660 research outputs found
Undoped Electron-Hole Bilayers in a GaAs/AlGaAs Double Quantum Well
We present the fabrication details of completely undoped electron-hole
bilayer devices in a GaAs/AlGaAs double quantum well heterostructure with a 30
nm barrier. These devices have independently tunable densities of the
two-dimensional electron gas and two-dimensional hole gas. We report
four-terminal transport measurements of the independently contacted electron
and hole layers with balanced densities from cm down
to cm at . The mobilities can exceed cm V s for electrons and
cm V s for holes.Comment: 3 pages, 3 figure
Scattering Mechanism in Modulation-Doped Shallow Two-Dimensional Electron Gases
We report on a systematic investigation of the dominant scattering mechanism
in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped
GaAs/Al_{x}Ga_{1-x}As heterostructures. The power-law exponent of the electron
mobility versus density, mu \propto n^{alpha}, is extracted as a function of
the 2DEG's depth. When shallower than 130 nm from the surface, the power-law
exponent of the 2DEG, as well as the mobility, drops from alpha \simeq 1.65
(130 nm deep) to alpha \simeq 1.3 (60 nm deep). Our results for shallow 2DEGs
are consistent with theoretical expectations for scattering by remote dopants,
in contrast to the mobility-limiting background charged impurities of deeper
heterostructures.Comment: 4 pages, 3 figures, modified version as accepted in AP
Giant microwave photoresistance of two-dimensional electron gas
We measure microwave frequency (4-40 GHz) photoresistance at low magnetic
field B, in high mobility 2D electron gas samples, excited by signals applied
to a transmission line fabricated on the sample surface. Oscillatory
photoresistance vs B is observed. For excitation at the cyclotron resonance
frequency, we find an unprecedented, giant relative photoresistance (\Delta
R)/R of up to 250 percent. The photoresistance is apparently proportional to
the square root of applied power, and disappears as the temperature is
increased.Comment: 4 pages, 3 figure
New Mexico Youth Risk & Resiliency 2013 Survey Results Report: Mental Health and Related Behaviors
Mental health is an integral part of student well-being. It is essential to youth for maintaining healthy relationships, supporting academic achievement, and living full and productive lives. NM youth 10–19 years of age experience a higher rate of death by suicide than those in the US (9.8 vs. 4.8 deaths per 100,000 population). The 2013 Youth Risk & Resiliency Survey (YRRS) questionnaire included three questions in the middle school survey and four questions in the high school survey about suicide ideation and attempts. The high school survey also included a question about feelings of sadness or hopelessness (a risk factor for depression) and a question about non-suicidal self-injury (NSSI)
Photoluminescence Detected Doublet Structure in the Integer and Fractional Quantum Hall Regime
We present here the results of polarized magneto-photoluminescence
measurements on a high mobility single-heterojunction. The presence of a
doublet structure over a large magnetic field range (2>nu>1/6) is interpreted
as possible evidence for the existence of a magneto-roton minima of the charged
density waves. This is understood as an indication of strong electronic
correlation even in the case of the IQHE limit.Comment: submitted to Solid State Communication
2D Metal-Insulator transition as a percolation transition
By carefully analyzing the low temperature density dependence of 2D
conductivity in undoped high mobility n-GaAs heterostructures, we conclude that
the 2D metal-insulator transition in this system is a density inhomogeneity
driven percolation transition due to the breakdown of screening in the random
charged impurity disorder background. In particular, our measured conductivity
exponent of approaches the 2D percolation exponent value of 4/3 at
low temperatures and our experimental data are inconsistent with there being a
zero-temperature quantum critical point in our system.Comment: 5 pages, 3 figure
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