12,362 research outputs found
Probing the Melting of a Two-dimensional Quantum Wigner Crystal via its Screening Efficiency
One of the most fundamental and yet elusive collective phases of an
interacting electron system is the quantum Wigner crystal (WC), an ordered
array of electrons expected to form when the electrons' Coulomb repulsion
energy eclipses their kinetic (Fermi) energy. In low-disorder, two-dimensional
(2D) electron systems, the quantum WC is known to be favored at very low
temperatures () and small Landau level filling factors (), near the
termination of the fractional quantum Hall states. This WC phase exhibits an
insulating behavior, reflecting its pinning by the small but finite disorder
potential. An experimental determination of a vs phase diagram for
the melting of the WC, however, has proved to be challenging. Here we use
capacitance measurements to probe the 2D WC through its effective screening as
a function of and . We find that, as expected, the screening
efficiency of the pinned WC is very poor at very low and improves at higher
once the WC melts. Surprisingly, however, rather than monotonically
changing with increasing , the screening efficiency shows a well-defined
maximum at a which is close to the previously-reported melting temperature
of the WC. Our experimental results suggest a new method to map out a vs
phase diagram of the magnetic-field-induced WC precisely.Comment: The formal version is published on Phys. Rev. Lett. 122, 116601
(2019
SRB ascent aerodynamic heating design criteria reduction study, volume 1
An independent set of solid rocket booster (SRB) convective ascent design environments were produced which would serve as a check on the Rockwell IVBC-3 environments used to design the ascent phase of flight. In addition, support was provided for lowering the design environments such that Thermal Protection System (TPS), based on conservative estimates, could be removed leading to a reduction in SRB refurbishment time and cost. Ascent convective heating rates and loads were generated at locations in the SRB where lowering the thermal environment would impact the TPS design. The ascent thermal environments are documented along with the wind tunnel/flight test data base used as well as the trajectory and environment generation methodology. Methodology, as well as, environment summaries compared to the 1980 Design and Rockwell IVBC-3 Design Environment are presented in this volume, 1
Wigner solids of wide quantum wells near Landau filling
Microwave spectroscopy within the Landau filling () range of the integer
quantum Hall effect (IQHE) has revealed pinning mode resonances signifying
Wigner solids (WSs) composed of quasi-particles or -holes. We study pinning
modes of WSs in wide quantum wells (WQWs) for , varying the
density, , and tilting the sample by angle in the magnetic field.
Three distinct WS phases are accessed. One phase, S1, is phenomenologically the
same as the WS observed in the IQHEs of narrow QWs. The second phase, S2,
exists at further from than S1, and requires a sufficiently large
or , implying S2 is stabilized by the Zeeman energy. The melting
temperatures of S1 and S2, estimated from the disappearance of the pinning
mode, show different behavior vs . At the largest or , S2
disappears and the third phase, S1A, replaces S1, also exhibiting a pinning
mode. This occurs as the WQW IQHE becomes a two-component,
Halperin-Laughlin \pone state. We interpret S1A as a WS of the excitations of
\pone, which has not been previously observed
Competition Between Fractional Quantum Hall Liquid, Bubble and Wigner Crystal Phases in the Third Landau Level
Magnetotransport measurements were performed in a ultra-high mobility
GaAs/AlGaAs quantum well of density . The
temperature dependence of the magnetoresistance was studied in detail
in the vicinity of . In particular, we discovered new minima in
at filling factor and , but only at
intermediate temperatures mK. We interpret these as
evidence for a fractional quantum Hall liquid forming in the N=2 Landau level
and competing with bubble and Wigner crystal phases favored at lower
temperatures. Our data suggest that a magnetically driven insulator-insulator
quantum phase transition occurs between the bubble and Wigner crystal phases at
T=0.Comment: Phys. Rev. Lett.93 266804 (2004
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