Charge Inhomogeneities in Strongly Correlated Systems

We review the problem of stripe states in strongly correlated systems,and some of the theoretical, numerical and experimental methods used in the last few years to understand these states. We compare these states to more traditional charge-ordered states such as charge density waves (CDW) and phase-separated systems. We focus on the origin of stripe states as an interplay between magnetic and kinetic energy, and argue that the stripe state is generated via a mechanism of kinetic energy release that can be described via strongly correlated models such as the t-J model. We also discuss phenomenological models of stripes, and their relevance for magnetism and for the pinning of stripes by the underlying lattice and by disordered impurities. Recent experimental evidence for the existence of stripe states in different cuprate systems is also reviewed.