Non-Fermi-Liquid Transport Phenomena in Infinite-Layer Nickelates

TL;DR

This work addresses the origin of non-Fermi-liquid, $T$-linear transport in the infinite-layer nickelate Nd$_{0.85}$Sr$_{0.15}$NiO$_2$ by employing a 3D three-orbital Hubbard model analyzed with FLEX for the Ni $d_{x^2-y^2}$ orbital and a T-matrix approach for Nd-site impurities. It demonstrates that 3D spin fluctuations can induce $ ho \\propto T$ at low temperatures, characterizing the system as quasi-2D despite a 3D Fermi surface, with a negative, $T$-linear Seebeck coefficient consistent with experiments on multi-layer nickelates. The study also shows a doping-dependent crossover toward Fermi-liquid-like behavior at higher hole doping, and argues that CDW fluctuations, while neglected here, would further enhance the resistivity slope near the CDW QCP. Overall, the results align Nd-based nickelates with CeCoIn$_5$-like quasi-2D transport driven by spin fluctuations and provide a framework to understand transport anomalies in these correlated oxides.

Abstract

Recently discovered superconducting infinite-layer nickelates $R$NiO$_2$ ($R$=Nd, La, Pr) attract increasing attention due to their similarities to cuprates. Both $R$NiO$_2$ and YBCO cuprates exhibit the non-Fermi-liquid transport behavior, characterized by resistivity proportional to temperature near the quantum critical point of the charge or spin density wave. In this study, we analyze the resistivity of infinite-layer nickelate Nd$_{0.85}$Sr$_{0.15}$NiO$_2$ based on a three-dimensional tight-binding model within the framework of the quasi-particle picture by applying linear response theory. We take account of the self-energy by the fluctuation-exchange approximation for the Ni orbital and the T-matrix approximation for an impurity effect on the Nd orbitals. We find that (i) the $T$-linear resistivity at low temperatures is derived from the spin fluctuations, and (ii) a negative and $T$-linear Seebeck coefficient is obtained. Therefore, NdNiO$_2$ behaves as a quasi-two-dimensional electron system, similar to CeCoIn$_5$.

Figures (9)

• Figure 1: (a) Bandstructure of the present Nd$_{0.85}$Sr$_{0.15}$NiO$_2$ model. Red, purple, and blue lines represent Ni $d_{x^2-y^2}$, Nd $d_{z^2}$, and Nd $d_{xy}$ orbitals, respectively. (b) 3D FSs in the present model.
• Figure 2: (a) ${ {\bm q} }$ dependences of $\chi^{s}({ {\bm q} },0)$ given by the FLEX approximation on $q_z=0$ plane, and (b) that on $q_z=\pi$ plane. (c) $T$ dependence of $\alpha_s$.
• Figure 3: (a) Obtained ${ {\bm k} }$ dependence of mass enhancement factor $z^{-1}({ {\bm k} })$ on $k_z=0$ plane, and (b) that on $k_z=\pi$ plane. Black line represents the FS.
• Figure 4: (a) $T$ dependence of $\rho$ for $I_{\rm Nd}=5,20$eV. (b) $T$ dependence of $\rho$ for $I_{\rm Nd}=20$eV, with $r_z=1,2,2.5$. Here, $r_z$ represents the magnification factor for the inter-layer hopping integrals. $r_z=1$ corresponds to the original 3D model.
• Figure 5: $T$ dependence of $\rho$ for $I_{\rm Nd}=20$eV in the 2D model.