Far-infrared spectroscopy in the spin-Peierls compoundCuGeO3under high magnetic fields

Abstract

Polarized far-infrared (FIR) spectroscopic measurements and FIR magneto-optical studies were performed on the inorganic spin-Peierls compound CuGeO3. An absorption line, which was found at 98 cm −1 in the dimerized phase (D phase), was assigned to a folded phonon mode of B3u symmetry. The splitting of the folded mode into two components in the incommensurate phase (IC phase) has been observed for the first time. A new broad absorption centered at 63 cm −1 was observed only in the E b axis polarization, which was assigned to a magnetic excitation from singlet ground state to a continuum state. 78.66.-w,78.30.-j,63.22.+m

Low-energy excitations in impurity substitutedCuGeO3

“…55 These measurements were performed using the infrared reflectance probe developed at the NHMFL; a gold mirror was available as a reference. In this configuration, the incident light is 15°from normal to the sample surface, which is analogous to the canting procedure described by Takehana et al 49 Thus, we are inherently sampling some a-axis contribution, although the majority of the response is from the bc plane. In order to track changes with the applied field, we calculated reflectance ratios ⌬RϭR(H)/R(Hϭ0).…”

“…Takehana et al also pointed out the broad absorption centered near 63 cm Ϫ1 , which is assigned as a magnetic excitation from the singlet ground state to a continuum state. 49 Low-energy excitations in doped CuGeO 3 have also been studied previously by far-infrared spectroscopy. McGuire et al observe several very low-frequency absorption lines with progressive Zn doping ͑10 and 20 cm Ϫ1 ) as well as a broader temperature independent absorption.…”

“…42 Far-infrared reflectance and transmission measurements have been used to explore the characteristics of the H-T phase diagram of CuGeO 3 . [43][44][45][46][47][48][49] In the pristine material, weak folded modes are observed at 98, 284, 312, and 800 cm Ϫ1 below T c . 44,45,49 The 98 cm Ϫ1 zone boundary mode ͑of B 3u symmetry͒ is polarized along the a axis.…”

“…44,45,49 The 98 cm Ϫ1 zone boundary mode ͑of B 3u symmetry͒ is polarized along the a axis. 49 Data through the dimerized → incommensurate transition are particularly striking. 47,48 Here, Zeeman splitting of the 44 cm Ϫ1 SP gap is observed; the lower and upper branches in the normalized spectra disappear in the incommensurate phase due to destruction of the singlet ground state.…”

Raman scattering from the spin-gap mode in the Ni-doped spin-Peierls compoundCuGeO3

“…46 Meanwhile, the SP-gap excitation at ͑0,0,0.5͒ point at 44 cm −1 is infrared-red active even in pure CuGeO 3 when the polarization of the far-infrared light E is along the b axis. 48 It is worthwhile to consider the emergence of the spin-gap mode by impurity doping in terms of Dzyaloshinskii-Moriya ͑DM͒ exchange interaction:…”