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The influence of quenched disorder on the critical behavior of superfluid He is studied by confinement of the helium to the pores of three diflerent porous media: Vycor, xerogel, and aerogel glasses. In each case a well defined power-law behavior for the superfluid density is observed as the transition temperature is approached. In Vycor the superfluid critical exponent is bulklike, whereas strikingly diff'erent critical exponents are seen in the other two media.

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For electrons tunneling between parallel two-dimensional electron systems, conservation of in-plane momentum produces sharply resonant currentvoltage characteristics and provides a uniquely sensitive probe of the underlying electronic spectral functions. We report here the application of this

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Articles you may be interested inHigh sensitivity and multifunctional micro-Hall sensors fabricated using InAlSb/InAsSb/InAlSb heterostructures J. Appl. Phys. 105, 07E909 (2009); 10.1063/1.3074513 Detection of magnetically labeled DNA using pseudomorphic AlGaAs ∕ InGaAs ∕ GaAs heterostructure micro-Hall biosensors J. Appl. Phys. 99, 08P103 (2006); 10.1063/1.2162041 Doped-channel micro-Hall devices: Size and geometry effects J. Appl. Phys. 98, 094503 (2005); 10.1063/1.2128472Second-generation quantum-well sensors for room-temperature scanning Hall probe microscopy Micro-Hall devices based on modulation-doped Al 0.12 In 0.88 Sb/ InSb heterostructures are fabricated and studied in terms of sensitivity and noise. Extremely high supply-current-related magnetic sensitivities of 1800 V A −1 T −1 at 77 K and 1220 V A −1 T −1 at 300 K are reported and observed to be independent of the bias current. The detection limit of the devices studied at low and room temperature are at nanotesla values throughout the broad frequency range from 20 Hz to 20 kHz. The low detection limit of 28 nT at 300 K and 18 nT at 77 K were found at high frequencies where the Johnson noise is dominant. A measured detection limit per unit device width of 630 pT mm Hz −1/2 is reported indicating the potential for picotesla detectivity.

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We report on the observation of Ising quantum Hall (QH) ferromagnetism in two-dimensional electronic systems based in single InSb/InAlSb quantum wells. Magneto-transport experiments in tilted magnetic fields reveal the preservation of the = 2 and = 3 QH states over the range in tilt angles where the single particle gap is expected to collapse for a noninteracting system. These preserved QH states are accompanied by broad resistance peaks which move towards higher filling factors as the tilt angle is increased and which display hysteresis. The maximum in the amplitude of these resistance peaks grows with increasing temperature and is activated as exp͑−1 / ͱ T͒.