Charge disproportionation and nano phase separation in $R$SrNiO$_4$

cond-mat.str-el

/ Authors

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

and 9 more authors

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

/ Abstract

We have successfully grown centimeter-sized layered $R$SrNiO$_4$ 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 $\sim$77 K that are accompanied by steep upwards dispersing spin excitations. Within the high-frequency Ni-O bond stretching phonon dispersion, a softening at the propagation vector for a checkerboard modulation can be observed. Together with our spin wave simulations these observations reveal that this Ni$^{3+}$ system exhibits charge disproportionation with charges segregating into a checkerboard pattern within a nano phase separation scenario rather than showing a Jahn-Teller effect.