Description
Altermagnets (AMs), recently proposed as a third category of collinear magnets, combine the features of zero net magnetization in antiferromagnets (AFMs) with a ferromagnet-like spin splitting. Although abundant spectroscopic evidence for altermagnetism has been reported, experimental observation of the anomalous Hall effect (AHE), a phenomenon well known in ferromagnets (FMs), remains scarce. Here, we shift the paradigm from charge to heat carriers and report a systematic study of the thermal Hall effect (THE) in two representative altermagnet candidates, MnTe and CrSb. In both materials, we observe a pronounced anomalous phonon thermal Hall signal, with no electrical counterpart observed, which we attribute to the coupling of the distinctive magnetic structure with phonons. Our findings establish the anomalous phonon thermal Hall effect as an intrinsic feature of altermagnets, and provide a sensitive probe for identifying this new kind of quantum magnet. Moreover, it directly links the Néel vector to lattice vibrations, opening prospects for low-loss phononic devices and thermally readable memories.
