Higher-order topological phase diagram revealed by anomalous Nernst effect in a Janus ScClI monolayer

Higher-order topological properties of two-dimensional (2D) magnetic materials have recently been proposed. In 2D ferromagnetic Janus materials, we find that ScClI is a second-order topological insulator. Using the tight-binding approximation, we develop a multiorbital model that adequately describes the high-order topological states of ScClI. Further, we give the complete high-order topological phase diagram of ScClI, based on the external field modulation of the magnetovalley coupling and energy levels. The 2D ScClI has a pronounced valley polarization. This type of magnetovalleytronics results in different insulating phases to exhibit completely different anomalous Nernst conductance. Through valleytronics, we establish a link between the topological insulator and the valley Nernst effect, thus constructing an anomalous valley Nernst conductance map that corresponds to the topological phase diagram. We utilize the characteristics of valley electronics to link higher-order topological materials with the anomalous Nernst effect, which has potential implications for high-order topological insulators and valley electronics.