Acoustic phonon softening and lattice instability driven by on-site $f$-$d$ hybridization in CeCoSi

Takeshi Matsumura, Takumi Hasegawa, Ryuma Nakajima +5

Soft phonon modes in tetragonal CeCoSi, which undergoes a structural transition at $T_0=12$ K followed by antiferromagnetic order at $T_{\text{N}}=9.5$ K, have been investigated us…