Magnetotransport studies of the Sb square-net compound LaAgSb2 under high pressure and rotating magnetic fields

Square-net-layered materials have attracted attention as an extended research platform of Dirac fermions and of exotic magnetotransport phenomena. In this study, we investigated the magnetotransport properties of $\mathrm{La}\mathrm{Ag}{\mathrm{Sb}}_2$, which has Sb-square-net layers and shows charge density wave (CDW) transitions at ambient pressure. The application of pressure suppresses the CDWs, and above a pressure of 3.2 GPa a normal metallic phase with no CDWs is realized. By utilizing a mechanical rotator combined with a high-pressure cell, we observed the angular dependence of the Shubnikov–de Haas (SdH) oscillation up to 3.5 GPa, and we confirmed the notable two-dimensional nature of the Fermi surface. In the normal metallic phase, we also observed a remarkable field-angular-dependent magnetoresistance (MR), which exhibited a “butterflylike” polar pattern. To understand these results, we theoretically calculated the Fermi surface and conductivity tensor at the normal metallic phase. We showed that the SdH frequency and Hall coefficient calculated based on the present Fermi surface model agree well with the experiment. The transport properties in the normal metallic phase are mostly dominated by the anisotropic Dirac band, which has the highest conductivity due to linear energy dispersions. We also proposed that momentum-dependent relaxation time plays an important role in the large transverse MR and negative longitudinal MR in the normal metallic phase, which is experimentally supported by the considerable violation of Kohler's scaling rule. Although quantitatively complete reproduction was not achieved, the calculation showed that the elemental features of the butterfly MR could be reasonably explained as the geometrical effect of the Fermi surface.