Dechanneling Anomalies of High-Energy Ions at the Charge-Density-Wave Transition in1T-TaS2

Backscattering yields of 1.00-MeV ${\mathrm{He}}^{+}$ ions on $1T$-Ta${\mathrm{S}}_2$ are reported from room temperature to 120 K. The temperature dependence of the backscattering yield exhibits the softening of an acoustic mode and an optical mode. An anomalously large peak in the backscattering yield with large hysteresis was observed around the nearly commensurate to commensurate transition temperature, indicating existence of a disordered state. A small peak around 280 K was observed on heating, indicating existence of a new transition in this material.