Transition metal oxides hold great potential for the development of new device paradigms because of the field-tunable functionalities driven by their strong electronic correlations, combined with their earth abundance and environmental friendliness. Recently, the interfaces between transition-metal oxides have revealed striking phenomena, such as insulator-metal transitions, magnetism, magnetoresistance and superconductivity. Such oxide interfaces are usually produced by sophisticated layer-by-layer growth techniques, which can yield high-quality, epitaxial interfaces with almost monolayer control of atomic positions. The resulting interfaces, however, are fixed in space by the arrangement of the atoms. Here we demonstrate a route to overcoming this geometric limitation. We show that the electrical conductance at the interfacial ferroelectric domain walls in hexagonal ErMnO(3) is a continuous function of the domain wall orientation, with a range of an order of magnitude. We explain the observed behaviour using first-principles density functional and phenomenological theories, and relate it to the unexpected stability of head-to-head and tail-to-tail domain walls in ErMnO(3) and related hexagonal manganites. As the domain wall orientation in ferroelectrics is tunable using modest external electric fields, our finding opens a degree of freedom that is not accessible to spatially fixed interfaces.

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.

, which needs to be positive owing to thermodynamic stability. However, this relation is also true if one of the local effective capacitances, for example, C 1 , is negative, as long as the condition C ≥ 0 is fulfilled. In this scenario, the application of an external voltage V results in V int = V(1 + C 2 /C 1) −1 at the interface between the two dielectrics, such that V int /V > 1 if C 1 < 0. That is, NC of one part of the system enables amplification of the voltage at the interface (fig. 1b). Contrary to the usual decrease in the overall capacitance when a regular (positive) capacitance is added in series, the addition of

Domain walls in ferroelectric semiconductors show promise as multifunctional two-dimensional elements for next-generation nanotechnology. Electric fields, for example, can control the direct-current resistance and reversibly switch between insulating and conductive domain-wall states, enabling elementary electronic devices such as gates and transistors. To facilitate electrical signal processing and transformation at the domain-wall level, however, an expansion into the realm of alternating-current technology is required. Here, we demonstrate diode-like alternating-to-direct current conversion based on neutral ferroelectric domain walls in ErMnO. By combining scanning probe and dielectric spectroscopy, we show that the rectification occurs at the tip-wall contact for frequencies at which the walls are effectively pinned. Using density functional theory, we attribute the responsible transport behaviour at the neutral walls to an accumulation of oxygen defects. The practical frequency regime and magnitude of the direct current output are controlled by the bulk conductivity, establishing electrode-wall junctions as versatile atomic-scale diodes.

One of the most interesting aspects of graphene is the tied relation between structural and electronic properties. The observation of ripples in the graphene samples both free standing and on a substrate has given rise to a very active investigation around the membrane-like properties of graphene and the origin of the ripples remains as one of the most interesting open problems in the system. The interplay of structural and electronic properties is successfully described by the modelling of curvature and elastic deformations by fictitious gauge fields that have become an experimental reality after the suggestion that Landau levels can form associated to strain in graphene and the subsequent experimental confirmation. Here we propose a device to detect microstresses in graphene based on a scanning-tunneling-microscopy setup able to measure Aharonov-Bohm interferences at the nanometer scale. The interferences to be observed in the local density of states are created by the fictitious magnetic field associated to elastic deformations of the sample.PACS numbers: I. LATTICE DEFORMATIONS AND FICTITIOUS MAGNETIC FIELDS IN GRAPHENE.Since graphite monolayers started to be isolated in a controlled way [1,2], graphene has been an optimal playground to test the most exciting ideas in condensed matter [3]. A great deal of attention was initially paid to its striking electronic properties, but it was soon realised that the structural and mechanical properties can be even more interesting both from a fundamental point of view as well as for applications [4]. The modelling of curvature by gauge fields in graphene was suggested in the early publications associated to topological defects needed to form the fullerene structures [5,6]. The main idea was that the phase acquired by an electron circling a pentagonal defect is the same as that arising when circling a solenoid with the appropriate magnetic flux in analogy with the Aharonov-Bohm effect. The fictitious magnetic fields were later applied to model the observed ripples [7][8][9] and elastic deformations [10][11][12][13][14][15]. The state of the art and an updated list of references can be found in [16].A turn of screw took place when the fictitious magnetic field became an experimental reality after the suggestion that Landau levels can form associated to strain in graphene [17,18] and their subsequent observation in [19]. The formation of Landau levels requires very high values of the fictitious magnetic fields and hence very strong deformations of the samples. Fields of up to 300 Tesla were estimated for the observed nano bubbles in [19]. In the present work, we consider the opposite limit where the fields are small and the electronic excitations can still be described in terms of plane waves (rather than Landau levels). As we show below, non-trivial amusing effects can also be generated by fictitious gauge fields in this limit. Specifically, we discuss the realisation of the Aharonov-Bohm (AB) effect via deformation fields and propose a simple scanning-tunneling-microsco...