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

Time-Dependent Density-Functional Theory beyond the Local-Density Approximation

URL:http://link.aps.org/doi/10.1103/PhysRevLett.97.036403 DOI:10.1103/PhysRevLett.97.036403Approximations for the ground-state exchange-correlation potential of density-functional theory have reached a high level of sophistication. By contrast, time- or frequency-dependent exchange-correlation potentials are still being treated in a local approximation. Here we propose a novel approximation scheme, which effectively brings the power of the generalized gradient approximation (GGA) and meta-GGA to time-dependent density-functional theory. The theory should allow a more accurate treatment of strongly inhomogeneous electronic systems (e.g. molecular junctions) while remaining essentially exact for slowly varying densities and slowly varying external potentials.This work was supported by DOE under Grant No. DE-FG02-05ER46203

Analytic expression for the diamagnetic susceptibility of a uniform electron gas

URL:http://link.aps.org/doi/10.1103/PhysRevB.74.193108 DOI:10.1103/PhysRevB.74.193108The diamagnetic (Landau) susceptibility is a key ingredient in current-density functional theory. We calculate this quantity of a uniform electron gas beyond the random-phase approximation and present an analytic expression for it which recovers the exact high-density limit.This work was supported by DOE under Grant No. DEFG02-05ER46203. We acknowledge very helpful discussions with John P. Perdew. Part of the computational work was done at Tulane University

Shattered Rim and Shelling of High-Speed Railway Wheels in The Very-High-Cycle Fatigue Regime Under Rolling Contact Loading

Due to the improvement of the wear property, rolling contact fatigue including shattered rim and shelling are the main failure causes of the high-speed railway wheels. In this paper, shattered rim and shelling occurred on the service wheels of the China Railway High-speed (CRH) trains were systematically investigated. The recorded data of the last ten years CRH operation indicated that all shattered rims and shelling were detected with serving \u3e106 km (corresponding to the fatigue life 107–109 cycles) which is very-high-cycle fatigue (VHCF). The crack initiationregion of shattered rim located at the depth of 10–25 mm from the tread, while that of shelling located at the depthsurfaces, i.e., similar VHCF features in uniaxial loading including the defect, fish-eye, and crack propagation region and unique VHCF features of the three dimensional crack surface feature, beach bands uniformly distributed in the crack propagation region, absence of fine granular area (FGA). The VHCF model considering the stress distribution, defect size and hardness were applied to discuss the failure mechanism of the shattered rim and shelling

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