For charged particles, their orbital angular momentum (OAM) in solids has a direct magnetic manifestation as an orbital magnetization. For charge-neutral particles, however, the physical manifestation of the OAM in solids remains unclear. Here, we show that a charge-neutral particle carrying a magnetic moment couples to an electric-field gradient through the Aharonov-Casher (AC) effect, thereby exhibiting the electric quadrupole in crystalline solids. This AC-induced electric quadrupole (AC-EQ) contains the scalar, toroidal dipole, and reduced quadrupole components, which are conjugate to the divergence, circulation, and shear of the electric field, respectively. As representative examples, we calculate the AC-EQ of magnons in two magnetic systems. In ferromagnetic pyrochlore, Dzyaloshinskii-Moriya interaction (DMI) induces a sizable AC-EQ, whereas in helical $\mathrm{Fe}$ langasite the AC-EQ emerges from the helical spin configuration even in the absence of DMI.

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• Aharonov-Casher effect
• Berry curvature
• Dzyaloshinskii-Moriya interaction
• Magnons
• Noncollinear magnets
• Linear spin wave theory
• Semiclassical methods