London Penetration Depth as a Test of Order Parameter Symmetry in Sodium Cobaltate Superconductors

Temperature dependence of the magnetic field penetration depth λ was calculated for water intercalated sodium cobaltate superconductor Na x CoO 2 · y H 2 O. Assuming that the system is in the chiral d+id–wave superconducting state, it was shown that the shifting of the excitation spectrum nodal points off the normal phase Fermi surface due to variation of the sodium content x changes the functional form of the temperature dependence of λ − 2 from exponential to linear in the low temperatures region. It is argued that this change in the functional form of T–dependence of the λ − 2 can serve as a proof for the chiral symmetry of the superconducting order parameter in the sodium cobaltate.

Thermopower Enhancement from Engineering the Na0.7CoO2 Interacting Fermiology via Fe Doping

The sodium cobaltate system NaxCoO2 is a prominent representant of strongly correlated materials with promising thermoelectric response. In a combined theoretical and experimental study we show that, by doping the Co site of the compound at x=0.7 with iron, a further increase of the Seebeck coefficient is achieved. The Fe defects give rise to effective hole doping in the high-thermopower region of larger sodium content x. Originally filled hole pockets in the angular-resolved spectral function of the material shift to low energy when introducing Fe, leading to a multisheet interacting Fermi surface. Because of the higher sensitivity of correlated materials to doping, introducing adequate substitutional defects is thus a promising route to manipulate their thermopower.

Bifunctional application of sodium cobaltate as a catalyst and captor through CO oxidation and subsequent CO2 chemisorption processes

Sodium cobaltate works as a bifunctional material, in the catalysis of CO oxidation and subsequent CO2 chemisorption.