Weak antilocalization effect and triply degenerate state in Cu-doped CaAuAs

The effect of 50% Cu doping at the Au site in the topological Dirac semimetal CaAuAs is investigated through electronic band structure calculations, electrical resistivity, and magnetotransport measurements. Electronic structure calculations suggest a broken-symmetry-driven topological phase transition from the Dirac to triple-point state in CaAuAs via alloy engineering. The electrical resistivity of both the CaAuAs and CaAu0.5Cu0.5As compounds shows metallic behavior. Nonsaturating quasilinear magnetoresistance (MR) behavior is observed in CaAuAs. On the other hand, MR of the doped compound shows a pronounced cusplike feature in the low-field regime. Such behavior of MR in CaAu0.5Cu0.5As is attributed to the weak antilocalization (WAL) effect. The WAL effect is analyzed using different theoretical models, including the semiclassical similar to root B one which accounts for the three-dimensional WAL and the modified Hikami-Larkin-Nagaoka model. A strong WAL effect is also observed in the longitudinal MR, which is well described by the generalized Altshuler-Aronov model. Our study suggests that the WAL effect originates from weak disorder and the spin-orbit coupled bulk state. Interestingly, we have also observed the signature of chiral anomaly in longitudinal MR when both the current and field are applied along the c axis. The Hall resistivity measurements indicate that the charge conduction mechanism in these compounds is dominated by the holes with a concentration similar to 10(20) cm(-3) and mobility similar to 10(2) cm(2) V-1 s(-1).

Automated summary

The effect of 50% Cu doping at the Au site in CaAuAs, a topological Dirac semimetal, is investigated. The study reveals a broken-symmetry-driven topological phase transition from the Dirac to triple-point state in CaAuAs through alloy engineering. The doped compound exhibits the weak antilocalization effect and the signature of chiral anomaly in longitudinal magnetoresistance.