Complex oxides are record holder materials for many phenomena, including ferroelectricity, piezoelectricity, superconductivity and multiferroicity. Complex oxides often have competing ground states with energies slightly higher than that of the true ground state. This competition is fortuitous because thermodynamic variables (for example, temperature, electric field, magnetic field, stress and chemical potentials) can access these metastable phases that are usually hidden but emerge as the energetic landscape is reshaped by adjusting the thermodynamic variables. Epitaxial superlattices are a platform for imposing thermodynamic boundary conditions to unleash the properties of hidden phases by altering the delicate balance between competing spin, charge, orbital and lattice degrees of freedom. Additionally, a feature of complex oxides with large responses (large property coefficients) is the coexistence of phases on the nanoscale. New phases can emerge at the heterointerfaces of oxide superlattices, and X-ray, electron, neutron and proximal probes as well as ab initio theoretical studies can provide insights into these emergent phenomena.

复合氧化物是许多现象的记录保持者材料，包括铁电，压电，超导电性和多铁性。复杂的氧化物通常具有竞争性的基态，其能量比真正的基态的能量略高。这种竞争是偶然的，因为热力学变量（例如温度，电场，磁场，应力和化学势）可以访问这些亚稳态相，这些亚稳态相通常是隐藏的，但随着通过调整热力学变量重塑能量景观而出现。外延超晶格是一个平台，可通过改变竞争自旋，电荷，轨道和晶格自由度之间的微妙平衡来施加热力学边界条件，以释放隐藏相的特性。此外，具有大响应（大特性系数）的复合氧化物的一个特征是纳米级上的相共存。新的相可能出现在氧化物超晶格的异质界面上，X射线，电子，中子和近端探针以及从头开始的理论研究都可以提供对这些新兴现象的见解。