Extremely large magnetoresistance in high-mobility ${\mathrm{SrNbO}}_3/{\mathrm{SrTiO}}_3$ heterostructures

An extremely large linear magnetoresistance (LMR) is a ubiquitous phenomenon emerging from topological Dirac and Weyl semimetals. However, the connection between an LMR and a nontrivial topology is under extensive debate. In this paper, by precisely controlling the thickness of ${\mathrm{SrNbO}}_3$ thin films grown on ${\mathrm{SrTiO}}_3$ substrates, we observe an LMR over a large carrier density range with a magnetoresistance as high as $150000\%$ at a carrier density $n\sim {10}^{21}{\mathrm{cm}}^{-3}$, far away from the quantum-limit regime. The temperature-, magnetic-field-, and carrier-density-dependent LMR in ${\mathrm{SrNbO}}_3/{\mathrm{SrTiO}}_3$ heterostructures provides compelling evidence of a mobility-driven LMR in coherent electronic systems. Our results uncover the general principle of an LMR and shed light on proper categorization of transport properties in topological and correlated materials.

Figure 1

Schematics of mechanisms to induce a large magnetoresistance. (a) Extreme quantum limit in topological semimetals. $S_F$ is the size of the Fermi surface. (b) Perfect electron/hole compensation. In scenarios (a) and (b), the LMR is expected to disappear when the chemical potential (dashed lines) is tuned away from the ”ideal condition” (solid line). (c) Strong-disorder limit where $e{V}_0\gg {\mu }_0$. $V_0$ is the average potential height of disorder, and ${\mu }_0$ is the chemical potential. Yellow islands represent local disorder and black arrows denote electron trajectories due to random scattering. (d) Guiding center model in the weak-disorder limit $e{V}_0\ll {\mu }_0$. Red circles represent charge carriers and black circles with arrows indicate cyclotron orbits. Yellow regions and the bright yellow line denote disorder potentials and the electron's squeezed trajectory. (e) Field dependence of the MR (solid blue curve) and Hall resistivity (solid orange curve) in sample 1 (S1; $4.8\mathrm{nm}$) at $2\mathrm{K},$ displaying an LMR of up to $150000\%$ at $14\mathrm{T}$. The nonlinear Hall curve fitting (dashed yellow curve) indicates electron/hole two-carrier behavior.

Figure 2

[(a)–(f)] MR (blue), $\mathrm{dMR}/\mathrm{d}B$ (orange), and Hall resistivity (solid purple) and two-carrier fitting (dashed orange) curves for three representative samples, S2 ($3.2\mathrm{nm}$), S3 ($4.3\mathrm{nm}$), and S4 ($16.0\mathrm{nm}$), with different carrier concentrations. (g) Field dependence of the MR in S1 at selective temperatures displaying a transition from an LMR to quadratic dependence at higher temperatures. Inset: First derivative of the MR showing saturation at $2\mathrm{K}$ (LMR) and linear dependence at $15\mathrm{K}$ (quadratic MR). The linear-to-saturation crossover field is denoted $B^{*}$. (h) Consistent temperature dependence of $1/B^{*}$ and mobility indicates an underlying relation between them.

Figure 3

Transport properties of S1. (a) Temperature dependence of longitudinal (solid line) and Hall resistivity (dashed line) at selected fields displaying anomalous behavior below $10\mathrm{K}$. Inset: Temperature dependence of the longitudinal resistivity at low fields showing an upturn above $0.5\mathrm{T}$. (b) Field dependence of $tan{\theta }_H$ at selected temperatures. Saturation of $tan{\theta }_H$ is demonstrated by the flat curves above $5\mathrm{T}$. (c) Temperature dependence of the saturated $tan{\theta }_H$ at $9\mathrm{T}$ taken from (b) and the corresponding $G$ evaluated from Eq. (1). $tan{\theta }_H$ crosses unity at $9\mathrm{K}$ and the peak indicates that $G$ reaches a maximum when $tan{\theta }_H=1$. (d) Temperature dependence of the longitudinal resistivity at $9\mathrm{T}, {\rho }_{xx}\left(9T\right)$, and $9·{\rho }_0·G\left(\theta \right)·\mu /{10}^4$ (calculated from extracted values), exhibiting qualitative agreement between the estimation from Eq. (2) and the experimental result.

Figure 4

MR as a function of (a) mobility and (b) carrier density from various materials exhibiting a large LMR with typical conditions of $2\mathrm{K}$ and $9\mathrm{T}$. Data are extracted from [14, 15, 16, 17, 18, 19, 20, 21, 22, 34, 42, 43, 44, 45]. Colors are the coded carrier density in (a) and mobility in (b), from low (blue) to high (red). *${\mathrm{SrNbO}}_3$ here is the ${\mathrm{SrNbO}}_3/{\mathrm{SrTiO}}_3$ heterostructure. Note that the parameters are extracted from the dominant carrier type for multicarrier materials.