Quadrupole Excitation in Tunnel Splitting Oscillation in NanoparticleMn12

摘要

We analyze the interference between tunneling paths that occurfor a spin system with special Hamiltonian both for dipole and quadrupoleexcitations. Using an instanton approach, we find that as the strengthof the second-order transverse anisotropy is increased, the tunnel splitting for both excitations is modulated, with zeros occurring periodically and the number of quenching points for quadrupole excitationdecreasing. This effect results from the interference of four tunnelingpaths connecting easy-axis spin orientations and occurs in the absenceof any magnetic field.