Long-range dynamics of magnetic impurities coupled to a two-dimensional Heisenberg antiferromagnet

Abstract

We consider a two-dimensional Heisenberg antiferromagnet on a square lattice with weakly coupled impurities, i.e. additional spins interacting with the host magnet by a small dimensionless coupling constant g<<1. Using linear spin-wave theory, we find that the magnetization disturbance at distance r from a single impurity behaves as g/r for 1<<r<<1/g and as 1/(gr^3) for r>>1/g. Surprisingly the disturbance is inversely proportional to the coupling constant! The interaction between two impurities separated by a distance r is proportional to g^2/r for 1<<r<<1/g and to 1/r^3 for r>>1/g. Hence at large distances, the interaction is universal and independent of the coupling constant. We also find that the frequency of Rabi oscillations between two impurities is proportional to g^2 ln(gr) at 1<<r<<1/g, logarithmically enhanced compared to the spin-wave width. This leads to a new mechanism for NMR, NQR and EPR line broadening. All these astonishing results are due to the gapless spectrum of the magnetic excitations in the quantum antiferromagnet.

6 pages, 5 figures

References in corpus (5)

• Quantum Impurities in the Two-Dimensional Spin One-Half Heisenberg Antiferromagnet
• Diluted quantum antiferromagnets: spin excitations and long-range order
• Quantum impurity in an antiferromagnet: non-linear sigma model theory
• Susceptibility of the 2D S=1/2 Heisenberg antiferromagnet with an impurity
• Long Range Dynamics Related to Magnetic Impurity in the 2D Heisenberg Antiferromagnet

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• Spin texture induced by non-magnetic doping and spin dynamics in 2D triangular lattice antiferromagnet h-Y(Mn,Al)O3
• Collective impurity effects in the Heisenberg triangular antiferromagnet
• Impurity spin textures across conventional and deconfined quantum critical points of two-dimensional antiferromagnets
• Geometry fluctuations in a two-dimensional quantum antiferromagnet
• Impact of Stealthy Hyperuniform Magnetic Impurity Configurations on Bulk Magnetism in a Two-dimensional Heisenberg Model
• Impurity-induced magnetization in three dimensional antiferromagnet at quantum critical point
• Casimir effect mechanism of pairing between fermions in the vicinity of a magnetic quantum critical point