Phonon anomaly on NaHfNCl superconductors with =22 K

Shamoto, Shinichi  ; Hirai, Atsuo*; Yamanaka, Shoji*; Aso, Naofumi*; Kajitani, Tsuyoshi*

Inelastic neutron scattering measurements have been performed on superconducting NaHfNCl powder samples with x=0.27 and 0.38 (T =22 K). We have observed several temperature dependent phonon anomalies, e.g., at E=15, 29, 76, and 81 meV for the former sample. A phonon peak with E=14.5 meV at Q=6 increases for both samples with decreasing temperature below T=40 K, which is much higher than T. The phonon peak is assigned to an ab-plane vibrational mode, E, of chlorine and hafnium atoms, which strongly modifies the electronic band structure. The phonon anomaly is discussed in terms of carrier inhomogeneity.