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Instruments / Technical Area	Publication Details	Published	Actions
I09-Surface and Interface Structural Analysis	Origin of itinerant carriers in antiferromagnetic LaF e 1 − x M o x O 3 studied by x-ray spectroscopies Dibya Phuyal , Soham Mukherjee , S. K. Panda , Somnath Jana , Carlo U. Segre , Laura Simonelli , Sergei M. Butorin , Hakan Rensmo , Olof Karis Physical Review Materials 4, 034405 DOI: 10.1103/PhysRevMaterials.4.034405 Diamond Proposal Number(s): [22648] Open Access Show Abstract ▼ Abstract: We report on the electronic structure of doped LaFeO3 at the crossover from an insulating-to-metallic phase Transition. Comprehensive x-ray spectroscopic methodologies are used to understand core and valence electronic structure as well as crystal structure distortions associated with the electronic transition. Despite the antiferromagnetic (AFM) ordering at room temperature, we show direct evidence of itinerant carriers at the Fermi level revealed by resonant photoemission spectroscopy (RPES) at the Mo L3 edge. RPES data taken at the Fe L3 edge show spectral weight near the valence band edge and significant hybridization with O 2p states required for AFM ordering. Resonant inelastic x-ray scattering spectra taken across Fe L2, 3 edges show electron correlation effects (U) driven by Coulomb interactions of d electrons as well as broad charge-transfer excitations for x > 0.2 where the compound crosses over to a metallic state. Site substitution of Fe by Mo ions in the Fe-O6 octahedra enhances the separation of the two Fe-O bonds and Fe-O-Fe bonding angles relative to the orthorhombic LaFeO3, but no considerable Distortions are present to the overall structure. Mo ions appear to be homogeneously doped, with average valency of both metal sites monotonically decreasing with increasing Mo concentration. This insulator-to-metal phase transition with AFM stability is primarily understood through intermediate interaction strengths between correlation (U) and bandwidth (W) at the Fe site, where an estimation of this ratio is given. These results highlight the important role of extrinsic carriers in stabilizing a unique phase transition that can guide future efforts in antiferromagnetic-metal spintronics.	Mar 2020
I09-Surface and Interface Structural Analysis	The origin of low bandgap and ferroelectricity of a co-doped BaTiO 3 D. Phuyal , S. Mukherjee , S. Das , S. Jana , K. O. Kvashnina , D. D. Sarma , H. Rensmo , S. M. Buortin , O. Karis Epl (europhysics Letters) 124 DOI: 10.1209/0295-5075/124/27005 Diamond Proposal Number(s): [19066] Show Abstract ▼ Abstract: We recently demonstrated the lowest bandgap bulk ferroelectric, BaTi1−x (Mn1/2Nb1/2) x O3, a promising candidate material for visible light absorption in optoelectronic devices. Using a combination of x-ray spectroscopies and density functional theory (DFT) calculations, we here elucidate this compound's electronic structure and the modifications induced by Mn doping. In particular, we are able to rationalize how this compound retains its ferroelectricity even through a significant reduction of the optical gap upon Mn doping. The local electronic structure and atomic coordination are investigated using x-ray absorption at the Ti K, Mn K, and O K edges, which suggests only small distortions to the parent tetragonal ferroelectric system, BaTiO3, thereby providing a clue to the substantial retention of ferroelectricity in spite of doping. Features at the Ti K edge, which are sensitive to local symmetry and an indication of Ti off-centering within the Ti-O6 octahedra, show modest changes with doping and strongly corroborates our measured polarization values. Resonant photoelectron spectroscopy results suggest the origin of the reduction of the bandgap in terms of newly created Mn d bands that hybridize with O 2p states. X-ray absorption spectra at the O K edge provide evidence for new states below the conduction band of the parent compound, illustrating additional contributions facilitating bandgap reduction.	Oct 2018

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