Abstract
The insulator-to-metal transition continues to be a challenging subject, especially when
electronic correlations are strong. In layered compounds, such as La2–xSrxNiO4 and
La2–xBaxCuO4, the doped charge carriers can segregate into periodically spaced charge
stripes separating narrow domains of antiferromagnetic order. Although there have been
theoretical proposals of dynamically fluctuating stripes, direct spectroscopic evidence of
charge-stripe fluctuations has been lacking. Here we report the detection of critical lattice
fluctuations, driven by charge-stripe correlations, in La2–xSrxNiO4 using inelastic neutron
scattering. This scattering is detected at large momentum transfers where the magnetic form
factor suppresses the spin fluctuation signal. The lattice fluctuations associated with the
dynamic charge stripes are narrow in q and broad in energy. They are strongest near the
charge-stripe melting temperature. Our results open the way towards the quantitative theory
of dynamic stripes and for directly detecting dynamical charge stripes in other strongly
correlated systems, including high-temperature superconductors such as La2–xSrxCuO4.
