Spectroscopic evidence for temperature-dependent convergence of light and heavy hole valence bands of PbQ (Q=Te, Se, S)

We have conducted temperature dependent Angle Resolved Photoemission Spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS. Our ARPES data provide direct evidence for the \emph{light} hole upper valence bands (UVBs) and hitherto undetected \emph{heavy} hole lower valence bands (LVBs) in these materials. An unusual temperature dependent relative movement between these bands leads to a monotonic decrease in the energy separation between their maxima with increasing temperature, which is referred as band convergence and has long been believed to be the driving factor behind extraordinary thermoelectric performances of these compounds at elevated temperatures.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with arXiv:1404.180

Dynamics of He Double Ionization in the Non-Perturbative Regime: The Reduction to an Effective Three-Particle Problem

Double ionization of He by 3.6 MeV u -1 Au 53+ impact is investigated in a kinematically complete experiment using an integrated multi-electron recoilion momentum spectrometer (reaction microscope). Surprisingly, the final-state correlation between the recoiling He 2+ target ion momentum and the momenta of both emitted electrons is found to be the strongest among the various two-body correlations. On this basis it is demonstrated that the four-body momentum balance can be reduced to a good approximation to an effective three-particle problem by considering the centre-of-mass motion of the two electrons instead of their individual momenta. Then, all essential dynamical features observed for single ionization earlier, like for example a strong forward-backward asymmetry in the longitudinal momentum balance resulting from the final-state interaction with the projectile, are naturally rediscovered. Moreover, important conclusions on the properties of the TS-2 double ionization mechanism are drawn

Triply Differential Single-Ionization Cross Sections in Fast Ion-Atom Collisions at Large Perturbation

We present experimental triply differential single-ionization cross sections for electrons emitted into the scattering plane in 3.6 MeV amu-1 Au53+ + He collisions, i.e. for a large perturbation. The data show that the post-collision interaction between the scattered projectile and the ionized electron strongly affects the recoil peak, but it influences the binary peak rather weakly. Surprisingly, the continuum distorted wave-eikonal initial state model, which describes differential electron spectra very well, fails to reproduce our data even qualitatively. Most notably, it does not show a recoil peak

Dynamics of He Double Ionization in the Non-Perturbative Regime: The Reduction to an Effective Three-Particle Problem

Double ionization of He by 3.6 MeV u -1 Au 53+ impact is investigated in a kinematically complete experiment using an integrated multi-electron recoilion momentum spectrometer (reaction microscope). Surprisingly, the final-state correlation between the recoiling He 2+ target ion momentum and the momenta of both emitted electrons is found to be the strongest among the various two-body correlations. On this basis it is demonstrated that the four-body momentum balance can be reduced to a good approximation to an effective three-particle problem by considering the centre-of-mass motion of the two electrons instead of their individual momenta. Then, all essential dynamical features observed for single ionization earlier, like for example a strong forward-backward asymmetry in the longitudinal momentum balance resulting from the final-state interaction with the projectile, are naturally rediscovered. Moreover, important conclusions on the properties of the TS-2 double ionization mechanism are drawn