Melting of quasi-two-dimensional charge stripes in La5/3Sr1/3NiO4

Commensurability effects for nickelates have been studied, for the first time, by neutron scattering on La5/3Sr1/3NiO4. Upon cooling, this system undergoes three successive phase transitions associated with quasi-two-dimensional (2D) commensurate charge and spin stripe ordering in the NiO2 planes. The two lower temperature phases are stripe lattice states with quasi-long-range in-plane charge correlation. When the lattice of 2D charge stripes melts. it goes through an intermediate glass state before becoming a disordered liquid state. This glass state shows short-range charge order without spin order, and may be called a ''stripe glass'' which resembles the hexatic/nematic state in 2D melting.