Quasi-particle peak

In condensed-matter physics, and are associated with quasi-particle peaks of photoelectron spectra, whereas E[ and are associated with satellites. The Dyson orbitals are also easily calculated, and we finally arrive at the matrix representation of Xip on the basis of the products of spatial orbitals... 

In this light, the appearance of the sharp peak in Figure 3.2.2.29a signals the appearance of a quasi-particle peak as soon as the surface state peak moves to within... 

In these pro-EDC maps, the kink phenomenon [6] is visualized as the crossover from the low energy quasi-particle branch to the high-energy incoherent branch. This crossover region is the region of low intensity (indicated by white dashed line, and blue and red arrows), where the two dispersions mix and give rise to a double peak structure, commonly referred to as a peak-dip-hump structure, of EDC s [6,12-14], In this terminology,... 

Table 4 lists the MBPT(2) band gaps of polyacetylene calculated with basis set 6-31G and DZP at three different geometries by us [36]. The cutoffs N and K are both 21. The geometries used in the calculations are listed in Table 5. The first two were given by Suhai [53,55] and the last one was an experimentally estimated geometry [97], The band gaps obtained are 4.033, 3.744, and 3.222 eV, respectively. There is no direct measurement of the band gap, defined as a quasi-particle energy difference of the lowest unoccupied and highest occupied orbitals. Instead, the absorption spectrum of polyacetylene crystalline films rises sharply at 1.4 eV and has a peak around 2.0 eV [97]. To explain this measured spectrum, one needs to calculate the density of the system s excited states and the absorption coefficients of the states.

The electrical resistivity is determined by the inverse lifetime of the quasi-particles averaged over the Fermi distribution. The calculated p(T) curve, shown in fig. 43, starts from zero at T = 0, rises exponentially until a peak is reached around T = ri/k, and drops smoothly to zero at higher temperatures. Again, variations of /i(0) produces only slightly different results. The low-temperature part is in disagreement with experiments, because the calculation fails to include the mutual scattering effect of quasi-particles. The resistivity peak reflects the breakdown of the band structure, which takes place when the temperature reaches rj/kg. The model does not shed light on the variety of resistivity behaviors shown in fig. 6. 

The explanation for this two-peak structure near cp lies not in a new surface state but in a complex line shape because of many-body effects in the electron-phonon system. In order to see behind these effects, we need to take a closer look at the spectral function A(k, E) for a coupled electron-phonon system. In general, A(k, E) is related to the self-energy E(k, E) of a quasi particle by the equation... 

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