arXiv subjects

Jun Ōiké

Publications and source records attributed to Jun Ōiké.

4 recordsLinked to original sources

arXiv2026

Correlation-Driven Nonlinear Magnetoelectric Response in an Altermagnet: A Dynamical Mean-Field Study

We investigate the optical nonlinear magnetoelectric effect (NMEE) in a strongly correlated altermagnet using dynamical mean-field theory. Unlike effective band descriptions with an imposed spin splitting, our approach determines the altermagnetic order, electronic spectrum, and optical nonlinear response self-consistently. We find that the NMEE is finite in the altermagnetic phase and vanishes in the paramagnetic phase. Its frequency dependence reflects the spin-resolved spectral structure and provides an estimate of the characteristic altermagnetic spin-splitting scale. Interaction and temperature tuning produce qualitatively different behavior: at low temperature, reducing the interaction strength toward the interaction-driven magnetic phase boundary enhances the response, whereas increasing the temperature suppresses it and drives it to zero above the critical temperature. These results establish the optical NMEE as a probe of correlated altermagnetic order and suggest that tuning parameters such as pressure, strain, or chemical substitution toward an interaction-driven phase boundary may provide a promising route to maximizing the response.

cond-mat.str-el↗

arXiv2025

Thermodynamic formulation of the spin magnetic octupole moment in bulk crystals

The discovery of unconventional antiferromagnets, such as altermagnets, has drawn significant attention to higher-rank magnetic multipoles, particularly magnetic octupoles. Despite the advances in research, attempts to understand their microscopic properties remain limited due to the unbounded nature of the position operator in bulk crystals. In this paper, we address this problem by using a well-known thermodynamic approach and derive a formula for the spin magnetic octupole moment (SMOM) that can be used in bulk crystals. The resulting formula is gauge invariant and satisfies Středa formulas that relate the SMOM to the spin magnetoelectric dipole-quadrupole susceptibilities. Furthermore, we apply this formula to several models and examine the fundamental properties of the SMOM. For example, in $d$-wave altermagnets, the nonrelativistic component of the SMOM, which is independent of spin-orbit coupling, is larger than the relativistic component, which is induced by spin-orbit coupling. These nonrelativistic SMOMs have the same microscopic origin as the nonrelativistic spin splitting that characterizes $d$-wave altermagnetism. Moreover, they exhibit a Néel vector dependence consistent with Landau theory for $d$-wave altermagnetism [Phys. Rev. Lett. $\textbf{132}$, 176702 (2024)].

cond-mat.mtrl-sci↗

arXiv2024

Nonlinear Magnetoelectric Effect under Magnetic Octupole Order: Its Application to a $d$-Wave Altermagnet and a Pyrochlore Lattice with All-In/All-Out Magnetic Order

Extensive investigation has recently been conducted into a new class of antiferromagnetic order known as magnetic octupole order. However, the high rank of octupoles makes it difficult to detect and manipulate them by using conventional methods such as the anomalous Hall effect. In this paper, we propose the nonlinear magnetoelectric effect (NMEE), a second-order response to an electric field that induces a spontaneous magnetization, as a finite response under magnetic octupole order. First, we classify the magnetic point groups to identify antiferromagnets with such order, and derive the NMEE tensor using quantum kinetic theory. Then, we confirm the effectiveness of the NMEE through model calculations for two specific examples: a $d$-wave altermagnet and a pyrochlore lattice with all-in/all-out magnetic order. In particular, the intrinsic NMEE exhibits a large response in a magnetic Weyl semimetal phase of the pyrochlore lattice. This enhanced response is explained by the fact that the response tensor involves the quantum metric, which is enhanced near Weyl points. Furthermore, our results show that the NMEE has a sizeable value that can be detected by the magneto-optical Kerr effect.

cond-mat.mtrl-sci↗

arXiv2024

Nonlinear Edelstein Effect in Strongly Correlated Electron Systems

Nonlinear spintronics, which combines nonlinear dynamics and spintronics, opens a new route for controlling spins and spin dynamics beyond conventional spintronics based on linear responses. Strongly correlated electron systems, which can have large nonlinear responses, are promising candidates for nonlinear spintronics. In this paper, we focus on the nonlinear Edelstein effect (NEE), a generalization of the Edelstein effect, and study the impact of electron correlations on the NEE by performing numerical calculations on a Hubbard model. We find that correlation effects can either enhance or suppress the nonlinear response. We show that the enhancement and suppression of the response are due to the real and imaginary components of the self-energy, respectively. Additionally, we have explored the relationship between the NEE and photomagnetic or optomagnetic effects. Our findings demonstrate that electron correlations can either enhance or suppress the optical spin injection, depending on the light frequency, while always strengthening the inverse Faraday effect.

cond-mat.str-el↗