3,388 research outputs found
Effective interactions between parallel-spin electrons in two-dimensional jellium approaching the magnetic phase transition
We evaluate the effective interactions in a fluid of electrons moving in a
plane, on the approach to the quantum phase transition from the paramagnetic to
the fully spin-polarized phase that has been reported from Quantum Monte Carlo
runs. We use the approach of Kukkonen and Overhauser to treat exchange and
correlations under close constraints imposed by sum rules. We show that, as the
paramagnetic fluid approaches the phase transition, the effective interactions
at low momenta develop an attractive region between parallel-spin electrons and
a corresponding repulsive region for antiparallel-spin electron pairs. A
connection with the Hubbard model is made and used to estimate the magnetic
energy gap and hence the temperature at which the phase transition may become
observable with varying electron density in a semiconductor quantum well.Comment: 11 pages, 3 figure
Pair densities at contact in the quantum electron gas
The value of the pair distribution function g(r) at contact (r = 0) in a
quantum electron gas is determined by the scattering events between pairs of
electrons with antiparallel spins. The theoretical results for g(0) as a
function of the coupling strength r_s in the paramagnetic electron gas in
dimensionality D=2 and 3, that have been obtained from the solution of the
two-body scattering problem with a variety of effective scattering potentials
embodying many-body effects, are compared with the results of many-body
calculations in the ladder approximation and with quantum Monte Carlo data.Comment: 7 pages, 2 figure
Many-body effective mass enhancement in a two-dimensional electron liquid
Motivated by a large number of recent magnetotransport studies we have
revisited the problem of the microscopic calculation of the quasiparticle
effective mass in a paramagnetic two-dimensional (2D) electron liquid (EL). Our
systematic study is based on a generalized approximation which makes use
of the many-body local fields and takes advantage of the results of the most
recent QMC calculations of the static charge- and spin-response of the 2D EL.
We report extensive calculations for the many-body effective mass enhancement
over a broad range of electron densities. In this respect we critically examine
the relative merits of the on-shell approximation, commonly used in
weak-coupling situations, {\it versus} the actual self-consistent solution of
the Dyson equation. We show that already for and higher, a
solution of the Dyson equation proves here necessary in order to obtain a well
behaved effective mass. Finally we also show that our theoretical results for a
quasi-2D EL, free of any adjustable fitting parameters, are in good qualitative
agreement with some recent measurements in a GaAs/AlGaAs heterostructure.Comment: 12 pages, 3 figures, CMT28 Conference Proceedings, work related to
cond-mat/041226
Spin polarization in a two-dimensional electron gas
We evaluate the charge and longitudinal spin response functions of a
two-dimensional electron gas with interactions in an arbitrary state of
spin polarization, using a structurally self-consistent approach to treat
exchange and correlations. From the results we assess the nature of the
magnetic order in the electronic ground state in zero magnetic field as a
function of electron density. We find that states of partial spin polarization
are thermodynamically unstable at all values of the coupling strength and that
a first-order phase transition occurs with increasing coupling strength from
the magnetically disorderd (paramagnetic) phase to the fully spin-polarized
(ferromagnetic) phase. This behavior is in qualitative agreement with diffusion
Monte Carlo data, although the location of the phase transition is
underestimated in our calculations.Comment: 12 pages, 10 figuer
Nonlocal Spin Transport as a Probe of Viscous Magnon Fluids
Magnons in ferromagnets behave as a viscous fluid over a length scale, the
momentum-relaxation length, below which momentum-conserving scattering
processes dominate. We show theoretically that in this hydrodynamic regime
viscous effects lead to a sign change in the magnon chemical potential, which
can be detected as a sign change in the nonlocal resistance measured in spin
transport experiments. This sign change is observable when the
injector-detector distance becomes comparable to the momentum-relaxation
length. Taking into account momentum- and spin-relaxation processes, we
consider the quasiconservation laws for momentum and spin in a magnon fluid.
The resulting equations are solved for nonlocal spin transport devices in which
spin is injected and detected via metallic leads. Because of the finite
viscosity we also find a backflow of magnons close to the injector lead. Our
work shows that nonlocal magnon spin transport devices are an attractive
platform to develop and study magnon-fluid dynamics
Bound on the multiplicity of almost complete intersections
Let be a polynomial ring over a field of characteristic zero and let be a graded ideal of height which is minimally generated by
homogeneous polynomials. If where has degree
and has height , then the multiplicity of is
bounded above by .Comment: 7 pages; to appear in Communications in Algebr
Ground-state and dynamical properties of two-dimensional dipolar Fermi liquids
Cataloged from PDF version of article.We study the ground-state properties of a two-dimensional spinpolarized fluid of dipolar fermions within the Euler-Lagrange Fermi-hypemetted-chain approximation. Our method is based on the solution of a scattering Schrodinger equation for the "pair amplitude" root g(r), where g(r) is the pair distribution function. A key ingredient in our theory is the effective pair potential, which includes a bosonic term from Jastrow-Feenberg correlations and a fermionic contribution from kinetic energy and exchange, which is tailored to reproduce the Hartree-Fock limit at weak coupling. Very good agreement with recent results based on quantum Monte Carlo simulations is achieved over a wide range of coupling constants up to the liquid-to-crystal quantum phase transition. Using the fluctuation-dissipation theorem and a static approximation for the effective inter-particle interactions, we calculate the dynamical density-density response function, and furthermore demonstrate that an undamped zero-sound mode exists for any value of the interaction strength, down to infinitesimally weak couplings. (C) 2013 Elsevier Inc. All rights reserved
Effect of disorder on the interacting Fermi gases in a one-dimensional optical lattice
Interacting two-component Fermi gases loaded in a one-dimensional (1D)
lattice and subjected to an harmonic trapping potential exhibit interesting
compound phases in which fluid regions coexist with local Mott-insulator and/or
band-insulator regions. Motivated by experiments on cold atoms inside
disordered optical lattices, we present a theoretical study of the effects of a
correlated random potential on these ground-state phases. We employ a lattice
version of density-functional theory within the local-density approximation to
determine the density distribution of fermions in these phases. The
exchange-correlation potential is obtained from the Lieb-Wu exact solution of
Fermi-Hubbard model. On-site disorder (with and without Gaussian correlations)
and harmonic trap are treated as external potentials. We find that disorder has
two main effects: (i) it destroys the local insulating regions if it is
sufficiently strong compared with the on-site atom-atom repulsion, and (ii) it
induces an anomaly in the inverse compressibility at low density from quenching
of percolation. For sufficiently large disorder correlation length the
enhancement in the inverse compressibility diminishes.Comment: 11 pages, 6 figures, submitte
Plasmons and Coulomb drag in Dirac/Schroedinger hybrid electron systems
We show that the plasmon spectrum of an ordinary two-dimensional electron gas
(2DEG) hosted in a GaAs heterostructure is significantly modified when a
graphene sheet is placed on the surface of the semiconductor in close proximity
to the 2DEG. Long-range Coulomb interactions between massive electrons and
massless Dirac fermions lead to a new set of optical and acoustic intra-subband
plasmons. Here we compute the dispersion of these coupled modes within the
Random Phase Approximation, providing analytical expressions in the
long-wavelength limit that shed light on their dependence on the Dirac velocity
and Dirac-fermion density. We also evaluate the resistivity in a Coulomb-drag
transport setup. These Dirac/Schroedinger hybrid electron systems are
experimentally feasible and open new research opportunities for fundamental
studies of electron-electron interaction effects in two spatial dimensions.Comment: 7 pages, 4 figure
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