Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
1999-06-03
Phys. Rev. B 61, 2535 (2000).
Physics
Condensed Matter
Strongly Correlated Electrons
Revtex, 19 pages, 16 postscript pictures embedded in the text, submitted to PRB. Find more stuff at http://www.stanford.edu/
Scientific paper
10.1103/PhysRevB.61.2535
We investigate the temperature dependent optical properties of NaV2O5, in the energy range 4meV-4eV. The symmetry of the system is discussed on the basis of infrared phonon spectra. By analyzing the optically allowed phonons at temperatures below and above the phase transition, we conclude that a second-order change to a larger unit cell takes place below 34 K, with a fluctuation regime extending over a broad temperature range. In the high temperature undistorted phase, we find good agreement with the recently proposed centrosymmetric space group Pmmn. On the other hand, the detailed analysis of the electronic excitations detected in the optical conductivity, provides direct evidence for a charge disproportionated electronic ground-state, at least on a locale scale: A consistent interpretation of both structural and optical conductivity data requires an asymmetrical charge distribution on each rung, without any long range order. We show that, because of the locally broken symmetry, spin-flip excitations carry a finite electric dipole moment, which is responsible for the detection of direct two-magnon optical absorption processes for E parallel to the a axis. The charged-magnon model, developed to interpret the optical conductivity of NaV2O5, is described in detail, and its relevance to other strongly correlated electron systems, where the interplay of spin and charge plays a crucial role in determining the low energy electrodynamics, is discussed.
Damascelli Andrea
der Marel Dirk van
Jegoudez J.
Presura C.
Revcolevschi Alexandre
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