Thermal transport by topological excitations in one-dimensional quantum magnets: experiment meets theory
Theoretical Condensed Matter Physics
Final Report Abstract
The focus of this project was to investigate the spin thermal transport of prototype cuprate-based quasi one-dimensional spin chain systems with large Heisenberg exchange interaction as compared to the Debye temperature, and to theoretically investigate scattering processes, in particular spinondefect and spinon-phonon scattering processes. In the cuprate chain materials SrCuO 2, CaCu2O3, and the ladder compound La5Ca9Cu24O41, we observe that at T>300 K spinon/triplon heat conduction dominates the transport at directions parallel to the chains/ladders up to the highest temperatures measured (~900 K). In all cases the magnetic heat conductivity decreases beyond a materials dependent threshold temperature, which signals strong temperature-activated scattering processes. In the theoretical work, in contrast to the XY model that maps to a free fermion model, we found power law dependence with system size of the scattering matrix elements. We linked the exponents to the fractional charge that characterizes the model and we attributed this behavior to the many-body topological nature of the spinon excitation. Furthermore, we studied the low and high temperature contribution of thermodynamic Bethe ansatz (TBA) dressed excitations in the thermodynamics and energy-magnetization relaxation within the Generalized Hydrodynamics approach in the linear response regime. We found new expressions for the specific heat, magnetic susceptibility, and in particular of the spin and thermal Drude weights from the finite wave-vector relaxation. Finally, by extending earlier models, we developed a phenomenological model to account for a ballistic magnetic transport coupled to a diffusive phononic one. Most importantly, for certain material parameters, we predict a magnetic temperature profile that separates in two wave-fronts propagating left-right while relaxing to the phonon bath. This would be a telltale sign of ballistic propagation in spin-1/2 Heisenberg chain experiments and is left for future experimental studies. In addition to the work on quasi one-dimensional Heisenberg systems, we carried out extensive thermal transport studies on honeycomb Kitaev system α-RuCl3. The main findings are a considerable coupling of the spins to the phonons in this material, evidenced by strong scattering of the phonons off spin fluctuations, and a sizeable thermal Hall effect. In our theory work, we studied the high-temperature spin dynamics and the operator growth of quantum compass models. Among other more specific findings, we thus obtained the frequency dependence of the energy autocorrelation function in the high temperature limit, demonstrating the diffusive behavior of thermal transport.
Publications
- Unusual Phonon Heat Transport in α-RuCl3: Strong Spin-Phonon Scattering and Field-Induced Spin Gap, Phys. Rev. Lett. 120, 117204 (2018)
R. Hentrich, A. U. B. Wolter, X. Zotos, W. Brenig, D. Nowak, A. Isaeva, T. Doert, A. Banerjee, P. Lampen-Kelley, D. G. Mandrus, S. E. Nagler, J. Sears, Y.-J. Kim, B. Büchner, C. Hess
(See online at https://doi.org/10.1103/PhysRevLett.120.117204) - Heat transport of cuprate-based low-dimensional quantum magnets with strong exchange coupling, Physics Reports 811, 1 (2019)
C. Hess
(See online at https://doi.org/10.1016/j.physrep.2019.02.004) - Large Thermal Hall Effect in α-RuCl3: Evidence for Heat Transport by Kitaev-Heisenberg Paramagnons, Phys. Rev. B 99, 085136 (2019)
R. Hentrich, M. Roslova, A. Isaeva, T. Doert, W. Brenig, B. Büchner, C. Hess
(See online at https://doi.org/10.1103/PhysRevB.99.085136) - Scattering of spinon excitations by potentials in the one-dimensional Heisenberg model, Phys. Rev. B 100, 134401 (2019)
A. Pavlis and X. Zotos
(See online at https://doi.org/10.1103/PhysRevB.100.134401) - High-field thermal transport properties of the Kitaev quantum magnet α-RuCl 3: evidence for low-energy excitations beyond the critical field, Phys. Rev. B 102, 235155 (2020)
R. Hentrich, X. Hong, M. Gillig, F. Caglieris, M. Culo, M. Shahrokhvand, U. Zeitler, M. Roslova, A. Isaeva, T. Doert, L. Janssen, M. Vojta, B. Büchner, C. Hess
(See online at https://doi.org/10.1103/PhysRevB.102.235155) - Ballistic magnetic thermal transport coupled to phonons, Phys. Rev. B 104, 024429 (2021)
P. Zavitsanos and X. Zotos
(See online at https://doi.org/10.1103/PhysRevB.104.024429)
