7,768 research outputs found
Nonequilibrium Energy Transfer at Nanoscale: A Unified Theory from Weak to Strong Coupling
We investigate the microscopic mechanism of quantum energy transfer in the
nonequilibrium spin-boson model. By developing a nonequilibrium
polaron-transformed Redfield equation based on fluctuation decoupling, we
dissect the energy transfer into multi-boson associated processes with even or
odd parity. Based on this, we analytically evaluate the energy flux, which
smoothly bridges the transfer dynamics from the weak spin-boson coupling regime
to the strong-coupling one. Our analysis explains previous limiting predictions
and provides a unified interpretation of several observations, including
coherence-enhanced heat flux and absence of negative differential thermal
conductance in the nonequilibrium spin-boson model. The results may find wide
applications for the energy and information control in nanodevices.Comment: 11 pages, 4 figure
Topological phase transition based on the attractive Hubbard model
We theoretically investigate the effect of an attractive on-site interaction
on the two-band magnetic Dirac fermion model based on a square lattice system.
When the attractive fermion interaction is taken into account by the mean-field
approximation, a phase diagram is obtained. It is found that a quantum phase
transition from a band insulator state to quantum anomalous Hall state occurs
with increased attractive interaction. For an existing quantum anomalous Hall
state, the attractive interaction enlarges its nontrivial band gap and makes
the topological edge states more localized, which protects the transport of
linear-dispersive edge states against finite-size and further disorder effects.Comment: 5 pages, 4 figure
Direct observation of ultrafast thermal and non-thermal lattice deformation of polycrystalline Aluminum film
The dynamics of thermal and non-thermal lattice deformation of nanometer
thick polycrystalline aluminum film has been studied by means of femtosecond
(fs) time-resolved electron diffraction. We utilized two different pump
wavelengths: 800 nm, the fundamental of Ti: sapphire laser and 1250 nm
generated by a home-made optical parametric amplifier(OPA). Our data show that,
although coherent phonons were generated under both conditions, the diffraction
intensity decayed with the characteristic time of 0.9+/-0.3 ps and 1.7+/-0.3 ps
under 800 nm and 1250 nm excitation, respectively. Because the 800 nm laser
excitation corresponds to the strong interband transition of aluminum due to
the 1.55 eV parallel band structure, our experimental data indicate the
presence of non-thermal lattice deformation under 800 nm excitation, which
occurs on a time-scale that is shorter than the thermal processes dominated by
electron-phonon coupling under 1250 nm excitation
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