2,628 research outputs found
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
Dynamic Light Scattering From Colloidal Gels
We present a brief, preliminary account of the interpretation of dynamic light scattering from fractal colloidal gels. For small scattering angles, and for high initial colloid particle volume fractions, the correlation functions exhibit arrested decay, reflecting the non-ergodic nature of these systems and allowing us to directly determine the elastic modulus of the gels. For smaller initial volume fractions, the correlation functions decay completely. In all cases, the initial decay is not exponential, but is instead described by a stretched exponential. We summarize the principles of a model that accounts for these data and discuss the scaling behavior of the measured parameters
Incompressible strips in dissipative Hall bars as origin of quantized Hall plateaus
We study the current and charge distribution in a two dimensional electron
system, under the conditions of the integer quantized Hall effect, on the basis
of a quasi-local transport model, that includes non-linear screening effects on
the conductivity via the self-consistently calculated density profile. The
existence of ``incompressible strips'' with integer Landau level filling factor
is investigated within a Hartree-type approximation, and non-local effects on
the conductivity along those strips are simulated by a suitable averaging
procedure. This allows us to calculate the Hall and the longitudinal resistance
as continuous functions of the magnetic field B, with plateaus of finite widths
and the well-known, exactly quantized values. We emphasize the close relation
between these plateaus and the existence of incompressible strips, and we show
that for B values within these plateaus the potential variation across the Hall
bar is very different from that for B values between adjacent plateaus, in
agreement with recent experiments.Comment: 13 pages, 11 figures, All color onlin
Atomic Interferometer with Amplitude Gratings of Light and its Applications to Atom Based Tests of the Equivalence Principle
We have developed a matter wave interferometer based on the diffraction of
atoms from effective absorption gratings of light. In a setup with cold
rubidium atoms in an atomic fountain the interferometer has been used to carry
out tests of the equivalence principle on an atomic basis. The gravitational
acceleration of the two isotopes 85Rb and 87Rb was compared, yielding a
difference Dg/g =(1.2 +-1.7)x10^{-7}. We also perform a differential free fall
measurement of atoms in two different hyperfine states, and obtained a result
of Dg/g =(0.4 +-1.2)x10^{-7}.Comment: 4 Pages, 4 figures, accepted for Physical Review Letter
Cross-link governed dynamics of biopolymer networks
Cytoskeletal networks of biopolymers are cross-linked by a variety of
proteins. Experiments have shown that dynamic cross-linking with physiological
linker proteins leads to complex stress relaxation and enables network flow at
long times. We present a model for the mechanical properties of transient
networks. By a combination of simulations and analytical techniques we show
that a single microscopic timescale for cross-linker unbinding leads to a broad
spectrum of macroscopic relaxation times, resulting in a weak power-law
dependence of the shear modulus on frequency. By performing rheological
experiments, we demonstrate that our model quantitatively describes the
frequency behavior of actin network cross-linked with -Actinin- over
four decades in frequency.Comment: 4 page
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