Local perturbations in complex oxides such as domain walls 1,2 , strain 3,4 and defects 5,6 are of interest because they can modify the conduction or the dielectric and magnetic response and even promote phase transitions. Here we show that the interaction between different types of local perturbations in oxide thin films is an additional source of functionality. Taking SrMnO 3 as a model system, we use nonlinear optics to verify the theoretical prediction that strain induces a polar phase, and density functional theory to show that strain simultaneously increases the concentration of oxygen vacancies. These vacancies couple to the polar domain walls where they establish an electrostatic barrier to electron migration. The result 2 is a state with locally structured room-temperature conductivity consisting of conducting nanosized polar domains encased by insulating domain boundaries, which we resolve using scanning probe microscopy. Our "nanocapacitor" domains can be individually charged, suggesting stable capacitance nanobits with a potential for information storage technology.At first we verify the occurrence of strain-induced polar order in SrMnO 3 thin films.Motivated by the search for novel multiferroic materials, which combine magnetic and ferroelectric orders in the same phase, density functional theory (DFT) predicted the occurrence of ferroelectricity in the perovskite-structure alkaline-earth manganites at larger-than-equilibrium lattice parameters 7,8,9 . For bulk SrMnO 3 this prediction was confirmed by partial substitution of Sr by Ba which induces negative chemical pressure and leads to a polar state 10 . According to DFT, epitaxial SrMnO 3 films should develop a polarisation along one of the pseudocubic <110> axes under >1% epitaxial tensile strain 8 .20-nm films of single-phase SrMnO 3 were grown using pulsed laser deposition on (001)-oriented (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT) with 1.7% tensile strain (see Methods). We characterised the strain state of the films using scanning transmission electron microscopy (STEM) and X-ray and electron diffraction. Figure 1a shows a cross-sectional STEM image evidencing the high quality of the films on the atomic scale with a sharp SrMnO 3 /LSAT (001) interface. The reciprocal space map in Fig. 1a verifies that the films are tetragonal and coherently strained. The electron diffraction In the anisotropy plot in Fig. 1c we present the optical polarisation analysis of the SHG signal obtained on a test area of 0.1 mm 2 . We fitted the angular dependence of the SHG signal by assuming a distribution of four polar domain states denoted as P 1+ , P 1− , P 2+ , P 2− . The indices refer to the orientation of the polar axis according to 1 ± ↔ ±[110] and 2 ± ↔ ±[1 10], see Fig. 1c. The coincidence of the measured data and the fit is excellent with a fitted ratio r = P 1 /P 2 = 0.53 in the population of P 1 -and P 2 -type domain states (r varied between different test areas). In contrast, fits assuming a polarisation along the[100] and [010] directions failed. We co...

Ferroelectric domain walls hold great promise as functional 2D-materials because of their unusual electronic properties. Particularly intriguing are the so-called charged walls where a polarity mismatch causes local, diverging electrostatic potentials requiring charge compensation and hence a change in the electronic structure. These walls can exhibit significantly enhanced conductivity and serve as a circuit path. The development of all-domain-wall devices, however, also requires walls with controllable output to emulate electronic nano-components such as diodes and transistors. Here we demonstrate electric-field control of the electronic transport at ferroelectric domain walls. We reversibly switch from resistive to conductive behavior at charged walls in semiconducting ErMnO 3. We relate the transition to the formation-and eventual activation-of an inversion layer that acts as the channel for the charge transport. The findings provide new insight to the domain-wall physics in ferroelectrics and foreshadow the possibility to design elementary digital devices for all-domain-wall circuitry.

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