Optical spectroscopy and ultrafast pump-probe study of a quasi-one-dimensional charge density wave in CuTe

CuTe is a two-dimensional (2D) layered material, yet forming quasi-one-dimensional (quasi-1D) charge-density-wave (CDW) along the a-axis in ab-plane at high transition temperature $T_{CDW}=335$ K. However, anisotropic properties of remain to be explored. Here we performed combined transport, polarized infrared reflectivity, and ultrafast pump-probe spectroscopy investigate underlying CDW physics CuTe. Polarized optical measurement clearly revealed that an energy gap gradually forms upon cooling, while evidence signature absent b-axis, suggesting pronounced electronic anisotropy this quasi-2D material. Time-resolved reflectivity amplitude relaxation time photo-excited quasiparticles change dramatically across phase transition. Taking fast Fourier transformation oscillation signals arising from collective excitations, identify 1.65-THz mode as mode, whose softens elevated temperatures. Consequently, provide further for formation completely order CuTe, which quite rare materials.