arXiv subjects

R. Shiina

Publications and source records attributed to R. Shiina.

5 recordsLinked to original sources

arXiv2026

Experimental Evidence for Reflected Ions and Ion Temperature Anisotropy in a Forming Supercritical Magnetized Collisionless Shock

Supercritical magnetized collisionless shocks require ion reflection for dissipation, yet its role during formation remains unclear. Using high-power lasers, self-emission imaging, and collective Thomson scattering, we investigate a forming quasi-perpendicular shock. An upstream emission tail is consistent with a foot-like structure, while ion heating and temperature anisotropy extend upstream of a ramp-like region. These observations provide evidence of reflected-ion-related heating during early shock formation, although the incident and reflected ion populations are not separately resolved. Future measurements of ion distributions and plasma waves could clarify how this heating mediates shock dissipation and particle energization.

physics.plasm-ph↗

arXiv2026

Identification of rippling interface between laser-ablated plasma and ambient uniform plasma at rest

We present laboratory experiments on the early stage of the formation process of quasi-perpendicular supercritical magnetized collisionless shocks using laser-produced plasmas in an ambient uniform nitrogen (N) gas with 1~Torr under the external magnetic field with controlled polarity. An expanding aluminum (Al) piston plasma arising from laser irradiation interacts with a magnetized ambient N plasma, producing a bright, asymmetric self-emission whose global morphology reverses with the magnetic-field polarity. Two-dimensional ideal-magnetohydrodynamics simulations reproduce the main features of the observed structures and indicate that the ripple formation is unlikely to be driven by the Kelvin--Helmholtz instability, but is instead associated with vortex formation at the rounded leading edge of the piston plasma. We show that the bright, rippling emission delineates the Al-N interface, whose intrinsic width is consistent with an electron kinetic scale, and that its upstream side is predominantly composed of N plasma. This identification allows the formation of a supercritical collisionless shock in the magnetized N plasma to be discussed with minimal Al contamination.

physics.plasm-ph↗

arXiv2014

Spin nematic interaction in multiferroic compound Ba$_{2}$CoGe$_{2}$O$_{7}$

We demonstrate the existence of the spin nematic interactions in an easy-plane type antiferromagnet Ba$_{2}$CoGe$_{2}$O$_{7}$ by exploring the magnetic anisotropy and spin dynamics. Combination of neutron scattering and magnetic susceptibility measurements reveals that the origin of the in-plane anisotropy is an antiferro-type interaction of the spin nematic operator. The relation between the nematic operator and the electric polarization in the ligand symmetry of this compound is presented. The introduction of the spin nematic interaction is useful to understand the physics of spin and electric dipole in multiferroic compounds.

cond-mat.str-el↗

arXiv2007

Neutron Scattering Study on the Field-Induced $O_{xy}$-type Antiferroquadrupolar Ordering of Heavy-Fermion Superconductor $PrOs_4Sb_{12}$

Neutron scattering experiments have revealed a field-induced antiferroquadrupolar order parameter in the Pr-based heavy-fermion superconductor PrOs$_4$Sb$_{12}$. We observed the field-induced antiferromagnetic dipole moment with the propagation vector {\textit{\textbf{q}}} = (1 0 0) for the applied field direction both {\textit{\textbf{H}}}${\parallel}$[1 1 0] and [0 0 1]. For {\textit{\textbf{H}}}${\parallel}$[1 1 0] at 8 T, it should be noted that the induced antiferromagnetic moment of 0.16(10) $μ_{\rm B}$/Pr orients parallel to the field within our experimental accuracy. This observation is strong evidence that the $O_{xy}$ electric quadrupole to be the primary order parameter for {\textit{\textbf{H}}}${\parallel}$[1 1 0]. A mean-field calculation, based on $Γ_1$ singlet and $Γ_4^{(2)}$ excited triplet with the $O_{xy}$ quadrupolar interaction, reproduces the induced moment direction and its field response. These facts indicate the predominance of $O_{xy}$-type antiferroquadrupolar interaction in PrOs$_4$Sb$_{12}$.

cond-mat.str-el↗

arXiv2000

Orbitally Degenerate Spin-1 Model for Insulating V2O3

Motivated by recent neutron, X-ray absorption and resonant scattering experiments, we revisit the electronic structure of V2O3. We propose a model in which S=1 V3+ ions are coupled in the vertical V-V pairs forming two-fold orbitally degenerate configurations with S=2. Ferro-orbital ordering of the V-V pairs gives a description which is consistent with all experiments in the antiferromagnetic insulating phase.

cond-mat.str-el↗