Nano phase separation in cuprates and nickelates
Final Report Abstract
Cobaltates required a rather deep re-examination due to two new publications that appeared and that highlighted the significance of a competing charge stripe model for the physical properties in this system. Cobaltate single crystals have been grown and a comprehensive study of these cobaltates has been performed including neutron, muSR and synchrotron measurements. Finally, the existence and also the relevance of our nano phase separation model could be confirmed for these cobaltates. After confirmation of the validity of our nano phase separation model in the prototypical cobaltate system we could continue with other systems, i.e. nickelates and cuprates. Single crystals have been synthesized and characterized and initial studies of cuprates with hard x-rays at the Cu K-edge show that such studies are difficult due to the low intensity. Here soft x-rays are look more promising. In addition, the magnetic signals can be detected with soft x-rays which is another advantage. Since the signal in nickelates is expected to be much stronger than in the cuprates, we intended to start with the study of nickelates. However, the beamtime at a soft x-ray beamline suitable for microdiffraction was canceled twice times due to technical problems, and then a third time due to COVID. Nevertheless, future microdiffraction experiments with soft x-rays are on their way. Regarding the study of the magnetic excitation spectra, we successfully performed elastic and inelastic neutron measurements on highly hole-doped nickelates (x=1). The general nano phase separation model that was able to explain the emergence of the famous hour-glass magnetic spectra in somewhat lower hole-doped cobaltates (x~0.37) now was for the first time able to describe the magnetic spectrum also in a nickelate in an adapted form. This gives hope that the nano phase separation model is also applicable to other systems as well. All in all, the project remains exciting and more experiments are to come.
Publications
- Suppression of the outwards-dispersing branches in hour-glass magnetic spectra induced by nanoscale phase separation in La2−xSrxCoO4. Phys. Rev. B 100, 014411 (2019)
H. Guo, Z. W. Li, S. Sakong, G. Ryu, L. Zhao, A. Piovano, W. Schmidt, M. Sprung, J. Strempfer, S. Francoual,D. Dzhigaev, S. Subakti, Z. Hu, H. J. Lin, C. T. Chen, H. Luetkens, O. Stockert and A. C. Komarek
(See online at https://doi.org/10.1103/PhysRevB.100.014411) - Charge disproportionation and nano phase separation in RSrNiO4. Sci. Rep. 10, 18012 (2020)
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 and A. C. Komarek
(See online at https://doi.org/10.1038/s41598-020-74884-2)
