Lattice vibrations of alpha'-NaV2O5 in the low-temperature phase. Magnetic bound states?
Abstract
We report high resolution polarized infrared studies of the quarter-filled spin ladder compound alpha'-NaV2O5 as a function of temperature (5K <= T <= 300K). Numerous new modes were detected below the temperature Tc=34K of the phase transition into a charge ordered nonmagnetic state accompanied by a lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice dimerization at Tc and show that some peculiarities of the low-temperature vibrational spectrum come from quadruplets folded from the BZ point (1/2, 1/2, 1/4). We discuss an earlier interpretation of the 70, 107, and 133cm-1 modes as magnetic bound states and propose the alternative interpretation as folded phonon modes strongly interacting with charge and spin excitations.
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