Metal oxide semiconductor field-effect transistors, formed using silicon dioxide and silicon, have undergone four decades of staggering technological advancement. With fundamental limits to this technology close at hand, alternatives to silicon dioxide are being pursued to enable new functionality and device architectures. We achieved ferroelectric functionality in intimate contact with silicon by growing coherently strained strontium titanate (SrTiO3) films via oxide molecular beam epitaxy in direct contact with silicon, with no interfacial silicon dioxide. We observed ferroelectricity in these ultrathin SrTiO3 layers by means of piezoresponse force microscopy. Stable ferroelectric nanodomains created in SrTiO3 were observed at temperatures as high as 400 kelvin.

The interplay between spin waves ͑magnons͒ and electronic structure in materials leads to the creation of additional bands associated with electronic energy levels which are called magnon sidebands. The large difference in the energy scales between magnons ͑meV͒ and electronic levels ͑eV͒ makes this direct interaction weak and hence makes magnon sidebands difficult to probe. Linear light absorption and scattering techniques at low temperatures are traditionally used to probe these sidebands. Here we show that optical secondharmonic generation, as the lowest-order nonlinear process, can successfully probe the magnon sidebands at room temperature and up to 723 K in bismuth ferrite, associated with large wave vector multimagnon excitations which linear absorption studies are able to resolve only under high magnetic fields and low temperatures. Polarized light studies and temperature dependence of these sidebands reveal a spin-charge coupling interaction of the type P s L 2 between the spontaneous polarization ͑P s ͒ and antiferromagnetic order parameter, L in bismuth ferrite, that persists with short-range correlation well into the paramagnetic phase up to high temperatures. These observations suggest a broader opportunity to probe the collective spin-charge-lattice interactions in a wide range of material systems at high temperatures and electronic energy scales using nonlinear optics.

Here we introduce angle-resolved piezoresponse force microscopy ͑AR-PFM͒, whereby the sample is rotated by 30°increments around the surface normal vector and the in-plane PFM phase signals are collected at each angle. We obtained the AR-PFM images of BaTiO 3 single crystal and cube-on-cube epitaxial ͑001͒ BiFeO 3 ͑BFO͒ thin film on SrRuO 3 / SrTiO 3 substrate, and confirmed that the AR-PFM provides more unambiguous information on the in-plane polarization directions than the conventional PFM method. Moreover, we found eight additional in-plane polarization variants in epitaxial BFO thin films, which are formed to mitigate highly unstable charged domain boundaries.