Charge density wave transition in Na2Ti2Sb2O probed by 23Na NMR

Herein we investigated the electronic properties of layered transition-metal oxides Na₂Ti₂Sb₂O by ²³Na nuclear magnetic resonance (NMR) measurement. The resistivity, susceptibility and specific heat measurements show a phase transition at approximately 114 K (T _A). No splitting or broadening in the central line of ²³Na NMR spectra is observed below and above the transition temperature indicating no internal field being detected. The spin-lattice relaxation rate divided by T (1/T ₁ T) shows a sharp drop at about 110 K which suggests a gap opening behavior. Below the phase transition temperature zone, 1/T ₁ T shows Fermi liquid behavior but with much smaller value indicating the loss of large part of electronic density of states (DOS) because of the gap. No signature of the enhancement of spin fluctuations or magnetic order is found with the decreasing temperature. These results suggest a commensurate charge-density-wave (CDW) phase transition occurring.