Possible structural transformation and enhanced magnetic fluctuations in exfoliated α-RuCl3.

We present Raman spectroscopy experiments on exfoliated α -RuCl 3 , from tens of nm thick down to single layers. Besides unexpectedly finding this material to be air stable, in the thinnest layers we observe the appearance with decreasing temperature of a symmetry-forbidden mode in crossed polarization, along with an anomalous broadening of a mode at 164 cm−1 that is known to couple to a continuum of magnetic excitations. This may be due to an enhancement of magnetic fluctuations and evidence for a distorted honeycomb lattice in single- and bilayer samples. • α-RuCl 3 , a layered candidate material to host the Kitaev quantum spin liquid, is exfoliated down to single- and few-layer flakes. • Raman spectroscopy is performed to study the evolution of structure with thickness and temperature. • A symmetry-forbidden mode appears in only the thinnest flakes at low temperature, evidencing a possible structural transformation. • Phonon width and energy of a mode sensitive to magnetic fluctuations shows a strong temperature dependence in contrast to bulk material. [ABSTRACT FROM AUTHOR]