Macroscopic quantum coherence of the Neel vector in antiferromagnetic system without Kramers' degeneracy |
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Authors: | R Lü J-L Zhu X Chen L Chang |
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Institution: | (1) Department of Physics, Tsinghua University, Beijing, 100084, P.R. China, CN |
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Abstract: | At low temperatures the Neel vector in a small antiferromagnetic particle can possess quantum coherence between the classically
degenerate minima. In some cases, the topological term in the magnetic action can lead to destructive interference between
the symmetry-related trajectories for the half-integer excess spin antiferromagnetic particle. By studying a macroscopic quantum
coherence problem of the Neel vector with biaxial crystal symmetry and a weak magnetic field applied along the hard axis,
we find that the quenching of tunnel splitting could take place in the system without Kramers' degeneracy. Both the Wentzel-Kramers-Brillouin
exponent and the pre-exponential factors are found exactly for the tunnel splitting. Results show that the tunnel splitting
oscillates with the weak applied magnetic field for both the integer and half-integer excess spin antiferromagnetic particles,
and vanishes at certain values of the field. All the calculations are performed based on the two sublattices model and the
instanton method in spin-coherent-state path integral.
Received: 24 July 1997 / Accepted: 30 September 1997 |
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Keywords: | PACS 75 10 Jm Quantized spin models - 73 40 Gk Tunneling - 75 50 Ee Antiferromagnetics |
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