Momentum-transfer q resolved electron energy loss spectroscopy

4 Momentum-transfer q) resolved electron energy loss spectroscopy 

Nucker et al. [8.16] first reported anisotropic dispersion of the free carrier plasmon in Bi2Sr2CaCu20g. Here, we will only discuss the anisotropic dispersion of the insulator case not only because of its simplicity but also for the subsequent understanding of the insulator-to-metal transition in the normal state of these compounds that occurs with doping. 

In this study, we have employed momentum-transfer (q) resolved EELS to probe the momentum-transfer dispersion of the valence band excitations in BaBiOs. We report an optically forbidden transition ( 4 eV) and the effective mass of the optical gap ( 2 eV), both of which exhibit crystalline anisotropy. 

The symmetry of the /7-wave function is shown in Fig. 8.9. Due to the effective hopping integral t of the quasiparticle, the excitons can move 

It should be pointed out that although these models can qualitatively explain the physical properties of these excitations, detailed calculation is needed for quantitative comparison. However, we believe that the symmetry information would not change significantly even in a more sophisticated model. As we will show in the next section, a more sophisticated model involving similar symmetry ideas is developed to explain the similar electron energy loss spectra for Sr2Cu02Cl2 [8.39]. 

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