Autoemission spectroscopy of high-temperature superconductors of YBa2Cu3O7 type in the normal state.
A theoretical approach to the description of the autoemission characteristics of copper-oxide high-temperature superconductors of YBa2Cu3O7 type in the normal state is proposed and developed. It is generally accepted that a detailed elucidation of the physical picture of the normal state can be the key to the creation of the theory of HTSC. In addition, the accumulated to date experimental material for the study of these materials by methods of autoemission spectroscopy does not fit into the framework of the traditional theory of autoemission of metals. It is important to emphasize that the study of the electronic properties of these materials by various experimental methods shows that the electronic structure of copper oxide HTSC is significantly different from the structure of simple metals.
The basic provisions of the developed approach are:
Taking into account the topological features of the essentially anisotropic band structure of copper-oxide HTSC compounds in the strong coupling approximation;
Measurement of the bending of the energy bands under conditions of field electron emission experiment, due to the low concentration of mobile carriers.
The proposed approach made it possible to investigate the penetration of an external electric field into the HTSC emitter of the YBa2Cu3O7 type taking into account the electronic structure of these materials, modeled in the strong coupling approximation. It is shown that a relatively small density of States at the Fermi level and its decreasing nonlinear dependence on energy causes a significant bend in the energy zone of charge carriers, the value of which can be commensurate with the full width of the zone of mobile carriers.
As part of the developed approach, the analysis of the formation of autoemission spectra of HTSC emitter type YBa2Cu3O7 in the normal state in the direction of the main crystallographic axes, taking into account the bending zone and topological features of the essentially anisotropic zone structure of these compounds. The results of the studies are summarized in Fig. 1. The obtained approximate analytical expressions for the emission spectra in the direction [100], [110] and [001]. Explained basic abnormal field emission characteristics of YBa2Cu3O7 with faces (100) observed experimentally. It is shown that complex data on photoemission spectroscopy of HTSC emitters of YBa2Cu3O7 type allow to study the main parameters of the band structure of these compounds.
Fig. 1. Calculated photoemission spectra of YBa2Cu3O7 at emission in the direction of the main crystallographic axes taking into account hardware broadening of the energy analyzer (resolution 55 meV)
Preprints: I.V. Uimanov. Band structure effects in the field electron emission from HTSC monocrystals I.V. Uimanov. The electric field effect in HTSC materials in the Field Electron Emission.
