arXiv subjects

Norimasa Sasabe

Publications and source records attributed to Norimasa Sasabe.

5 recordsLinked to original sources

arXiv2026

Intrinsic single crystals of MnTe altermagnet

We report the synthesis methodology, structure, and intrinsic properties of ultra-high quality single crystals of MnTe, an archetypal altermagnet. The crystals, obtained from self-flux method, are nearly free from crystal imperfections and disproportionate chemical compositions as seen by various investigation methods. In measurements under quasi free-standing configuration minimizing stress induced effects, the crystals exhibit complex and anisotropic domain kinetics in both superheating and supercooling regimes around the altermagnetic transition at $T_{\mathrm{N}} = 310\,\mathrm{K}$. An Anderson insulating state is observed below $T_{\mathrm{MI}}\approx 150\,\mathrm{K}$ with a carrier density of about $1.6\times 10^{17}\,\mathrm{cm}^{-3}$, being sharply contrast to metallic states usually seen in Te-deficit samples. Nevertheless, hallmarks of altermagnetism, anomalous Hall effect and X-ray magnetic circular dichroism signal, are robust in this intrinsic limit, however with significantly reduced magnitudes.

cond-mat.str-el↗

arXiv2026

Visualization of Co 3d high- and low-spin states via valence electron density

Properties of trivalent cobalt oxides are governed by the spin and orbital states of Co3+ ions, which are strongly coupled to their local coordination environments and chemical bonding. However, direct real-space access to the electronic states has remained challenging. Here, we determine the Co 3d states in the quasi-one-dimensional cobalt oxide Ca3Co2O6 by combining synchrotron X-ray diffraction with valence electron density (VED) analysis based on core differential Fourier synthesis. The reconstructed VED reveals distinct anisotropic distributions at two crystallographically inequivalent Co sites with octahedral and trigonal-prismatic coordination geometries. The octahedral site exhibits a characteristic VED consistent with a low-spin configuration, whereas the trigonal-prismatic site shows pronounced anisotropy that cannot be described solely by crystal electric field (CEF) effects. Quantitative analysis demonstrates that this anisotropy originates from the interplay of CEF effects, spin-orbit coupling, and ligand-assisted 3d-4p hybridization, reflecting partially unquenched orbital angular momentum and its role in the Ising magnetism. These results establish a general framework for understanding site-dependent electronic structure and chemical bonding in transition-metal oxides through real-space VED analysis.

cond-mat.str-el↗

arXiv2025

Detection of ferroic octupole ordering in $d$-wave altermagnetic rutile-type compounds

We propose that X-ray absorption and emission magnetic circular dichroism (XAS-MCD and XES-MCD) are promising measurements to directly detect ferroic higher-rank multipoles as candidate order parameters in altermagnets. Using the sum rules for XES-MCD and connecting them to multipole language, we demonstrate that the expectation value of the magnetic octupole moment is finite in the $d$-wave altermagnetic candidate rutile-type compounds TF$_2$ (T=transition metal). We also perform spectral calculations of XAS-MCD and XES-MCD based on an effective model with a full multiplet approach. While the intensity of the XAS-MCD spectra vanishes, the XES-MCD spectra exhibit finite intensity, whose spectrum becomes opposite by inverting the Nèel vector. These results clearly indicate ferroic magnetic octupole order in these compounds.

cond-mat.str-el↗

arXiv2025

X-ray magnetic circular dichroism originating from the $T_{z}$ term in collinear altermagnets under trigonal crystal field

We investigate the microscopic origin and spectral features of X-ray magnetic circular dichroism (XMCD) in collinear antiferromagnets with trigonal crystal fields, using $α$-MnTe as a prototypical example. Although such systems exhibit zero net magnetization, we demonstrate that XMCD can emerge from the anisotropic magnetic dipole operator $T_{z}$, arising from quadrupolar spin distributions. By constructing a complete multipole basis and analyzing the symmetry conditions under trigonal distortion, we identify specific spin and orbital configurations that enable a finite XMCD response. Further, we employ both one-electron and multi-electron models, including spin-orbit coupling and Coulomb interactions, to calculate the XMCD spectra for various $d^n$ configurations. Our findings provide theoretical benchmarks for XMCD in altermagnets and highlight the key role of orbital symmetry and magnetic anisotropy in realizing observable dichroic effects.

cond-mat.mtrl-sci↗

arXiv2023

Impact of the Ce $4f$ states in the electronic structure of the intermediate-valence superconductor CeIr$_3$

The electronic structure of the $f$-based superconductor $\mathrm{CeIr_3}$ was studied by photoelectron spectroscopy. The energy distribution of the $\mathrm{Ce}~4f$ states were revealed by the $\mathrm{Ce}~3d-4f$ resonant photoelectron spectroscopy. The $\mathrm{Ce}~4f$ states were mostly distributed in the vicinity of the Fermi energy, suggesting the itinerant character of the $\mathrm{Ce}~4f$ states. The contribution of the $\mathrm{Ce}~4f$ states to the density of states (DOS) at the Fermi energy was estimated to be nearly half of that of the $\mathrm{Ir}~5d$ states, implying that the $\mathrm{Ce}~4f$ states have a considerable contribution to the DOS at the Fermi energy. The $\mathrm{Ce}~3d$ core-level and $\mathrm{Ce}~3d$ X-ray absorption spectra were analyzed based on a single-impurity Anderson model. The number of the $\mathrm{Ce}~4f$ states in the ground state was estimated to be $0.8-0.9$, which is much larger than the values obtained in the previous studies (i.e., $0-0.4$).

cond-mat.str-el↗