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In this work, a transparent and free-standing ionic gel as the dielectric layer for polarization switching in leaky ferroelectric thin films is reported. By applying an electric field over an ionic liquid dielectric layer used as an electrostatic field gated capacitor, one can avoid electronic conduction. The association of the electrical double layer with depolarization at the solid-liquid interface contributes to the reversible switching in PbZrxTi1-xO3 (x = 0.6) (PZT). Using such ionic gels, the anisotropic ferroelastic switching from mono-c-domain toward a-domain is studied in PZT grown on CaF2 substrates. Our results demonstrate that an electrostatic field, induced by the free-standing ionic gel, is an effective and promising way to investigate leaky ferroelectrics.

A new mechanism to understand time‐dependent features in the conduction of a two‐dimensional electron gas (2 DEG) in high electric fields is proposed and discussed. The mechanism is based on the idea that not only the properties of the GaAs/AlGaAs heterostructure have to be included, but also the properties of the transition from the ohmic contact to the heterostructure. We show that the ohmic contact to the heterostructure is fundamentally different from the contact to a bulk semiconductor. In low electric fields electrons cannot move from the contact into the AlGaAs since the conduction band normally lies above the Fermi level. However, when high enough electric fields are applied, the barrier between the contact and AlGaAs is pulled down, allowing conduction in both the AlGaAs and the 2 DEG. We propose a model, in which time‐dependent phenomena in the conduction of the 2 DEG can be associated with trapping and detrapping of charge carriers in the AlGaAs. Time‐resolved experiments are shown which confirm this hypothesis.

Shubnikov-de Haas measurements have been performed on a high-mobility AlxGa1−xAs/GaAs heterostructure as a function of temperature (1.7⩽T⩽4.2 K) and magnetic field strength (0.25 ⩽B⩽0.70T). The temperature dependence of the amplitude of the Shubnikov-de Haas oscillations is used to define an effective mass of the two-dimensional electron gas. This apparent mass depends strongly on temperature and magnetic field and decreases to values much smaller than that for the cyclotron mass. The apparent mass shows a scaling behavior as a function of the dimensionless quantity k B T h ω c .

The magnetocapacitance of a two-dimensional electron system (2DES) is investigated experimentally, both under and away from Quantum Hall (QH) conditions, at frequencies between 1 kHz and 100 MHz. The nature of the capacitive signal in a bounded 2DES is determined by a resistive cut-off frequency 1/$\tau \propto \sigma_{xx}$, the longitudinal magnetoconductivity. A new response mechanism is reported for angular frequencies $\omega > 1/\tau$, which is controlled by the $\em transverse$ or Hall conductivity $\sigma_{xy}$ and the boundaries of the sample, even at frequencies far below those of the Edge Magnetoplasma resonances and away from the QH-conditions., Comment: Experimental paper, 4 figures

Magnetoplasma reflectivity measurements were performed on Cd3As2 in order to obtain more experimental details about the structure of the plasma reflectivity edge. The experimental results can be explained by assuming the existence of a surface layer with a carrier concentration-gradient which is responsible for optical interference effects.

We present a new model to interpret recent measurements on Hg1-xMnxSe which show an angular dependence of the nodes in the Shubnikov-de Haas amplitude. The model is based on an infinite Hamiltonian matrix including inversion asymmetry terms. We additionally took into account the exchange interaction, typical for Semimagnetic Semiconductors. By truncating the matrix we can calculate the electron energy levels, allowing us to describe the experimentally observed nodal field positions.

Absorption measurements at room temperature and 90K on single crystals of Cd3P2 are given. Free carrier absorption can be interpreted in the simple classical model while the interband absorption is interpreted in the Kane band model using exact solutions of the secular equation and without neglecting the free electron term. The best fit of the theory to experimental points is found for Eg(300K)=0.53 eV, Eg(90K)=0.56 eV, P=6.7*10-10 eVm, Delta =0.1 eV and mv1=0.5 m0. Some results of thermomagnetic transport properties are discussed in the same model.

The concentration of occupied deep centers in Si‐doped AlxGa1−xAs for x≥0.2 has been calculated from a three‐level donor model, in which the shallow levels are treated as excited states of the deep (DX) ground state. The deep level is assumed to be tied to the L valley, and the shallow levels to the Γ and X valleys. The behavior of the free‐electron density and the thermal activation energy as function of composition is in good agreement with experimental results reported in the literature. In this model of dependent donor levels the deep‐level occupancy can be directly calculated without needing deep‐level transient spectroscopy measurements. A two‐level donor model is used to calculate the pressure dependence of the deep level from a hydrostatic pressure experiment on a GaAs/Al0.3Ga0.7As heterostructure reported in the literature. We assume a shallow level tied to the Γ valley and an arbitrary deep level which is not coupled to any of the conduction bands. The calculation of the position of the deep lev...

From measurements of the temperature dependence of the electron concentration in Cd 3 As 2 , we found values for the conduction-band parameters that are in good agreement with those recently reported by Aubin, Caron, and Jay-Gerin. However, in contrast with these authors we found no small overlap, but a relatively large gap of 26 meV between the heavy-hole band maximum and the conduction-band minimum.

Blom Frans. San Clemente ruins, Peten (Guatemala). In: Journal de la Société des Américanistes. Tome 20, 1928. pp. 93-102.

Blom Frans. Ossuaries, cremation and secondary burials among the Maya of Chiapas, Mexico.. In: Journal de la Société des Américanistes. Tome 43, 1954. pp. 123-136.