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Register a new userHeat transport of cuprate-based low-dimensional quantum magnets with strong exchange coupling
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Christian Hess
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Transport properties provide important access to a solids quasiparticles, such as quasiparticle density, mobility, and scattering. The transport of heat can be particularly revealing because, in principle, all types of excitations in a solid may contribute. Heat transport is well understood for phonons and electrons, but relatively little is known about heat transported by magnetic excitations. However, during the last about two decades, the magnetic heat transport attracted increasing attention after the discovery of large and unusual signatures of it in low-dimensional quantum magnetic cuprate materials. Today it constitutes an important probe to otherwise often elusive, topological quasiparticles in a broader class of quantum magnets. This review summarizes the experimental foundation of this research, i.e. the state of the art for the magnetic heat transport in the mentioned cuprate materials which host prototypical low-dimensional antiferromagnetic $S=1/2$ Heisenberg models. These comprise, in particular, the two-dimensional square lattice, and one-dimensional spin chain and two-leg ladder spin models. It is shown, how studying the heat transport provides direct access to the thermal occupation and the scattering of the already quite exotic quasiparticles of these models which range from spin-1 spin wave and triplon excitations to fractionalized spin-1/2 spinons. Remarkable transport properties of these quasiparticles have been revealed: the spin-heat transport often is highly efficient and in some cases even ballistic, in agreement with theoretical predictions.
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The low-temperature thermal conductivity (kappa) of GdFeO_3 single crystals is found to be strongly dependent on magnetic field. The low-field kappa (H) curves show two dips for H parallel a and only one dip for H parallel c, with the characteristic fields having good correspondence with the spin-flop and the spin-polarization transitions. A remarkable phenomenon is that the subKelvin thermal conductivity shows hysteretic behaviors on the history of applying magnetic field, that is, the kappa(H) isotherms measured with field increasing are larger than those with field decreasing. Intriguingly, the broad region of magnetic field (sim 0--3 T) showing the irreversibility of heat transport coincides with that presenting the ferroelectricity. It is discussed that the irreversible kappa(H) behaviors are due to the phonon scattering by ferroelectric domain walls. This result shows an experimental feature that points to the capability of controlling the ferroelectric domain structures by magnetic field in multiferroic materials.
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