Charge disproportionation and nano phase separation in RSrNiO4

H. Guo, Z. W. Li, C. F. Chang, Z. Hu, C.-Y. Kuo, T. G. Perring, W. Schmidt, A. Piovano, K. Schmalzl, H. C. Walker, H. J. Lin, C. T. Chen, S. Blanco-Canosa, J. Schlappa, C. Schüßler-Langeheine, P. Hansmann, D. I. Khomskii, L. H. Tjeng, A. C. Komarek

We have successfully grown centimeter-sized layered RSrNiO4 single crystals under high oxygen pressures of 120 bar by the floating zone technique. This enabled us to perform neutron scattering experiments where we observe close to quarter-integer magnetic peaks below 77 K that are accompanied by steep upwards dispersing spin excitations. Within the high-frequency Ni-O bond stretching phonon dispersion, a softening at the propagation vector for a checkerboard modulation can be observed. Together with our spin wave simulations these observations reveal that this Ni3+system exhibits charge disproportionation with charges segregating into a checkerboard pattern within a nano phase separation scenario rather than showing a Jahn-Teller effect.

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