859 research outputs found
Non-volatile resistive switching in dielectric superconductor YBCO
We report on the reversible, nonvolatile and polarity dependent resistive
switching between superconductor and insulator states at the interfaces of a
Au/YBaCuO (YBCO)/Au system. We show that the
superconducting state of YBCO in regions near the electrodes can be reversibly
removed and restored. The possible origin of the switching effect may be the
migration of oxygen or metallic ions along the grain boundaries that control
the intergrain superconducting coupling. Four-wire bulk resistance measurements
reveal that the migration is not restricted to interfaces and produce
significant bulk effects.Comment: 4 pages, 4 figures, corresponding author: C. Acha ([email protected]
Mechanism for bipolar resistive switching in transition metal oxides
We introduce a model that accounts for the bipolar resistive switching
phenomenom observed in transition metal oxides. It qualitatively describes the
electric field-enhanced migration of oxygen vacancies at the nano-scale. The
numerical study of the model predicts that strong electric fields develop in
the highly resistive dielectric-electrode interfaces, leading to a spatially
inhomogeneous oxygen vacancies distribution and a concomitant resistive
switching effect. The theoretical results qualitatively reproduce non-trivial
resistance hysteresis experiments that we also report, providing key validation
to our model.Comment: Accepted for publication in Physical Review B, 6 twocolumn pages, 5
figure
First-Order Insulator-to-Metal Mott Transition in the Paramagnetic 3D System GaTa4Se8
The nature of the Mott transition in the absence of any symmetry braking
remains a matter of debate. We study the correlation-driven insulator-to-metal
transition in the prototypical 3D Mott system GaTa4Se8, as a function of
temperature and applied pressure. We report novel experiments on single
crystals, which demonstrate that the transition is of first order and follows
from the coexistence of two states, one insulating and one metallic, that we
toggle with a small bias current. We provide support for our findings by
contrasting the experimental data with calculations that combine local density
approximation with dynamical mean-field theory, which are in very good
agreement.Comment: 5 pages and 4 figures. Supplemental material: 2 pages, 2 figure
Pressure effects in the triangular layered cobaltites NaxCoO2
We have measured transport properties as a function of temperature and
pressure up to 30GPa in the NaxCoO2 system. For the x=0.5 sample the transition
temperature at 53K increases with pressure, while paradoxically the sample
passes from an insulating to a metallic ground state. A similar transition is
observed in the x=0.31 sample under pressure. Compression on the x=0.75 sample
transforms the sample from a metallic to an insulating state. We discuss our
results in terms of interactions between band structure effects and Na+ order.Comment: 18 pages, 5 figure
Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals
We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation.Comment: 5 pages, 6 figures, corresponding author: C. Acha ([email protected]
Revestimiento de mortero termocrómico en fachada: impacto en la eficiencia energética del edificio
Thermochromic materials, with optical properties changing with temperature, optimize the use of solar energy by the building envelope for the improvement of energy efficiency. The purpose of this research is to determine the impact of a thermochromic mortar (TM) façade coating on the building energy performance in a Mediterranean climate. A new calculation methodology is proposed to implement the dynamical optical properties of the mortar in conventional energetic simulation tools. This study considers a coating with variable optical properties that move from 0,65 to 0,60 solar absorptance value, and a transition temperature moving from 20ºC to 35ºC. The mortar shows a dark grey colour for low temperatures and a light colour for high temperatures. The building with TM coating shows a 3 % lower yearly energy demand than the building with non-variable optical properties, with a maximum heating demand reduction reaching 8 %.Los materiales termocrómicos, con propiedades ópticas variables con la temperatura, optimizan el aprovechamiento de la energÃa solar por la envolvente del edificio para mejorar su eficiencia energética. El objeto de este estudio es determinar el impacto de un revestimiento de mortero termocrómico (MT) en fachada sobre la eficiencia energética del edificio en un clima mediterráneo. Se propone una metodologÃa de cálculo para implementar las propiedades ópticas variables del mortero en la simulación energética. Se estudia un revestimiento de MT con absortancia solar entre 0,65 y 0,60, y una temperatura de transición entre 20ºC y 35ºC. El mortero muestra color gris oscuro para temperaturas bajas y color claro para temperaturas altas. El edificio presenta una demanda energética anual un 3 % inferior que con revestimiento de propiedades ópticas no variables. La reducción de demanda de calefacción puede llegar a un 8%
- …