Effective Hamiltonian of Three-orbital Hubbard Model on Pyrochlore Lattice: Application to LiV_2O_4

We investigate heavy fermion behaviors in the vanadium spinel LiV_2O_4. We start from a three-orbital Hubbard model on the pyrochlore lattice and derive its low-energy effective Hamiltonian by an approach of real-space renormalization group type. One important tetrahedron configuration in the rochlore lattice has a three-fold orbital degeneracy and spin S=1, and correspondingly, the effective Hamiltonian has spin and orbital exchange interactions of Kugel-Khomskii type as well as correlated electron hoppings. Analyzing the effective Hamiltonian, we find that ferromagnetic double exchange processes compete with antiferromagnetic superexchange processes and various spin and orbital exchange processes are competing to each other. These results suggest the absence of phase transition in spin and orbital spaces down to very low temperatures and their large fluctuations in the low-energy sector, which are key issues for understanding the heavy fermion behavior in LiV_2O_4.Comment: 26 pages, 26 figure

Bipolaron-SO(5) Non-Fermi Liquid in a Two-channel Anderson Model with Phonon-assisted Hybridizations

We analyze non-Fermi liquid (NFL) properties along a line of critical points in a two-channel Anderson model with phonon-assisted hybridizations. We succeed in identifying hidden nonmagnetic SO(5) degrees of freedom for valence-fluctuation regime and analyze the model on the basis of boundary conformal field theory. We find that the NFL spectra along the critical line, which is the same as those in the two-channel Kondo model, can be alternatively derived by a fusion in the nonmagnetic SO(5) sector. The leading irrelevant operators near the NFL fixed points vary as a function of Coulomb repulsion U; operators in the spin sector dominate for large U, while those in the SO(5) sector do for small U, and we confirm this variation in our numerical renormalization group calculations. As a result, the thermodynamic singularity for small U differs from that of the conventional two-channel Kondo problem. Especially, the impurity contribution to specific heat is proportional to temperature and bipolaron fluctuations, which are coupled electron-phonon fluctuations, diverge logarithmically at low temperatures for small U.Comment: 16 pages, 4 figures, 3 table

When the Natural Toxin Concentration in Crotalaria Increase in Japan?

A green manure crop, sunn hemp (Crotalaria juncea L.), legumes, has a nematode-suppressive effect. It is also used as feed in India. However, it is not used as feed in Japan because it contains natural toxins: Pyrrolizidine alkaloids (PAs). PAs has the negative effects for not only livestock but also human health. The PAs, which are abundant in sunn hemp seeds and which are contained only slightly in leaves and stems. Therefore, if sunn hemp harvested before flowering, then no poison problem is posed by PAs. However, if it is harvested at the podding stage, a poisonous concentration of PAs occurs. For increasing yield, it is necessary to harvest it as late as possible. For obtaining both safe feed without PAs and increase in yield, we clarify when the PAs concentration will be increased from flowering to podding. We cultivated the varieties of crotalaria which are distributed currently in Japan and USA for green manure during July–October 2019. We observed the period from flowering to podding. We harvested bud, flower, immature pods (under 15 mm) and pods. Then one PAs component that is abundant in seeds, the trichodesmine content, was analyzed. In the case of late July seeding, the first flowers blossomed in about 50 days after seeding. No difference was found between varieties. The flowers wilted about two days after flowering. The ovaries grew to immature buds about five days after flowering. Trichodesmine in seeded seeds was greater than 1000 mg/kg. That in buds, flowers, and immature pods was less than 1.0 mg/kg. Also, that in pods (over 15 mm length) was greater than 10 mg/kg. If harvested within one week from the first flower blooming, then sunn hemp can be used as forage with low PAs concentration

Anisotropic magnetic fluctuations in the ferromagnetic superconductor UCoGe studied by angle-resolved ^{59}Co NMR

We have carried out direction-dependent ^{59}Co NMR experiments on a single crystal sample of the ferromagnetic superconductor UCoGe in order to study the magnetic properties in the normal state. The Knight shift and nuclear spin-lattice relaxation rate measurements provide microscopic evidence that both static and dynamic susceptibilities are ferromagnetic with strong Ising anisotropy. We discuss that superconductivity induced by these magnetic fluctuations prefers spin-triplet pairing state.Comment: 4 pages, 4 figure

Ozone decomposition in four types of spouted beds, with or without a draft-tube

ArticleJOURNAL OF CHEMICAL ENGINEERING OF JAPAN. 40(9): 761-764 (2007)journal articl

Magnetic properties of the Ag-In-rare-earth 1/1 approximants

We have performed magnetic susceptibility and neutron scattering measurements on polycrystalline Ag-In-RE (RE: rare-earth) 1/1 approximants. In the magnetic susceptibility measurements, for most of the RE elements, inverse susceptibility shows linear behaviour in a wide temperature range, confirming well localized isotropic moments for the RE$^{3+}$ ions. Exceptionally for the light RE elements, such as Ce and Pr, non-linear behaviour was observed, possibly due to significant crystalline field splitting or valence fluctuation. For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the field-cooled and zero-field-cooled susceptibility at $T_{\rm f} = 3.7$~K, suggesting a spin-glass-like freezing. On the other hand, neutron scattering measurements detect significant development of short-range antiferromagnetic spin correlations in elastic channel, which accompanied by a broad peak at $\hbar\omega = 4$~meV in inelastic scattering spectrum. These features have striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the short-range spin freezing behaviour is due to local high symmetry clusters commonly seen in both the systems.Comment: 14 pages, 12 figure

A Mass Function Constraint on Extrasolar Giant Planet Evaporation Rates

The observed mass function for all known extrasolar giant planets (EGPs) varies approximately as M^{-1} for mass M between 0.2 Jupiter masses (M_J) and 5 M_J. In order to study evaporation effects for highly-irradiated EGPs in this mass range, we have constructed an observational mass function for a subset of EGPs in the same mass range but with orbital radii <0.07 AU. Surprisingly, the mass function for such highly-irradiated EGPs agrees quantitatively with the M^{-1} law, implying that the mass function for EGPs is preserved despite migration to small orbital radii. Unless there is a remarkable compensation of mass-dependent orbital migration for mass-dependent evaporation, this result places a constraint on orbital migration models and rules out the most extreme mass loss rates in the literature. A theory that predicts more moderate mass loss gives a mass function that is closer to observed statistics but still disagrees for M < 1 M_J.Comment: accepted by Astrophys. J. Letters on 1 February 200

Charged particle display

An optical shutter based on charged particles is presented. The output light intensity of the proposed device has an intrinsic dependence on the interparticle spacing between charged particles, which can be controlled by varying voltages applied to the control electrodes. The interparticle spacing between charged particles can be varied continuously and this opens up the possibility of particle based displays with continuous grayscale.Comment: typographic errors corrected in Eqs (37) and (39); published in Journal of Applied Physics; doi:10.1063/1.317648