23,750 research outputs found
Conformal Symmetry on the Instanton Moduli Space
The conformal symmetry on the instanton moduli space is discussed using the
ADHM construction, where a viewpoint of "homogeneous coordinates" for both the
spacetime and the moduli space turns out to be useful. It is shown that the
conformal algebra closes only up to global gauge transformations, which
generalizes the earlier discussion by Jackiw et al. An interesting
5-dimensional interpretation of the SU(2) single-instanton is also mentioned.Comment: 7 pages, LaTeX, version to appear in J. Phys. A: Math. Ge
The perfect spin injection in silicene FS/NS junction
We theoretically investigate the spin injection from a ferromagnetic silicene
to a normal silicene (FS/NS), where the magnetization in the FS is assumed from
the magnetic proximity effect. Based on a silicene lattice model, we
demonstrated that the pure spin injection could be obtained by tuning the Fermi
energy of two spin species, where one is in the spin orbit coupling gap and the
other one is outside the gap. Moreover, the valley polarity of the spin species
can be controlled by a perpendicular electric field in the FS region. Our
findings may shed light on making silicene-based spin and valley devices in the
spintronics and valleytronics field.Comment: 6 pages, 3 figure
Observations of Subarcsecond Bright Dots in the Transition Region above Sunspots with the Interface Region Imaging Spectrograph
Observations with the Interface Region Imaging Spectrograph (IRIS) have
revealed numerous sub-arcsecond bright dots in the transition region above
sunspots. These bright dots are seen in the 1400\AA{} and 1330\AA{} slit-jaw
images. They are clearly present in all sunspots we investigated, mostly in the
penumbrae, but also occasionally in some umbrae and light bridges. The bright
dots in the penumbrae typically appear slightly elongated, with the two
dimensions being 300--600 km and 250--450 km, respectively. The long sides of
these dots are often nearly parallel to the bright filamentary structures in
the penumbrae but sometimes clearly deviate from the radial direction. Their
lifetimes are mostly less than one minute, although some dots last for a few
minutes or even longer. Their intensities are often a few times stronger than
the intensities of the surrounding environment in the slit-jaw images. About
half of the bright dots show apparent movement with speeds of
10--40~km~s in the radial direction. Spectra of a few bright dots
were obtained and the Si~{\sc{iv}}~1402.77\AA{} line profiles in these dots are
significantly broadened. The line intensity can be enhanced by one to two
orders of magnitude. Some relatively bright and long-lasting dots are also
observed in several passbands of the Atmospheric Imaging Assembly onboard the
Solar Dynamics Observatory, and they appear to be located at the bases of
loop-like structures. Many of these bright dots are likely associated with
small-scale energy release events at the transition region footpoints of
magnetic loops.Comment: 5 figures, will appear in ApJ
Superconducting correlations in ultra-small metallic grains
To describe the crossover from the bulk BCS superconductivity to a
fluctuation-dominated regime in ultrasmall metallic grains, new order
parameters and correlation functions, such as ``parity gap'' and ``pair-mixing
correlation function'', have been recently introduced. In this paper, we
discuss the small-grain behaviour of the Penrose-Onsager-Yang off-diagonal
long-range order (ODLRO) parameter in a pseudo-spin representation. Relations
between the ODLRO parameter and those mentioned above are established through
analytical and numerical calculations.Comment: 7 pages, 1 figur
Integer quantum Hall effect and topological phase transitions in silicene
We numerically investigate the effects of disorder on the quantum Hall effect
(QHE) and the quantum phase transitions in silicene based on a lattice model.
It is shown that for a clean sample, silicene exhibits an unconventional QHE
near the band center, with plateaus developing at and
a conventional QHE near the band edges. In the presence of disorder, the Hall
plateaus can be destroyed through the float-up of extended levels toward the
band center, in which higher plateaus disappear first. However, the center
Hall plateau is more sensitive to disorder and disappears at a
relatively weak disorder strength. Moreover, the combination of an electric
field and the intrinsic spin-orbit interaction (SOI) can lead to quantum phase
transitions from a topological insulator to a band insulator at the charge
neutrality point (CNP), accompanied by additional quantum Hall conductivity
plateaus.Comment: 7 pages, 4 figure
Charged and spin-excitation gaps in half-filled strongly correlated electron systems: A rigorous result
By exploiting the particle-hole symmetries of the Hubbard model, the periodic
Anderson model and the Kondo lattice model at half-filling and applying a
generalized version of Lieb's spin-reflection positivity method, we show that
the charged gaps of these models are always larger than their spin excitation
gaps. This theorem confirms the previous results derived by either the
variational approach or the density renormalization group approach.Comment: 20 pages, no figur
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