Macroscopic Quantum Coherence in Small Antiferromagnetic Particle and the Quantum Interference Effects

TL;DR

This paper investigates macroscopic quantum coherence and interference effects in small antiferromagnetic particles, revealing how external magnetic fields influence energy splitting and degeneracy through tunneling and quantum interference.

Contribution

It derives an effective Lagrangian for biaxial antiferromagnetic particles in magnetic fields and uncovers novel quantum interference effects affecting energy splitting.

Findings

External magnetic field removes Kramers' degeneracy.

Quantum interference causes field-dependent quenching of energy splitting.

Energy spectrum modeled as a superlattice using Bloch theory.

Abstract

Starting from the Hamiltonian operator of the noncompensated two-sublattice model of a small antiferromagnetic particle, we derive the effective Lagrangian of a biaxial antiferromagnetic particle in an external magnetic field with the help of spin-coherent-state path integrals. Two unequal level-shifts induced by tunneling through two types of barriers are obtained using the instanton method. The energy spectrum is found from Bloch theory regarding the periodic potential as a superlattice. The external magnetic field indeed removes Kramers' degeneracy, however a new quenching of the energy splitting depending on the applied magnetic field is observed for both integer and half-integer spins due to the quantum interference between transitions through two types of barriers.