1,700 research outputs found
Recent Experimental Progress of Fractional Quantum Hall Effect: 5/2 Filling State and Graphene
The phenomenon of fractional quantum Hall effect (FQHE) was first
experimentally observed 33 years ago. FQHE involves strong Coulomb interactions
and correlations among the electrons, which leads to quasiparticles with
fractional elementary charge. Three decades later, the field of FQHE is still
active with new discoveries and new technical developments. A significant
portion of attention in FQHE has been dedicated to filling factor 5/2 state,
for its unusual even denominator and possible application in topological
quantum computation. Traditionally FQHE has been observed in high mobility GaAs
heterostructure, but new materials such as graphene also open up a new area for
FQHE. This review focuses on recent progress of FQHE at 5/2 state and FQHE in
graphene.Comment: 17 pages, 13 figure
Low-Temperature Conductivity of Weakly Interacting Quantum Spin Hall Edges in Strained-Layer InAs/GaInSb
We report low-temperature transport measurements in strained
InAs/Ga0.68In0.32Sb quantum wells, which supports time-reversal
symmetry-protected helical edge states. The temperature and bias voltage
dependence of the helical edge conductance for devices of various sizes are
consistent with the theoretical expectation of a weakly interacting helical
edge state. Moreover, we found that the magnetoresistance of the helical edge
states is related to the edge interaction effect and the disorder strength.Comment: 20 pages, 7 figure
Observation of spin-tensor induced topological phase transitions of triply degenerate points with a trapped ion
Triply degenerate points (TDPs), which correspond to new types of topological
semimetals, can support novel quasiparticles possessing effective integer spins
while preserving Fermi statistics. Here by mapping the momentum space to the
parameter space of a three-level system in a trapped ion, we experimentally
explore the transitions between different types of TDPs driven by
spin-tensor--momentum couplings. We observe the phase transitions between TDPs
with different topological charges by measuring the Berry flux on a loop
surrounding the gap-closing lines, and the jump of the Berry flux gives the
jump of the topological charge (up to a factor) across the transitions.
For the Berry flux measurement, we employ a new method by examining the
geometric rotations of both spin vectors and tensors, which lead to a
generalized solid angle equal to the Berry flux. The controllability of
multi-level ion offers a versatile platform to study high-spin physics and our
work paves the way to explore novel topological phenomena therein.Comment: 9 pages, 10 figure
De-Pinning Transition of Bubble Phases in a High Landau Level
While in the lowest Landau level the electron-electron interaction leads to
the formation of the Wigner crystal, in higher Landau levels a solid phase with
multiple electrons in a lattice site of crystal was predicted, which was called
the bubble phase. Reentrant integer quantum Hall states are believed to be the
insulating bubble phase pinned by disorder. We carry out nonlinear transport
measurements on the reentrant states and study the de-pinning of the bubble
phase, which is complementary to previous microwave measurements and provides
unique information. In this study, conductivity is directly measured with
Corbino geometry. Based on the threshold electric field of de-pinning, a phase
diagram of the reentrant state is mapped. We discuss an interaction-driven
topological phase transition between the integer quantum Hall state and the
reentrant integer quantum Hall state.Comment: 11 pages, 3 figure
Relations between near-field enhancements and Purcell factors in hybrid nanostructures of plasmonic antennas and dielectric cavities
Strong near-field enhancements (NFEs) of nanophotonic structures are believed
to be closely related to high Purcell factors (FP). Here, we theoretically show
that the correlation is partially correct; the extinction cross section
({\sigma}) response is also critical in determining FP. The divergence between
NFE and FP is especially pronounced in plasmonic-dielectric hybrid systems,
where the plasmonic antenna supports dipolar plasmon modes and the dielectric
cavity hosts Mie-like resonances. The cavity's enhanced-field environment can
boost the antenna's NFEs, but the FP is not increased concurrently due to the
larger effective {\sigma} that is intrinsic to the FP calculations.
Interestingly, the peak FP for the coupled system can be predicted by using the
NFE and {\sigma} responses. Furthermore, the limits for FP of coupled systems
are considered; they are determined by the sum of the FP of a redshifted (or
modified, if applicable) antenna and an individual cavity. This contrasts
starkly with the behavior of NFE which is closely associated with the
multiplicative effects of the NFEs provided by the antenna and the dielectric
cavity. The differing behaviors of NFE and FP in hybrid cavities have varied
impacts on relevant nanophotonic applications such as fluorescence, Raman
scattering and enhanced light-matter interactions
Observation of a Helical Luttinger-Liquid in InAs/GaSb Quantum Spin Hall Edges
We report on the observation of a helical Luttinger-liquid in the edge of
InAs/GaSb quantum spin Hall insulator, which shows characteristic suppression
of conductance at low temperature and low bias voltage. Moreover, the
conductance shows power-law behavior as a function of temperature and bias
voltage. The results underscore the strong electron-electron interaction effect
in transport of InAs/GaSb edge states. Because of the fact that the Fermi
velocity of the edge modes is controlled by gates, the Luttinger parameter can
be fine tuned. Realization of a tunable Luttinger-liquid offers a
one-dimensional model system for future studies of predicted correlation
effects.Comment: 23 pages, 9 figure
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