Critical conditions for instability in the isovector unnatural-parity channel in nuclei are investigated in terms of the random-phase approximation. The particle-hole residual interaction consists of the $\pi$ and $\rho$ ($2\pi$) meson-exchange attractive components in addition to the short-range repulsive Landau term. It is found that the nonresonant part of the iterated two-pion exchange moves the characteristics of the nuclear phase transition closer to those for rho-meson condensation. This mode may dominate at high density.

• Received 11 May 1981

DOI:https://doi.org/10.1103/PhysRevLett.47.1716