3,195 research outputs found
Quantum spin circulator in Y junctions of Heisenberg chains
We show that a quantum spin circulator, a nonreciprocal device that routes
spin currents without any charge transport, can be achieved in Y junctions of
identical spin- Heisenberg chains coupled by a chiral three-spin
interaction. Using bosonization, boundary conformal field theory, and
density-matrix renormalization group simulations, we find that a chiral fixed
point with maximally asymmetric spin conductance arises at a critical point
separating a regime of disconnected chains from a spin-only version of the
three-channel Kondo effect. We argue that networks of spin-chain Y junctions
provide a controllable approach to construct long-sought chiral spin liquid
phases.Comment: 9 pages, 3 figure
Abnormal directed migration of blood polymorphonuclear leukocytes in rheumatoid arthritis. Potential role in increased susceptibility to bacterial infections.
Rheumatoid arthritis (RA) patients are at higher risks of bacterial infection than healthy subjects. Polymorphonuclear leukocytes (PMN) are the first line of nonspecific cellular defence against these infections. We tested the hypothesis that abnormal directed migration of PMN may be one reason for the increased infection rate of RA patients. PMN migration was investigated in 68 peripheral blood samples of 15 RA patients compared with 64 samples of healthy controls in a novel whole blood in vitro membrane filter assay. The migration of PMNs from RA patients and controls was stimulated using the bacterial chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP). Unstimulated PMN migration of RA patients was increased compared with healthy controls as measured by the following parameters: (a) absolute number of migrant PMNs (1954+/-87 vs. 1238 +/-58 PMN/mm2), (b) percentage of PMNs migrated into the filter (total migration index, TMI) (28.6+/-0.9 vs. 24.0+/-0.8%), (c) the distance half the migrating PMNs had covered (distribution characteristic, DC) (22.6+/-1.1 vs. 16.1+/-0.6 mm) and (d) the product of TMI and DC (neutrophil migratory activity, NMA) (669.0+/-45.0 vs. 389.0+/-18.9). fMLP stimulated PMNs of RA patients showed defective migration compared to unstimulated samples as shown by (a) a reduced number of migrant PMNs (1799+/-93 PMN/mm2), (b) lower TMI (26.1+/-0.9%), (c) unremarkable altered distribution characteristic (22.9+/-0.8 mm) and (d) significant reduced migratory activity (600.0+/-30.0). Our data suggest that the high incidence of infections in RA patients may partly be caused by defective migratory activity of PMNs to bacterial chemoattractants as demonstrated by fMLP
Comparative study of theoretical methods for nonequilibrium quantum transport
We present a detailed comparison of three different methods designed to
tackle nonequilibrium quantum transport, namely the functional renormalization
group (fRG), the time-dependent density matrix renormalization group (tDMRG),
and the iterative summation of real-time path integrals (ISPI). For the
nonequilibrium single-impurity Anderson model (including a Zeeman term at the
impurity site), we demonstrate that the three methods are in quantitative
agreement over a wide range of parameters at the particle-hole symmetric point
as well as in the mixed-valence regime. We further compare these techniques
with two quantum Monte Carlo approaches and the time-dependent numerical
renormalization group method.Comment: 19 pages, 7 figures; published versio
Charge qubit entanglement in double quantum dots
We study entanglement of charge qubits in a vertical tunnel-coupled double
quantum dot containing two interacting electrons. Exact diagonalization is used
to compute the negativity characterizing entanglement. We find that
entanglement can be efficiently generated and controlled by sidegate voltages,
and describe how it can be detected. For large enough tunnel coupling, the
negativity shows a pronounced maximum at an intermediate interaction strength
within the Wigner molecule regime.Comment: revised version of the manuscript, as published in EPL, 7 pages, 4
figure
Form-factors computation of Friedel oscillations in Luttinger liquids
We show how to analytically determine for the "Friedel
oscillations" of charge density by a single impurity in a 1D Luttinger liquid
of spinless electrons.Comment: Revtex, epsf, 4pgs, 2fig
Superconductivity from piezoelectric interactions in Weyl semimetals
We present an analytical low-energy theory of piezoelectric electron-phonon interactions in undoped Weyl semimetals, taking into account also Coulomb interactions. We show that piezoelectric interactions generate a long-range attractive potential between Weyl fermions. This potential comes with a characteristic angular anisotropy. From the one-loop renormalization group approach and a mean-field analysis, we predict that superconducting phases with either conventional s-wave singlet pairing or nodal-line triplet pairing could be realized for sufficiently strong piezoelectric coupling. For small couplings, we show that the quasiparticle decay rate exhibits a linear temperature dependence where the prefactor vanishes only in a logarithmic manner as the quasiparticle energy approaches the Weyl point. For practical estimates, we consider the Weyl semimetal TaAs
Raman signatures of classical and quantum phases in coupled dots: A theoretical prediction
We study electron molecules in realistic vertically coupled quantum dots in a
strong magnetic field. Computing the energy spectrum, pair correlation
functions, and dynamical form factor as a function of inter-dot coupling via
diagonalization of the many-body Hamiltonian, we identify structural
transitions between different phases, some of which do not have a classical
counterpart. The calculated Raman cross section shows how such phases can be
experimentally singled out.Comment: 9 pages, 2 postscript figures, 1 colour postscript figure, Latex 2e,
Europhysics Letters style and epsfig macros. Submitted to Europhysics Letter
Fluctuation relations and rare realizations of transport observables
Fluctuation relations establish rigorous identities for the nonequilibrium
averages of observables. Starting from a general transport master equation with
time-dependent rates, we employ the stochastic path integral approach to study
statistical fluctuations around such averages. We show how under nonequilibrium
conditions, rare realizations of transport observables are crucial and imply
massive fluctuations that may completely mask such identities. Quantitative
estimates for these fluctuations are provided. We illustrate our results on the
paradigmatic example of a mesoscopic RC circuit.Comment: 4 pages, 3 figures; v2: minor changes, published versio
Exact results for nonlinear ac-transport through a resonant level model
We obtain exact results for the transport through a resonant level model
(noninteracting Anderson impurity model) for rectangular voltage bias as a
function of time. We study both the transient behavior after switching on the
tunneling at time t = 0 and the ensuing steady state behavior. Explicit
expressions are obtained for the ac-current in the linear response regime and
beyond for large voltage bias. Among other effects, we observe current ringing
and PAT (photon assisted tunneling) oscillations.Comment: 7 page
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