Investigating the cause of crossover from charge/spin stripe insulator to correlated metallic phase in layered T' nickelates -- R${}_4$Ni${}_3$O${}_8$

Abstract

The $T^{\prime }$ infinite layered nickelates have recently garnered significant attention owing to the discovery of superconductivity in hole-doped RNiO${}_2$ (R $=$ La, Pr, or Nd), which is the $n=\infty$ member of the series R${}_{n+1}$Ni${}_n$O${}_{2n+2}$. Here, we investigate the $n=3$ member, namely R${}_4$Ni${}_3$O${}_8$ (R $=$ La, Pr, or Nd) of this family. The compound La${}_4$Ni${}_3$O${}_8$ exhibits simultaneous charge/spin-stripe ordering at T${}_N^{\ast }$ $=$ 105 K, which is also concomitant with the onset of metal-to-insulator (MIT) transition upon lowering the temperature below T${}_N^{\ast }$. We investigate the conspicuous absence of this transition in the Pr and Nd analogues of La${}_4$Ni${}_3$O${}_8$. To achieve this purpose, we synthesized solid-solutions of the form (La, Pr)${}_4$Ni${}_3$O${}_8$ and (La, Nd)${}_4$Ni${}_3$O${}_8$ and examined the behavior of T${}_N^{\ast }$ as a function of the average R-site ionic radius ($r_{\overline{R}}$). We show that after an initial quasilinear decrease with decreasing $r_{\overline{R}}$, T${}_N^{\ast }$ suddenly vanishes in the narrow range 1.134 $\mathring{A}$ $\le$ $r_{\overline{R}}$ $\le$ 1.143 $\mathring{A}$. In the same range, we observed the emergence of a new transition below T${}^{\ast }$, whose onset temperature increases as $r_{\overline{R}}$ further decreases. We, therefore, argue that the sudden vanishing of charge/spin-stripe/MIT ordering upon decreasing $r_{\overline{R}}$ is due to the appearance of a new competing phase. The point $r_{\overline{R}}$ $\approx$ $r_c$, where T${}_N^{\ast }$ vanishes and T${}^{\ast }$ appears -- a quantum critical point -- should be investigated further. In this regard, Pr${}_4$Ni${}_3$O${}_8$ and Pr-rich samples should be useful due to the weak magnetization response associated with the Pr-sublattice, as shown here.

18 pages, 16 figures