Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNew Far Infrared Vibrational Mode in Zn Doped CuGeO3
137
0
0.0
(
0
)
Added by
Jeffrey Joseph McGuire
Publication date
1997
fields
Physics
and research's language is
English
Authors
J. J. McGuire
Ask ChatGPT about the research
No Arabic abstract
We report on far infrared measurements on Zn and Si doped crystals of the spin-Peierls compound CuGeO3. Zn doping has the effect of introducing several new absorption lines, polarized in the ab-plane, between 5 and 55 cm-1. The intensity of the absorption grows with Zn concentration but saturates above 2% Zn. One line at 10 cm-1 loses intensity above 4K, and a second line at 20 cm-1 is absent at low temperatures but grows to peak at about 40K in agreement with a three level model with two excited states 10 and 30 cm-1 above the ground state. As the doping is increased these lines broaden, and a temperature independent absorption developes over the entire range from 5 to 55 cm-1. These features are magnetic field independent up to 16T and are absent in Si doped samples. We suggest the new absorption is due to localized lattice modes of the zinc ion and the surrounding GeO4 tetrahedra.
rate research
Read More
We investigated the far- and mid-infrared reflectivity (20-6000 wavenumber) of several pure and doped CuGeO3 single crystals. The b-axis and c-axis optical response is presented for different temperatures between 4 K and 300 K. Moreover, a full group theoretical analysis of the lattice vibrational modes of CuGeO3 in the high temperature undistorted phase as well as in the low temperature spin-Peierls phase is reported and compared to the experimental results. We observe the activation of zone boundary phonons along the b axis of the crystal below the spin-Peierls transition temperature.
We investigated in detail the optical properties of several Cu(1-delta)Mg(delta)GeO3 (with delta=0,0.01), and CuGe(1-x)B(x)O3 with B=Si (x=0,0.007,0.05,0.1), and Al (x=0,0.01) single crystals, in the frequency range 20-32000 cm^-1. We report temperature dependent reflectivity and transmission measurements, performed with polarized light in order to probe the anisotropy of the crystals along the b and c axes, and optical conductivity spectra obtained by Kramers-Kronig transformation or direct inversion of the Fresnel formula. Special emphasis is given to the far-infrared phonon spectra. The temperature dependence of the phonon parameters is presented and discussed in relation to the soft mode issue in CuGeO3. For T<Tsp we could detect zone boundary folded modes activated by the spin-Peierls phase transition. Following the temperature dependence of these modes, which shows the second order character of the phase transition, we were able to study the effect of doping on Tsp. Moreover, in transmission experiments we detected a direct singlet-triplet excitation at 44 cm^-1, across the magnetic gap, which is not understandable on the basis of the magnetic excitation spectrum so far assumed for CuGeO3. The optical activity of this excitation and its polarization dependence confirm the existence of a second (optical) magnetic branch, recently suggested on the basis of inelastic neutron scattering data. The anisotropy in the magnetic exchange constants along the b axis, necessary for the optical triplet mode to gain a finite intensity, and the strong effect of Si substitution on the phonon spectra are discussed in relation to the alternative space group P2(1)2(1)2(1), recently proposed for CuGeO3 in the high temperature uniform phase.
Using high frequency (up to 450 GHz) ESR and low temperature specific heat measurements we find that insertion of 1% Fe and 2% Co damps spin-Peierls and Neel transitions and for T<30K gives rise to onset of a quantum critical behaviour characteristic for a random dimer Griffiths phase.
We investigated the infrared reflectivity of several Mg- and Si-substituted CuGeO3 single crystals. The temperature dependent b-axis and c-axis optical response is reported. For T<Tsp we detected the activation of zone-boundary phonons along the b axis of the crystal on the pure sample and for 1% Mg and 0.7% Si concentrations. From a detailed analysis of the phonon parameters the redshift of the B2u mode at 48 cm^-1 is observed and discussed in relation to the soft mode expected to drive the spin-Peierls phase transition in CuGeO3. Moreover, the polarization dependence of a magnetic excitation measured in transmission at 44 cm^-1 has been investigated.
Infrared spectroscopy, especially for molecular vibrations in the fingerprint region between 600 and 1500 cm-1, is a powerful characterization method for bulk materials. However, molecular fingerprinting at the nanoscale level still remains a significant challenge, due to weak light-matter interaction between micron-wavelengthed infrared light and nano-sized molecules. Here, we demonstrate molecular fingerprinting at the nanoscale level using our specially designed graphene plasmonic structure on CaF2 nanofilm. This structure not only avoids the plasmon-phonon hybridization, but also provides in situ electrically-tunable graphene plasmon covering the entire infrared fingerprint region, which was previously unattainable. In addition, undisturbed and highly-confined graphene plasmon offers simultaneous detection of in-plane and out-of-plane vibrational modes with ultrahigh detection sensitivity down to the sub-monolayer level, significantly pushing the current detection limit of far-field mid-infrared spectroscopy. Our results provide a platform, fulfilling the long-awaited expectation of high sensitivity and selectivity far-field fingerprint detection of nano-scale molecules for numerous applications.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
