arXiv subjects

Yuto Yokoyama

Publications and source records attributed to Yuto Yokoyama.

21 records · Page 2Linked to original sources

arXiv2018

Spin nematics next to spin singlets

We provide a route to generate nematic order in a spin-1/2 system. Unlike the well-known magnon-binding mechanism, our spin nematics requires neigher the frustration effect nor a spin polarization in a high field or in the vicinity of a ferromagnet, but instead appears next to the spin singlet phase. We start from a state consisting of a quantum spin-1/2 singlet dimer placed on each site of a triangular lattice, and show that inter-dimer ring exchange interactions efficiently dope the SU(2) triplets that itinerate and interact, easily driving a stable singlet state to either Bose Einstein condensates or a triplet crystal, some hosting a spin nematic order. A variety of roles the ring exchange serves include the generation of a bilinear-biquadratic interaction between nearby triplets, which is responsible for the emergent nematic order separated from the singlet phase by a first order transition.

cond-mat.str-el↗

arXiv2018

Origin of Biquadratic Exchange Interactions in a Mott Insulator as a Driving Force of Spin Nematic Order

We consider a series of Mott insulators in unit of two orbitals each hosting spin-1/2 electron, and by pairing two spin-1/2 into spin-1 triplet, derive the effective exchange interaction between the adjacent units via fourth order perturbation theory. It turns out that the biquadratic exchange interaction between spin-1, which is one of the origins of the nematic order, arises only in processes where the four different electrons exchange cyclically along the twisted loop, which we call "twisted ring exchange" processes. We show that the term becomes the same order with the Heisenberg exchange interactions when the on-orbital Coulomb interaction is not too large. Whereas, the inter-orbital Coulomb interactions give rise to additional processes that cancel the twisted ring exchange, and strongly suppresses the biquadratic term. The Mott insulator with two electrons on degenerate two orbitals is thus not an ideal platform to study such nematic orders.

cond-mat.str-el↗

arXiv2018

Impact of Dzyaloshinsky-Moriya Interactions and Tilts of the g Tensors on the Magnetization Process of a Spherical Kagome Cluster in {W72V30}

In order to clarify why the experimental magnetization curve of the spherical kagome cluster in {W72V30} at 0.5 K shows no sign of staircase behavior up to 50 T, we study the effects of Dzyaloshinsky-Moriya (DM) interactions and tilts of the g tensors, both of which lead to the breaking of the total-S z conservation, by using the exact diagonalization method. It is found that the D vector component parallel to the radiation direction of the polyhedron cancels out the staircase in a low magnetic field region efficiently. The tilts of the g tensors are inherent to systems defined on the poly- hedrons and lead to induced magnetic fields varying site by site. This induced magnetic field affects the magnetization only at high magnetic fields. We also discuss two existing experimental results on the basis of our calculated results.

cond-mat.str-el↗