  We have studied the temperature-dependent electronic structure near the Fermi
level (EF) of the layered cobaltate superconductor, Na0.35CoO2.1.3H2O, and
related materials, using laser-excited ultrahigh-resolution photoemission
spectroscopy. We observe the formation of a pseudogap with an energy scale of ~
20 meV in Na0.35CoO2.1.3H2O and Na0.35CoO2.0.7H2O, which is clearly absent in
Na0.7CoO2. The energy scale of the pseudogap is larger than the expected value
for the superconducting gap, suggesting an additional competing order parameter
at low temperatures. We discuss implications of the pseudogap in relation to
available transport and magnetic susceptibility results.
