85 research outputs found
Density of States of GaAs-AlGaAs Heterostructures Deduced from Temperature Dependend Magnetocapacitance Measurements
Abstract We have analyzed the density of states of a two dimensional electron gas in a GaAs- AlGaAs hetereostructure by measuring the magnetocapacitance in magnetic fields up to 6 Tesla at temperatures below 10 K. The experimental data are well described by a Gaussian-like density of states where the linewidth Ă is proportional to B
Density of States in Landau Level Tails of GaAs-AlxGa1-xAs Heterostructures
From an analysis of the thermally activated resistivity as a function of the magnetic field in the quantum Hall regime we deduced the position of the Fermi energy in the mobility gap as a function of the filling factor and therefore the density of states. The measured density of states is best described by a Gaussian like profile superimposed on a constant background
Transconductance fluctuations as a probe for interaction induced quantum Hall states in graphene
Transport measurements normally provide a macroscopic, averaged view of the
sample, so that disorder prevents the observation of fragile interaction
induced states. Here, we demonstrate that transconductance fluctuations in a
graphene field effect transistor reflect charge localization phenomena on the
nanometer scale due to the formation of a dot network which forms near
incompressible quantum states. These fluctuations give access to fragile
broken-symmetry and fractional quantum Hall states even though these states
remain hidden in conventional magnetotransport quantities.Comment: 6 pages, 3 figure
What Were They Thinking? Fourth Amendment Unreasonableness in Atwater v. City of Lago Vista
Half-filled Landau levels host an emergent Fermi liquid that displays instability toward pairing, culminating in a gapped even-denominator fractional quantum Hall ground state. While this pairing may be probed by tuning the polarization of carriers in competing orbital and spin degrees of freedom, sufficiently high quality platforms offering such tunability remain few. We explore the ground states at filling factor Μ = 5/2 in ZnO-based two-dimensional electron systems through a forced intersection of opposing spin branches of Landau levels taking quantum numbers N = 1 and 0. We reveal a cascade of phases with distinct magnetotransport features including a gapped phase polarized in the N = 1 level and a compressible phase in N = 0, along with an unexpected Fermi liquid, a second gapped, and a strongly anisotropic nematic-like phase at intermediate polarizations when the levels are near degeneracy. The phase diagram is produced by analyzing the proximity of the intersecting levels and highlights the excellent reproducibility and controllability that ZnO offers for exploring exotic fractionalized electronic phases
Characterization of the Local Density of States Fluctuations near the Integer Quantum Hall Transition in a Quantum Dot Array
We present a calculation for the second moment of the local density of states
in a model of a two-dimensional quantum dot array near the quantum Hall
transition. The quantum dot array model is a realistic adaptation of the
lattice model for the quantum Hall transition in the two-dimensional electron
gas in an external magnetic field proposed by Ludwig, Fisher, Shankar and
Grinstein. We make use of a Dirac fermion representation for the Green
functions in the presence of fluctuations for the quantum dot energy levels. A
saddle-point approximation yields non-perturbative results for the first and
second moments of the local density of states, showing interesting fluctuation
behaviour near the quantum Hall transition. To our knowledge we discuss here
one of the first analytic characterizations of chaotic behaviour for a
two-dimensional mesoscopic structure. The connection with possible experimental
investigations of the local density of states in the quantum dot array
structures (by means of NMR Knight-shift or single-electron-tunneling
techniques) and our work is also established.Comment: 11 LaTeX pages, 1 postscript figure, to appear in Phys.Rev.
Design of a dual species atom interferometer for space
Atom interferometers have a multitude of proposed applications in space
including precise measurements of the Earth's gravitational field, in
navigation & ranging, and in fundamental physics such as tests of the weak
equivalence principle (WEP) and gravitational wave detection. While atom
interferometers are realized routinely in ground-based laboratories, current
efforts aim at the development of a space compatible design optimized with
respect to dimensions, weight, power consumption, mechanical robustness and
radiation hardness. In this paper, we present a design of a high-sensitivity
differential dual species Rb/Rb atom interferometer for space,
including physics package, laser system, electronics and software. The physics
package comprises the atom source consisting of dispensers and a 2D
magneto-optical trap (MOT), the science chamber with a 3D-MOT, a magnetic trap
based on an atom chip and an optical dipole trap (ODT) used for Bose-Einstein
condensate (BEC) creation and interferometry, the detection unit, the vacuum
system for mbar ultra-high vacuum generation, and the
high-suppression factor magnetic shielding as well as the thermal control
system. The laser system is based on a hybrid approach using fiber-based
telecom components and high-power laser diode technology and includes all laser
sources for 2D-MOT, 3D-MOT, ODT, interferometry and detection. Manipulation and
switching of the laser beams is carried out on an optical bench using Zerodur
bonding technology. The instrument consists of 9 units with an overall mass of
221 kg, an average power consumption of 608 W (819 W peak), and a volume of 470
liters which would well fit on a satellite to be launched with a Soyuz rocket,
as system studies have shown.Comment: 30 pages, 23 figures, accepted for publication in Experimental
Astronom
STE-QUEST - Test of the Universality of Free Fall Using Cold Atom Interferometry
In this paper, we report about the results of the phase A mission study of the atom
interferometer instrument covering the description of the main payload elements, the
atomic source concept, and the systematic error sources
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