High-Mobility Two-Dimensional Carriers from Surface Fermi Arcs in Ferromagnetic Weyl Semimetal SrRuO₃ Films

Leveraging two-dimensional quantum transport phenomena and exploiting them in topological and spin electronics require thorough investigation into magnetic Weyl semimetals. Two-dimensional charge/spin carriers arising from pairs of Weyl nodes are realized in the presence of surface Fermi arcs in topological semimetals. To demonstrate such topological quantum transport phenomena, high-quality epitaxial films of Weyl semimetals are vital. Prior to the present study, we recently demonstrated that ultrahigh-quality thin films of SrRuO₃ exhibit quantum transport phenomena specific to bulk three-dimensional Weyl fermions [1,2], implying that they serve as a promising platform also for investigating novel two-dimensional transport in a topological state.<br/>Here we present our findings on the thickness- and angle-dependent magnetotransport properties of SrRuO₃, a magnetic Weyl semimetal. Utilizing machine-learning-assisted molecular beam epitaxy [3], we grew SrRuO₃ films with 10 nm and 63 nm thicknesses. Quantum oscillations in the 10-nm film demonstrate a high quantum mobility of 3.5×10³cm²/Vs, a light cyclotron mass of 0.25<i>m</i>₀ (<i>m</i>₀: the free electron mass in a vacuum), and two-dimensional angular dependence. The two-dimensional, angular transport dependence might be regarded within two scenarios: (1) the surface Fermi arcs, or (2) the quantum confinement of the three-dimensional Weyl fermions. The former is plausible as the identical angular dependence is also observed in the 63-nm film, which is too thick to observe the quantum confinement effect in it. In addition, the linear thickness dependence of the phase shift provides evidence of the non-trivial nature of the quantum oscillations mediated by the surface Fermi arcs. Furthermore, magnetoresistance (MR) measurements while applying magnetic field parallel to the film surface up to 52 T confirmed the saturation of negative MR in the quantum limit (chiral anomaly), assuring that the carriers arise from a pair of Weyl nodes. These results endorse SrRuO₃ as a promising material for topological oxide electronics and for physics investigation of two-dimensional quantum transport phenomena in magnetic Weyl semimetals [4].<br/><br/><b>References: </b>[1] K. Takiguchi, Y. K. Wakabayashi^* <i>et al.</i>, Nat. Commun.<b> 11</b>, 4969 (2020). [2] S. Kaneta-Takada, Y. K. Wakabayashi^* <i>et al</i>., Appl. Phys. Lett. <b>118</b>, 092408 (2021). [3] Y. K. Wakabayashi^*<i> et al</i>., APL Mater. <b>7</b>, 101114 (2019). [4] S. Kaneta-Takada, Y. K. Wakabayashi* <i>et al</i>., npj Quantum Materials <b>7</b>, 102 (2022).