PSTEP: Project for solar-terrestrial environment prediction

Kusano, Kanya*; Ichimoto, Kiyoshi*; Ishii, Mamoru*; Miyoshi, Yoshizumi*; Yoden, Shigeo*; Akiyoshi, Hideharu*; Asai, Ayumi*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Goto, Tadanori*; et al.

Earth, Planets and Space (Internet), 73(1), p.159_1 - 159_29, 2021/12

https://doi.org/10.1186/s40623-021-01486-1

The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.

Influence of lattice structure on multipole interactions in non-Kramers doublet systems

Kubo, Katsunori; Hotta, Takashi*

Physical Review B, 95(5), p.054425_1 - 054425_6, 2017/02

https://doi.org/10.1103/PhysRevB.95.054425

Multipole as -electron spin-charge density in filled skutterudites

Hotta, Takashi

Journal of the Physical Society of Japan, 77(Suppl.A), p.96 - 101, 2008/00

https://doi.org/10.1143/JPSJS.77SA.96

In general, spin-orbit coupling is strong for electrons and then, spin-orbital complex degrees of freedom, i.e., , become active in -electron compounds. Due to recent advances in experimental techniques, multipole ordering phenomena have been actually observed in filled skutterudites with high symmetry. To understand multipole ordering, phenomenological theory has been developed and several experimental results could be explained, but it is necessary to make more effort to clarify microscopic aspects of multipole degrees of freedom in -electron systems. Here I propose to define -electron multipole as spin-charge density operator in one-body form from the viewpoint of multipole expansion of electron density in electromagnetism. Then, I analyze a seven-orbital Anderson model by using a numerical renormalization group method. I discuss possible multipole state of heavy lanthanide filled skutterudites.

Multipoles in -Pu

Hotta, Takashi

Journal of Alloys and Compounds, 444-445, p.162 - 167, 2007/10

https://doi.org/10.1016/j.jallcom.2006.11.028

In order to develop microscopic theories of magnetism and superconductivity in -electron compounds, we have proposed the construction of an -electron model on the basis of a - coupling scheme. Using this model, we have explained spin and orbital structure of UMGa and NpMGa. Recently, octupole ordering in NpO has been also understood from the microscopic viewpoint. Encouraged by such successes of the j-j coupling model in actinide materials, we attempt to understand magnetism and superconductivity of Pu and PuMGa. We focus on a key role of 5f orbital state for the appearance of superconductivity in PuMGa and the absence of magnetism in -Pu. We discuss multipoles as spin-orbital complex degrees of freedom.

Multipole state of heavy lanthanide filled skutterudites

Hotta, Takashi

Journal of the Physical Society of Japan, 76(8), p.083705_1 - 083705_5, 2007/08

https://doi.org/10.1143/JPSJ.76.083705

We discuss multipole properties of filled skutterudites containing heavy lanthanide Ln from a microscopic viewpoint on the basis of a seven-orbital Anderson model. For Ln=Gd, in contrast to naive expectation, quadrupole moments remain in addition to main dipole ones. For Ln=Ho, we find an exotic state governed by octupole moment. For Ln=Tb and Tm, no significant multipole moments appear at low temperatures, while for Ln=Dy, Er, and Yb, dipole and higher-order multipoles are dominant. We briefly discuss possible relevance of these multipole states with actual materials.

Superconductivity in f-electron systems controlled by crystalline electric fields

Kubo, Katsunori; Hotta, Takashi

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.572 - 574, 2007/03

To elucidate the mechanism and controlling parameter of the superconductivity in CeTIn (T=Co, Rh, and Ir), we study an -electron model based on a - coupling scheme on a square lattice. In this study, we consider electrons with total angular momentum =5/2. These states split into one and two doublets under a tetragonal CEF. By choosing appropriate CEF potential, we can control the CEF wave-functions without changing the level splitting. Although the Fermi surface does not change so much as long as the splitting is fixed, the ground state changes depending on the CEF wave-function among paramagnetic, antiferromagnetic, and -wave superconducting states. Thus, in addition to the Fermi-surface topology and the carrier density, the wave-function of the CEF state is an important ingredient to control the appearance of superconductivity in such systems. We will discuss possible relevance of our scenarioto the superconductivity in CeTIn.

Relativistic band-structure calculations for electronic properties of actinide dioxides

Maehira, Takahiro*; Hotta, Takashi

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.754 - 756, 2007/03

https://doi.org/10.1016/j.jmmm.2006.10.127

Energy band structures of actinide dioxides AnO (An=Th, U, Np, and Pu) are investigated by a relativistic linear augmented-plane-wave method with the exchange-correlation potential in a local density approximation (LDA). It is found in common that the energy bands in the vicinity of the Fermi level are mainly due to the hybridization between actinide 5f and oxygen 2p electrons. By focusing on the crystalline electric field states, we point out the problem in the application of the LDA to AnO.

Kondo effect in an electron system with dynamical Jahn-Teller impurity

Hotta, Takashi

Journal of the Physical Society of Japan, 76(2), p.023705_1 - 023705_5, 2007/02

https://doi.org/10.1143/JPSJ.76.023705

We investigate how Kondo phenomenon occurs in the Anderson model dynamically coupled with local Jahn-Teller phonons. It is found that the total angular moment composed of electron pseudo-spin and phonon angular moments is screened by conduction electrons. Namely, phonon degrees of freedom essentially contribute to the formation of singlet ground state. A characteristic temperature of the Kondo effect due to dynamical Jahn-Teller phonons is explained by an effective - Hamiltonian with anisotropic exchange interaction obtained from the Jahn-Teller-Anderson model in a non-adiabatic region.

Effective crystalline electric field potential in a - coupling scheme

Hotta, Takashi; Harima, Hisatomo

Journal of the Physical Society of Japan, 75(12), p.124711_1 - 124711_5, 2006/12

https://doi.org/10.1143/JPSJ.75.124711

We propose a systematic method to include effectively a crystalline electric field (CEF) potential into an -electron model on the basis of a - coupling scheme by the expansion in terms of , where is a spin-orbit interaction. When we correctly take into account the corrections in the order of in addition to the CEF terms and Coulomb interactions which remain in the limit of =, the CEF energy levels of an coupling scheme can be quantitatively reproduced even in the - coupling scheme. As a potential application of our modified - coupling scheme, we briefly discuss the CEF energy levels of filled skutterudite compound with symmetry.

Multipole correlations in low-dimensional -electron systems

Onishi, Hiroaki; Hotta, Takashi

Journal of the Physical Society of Japan, 75(Suppl.), p.266 - 269, 2006/08

In order to clarify multipole correlations in -electron systems, we investigate a one-dimensional -electron model based on a - coupling scheme by exploiting a density-matrix renormalization group method. We discuss the effect of a crystalline electric field and the dependence on the change of -electron numbers in detail.