46 research outputs found
Carbon-doped high mobility two-dimensional hole gases on (110) faced GaAs
Carbon-doped high mobility two-dimensional hole gases grown on (110) oriented
GaAs substrates have been grown with hole mobilities exceeding 10^6 cm^2/Vs in
single heterojunction GaAs/AlGaAs structures. At these high mobilities, a
pronounced mobility anisotropy has been observed. Rashba induced spin-splitting
in these asymmetric structures has been found to be independent on the
transport direction
Interlayer tunneling in counterflow experiments on the excitonic condensate in quantum Hall bilayers
The effect of tunneling on the transport properties of} quantum Hall double
layers in the regime of the excitonic condensate at total filling factor one is
studied in counterflow experiments. If the tunnel current is smaller than a
critical , tunneling is large and is effectively shorting the two layers.
For tunneling becomes negligible. Surprisingly, the transition
between the two tunneling regimes has only a minor impact on the features of
the filling-factor one state as observed in magneto-transport, but at currents
exceeding the resistance along the layers increases rapidly
Carbon doped symmetric GaAs/AlGaAs quantum wells with hole mobilities beyond 10^6 cm^2/Vs
Utilizing a novel carbon doping source, we prepared two-dimensional hole
gases in a symmetric quantum well structure in the GaAs/AlGaAs heterosystem.
Low temperature hole mobilities up to 1.2 x 10^6 cm^2/Vs at a density of 2.3 x
10^11 cm^-2 were achieved on GaAs (001) substrates. In contrast to electron
systems, the hole mobility sensitively depends on variations of the quantum
well width and the spacer thickness. In particular an increase of the quantum
well width from an optimal value of 15 nm to 18 nm is accompanied by a 35 %
reduction of the hole mobility. The quality of ultrahigh-mobility electron
systems is not affected by the employed carbon doping source
Design of a real-time inspection system for NDE of reactor vessels and piping components
Progress in the development of a special-purpose system for use in a real-time in-service inspection system for reactor vessels and piping components is described in this report. An analysis of the synthetic aperture processing algorithm is presented and new methods of speedup are described. A number of special purpose processor architectures are presented and two of the more promising ones are described in detail and are compared and evaluated. Proposed specifications for an initial field inspection system are presented. A brief description of the capabilities of a laboratory prototype processor (to be fabricated) is given.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25794/1/0000356.pd
Enhanced spin-orbit scattering length in narrow Al_xGa_{1-x}N/GaN wires
The magnetotransport in a set of identical parallel AlGaN/GaN quantum wire
structures was investigated. The width of the wires was ranging between 1110 nm
and 340 nm. For all sets of wires clear Shubnikov--de Haas oscillations are
observed. We find that the electron concentration and mobility is approximately
the same for all wires, confirming that the electron gas in the AlGaN/GaN
heterostructure is not deteriorated by the fabrication procedure of the wire
structures. For the wider quantum wires the weak antilocalization effect is
clearly observed, indicating the presence of spin-orbit coupling. For narrow
quantum wires with an effective electrical width below 250 nm the weak
antilocalization effect is suppressed. By comparing the experimental data to a
theoretical model for quasi one-dimensional structures we come to the
conclusion that the spin-orbit scattering length is enhanced in narrow wires.Comment: 6 pages, 5 figure
Extra Spin-Wave mode in Quantum Hall systems. Beyond the Skyrmion Limit
We report on the observation of a new spin mode in a quantum Hall system in
the vicinity of odd electron filling factors under experimental conditions
excluding the possibility of Skyrmion excitations. The new mode having
presumably zero energy at odd filling factors emerges at small deviations from
odd filling factors and couples to the spin-exciton. The existence of an extra
spin mode assumes a nontrivial magnetic order at partial fillings of Landau
levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal.Comment: 9 pages, 4 figure