Angle-dependent high-order harmonic generation in a topological phase transition of monolayer black phosphorous

Identifying all-optical high-order harmonic observables as reliable signatures to probe the topology of matter has triggered intense interest. Recently, extensive ab initio simulations challenged the previously explored approaches and proposed a new potential feature, i.e., angular dependence of harmonic yield, as a possible fingerprint of material topology [O. Neufeld et al., Phys. Rev. X 13, 031011 (2023)]. However, nontopological contributions from the band structure, spin-orbit coupling (SOC), and Berry curvature have not been ruled out. Here, we clarify this point by studying the elaborately chosen sample system of monolayer black phosphorus, which exhibits similar band structures and are free from SOC as well as Berry curvature effects for both the trivial and topological phases induced by strain. We find the previously proposed angle-dependent harmonic difference to vanish, suggesting it to be an unreliable observable to probe material topology.