Kavli Affiliate: James Analytis
| Summary:
Manganese telluride ($textMnTe$) has recently emerged as a prototypical $g$-wave altermagnet, providing an ideal platform to investigate the non-equilibrium excitations of altermagnetic order. Here, we report simultaneous spatial mapping of the local equilibrium orientation of the Néel vector, $varphi_L(mathbfr)$, alongside the amplitude, $Δvarphi(mathbfr,t)$, and frequency, $Ω(mathbfr)$, of photoexcited spin waves. Based on these measurements, we place a remarkably low upper bound of $approx 60~μtexteV$ (0.7 K) on the spin-wave gap arising from intrinsic anisotropy. This exceptionally weak hexagonal anisotropy ($K_6$) renders the altermagnetic order highly susceptible to optical tuning, allowing coherent spin waves to be driven by a photoinduced enhancement of $K_6$. Above a threshold pump fluence, our spatial maps reveal that this photomodulation manifests as a six-fold symmetric sawtooth dependence of $Δvarphi$ on $varphi_L$ and a cycloid-like modulation of $Ω$. Ultimately, the near-isotropy of the Néel vector in $textMnTe$ enables optical and mechanical control over the orientation of spin-splitting in the electronic band structure, offering new pathways for altermagnetic spintronics.
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