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  • 1
    Electronic Resource
    Electronic Resource
    Effect of the nuclear hyperfine field on the 2D electron conductivity in the quantum Hall regime (1999)
    Springer
    JETP letters 69 (1999), S. 64-70 
    Details
    ISSN: 1090-6487
    Keywords: 73.40.Hm ; 72.15.−v ; 73.20.Dx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effect of the nuclear hyperfine interaction on the dc conductivity of 2D electrons under quantum Hall effect conditions at filling factor ν=1 is observed for the first time. The local hyperfine field enhanced by dynamic nuclear polarization is monitored via the Overhauser shift of the 2D conduction electron spin resonance in AlGaAs/GaAs multiquantum-well samples. The experimentally observed change in the dc conductivity resulting from dynamic nuclear polarization is in agreement with a thermal activation model incorporating the Zeeman energy change due to the hyperfine interaction. The relaxation decay time of the dc conductivity is, within experimental error, the same as the relaxation time of the nuclear spin polarization determined from the Overhauser shift. These findings unequivocally establish the nuclear spin origins of the observed conductivity change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567985
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  • 2
    Electronic Resource
    Electronic Resource
    THE GROUND WATER FLUX OF NITROGEN AND PHOSPHORUS TO BERMUDA'S COASTAL WATERS (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 30 (1994), S. 0 
    Details
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : The concentrations of dissolved fixed inorganic nitrogen (ΣN) in Bermuda ground waters can be very high due to both natural and anthropogenic processes. The high anthropogenic flux is due to domestic cesspit operation. Mass balance calculations indicate that ground water seepage, especially rich in ΣN, is a major source of nutrients into the near shore coastal zone of Bermuda. The ground water flux of ΣN is approximately 1.5 to 4 times that of the sewage flux of ΣN to Bermuda's nearshore waters. This input of ΣN may be important in the development of algal blooms in these waters. Our work, coupled with other recent investigations, suggests that the ground water input of nutrients into nearshore marine waters is an important process globally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1752-1688.1994.tb03346.x
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  • 3
    Electronic Resource
    Electronic Resource
    Parallel quantum point contacts fabricated with independently biased gates and a submicrometer airbridge post (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2326-2328 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using an integrated airbridge and submicrometer gate post technology, coupled quantum point contacts (QPCs) arranged in a parallel configuration were fabricated. The airbridge and gate post are fabricated by e-beam lithography and Ti/Au evaporation in a single step. Gate post diameters as small as 0.1 μm have been achieved. The two QPCs are fabricated with two conventional gates and a central airbridged gate, each of which can be biased independently. Conductance measurements clearly exhibit coupling of the two QPCs, as the quantized conductance steps are in units of 4 e2/h. Independent measurements of each QPC show conductance steps in units of 2 e2/h.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112731
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  • 4
    Electronic Resource
    Electronic Resource
    Unipolar complementary circuits using double electron layer tunneling transistors (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 314-316 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate unipolar complementary circuits consisting of a pair of resonant tunneling transistors based on the gate control of two-dimensional–two-dimensional interlayer tunneling, where a single transistor—in addition to exhibiting a well-defined negative-differential resistance—can be operated with either positive or negative transconductance. Details of the device operation are analyzed in terms of the quantum capacitance effect and bandbending in a double quantum well structure, and show good agreement with experiment. Application of resonant tunneling complementary logic is discussed by demonstrating complementary static random access memory using two devices connected in series. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123009
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  • 5
    Electronic Resource
    Electronic Resource
    Planar quantum transistor based on 2D–2D tunneling in double quantum well heterostructures (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5626-5634 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on our work on the double electron layer tunneling transistor (DELTT), based on the gate control of two-dimensional–two-dimensional (2D–2D) tunneling in a double quantum well heterostructure. While previous quantum transistors have typically required tiny laterally defined features, by contrast the DELTT is entirely planar and can be reliably fabricated in large numbers. We use a novel epoxy-bond-and-stop-etch flip-chip process, whereby submicron gating on opposite sides of semiconductor epitaxial layers as thin as 0.24 μm can be achieved. Because both electron layers in the DELTT are 2D, the resonant tunneling features are unusually sharp, and can be easily modulated with one or more surface gates. We demonstrate DELTTs with peak-to-valley ratios in the source-drain I–V curve of order 20:1 below 1 K. Both the height and position of the resonant current peak can be controlled by gate voltage over a wide range. DELTTs with larger subband energy offsets (∼21 meV) exhibit characteristics that are nearly as good at 77 K, in good agreement with our theoretical calculations. Using these devices, we also demonstrate bistable memories operating at 77 K. Finally, we briefly discuss the prospects for room temperature operation, increases in gain and high speed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368610
