151,666 research outputs found
Evidence for very strong electron-phonon coupling in YBa_{2}Cu_{3}O_{6}
From the observed oxygen-isotope shift of the mid-infrared two-magnon
absorption peak of YBaCuO, we evaluate the oxygen-isotope
effect on the in-plane antiferromagnetic exchange energy . The exchange
energy in YBaCuO is found to decrease by about 0.9% upon
replacing O by O, which is slightly larger than that (0.6%) in
LaCuO. From the oxygen-isotope effects, we determine the lower
limit of the polaron binding energy, which is about 1.7 eV for
YBaCuO and 1.5 eV for LaCuO, in quantitative
agreement with angle-resolved photoemission data, optical conductivity data,
and the parameter-free theoretical estimate. The large polaron binding energies
in the insulating parent compounds suggest that electron-phonon coupling should
also be strong in doped superconducting cuprates and may play an essential role
in high-temperature superconductivity.Comment: 4 pages, 1 figur
Effect of oxygen stoichiometry on T(sub c) of Bi-based superconductors
The role of oxygen stoichiometry on T(sub c) is relatively well established on La2CuO(4+x) and the YBa2Cu3O(7-x) (123) superconductors, as compared to the Bi-based superconductors. Results are presented of investigations on the effects of oxygen stoichiometry on the transition temperature T(sub c) of Bi2Sr2CaCu2O(8+x) (2212 phase), and Pb-doped Bi2Sr2Ca2Cu3O(10+X) (2223 phase). It is shown that the effects of oxygen stoichiometry on T(sub c) of these two phases are very different. These results may be helpful in understanding the mechanism of superconductivity in the Bi-based superconductors
Dependence of transition temperature on hole concentration per CuO2 sheet in the Bi-based superconductors
The recently observed variations of the transition temperature (T sub c) with oxygen content in the Bi based (2212) and (2223) superconductors are analyzed in terms of p+, the hole concentration per CuO2 sheet. This analysis shows that in this system, T sub c increases with p+ initially, reaching maxima at p+ = 0.2 approx. 0.3, followed by monotonic decrease of T sub c with p+. The forms of these variations are similar to those observed in the La(2-x)Sr(x)CuO4 and YBa2Cu3Oy systems, suggesting that p+ may be an important variable governing superconductivity in the cuprate superconductors
BCS-BEC crossover on the two-dimensional honeycomb lattice
The attractive Hubbard model on the honeycomb lattice exhibits, at
half-filling, a quantum critical point (QCP) between a semimetal with massless
Dirac fermions and an s-wave superconductor (SC). We study the BCS-BEC
crossover in this model away from half-filling at zero temperature and show
that the appropriately defined crossover line (in the interaction-density
plane) passes through the QCP at half-filling. For a range of densities around
half-filling, the ``underlying Fermi surface'' of the SC, defined as the
momentum space locus of minimum energy quasiparticle excitations, encloses an
area which evolves nonmonotonically with interactions. We also study
fluctuations in the SC and the semimetal, and show the emergence of an undamped
Leggett mode deep in the SC. We consider possible implications for experiments
on ultracold atoms and high temperature SCs.Comment: Revised - added section on the Fermi surface evolution, corrected
error in superfluid density, added possible implications for cuprate
Lithium-ion battery thermal-electrochemical model-based state estimation using orthogonal collocation and a modified extended Kalman filter
This paper investigates the state estimation of a high-fidelity spatially
resolved thermal- electrochemical lithium-ion battery model commonly referred
to as the pseudo two-dimensional model. The partial-differential algebraic
equations (PDAEs) constituting the model are spatially discretised using
Chebyshev orthogonal collocation enabling fast and accurate simulations up to
high C-rates. This implementation of the pseudo-2D model is then used in
combination with an extended Kalman filter algorithm for differential-algebraic
equations to estimate the states of the model. The state estimation algorithm
is able to rapidly recover the model states from current, voltage and
temperature measurements. Results show that the error on the state estimate
falls below 1 % in less than 200 s despite a 30 % error on battery initial
state-of-charge and additive measurement noise with 10 mV and 0.5 K standard
deviations.Comment: Submitted to the Journal of Power Source
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