Electronic orbital currents and polarization in Mott insulators

Strongly correlated electron insulators are one of the most important classes of materials in modern solid-state physics. We demonstrate that certain classes of Mott insulators, that usually are geometrically frustrated, exhibit unexpected charge effects: for certain spin textures, spontaneous circular electric currents or nonuniform charge distribution exist in the ground state of Mott insulators. In addition, low-energy "magnetic" states contribute comparably to the dielectric and magnetic response functions, epsilon(ik)(omega) and mu(ik)(omega), leading to interesting phenomena such as dipole-active ESR transitions, rotation of the electric-field polarization, and resonances which may be common to both functions producing a negative refraction index in a window of frequencies.