Determining Hole Locations in High-Temperature Superconductors via Spectral Analysis of Gap Tensor Parameters

Abstract

The nuclear quadrupole resonance (NQR) method using 63,65Cu isotopes allows for the experimental determination of the total electric field intensity (EFI) on 63,65Cu nuclei in the lattices of high-temperature superconductors (HTSC). Consequently, it is typically not possible to compare the experimental parameters of the electric field gradient (EFG) tensor with those calculated using the point charge model. The emission Mössbauer spectroscopy method with the 67Cu (67Zn) isotope enables us to experimentally determine only the contribution to the total EFG on 67Zn nuclei from the HTSC crystal lattice ions. However, even in this case, there is no quantitative agreement between the calculated and experimental values of the main component of the EFG tensor. This discrepancy is attributed to the lack of reliable data on Sternheimer coefficients and criteria for selecting the lattice charge contrast. Nevertheless, these issues can be resolved if the EFG tensor parameters are determined for two structurally equivalent positions.