Bipolarity of large transverse thermoelectric effect in van der Waals ferromagnet semimetal lanthanum monochloride

Abstract

This study investigates the electronic properties and transverse thermoelectric effect in the ferromagnetic semimetal LaCl. While the bulk and bilayer structures of LaCl exhibit semimetal properties, the single-layer LaCl demonstrates Chern insulator characteristics, marked by a Chern number of −1. The anomalous Hall conductivity (AHC) of the monolayer, bilayer, trilayer, and bulk LaCl is analyzed using Berry connection across the discretized Brillouin zone. The large AHC observed in the bulk structure of LaCl is attributed to the contribution of each layer, with Berry curvature increasing as more layers are added. This significant AHC at the Fermi level leads to a large anomalous Nernst conductivity, reaching 8.362 (−8.893) (A/mK) at 100 K for hole (electron) doping. The anomalous Nernst coefficient (N) was also investigated. The magnitude of N is notably large, reaching magnitudes of 49.25 μV/K for hole doping and −52.66 μV/K for electron doping. These findings indicate that both positive and negative of N can be achieved through carrier doping in LaCl, highlighting its potential application in thermopile devices.