arXiv subjects

H. Kondo

Publications and source records attributed to H. Kondo.

6 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↗

arXiv2026

Characterizing the temporal evolution of Biermann-battery-driven magnetic reconnection in laser-ablated plasmas

This paper presents an experimental investigation of magnetic reconnection between two laser-produced expanding plasmas, focusing on the quantitative evaluation of the reconnection rate and energy conversion under varying initial conditions. By changing the separation distance between the drive laser focal spots (1 mm and 2 mm), we systematically controlled the inflow parameters. The reconnection region was probed using a two-directional laser Thomson scattering (LTS) system, which simultaneously measured the local plasma parameters parallel to the outflows and along the current sheet. Based on our established method incorporating macroscopic energy and mass conservation laws to derive the upstream magnetic field directly from LTS spectra, we characterized the temporal evolution of the current sheet and the reconnection rate. The larger spot separation allows the plasma bubbles to expand for a substantially longer time before the formation of a reconnection current sheet, resulting in different upstream conditions. Nevertheless, both configurations yielded comparable upstream magnetic fields and reconnection rates. These results suggest that the reconnection rate is relatively insensitive to the global inflow conditions and is primarily controlled by the local physics of the reconnection layer once a current sheet is formed.

physics.plasm-ph↗

arXiv2010

Magnetic and Electronic Properties of Li$_x$CoO$_2$ Single Crystals

Measurements of electrical resistivity ($ρ$), DC magnetization ($M$) and specific heat ($C$) have been performed on layered oxide Li$_x$CoO$_2$ (0.25$\leq$$x$$\leq$0.99) using single crystal specimens. The $ρ$ versus temperature ($T$) curve for $x$=0.90 and 0.99 is found to be insulating but a metallic behavior is observed for 0.25$\leq$$x$$\leq$0.71. At $T_{\rm S}$$\sim$155 K, a sharp anomaly is observed in the $ρ$$-$$T$, $M$$-$$T$ and $C$$/$$T$$-$$T$ curves for $x$=0.66 with thermal hysteresis, indicating the first-order charactor of the transition. The transition at $T_{\rm S}$$\sim$155 K is observed for the wide range of $x$=0.46$-$0.71. It is found that the $M$$-$$T$ curve measured after rapid cool becomes different from that after slow cool below $T_{\rm F}$, which is $\sim$130 K for $x$=0.46$-$0.71. $T_{\rm F}$ is found to agree with the temperature at which the motional narrowing in the $^7$Li NMR line width is observed, indicating that the Li ions stop diffusing and order at the regular site below $T_{\rm F}$. The ordering of Li ions below $T_{\rm F}$$\sim$130 K is likely to be triggered and stabilized by the charge ordering in CoO$_2$ layers below $T_{\rm S}$.

cond-mat.str-el↗

arXiv2001

Orbital excitations in CMR progenitor of LaMnO3 studied by resonant inelastic x-ray scattering

We report resonant inelastic x-ray scattering experiments of the orbital ordered manganite LaMnO3. When the incident photon energy is tuned near the Mn K absorption edge, the spectra reveal three features at 2.5 eV, 8 eV and 11 eV. The 8 eV and 11 eV peaks are considered charge-transfer type excitations. On the other hand, theoretical calculations identify the 2.5 eV peak as an orbital excitation across the Mott gap, i.e. an electron excitation from the lower Hubbard band with the d3x2-r2 and d3y2-r2 orbital characters to the upper Hubbard band with the dy2-z2 and dz2-x2 ones. The observed weak dispersion and characteristic azimuthal angle dependence of this new type of excitations are well reproduced by the theory which includes orbital degeneracy and strong electron correlation.

cond-mat.str-el↗

arXiv2000

Resonant Inelastic X-ray Scattering from Charge and Orbital Excitations in Manganites

We present a theory of the resonant inelastic x-ray scattering (RIXS) to study electronic excitations in orbital ordered manganites. The charge and orbital excitations of the Mn 3d electron are caused by the Coulomb interactions in the intermediate scattering state. The scattering cross section is formulated by the Liouville operator method where the local and itinerant natures of the excitations are taken into account on an equal footing. As a result, the cross section is expressed by the charge and orbital correlation functions associated with local corrections. The RIXS spectra are calculated numerically as functions of momentum and polarization of x ray. Through the calculations, we propose that RIXS provides a great opportunity to study the unique electronic excitations in correlated electron systems with orbital degeneracy.

cond-mat.str-el↗