A Mechanism of Spin-Triplet Superconductivity in Hubbard Model on Triangular La ttice: Application to UNi_2Al_3

We discuss the possibility of spin-triplet superconductivity in a two-dimensional Hubbard model on a triangular lattice within the third-order perturbation theory. When we vary the symmetry in the dispersion of the bare energy band from D_2 to D_6, spin-singlet superconductivity in the D_2-symmetric system is suppressed and we obtain spin-triplet superconductivity in near the D_6-symmetric system. In this case, it is found that the vertex terms, which are not included in the interaction mediated by the spin fluctuation, are essential for realizing the spin-triplet pairing. We point out the possibility that obtained results correspond to the difference between the superconductivity of UNi_2Al_3 and that of UPd_2Al_3.Comment: 11pages, 5figure

Kondo screening of a high-spin Nagaoka state in a triangular quantum dot

We study transport through a triangle triple quantum dot connected to two noninteracting leads using the numerical renormalization group (NRG). The triangle has a high-spin ground state of S=1 caused by a Nagaoka ferromagnetism, when it is isolated and has one extra electron introduced into a half-filling. The results show that the conduction electrons screen the local moment via two separate stages with different energy scales. The half of the S=1 is screened first by one of the channel degrees, and then at very low temperature the remaining half is fully screened to form a Kondo singlet. The transport is determined by two phase shifts for quasi-particles with even and odd parities, and then a two-terminal conductance in the series configuration is suppressed $g_{\rm series} \simeq 0$, while plateau of a four-terminal parallel conductance reaches a Unitary limit value $g_{\rm parallel} \simeq 4e^2/h$ of two conducting modes.Comment: 2pages, 2figures: fig1 is revised to show a narrow dip found in the series conductanc

Transport through a double quantum dot with interdot repulsion

We study transport through a double quantum dot with interdot hopping $t$, intradot repulsion $U$ and interdot repulsion $U^{\prime}$, using the numerical renormalization group (NRG) method. At half-filling, the conductances in two-terminal series and four-terminal parallel configuration are calculated via two phase shifts for quasi-particles of double quantum dot connected to two noninteracting leads with hybridization strength $\Gamma$. For small values of $t/\Gamma$ and $U^{\prime}/U$, conductance in the two-terminal series configuration is suppressed to almost zero. In this region, plateau of conductance in the four-terminal parallel configuration appears and almost reaches a unitary limit value $4e^{2}/h$ of two conducting modes. For large values of $t/\Gamma$ or $U^{\prime}/U$, both conductances are suppressed to almost zero. The conductance in the two-terminal series configuration almost reaches a unitary limit value $2e^{2}/h$ only around cross-over regions of electron-configuration in double quantum dot. Through the behavior of the local charge and some thermodynamic quantities, we discuss the relation between transport and electron-configuration.Comment: To be published in "Journal of Physics: Condensed Matter

Numerical renormalization group approach to a quartet quantum-dot array connected to reservoirs:gate-voltage dependence of the conductance

The ground-state properties of quartet quantum-dot arrays are studied using the numerical renormalization group (NRG) method with a four-site Hubbard model connected to two non-interacting leads. Specifically, we calculate the conductance and local charge in the dots from the many-body phase shifts, which can be deduced from the fixed-point eigenvalues of NRG. As a function of the on-site energy $\epsilon_d$ which corresponds to the gate voltage, the conductance shows alternatively wide peak and valley. Simultaneously, the total number of electrons $N_{\rm el}$ in the four dots shows a quantized stair case behavior due to a large Coulomb interaction $U$. The conductance plateaus of the Unitary limit emerging for odd $N_{\rm el}$ are caused by the Kondo effect. The valleys of the conductance emerge for even $N_{\rm el}$, and their width becomes substantially large at half-filling. It can be regarded as a kind of the Mott-Hubbard insulating behavior manifesting in a small system. These structures of the plateaus and valleys become weak for large values of the hybridization strength $\Gamma$ between the chain and leads. We also discuss the parallel conductance for the array connected to four leads.Comment: 8 pages, 9 figure

Gate-voltage dependence of Kondo effect in a triangular quantum dot

We study the conductance through a triangular triple quantum dot, which are connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occurring.Comment: 4 pages, 4 figs: typos just below (4) are corrected, results are not affecte

Small-clawed otters (Aonyx cinereus) in Indonesian rice fields: latrine site characteristics and visitation frequency

金沢大学環日本海域環境研究センターLatrine sites, or areas where otters scent-mark and deposit feces, are a habitat feature that serve an important role in communication for many otter species. The small-clawed otter (Aonyx cinereus) inhabits both natural and rice field landscapes in Southeast Asia. However, latrine site use by small-clawed otters in rice field landscapes is largely unknown. Based on a 53-week field survey and landscape analyses, we investigated latrine site use by small-clawed otters in rice field landscapes in West Sumatra, Indonesia. Using land use and/or local environmental variables as predictors, we performed generalized linear model analyses to explain the spatial patterns of latrine site occurrence and otter visitation frequency to latrine sites. We determined that small-clawed otters use some latrine sites repeatedly over time; 10 latrine sites were still in use more than 7 years after their initial discovery. Generalized linear model analyses revealed that an intermediate number of rice field huts was the single most important predictor of latrine site occurrence, whereas distance to the nearest settlement, distance to the river, and mean water depth of the rice field adjacent to the latrine site were important predictors of otter visitation frequency to latrine sites. These results indicate that the latrine site preferences of small-clawed otters in rice field landscapes are strongly associated with intermediate levels of rice farming activities. Indonesian rice fields are being degraded or disappearing at an accelerated rate because of land conversion and modernization of agriculture. We emphasize an urgent need for design and implementation of otter-friendly rice farming to conserve small-clawed otters. © 2017 The Ecological Society of JapanEmbargo Period 12 month

Possible spin triplet superconductivity in Nax_xCoO2⋅y_{2}\cdot yH2_{2}0

Combining symmetry based considerations with inputs from available experimental results, we make the case that a novel spin-triplet superconductivity triggered by antiferromagnetic fluctuations may be realized in the newly discovered layered cobaltide Na$_x$CoO$_{2}\cdot y$H$_2$O. In the proposed picture, unaccessable via resonating-valence-bond physics extrapolated from half-filling, the pairing process is similar to that advanced for Sr$_{2}$RuO$_4$, but enjoys a further advantage coming from the hexagonal structure of the Fermi-surface which gives a stronger pairing tendency.Comment: 4 page