Group Seminar at MPQ and via Zoom: Epitaxial Growth and Spectroscopic Investigation of the Strongly Correlated Compound Tm_xTe_y

Felix Spriestersbach, University of Würzburg
Group Seminar at MPQ in the Herbert-Walther-Lecture Hall and via zoom
Thursday, August 11, 9.00 am (MEZ)

Abstract:

While it is well known that strong spin orbit couplings and particular point groupe symmetries give rise to topologically non-trivial states of matter, a new approach is to investigate the possibility to find topological states of matter in strongly correlated compounds. In this work the epitaxial growth of the strongly correlated 4f compound Tm_xTe_y on SrF2(111) is investigated, whose bandgap is expected to be tuned as a function of lattice constant. The Tm_xTe_y films were grown with molecular beam epitaxy (MBE). In order to find the best growing parameters a stoichiometry series was conducted where the Te:Tm flux ratio offered during the growth is changed with each sample of the series. The crystalline structure and orientation of the grown films are analysed by X-ray diffraction (XRD), reflection high energy electron diffraction (RHEED) and low energy electron diffraction (LEED). Two phases, the telluriumrich Tm_2Te_3 phase and the stoichiometric Tm_1Te_1 phase, can be consistently distinguished with XRD as well as with X-ray photoelectron spectroscopy (XPS). We could verify that the Tm ions in Tm_2Te_3 are in a trivalent state (Tm3+) whereas in Tm1Te1 they exhibit a divalent valency (Tm2+). Additionally, we could verify the Tm_1Te_1 film’s surface orientation to be (hkl ) = (111) by measuring X-ray diffraction reciprocal space maps and LEED. Thereby we proved the epitaxial growth on top of SrF2(111). In order to improve the crystalline quality of the films an additional substrate temperature series was conducted. Thereby, the influence of different SrF2 substrate temperatures between T=375°C and T=575°C on the Tm_1Te_1 film quality was investigated. Due to the fact that thulium tellurides show an extreme tendency to oxidise when exposed to air, a thorough investigation of several capping materials, namely Te, Bi2Te3, and BaF2 was conducted. Thereby, the protective capabilities of those capping layers was analysed by X-ray diffraction.