293 research outputs found
Multifractality and its role in anomalous transport in the disordered XXZ spin-chain
The disordered XXZ model is a prototype model of the many-body localization
transition (MBL). Despite numerous studies of this model, the available
numerical evidence of multifractality of its eigenstates is not very conclusive
due severe finite size effects. Moreover it is not clear if similarly to the
case of single-particle physics, multifractal properties of the many-body
eigenstates are related to anomalous transport, which is observed in this
model. In this work, using a state-of-the-art, massively parallel, numerically
exact method, we study systems of up to 24 spins and show that a large fraction
of the delocalized phase flows towards ergodicity in the thermodynamic limit,
while a region immediately preceding the MBL transition appears to be
multifractal in this limit. We discuss the implication of our finding on the
mechanism of subdiffusive transport.Comment: 13 pages, 8 figure
Transport in quasiperiodic interacting systems: from superdiffusion to subdiffusion
Using a combination of numerically exact and renormalization-group techniques
we study the nonequilibrium transport of electrons in an one-dimensional
interacting system subject to a quasiperiodic potential. For this purpose we
calculate the growth of the mean-square displacement as well as the melting of
domain walls. While the system is nonintegrable for all studied parameters,
there is no on finite region default of parameters for which we observe
diffusive transport. In particular, our model shows a rich dynamical behavior
crossing over from superdiffusion to subdiffusion. We discuss the implications
of our results for the general problem of many-body localization, with a
particular emphasis on the rare region Griffiths picture of subdiffusion.Comment: 6 pages, 5 figures. A more detailed analysis of the dynamical
exponents extraction and discussion of the relevant times. Adds a
log-derivative for the FRG sectio
A Dynamic P53-MDM2 Model with Time Delay
Specific activator and repressor transcription factors which bind to specific
regulator DNA sequences, play an important role in gene activity control.
Interactions between genes coding such transcription factors should explain the
different stable or sometimes oscillatory gene activities characteristic for
different tissues. Starting with the model P53-MDM2 described into [6] and the
process described into [5] we developed a new model of this interaction.
Choosing the delay as a bifurcation parameter we study the direction and
stability of the bifurcating periodic solutions. Some numerical examples are
finally given for justifying the theoretical results.Comment: 16 pages, 12 figure
Temporal fluctuations of correlators in integrable and chaotic quantum systems
We provide bounds on temporal fluctuations around the infinite-time average
of out-of-time-ordered and time-ordered correlators of many-body quantum
systems without energy gap degeneracies. For physical initial states, our
bounds predict the exponential decay of the temporal fluctuations as a function
of the system size. We numerically verify this prediction for chaotic and
interacting integrable spin-1/2 chains, which satisfy the assumption of our
bounds. On the other hand, we show analytically and numerically that for the XX
model, which is a noninteracting system with gap degeneracies, the temporal
fluctuations decay polynomially with system size for operators that are local
in the fermion representation and decrease exponentially in the system size for
non-local operators. Our results demonstrate that the decay of the temporal
fluctuations of correlators cannot be used as a reliable metric of chaos or
lack thereof.Comment: 14 pages, 4 figure
Noise-induced transport in the Aubry-Andr\'e-Harper model
We study quantum transport in a quasiperiodic Aubry-Andr\'e-Harper (AAH)
model induced by the coupling of the system to a Markovian heat bath. We find
that coupling the heat bath locally does not affect transport in the
delocalized and critical phases, while it induces logarithmic transport in the
localized phase. Increasing the number of coupled sites at the central region
introduces a transient diffusive regime, which crosses over to logarithmic
transport in the localized phase and in the delocalized regime to ballistic
transport. On the other hand, when the heat bath is coupled to equally spaced
sites of the system, we observe a crossover from ballistic and logarithmic
transport to diffusion in the delocalized and localized regimes, respectively.
We propose a classical master equation, which captures our numerical
observations for both coupling configurations on a qualitative level and for
some parameters, even on a quantitative level. Using the classical picture, we
show that the crossover to diffusion occurs at a time that increases
exponentially with the spacing between the coupled sites, and the resulting
diffusion constant decreases exponentially with the spacing.Comment: 11 pages, 7 fig
Generalization of Kirchhoff's Law of Thermal Radiation: The Inherent Relations Between Quantum Efficiency and Emissivity
Planck's law of thermal radiation depends on the temperature, , and the
emissivity, , of a body, where emissivity is the coupling of heat to
radiation that depends on both phonon-electron nonradiative interactions and
electron-photon radiative interactions. Another property of a body is
absorptivity, , which only depends on the electron-photon radiative
interactions. At thermodynamic equilibrium, nonradiative interactions are
balanced, resulting in Kirchhoff's law of thermal radiation that equals these
two properties, i.e., . For non-equilibrium, quantum
efficiency () describes the statistics of photon emission, which like
emissivity depends on both radiative and nonradiative interactions. Past
generalized Planck's equation extends Kirchhoff's law out of equilibrium by
scaling the emissivity with the pump-dependent chemical-potential ,
obscuring the relations between the body properties. Here we theoretically and
experimentally demonstrate a prime equation relating these properties in the
form of , which is in agreement with a recent
universal modal radiation law for all thermal emitters. At equilibrium, these
relations are reduced to Kirchhoff's law. Our work lays out the fundamental
evolution of non-thermal emission with temperature, which is critical for the
development of lighting and energy devices.Comment: 14 pages, 16 figures. arXiv admin note: substantial text overlap with
arXiv:2104.1013
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