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arXiv · 2607.21221

Circular phonon dichroism in $d$-wave altermagnets

Ding Li·Tao Qin·Jianhui Zhou
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Abstract

Altermagnets, a new class of collinear antiferromagnets, exhibit momentum-dependent spin splitting and offer compelling advantages for antiferromagnetic spintronics. However, the magnetic order is intrinsically difficult to read out, which hinders practical applications. We propose finite-momentum circular phonon dichroism as a direct probe of N\'eel vector in two-dimensional $d$-wave altermagnets. Combining Onsager reciprocity with $C_{2z}$ lattice symmetry, we find that the dichroic signal reverses sign when the N\'eel vector is flipped for the in-plane phonon wave vectors. Moreover, a channel-resolved decomposition identifies the circular phonon dichroism originates from the interband coherent transitions. Representative finite-momentum cuts show pronounced dichroic asymmetric ratio, with $|\eta_{\mathrm{CPD}}|=37.3\%$. Our work reveals that the circular-ultrasound absorption acts as a direct probe of the N\'eel vector of $d$-wave altermagnets.

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Ding Li, Tao Qin, Jianhui Zhou. 2026-07-23. Circular phonon dichroism in $d$-wave altermagnets. https://arxiv.org/abs/2607.21221

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