Bond-stretching-phonon anomalies in stripe-ordered La1.69Sr0.31NiO4.
We report a neutron scattering study of bond-stretching phonons in La1.69Sr0.31NiO4, a doped antiferromagnet in which the added holes order in diagonal stripes at 45 to the Ni-O bonds. For the highest-energy longitudinal optical mode along the bonds, a softening of 20% is observed between the Brillouin zone center and the zone boundary. At 45 to the bonds, a splitting of the same magnitude is found across much of the zone. Surprisingly, the charge-ordering wave vector plays no apparent role in the anomalous dispersions. The implications for related anomalies in the cuprates are discussed.
Tranquada
J M
JM
Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA. jtran@bnl.gov
Nakajima
K
K
Braden
M
M
Pintschovius
L
L
McQueeney
R J
RJ