Electronic structure and properties of quasi-two-dimensional layered superconducting perovskites:La2−xMxCuO4(M=Ba,Sr, …)

Results of highly precise all-electron local-density calculations are presented for the quasi-two-dimensional superconductors ${\mathrm{La}}_{2-x}{M}_x\mathrm{Cu}{\mathrm{O}}_x$ ($M=\mathrm{B}\mathrm{a},\mathrm{S}\mathrm{r}, \dots$) with $x=0\mathrm{}$ and correlated with a number of observed properties of these materials for varying $x$. The dominant role of the van Hove saddle-point singularity (SPS) on the density of states (DOS) and the DOS-derived properties (specific heat, magnetic susceptibility, $T_c$) is emphasized—as is the fact that this SPS represents the classic Lifshitz transition versus $x$ (and/or pressure) with its possible thermodynamic and galvanomagnetic anomalies. Estimates of the enhancement factor $\lambda$ from a variety of measured specific-heat values and our calculated DOS indicate that these materials may possibly be weak-coupling superconductors. Crude estimates of coherent lengths (${\xi }_{\parallel }$ and ${\xi }_{\perp }$) and upper critical fields ($H_{c2\mathrm{}\parallel }$ and $H_{c2\mathrm{}\perp }$) are presented.