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Almost free-standing single crystal mesoscale and nanoscale dots of ferroelectric BaTiO(3) have been made by direct focused ion beam patterning of bulk single crystal material. The domain structures which appear in these single crystal dots, after cooling through the Curie temperature, were observed to form into quadrants, with each quadrant consisting of fine 90 degrees stripe domains. The reason that these rather complex domain configurations form is uncertain, but we consider and discuss three possibilities for their genesis: first, that the quadrant features initially form to facilitate field-closure, but then develop 90 degrees shape compensating stripe domains in order to accommodate disclination stresses; second, that they are the result of the impingement of domain packets which nucleate at the sidewalls of the dots forming "Forsbergh" patterns (essentially the result of phase transition kinetics); and third, that 90 degrees domains form to conserve the shape of the nanodot as it is cooled through the Curie temperature but arrange into quadrant packets in order to minimize the energy associated with uncompensated surface charges (thus representing an equilibrium state). While the third model is the preferred one, we note that the second and third models are not mutually exclusive.

A current-carrying superconducting strip partly penetrated by magnetic flux and surrounded by a bulk magnet of high permeability is considered. Two types of samples are studied: those with critical current controlled by an edge barrier dominating over the pinning, and those with high pinning-mediated critical current masking the edge barrier. It is shown for both cases that the current distribution in a central flux-free part of the strip is strongly affected by the actual shape of the magnetic surroundings. Explicit analytical solutions for the sheet current and self-field distributions are obtained which show that, depending on the geometry, the effect may suppress the total loss-free transport current of the strip or enhance it by orders of magnitude. The effect depends strongly on the shape of the magnet and its distance to the superconductor but only weakly on the magnetic permeability.

Universal scaling features of polarization switching are established experimentally in rather different classes of disordered ferroelectrics: in well-studied lead-zirconate titanate (PZT) ferroelectrics, in recently synthesized Custabilized 0.94(Bi 1/2 Na 1/2 )TiO 3 -0.06BaTiO 3 (BNT-BT) relaxor ferroelectrics, and in classical organic ferroelectrics P(VDF-TrFE). These scaling properties are explained by an extended concept of an inhomogeneous fi eld mechanism (IFM) of polarization dynamics in ferroelectrics. Accordingly, disordered ferroelectrics exhibit a wide spectrum of characteristic switching times due to a statistical distribution of values of the local electric fi eld. How this distribution can be extracted from polarization measurements is demonstrated. Generally, it is shown that the polarization response is primarily controlled by the statistical characteristics of disorder rather than by a temporal law of the local polarization switching.

No abstract

Hybrid structures composed of ferroelectric thin films and functional two-dimensional (2D) materials may exhibit unique characteristics and reveal new phenomena due to the cross-interface coupling between their intrinsic properties. In this report, we demonstrate a symbiotic interplay between spontaneous polarization of the ultrathin BaTiO ferroelectric film and conductivity of the adjacent molybdenum disulfide (MoS) layer, a 2D narrow-bandgap semiconductor. Polarization-induced modulation of the electronic properties of MoS results in a giant tunneling electroresistance effect in the hybrid MoS-BaTiO-SrRuO ferroelectric tunnel junctions (FTJs) with an OFF-to-ON resistance ratio as high as 10, a 50-fold increase in comparison with the same type of FTJs with metal electrodes. The effect stems from the reversible accumulation-depletion of the majority carriers in the MoS electrode in response to ferroelectric switching, which alters the barrier at the MoS-BaTiO interface. Continuous tunability of resistive states realized via stable sequential domain structures in BaTiO adds memristive functionality to the hybrid FTJs. The use of narrow band 2D semiconductors in conjunction with ferroelectric films provides a novel pathway for development of the electronic devices with enhanced performance.

A transport current distribution over a wide superconducting sheet is shown to strongly change in the presence of bulk magnetic screens of a soft magnet with a high permeability. Depending on the geometry, the effect may drastically suppress or protect the Meissner state of the sheet through the enhancement or suppression of the edge barrier critical current. The total transport current in the magnetically screened Meissner state is expected to compete with the critical current of the flux-filled sheet only for samples whose critical current is initially essentially controlled by the edge barrier effect.

The reorientation of defect dipoles and the drift of free charge carriers are the most prominent microscopic mechanisms under discussion to provoke the aging effect in ferroelectrics. These two mechanisms are contrasted taking into account the influence of grain boundaries in a polycrystalline material. For the drift model, clamping pressures on domain walls only depend on geometry and on the transport properties of the mobile defect charge carrier independent of its electronic or ionic nature. For a numerical example clamping pressures as a result of drift of oxygen vacancies are determined in BaTiO3. They range from 106 to 107 Pa corresponding to experimental values.