Enhancement of quantum tunneling for excited states in ferromagnetic particles

Abstract

A formula suitable for a quantitative evaluation of the tunneling effect in a\nferromagnetic particle is derived with the help of the instanton method. The\ntunneling between n-th degenerate states of neighboring wells is dominated by a\nperiodic pseudoparticle configuration. The low-lying level-splitting previously\nobtained with the LSZ method in field theory in which the tunneling is viewed\nas the transition of n bosons induced by the usual (vacuum) instanton is\nrecovered. The observation made with our new result is that the tunneling\neffect increases at excited states. The results should be useful in analyzing\nresults of experimental tests of macroscopic quantum coherence in ferromagnetic\nparticles.\n