22,464 research outputs found
Relation between Kitaev magnetism and structure in -RuCl
Raman scattering has been employed to investigate lattice and magnetic
excitations of the honeycomb Kitaev material -RuCl and its
Heisenberg counterpart CrCl. Our phonon Raman spectra give evidence for a
first-order structural transition from a monoclinic to a rhombohedral structure
for both compounds. Significantly, only -RuCl features a large
thermal hysteresis, consistent with the formation of a wide phase of
coexistence. In the related temperature interval of K, we observe a
hysteretic behavior of magnetic excitations as well. The stronger magnetic
response in the rhombohedral compared to the monoclinic phase evidences a
coupling between the crystallographic structure and low-energy magnetic
response. Our results demonstrate that the Kitaev magnetism concomitant with
fractionalized excitations is susceptible to small variations of bonding
geometry.Comment: 9 pages, 8 figures, To appear in PR
Electronic and phonon excitations in {\alpha}-RuCl
We report on THz, infrared reflectivity and transmission experiments for wave
numbers from 10 to 8000 cm ( 1 meV - 1 eV) and for temperatures
from 5 to 295 K on the Kitaev candidate material {\alpha}-RuCl. As reported
earlier, the compound under investigation passes through a first-order
structural phase transition, from a monoclinic high-temperature to a
rhombohedral low-temperature phase. The phase transition shows an extreme and
unusual hysteretic behavior, which extends from 60 to 166 K. In passing this
phase transition, in the complete frequency range investigated we found a
significant reflectance change, which amounts almost a factor of two. We
provide a broadband spectrum of dielectric constant, dielectric loss and
optical conductivity from the THz to the mid infrared regime and study in
detail the phonon response and the low-lying electronic density of states. We
provide evidence for the onset of an optical energy gap, which is of order 200
meV, in good agreement with the gap derived from measurements of the DC
electrical resistivity. Remarkably, the onset of the gap exhibits a strong blue
shift on increasing temperatures.Comment: 18 pages, 7 figure
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