Physical Review B 75,1 (2007) 012414;
Recent neutron scattering measurements reveal spin and charge ordering in the half-doped nickelate, La3/2Sr1/2NiO4. Many of the features of the magnetic excitations have been explained in terms of the spin waves of diagonal stripes with a magnetic coupling structure which is fourfold symmetric. However, an optical mode dispersing away from the (pi,pi) point was not captured by this theory. We show here that this apparent optical mode is a natural consequence of stripe twinning in a diagonal stripe pattern with a magnetic coupling structure which is twofold symmetric, i.e., one possessing the same spatial rotational symmetry as the ground state.
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