Phase coexistence and competing interactions in complex oxides

A significant progress in the materials physics research of the past decades, has been associated with the emerging paradigm of naturally or artificially fabricated heterogeneous structures/phases of complex materials with distinct physical phases, in which various physical degrees of freedoms are intricately coupled and charge carriers are strongly interacting. The heterogeneous structures/phases can be associated with various architectures and length-scales. For example, in the intrinsic multiferroics, magnetism and ferroelectricity are intricately mixed in atomic length-scales, but they coexist with much larger length scales such as micro-meters in the composite multiferroics. The recent investigation has revealed that the interplay between magnetism and ferroelectricity can be significant in magnetically-driven multiferroics where magnetic orders with broken inversion symmetry induce ferroelectric lattice distortions through exchange-striction. Herein, we focus on three systems with the coexistence of distinct physical phases: (1) an intrinsic multiferroic of a S = 1/2 chain cuprate, (2) a composite multiferroic fabricated by utilizing chemical/structural phase separation, and (3) a heterogeneous mixture where antiferromagnetic-insulating and high TC superconducting phases coexist. These novel systems reveal unprecedented physical properties and phenomena due to the presence of physical distinct phases in spatial proximity.