Using large supercell empirical pseudopotential calculations, we show that alloying of GaN with In induces localization in the hole wave function, resonating within the valence band. This occurs even with perfectly homogeneous In distribution ͑i.e., no clustering͒. This unusual effect can explain simultaneously exciton localization and a large, composition-dependent band gap bowing coefficient in InGaN alloys. This is in contrast to conventional alloys such as InGaAs that show a small and nearly composition-independent bowing coefficient. We further predict that ͑i͒ the hole wave function localization dramatically affects the photoluminescence intensity in InGaN alloys and ͑ii͒ the optical properties of InGaN alloys depend strongly on the microscopic arrangement of In atoms.
Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched LaMnO3/SrTiO3 (001) heterostructures. Using a combination of element-specific X-ray absorption spectroscopy and dichroism, and first-principles calculations, interfacial electron accumulation and ferromagnetism have been observed within the polar, antiferromagnetic insulator LaMnO3.Our results show that the critical thickness for the onset of electron accumulation is as thin as 2 unit cells (UC), significantly thinner than the observed critical thickness for ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely induced by electron over-accumulation.In turn, by controlling the doping of the LaMnO3, we are able to neutralize the excessive electrons from the polar mismatch in ultrathin LaMnO3 films and thus enable ferromagnetism in films as thin as 3 UC, extending the limits of our ability to synthesize and tailor emergent phenomena at interfaces and demonstrating manipulation of the electronic and magnetic structures of materials at the shortest length scales.
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