729 research outputs found
Theory of time-resolved spectral function in high-temperature superconductors with bosonic modes
We develop a three-temperature model to simulate the time dependence of
electron and phonon temperatures in high-temperature superconductors displaying
strong anistropic electron-phonon coupling. This model not only takes the
tight-binding band structure into account, but also is valid in superconducting
state. Based on this model, we calculate the time-resolved spectral function
via the double-time Green's functions. We find that the dip-hump structure
evolves with the time delay. More interestingly, new phononic structures are
obtained when the phonons are excited by a laser field. This signature may
serve as a direct evidence for electron-vibration mode coupling.Comment: 5 pages, 3 figure
Performance of a non-empirical meta-GGA density functional for excitation energies
It is known that the adiabatic approximation in time-dependent density
functional theory usually provides a good description of low-lying excitations
of molecules. In the present work, the capability of the adiabatic nonempirical
meta-generalized gradient approximation (meta-GGA) of Tao, Perdew, Staroverov,
and Scuseria (TPSS) to describe atomic and molecular excitations is tested. The
adiabatic (one-parameter) hybrid version of the TPSS meta-GGA and the adiabatic
GGA of Perdew, Burke, and Ernzerhof (PBE) are also included in the test. The
results are compared to experiments and to two well-established hybrid
functionals PBE0 and B3LYP. Calculations show that both adiabatic TPSS and
TPSSh functionals produce excitation energies in fairly good agreement with
experiments, and improve upon the adiabatic local spin density approximation
and, in particular, the adiabatic PBE GGA. This further confirms that TPSS is
indeed a reliable nonhybrid universal functional which can serve as the
starting point from which higher-level approximations can be constructed. The
systematic underestimate of the low-lying vertical excitation energies of
molecules with time-dependent density functionals within the adiabatic
approximation suggests that further improvement can be made with nonadiabatic
corrections.Comment: 7 page
Theory of ultrafast quasiparticle dynamics in high-temperature superconductors: Pump fluence dependence
We present a theory for the time-resolved optical spectroscopy of
high-temperature superconductors at high excitation densities with strongly
anisotropic electron-phonon coupling. A signature of the strong coupling
between the out-of-plane, out-of-phase O buckling mode () and
electronic states near the antinode is observed as a higher-energy peak in the
time-resolved optical conductivity and Raman spectra, while no evidence of the
strong coupling between the in-plane Cu-O breathing mode and nodal electronic
states is observed. More interestingly, it is observed that under appropriate
conditions of pump fluence, this signature exhibits a re-entrant behavior with
time delay, following the fate of the superconducting condensate.Comment: 5 pages, 3 embedded eps figures, to appear in PR
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