2,401 research outputs found
Field-assisted doublon manipulation in the Hubbard model. A quantum doublon ratchet
For the fermionic Hubbard model at strong coupling, we demonstrate that
directional transport of localized doublons (repulsively bound pairs of two
particles occupying the same site of the crystal lattice) can be achieved by
applying an unbiased ac field of time-asymmetric (sawtooth-like) shape. The
mechanism involves a transition to intermediate states of virtually zero double
occupation which are reached by splitting the doublon by fields of the order of
the Hubbard interaction. The process is discussed on the basis of numerically
exact calculations for small clusters, and we apply it to more complex states
to manipulate the charge order pattern of one-dimensional systems.Comment: 6 pages, 6 figure
Electronic double-excitations in quantum wells: solving the two-time Kadanoff-Baym equations
For a quantum many-body system, the direct population of states of
double-excitation character is a clear indication that correlations importantly
contribute to its nonequilibrium properties. We analyze such
correlation-induced transitions by propagating the nonequilibrium Green's
functions in real-time within the second Born approximation. As crucial
benchmarks, we compute the absorption spectrum of few electrons confined in
quantum wells of different width. Our results include the full two-time
solution of the Kadanoff-Baym equations as well as of their time-diagonal limit
and are compared to Hartree-Fock and exact diagonalization data
Ultrafast and reversible control of the exchange interaction in Mott insulators
The strongest interaction between microscopic spins in magnetic materials is
the exchange interaction . Therefore, ultrafast control of
holds the promise to control spins on ultimately fast timescales.
We demonstrate that time-periodic modulation of the electronic structure by
electric fields can be used to reversibly control on ultrafast
timescales in extended antiferromagnetic Mott insulators. In the regime of weak
driving strength, we find that can be enhanced and reduced for
frequencies below and above the Mott gap, respectively. Moreover, for strong
driving strength, even the sign of can be reversed and we show
that this causes time reversal of the associated quantum spin dynamics. These
results suggest wide applications, not only to control magnetism in condensed
matter systems, for example, via the excitation of spin resonances, but also to
assess fundamental questions concerning the reversibility of the quantum
many-body dynamics in cold atom systems.Comment: 9 pages, 4 figure
Invariance of the Kohn (sloshing) mode in a conserving theory
It is proven that the center of mass (COM or Kohn) oscillation of a many-body
system in a harmonic trap coincides with the motion of a single particle as
long as conserving approximations are applied to treat the interactions. The
two conditions formulated by Kadanoff and Baym \cite{kb-book} are shown to be
sufficient to preserve the COM mode. The result equally applies to zero and
finite temperature, as well as to nonequilibrium situations, and to the linear
and nonlinear response regimes
Non-equilibrium Green's function approach to inhomogeneous quantum many-body systems using the Generalized Kadanoff Baym Ansatz
In non-equilibrium Green's function calculations the use of the Generalized
Kadanoff-Baym Ansatz (GKBA) allows for a simple approximate reconstruction of
the two-time Green's function from its time-diagonal value. With this a drastic
reduction of the computational needs is achieved in time-dependent
calculations, making longer time propagation possible and more complex systems
accessible. This paper gives credit to the GKBA that was introduced 25 years
ago. After a detailed derivation of the GKBA, we recall its application to
homogeneous systems and show how to extend it to strongly correlated,
inhomogeneous systems. As a proof of concept, we present results for a
2-electron quantum well, where the correct treatment of the correlated electron
dynamics is crucial for the correct description of the equilibrium and dynamic
properties
Electronic correlations in double ionization of atoms in pump-probe experiments
The ionization dynamics of a two-electron atom in an attosecond XUV-infrared
pump-probe experiment is simulated by solving the time-dependent two-electron
Schr\"odinger equation. A dramatic change of the double ionization (DI) yield
with variation of the pump-probe delay is reported and the governing role of
electron-electron correlations is shown. The results allow for a direct control
of the DI yield and of the relative strength of double and single ionization
Phosphorylation of Subunit Proteins of Intermediate Filaments from Chicken Muscle and Nonmuscle Cells
The phosphorylation of the subunit proteins of intermediate (10-nm) filaments has been investigated in chicken muscle and nonmuscle cells by using a two-dimensional gel electrophoresis system. Desmin, the 50,000-dalton subunit protein of the intermediate filaments of muscle, had previously been shown to exist as two major isoelectric variants--alpha and ß --in smooth, skeletal, and cardiac chicken muscle. Incubation of skeletal and smooth muscle tissue with 32PO4{}3- reveals that the acidic variant, alpha -desmin, and three other desmin variants are phosphorylated in vivo and in vitro. Under the same conditions, minor components of alpha - and ß -tropomyosin from skeletal muscle, but not smooth muscle, are also phosphorylated. Both the phosphorylated desmin variants and the nonphosphorylated ß -desmin variant remain insoluble under conditions that solubilize actin and myosin filaments, but leave Z-discs and intermediate filaments insoluble. Primary cultures of embryonic chicken muscle labeled with 32PO4{}3- possess, in addition to the desmin variants described above, a major nonphosphorylated and multiple phosphorylated variants of the 52,000-dalton, fibroblast-type intermediate filament protein (IFP). Filamentous cytoskeletons, prepared from primary myogenic cultures by Triton X-100 extraction, contain actin and all of the phosphorylated and nonphosphorylated variants of both desmin and the IFP. Similarly, these proteins are the major components of the caps of aggregated 10-nm filaments isolated from the same cell cultures previously exposed to Colcemid. These results demonstrate that a nonphosphorylated and several phosphorylated variants of desmin and IFP are present in assembled structures in muscle and nonmuscle cells
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