We have measured the quantum critical behavior of the plateau-insulator (PI) transition in a low-mobility InGaAs/GaAs quantum well. The longitudinal resistivity measured for two different values of the electron density follows an exponential law, from which we extract critical exponents κ = 0.54 and 0.58, in good agreement with the value (κ = 0.57) previously obtained for an InGaAs/InP heterostructure. This provides evidence for a non-Fermi liquid critical exponent. By reversing the direction of the magnetic field we find that the averaged Hall resistance remains quantized at the plateau value h/e 2 through the PI transition. From the deviations of the Hall resistance from the quantized value, we obtain the corrections to scaling.

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Ê Ú ¿½ Å Ý ¾¼½¼ ÔØ ¾  ÒÙ ÖÝ ¾¼½½ ×ØÖ ØCompounds with the general formula Mg 1− Al B 2 were obtained by two-step ceramic synthesis. All compounds were characterized by X-ray diffraction, NMR spectroscopy, and by four point probe resistivity measurements in various magnetic fields method. The diborides unit cell parameters were determined as a function of the Al mole fraction. With the vaues of up to 0.40 (where is the composition of the stock prepared for sintering), the unit cell parameters of Mg 1− Al B 2 are similar to those of pure MgB 2 and the superconducting transition temperature was lowered. For stock compositions of 0 25 ≤ ≤ 0 60, the products contain a superstructure, also superconducting phase, which becomes the only product at = 0 50, and at > 0 60 this phase is replaced by AlB 2 -based solid solutions.

One or two step reactions of potassium and rubidium fullerides with composition M k C 60 (M = K, Rb; k = 3-6) and K 6 C 60 + m K mixtures (m = 1, 3) with anhydrous salts M´Cl 3 (M´ = La, Pr, Nd, Sm, Gd, Tb, Yb, Lu, Y, Sc) and YbI 2 in a toluene-THF medium afforded heterometallic fullerides M 3-n M´nC 60 (n = 1-3). Among these compounds, substituted fullerides with composition M 2 M´C 60 (M´ = Yb, Lu, Sc) display superconducting properties with critical temperatures of 14-20 K.

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