  The negative parity states of $^{11}$B and $^{11}$C were studied based on the
calculations of antisymmetrized molecular dynamics(AMD). The calculations well
reproduced the experimental strengths of Gamov-Teller(GT), $M1$ and monopole
transitions. We, especially, focused on the $3/2^-_3$ and $5/2^-_2$ states, for
which GT transition strengths were recently measured. The weak $M1$ and GT
transitions for the $3/2^-_3$ in $^{11}$B and $^{11}$C are described by a
well-developed cluster structure of $2\alpha$+$t$ and $2\alpha$+$^3$He,
respectively, while the strong transitions for the $5/2^-_2$ is characterized
by an intrinsic spin excitation with no cluster structure. It was found that
the $3/2^-_3$ state is a dilute cluster state, and its features are similar to
those of the $^{12}$C$(0^+_2)$ which is considered to be a gas state of three
$\alpha$ clusters.
