We establish the double perovskite Ba2CeIrO6 as a nearly ideal model system for j = 1/2 moments, with resonant inelastic x-ray scattering indicating that the ideal j = 1/2 state contributes by more than 99 % to the ground-state wavefunction. The local j = 1/2 moments form an fcc lattice and are found to order antiferromagnetically at TN = 14 K, more than an order of magnitude below the Curie-Weiss temperature. Model calculations show that the geometric frustration of the fcc Heisenberg antiferromagnet is further enhanced by a next-nearest neighbor exchange, and a significant size of the latter is indicated by ab initio theory. Our theoretical analysis shows that magnetic order is driven by a bond-directional Kitaev exchange and by local distortions via a strong magneto-elastic effect. Both, the suppression of frustration by Kitaev exchange and the strong magneto-elastic effect are typically not expected for j = 1/2 compounds making Ba2CeIrO6 a riveting example for the rich physics of spin-orbit entangled Mott insulators.

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Purpose This study aims to investigate the effects of indium composition on surface morphology and optical properties of indium gallium nitride on gallium nitride (InGaN/GaN) heterostructures. Design/methodology/approach The InGaN/GaN heterostructures were grown on flat sapphire substrates using a metal-organic chemical vapour deposition reactor with a trimethylindium flow rate of 368  sccm. The indium composition of the InGaN epilayers was controlled by applying different substrate temperatures. The surface morphology and topography were observed using field emission scanning electron microscope (F.E.I. Nova NanoSEM 450) and atomic force microscopy (Bruker Dimension Edge) with a scanning area of 10 µm × 10 µm, respectively. The compositional analysis was done by Energy Dispersive X-Ray Analysis. Finally, the ultraviolet-visible (UV-Vis) spectrophotometer (Agilent Technology Cary Series UV-Vis-near-infrared spectrometer) was measured from 200 nm to 1500 nm to investigate the optical properties of the samples. Findings The InGaN/GaN thin films have been successfully grown at three different substrate temperatures. The indium composition reduced as the temperature increased. At 760 C, the highest indium composition was obtained, 21.17%. This result was acquired from the simulation fitting of ω−2θ scan on (0002) plane using LEPTOS software by Bruker D8 Discover. The InGaN/GaN shows significantly different surface morphologies and topographies as the indium composition increases. The thickness of InGaN epilayers of the structure was ∼300 nm estimated from the field emission scanning electron microscopy. The energy bandgap of the InGaN was 2.54 eV – 2.79 eV measured by UV-Vis measurements. Originality/value It can be seen from this work that changes in substrate temperature can affect the indium composition. From all the results obtained, this work can be helpful towards efficiency improvement in solar cell applications.

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The surging interest in manipulating the polarization of piezo/ferroelectric materials by means of light has driven an increasing number of studies toward their light-polarization interaction. One way to investigate such interaction is by performing piezoresponse force microscopy (PFM) while/after the sample is exposed to light illumination. However, caution must be exercised when analyzing and interpreting the data, as demonstrated in this paper, because sizeable photo-response observed in the PFM amplitude image of the sample is shown to be caused by the electrostatic interaction between the photo-induced surface charge and tip. Through photo-assisted Kelvin probe force microscopy (KPFM), positive surface potential is found to be developed near the sample's surface under 405 nm light illumination, whose effects on the measured PFM signal is revealed by the comparative studies on its amplitude curves that are obtained using PFM spectroscopy mode with/without illumination. This work exemplifies the need for complementary use of KPFM, PFM imaging mode, and PFM spectroscopy mode in order to distinguish real behavior from artifacts.