Anomalous electronic Raman scattering in Na_xCoO_2 H_2O

TL;DR

This study investigates the electronic Raman scattering in Na_xCoO_2·yH_2O, revealing a pseudogap and charge ordering phenomena associated with superconductivity and doping levels.

Contribution

It provides new insights into the electronic excitations and pseudogap formation in hydrated sodium cobaltate across different doping levels.

Findings

Presence of a broad electronic continuum with a peak at 100 cm-1

Pseudogap opening below 150K in superconducting samples

Charge ordering indicated by additional phonon modes

Abstract

Raman scattering experiments on Na_{x}CoO_2 yH_2O single crystals show a broad electronic continuum with a pronounced peak around 100 cm-1 and a cutoff at approximately 560 cm-1over a wide range of doping levels. The electronic Raman spectra in superconducting and non-superconducting samples are similar at room temperature, but evolve in markedly different ways with decreasing temperature. For superconducting samples, the low-energy spectral weight is depleted upon cooling below T* sim 150K, indicating a opening of a pseudogap that is not present in non-superconducting materials. Weak additional phonon modes observed below T* suggest that the pseudogap is associated with charge ordering.