Abstract
Motivated by recent experimental progress in 2D magnetism, we theoretically study spin transport in 2D easy-plane magnets at finite temperatures across the Berezinskii-Kosterlitz-Thouless (BKT) phase transition, by developing a duality mapping to the 2+1D electromagnetism with the full account of spin’s finite lifetime. In particular, we find that the non-conservation of spin gives rise to a distinct signature across the BKT transition, with the spin current decaying with distance power-law (exponentially) below (above) the transition; this is detectable in the proposed experiment with NiPS_33 and CrCl_33.
Highlights
Progress in the experimental detection of the celebrated Brezinskii-Kosterlitz-Thouless (BKT) phase transition has varied between the different types of physical systems
Transport signature of a BKT transition should arise from the presence or the absence of the finite density nf of topological defects in any 2D XY systems, yet we have shown that its manifestation would be different in 2D easy-plane magnets due to the spin non-conservation of Eq (4a), which contrasts with thin superconductor / superfluid films possessing the charge / mass conservation of Eq (4)
For the 2D easy-plane magnet, the main impact at TBKT lies in the transport range rather than the disspation, which is present even at the low temperature and is the cause of the spin non-conservation
Summary
Progress in the experimental detection of the celebrated Brezinskii-Kosterlitz-Thouless (BKT) phase transition has varied between the different types of physical systems This phase transition was one of the first example of the continuous phase transition outside the Landau paradigm, involving not the symmetry breaking but rather the topological defect pair unbinding. We examine the possibility of the long-distance spin transport in proximity to the magnetic BKT transition using the duality mapping from the 2D easy-plane magnetism to the electromagnetism (EM) in the d = 2 + 1 spacetime [32,33,34,35] This allows us to both pursue close analogy to the current transport and pinpoint the difference that arises when the phenomenological finite spin lifetime is inserted.
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