PhD: Carmen Gómez Carbonell

Director:

ICREA Prof. Sergio O. Valenzuela, Group Leader of the Physics and Engineering of Nanodevices group at Institut Català de Nanociència i Nanotecnologia (ICN2)

Short Abstract: Intrinsic magnetic topological insulators combine band topology with magnetic order, offering access to phenomena such as the quantum anomalous Hall effect (QAHE). This thesis investigates the molecular beam epitaxy (MBE) growth and characterisation of MnBi₂Te₄ and MnSb₂Te₄ thin films, with emphasis on a digital alloy (DA) growth strategy. The DA approach enabled the synthesis of both compounds, as well as members of the (MnBi₂Te₄)ₘ(Bi₂Te₃)ₙ homologous family, including MnBi₄Te₇ and MnBi₆Te₁₀. Compared with co-evaporation, DA growth improved Mn incorporation and stoichiometry control, leading to higher-quality films. Structural, transport and electronic characterisation confirmed the magnetic and topological nature of the films. Analysis combining HAADF-STEM imaging and multislice simulations revealed an antisite defect mechanism in MnBi₂Te₄ and MnSb₂Te₄, involving Bi(Sb) occupation of Mn sites and excess Mn incorporation at Bi(Sb) sites. These results provide insights into growth and defect formation mechanisms and establish a basis for optimisation of magnetic topological materials.

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