Quadrupole Excitation in Tunnel Splitting Oscillation in Nano-Particle $Mn_{12}$

TL;DR

This paper investigates how quadrupole and dipole excitations influence tunnel splitting in a spin system with a special Hamiltonian, revealing interference effects and periodic quenching points without magnetic fields.

Contribution

It introduces an instanton-based analysis of interference effects in tunnel splitting modulated by second-order transverse anisotropy in a spin system.

Findings

Tunnel splitting is periodically modulated by anisotropy strength.

Number of quenching points decreases for quadrupole excitation.

Interference of four tunneling paths causes the observed effects.

Abstract

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