Topological phase transitions without symmetry indication in NaZnSb1-xBix

We study topological phase transitions in tetragonal NaZnSb1-xBix, driven by the chemical composition x. Notably, we examine mirror Chern numbers that change without symmetry indicators. First-principles calculations are performed to show that NaZnSb1-xBix experiences consecutive topological phase transitions, diagnosed by the strong Z2 topological index nu 0 and two mirror Chern numbers mu(x) and mu(xy). As the chemical composition x increases, the topological invariants (mu(x)mu(xy)nu(0)) change from (000), (020), (220), to (111) at x = 0.15, 0.20, and 0.53, respectively. A simplified low-energy effective model is developed to examine the mirror Chern number changes, highlighting the central role of spectator Dirac fermions in avoiding symmetry indicators. Our findings suggest that NaZnSb1-xBix can be an exciting testbed for exploring the interplay between the topology and symmetry.

Automated summary

This study investigates the topological phase transitions in tetragonal NaZnSb1-xBix driven by the chemical composition x. The research finds that mirror Chern numbers can change without symmetry indicators. First-principles calculations and a simplified low-energy effective model are used to diagnose the consecutive topological phase transitions and highlight the role of spectator Dirac fermions in avoiding symmetry indicators.