Increasing property of B(M1)/B(E2) ratios in πh11/2 direct x vi13/2 bands of rare-earth doubly odd nuclei

It is systematically observed that the B(M1)/B(E2) plots with the increasing of rotational frequency, behaves as a so-called parabola-like shape in the πh11/2 direct x νi13/2 bands of rare-earth doubly odd nuclei (i.e., the B(M1)/B(E2) ratios increase rapidly after a certain rotational frequency). Such a phenomenon is discussed based on the formula of magnetic dipole reduced transition probability deduced from the Cranking Shell Model and Particle Rotor Model respectively. It is pointed out that, the occurrence of this behavior is closely related to the alignment nature of the νi13/2 quasineutron. The increasing of B(M1)/B(E2) occurring at large frequency approaching the second BC crossing can be understood as mainly resulted from the mixing of wave function with the 4 quasiparticle band caused by the band crossing. Insight into the angular momentum coupling scheme between the quasiparticles and collective core in the πh11/2 direct x νi13/2 structures of rare-earth doubly odd nuclei is gained by analyzing the increasing behavior of B(M1)/B(E2) ratios occurring at low rotational frequency. (authors)