PHYSICAL REVIEW B 108, 035408 (2023) Local surface electronic response of Bi 2 Te 3 topological insulator upon europium doping Gilberto Rodrigues-Junior, 1 Thaís Chagas , 2 Rafael Reis, 1 Paulo Victor Sciammarella, 3 Celso I. Fornari , 4 Paulo H. O. Rappl, 5 Eduardo Abramof, 5 Rogério Magalhães-Paniago, 1 and Ângelo Malachias 1 , * 1 Departamento de Física, ICEx, Universidade Federal de Minas Gerais–UFMG, Avenida Antonio Carlos, 6627, Belo Horizonte–MG, CEP 30123-970, Brazil 2 Department Physik, Universität Siegen, Walter-Flex-Straße 3, 57072 Siegen, Germany 3 Departamento de Física, Universidade Federal de Viçosa–UFV, Viçosa–MG, CEP 36570-000, Brazil 4 Experimentelle Physik VII and Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany 5 Grupo de Pesquisa e Desenvolvimento em Materiais e Plasma, GPDMP, Instituto Nacional de Pesquisas Espaciais–INPE, São José dos Campos–SP, CEP 12245-970, Brazil (Received 23 March 2023; revised 25 May 2023; accepted 28 June 2023; published 13 July 2023) The most relevant characteristic of a topological insulator material is the presence of edge/surface states that are protected by the bulk topology, and therefore, insensitive to nonmagnetic disorder. However, if such disorder is induced by magnetic atoms or the topological insulator is subjected to an external magnetic ﬁeld, the time- reversal symmetry is expected to break down, affecting the robustness of the edge/surface states. In this work, europium (Eu)-doped bismuth telluride thin ﬁlms were grown by molecular beam epitaxy in order to analyze the effect of a small fraction of atoms with magnetic properties on topologically protected surface states. For ﬁlms with different Eu concentrations, morphological and electronic characterizations were carried out using atomic force microscopy, scanning tunnelling microscopy, and scanning tunnelling spectroscopy (STS) techniques. The results show that, regardless of the Eu concentration, the layered structure characteristic of the Bi 2 Te 3 phase is maintained. However, large (>2%) Eu concentrations induce the appearance of protrusions and clusters on the surface of the ﬁlms. The STS measurements show the presence of surface states for pure and low-content Eu:Bi 2 Te 3 . The suppression of surface states is indicated by STS spectra in regions with well-deﬁned gaps for some locally limited regions of our samples with large concentration of Eu atoms. From density functional theory we are able to show that the Eu substitutional impurity at the Bi site is not the main mechanism responsible for the observed changes in the topological insulator band structure. Furthermore, the magnetic properties of europium are not the key factor dictating the different Bi 2 Te 3 local surface electronic properties experimentally observed by STS, which are mostly affected by alloying and atom replacement, which induce a chemical modiﬁcation of the surface potential. DOI: 10.1103/PhysRevB.108.035408 I. INTRODUCTION Topological insulators (TIs) are among the most important recent discoveries in material physics. They have been the focus of intensive research by several theoretical and exper- imental groups in the last years, not only for their new and exotic physics but also for the considerable potential appli- cations in spintronics devices and quantum computing [1–3]. These materials are characterized by having an energy gap separating the valence and conduction bands, but exhibiting gapless metallic states in their edges or surfaces, protected by time-reversal symmetry (TRS) [4]. Consequently, backscat- tering of the topological states by nonmagnetic disorders is completely suppressed [5–7]. Three-dimensional topological insulators were theoret- ically predicted [8–10] and later experimentally veriﬁed [11–13] for stoichiometric compounds of group V-VI chalco- genide semiconductors, which exhibit topological properties * angeloms@ﬁsica.ufmg.br at room temperature. Bi 2 Te 3 , Bi 2 Se 3 , and Sb 2 Te 3 have a sim- ple band structure with a band gap of the order of a few hundred meV (up to 300 meV in Bi 2 Se 3 and 170 meV in Bi 2 Te 3 )[14–17]. As in a typical semiconductor, the valence and conduction bands are associated with the p and s orbitals, respectively. Due to the strong spin-orbit coupling (SOC), the p orbital can be pulled up in energy above the s orbital resulting in a band inversion at the center of the Brillouin zone ( point). This property assigns a bulk nontrivial topological characteristic and, consequently, robust spin-polarized states with a linear dispersion are observed at the surface, forming a single Dirac cone. The quantitative inﬂuence of magnetic dopants on ma- terials with topological properties is still an open question. From the theoretical point of view, a magnetic impurity dis- tributed in the crystalline lattice of a TI material acts as a locally applied magnetic ﬁeld, breaking the TRS [18–20]. Consequently, Kramer’s degeneracy at the  point is lifted giving rise to massive fermions subjected to backscattering processes. 2469-9950/2023/108(3)/035408(11) 035408-1 ©2023 American Physical Society