Terahertz Spectra Revealing the Collective Excitation Mode in Charge-Density-Wave Single Crystal LuFe2O4
A low-energy collective excitation mode in charge-ordered multiferroic LuFe 2 O 4 is reported via terahertz time-domain spectroscopy. Upon cooling from 300 to 40 K, the central resonance frequency showed a pronounced hardening from 0.85 to 1.15 THz. In analogy to the well-known low-energy optical properties of LuFe 2 O 4 , this emerging resonance was attributed to the charge-density-wave (CDW) collective excitations. By using the Drude-Lorentz model fitting, the CDW collective mode becomes increasingly damped with the increasing temperature. Furthermore, the kinks of the CDW collective mode at the magnetic transition temperature are analyzed, which indicate the coupling of spin order with electric polarization.