  Despite the intensive interest in copper- and nickel-based superconductivity
in infinite-layer structures, the physical properties of many other
infinite-layer transition-metal oxides remain largely unknown. Here we unveil,
by the first-principles calculations, the electronic correlation-driven quantum
phase transitions in infinite-layer SrMnO2, where spin and charge orders are
strongly interwoven. At weak electronic correlation region, SrMnO2 is a
ferromagnetic metal with anisotropic spin transportation, as a promising spin
valve under room-temperature. At middle electronic correlation region, a
structural transition accompanied by charge/bond disproportion occurs as a
consequence of Fermi surface nesting, resulting in a ferromagnetic insulator
with reduced Curie temperature. At strong electronic correlation region,
another structural transition occurs that drives the system into degenerately
antiferromagnetic insulators with tunable magnetic order by piezoelectricity, a
new type of multiferroics. Therefore, infinite-layer SrMnO2 is possibly a
unique system on the quantum critical point, where electronic correlation can
induce noticeable Fermi surface evolutions and small perturbations can realize
remarkable quantum phase transitions.
