Superconducting- and Insulating-Ground States in La₂CuO₄ Structural Isomers

Reassessment of the electronic state, magnetism, and superconductivity in high-Tc cuprates with the Nd2CuO4 structure

“…This result indicates that the T c -vs-x is not universal in T'-RE 2-x Ce x CuO 4 [13]. [footnote: We could not achieve superconductivity at that time, but achieved in 2014 [15]. ]…”

“…Therefore it was initially supposed that the stabilization of this structure would require two RE ions with significantly different ionic sizes: one large La 3+ and the other smaller RE 3+ . Later, however, this turned out not to be a necessary requirement, for pure T * -La 2 CuO 4 has recently synthesized by MBE using lattice matched substrates [15].…”

Electron Doping of the Parent CuprateLa2CuO4without Cation Substitution

“…Previous reports by Yamamoto et al [15] and Krockenberger et al [16] on T cuprates without cation doping suggest that T c may be even higher in thin-film samples, which could arise from a reduction of disorder due to an ordering of defect dopants. This is analogous to the case of ortho-ordered YBa 2 Cu 3 O 7−δ , in which oxygen ordering, combined with the lack of cation dopants, has been critical in realizing quantum oscillations in the hole-doped cuprates and greatly enhancing understanding of their Fermiology [8-11, 56, 57].…”

“…Finally, we discuss possible origins for the doped electrons in as-grown T -La 2 CuO 4 . In earlier studies of nominally undoped thin films of T -R 2 CuO 4 [14,16,39], it was speculated that the observed metallic and superconducting behaviors may originate from the collapse of the Mott gap, possibly caused by weakened correlations in the T phase. It has been suggested by DMFT calculations [17,18] that due to the lack of apical oxygens, the T -phase parent cuprates may exhibit weaker correlations and might be better described as Slater rather than Mott or charge-transfer insulators.…”

“…The necessity of doping in achieving superconductivity and the validity of the doped Mott insulator paradigm in the n-type cuprates has recently been called into question by work on epitaxial thin films of nominally undoped RE 2 CuO 4 (RE = La, Pr, Nd, Sm, Eu, Gd) synthesized in the so-called T phase [14][15][16]. The authors have observed metallic and even superconducting behavior in the absence of cation doping, a scenario which may be consistent with dynamical mean field theory (DMFT) studies showing that the parent T compounds may be better described as weakly correlated Slater insulators rather than strongly correlated charge transfer insulators [17,18].…”