Abstract:We report far-infrared reflectance measurements of Zn-and Si-doped CuGeO 3 single crystals as a function of applied magnetic field at low temperature. Overall, the low-energy far-infrared spectra are extraordinarily sensitive to the various phase boundaries in the H-T diagram, with the features being especially rich in the low-temperature dimerized state. Zn impurity substitution rapidly collapses the 44 cm Ϫ1 zone-boundary spin Peierls gap, although broadened magnetic excitations are observed at the lightest … Show more
“…Magnetooptics experiments provide additional support for the assignment of the 88-cm -1 feature as a Na + rattling mode in the tube. The inset of Figure b displays the transmittance ratio spectra of Na 2 V 3 O 7 nanotubes in several different applied magnetic fields up to 17 T. If the 88-cm -1 feature is related to the predicted spin gap, the signature will change with field; Zeeman splitting of such structures has been observed in other low-dimensional magnetic materials in the past . Judging from the lack of field-dependence in the transmittance ratio spectra near 88 cm -1 , we conclude that this feature is not related to the spin gap.…”
We report the electronic and vibrational properties of Na 2 V 3 O 7 nanotubes and compare the response with other layered and nonlayered vanadates. The electronic structure of Na 2 V 3 O 7 displays a strong similarity to that of nontubular vanadates. We assign the 1.2-eV band as a V d f d excitation and the 3.3-and 3.9-eV bands as O 2p f V 3d charge-transfer structures. Although band structure calculations predict additional fine structure in the density of states because of the tubular morphology, such features are not observed in the absorption spectrum. The vibrational spectrum displays triplet mode splitting as a result of reduced site symmetry, consistent with the three sightly different vanadium atoms that form the basic structural unit. A low-frequency rattling mode is observed in Na 2 V 3 O 7 at 88 cm -1 . This unique characteristic of the Na + -ion intercalated tubes might be connected with the ionic conductivity.
“…Magnetooptics experiments provide additional support for the assignment of the 88-cm -1 feature as a Na + rattling mode in the tube. The inset of Figure b displays the transmittance ratio spectra of Na 2 V 3 O 7 nanotubes in several different applied magnetic fields up to 17 T. If the 88-cm -1 feature is related to the predicted spin gap, the signature will change with field; Zeeman splitting of such structures has been observed in other low-dimensional magnetic materials in the past . Judging from the lack of field-dependence in the transmittance ratio spectra near 88 cm -1 , we conclude that this feature is not related to the spin gap.…”
We report the electronic and vibrational properties of Na 2 V 3 O 7 nanotubes and compare the response with other layered and nonlayered vanadates. The electronic structure of Na 2 V 3 O 7 displays a strong similarity to that of nontubular vanadates. We assign the 1.2-eV band as a V d f d excitation and the 3.3-and 3.9-eV bands as O 2p f V 3d charge-transfer structures. Although band structure calculations predict additional fine structure in the density of states because of the tubular morphology, such features are not observed in the absorption spectrum. The vibrational spectrum displays triplet mode splitting as a result of reduced site symmetry, consistent with the three sightly different vanadium atoms that form the basic structural unit. A low-frequency rattling mode is observed in Na 2 V 3 O 7 at 88 cm -1 . This unique characteristic of the Na + -ion intercalated tubes might be connected with the ionic conductivity.
“…Replacing Cu 2+ ions with Zn 2+ ions breaks the linear magnetic chain. Impurity substitution is also of interest in other transition metal oxides. − 1 Crystal structure of copper pyrazine dinitrate.…”
We report the temperature-dependent infrared spectra of pure, deuterated, Zn-doped, and 2,6-dimethyl-substituted samples of the S ) 1 / 2 , one-dimensional Quantum Heisenberg Antiferromagnet (QHAF) copper pyrazine dinitrate (Cu(C 4 H 4 N 2 )(NO 3 ) 2 ). Of the more than 100 vibrational modes observed in the spectra, nearly one-third of them unexpectedly soften throughout the temperature range of investigation (300-5 K). We discuss the temperature dependence of the vibrational spectra in terms of several different models for mode softening. On the basis of detailed structural information and a comparison of the infrared spectra between pure copper pyrazine dinitrate and its chemically modified relatives, we conclude that the unusual softening observed in this low-dimensional molecular magnet is due to enhanced interchain hydrogen bonding with decreasing temperature.
“…Previous detailed studies of IR-active phonons provided valuable insights into the charge density wave transition in solids, as well as into the spin Pierels physics [54][55][56].…”
Section: Charge Density Wave and Spin Density Wave Systemsmentioning
confidence: 99%
“…The formation of rigid charge density waves is also known to have dramatic implications for optical phonons in solids: new modes are observed corresponding to the lower symmetry of a crystal [34,41,42,43,44,45,46,47,48,49,50], and also some of the resonances acquire oscillator strengths characteristic of electronic transitions [51]. Previous detailed studies of IR-active phonons provided valuable insights into the charge density wave transition in solids, as well as into the spin Pierels physics [52,53,54].…”
Section: Charge Density Wave and Spin Density Wave Systemsmentioning
Infrared spectroscopy has emerged as a premier experimental technique to
probe enigmatic effects arising from strong correlations in solids. Here we
report on recent advances in this area focusing on common patterns in
correlated electron systems including transition metal oxides, intermetallics
and organic conductors. All these materials are highly conducting substances
but their electrodynamic response is profoundly different from the canonical
Drude behavior observed in simple metals. These unconventional properties can
be attributed in several cases to the formation of spin and/or charge ordered
states, zero temperature phase transitions and strong coupling to bosonic
modes
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