Electrodynamics of a prototypical altermagnetic compound MnTe

Abstract

Abstract Altermagnetism, characterized by compensated antiparallel spins and momentum-dependent spin splitting, has offered a promising platform for novel spintronic phenomena. Among this class of materials, hexagonal MnTe stands out due to its high Néel temperature and giant spin splitting. However, a comprehensive understanding of its charge dynamics remains incomplete. Here, we employ infrared spectroscopy to investigate the charge dynamics of single crystalline MnTe. The low energy optical conductivity reveals a suppressed Drude response across all temperatures, consistent with the reported p-type doping as indicated by previous angle-resolved photoemission spectroscopy(ARPES) measurement. An indirect band gap of about 0.48 eV attributed to impurity-assisted transitions, and a direct gap of 1.60 eV are identified via the Tauc relation at 10 K. Moreover, we observe a subtle difference at around 1.44 eV in the optical conductivity between the antiferromagnetic and paramagnetic states, which might be linked to altermagnetism-related band splitting. Additionally, Fano line shape analysis of a phonon mode at around 135 cm -1 reveals appreciable coupling between the phonon and spin fluctuations near the Néel temperature. Our results provide key insights into the charge dynamics of MnTe, underscoring its rich physics beyond a conventional semiconductor.

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