the results of a detailed time-resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the setup, allowing us to keep the observation of these two separate contributions over a broad range of times and densities. This allows us to directly evidence the exciton formation time, which depends on the density as expected from theory. We also denote the dominant contribution of excitons to the luminescence signal, and the lack of thermodynamical equilibrium at low densities.

Electron paramagnetic resonance was measured in ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ epilayers with $0.002<~x<~\mathrm{0.01.}$ Data were taken as a function of magnetic field orientation at low temperatures. The observed spectra were attributed to ionized Mn acceptor $A^{-}.$ No neutral Mn acceptor centers were detected. The observed anisotropy of $A^{-}$ is interpreted in terms of sizable demagnetizing fields resulting from ferromagnetic coupling between Mn ions.