355 research outputs found
Tunneling of correlated electrons in ultra high magnetic field
Effects of the electron-electron interaction on tunneling into a metal in
ultra-high magnetic field (ultra-quantum limit) are studied. The range of the
interaction is found to have a decisive effect both on the nature of the
field-induced instability of the ground state and on the properties of the
system at energies above the corresponding gap. For a short-range repulsive
interaction, tunneling is dominated by the renormalization of the coupling
constant, which leads eventually to the charge-density wave instability. For a
long-range interaction, there exists an intermediate energy range in which the
conductance obeys a power-law scaling form, similar to that of a 1D Luttinger
liquid. The exponent is magnetic-field dependent, and more surprisingly, may be
positive or negative, i. e., interactions may either suppress or enhance the
tunneling conductance compared to its non-interacting value. At energies near
the gap, scaling breaks down and tunneling is again dominated by the
instability, which in this case is an (anisotropic) Wigner crystal instability.Comment: 4 pages, 2 .eps figure
Non-magnetic pair-breaking effect on La(Fe_{1-x}Zn_{x})AsO_{0.85} studied by NMR and NQR
As and La NMR and nuclear quadrupole resonance (NQR) studies
on Zn-substituted LaFeAsO have been performed to investigate the
Zn-impurity effects microscopically. Although superconductivity in
LaFeAsO disappears by 3% Zn substitution, we found that NMR/NQR
spectra and NMR physical quantities in the normal state are hardly changed,
indicating that the crystal structure and electronic states are not modified by
Zn substitution. Our results suggest that the suppression of superconductivity
by Zn substitution is not due to the change of the normal-state properties, but
due to strong non-magnetic pair-breaking effect to superconductivity.Comment: 5 pages, 4 figures, This paper was chosen as "Paper of Editors'
Suggestion
Unconventional superconductivity and antiferromagnetic quantum critical behavior in the isovalent-doped BaFe2(As1-xPx)2
Spin dynamics evolution of BaFe(AsP) was probed as a
function of P concentration via P NMR. Our NMR study reveals that
two-dimensional antiferromagnetic (AF) fluctuations are notably enhanced with
little change in static susceptibility on approaching the AF phase from the
superconducting dome. Moreover, magnetically ordered temperature
deduced from the relaxation rate vanishes at optimal doping. These results
provide clear-cut evidence for a quantum-critical point (QCP), suggesting that
the AF fluctuations associated with the QCP play a central role in the
high- superconductivity.Comment: 5 pages, 3 figure
Observation of Spin-Orbit Berry's Phase in Magnetoresistance of a Two-Dimensional Hole Anti-dot System
We report observation of spin-orbit Berry's phase in the Aharonov-Bohm (AB)
type oscillation of weak field magnetoresistance in an anti-dot lattice (ADL)
of a two-dimensional hole system. An AB-type oscillation is superposed on the
commensurability peak, and the main peak in the Fourier transform is clearly
split up due to variation in Berry's phase originating from the spin-orbit
interaction. A simulation considering Berry's phase and the phase arising from
the spin-orbit shift in the momentum space shows qualitative agreement with the
experiment.Comment: 13 pages, 5 figure
SuprimeCam Observation of Sporadic Meteors during Perseids 2004
We report the serendipitous findings of 13 faint meteors and 44 artificial
space objects by Subaru SuprimeCam imaging observations during 11-16 August
2004. The meteors, at about 100km altitude, and artificial satellites/debris in
orbit, at 500km altitude or higher, were clearly discriminated by their
apparent defocused image sizes. CCD photometry of the 13 meteors, including 1
Perseid, 1 Aquarid, and 11 sporadic meteors, was performed. We defined a peak
video-rate magnitude by comparing the integrated photon counts from the
brightest portion of the track traversed within 33ms to those from a 0-mag star
during the same time duration. This definition gives magnitudes in the range
4.0< V_{vr} <6.4 and 4.1< I_{vr}<5.9 for these 13 meteors. The corresponding
magnitude for virtual naked-eye observers could be somewhat fainter especially
for the V-band observation, in which the [OI] 5577 line lasting about 1 sec as
an afterglow could contribute to the integrated flux of the present 5-10 min
CCD exposures. Although the spatial resolution is insufficient to resolve the
source size of anything smaller than about 1 m, we developed a new estimate of
the collisionally excited column diameter of these meteors. A diameter as small
as a few mm was derived from their collisionally excited photon rates, meteor
speed, and the volume density of the oxygen atoms at the 100km altitude. The
actual column diameter of the radiating zone, however, could be as large as few
100m because the excited atoms travel that distance before they emit forbidden
lines in 0.7 sec of its average lifetime. Among the 44 artificial space
objects, we confirmed that 17 were cataloged satellites/space debris.Comment: 14 pages, 13 figures, 5 tables, submitted to PAS
Spectroscopy of i-Dropout Galaxies with an NB921-Band Depression in the Subaru Deep Field
We report new spectroscopy of two star-forming galaxies with strong Ly_alpha
emission at z=6.03 and z=6.04 in the Subaru Deep Field. These two objects are
originally selected as i'-dropouts (i'-z' > 1.5) showing an interesting
photometric property, the ``NB921 depression''. The NB921-band (centered at
9196A) magnitude is significantly depressed with respect to the z'-band
magnitude. The optical spectra of these two objects exhibit asymmetric
emission-lines at lambda_obs ~ 8540A and ~ 8560A, suggesting that these objects
are Ly_alpha emitters at z~6. The rest-frame equivalent widths of the Ly_alpha
emission of the two objects are 94A and 236A; the latter one is the Ly_alpha
emitter with the largest Ly_alpha equivalent width at z > 6 ever
spectroscopically confirmed. The spectroscopically measured Ly_alpha fluxes of
these two objects are consistent with the interpretation that the NB921
depression is caused by the contribution of the strong Ly_alpha emission to the
z'-band flux. Most of the NB921-depressed i'-dropout objects are thought to be
strong Ly_alpha emitters at 6.0 < z < 6.5; Galactic L and T dwarfs and
NB921-dropout galaxies at z > 6.6 do not dominate the NB921-depressed
i'-dropout sample. Thus the NB921-depression method is very useful for finding
high-z Ly_alpha emitters with a large Ly_alpha equivalent width over a large
redshift range, 6.0 < z < 6.5. Although the broadband-selected sample at z ~ 3
contains only a small fraction of objects with a Ly_alpha equivalent width
larger than 100A, the i'-dropout sample of the Subaru Deep Field contains a
much larger fraction of such strong Ly_alpha emitters. This may imply a strong
evolution of the Ly_alpha equivalent width from z > 6 to z ~ 3.Comment: 21 pages, 6 figures, to appear in The Astrophysical Journa
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