Spins and phonons in the spin-Peierls compound CuGeO3

Abstract

An overview is given of Raman and infrared spectroscopic studies of the inorganic spin-Peierls compound CuGeO 3 , with an emphasis on the magnetic fluctuations in the uniform, dimerized, and high field phases of this quasi one dimensional magneto-elastic compound.

Revival of the spin-Peierls transition inCu1−xZnxGeOFischer1, Loosdrecht2, Lemmens3 et al. 1998Phys. Rev. BSelf Cite12050View full textAdd to dashboardCite

“…This is not surprising since the singlet energy directly correlates with the SP gap ∆, which itself is related to the structural order parameter δ (∆ = δ 2/3 within Cross-Fisher theory 39 ). This indicates that the intensity of the 370-cm −1 mode may not be induced by the structural distortion in the SP phase, but rather by the doubling of the magnetic unit cell 40 . It furthermore strongly suggests that the relation between the structural distortion and the size of the SP gap may drastically change upon substitutions, strongly deviating from the Cross-Fisher prediction 39 .…”

“…This indicates that the intensity of the 370-cm Ϫ1 mode may not be induced by the structural distortion in the SP phase, but rather by the doubling of the magnetic unit cell. 40 It furthermore strongly suggests that the relation between the structural distortion and the size of the SP gap may drastically change upon substitutions, strongly deviating from the Cross-Fisher prediction.…”

Optical Spectroscopy on the Spin-Peierls Compound CuGeO₃

“…of the spin-Peierls gap. A clear two magnon peak is, though weaker, still observed [42,58], indicating that there still exist more or less well defined, propagating triplet excitations in the center of the Brillouin zone with energies of the order of πJ. Also the SP induced phonons observed in the D phase at 105 and 370 cm −1 persist in the IC phase, but again with a much weaker intensity.…”

“…The spin-Peierls transition leads to several new features in the (cc) polarized Raman spectra (see figure 3). In the first place, three zone boundary phonons appear in the (cc) spectra of the dimerized phase, at 105, 370, and 820 cm −1 , which are activated either by magneto-elastic interactions or by the structural distortion [34,42,43]. Note that the 105 cm −1 mode shows a strong Fano lineshape distortion due to interactions with the spin excitations [33].…”

“…The high field, or incommensurate phase of CuGeO 3 occurs for magnetic fields above 12.5 T and temperatures below about 9 K (see figure 1). There have been only a few reports on optical spectroscopy in the IC phase [16,42,55,58]. In the dimerized phase, the presence of well defined triplet excitations led to a scattering continuum in the A g (cc) channel at energies between the singlet response at 30 cm −1 , and the two magnon peak at 228 cm −1 .…”