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  • 6
    Electronic Resource
    Electronic Resource
    High quality single and double two-dimensional electron gases grown by metalorganic vapor phase epitaxy (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1911-1913 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate the metalorganic vapor phase epitaxy (MOVPE) growth of AlGaAs/GaAs two-dimensional electron gases (2DEGs) with mobilities as high as 786 000 cm2/V s at a carrier density of 3.0×1011 cm−2 at 0.3 K. The mobility figures of merit (μ/n3/2) for these 2DEGs are the highest reported to date for MOVPE materials. These 2DEGs also exhibit the fractional quantum Hall effect (FQHE) with minima in longitudinal resistance corresponding to Landau level filling factors 2/3, 4/3, and 5/3. The temperature dependence and carrier density dependence of mobility were characterized, and the mobility was found to vary linearly with carrier density, implying that the mobility is probably limited by background ionized impurity scattering. A delta-doped 2DEG was also compared with uniformly doped 2DEGs and was found to have a slightly higher mobility. Finally, we obtained high mobility in a coupled double 2DEG structure for 2D to 2D tunneling applications. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114374
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  • 7
    Electronic Resource
    Electronic Resource
    Low-frequency noise in transport through quantum point contacts (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 774-776 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the noise characteristics of quantum point contacts between 100 Hz and 100 kHz at 4.2 K. The noise consists of a 1/f component on top of a white background. The 1/f noise increases as the contact width decreases and shows peaks between the quantized resistance plateaus. The white noise background increases with current but is much lower than the full shot noise level, suggesting that shot noise is not generated in an ideal quantum point contact, where the electrons do not suffer backscattering as they enter and traverse the contact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104094
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  • 8
    Electronic Resource
    Electronic Resource
    2×106 cm2/V s electron mobility by metalorganic chemical vapor deposition with tertiarybutylarsine (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 208-210 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate the metalorganic chemical vapor deposition (MOCVD) growth of two-dimensional electron gases (2DEGs) with electron mobilities up to 2.0×106 cm2/V s at 0.3 K. These are the highest mobilities to date for MOCVD materials, and were achieved using a safer replacement precursor for arsine, tertiarybutylarsine (TBA). For structures grown using arsine, we obtained a maximum mobility of 1.0×106 cm2/V s, which although comparable to the best by MOCVD to date, is half that obtained using TBA. Our studies on thick GaAs and AlGaAs layers indicate that the use of TBA in place of arsine reduces both the carbon and donor impurity concentrations. Thus, TBA is not only a safe alternative to arsine, but also produces significantly purer films. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116462
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  • 9
    Electronic Resource
    Electronic Resource
    Higher order magnetoresistance commensurability oscillations in low aspect ratio antidot lattice and focusing structures (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 656-658 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We observe unusually strong magnetoresistance commensurability oscillations in two different types of artificial arrays of scattering centers, multiparallel focusing slits and a square antidot lattice, both fabricated on a two-dimensional electron gas by electron-beam lithography and damageless wet etching. The strength of the magnetoresistance peaks is attributed to a high reflection specularity and a small effective antidot cross section. The absence of commensurability effects near Landau level filling factor υ=3/2 is attributed to the composite fermion mean free path being smaller than the slit and antidot spacings. The mechanism for the observed commensurability is discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119820
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  • 10
    Electronic Resource
    Electronic Resource
    Physiological Mechanisms for Spatial Filtering and Image Enhancement in the Sonar of Bats (1984)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 46 (1984), S. 599-614 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ph.46.030184.003123
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