${H}$-linear magnetoresistance in the ${T^2}$ resistivity regime of overdoped infinite-layer nickelate La$_{1-x}$Sr$_{x}$NiO$_2$

Abstract

We report a systematic magnetotransport study on high-crystallinity La$_{1-x}$Sr$_{x}$NiO$_2$ (LSNO) thin films with $x=0.20-0.24$. By conducting pulsed-field transport experiment up to 62 T, we reveal two salient features of the normal-state transport in overdoped LSNO thin films: (1) the magnetoresistance does not follow the Kohler's rule but exhibits a $H$-linear behavior in the high $H/T$ limit and (2) the normal-state $ρ(T)$ below 30 K consistently follows a $T^2$ behavior across the overdoped regime. Our results demonstrate a coexistence of $H$-linear magnetoresistance and $T^2$ resistivity in a model unconventional superconductor and provide new information on the transport characteristics of the normal ground state that host superconductivity in infinite-layer nickelates.

Figures (4)

• Figure 1: Phase diagram of La$_{1-x}$Sr$_x$NiO$_2$ (LSNO) and zero-field resistivity of samples studied in this work. (a) Characteristic temperatures of LSNO thin films as a function of Sr doping $x$. $T_{\rm c}$: superconducting critical temperature; $T_{\rm H}$: Hall-coefficient sign-change temperature; $T_{\rm S}$: Seebeck-coefficient sign-change temperature. Color shadings mark the doping levels studied in this work. $T_{\rm c}, T_{\rm H}$ and $T_{\rm S}$ reproduced from osada2025. (b) In-plane resistivity versus temperature $\rho(T)$ measured at zero applied magnetic field for $x$ = 0.20, 0.22, and 0.24. $T_{\rm c}$ values are 15.6, 12.6, 6.4 K, respectively, for the $x=0.20$, 0.22 and 0.24 films (marked by the vertical arrows in the inset), corresponding to the onset temperature of a deviation from the linearly extrapolated normal-state behavior (gray dash lines).
• Figure 2: (a) Isothermal magneto-resistivity of overdoped LSNO thin film ($x=0.24$) measured in pulsed magnetic fields up to 62 T at the following temperatures: [35, 30, 25, 20, 17.5, 15, 12.5, 10, 8, 6, 4.2, 2.6] K. Below 7 K, a transition from superconducting to normal state can be clearly seen. (b) Fractional MR ($\Delta\rho(H)/\rho(0)$) versus magnetic fields divided by zero-field resistivity ($\mu_0H/\rho(0)$), known as the Kohler plot. (c) Magnetoresistance divided by temperature ($[\rho(H, T)-\rho(0,T)]/T$) versus magnetic fields divided by temperature ($\mu_0H/T$). Gray line is a fit made to the normal-state data using an empirical function: $f(H/T) =\sqrt{1+c(\mu_0H/T)^2}-1$, where $c$ is a numeric constant and $f=0$ at $H=0$ is ensured.
• Figure 3: (a, d) Isothermal magneto-resistivity of overdoped LSNO films: (a) $x=0.20$ measured at the following temperatures: $T=$ [35, 30, 25, 20, 15, 10, 8, 6, 4.2, 2.6] K and (d) $x=0.22$ at [35, 30, 25, 20, 15, 12.5, 10, 7, 4.2, 2.6] K. (b, e) Kohler plot for (b) $x=0.20$ and (e) $x=0.22$ films. (c, f) $[\rho(H, T)-\rho(0,T)]/T$ versus $\mu_0H/T$ for (c) $x=0.20$ and (f) $x=0.22$ films. Grey lines are fits made using the empirical function: $\sqrt{1+c(\mu_0H/T)^2}-1$.
• Figure 4: (a) Magnetoresistivity $\rho(H)$ at selected temperatures for $x=0.20$ film. Dashed lines are linear fits made to the normal-state $\rho(H)$ to find initial estimates of the normal-state resistivity at zero field. Open circles on the $H=0$ axis are the corresponding values resulting the $H/T$ scaling collapse in Fig. \ref{['Fig_LSNO20_22']}(c), used as the zero-field resistivity shown in panel (b) here. (b-d) Normal-state resistivity versus temperature for LSNO films with doping as specified. Solid lines are measured zero-field resistivity; filled and open points are normal-state resistivity measured at 60 T and extrapolated at 0 T, respectively. Dash lines are fits made to extrapolated $\rho(T, H=0)$ below 25 K using: $\rho(T) = \rho_0 + A_nT^n$. The gray shadings in (c, d) mark the temperature regime in which a slight upturn in $\rho(T)$ is found and excluded from the power-law fits.