Ⅲ-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 51 (2018)

Eﬀect of Supercell Calculation on Muon Sites in La2 CuO4
M. R. Ramadhan,∗1,∗3 M. I. Mohamed-Ibrahim,∗2 S. Sulaiman,∗2 and Watanabe∗1,∗2,∗3The muon spin relaxation (µSR) is a powerful toolfor investigating the electronic states of Cu-based highTc superconducting oxides. It is important to understand the µSR data of the base material, La2 CuO4(LCO), especially in the magnetically ordered states,
as it provides an insight to the other phases of this material. Although the µSR data can provide informationon the local magnetic ﬁelds at the muon site, it is not
so easy to obtain the details of the electronic structure
surrounding the muons, which is the origin of the local
ﬁelds at the muon site. This is because, we need tohave the exact information on where the muon is located inside the material. Several attempts have been
made to tackle this problem in the past.1–3) However,a uniﬁed method to obtain the muon positions inside
the material has not yet been established.
In this study, the eﬀect of supercell calculation onmuon sites inside La2 CuO4 system were investigated.
DFT method was applied to determine possible muonsites in LCO. To account for the correlation energy ofthe strongly localized copper 3d orbitals, we employed
Hubbard correction within our calculations (DFT +U) with the Hubbard parameter U = 10 eV, which
opens the gap in the Fermi level of the system (2.6 eV)showing an insulating nature as predicted in the experiments. Three minimum potentials were found at positions near the apical and planar oxygens, which correspond well to the µSR experimental results shownin Fig. 1. These three positions (M1, M2, and M3)
were set to be the initial muon positions on a 4 × 2 × 4
LCO supercell for subsequent calculations in order toinclude the eﬀect of local deformations caused by thepresence of muons inside the material, as the inclusionof lattice deformations were found to be important tosimulate the muon presence in the system realistically.
The local deformations induced by muons on each site
is shown in Fig. 2. From our current results, it wasobserved that M1 and M3 relaxation will aﬀect theposition of Cu inside the octahedra and the nearest
planar oxygen. M2 relaxation only aﬀects the nearest planar oxygen in the system without shifting theCu atoms. It was also observed from our calculationthat the magnetic moment on the nearest Cu atom ischanged by the presence of a muon. The initial value of
0.7 µB in the case without the muon system is slightly
lowered by the presence of muon. However, these local
deformations do not change the insulating and antiferromagnetic nature for our material.

Fig. 1. Three minimum positions observed by the DFT
method (muon positions are enlarged for clarity).

Fig. 2. Comparison of CuO6 octahedra after relaxation (a)Without muon (b) M1 (c) M2 (d) M3.

References∗1∗2∗31) R. Saito, et al., Physica (Utrecht) C 185–189, 1217(1991).
2) S. B. Sulaiman, et al., Phys. Rev. B 49, 9879 (1994).
3) H. U. Suter, et al., Physica (Utrecht) B 326, 329 (2003).

Department of Physics, Universitas Indonesia
School of Distance Education, Universiti Sains Malaysia
RIKEN Nishina Center- 197 -