Polarons, the combined motion of electrons in a cloth of their lattice distortions, are a key transport feature in doped manganites. To develop a profound understanding of the colossal resistance effects induced by external fields, the study of polaron correlations and the resulting collective polaron behavior, i.e., polaron ordering and transition from polaronic transport to metallic transport is essential. We show that static long-range ordering of Jahn-Teller polarons forms a polaron solid which represents a new type of charge and orbital ordered state. The related noncentrosymmetric lattice distortions establish a connection between colossal resistance effects and multiferroic properties, i.e., the coexistence of ferroelectric and antiferromagnetic ordering. Colossal resistance effects due to an electrically induced polaron solid-liquid transition are directly observed in a transmission electron microscope with local electric stimulus applied in situ using a piezo-controlled tip. Our results shed light onto the colossal resistance effects in magnetic field and have a strong impact on the development of correlated electron-device applications such as resistive random access memory (RRAM).correlated electrons ͉ magnetism ͉ oxide M aterials with a coexistence of a variety of electronic and lattice interactions of similar strength are able to create fundamentally differing electronic ground states (1). In doped manganites (Re 1Ϫx A x MnO 3 ; Re and A are rare-and alkaline-earth cations), this includes ferromagnetic metallic, paramagnetic insulating and antiferromagnetic charge and orbital ordered states, representing different collective behavior of the microscopic lattice, charge, orbital, and spin degrees of freedom (2). External fields influence the subtle balance of the interactions and the induced phase transitions between different ground states are related to colossal resistance effects in magnetic (3, 4), electric (5), photon (6), and strain fields (7). They offer great opportunities for new correlated electron devices (8), e.g., in magnetoelectronics and nonvolatile electronic data storage.Among various interactions, two different basic types of electron-lattice coupling (9) play a distinct role in manganites: One is the effect of the static crystal structure on electron transport and bonding. Different ion radii of the involved Re and A cations generate different internal stress on the MnOOOMn bonds. The different resulting types of lattice distortions involve transitions from the ideal cubic to hexagonal, rhombohedral, and orthorhombic structures (10, 11), which may induce polar distortions or even multiferroic ordering, i.e., the presence of electric and magnetic order of electrons in a single phase (12). In doped systems, the decrease of the MnOOOMn bonding angle below 180°due to rigid rotations of the MnO 6 octahedra (for example, see Fig. 2a) results in a strong reduction of the bandwidth of the e g conduction electrons, the conductivity, and the related ferromagnetic double exchange (13).In addit...

Quality control in the growing field of microsystems technology (MST) demands much higher resolution and accuracy of the testing equipment than conventional products. This is especially challenging in the field of probing. For tactile (i.e., contacting) measurement systems this is equivalent to a demand for miniaturization (in terms of form deviation and size of the contacting element, moving mass, probing force) and hence leads to a top down approach. Another approach is to qualify existing picturing microscopy techniques for three-dimensional measurements such as scanning probe microscopy and various optical microscopy techniques (bottom up approach) emphasizing the improvement of repeatability, linearity and calibration. The challenges and demands of micro systems technology on probing systems and different practical approaches for satisfying them will be presented with their special characteristics, fields and limits of application.

The temperature-dependent resistivity and the colossal resistance effect induced by strong electric fields of the small-band Pr1−xCaxMnO3 (PCMO) manganites are analysed with respect to the influence of the Ca doping, post-annealing, the prehistory of the electric stimulation, and the physical dimensions of the sample. Despite the phase separation between charge and orbital ordered and disordered phases, PCMO reveals the properties of a homogeneous medium with a conductivity governed by the hopping of small polarons if the electric field is not too strong. In contrast, high electric fields induce a structural transition which gives rise to a glassy behaviour in the transient regime. In the low resistance state the small activation energy of charge carrier hopping implies a transition to large polaron hopping.

Combining pulse-probe measurements as well as local transport measurements in an electron microscope system by a simultaneous monitoring of the structural changes, we show that the nonvolatile electric pulse induced resistance change in Ca-doped praseodymium manganite is related to a polaron order-disorder transition, modified by electronic band bending in the vicinity of an interface to a metallic electrode. A pronounced resistance change requires a critical distance between the two electrode and/or oxide interfaces to form an insulating incommensurate polaron-ordered phase during the initialization of the device. Based on these observations, a qualitative model for the electronic structure of the metal-oxide interface is developed.

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