  We propose a novel method for low-lying states of hypernuclei based on the
particle-rotor model, in which hypernuclear states are constructed by coupling
the hyperon to low-lying states of the core nucleus. In contrast to the
conventional particle-rotor model, we employ a microscopic approach for the
core states, that is, the generator coordinate method (GCM) with the particle
number and angular momentum projections. We apply this microscopic
particle-rotor model to $^9_\Lambda $Be employing a point-coupling version of
the relativistic mean-field Lagrangian. A reasonable agreement with the
experimental data for the low-spin spectrum is achieved using the $\Lambda N$
coupling strengths determined to reproduce the binding energy of the $\Lambda$
particle.
