Scanning tunneling microscopy/spectroscopy studies of monolayer FeTe on SrTiO₃(001)-√13×√13

<p>Bulk iron telluride (FeTe) shows a bicollinear antiferromagnetic (AFM) order under 65 K [1]. The bicollinear AFM order can be tuned to a magnetic helix order by adding extra Fe [1, 2]. Recent angle-resolved photoemission and scanning tunneling spectroscopy research indicate that FeTe also shows Kondo-lattice behavior [3]. In our previous research, we found that SrTiO₃-√ 13⨯√ 13 substrate leads to a lowered C₂ symmetry on monolayer iron selenide (ML FeSe); furthermore, the electron doping from SrTiO₃-√ 13⨯√ 13 substrate surface locally modulates the superconducting gap size of the ML FeSe [4]. Considering these facts, several questions are raised: 1. Can the SrTiO₃-√ 13⨯√ 13 substrates also lower the rotational symmetry on the isostructural ML FeTe? 2. Can the Kondo-lattice behavior be confirmed on the ML FeTe film? (The AFM ordering has been confirmed [5].) 3. Can the SrTiO₃ substrate locally modulate the ground state of ML FeTe?</p><p></p><p>To clarify the above points, we performed low-temperature scanning tunneling microscopy/spectroscopy (STM/STS, T: 5 K ~ 77 K) experiments to measure the surface and electronic structure of ML FeTe/SrTiO₃-√ 13⨯√ 13.</p><p></p><p>The following are the main results of our present study:</p><p>1. In the atomically resolved STM images, as shown in Fig. 1(a), we observed that bright atoms form  2⨯ 3 cells arranged in √ 13⨯√ 13 periodicities. The bright  2⨯ 3 cells lead to a C₂ rotational symmetry on the monolayer FeTe film, which originates from the SrTiO₃ substrate.</p><p>2. The STS spectra obtained on the monolayer FeTe show asymmetric dip-like features near the Fermi level, as shown in Fig. 1(b), which fit well with the Fano functions, illustrating a Kondo scenario that localized Fe spins are screened by the conduction electrons.</p><p>3. The spatial dependence of the Fano-shaped STS spectra was observed to follow the √ 13⨯√ 13 periodicities and two types of spectra were confirmed (Fig. 1(b)), indicating that the SrTiO₃ substrate can modulate the interaction between the localized spin and conduction electrons mentioned above.</p><p>The details concerning the similarities and differences between the two cases of ML FeSe/SrTiO₃ and ML FeTe/SrTiO₃will be discussed in the presentation.</p><p></p><p>References:</p><p>[1] Shiliang Li et al., Phys. Rev. B 79, 054503 (2009).</p><p>[2] Mostafa Enayat et al., Science 345, 653-656 (2014).</p><p>[3] Younsik Kim et al., Nat. Commun. 14, 4145 (2023).</p><p>[4] Wen Si et al., Phys. Rev. B 105, 104502 (2022).</p><p>[5] S. Manna et al., Nat. Commun. 8, 14074 (2017).</p><p></p><p></p>