Interface effects of Pb films on TlBiSe 2 and Bi 2 Se 3 topological insulators

We present an experimental investigation of the Pb-induced changes on the electronic structure of selected topological insulators, namely, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>TlBiSe</a:mi> <a:mn>2</a:mn> </a:msub> </a:math> and <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:msub> <b:mi>Bi</b:mi> <b:mn>2</b:mn> </b:msub> <b:msub> <b:mi>Se</b:mi> <b:mn>3</b:mn> </b:msub> </b:mrow> </b:math> . Using spatially resolved and surface-sensitive techniques, including micro-angle-resolved photoemission ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mi>μ</c:mi> </c:math> -ARPES) and micro-core-level photoemission ( <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mi>μ</d:mi> </d:math> -PES), we track the evolution of the electronic states during adsorbate growth. For low Pb coverage on <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:msub> <e:mi>TlBiSe</e:mi> <e:mn>2</e:mn> </e:msub> </e:math> , we identify the formation of a disordered interface. For thicker films, <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mi>μ</f:mi> </f:math> -ARPES measurements clearly resolve well-defined electron confinement (quantum well) states within the metallic Pb layers and no migration of the topological surface state onto the Pb film is observed. Furthermore, <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:mi>μ</g:mi> </g:math> -PES results on both Pb/ <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:msub> <h:mi>TlBiSe</h:mi> <h:mn>2</h:mn> </h:msub> </h:math> and Pb/ <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:msub> <i:mi>Bi</i:mi> <i:mn>2</i:mn> </i:msub> <i:msub> <i:mi>Se</i:mi> <i:mn>3</i:mn> </i:msub> </i:mrow> </i:math> heterostructures can be rationalized in terms of a significant chemical interaction between Pb and Se, leading to substantial surface degradation and Bi atom segregation. The modeling performed on the adsorption of lead on topological insulator surfaces, which includes the consideration of the swapping of Pb adsorbates with Bi substrate atoms, validates the scenario derived from experimental observations. It also suggests that the development of a disordered interface is due to the formation of PbSe nuclei, whose size is constrained by the compressive stresses exerted by the TI substrate.