Phase transition of the three-dimensional chiral Ginzburg-Landau model -- search for the chiral phase

Nature of the phase transition of regularly frustrated vector spin systems in three dimensions is investigated based on a Ginzburg-Landau-type effective Hamiltonian. On the basis of the variational analysis of this model, Onoda et al recently suggested the possible occurrence of a chiral phase, where the vector chirality exhibits a long-range order without the long-range order of the spin [Phys. Rev. Lett. 99, 027206 (2007)]. In the present paper, we elaborate their analysis by considering the possibility of a first-order transition which was not taken into account in their analysis. We find that the first-order transition indeed occurs within the variational approximation, which significantly reduces the stability range of the chiral phase, while the chiral phase still persists in a restricted parameter range. Then, we perform an extensive Monte Carlo simulation focusing on such a parameter range. Contrary to the variational result, however, we do not find any evidence of the chiral phase. The range of the chiral phase, if any, is estimated to be less than 0.1% in the temperature width.Comment: 19 pages, 17 figure

Multiple-q states and skyrmion lattice of the triangular-lattice Heisenberg antiferromagnet under magnetic fields

Ordering of the frustrated classical Heisenberg model on the triangular-lattice with an incommensurate spiral spin structure is studied under magnetic fields by means of a mean-field analysis and a Monte Carlo simulation. Several types of multiple-q states including the "skyrmion-lattice" state is observed in addition to the standard single-q state. In contrast to the Dzyaloshinskii-Moriya interaction driven system, the present model allows both skyrmions and anti-skyrmions, together with a new thermodynamic phase where skyrmion and anti-skyrmion lattices form a domain state.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let

Multiple-qq states of the J1J_1-J2J_2 classical honeycomb-lattice Heisenberg antiferromagnet under magnetic fields

Motivated by the recent theoretical study by Okubo $et \ al$ [Phys. Rev. Lett. ${\bf 108}$, 017206 (2012)] on the possible realization of the frustration-induced $symmetric$ skyrmion-lattice state in the $J_1$-$J_2$ (or $J_1$-$J_3$) triangular-lattice Heisenberg model without the Dzyaloshinskii-Moriya interaction, we investigate the ordering of the classical $J_1$-$J_2$ honeycomb-lattice Heisenberg antiferromagnet under magnetic fields by means of a Monte Carlo simulation, a mean-field analysis and a low-temperature expansion. The model has been known to have an infinite ring-like degeneracy in the wavevector space in its ground state for $1/6<J_2/J_1<0.5$, in distinction with the triangular-lattice model. As reported by Okumura $et \ al$ [J. Phys. Soc. Jpn. ${\bf 79}$, 114705 (2010)], such a ring-like degeneracy gives rise to exotic spin liquid states in zero field, $e.g$, the "ring-liquid" state and the "pancake-liquid" state. In this paper, we study the in-field ordering properties of the model paying attention to the possible appearance of exotic multiple-$q$ states. Main focus is made on the $J_2/J_1=0.3$ case, where we observe a rich variety of multiple-$q$ states including the single-$q$, double-$q$ and triple-$q$ states. While the skyrmion-lattice triple-$q$ state observed in the triangular-lattice model is not realized, we instead observe an exotic double-$q$ state consisting of meron/antimeron lattice textures.Comment: 17+8 pages, 19+3 figure

Automation and crew time saving in the space experiment

We describe preliminary results of the feasibility study of automation and crew workload saving in space experiments on the space station. Some functions have been studied that can be automated within a single rack and without major impact to the development process and costs. In addition, we assume the following premises: (1) applicable as the second generation apparatuses; (2) maximum reduction of the crew workload; and (3) automation between racks including storage. Four apparatuses have been selected as the study case; results for three are summarized

Spectral detection of grazing degradation in the Xilingol Steppe, Inner Mongolia

In order to detect the grazing degradation of steppe vegetation, spectral reflectance was measured using a portable spectral radiometer in the Xilingol steppe, Inner Mongolia. There is only one main drinking place for animals, which is supplied by a water tank at the center of Branch No.4 site-00. In addition to the measurement of surface reflectance, vegetation surveys were carried out involving floristic composition and plant growth parameters as a function of the distance from site-00 at every 1-km interval until the 5-km point. It becomes clear that the effects of grazing on vegetation and soil mitigated according to the distance from site-00. Negative plant indicators of grazing intensity such as Stipa grandis and Filifolium sibiricum increased in dominance with distance from site-00, whereas positive indicators of grazing intensity, such as Cleistogenens squarrosa and Agropyron cristatum, decreased in dominance. Changes in growth parameters along the environmental gradients were reflected on NDVI (Normalized Difference Vegetation Index), in which NDVI was positively correlated with the aboveground biomass (r=0.77, P<0.001), plant height (r=0.69, P<0.001) and coverage (r=0.89, P<0.001), respectively. These results suggested that a spectral vegetation index is effective in the detection of the degradation of grazing grassland in a non-destruction way.Original Pape