The response of transport properties to static electric field in La0.7Ce0.3MnO3 epitaxial thin films

We investigated the influence of static electric field on the transport properties in La0.7Ce0.3MnO3 epitaxial thin films by using a simple field effect configuration (FEC), which was formed on a single layer film. Substrates act as gates and films as channels. Such an easily manipulative technique avoids many possible problems appeared in multilayer structures, such as poor interface and severe inter-diffusion, which may influence the intrinsic characteristics of investigated targets. One knows that tetravalence-doped La0.7Ce0.3MnO3 (LEMO) systems exhibit metal-insulator transition and ferromagnetic behavior, similar to the ditravalence-doped La0.7Ca0.3MnO3. However, for the conductive mechanism of LEMO, strong controversies have existed for a long time with whether it is intrinsically electron-type or hole-type. Our experiments give evidence of the hole-type nature in LEMO. In the device with LEMO as channel and LaAlO3(LAO) as gate, applied positive bias poles gate and induces charge at the area between gate and channel. The polarized charge in the gate is compensated by inducing electrons in the channel. If LEMO is of electron-type, the increased carrier density would cause a decease of channel resistance. However, we experimentally found the channel resistance remarkably increases upon a positive bias. Such a fact is completely the same as the behavior observed in hole-doped La0 7Ca0.3MnO3channel, and thus strongly supports the hole-type nature in LEMO channel. Furthermore, we found that the large field effect in LEMO is nonlinear and polarity dependent on the applied bias. A percolative phase separation picture is taking into account to interpret the observed field effect.published_or_final_versio

Current-sensitive electroresistance and the response to a magnetic field in La0.8Ca0.2MnO3 epitaxial thin films

The influence of a transport dc current on the resistivity of La0.8Ca0.2MnO3 epitaxial thin films and their response to a magnetic field has been investigated. We found that when the applied dc current exceeds a threshold value, the electric resistivity in these films could be significantly enhanced. Such observations are completely repeatable. More attractive is that the enhanced resistance turns out to be sensitive to a weak current in a wide temperature range from 10 to 300 K. Even a very small dc current could remarkably depress the high resistance, showing a colossal electroresistance (ER) effect. ER reaches ~1175% at temperatures lower than ~50 K, and ~705% at 300 K for a current changing from 0.72 to 10.5 µA. A highly nonlinear behavior of the I–V curves persists even to room temperature. Significant influence of the magnetic field on the electric transports was also observed. It is found that a low field of 0.25 T could remarkably affect the I–V curves, resulting in a considerable magnetoresistance (MR). ©2005 American Institute of Physics.published_or_final_versio

Current-induced metastable resistive state in epitaxial thin films of La1-xCaxMnO3 (x=0.2, 0.3)

The influence of a transport dc current on electric resistivity has been investigated in epitaxial thin films of La1–xCaxMnO3 (x = 0.2, 0.3). A most prominent finding is the appearance of a remarkable resistive peak at temperatures well below the Curie temperature Tc. Such a resistive peak is developed when the dc current over a critical value was applied in a temperature cycling from 300 to 10 K. The resistance peak turns out to be extremely sensitive to a weak current. Even a very small current could greatly depress the height of the peak. Such a current-induced state with high resistivity is metastable compared to the pristine state. The stability of the induced state has been also studied. © 2005 American Institute of Physics.published_or_final_versio

Unusual current-induced electroresistance in epitaxial thin films of La0.8Ca0.2MnO3

The transport behavior of La0.8Ca0.2MnO3 thin films with Curie temperature TC at ~286 K has been investigated under various applied currents in the absence of magnetic field. An unusual current-induced electroresistance (ER) was observed. When the applied current density reaches a critical value, the films could not revert to the initial state. A novel state can be induced by a suitable large current, in which the insulation-metal transition temperature remains almost unchanged comparing with the initial state, whereas the value of the peak resistance is very sensitive to the applied current. Even a rather low current density can depress it significantly. ER reaches ~43% under a small current of 0.5 mA (density ~1×104 A cm–2). The observed ER effect seems to favor a percolative phase separation picture.published_or_final_versio

Good rectifying characteristic in p–n junctions composed of La0.67Ca0.33MnO3-δ/Nb–0.7 wt %-doped SrTiO3

