［物理所报告] Relativistic first-principles study of pyrochlore oxides

时间： 2016年06月07日 10:00 地点： M830 报告人： Hiroshi Shinaoka Department of Physics, Saitama University, Japan Abstract： Fascinating phenomena are induced by the competition of strong electron correlations and spin-orbit coupling (SOC) in transition metal oxides. Geometrical frustration brings about a further intriguing situation in pyrochlore oxides. In this talk, we review our relativistic first-principles studies on 4d and 5d compounds using local density approximation (LDA)+U and LDA+dynamical mean-field theory (DMFT).
The 4d A2Mo2O7 with relatively small A-site ionic radii, e.g., Y, are insulating and exhibit a spin-glass transition instead of conventional long-range ordering. Although the compounds have been known as typical geometrically frustrated spin-glass systems, the nature of the spin-glass phase remains to be clarified. Using LDA+U calculations, we reveal that the ground state of the compounds is a Mott insulating state of a composite object of spin and orbital. The magnetic frustration is tightly connected with the competition in the orbital sector through SOC [1]. In our phase diagram, the system is close to a two-in/two-out “spin-ice” magnetically disordered phase. A recent detailed analysis of local structure of Y2Mo2O7 supports the existence of the spin-ice correlations [2].
Second, we study strong electron correlation effects in the iridates A2Ir2O7 (A=Pr, Nd, Y, etc.) using the state of the art LDA+DMFT calculations [3]. Their magnetic and electronic states can be tuned by chemical substitution, pressure, and temperature. Recently, a recent LDA+U study indicates that a Weyl semimetallic phase is the ground state of some compounds in this series [4]. We map out the phase diagram with respect to onsite Coulomb interaction and temperature. We predict non-Fermi liquid behavior in doped compounds. The Weyl semimetallic phase is found to be unstable against strong correlation effects.
[1] H. Shinaoka, Y. Motome, T. Miyake and S. Ishibashi, Phys. Rev. B 88, 174422 (2013).
[2] P. M. M. Thygesen et al., arXiv:1603.03087.
[3] H. Shinaoka, S. Hoshino, M. Troyer and P. Werner, Phys. Rev. Lett. 115, 156401 (2015).
[4] X. Wan et al., Physical Review B 83, 205101 (2011). 联系人： Lei Wang