3,695 research outputs found
Hidden Charge 2e Boson in Doped Mott Insulators: Field Theory of Mottness
We construct the low energy theory of a doped Mott insulator, such as the
high-temperature superconductors, by explicitly integrating over the degrees of
freedom far away from the chemical potential. For either hole or electron
doping, a charge 2e bosonic field emerges at low energy. The charge 2e boson
mediates dynamical spectral weight transfer across the Mott gap and creates a
new charge e excitation by binding a hole. The result is a bifurcation of the
electron dispersion below the chemical potential as observed recently in
angle-resolved photoemission on Pb-doped Bi_2Sr_2CaCu_2O_{8+\delta} (Pb2212).Comment: 4 pages, 2 figures: Correct version to appear in PRL. Revisions
include a derivation of the electron operator at low energies which reveals a
branching structure seen recently in ARPES on Pb221
Array-based iterative measurements of SmKS travel times and their constraints on outermost core structure
Vigorous convection in Earth's outer core led to the suggestion that it is chemically homogeneous. However, there is increasing seismic evidence for structural complexities close to the outer core's upper and lower boundaries. Both body waves and normal mode data have been used to estimate a P wave velocity, V_p, at the top of the outer core (the E’ layer), which is lower than that in the Preliminary Reference Earth Model. However, these low V_p models do not agree on the form of this velocity anomaly. One reason for this is the difficulty in retrieving and measuring SmKS arrival times. To address this issue, we propose a novel approach using data from seismic arrays to iteratively measure SmKS-SKKS-differential travel times. This approach extracts individual SmKS signal from mixed waveforms of the SmKS series, allowing us to reliably measure differential travel times. We successfully use this method to measure SmKS time delays from earthquakes in the Fiji‐Tonga and Vanuatu subduction zones. SmKS time delays are measured by waveform cross correlation between SmKS and SKKS, and the cross‐correlation coefficient allows us to access measurement quality. We also apply this iterative scheme to synthetic SmKS seismograms to investigate the 3‐D mantle structure's effects. The mantle structure corrections are not negligible for our data, and neglecting them could bias the V_p estimation of uppermost outer core. After mantle structure corrections, we can still see substantial time delays of S3KS, S4KS, and S5KS, supporting a low V_p at the top of Earth's outer core
Evolutionary Subnetworks in Complex Systems
Links in a practical network may have different functions, which makes the
original network a combination of some functional subnetworks. Here, by a model
of coupled oscillators, we investigate how such functional subnetworks are
evolved and developed according to the network structure and dynamics. In
particular, we study the case of evolutionary clustered networks in which the
function of each link (either attractive or repulsive coupling) is updated by
the local dynamics. It is found that, during the process of system evolution,
the network is gradually stabilized into a particular form in which the
attractive (repulsive) subnetwork consists only the intralinks (interlinks).
Based on the properties of subnetwork evolution, we also propose a new
algorithm for network partition which is distinguished by the convenient
operation and fast computing speed.Comment: 4 pages, 4 figure
Exact Integration of the High Energy Scale in Doped Mott Insulators
We expand on our earlier work (cond-mat/0612130, Phys. Rev. Lett. {\bf 99},
46404 (2007)) in which we constructed the exact low-energy theory of a doped
Mott insulator by explicitly integrating (rather than projecting) out the
degrees of freedom far away from the chemical potential. The exact low-energy
theory contains degrees of freedom that cannot be obtained from projective
schemes. In particular a new charge bosonic field emerges at low
energies that is not made out of elemental excitations. Such a field accounts
for dynamical spectral weight transfer across the Mott gap. At half-filling, we
show that two such excitations emerge which play a crucial role in preserving
the Luttinger surface along which the single-particle Green function vanishes.
In addition, the interactions with the bosonic fields defeat the artificial
local SU(2) symmetry that is present in the Heisenberg model. We also apply
this method to the Anderson-U impurity and show that in addition to the Kondo
interaction, bosonic degrees of freedom appear as well. Finally, we show that
as a result of the bosonic degree of freedom, the electron at low energies is
in a linear superposition of two excitations--one arising from the standard
projection into the low-energy sector and the other from the binding of a hole
and the boson.Comment: Published veriso
Improving efficiency of electrostatic spray-assisted vapor deposited Cu2ZnSn(S,Se)4 solar cells by modification of Mo/absorber interface
Electrostatic spray-assisted vapor deposition (ESAVD) is a non-vacuum, low cost and eco-friendly method to produce
Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 (CZTSSe) absorbers for thin film solar cells, and it is a very promising
method for industrialization due to it is high deposition speed and close to unity deposition efficiency. In this
work, in order to improve the efficiency of ESAVD deposited CZTSSe solar cells, an ultrathin ZnO (circa 10 nm) layer was employed as an intermediate layer between CZTSSe and Mo back contact to avoid the direct contact
between Mo and CZTSSe and reduce the decomposition of CZTSSe during annealing process. XRF and EDX were used to characterize the chemical composition of CZTSSe before and after selenization respectively. SEM and Raman results showed the improved absorber morphology and the reduced direct interfacial reaction between CZTSSe and Mo. The improvement of the CZTSSe/Mo interface due to the intermediate layer was also reflected in the quality of the derived photovoltaic devices, leading to an improved efficiency of ESAVDdeposited kesterite solar cells from 3.25% to 4.03%
Energy Flow in Acoustic Black Holes
We present the results of an analysis of superradiant energy flow due to
scalar fields incident on an acoustic black hole. In addition to providing
independent confirmation of the recent results in [5], we determine in detail
the profile of energy flow everywhere outside the horizon. We confirm
explicitly that in a suitable frame the energy flow is inward at the horizon
and outward at infinity, as expected on physical grounds.Comment: 8 pages, 9 figures, Comments added to discussion of energy flow and
introductory section abbreviate
Discussion on Quaternary sea-level change on the continental shelf of Hong Kong
Yim et al comment on Fyfe et al's sequence stratigraphical interpretation of the Quaternary inner shelf sediments of Hong Kong. Fyfe et al respond to the comments.published_or_final_versio
A standing wave-type noncontact linear ultrasonic motor
2000-2001 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
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