Challenges to magnetic doping of thin films of the Dirac semimetal Cd$_3$As$_2$

TL;DR

This study investigates the challenges of magnetic doping in Cd3As2 thin films, revealing phase separation, ferromagnetism, and quantum transport phenomena, which are crucial for understanding time-reversal symmetry breaking in topological materials.

Contribution

It uncovers the surfactant role of Mn during epitaxial growth, leading to phase separation and ferromagnetism, and demonstrates robust quantum transport in disordered magnetic films.

Findings

Mn forms a Mn-rich phase at the surface of Cd3As2 films.

Mn-doped films exhibit ferromagnetism with out-of-plane anisotropy.

Quantum transport persists despite surface disorder and ferromagnetic overlayer.

Abstract

Magnetic doping of topological quantum materials provides an attractive route for studying the effects of time-reversal symmetry breaking. Thus motivated, we explore the introduction of the transition metal Mn into thin films of the Dirac semimetal Cd3As2 during growth by molecular beam epitaxy. Scanning transmission electron microscopy measurements show the formation of a Mn-rich phase at the top surface of Mn-doped Cd3As2 thin films grown using both uniform doping and delta doping. This suggests that Mn acts as a surfactant during epitaxial growth of Cd3As2, resulting in phase separation. Magnetometry measurements of such samples indicate a ferromagnetic phase with out-of-plane magnetic anisotropy. Electrical magneto-transport measurements of these films as a function of temperature, magnetic field, and chemical potential reveal a lower carrier density and higher electron mobility compared to pristine Cd3As2 films grown under similar conditions. This suggests that the surfactant effect might also serve to getter impurities. We observe robust quantum transport (Shubnikov-de Haas oscillations and an incipient integer quantum Hall effect) in very thin (7 nm) Cd3As2 films despite being in direct contact with a structurally disordered surface ferromagnetic overlayer.