Backbending and $Gamma$-Vibrations

We propose that the backbending phenomenon can be explained as a result of the disappearance of collective $gamma$-vibrational mode in the rotating frame. Using a cranking+random phase approximation approach for the modified Nilsson potential + monopole pairing forces, we show that this mechanism is responsible for the backbending in $^{156}$Dy, $^{158}$Er and obtain a good agreement between theoretical and experimental results.