Distinctive features of metal/superconductor-insulator transitions in doped La-based cuprates with large–radius impurities and their influence on enhancement of high-Tc superconductivity

Abstract

We study the possibility of the localization of hole carriers and the distinctive features of the metal/ superconductor–insulator transitions in doped $La$-based cuprates with large-radius dopants (impurities) within the single–carrier cuprate superconductor model and obtain important insights in the role of large-radius impurities, strong electron–phonon interaction and polaronic (including also charge-density-wave (CDW) and pseudogap) effects in these electronic processes. We show that when the value of the high-frequency dielectric constant ${\varepsilon }_{\infty }$ of the cuprates changes from 5 to 2.5 and the ratio $\eta ={\varepsilon }_{\infty }/{\varepsilon }_0$ (where ${\varepsilon }_0$ is the static dielectric constant of the cuprates) decreases from 0.14 down to 0.02 the new metal/superconductor–insulator transitions in doped cuprates $L{a}_{2-x}S{r}_{x}Cu{O}_4$ (LSCO) and $L{a}_{2-x}B{a}_{x}Cu{O}_4$ (LBCO) are caused by the strong hole–lattice interactions and polaronic effects and occur in a wide doping range from the lightly doped to overdoped regime. We find that such metal/superconductor–insulator transitions depending on the values of ${\varepsilon }_{\infty }$ and $\eta ={\varepsilon }_{\infty }/{\varepsilon }_0$ (e.g., for ${\varepsilon }_{\infty }\ge 2.5$ and $\eta \ge 0.02$) and the types of the ordering of polaronic carriers occur in these materials even in the overdoped regime (when the binding energy $E_p$ of large polarons is increased significantly from 0.05 eV (at ${\varepsilon }_{\infty }=5$) up to 0.2 eV (at ${\varepsilon }_{\infty }=2.5$)), as observed experimentally in ARPES studies. Our theoretical results for metal/superconductor–insulator transitions in doped $La$-based cuprates are in good agreement with the experimental findings. We examine the possible effects of the superconductor–insulator transitions and the different disorders (e.g., polaron formation, CDWs and irradiation–induced disorders (anion vacancies)) on high-$T_c$ superconductivity in underdoped and optimally doped cuprates.