42,548 research outputs found
Full-counting statistics of charge and spin transport in the transient regime: A nonequilibrium Green's function approach
We report the investigation of full-counting statistics (FCS) of transferred
charge and spin in the transient regime where the connection between central
scattering region (quantum dot) and leads are turned on at . A general
theoretical formulation for the generating function (GF) is presented using a
nonequilibrium Green's function approach for the quantum dot system. In
particular, we give a detailed derivation on how to use the method of path
integral together with nonequilibrium Green's function technique to obtain the
GF of FCS in electron transport systems based on the two-time quantum
measurement scheme. The correct long-time limit of the formalism, the
Levitov-Lesovik's formula, is obtained. This formalism can be generalized to
account for spin transport for the system with noncollinear spin as well as
spin-orbit interaction. As an example, we have calculated the GF of
spin-polarized transferred charge, transferred spin, as well as the spin
transferred torque for a magnetic tunneling junction in the transient regime.
The GF is compactly expressed by a functional determinant represented by
Green's function and self-energy in the time domain. With this formalism, FCS
in spintronics in the transient regime can be studied. We also extend this
formalism to the quantum point contact system. For numerical results, we
calculate the GF and various cumulants of a double quantum dot system connected
by two leads in transient regime. The signature of universal oscillation of FCS
is identified. On top of the global oscillation, local oscillations are found
in various cumulants as a result of the Rabi oscillation. Finally, the
influence of the temperature is also examined
Cylindrical Lenses Based Spectral Domain Low-Coherence Interferometry for On-line Surface Inspection
This paper presents a spectral domain low-coherence interferometry (SD-LCI) method that is effective for applications in on-line surface inspection because it can obtain a surface profile in a single shot. It has an advantage over existing spectral interferometry techniques because it uses cylindrical lenses as the objective lens in a Michelson interferometric configuration to enable the measurement of long profiles. The adjustable profile length in our experimental setup, determined by the NA of the illuminating system and the aperture of cylindrical lenses, is up to 10 mm. To simulate real-time surface inspection, large-scale 3D surface measurement was carried out by translating the tested sample during the measurement procedure. Two step height surfaces were measured and the captured interferograms were analysed using a fast Fourier transform algorithm. Both 2D profile results and 3D surface maps closely align with the calibrated specifications given by the manufacturer
A Universal Constraint on the Infrared Behavior of the Ghost Propagator in QCD
With proposing a unified description of the fields variation at the level of
generating functional, we obtain a new identity for the quark-gluon interaction
vertex based on gauge symmetry, which is similar to the Slavnov-Taylor
Identities(STIs) based on the Becchi-Rouet-Stora-Tyutin transformation. With
these identities, we find that in Landau gauge, the dressing function of the
ghost propagator approaches to a constant as its momentum goes to zero, which
provides a strong constraint on the infrared behaviour of ghost propagator.Comment: 4 pages, no figur
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