Pressure tuning of the Berry phase in BaMnSb2

The Sb square net in BaMnSb2 is reported to host nearly massless Dirac fermions. At ambient pressure, BaMnSb2 shows strong Shubnikov-de Haas (SdH) oscillations with a π Berry phase. In this work, we study BaMnSb2 under different pressures. It is found that the frequency of the SdH oscillation remains almost unchanged, hence the cross-section area of the Fermi surface does not change much with pressure. Notably, there is a sudden change in the phase factor of the oscillations around a critical pressure of P= 2.5 GPa, which suggests a possible topological phase transition in BaMnSb2.