Polarization-resolved Raman spectroscopy of \alpha-RuCl3 and evidence of room temperature two-dimensional magnetic scattering
Thuc T. Mai, Amber D. McCreary, P. Lampen-Kelley, Nicholas P. Butch, Jeffrey R. Simpson, J.-Q. Yan, S. E. Nagler, D. Mandrus, Angela R. Hight Walker, Rolando Valdes Aguilar
Polarization-resolved Raman spectroscopy was performed and analyzed from large, high quality, mono-domain single crystal of \alpha-RuCl3, a proximate Kitaev quantum spin liquid. Spectra were collected with laser polarizations parallel and perpendicular to the honeycomb plane. Pairs of nearly degenerate phonons were discovered and show either a 4-fold or 2-fold polarization angle dependence in their Raman intensity, thereby providing evidence to definitively assign the bulk crystal point group as C2h. The low frequency continuum that is often attributed to scattering from pairs of Majorana fermions was also examined and found to disappear when the laser excitation and scattered photon polarizations were perpendicular to the honeycomb plane. This disappearance, along with the behavior of the phonon spectrum in the same polarization configuration, strongly suggests that the scattering continuum is 2- dimensional. Based on the electronic structure of \alpha-RuCl3, we argue that this scattering continuum is of magnetic origin that survives all the way up to room temperature, a scale much larger than the magnetic ordering temperature of TN 7 K.