15,641 research outputs found
Dynamical symmetry breaking as the origin of the zero--resistance state in an -driven system
Under a strong drive the zero-frequency linear response dissipative
resistivity of a homogeneous state is allowed to become
negative. We show that such a state is absolutely unstable. The only
time-independent state of a system with a is characterized by
a current which almost everywhere has a magnitude fixed by the
condition that the nonlinear dissipative resistivity .
As a result, the dissipative component of the electric field vanishes. The
total current may be varied by rearranging the current pattern appropriately
with the dissipative component of the -electric field remaining zero. This
result, together with the calculation of Durst \emph{et. al.}, indicating the
existence of regimes of applied microwave field and magnetic field
where , explains the zero-resistance state observed by Mani
\emph{et. al.} and Zudov \emph{et. al.}.Comment: Published versio
Investigation into O(N) Invariant Scalar Model Using Auxiliary-Mass Method at Finite Temperature
Using auxiliary-mass method, O(N) invariant scalar model is investigated at
finite temperature. This mass and an evolution equation allow us to calculate
an effective potential without an infrared divergence. Second order phase
transition is indicated by the effective potential. The critical exponents are
determined numerically.Comment: LaTex 8 pages with 3 eps figure
Flow Equations for U_k and Z_k
By considering the gradient expansion for the wilsonian effective action S_k
of a single component scalar field theory truncated to the first two terms, the
potential U_k and the kinetic term Z_k, I show that the recent claim that
different expansion of the fluctuation determinant give rise to different
renormalization group equations for Z_k is incorrect. The correct procedure to
derive this equation is presented and the set of coupled differential equations
for U_k and Z_k is definitely established.Comment: 5 page
A Note on the Local Cosmological Constant and the Dark Energy Coincidence Problem
It has been suggested that the Dark Energy Coincidence Problem could be
interpreted as a possible link between the cosmological constant and a massive
graviton. We show that by using that link and models for the graviton mass a
dark energy density can be obtained that is indeed very close to measurements
by WMAP. As a consequence of the models, the cosmological constant was found to
depend on the density of matter. A brief outline of the cosmological
consequences such as the effect on the black hole solution is given
Renormalization Group Flow Equations and the Phase Transition in O(N)-models
We derive and solve flow equations for a general O(N)-symmetric effective
potential including wavefunction renormalization corrections combined with a
heat-kernel regularization. We investigate the model at finite temperature and
study the nature of the phase transition in detail. Beta functions, fixed
points and critical exponents \beta, \nu, \delta and \eta for various N are
independently calculated which allow for a verification of universal scaling
relations.Comment: 34 pages, 3 tables, 11 postscript figures, LaTe
The Assembly History of Field Spheroidals: Evolution of Mass-to-light Ratios and Signatures of Recent Star Formation
We present a comprehensive catalog of high signal-to-noise spectra obtained
with the DEIMOS spectrograph on the Keck II telescope for a sample of
F850LP<22.43 (AB) field spheroidal (E+S0s; 163) and bulge dominated disk (61)
galaxies in the redshift range 0.2<z<1.2. We examine the zero point, tilt and
scatter of the Fundamental Plane (FP) as a function of redshift and
morphological properties, carefully accounting for luminosity-dependent biases
via Montecarlo simulations. The evolution of the overall FP can be represented
by a mean change in effective mass-to-light ratio given by <d \log (M/L_{\rm
B})/dz>=-0.72^{+0.07}_{-0.05}\pm0.04. However, this evolution depends
significantly on the dynamical mass, being slower for larger masses as reported
in a previous letter. In addition, we separately show the intrinsic scatter of
the FP increases with redshift as d(rms(M/L_{\rm B}))/dz=0.040\pm0.015.
Although these trends are consistent with single burst populations which formed
at for high mass spheroidals and z_{f}~1.2 for lower mass systems, a
more realistic picture is that most of the stellar mass formed in all systems
at z>2 with subsequent activity continuing to lower redshifts (z<1.2). The
fraction of stellar mass formed at recent times depend strongly on galactic
mass, ranging from <1% for masses above 10^{11.5} M_{\odot} to 20-40% below
10^{11} M_{\odot}. Independent support for recent activity is provided by
spectroscopic ([\ion{O}{2}] emission, H\delta) and photometric (blue cores and
broad-band colors) diagnostics. Via the analysis of a large sample with many
independent diagnostics, we are able to reconcile previously disparate
interpretations of the assembly history of field spheroidals. [Abridged]Comment: 26 pages including 24 figures, submitted to ApJ. Complete and compact
version with full resolution images available at
http://www.astro.ucla.edu/~ttreu/ms.pd
Influence of disorder on antidot vortex Majorana states in 3D topological insulators
Topological insulator/superconductor two-dimensional heterostructures are
promising candidates for realizing topological superconductivity and Majorana
modes. In these systems, a vortex pinned by a pre-fabricated antidot in the
superconductor can host Majorana zero-energy modes (MZMs), which are exotic
quasiparticles that may enable quantum information processing. However, a major
challenge is to design devices that can manipulate the information encoded in
these MZMs. One of the key factors is to create small and clean antidots, so
that the MZMs, localized in the vortex core, have a large gap to other
excitations. If the antidot is too large or too disordered, the level spacing
for the subgap vortex states may become smaller than temperature. In this
paper, we numerically investigate the effects of disorder, chemical potential,
and antidot size on the subgap vortex spectrum, using a two-dimensional
effective model of the topological insulator surface. Our model allows us to
simulate large system sizes with vortices up to 1.8 m in diameter. We also
compare our disorder model with the transport data from existing experiments.
We find that the spectral gap can exhibit a non-monotonic behavior as a
function of disorder strength, and that it can be tuned by applying a gate
voltage.Comment: 10 pages, 6 figure
Drag on particles in a nematic suspension by a moving nematic-isotropic interface
We report the first clear demonstration of drag on colloidal particles by a moving nematic-isotropic
interface. The balance of forces explains our observation of periodic, strip-like structures that are produced by the movement of these particles
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