Berry phase manipulation in ultrathin SrRuO3 films

Berry phase is a powerful concept that unravels the nontrivial role of topology in phenomena observed in chiral magnetic materials and structures. A celebrated example is the anomalous Hall effect (AHE) driven by the nonvanishing Berry phase in momentum space. As the AHE is dependent on details of the band structure near the Fermi edge, the Berry phase and AHE can be altered in thin films whose chemical potential is tunable by dimensionality and disorder. Here, we demonstrate how Berry phase in ultrathin SrRuO3 films provides a comprehensive explanation for the nontrivial Hall response which is conventionally attributed to the topological Hall effect (THE). Particularly, the Berry phase contribution to this effect can be altered, enhanced, and even change signs in response to the number of layers, temperature, and importantly, disorder. By comparing the effects of disorder theoretically on a skyrmion model and a spin-orbit coupled model, we show that disorder suppresses the THE while it can enhance the AHE. The experiments on more disordered samples confirm this interpretation, and proposed multichannel analysis judiciously explains the observed THE-like feature.