Interaction of in-plane Drude carrier with c-axis phonon in PdCoO2

Abstract

AbstractWe performed polarized reflection and transmission measurements on the layered conducting oxide PdCoO2thin films. For theab-plane, an optical peak near Ω ≈ 750 cm−1drives the scattering rate 1/τ(ω) and effective massm*(ω) of the Drude carrier to increase and decrease respectively forω ≧ Ω. For thec-axis, a longitudinal optical phonon (LO) is present at Ω as evidenced by a peak in the loss function Im[−1/εc(ω)]. Further polarized measurements in different light propagation (q) and electric field (E) configurations indicate that the Peak at Ω results from an electron-phonon coupling of theab-plane carrier with thec-LO phonon, which leads to the frequency-dependent 1/τ(ω) andm*(ω). This unusual interaction was previously reported in high-temperature superconductors (HTSC) between a non-Drude, mid-infrared (IR) band and ac-LO. On the contrary, it is the Drude carrier that couples in PdCoO2. The coupling between theab-plane Drude carrier andc-LO suggests that thec-LO phonon may play a significant role in the characteristicab-plane electronic properties of PdCoO2, including the ultra-high dc-conductivity, phonon-drag, and hydrodynamic electron transport.