Intrinsic anomalous Hall conductivity and field-enhanced diamagnetism in untwinned Weyl metal SrRuO₃ thin films

The anomalous Hall effect (AHE) manifests in solids with broken time-reversal symmetry. In a ferromagnetic metal, intrinsic and extrinsic AHE can contribute to the Hall signal. In this report, we studied the low-temperature magnetotransport properties of ferromagnetic untwinned SrRuO₃ (SRO) thin films grown on SrTiO₃ (001) substrates with low residual resistivity for various thicknesses (ts) ranging from 3.9 nm to 37.1 nm. The magnitude of the Hall conductivity |σ_xy| at zero magnetic fields in the low-temperature regime was found to be nearly t-independent and approaching a constant value of about 2×10⁴ Ω^-1m^-1, which is close to the estimated intrinsic anomalous Hall conductivity due to Berry curvatures of the bulk band of about e²/hc_o ≈ 5×10⁴ Ω^-1m^-1 (c_o being the lattice constant). The negligible variation of |σ_xy| with σ_xx in the low-temperature regime at zero magnetic field reveals that the |σ_xy| is nearly independent of the electron scattering lifetime. This suggests a small contribution of extrinsic skew scattering effect to the AHE, and the intrinsic AHE dominates the zero-field Hall signals in SRO at low temperatures. Interestingly, a rigorous magnetization measurement on a SRO film using a SQUID magnetometer reveals a field-enhanced diamagnetic response that increases as the temperature drops. The intrinsic value of the |σ_xy|~ e²/hc_o and the field-enhanced diamagnetic response in the SRO film in the low-temperature regime strongly support the presence of the Weyl metal phase in SRO. A systematic study on the temperature and thickness-dependent Hall conductivity and magnetization will be presented and discussed.