Effect of pressure on the superconducting critical temperature of La[O0.89F0.11]FeAs and Ce[O0.88F0.12]FeAs

We have performed several high-pressure resistivity experiments on the recently discovered superconductors La[O0.89F0.11]FeAs and Ce[O0.88F0.12]FeAs. At ambient pressure, these materials have superconducting onset temperatures Tc of 28 K and 44 K, respectively. While the Tc of La[O0.89F0.11]FeAs goes through a maximum between 10 and 68 kbar, in qualitative agreement with a recent report by Takahashi et al., the Tc of Ce[O0.88F0.12]FeAs decreases monotonically over the measured pressure range. At 265 kbar, the Tc of the cerium-based compound has been suppressed below 1.1 K.