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We demonstrate that the introduction of an elemental beam of Mn during the molecular beam epitaxial growth of Bi 2 Se 3 results in the formation of layers of Bi 2 MnSe 4 that intersperse between layers of pure Bi 2 Se 3 . This study revises the assumption held by many who study magnetic topological insulators (TIs) that Mn incorporates randomly at Bi-substitutional sites during epitaxial growth of Mn:Bi 2 Se 3 . Here, we report the formation of thin film magnetic TI Bi 2 MnSe 4 with stoichiometric composition that grows in a self-assembled multilayer heterostructure with layers of Bi 2 Se 3 , where the number of Bi 2 Se 3 layers separating the single Bi 2 MnSe 4 layers is approximately defined by the relative arrival rate of Mn ions to Bi and Se ions during growth, and we present its compositional, structural, and electronic properties. We support a model for the epitaxial growth of Bi 2 MnSe 4 in a near-periodic self-assembled layered heterostructure with Bi 2 Se 3 with corresponding theoretical calculations of the energetics of this material and those of similar compositions. Computationally derived electronic structure of these heterostructures demonstrates the existence of topologically nontrivial surface states at sufficient thickness. New J. Phys. 19 (2017) 085002 J A Hagmann et al

We report the first use of the resonant two-photon photo-Hall effect as a nonlinear optical technique to measure the temperature dependence of the energy gap of InSb. Values of Eg for the temperature range 2–210 K are determined and compared with theoretical predictions and past experimental work. The technique is shown to provide an accurate, straightforward means of measuring Eg as a function of temperature in semiconductor materials.