5,124 research outputs found
On the origin of the hump structure in the in-plane optical conductivity of high Tc cuprates based on a SU(2) slave-boson theory
An improved version of SU(2) slave-boson approach is applied to study the
in-plane optical conductivity of the two dimensional systems of high Tc
cuprates. We investigate the role of fluctuations of both the phase and
amplitude of order parameters on the (Drude) peak-dip-hump structure in the
in-plane conductivity as a function of hole doping concentration and
temperature. The mid-infrared(MIR) hump in the in-plane optical conductivity is
shown to originate from the antiferromagnetic spin fluctuations of short
range(the amplitude fluctuations of spin singlet pairing order parameters),
which is consistent with our previous U(1) study. However the inclusion of both
the phase and amplitude fluctuations is shown to substantially improve the
qualitative feature of the optical conductivity by showing substantially
reduced Drude peak widths for entire doping range. Both the shift of the hump
position to lower frequency and the growth of the hump peak height with
increasing hole concentration is shown to be consistent with observations.Comment: 7 pages, 6 figure
A Near-Infrared Study of the Highly-Obscured Active Star-Forming Region W51B
We present wide-field JHKs-band photometric observations of the three compact
HII regions G48.9-0.3, G49.0-0.3, and G49.2-0.3 in the active star-forming
region W51B. The star clusters inside the three compact HII regions show the
excess number of stars in the J-Ks histograms compared with reference fields.
While the mean color excess ratio E(J-H)/E(H-Ks) of the three compact HII
regions are similar to ~ 2.07, the visual extinctions toward them are somewhat
different: ~ 17 mag for G48.9-0.3 and G49.0-0.3; ~ 23 mag for G49.2-0.3. Based
on their sizes and brightnesses, we suggest that the age of each compact HII
region is =< 2 Myr. The inferred total stellar mass, ~ 1.4 x 10^4 M_sun, of
W51B makes it one of the most active star forming regions in the Galaxy with
the star formation efficiency of ~ 10 %.Comment: 12 pages, 10 eps figures, uses jkas.st
Ab initio holography
We apply the quantum renormalization group to construct a holographic dual
for the U(N) vector model for complex bosons defined on a lattice. The bulk
geometry becomes dynamical as the hopping amplitudes which determine
connectivity of space are promoted to quantum variables. In the large N limit,
the full bulk equations of motion for the dynamical hopping fields are
numerically solved for finite systems. From finite size scaling, we show that
different phases exhibit distinct geometric features in the bulk. In the
insulating phase, the space gets fragmented into isolated islands deep inside
the bulk, exhibiting ultra-locality. In the superfluid phase, the bulk exhibits
a horizon beyond which the geometry becomes non-local. Right at the horizon,
the hopping fields decay with a universal power-law in coordinate distance
between sites, while they decay in slower power-laws with continuously varying
exponents inside the horizon. At the critical point, the bulk exhibits a local
geometry whose characteristic length scale diverges asymptotically in the IR
limit.Comment: 44+11 pages, many figures, added how to extract critical exponent
from bulk (Fig. 13), other minor change
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