Quantum transport evidence of Weyl fermions in an epitaxial ferromagnetic oxide

Abstract

Magnetic Weyl semimetals have novel transport phenomena related to pairs of Weyl nodes in the band structure. Although the existence of Weyl fermions is expected in various oxides, the evidence of Weyl fermions in oxide materials remains elusive. Here we show direct quantum transport evidence of Weyl fermions in an epitaxial 4d ferromagnetic oxide SrRuO3. We employ machine-learning-assisted molecular beam epitaxy to synthesize SrRuO3 films whose quality is sufficiently high to probe their intrinsic transport properties. Experimental observation of the five transport signatures of Weyl fermions—the linear positive magnetoresistance, chiral-anomaly-induced negative magnetoresistance, π phase shift in a quantum oscillation, light cyclotron mass, and high quantum mobility of about 10,000 cm2V−1s−1—combined with first-principles electronic structure calculations establishes SrRuO3 as a magnetic Weyl semimetal. We also clarify the disorder dependence of the transport of the Weyl fermions, which gives a clear guideline for accessing the topologically nontrivial transport phenomena.

Large Linear Magnetoresistance of High‐Mobility 2D Electron System at Nonisostructural γ‐Al2O3/SrTiO3 Heterointerfaces

“…Recently, linear MR was observed in the topological materials, [ 45 ] such as the Weyl semimetal of SrRuO 3 thin film, which was ascribed to the linear energy dispersion. [ 46 ] Moreover, the guiding center motion‐induced linear magnetoresistance is reported in the half‐metallic perovskite Sr 2 CrMoO 6 thin films, [ 47 ] which is similar to the topological semimetals of TlBiSSe [ 48 ] and Cd 3 As 2 . [ 49 ] Without the topological band structures, unsaturated linear MR can generally be attributed to either the quantum limit model, [ 50 ] or the inhomogeneities in the conductivity mechanism.…”

Manipulating Berry curvature of SrRuO3thin films via epitaxial strain

“…Transition metal oxide SrRuO 3 provides an ideal platform to investigate Berry curvature, because it is a 4d metallic ferromagnet with a sizable SOC (17)(18)(19)(20), in which the AHE mainly arises from the Berry curvature of its electronic band structure (11,21,22). Due to the strong coupling between lattice distortions and electronic structure in transition metal oxides, previous studies have already revealed that epitaxial strain has profound effects on magnetic properties of SrRuO 3 films (23)(24)(25)(26)(27)(28)(29)(30)(31)(32).…”

Correlated Magnetic Weyl Semimetal State in Strained Pr2Ir2O7

“…It should be mentioned that we did not observe the quantum oscillations in our PIO film. That is because the mobility in the PIO system is very low (single crystal: [ 36 ] ≈10 cm 2 V −1 s −1 ; our film: ≈ 0.74 cm 2 V −1 s −1 ), which is far from those observed in TaAs [ 19 ] or SrRuO 3 [ 45 ] systems and the requirement for the quantum oscillation at few Tesla (>10 3 cm 2 V −1 s −1 ). [ 46,47 ] Moreover, the PIO is known as a heavy fermion system with strong hybridization between the Pr 4f and Ir 5d electrons.…”