2005/07/31 by A. V. Syromyatnikov, S. V. Maleyev · 1 citation
Physics and Astronomy · #Advanced Condensed Matter Physics #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #cond-mat.str-el
paper · pdf · doi:10.1103/physrevb.72.174419
published as Phys. Rev. B 72, 174419 (2005) · 22 pages, 6 figures
openalex publication_date 2005/11/16 · arxiv created 2005/11/17 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Dynamical properties of the impurity spin-(1)/(2) in two-dimensional (2D) and quasi-2D Heisenberg antiferromagnets (AFs) at T\ensuremath\geqslant0 are discussed. The specific case of an impurity coupled symmetrically to two neighboring host spins is considered. The specific feature of this problem is that the defect is degenerate (frustrated) being located in zero molecular field. It is shown that this problem can be described by the spin-boson model without a tunneling term and with a more complex interaction. We demonstrate that the effect of the host system on the defect is completely described by the spectral function. It is found within the spin-wave approximation that for not too small \ensuremathω the spectral function is proportional to \ensuremathω2∕J3, where J is the exchange constant between the host spins. The defect dynamical susceptibility is derived using Abrikosov's pseudofermion technique and diagrammatic expansion. The calculations are performed within the fourth order of the dimensionless coupling parameter f. It is found that transverse impurity susceptibility \ensuremathχ_\ensuremath⊥(\ensuremathω) has a Lorenz peak, with the width proportional to f4J(T∕J)3 which disappears at T=0, and a nonresonant term. The latter term diverges logarithmically as \ensuremathω,\phantom\rule0.2em0exT\ensuremath→0. The static susceptibility \ensuremathχ(0) has the free-spin-like contribution 1∕(4T), and a logarithmic correction proportional to f2ln(J∕T). The influence of finite concentration of the defects n on the low-temperature properties of AFs is also investigated. A logarithmic correction to spin-wave velocity of the form nf4ln\ensuremath|J∕\ensuremathω\ensuremath| and an anomalous damping of spin waves proportional to nf4\ensuremath|\ensuremathω\ensuremath| are obtained. The results of the present paper can be applied to other systems with a frustrated impurity in which the spectral function is proportional to \ensuremathω2.