Quantum dynamics of hard-core bosons in tilted bichromatic optical lattices

Polycrystalline samples of the perovskite family Sr1-xCaxCrO3 have been prepared at high pressure and temperature in steps of 1/6 over the range 0 <= x <= 1. Rietveld analysis shows a series of structural phase transitions from cubic to tetragonal to orthorhombic with increasing x. The cubic samples have no long-range magnetic order; the other samples become antiferromagnetically ordered below a T-N that increases with x. At ambient pressure, the electric transport properties of the cubic and tetragonal phases are semiconducting with a small (meV range) activation energy that increases with x; the orthorhombic phase exhibits variable-range hopping rather than the small-polaron behavior typically found for mixed-valent, localized-electron configurations. Above a pressure P = P-C, a smooth insulator-metal transition is found at a T-IM that decreases with increasing P for a fixed x; P-C increases with x. These phenomena are rationalized qualitatively with a pi*-band model having a width W-pi that approaches crossover from itinerant-electron to localized-electron behavior as W-pi decreases with increasing x. The smaller size of the Ca2+ ion induces the structural changes and the greater acidity of the Ca2+ ion is primarily responsible for narrowing W-pi as x increases.