Thinning films induces ferroelectricity: Thin ferroelectric films are needed in computers and medical devices. However, traditional ferroelectric films typically become less and less polarized the thinner the films become. Instead of using a good ferroelectric and making it thinner, Lee et al. started with SrTiO ³ , which in its bulk form is not ferroelectric. This material does have naturally occurring nanosized polarized regions. and when the thickness of the SrTiO ₃ films reaches the typical size of these regions, the whole film aligns and becomes ferroelectric. Science , this issue p. 1314

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO₃) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO₃ matrix. Such correlation effects can lead to new functionalities in designed heterostructures.

We show that despite the low anisotropy, strong vortex pinning, and high irreversibility field $H_{\text{irr}}$ close to the upper critical field $H_{c2}$ of $\text{Ba}{\left({\text{Fe}}_{1-\text{x}}{\text{Co}}_{\text{x}}\right)}_2{\text{As}}_2$ , the critical current density $J_{\text{gb}}$ across [001] tilt grain boundaries (GBs) of thin film $\text{Ba}{\left({\text{Fe}}_{1-\text{x}}{\text{Co}}_{\text{x}}\right)}_2{\text{As}}_2$ bicrystals is strongly depressed, similar to high-$T_c$ cuprates. Our results suggest that weak-linked GBs are characteristic of both cuprates and pnictides because of competing orders, low carrier density, and unconventional pairing symmetry.