Cluster structures in $^{11}$B

Structures of excited states in $^{11}$B are investigated with a method of $\beta$-$\gamma$ constraint antisymmetrized molecular dynamics in combination with the generator coordinate method. Various excited states with developed cluster core structures are suggested in positive- and negative-parity states. For negative-parity states, we suggest a band with a $2\alpha+t$ cluster structure. This band starts from the $3/2^{-}_{3}$ state and can correspond to the experimental band observed recently. In positive-parity states, two $\alpha$ core cluster structures with surrounding nucleons are found. A $K^\pi=1/2^+$ band is suggested to be constructed from a remarkably developed cluster structure with a large prolate deformation. We discuss features of the cluster structure in association with molecular orbital structures of $^{10}$Be.