103 research outputs found
Bilayer manganites: polarons in the midst of a metallic breakdown
The exact nature of the low temperature electronic phase of the manganite
materials family, and hence the origin of their colossal magnetoresistant (CMR)
effect, is still under heavy debate. By combining new photoemission and
tunneling data, we show that in La{2-2x}Sr{1+2x}Mn2O7 the polaronic degrees of
freedom win out across the CMR region of the phase diagram. This means that the
generic ground state is that of a system in which strong electron-lattice
interactions result in vanishing coherent quasi-particle spectral weight at the
Fermi level for all locations in k-space. The incoherence of the charge
carriers offers a unifying explanation for the anomalous charge-carrier
dynamics seen in transport, optics and electron spectroscopic data. The
stacking number N is the key factor for true metallic behavior, as an
intergrowth-driven breakdown of the polaronic domination to give a metal
possessing a traditional Fermi surface is seen in the bilayer system.Comment: 7 pages, 2 figures, includes supplementary informatio
Tunneling electroresistance effect in ferroelectric tunnel junctions at the nanoscale
Stable and switchable polarization of ferroelectric materials opens a
possibility to electrically control their functional behavior. A particularly
promising approach is to employ ferroelectric tunnel junctions where the
polarization reversal in a ferroelectric barrier changes the tunneling current
across the junction. Here, we demonstrate the reproducible tunneling
electroresistance effect using a combination of Piezoresponse Force Microscopy
(PFM) and Conducting Atomic Force Microscopy (C-AFM) techniques on
nanometer-thick epitaxial BaTiO3 single crystal thin films on SrRuO3 bottom
electrodes. Correlation between ferroelectric and electronic transport
properties is established by the direct nanoscale visualization and control of
polarization and tunneling current in BaTiO3 films. The obtained results show a
change in resistance by about two orders of magnitude upon polarization
reversal on a lateral scale of 20 nm at room temperature. These results are
promising for employing ferroelectric tunnel junctions in non-volatile memory
and logic devices, not involving charge as a state variable.Comment: 18 pages, 4 figure
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