Predicting stable crystal structures only from information on the molecular shape and intermolecular interactions is a very difficult problem of modern physics. We have used computers to study the crystal structures of water under various thermodynamic conditions and found several new ice structures. This is an interesting area of research involving a variety of unsolved problems.
We show that a class of organic antiferromagnets with checker-plate type molecular arrangements, such as a typical strongly correlated system κ-(BEDT-TTF)2 X, can serve as a new type of spin current generator, even without relying on the atomic spin-orbit coupling. The mechanism relies on a peculiar spin splitting of the energy bands and a real space anisotropy of the magnon or electron transfers owing to another type of “spin-orbit coupling”. This is activated by glide symmetry breaking of the molecular arrangement due to the antiferromagnetic ordering. Based on the multi-site Hubbard model and the effective Heisenberg model, we analyze the spin current transport properties. When a thermal gradient is applied to the antiferromagnetic insulating state, the up- and down-spin magnons drift to opposite ways due to the anisotropic transfer integrals, resulting in a spin current perpendicular to the thermal gradient. In the doped antiferromagnetic metallic phase, a similar spin current generation occurs by replacing the magnons and the external field to electrons and an electric field. We find that the spin current conductivities are given by symmetric tensors, in stark contrast to the conventional spin Nernst and spin Hall effects described by antisymmetric tensors. Our findings provide another route to generate a spin current and open a new field of spintronics based on organic magnets.
Weak gravitational lensing effect due to the large-scale structure in the Universe, i.e., cosmic shear, provides a unique probe to trace the growth of the total matter distribution including invisible dark matter. Subaru Hyper Suprime-Cam (HSC) project is a wide and deep galaxy imaging survey and enables us to perform a precision cosmological study from the cosmic shear measurement. Here I present a first cosmological result from cosmic shear power spectrum using HSC data.
Magnetic structures of molecular Mott insulators X[Pd (dmit)2 ]2( X=Me4P, Me4Sb), of which electronic states are located near quantum spin liquid, are demonstrated by 13C NMR. Antiferromagnetic spectra show two distinct magnetic moments within each Pd (dmit)2 molecule, which cannot be described by single band dimer-Mott model and requires intramolecular electronic correlation. This unconventional fragmentation of S=1/ 2 electron spin with strong quantum fluctuation is presumably caused by nearly degenerated intramolecular multiple orbitals, and shares a notion of quantum liquids where electronic excitations are fractionalized and S=1/ 2 spin is no longer an elementary particle.
Scintillation detectors with a fast response are widely required for high-energy photon detection. Inorganic crystals doped with rare-earth ions have scintillation decay time constants down to several tens of nanoseconds. To achieve much shorter scintillation decay, we developed several types of scintillators. Fast scintillation owing to core holes or self-trapped excitons have been achieved in insulator crystals. Fast and efficient scintillation of quantum-confined Wannier excitons was obtained in self-organized quantum well structure in organic-inorganic layered hybrid compounds. For plastic scintillators, their disadvantage for high-energy photon detection, i.e., low atomic numbers of the constituent elements resulting in low interaction probability and detection efficiency, has been overcome by addition of heavy metal oxide nanoparticles.