Dissipative dynamics of topological defects in frustrated Heisenberg spin systems

Juricic, Vladimir
Department of Physics, University of Fribourg, Switzerland  Institute for Theoretical Physics, University of Utrecht, The Netherlands

Benfatto, Larra
Department of Physics, University of Fribourg, Switzerland

Caldeira, A. O.
Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, São Paulo, Brazil

Morais Smith, Cristiane de
Department of Physics, University of Fribourg, Switzerland  Institute for Theoretical Physics, University of Utrecht, The Netherlands
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Published in:
 Physical Review B.  2005, vol. 71, no. 064421
English
We study the dynamics of topological defects of a frustrated spin system displaying spiral order. As a starting point we consider the SO(3) nonlinear sigma model to describe longwavelength fluctuations around the noncollinear spiral state. Besides the usual spinwave magnetic excitations, the model allows for topologically nontrivial static solutions of the equations of motion, associated with the change of chirality (clockwise or counterclockwise) of the spiral. We consider two types of these topological defects, single vortices and vortexantivortex pairs, and quantize the corresponding solutions by generalizing the semiclassical approach to a nonAbelian field theory. The use of the collective coordinates allows us to represent the defect as a particle coupled to a bath of harmonic oscillators, which can be integrated out employing the FeynmanVernon pathintegral formalism. The resulting effective action for the defect indicates that its motion is damped due to the scattering by the magnons. We derive a general expression for the damping coefficient of the defect, and evaluate its temperature dependence in both cases, for a single vortex and for a vortexantivortex pair. Finally, we consider an application of the model for cuprates, where a spiral state has been argued to be realized in the spinglass regime. By assuming that the defect motion contributes to the dissipative dynamics of the charges, we can compare our results with the measured inverse mobility in a wide range of temperature. The relatively good agreement between our calculations and the experiments confirms the possible relevance of an incommensurate spiral order for lightly doped cuprates.

Faculty
 Faculté des sciences

Department
 Physique

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Physics

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https://folia.unifr.ch/unifr/documents/299895
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