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Photosensitivity of thermally evaporated chalcogenide amorphous films of xGe45Se55-(1-x)As45Se55 (x = 0, 0.25, 0.5, 0.75, 1) composition is investigated when exposed to the laser light of 660 nm wavelength. The photo-induced effects transition from photodarkening (PD) to photobleaching (PB) as Ge45Se55 x increases from 0 to 1. The degree of PB correlates with the concentration of Ge-Ge homopolar bonds. The kinetics of PD and PB can be well described by a stretched exponential function. The dynamic response of PB is much faster than that of PD films in the present glass system. [ABSTRACT FROM AUTHOR]

Chalcogenide glasses have attracted considerable attention and found various applications due to their infrared transparency and other optical properties. The As–S–Se chalcogenide glass, with its large glass-formation domain and favorable nonlinear property, is a promising candidate system for tailoring important optical properties through modification of glass composition. In this context, a systematic study on ternary As–S–Se glass, chalcogen-rich versus well-studied stochiometric compositions, has been carried out using three different techniques: Raman spectroscopy, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. These complementary techniques lead to a consistent understanding of the role of S/Se ratio in chalcogen-rich As–S–Se glasses, as compared to stochiometric composition, and to provide insight into the structural units (such as the mixed pyramidal units) and evidence for the existence of homopolar bonds (such as Se–Se, S–S, and Se–S), which are the possible structural origin of the high nonlinearity in these glasses. [ABSTRACT FROM AUTHOR]

Transient grating experiments after optical band-gap pulsed illumination of amorphous a-As2Se3 thin films reveal the existence of a well defined transport process occurring on length- and time-scales of the order of micrometers and microseconds, respectively. We tentatively assign this fast process, corresponding to a mobility of 0.04 ± 0.005 cm2 V-1 s-1, to the diffusion of photoexcited charge carriers with microsecond lifetime. [ABSTRACT FROM AUTHOR]

We report a dramatic change in effective three-photon absorption coefficient of amorphous Ge16As29Se55 thin films, when its optical band gap decreases by 10 meV with 532 nm light illumination. This large change provides valuable information on the higher excited states, which are otherwise inaccessible via normal optical absorption. The results also indicate that photodarkening in chalcogenide glasses can serve as an effective tool to tune the multiphoton absorption in a rather simple way. [ABSTRACT FROM AUTHOR]

Quick scanning extended x-ray absorption fine-structure spectroscopy is used to obtain in situ structural information on the real-time response of network glasses at the nanoscale level of atomic organization to the temperature ramp through the glass transition range. The results testify nonlinear, real-time temperature response indicative of nanoscale dynamic heterogeneity in disordered systems with intermediate fragility, related to the intermetabasin transitions within potential energy/enthalpy landscape. [ABSTRACT FROM AUTHOR]

We show that strong nonlinear electron transport in the ferromagnetic insulating (FMI) state of manganites, responsible for phenomena such as colossal electroresistance and current induced resistance switching, can occur due to a hot electron effect. In the FMI state, which we show is an insulator with a Coulomb gap, the temperature of the electron and lattice baths can decouple at high input power levels, leading to heating of the electron bath. Parameters of the hot electron effect model were independently determined via time dependence experiments and are in good agreement with the experimental values. [ABSTRACT FROM AUTHOR]

Colossal electroresistance and current induced resistivity switching have been measured in the ferromagnetic insulating (FMI) state of single crystal manganite La0.82Ca0.18MnO3. The sample has a Curie transition temperature TC=165 K and the FMI state is realized for temperatures T<100 K. The electroresistance (ER), arising from a strong nonlinear resistivity, attains a large value (≈100%) in the FMI state. However, this is accompanied by a collapse of the magnetoresistance (MR) to a small value even in magnetic field (H) of 10 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled. [ABSTRACT FROM AUTHOR]

Colossal electroresistance and current induced resistivity switching have been measured in the ferromagnetic insulating (FMI) state of single crystal manganite La0.82Ca0.18MnO3. The sample has a Curie transition temperature TC=165 K and the FMI state is realized for temperatures T<100 K. The electroresistance (ER), arising from a strong nonlinear resistivity, attains a large value (≈100%) in the FMI state. However, this is accompanied by a collapse of the magnetoresistance (MR) to a small value even in magnetic field (H) of 10 T. This demonstrates that the mechanisms that give rise to ER and MR are effectively decoupled. [ABSTRACT FROM AUTHOR]

The atomistic origin of photoinduced vector (polarization-dependent) phenomena in As-Se films is determined by extended x-ray absorption fine structure with in situ exposure to polarized laser light. A vector structural change is observed directly for any material: there is an expansion of the nearest-neighbor distance around the Se atoms, the magnitude of which depends on the direction of light polarization; the effect around As atoms is relatively smaller. The results point to the origin of scalar as well as vector changes in properties, which either persist after the light is removed, or exist only when light is incident on the sample. [ABSTRACT FROM AUTHOR]