Tunable ferroelectricity in artificial tri-layer superlattices comprised of non-ferroic components.

Heterostructured material systems devoid of ferroic components are presumed not to display ordering associated with ferroelectricity. In heterostructures composed of transition metal oxides, however, the disruption introduced by an interface can affect the balance of the competing interactions among electronic spins, charges and orbitals. This has led to the emergence of properties absent in the original building blocks of a heterostructure, including metallicity, magnetism and superconductivity. Here we report the discovery of ferroelectricity in artificial tri-layer superlattices consisting solely of non-ferroelectric NdMnO(3)/SrMnO(3)/LaMnO(3) layers. Ferroelectricity was observed below 40 K exhibiting strong tunability by superlattice periodicity. Furthermore, magnetoelectric coupling resulted in 150% magnetic modulation of the polarization. Density functional calculations indicate that broken space inversion symmetry and mixed valency, because of cationic asymmetry and interfacial polar discontinuity, respectively, give rise to the observed behaviour. Our results demonstrate the engineering of asymmetric layered structures with emergent ferroelectric and magnetic field tunable functions distinct from that of normal devices, for which the components are typically ferroelectrics.

Phonon- and surface-roughness-limited mobility of gate-all-around 3C-SiC and Si nanowire FETs.

We present numerical simulations of gate-all-around (GAA) 3C-SiC and Si nanowire (NW) field effect transistors (FETs) using a full quantum self-consistent Poisson-Schrödinger algorithm within the non-equilibrium Green's function (NEGF) formalism. A direct comparison between Si and 3C-SiC device performances sheds some light on the different transport properties of the two materials. Effective mobility extraction has been performed in a linear transport regime and both phonon- (PH) and surface-roughness-(SR) limited mobility values were computed. 3C-SiC FETs present stronger acoustic phonon scattering, due to a larger deformation potential, resulting in lower phonon-limited mobility values. Although Si NW devices reveal a slightly better electrostatic control compared to 3C-SiC ones, SR-limited mobility shows a slower degradation with increasing charge density for 3C-SiC devices. This implies that the difference between Si and 3C-SiC device mobility is reduced at large gate voltages. 3C-SiC nanowires, besides their advantages compared to silicon ones, present electrical transport properties that are comparable to the Si case.