Drude-like peak

The Drude-like peak may be attributed to the coherent motion of doped-holes. This assignment is based on the assumption that the conventional transport theory is applicable in the cuprate although a number of experiments indicate that metallic... 

The mid-IR peak has been explained due to the small polaron formation since the early days of the cuprate research. A support for this assignment is the photoinduced conductivity measurement [4] the photoinduced conductivity in LSCO (Fig. 4) shows a very similar peak to the mid-IR peak of the optical conductivity in the V = 0.02 sample. It is also qualitatively explained by the small polaron transport theory [4]. However, this mid-IR peak assignment contradicts the assignment that the Drude-like peak is due to the coherent motion of holes since the former assumes that the hole-lattice interaction is so strong that doped holes become small polarons, while the latter does opposite. Therefore, if we assign that the mid-IR peak is due to small polaron formation, we have to abandon the assignment that the Drude-like peak is due to the coherent motion of doped-holes. 

The detailed analysis of the optical conductivity in the CT gap region reveals several distinct features which are particularly well resolved in samples with dilute concentration of charge carriers (figs. 2 and 5) (i) a broad resonance at 0.5 ey which shows considerable softening as doping increases (ii) a resonance at 0.25 eV (iii) a Drude-like peak at m = 0. The existence of well-separated absorption features in the fi uency dependence of Oab (o) is the basis for multicomponent analysis of the conductivity. Within this approach (Tanner and Hmusk 1992) the conductivity is assumed to have the form... 

Figure 5 (top) shows that adding carriers to the insulating phase leads to a doping-induced MI transition near x 0.35 in Bai-xKxBiOs, as evidenced in the optical data by [121, 125, 126, 136, 137, 139-141] (i) the development of a Drude-like response, (ii) the dramatic decrease of the peak energy of the fundamental absorption cOq, (iii) a decrease in the low frequency optical... 

The characteristic composite behavior of (t maM for medium consisting of spherical particles with volume fractions / of Drude conductor and 1 - / of insulator is shown in Figure 15.5. For a volume fraction / less than the percolation value (/ = 1/3 for spheres), (Tema (impurity band of localized plasmon-like excitations. As the system approaches the percolation threshold, the localized peak o-ema(w) shifts to lower frequency. Above the percolation threshold, a Drude peak corresponding to the carriers that have percolated through the composite structure occurs at low frequency. Only a fraction ( (3/— l)/2 [119]) of the full conduction electron plasma frequency appears in the Drude peak, depending on the proximity to the percolation threshold. The same percolating free electron behavior is observable in the dielectric response ema(w) for the system. 

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