  We present a new mechanism of generating large planetary eccentricities. This
mechanism applies to planets within the inner cavities of their companion
protoplanetary disks. A massive disk with an inner truncation may become
eccentric due to non-adiabatic effects associated with gas cooling, and can
retain its eccentricity in long-lived coherently-precessing eccentric modes; as
the disk disperses, the inner planet will encounter a secular resonance with
the eccentric disk when the planet and the disk have the same apsidal
precession rates; the eccentricity of the planet is then excited to a large
value as the system goes through the resonance. In this work, we solve the
eccentric modes of a model disk for a wide range of masses. We then adopt an
approximate secular dynamics model to calculate the long-term evolution of the
"planet + dispersing disk" system. The planet attains a large eccentricity
(between 0.1 and 0.6) in our calculations, even though the disk eccentricity is
quite small ($\lesssim0.05$). This eccentricity excitation can be understood in
terms of the mode conversion (``avoided crossing'') phenomenon associated with
the evolution of the "planet + disk" eccentricity eigenstates.
