arXiv subjects

Takanori Kida

Publications and source records attributed to Takanori Kida.

23 records · Page 2Linked to original sources

arXiv2017

Direct observation of spin-quadrupolar excitations in Sr$_2$CoGe$_2$O$_7$ by high field ESR

Exotic spin-multipolar ordering in spin transition metal insulators has so far eluded unambiguous experimental observation. A less studied, but perhaps more feasible fingerprint of multipole character emerges in the excitation spectrum in the form of quadrupolar transitions. Such multipolar excitations are desirable as they can be manipulated with the use of light or electric field and can be captured by means of conventional experimental techniques. Here we study single crystals of multiferroic Sr$_2$CoGe$_2$O$_7$, and show that due to its nearly isotropic nature a purely quadrupolar bimagnon mode appears in the electron spin resonance (ESR) spectra. This non-magnetic spin-excitation couples to the electric field of the light and becomes observable for a specific experimental configuration, in full agreement with a theoretical analysis of the selection rules.

cond-mat.str-el↗

arXiv2017

Magnetic properties of quasi-two-dimensional $S$ = 1/2 Heisenberg antiferromagnet with distorted square lattice

We successfully synthesize single crystals of the verdazyl radical $α$-2,3,5-Cl$_3$-V. $Ab$ $initio$ molecular orbital calculations indicate that the two dominant antiferromagnetic interactions, $J_{\rm{1}}$ and $J_{\rm{2}}$ ($α=J_{\rm{2}}/J_{\rm{1}}\simeq 0.56$), form an $S$ = 1/2 distorted square lattice. We explain the magnetic properties based on the $S$ = 1/2 square lattice Heisenberg antiferromagnet using the quantum Monte Carlo method, and examine the effects of the lattice distortion and the interplane interaction contribution. In the low-temperature regions below 6.4 K, we observe anisotropic magnetic behavior accompanied by a phase transition to a magnetically ordered state. The electron spin resonance signals exhibit anisotropic behavior in the temperature dependence of the resonance field and the linewidth. We explain the frequency dependence of the resonance fields in the ordered phase using a mean-field approximation with out-of-plane easy-axis anisotropy, which causes a spin-flop phase transition at approximately 0.4 T for the field perpendicular to the plane. Furthermore, the anisotropic dipole field provides supporting information regarding the presence of the easy-axis anisotropy. These results demonstrate that the lattice distortion, anisotropy, and interplane interaction of this model are sufficiently small that they do not affect the intrinsic behavior of the $S$ = 1 / 2 square lattice Heisenberg antiferromagnet.

cond-mat.str-el↗

arXiv2017

Absence of magnetic long range order in Ba$_3$ZnRu$_2$O$_9$: A spin-liquid candidate in the $S=3/2$ dimer lattice

We have discovered a novel candidate for a spin liquid state in a ruthenium oxide composed of dimers of $S = $ 3/2 spins of Ru$^{5+}$,Ba$_3$ZnRu$_2$O$_9$. This compound lacks a long range order down to 37 mK, which is a temperature 5000-times lower than the magnetic interaction scale of around 200 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a spin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance of inter- and intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.

cond-mat.str-el↗

arXiv2016

Long-range magnetic order and interchain interactions in the $S=2$ chain system MnCl$_3$(bpy)

A compound with very weakly interacting chains, MnCl$_3$(bpy), has attracted a great deal of attention as a possible $S=2$ Haldane chain. However, long-range magnetic order of the chains prevents the Haldane gap from developing below 11.5~K. Based on a four-sublattice model, a description of the antiferromagnetic resonance (AFMR) spectrum up to frequencies of 1.5~THz and magnetic fields up to 50~T indicates that the interchain coupling is indeed quite small but that the Dzaloshinskii-Moriya interaction produced by broken inversion symmetry is substantial (0.12~meV). In addition, the antiferromagnetic, nearest-neighbor interaction within each chain (3.3~meV) is significantly stronger than previously reported. The excitation spectrum of this $S=2$ compound is well-described by a $1/S$ expansion about the classical limit.

cond-mat.mtrl-sci↗

arXiv2009

Upper critical fields of the 11-system iron-chalcogenide superconductor FeSe$_{0.25}$Te$_{0.75}$

We have performed electrical resistivity measurements of a polycrystalline sample of FeSe$_{0.25}$Te$_{0.75}$, which exhibits superconductivity at $T_{\rm c} \sim 14$ K, in magnetic fields up to 55 T to determine the upper critical field $μ_{0}H_{\rm c2}$. In this compound, very large slopes of $μ_{0}H_{\rm c2}$ at the onset, the mid-point, the zero-resistivity temperatures on superconductivity are determined to be -13.7, -10.1, and -6.9 T/K, respectively. The observed $μ_{0}H_{\rm c2}(T)$s of this compound are considerably smaller than those expected from the Werthamer-Helfand-Hohenberg model, manifesting the Pauli limiting behavior. These results suggest that this compound has a large Maki parameter, but it is smaller than that calculated for a weak-coupling superconductor, indicating a large superconducting gap of this compound as a strong-coupling superconductor.

cond-mat.supr-con↗