1,735 research outputs found
Spin lifetimes and strain-controlled spin precession of drifting electrons in zinc blende type semiconductors
We study the transport of spin polarized electrons in n-GaAs using spatially
resolved continuous wave Faraday rotation. From the measured steady state
distribution, we determine spin relaxation times under drift conditions and, in
the presence of strain, the induced spin splitting from the observed spin
precession. Controlled variation of strain along [110] allows us to deduce the
deformation potential causing this effect, while strain along [100] has no
effect. The electric field dependence of the spin lifetime is explained
quantitatively in terms of an increase of the electron temperature.Comment: 5 pages, 6 figure
Electrical resistivity near Pomeranchuk instability in two dimensions
We analyze the DC charge transport in the quantum critical regime near a
d-wave Pomeranchuk instability in two dimensions. The transport decay rate is
linear in temperature everywhere on the Fermi surface except at cold spots on
the Brillouin zone diagonal. For pure systems, this leads to a DC resistivity
proportional to T^{3/2} in the low-temperature limit. In the presence of
impurities the residual impurity resistance at T=0 is approached linearly at
low temperatures.Comment: 9 pages, no figure
From infinite to two dimensions through the functional renormalization group
We present a novel scheme for an unbiased and non-perturbative treatment of
strongly correlated fermions. The proposed approach combines two of the most
successful many-body methods, i.e., the dynamical mean field theory (DMFT) and
the functional renormalization group (fRG). Physically, this allows for a
systematic inclusion of non-local correlations via the flow equations of the
fRG, after the local correlations are taken into account non-perturbatively by
the DMFT. To demonstrate the feasibility of the approach, we present numerical
results for the two-dimensional Hubbard model at half-filling.Comment: 5 pages, 4 figure
Fermion loops, loop cancellation and density correlations in two dimensional Fermi systems
We derive explicit results for fermion loops with an arbitrary number of
density vertices in two dimensions at zero temperature. The 3-loop is an
elementary function of the three external momenta and frequencies, and the
N-loop can be expressed as a linear combination of 3-loops with coefficients
that are rational functions of momenta and frequencies. We show that the
divergencies of single loops for low energy and small momenta cancel each other
when loops with permuted external variables are summed. The symmetrized N-loop,
i.e. the connected N-point density correlation function of the Fermi gas, does
not diverge for low energies and small momenta. In the dynamical limit, where
momenta scale to zero at fixed finite energy variables, the symmetrized N-loop
vanishes as the (2N-2)-th power of the scale parameter.Comment: 24 pages (including 3 EPS figures), LaTeX2e; submitted to Phys. Rev.
Crossover from Luttinger- to Fermi-liquid behavior in strongly anisotropic systems in large dimensions
We consider the low-energy region of an array of Luttinger liquids coupled by
a weak interchain hopping. The leading logarithmic divergences can be re-summed
to all orders within a self-consistent perturbative expansion in the hopping,
in the large-dimension limit. The anomalous exponent scales to zero below the
one-particle crossover temperature. As a consequence, coherent quasiparticles
with finite weight appear along the whole Fermi surface. Extending the
expansion self-consistently to all orders turns out to be crucial in order to
restore the correct Fermi-liquid behavior.Comment: Shortened version to appear in Physical Review Letter
Time-dependent Gutzwiller approximation for the Hubbard model
We develop a time-dependent Gutzwiller approximation (GA) for the Hubbard
model analogous to the time-dependent Hartree-Fock (HF) method. The formalism
incorporates ground state correlations of the random phase approximation (RPA)
type beyond the GA. Static quantities like ground state energy and double
occupancy are in excellent agreement with exact results in one dimension up to
moderate coupling and in two dimensions for all couplings. We find a
substantial improvement over traditional GA and HF+RPA treatments. Dynamical
correlation functions can be easily computed and are also substantially better
than HF+RPA ones and obey well behaved sum rules.Comment: 4 pages, 2 figure
Stratosphere troposphere coupling: the influence of volcanic eruptions
Stratospheric sulfate aerosols produced by major volcanic eruptions modify the radiative and dynamical properties of the troposphere and stratosphere through their reflection of solar radiation and absorption of infrared radiation. At the Earth's surface, the primary consequence of a large eruption is cooling, however, it has long been known that major tropical eruptions tend to be followed by warmer than usual winters over the Northern Hemisphere (NH) continents. This volcanic "winter-warming" effect in the NH is understood to be the result of changes in atmospheric circulation patterns resulting from heating in the stratosphere, and is often described as positive anomalies of the Northern Annular Mode (NAM) that propagate downward from the stratosphere to the troposphere. In the southern hemisphere, climate models tend to also predict a positive Southern Annular Mode (SAM) response to volcanic eruptions, but this is generally inconsistent with post-eruption observations during the 20th century. We review present understanding of the influence of volcanic eruptions on the large scale modes of atmospheric variability in both the Northern and Southern Hemispheres. Using models of varying complexity, including an aerosol-climate model, an Earth system model, and CMIP5 simulations, we assess the ability of climate models to reproduce the observed post-eruption climatic and dynamical anomalies. We will also address the parametrization of volcanic eruptions in simulations of the past climate, and identify possibilities for improvemen
Hole dynamics in generalized spin backgrounds in infinite dimensions
We calculate the dynamical behaviour of a hole in various spin backgrounds in
infinite dimensions, where it can be determined exactly. We consider hypercubic
lattices with two different types of spin backgrounds. On one hand we study an
ensemble of spin configurations with an arbitrary spin probability on each
sublattice. This model corresponds to a thermal average over all spin
configurations in the presence of staggered or uniform magnetic fields. On the
other hand we consider a definite spin state characterized by the angle between
the spins on different sublattices, i.e a classical spin system in an external
magnetic field. When spin fluctuations are considered, this model describes the
physics of unpaired particles in strong coupling superconductors.Comment: Accepted in Phys. Rev. B. 18 pages of text (1 fig. included) in Latex
+ 2 figures in uuencoded form containing the 2 postscripts (mailed
separately
Many-body position operator in lattice fermionic systems with periodic boundary conditions
A total position operator in the position representation is derived for
lattice fermionic systems with periodic boundary conditions. The operator is
shown to be Hermitian, the generator of translations in momentum space, and its
time derivative is shown to correspond to the total current operator in a
periodic system. The operator is such that its moments can be calculated up to
any order. To demonstrate its utility finite size scaling is applied to the
Brinkman-Rice transition as well as metallic and insulating Gutzwiller
wavefunctions.Comment: to appear in Journal of Physics A: Mathematical and General
(reference will be added later
Universality relations in non-solvable quantum spin chains
We prove the exact relations between the critical exponents and the
susceptibility, implied by the Haldane Luttinger liquid conjecture, for a
generic lattice fermionic model or a quantum spin chain with short range weak
interaction. The validity of such relations was only checked in some special
solvable models, but there was up to now no proof of their validity in
non-solvable models
- …