5,246 research outputs found
D0 Silicon Microstrip Tracker
The D0 Run II silicon microstrip tracker (SMT) has 3 square meters of Si
area. There are 792,576 channels read out by 6192 SVXIIe chips on 912 read out
modules. The SMT provides track and vertex reconstruction capabilities over the
full pseudorapidity coverage of the D0 detector. The full detector has been
running successfully since April 2002. This presentation covers the experience
in commissioning and operating, the recent electronics upgrade which improved
stability of the SMT and estimates of the radiation damage.Comment: 5 pages, 10 figures, Presented at IEEE NSS 2005, Puerto Ric
Low energy scales of Kondo lattices: mean-field perspective
A review of the low temperature properties of Kondo lattice systems is
presented within the mean-field approximation, focusing on the different
characteristic energy scales. The Kondo temperature, T_K, and the Fermi liquid
coherence energy, T_0, are analyzed as functions of the electronic filling, the
shape of the non-interacting density of states, and the concentration of
magnetic moments. These two scales can vanish, corresponding to a breakdown of
the Kondo effect when an external magnetic field is applied. The Kondo
breakdown can also be reached by adding a superexchange term to the Kondo
lattice model, which mimics the intersite magnetic correlations neglected at
the mean-field level.Comment: 17 pages, 9 figures. Proceedings of the NATO Advanced Research
Workshop of Hvar, Croatia (2008
Lifshitz transition in Kondo alloys
We study the low energy states of Kondo alloys as function of the magnetic
impurity concentration per site, x, and the conduction electron average site
occupation, nc. Using two complementary approaches, the mean-field coherent
potential approximation and the strong coupling limit, we identify and
characterize two different Fermi liquid regimes. We propose that both regimes
are separated by a Lifshitz transition at x = nc. Indeed, we predict a
discontinuity of the number of quasiparticles which are enclosed in the Fermi
surface. This feature could provide a scenario for the non-Fermi liquid
properties that were recently observed in Kondo alloy systems around x = nc.Comment: 5 pages, 2 figure
Kondo screening by the surface modes of a strong topological insulator
We consider a magnetic impurity deposited on the surface of a strong
topological insulator and interacting with the surface modes by a Kondo
exchange interaction. Taking into account the warping of the Fermi line of the
surface modes, we derive a mapping to an effective one dimensional model and
show that the impurity is fully screened by the surface electrons except when
the Fermi level lies exactly at the Dirac point. Using an Abrikosov fermion
mean-field theory, we calculate the shape of the electronic density Friedel
oscillation resulting from the presence of the Kondo screening cloud. We
analyze quantitatively the observability of a six-fold symmetry in the Friedel
oscillations for two prototype compounds: BiSe and BiTe.Comment: 22 pages, 6 figure
A large-N analysis of the local quantum critical point and the spin-liquid phase
We study analytically the Kondo lattice model with an additional
nearest-neighbor antiferromagnetic interaction in the framework of large-N
theory. We find that there is a local quantum critical point between two
phases, a normal Fermi-liquid and a spin-liquid in which the spins are
decoupled from the conduction electrons. The local spin susceptibility displays
a power-law divergence throughout the spin liquid phase. We check the
reliability of the large-N results by solving by quantum Monte Carlo simulation
the N=2 spin-liquid problem with no conduction electrons and find qualitative
agreement. We show that the spin-liquid phase is unstable at low temperatures,
suggestive of a first-order transition to an ordered phase.Comment: 4 pages and 1 figur
An analysis of B_{d,s} mixing angles in presence of New Physics and an update of Bs -> K0* anti-K0*
We discuss a simple approach to measure the weak mixing angles phi_s and
phi_d of the Bs and Bd systems in the presence of New Physics. We present a new
expression that allows one to measure directly the New Physics mixing angles if
New Physics contributes significantly to the mixing only. We apply the method
to specific penguin-mediated B->PP, B->PV and B ->VV modes. We provide a very
stringent and simple bound on the direct CP asymmetries of all these modes, the
violation of which is a signal of New Physics in decay. Within the same
theoretical framework, an updated prediction for the branching ratio of Bs->K0*
anti-K0* is presented, which can be compared with a recent LHCb analysis.Comment: 11 pages, 3 figure
Mesoscopic Anderson Box: Connecting Weak to Strong Coupling
Both the weakly coupled and strong coupling Anderson impurity problems are
characterized by a Fermi-liquid theory with weakly interacting quasiparticles.
In an Anderson box, mesoscopic fluctuations of the effective single particle
properties will be large. We study how the statistical fluctuations at low
temperature in these two problems are connected, using random matrix theory and
the slave boson mean field approximation (SBMFA). First, for a resonant level
model such as results from the SBMFA, we find the joint distribution of energy
levels with and without the resonant level present. Second, if only energy
levels within the Kondo resonance are considered, the distributions of
perturbed levels collapse to universal forms for both orthogonal and unitary
ensembles for all values of the coupling. These universal curves are described
well by a simple Wigner-surmise type toy model. Third, we study the
fluctuations of the mean field parameters in the SBMFA, finding that they are
small. Finally, the change in the intensity of an eigenfunction at an arbitrary
point is studied, such as is relevant in conductance measurements: we find that
the introduction of the strongly-coupled impurity considerably changes the wave
function but that a substantial correlation remains.Comment: 17 pages, 7 figure
Worker-managed firms reduce their internal wage gap, but top performers tend to quit
Gabriel Burdin discusses the role of workplace democracy in the reduction of income inequalit
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