• DOI:10.1103/physrevb.102.235155
• Corpus ID: 226221927

High-field thermal transport properties of the Kitaev quantum magnet α−RuCl3 : Evidence for low-energy excitations beyond the critical field

@article{Hentrich2020HighfieldTT,
  title={High-field thermal transport properties of the Kitaev quantum magnet 
$\alpha$−RuCl3
: Evidence for low-energy excitations beyond the critical field},
  author={Richard Hentrich and Xiaochen Hong and Matthias Gillig and Federico Caglieris and Matija {\vC}ulo and M. Shahrokhvand and Uli Zeitler and Maria Roslova and Anna Isaeva and Thomas Doert and Lukas Janssen and Matthias Vojta and Bernd B{\"u}chner and Christian Hess},
  journal={Physical Review B},
  year={2020}
}

• Richard Hentrich, X. Hong, +11 authors C. Hess
• Published 30 October 2020
• Physics
• Physical Review B

We investigate the phononic in-plane longitudinal low-temperature thermal conductivity kappa_ab of the Kitaev quantum magnet alpha-RuCl3 for large in-plane magnetic fields up to 33 T. Our data reveal for fields larger than the critical field Bc ~ 8 T, at which the magnetic order is suppressed, a dramatic increase of kappa_ab at all temperatures investigated. The analysis of our data shows that the phonons are not only strongly scattered by a magnetic mode at relatively large energy which scales roughly linearly with the magnetic field, but also by a small-energy mode which emerges near Bc with a square-root-like field dependence. While the former is in striking agreement with recent spin wave theory (SWT) results of the magnetic excitation spectrum at the Gamma point, the energy of the latter is too small to be compatible with the SWT-expected magnon gap at the M point, despite the matching field dependence. Therefore, an alternative scenario based on phonon scattering off the thermal excitation of random-singlet states is proposed.