12,513 research outputs found
Interfacial thermal transport in atomic junctions
We study ballistic interfacial thermal transport across atomic junctions.
Exact expressions for phonon transmission coefficients are derived for thermal
transport in one-junction and two-junction chains, and verified by numerical
calculation based on a nonequilibrium Green's function method. For a
single-junction case, we find that the phonon transmission coefficient
typically decreases monotonically with increasing freqency. However, in the
range between equal frequency spectrum and equal acoustic impedance, it
increases first then decreases, which explains why the Kapitza resistance
calculated from the acoustic mismatch model is far larger than the experimental
values at low temperatures. The junction thermal conductance reaches a maximum
when the interfacial coupling equals the harmonic average of the spring
constants of the two semi-infinite chains. For three-dimensional junctions, in
the weak coupling limit, we find that the conductance is proportional to the
square of the interfacial coupling, while for intermediate coupling strength
the conductance is approximately proportional to the interfacial coupling
strength. For two-junction chains, the transmission coefficient oscillates with
the frequency due to interference effects. The oscillations between the two
envelop lines can be understood analytically, thus providing guidelines in
designing phonon frequency filters.Comment: 10 pages, 13 figures. Accepted by Phys. Rev.
Semiquantum key distribution using entangled states
Recently, Boyer et al. presented a novel semiquantum key distribution
protocol [M. Boyer, D. Kenigsberg, and T. Mor, Phys. Rev. Lett. 99, 140501
(2007)], by using four quantum states, each of which is randomly prepared by Z
basis or X basis. Here we present a semiquantum key distribution protocol by
using entangled states in which quantum Alice shares a secret key with
classical Bob. We also show the protocol is secure against eavesdropping.Comment: 6 page
Numerical Study of the Spin Hall Conductance in the Luttinger Model
We present first numerical studies of the disorder effect on the recently
proposed intrinsic spin Hall conductance in a three dimensional (3D) lattice
Luttinger model. The results show that the spin Hall conductance remains finite
in a wide range of disorder strength, with large fluctuations. The
disorder-configuration-averaged spin Hall conductance monotonically decreases
with the increase of disorder strength and vanishes before the Anderson
localization takes place. The finite-size effect is also discussed.Comment: 4 pages, 4 figures; the final version appearing in PR
Characteristics of phonon transmission across epitaxial interfaces: a lattice dynamic study
Phonon transmission across epitaxial interfaces is studied within the lattice
dynamic approach. The transmission shows weak dependence on frequency for the
lattice wave with a fixed angle of incidence. The dependence on azimuth angle
is found to be related to the symmetry of the boundary interface. The
transmission varies smoothly with the change of the incident angle. A critical
angle of incidence exists when the phonon is incident from the side with large
group velocities to the side with low ones. No significant mode conversion is
observed among different acoustic wave branches at the interface, except when
the incident angle is near the critical value. Our theoretical result of the
Kapitza conductance across the Si-Ge (100) interface at temperature
K is 4.6\times10^{8} {\rm WK}^{-1}{\rmm}^{-2}. A scaling law at low temperature is also reported. Based on the features of
transmission obtained within lattice dynamic approach, we propose a simplified
formula for thermal conductanceacross the epitaxial interface. A reasonable
consistency is found between the calculated values and the experimentally
measured ones.Comment: 8 figure
Anomalous quantum confined Stark effects in stacked InAs/GaAs self-assembled quantum dots
Vertically stacked and coupled InAs/GaAs self-assembled quantum dots (SADs)
are predicted to exhibit a strong non-parabolic dependence of the interband
transition energy on the electric field, which is not encountered in single SAD
structures nor in other types of quantum structures. Our study based on an
eight-band strain-dependent Hamiltonian indicates that
this anomalous quantum confined Stark effect is caused by the three-dimensional
strain field distribution which influences drastically the hole states in the
stacked SAD structures.Comment: 4 pages, 4 figure
Gravity waves over topographical bottoms: Comparison with the experiment
In this paper, the propagation of water surface waves over one-dimensional
periodic and random bottoms is investigated by the transfer matrix method. For
the periodic bottoms, the band structure is calculated, and the results are
compared to the transmission results. When the bottoms are randomized, the
Anderson localization phenomenon is observed. The theory has been applied to an
existing experiment (Belzons, et al., J. Fluid Mech. {\bf 186}, 530 (1988)). In
general, the results are compared favorably with the experimental observation.Comment: 15 pages, 7 figure
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