Polarized infrared reflectivity study in charge density wave conductor Tl0.3MoO3

Polarized infrared reflectivity measurements between 300 and 10 K have been carried out on charge density waves (CDW) conductor blue bronze Tl0.3MoO3. Three important features are observed: (i) A bump at 1155 cm−1 in the reflectivity spectra of Tl0.3MoO3 at 300 K is a precursor of the Peierls gap due to optical excitations across a pseudogap, and this kind of Peierls-like gap opens gradually with decreasing temperature from 180 to 160 K. (ii) The three sharp modes as “triplet” of infrared reflectivity between 800 and 1000 cm−1 of Tl0.3MoO3 along [1 0 2] axis show red shift compared to K0.3MoO3 and Rb0.3MoO3, which is assigned to the increase of the distance of Mo–O bond with the substitution of thallium ions. (iii) Two peaks at about 514 and 644 cm−1 in the far-infrared reflectivity spectra of Tl0.3MoO3 along [1 0 2] direction are suggested to be the electronic transitions from the valence band to the midgap state and from occupied midgap state to the conduction band, respectively.