Fermiology and transport properties of the proposed topological crystalline insulator SrAg4Sb2

Abstract

Compared to time-reversal symmetry-protected Z2 topological insulators and Dirac/Weyl semimetals, there are significantly fewer candidates for topological crystalline insulators. SrAg4Sb2 is predicted to exhibit topological crystalline insulator behavior when considering spin-orbit coupling. In this study, we systematically investigate single crystals of SrAg4Sb2 using electrical transport and magnetic torque measurements, along with first-principles calculations. Our transport data reveals its compensated semimetal nature with a magnetoresistance up to around 700% at 2 K and 9 T. Analysis of de Haas-van Alphen oscillations uncovers a Fermi surface consisting of three distinct Fermi pockets with light effective masses. Comparison between the three-dimensional fermiology obtained from our oscillation data and the first-principles calculations demonstrates excellent agreement. This confirms the accuracy of the calculations, which indicate a band inversion centered at the {\Gamma} point and identify the existence of nontrivial tube and needle hole Fermi pockets at {\Gamma}, alongside one trivial diamond electron pocket at the T point in the Brillouin zone. Furthermore, symmetry and topology analysis results in two potential sets of topological invariants, suggesting the emergence of two-dimensional gapless Dirac surface states either on the ab planes or on both the ab planes and mirror planes, protected by crystal symmetries. Therefore, SrAg4Sb2 emerges as a promising candidate topological crystalline insulator.