Orbital ordering in low-moment ground-state of parent compounds in iron-based superconductors

Machida, Masahiko; Nakamura, Hiroki

Journal of the Physical Society of Japan, 80(Suppl.B), p.SB022_1 - SB022_4, 2011/12

https://doi.org/10.1143/JPSJS.80SB.SB022

Since the discovery of the iron-based superconductor, a large discrepancy between experimental observations and first-principles calculations in the magnetic moment of the antiferromagnetic state of the parent compounds has been intensively debated. The observed moment values are about 3 to 5 times smaller than those of the calculation although there is a variety of the difference depending on the materials. Very recently, an interesting calculation data fully reproducing the observed low moment has been suggested by F. Cricchio et al., who performed first-principles calculations using a LDA+U scheme. In this study, we suggest that the new state is a possible candidate to well explain the other data, e.g., strong anisotropy in spatial patterns measured by STM and magnetic excitations found by neutron scattering. Furthermore, we compare the result with other theoretical works reproducing similar low moment in terms of orbital ordering.

Theoretical analysis for inelastic neutron scattering on BaFe(As,P) using realistic three-dimensional 10-orbital tight-binding model

Nagai, Yuki; Nakamura, Hiroki; Suzuki, Katsuhiro*; Usui, Hidetomo*; Kuroki, Kazuhiko*; Machida, Masahiko

Journal of the Physical Society of Japan, 80(Suppl.B), p.SB021_1 - SB021_4, 2011/12

https://doi.org/10.1143/JPSJS.80SB.SB021

We calculate spin susceptibility on the basis of the multi-orbital random-phase approximation with use of the realistic three-dimensional 10-orbital tight-binding model for an iron-based superconductor BaFe(As,P) which seems to have gap-nodes. We show that the shape of nodes on the Fermi surface for BaFe(As,P) is distinguishable according to inelastic neutron scattering experiments. Our results are consistent with the recent neutron scattering experiments for BaFe(As,P) with Tc = 30 K.

Phonon spectra of PrFeAsO via inelastic X-ray scattering

Fukuda, Tatsuo; Baron, A. Q. R.*; Nakamura, Hiroki; Shamoto, Shinichi; Ishikado, Motoyuki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.

Journal of the Physical Society of Japan, 80(Suppl.B), p.SB015_1 - SB015_4, 2011/01

https://doi.org/10.1143/JPSJS.80SB.SB015

We have investigated phonons of PrFeAsO using high-resolution inelastic X-ray scattering and calculations. Extensive measurements show that there are some changes in phonon spectra with temperature and/or doping. However, we compare our data with several calculations and find that the experimentally observed changes are much smaller than differences between the experiment. data and the calculations. Agreement is improved if magnetism is included in the calculations. However, still in disagreement even in the parent sample below T. We consider several modifications of the calculations. The best agreement is obtained from modifying the nonmagnetic calculation. by softening only the in-plane nearest-neighbor Fe-As force constant. Fluctuating magnetism may be a partial explanation for the failure of the calculations, but seems incomplete in the face of the similarity of the measured phonon response in all the systems investigated including those known to have static magnetism.

Numerical study on the spin dynamics of the Kagome lattice antiferromagnet

Sakai, Toru

no journal, , 

The Kagome lattice antiferromagnet is one of interesting frustrated spin systems. Particularly since several candidate materials of the S=1/2 quantum Kagome lattice antiferromagnet were synthesized, the experimental and theoretical studies have been accelerated very much. However, the spin dynamics of the Kagome lattice antiferromagnet is still unclear, although the neutron scattering, nuclear spin resonance, electron spin resonance etc. have already been performed for those materials. In order to solve the spin dynamics theoretically, we investigated some anisotropic Kagome lattice by the numerical diagonalization of finite-size clusters. As a result, a mechanism of the double peak structure in the temperature dependence of the specific heat was clarified. In addition we found an interesting field induced phenomenon, so called the magnetization ramp. We also calculate the dynamical spin correlation to compare with the neutron scattering experiment.

Structural analyses on iron-based superconductors PrFeAsO and PrFeAsOF

Kodama, Katsuaki; Ishikado, Motoyuki; Esaka, Fumitaka; Iyo, Akira*; Eisaki, Hiroshi*; Shamoto, Shinichi

no journal, , 

Effect of magnetic field in non-centrosymmetric heavy-fermion superconductor CePtSi

Kaneko, Koji; Stockert, O.*; Skoulatos, M.*; Schneidewind, A.*; Takeuchi, Tetsuya*; Matsuda, Tatsuma; Haga, Yoshinori; Settai, Rikio*; Onuki, Yoshichika; Metoki, Naoto

no journal, , 

AMATERAS; Cold-neutron disk-chopper spectrometer

Nakajima, Kenji; Kawamura, Seiko; Kikuchi, Tatsuya; Nakamura, Mitsutaka; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Aizawa, Kazuya; Suzuya, Kentaro; Shibata, Kaoru; et al.

no journal, ,