Simple p–n junctions have been fabricated using a simple heteroepitaxial structure of La0.67Ca0.33MnO3–/Nb-doped SrTiO3. In such junctions, the La0.67Ca0.33MnO3– exhibits semiconductor behavior due to oxygen deficiency, whereas the Nb–0.7 wt %-doped SrTiO3 shows a metal behavior. These junctions demonstrate good rectifying characteristic in a wide temperature range from 5 to 350 K. An intriguing observation is that the rectifying behavior is nearly independent of temperature. © 2003 American Institute of Physics.published_or_final_versio

Resonances in an external field: the 1+1 dimensional case

Using non-relativistic effective field theory in 1+1 dimensions, we generalize Luescher's approach for resonances in the presence of an external field. This generalized approach provides a framework to study the infinite-volume limit of the form factor of a resonance determined in lattice simulations.Comment: 13 pages, 2 postscript figure

Development of an antibody fragment that stabilizes GPCR/G-protein complexes.

Single-particle cryo-electron microscopy (cryo-EM) has recently enabled high-resolution structure determination of numerous biological macromolecular complexes. Despite this progress, the application of high-resolution cryo-EM to G protein coupled receptors (GPCRs) in complex with heterotrimeric G proteins remains challenging, owning to both the relative small size and the limited stability of these assemblies. Here we describe the development of antibody fragments that bind and stabilize GPCR-G protein complexes for the application of high-resolution cryo-EM. One antibody in particular, mAb16, stabilizes GPCR/G-protein complexes by recognizing an interface between Gα and Gβγ subunits in the heterotrimer, and confers resistance to GTPγS-triggered dissociation. The unique recognition mode of this antibody makes it possible to transfer its binding and stabilizing effect to other G-protein subtypes through minimal protein engineering. This antibody fragment is thus a broadly applicable tool for structural studies of GPCR/G-protein complexes

Metastable resistivity of La0.8Ca0.2MnO3 manganite thin films

Transport properties of La0.8Ca0.2MnO3 thin films 15 and 130 nm thick have been investigated and confronted with the properties of bulk single crystals of the same composition. It has been found that low-temperature resistivity of the films is sensitive to electric current and/or field treatment and thermal history of the sample. Thin films exhibit a variety of metastable resistive states and spontaneously evolve toward high-resistivity state in which the films exhibit highly nonlinear transport behavior at low temperatures. Nonlinear V-I characteristics are well described by indirect tunneling model. The memory of the resistivity can be, at least partly, erased by a heat treatment at temperatures above the memory erasing temperature. The memory erasing temperature for thin films, T=450 K, is significantly higher than that of single crystals. The results are interpreted in the context of strain driven phase separation. Coexistence of two ferromagnetic phases with different orbital orders and different conductivities is influenced by strains due to thermal cycling and current flow.published_or_final_versio

Magnetoresistance in LaFe11.2Co0.7Si1.1 compound

Magnetoresistance has been studied in LaFe/sub 11.2/Co/sub 0.7/Si/sub 1.1/ compound. The ferromagnetic ordering at Curie temperature T/sub C/ of 274 K was found being accompanied by a drastic negative lattice expansion due to the strong structural and magnetic interplay. Such a simultaneous magnetic and lattice change would cause changes in transport properties. The measured transport properties indicate that the transition can be induced by temperature or applied magnetic field. The sample shows a metallic character below T/sub C/, whereas the electrical resistance decreases dramatically and then recovers the metal-like behavior above T/sub C/. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase of field leads to an increase of resistance at temperatures near but above T/sub C/, which is a result of the field-induced metamagnetic transition from paramagnetic to ferromagnetic state.published_or_final_versio

Magnetocaloric effect in itinerant electron metamagnetic systems La(Fe1-xCox)11.9Si1.1

The NaZn13-type compounds La(Fe1–xCox)11.9Si1.1 (x=0.04, 0.06, 0.08) were successfully synthesized, in which the Si content is the limit that can be reached by arc-melting technique. TC is tunable from 243 to 301 K with Co doping from x=0.04 to 0.08. Great magnetic entropy change S in a wide temperature range from ~230 to ~320 K has been observed. The adiabatic temperature change Tad upon changing magnetic field was also directly measured. Tad of sample x=0.06 reaches ~2.4 K upon a field change from 0 to 1.1 T. The temperature hysteresis upon phase transition is small, ~1 K, for all samples. The influence of Co doping on itinerant electron metamagnetic transition and magnetic entropy change is discussed. ©2005 American Institute of Physics.published_or_final_versio