Evolution of Mn(1−x)Ge(x)Bi(2)Te(4) Electronic Structure under Variation of Ge Content

One of the approaches to manipulate MnBi [Formula: see text] Te [Formula: see text] properties is the magnetic dilution, which inevitably affects the interplay of magnetism and band topology in the system. In this work, we carried out angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations for analysing changes in the electronic structure of Mn [Formula: see text] Ge [Formula: see text] Bi [Formula: see text] Te [Formula: see text] that occur under parameter x variation. We consider two ways of Mn/Ge substitution: (i) bulk doping of the whole system; (ii) surface doping of the first septuple layer. For the case (i), the experimental results reveal a decrease in the value of the bulk band gap, which should be reversed by an increase when the Ge concentration reaches a certain value. Ab-initio calculations show that at Ge concentrations above 50%, there is an absence of the bulk band inversion of the Te [Formula: see text] and Bi [Formula: see text] contributions at the [Formula: see text]-point with significant spatial redistribution of the states at the band gap edges into the bulk, suggesting topological phase transition in the system. For case (ii) of the vertical heterostructure Mn [Formula: see text] Ge [Formula: see text] Bi [Formula: see text] Te [Formula: see text] /MnBi [Formula: see text] Te [Formula: see text] , it was shown that an increase of Ge concentration in the first septuple layer leads to effective modulation of the Dirac gap in the absence of significant topological surface states of spatial redistribution. The results obtained indicate that surface doping compares favorably compared to bulk doping as a method for the Dirac gap value modulation.