Recently, a research team identified two possible magnetic interaction scenarios in Sr2IrO4, which marked a new progress in the study of the magnetic properties in this unique 5d correlated system.
The main team members are Dr. ZHANG Guoren from Institute of Solid State Physics (ISSP), Hefei Institutes of Physical Science (HFIPS), Chinese Academy of Sciences and Prof. Eva Pavarini from Jülich Research Centre, Germany.
"We investigated the magnetic couplings in Sr2IrO4 in the Mott-insulating picture by combing different theories” said ZHANG Guoren, “and identified two possible scenarios of them."
After determining the form of the jeff=1/2 pseudospin via the local-density-approximation + dynamical mean-field theory approach, they studied the magnetic interactions in the strong-to-intermediate coupling regime.
The superexchange pseudospin tensors was calculated up to fourth order, and their dependence on the screened Coulomb interaction integrals U and J and crystal-field splitting was analyzed. Due to term cancellations, the experimental nearest-neighbor coupling is reasonably well reproduced for a whole range of realistic (U,J) values. The team displayed that increasing the Hund’s rule coupling J (within the window of realistic values) can lead to large fourth-order contributions, which could explain the ferromagnetic next-nearest-neighbor coupling extracted from the spin-wave dispersion.
This regime is characterized by a sizable ring exchange K. For (U,J) values that yield a Mott insulator with a half-filled jeff =1/2 state, but fourth-order terms remain minor even if the gap is small.
"The electronic properties of Sr2IrO4 and La2CuO4 are similar,” said ZHANG, “so it can help to understand the mechanism for superconductivity in doped La2CuO4.”
This work could also shed light on the correct modelization for other systems, such as the bilayer Sr3Ir2O7.
Link to paper: Magnetic superexchange couplings in Sr2IrO4
FIG. 1. Total nearest- (left) and next-nearest- (right) neighbor couplings as a function of screened Coulomb interaction integrals crystal-field splitting. (Image by ZHU Damei)
Contact:
ZHAO Weiwei
Hefei Institutes of Physical Science (http://english.hf.cas.cn/)
Email: annyzhao@ipp.ac.cn