QUANTUM TUNNELING AT EXCITED-STATES AND MACROSCOPIC QUANTUM COHERENCEIN FERROMAGNETIC PARTICLES

The consideration of the level splitting of the ground state of a sing le ferromagnetic particle due to tunneling through energy barriers is extended to low-lying excited states with the help of the LSZ method i n field theory, and is calculated up to the one loop correction, Contr ary to the leading order WKB approximation, the prefactor of the expon ential increases with the spin s of the particle, and therefore decrea ses the slope of the resonant frequency as a function of the volume of the particle. The temperature dependence of the tunneling probability is also calculated by means of a Boltzmann average, The results shoul d be useful in analysing results of experimental tests of macroscopic quantum coherence. (C) 1997 Elsevier Science B.V.