Thermal transport in antiferromagnetic spin-chain materials

Abstract

We study the problem of heat transport in one-dimensional (1D) spin-chain systems weakly coupled to three-dimensional phonons and impurities. We consider the limit of fast spin excitations and slow phonons, applicable to a number of compounds of the cuprates family, such as Sr2CuO3, where the superexchange J is much larger than the Debye energy, ΘD. In this case the Umklapp scattering among the spin excitations is strongly suppressed for all relevant temperatures. We argue that the leading scattering mechanism for the spin excitations at not too low temperatures is the "normal" (as opposed to the Umklapp) spin-phonon scattering in which the non-equilibrium momentum is transferred from the spin subsystem to phonons where it quickly relaxes through the "phonon bath". Because of the lower dimensionality of the spin excitations it is only the momentum along the chains which is conserved in such a scattering. We find that this effect leads to a particular momentum-and temperature-dependence of the spin-phonon relaxation rate valid for the broad class of low-dimensional spin systems. Subsequently we demonstrate that the spin-phonon relaxation mechanism is insufficient for the low-energy, long-wavelength 1D spin-chain excitations, which make the thermal conductivity diverge. We complete our consideration by taking into account the impurity scattering, which in 1D cuts off the quasi-ballistic spin excitations and renders the thermal conductivity finite. Altogether, these effects yield the following spin-boson thermal conductivity behavior: κs ∝ T 2 at low temperatures, κs ∝ T −1 at intermediate temperatures, and κs = const at higher temperatures T ∼ ΘD. The saturation at higher temperatures is of rather non-trivial origin and we provide a detailed discussion of it. Our results compare very well with the existing experimental data for Sr2CuO3. Using our microscopic insight into the problem we propose further experiments and predict an unusual impurity concentration dependence for a number of quantities.

Thermal conductivity inlarge−Jtwo-dimensional antiferromagnets: Role of phonon scattering

“…We note that the same arguments have been used previously for the spin-phonon coupling in 1D spin chains, see Ref. 17.…”

“…In a similar situation in 1D, 17 this leads to a strong infrared divergence of the spin component of the thermal conductivity. This means that the spin-phonon scattering is not sufficient to render conductivity finite and one needs to take into consideration other scattering mechanisms.…”

Magnetodielectric effect in theS=1∕2quasi-two-dimensional antiferromagnetK2V3Rai1, Cao2, Musfeldt3 et al. 2006Phys. Rev. B250380View full textAdd to dashboardCite

“…Apparently, the high magnetic field reduces the antiferromagnetic coupling strength at low temperatures. Based on the work of Chernyshev, 50 we estimate the canting angle to be ∼29 • at 33 T (H c).…”

“…50 For applied field in the ab plane, one of the magnon branches is predicted to have an unusual dependence on the Dzyaloshinskii-Moriya coupling that changes with the size of the field, giving rise to a possible non-analytic behavior of the spin gap. 50 In order to investigate the interplay between spin, lattice, and charge degrees of freedom in low-dimensional, inhomogeneously mixed-valent vanadates, we measured the optical and magneto-optical properties of K 2 V 3 O 8 . We observed two prominent magneto-dielectric effects at base temperature that derive from the field-induced changes in the local crystal field environment around the VO 5 square pyramid.…”

Magnetic excitation spectrum of the square latticeS=1∕2Heisenberg antiferromagnetK2VLumsden1, Nagler2, Sales3 et al. 2006Phys. Rev. B210260View full textAdd to dashboardCite

“…48 This work pointed out that weak ferromagnetism induced by the DM interaction is "hidden" in K 2 V 3 O 8 in the zero field limit by a dominant c-axis anisotropy. The effects of the DM interaction are revealed in the presence of an applied magnetic field and analytic expressions for the field strength required to induce both the spin-flop and spin reorientation transitions were provided.…”