Spin-polarized scanning tunneling spectroscopy on correlated electron systems

• Applicant: Dr. Torben Hänke
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 219591251

• Final Report Year: 2019

Final Report Abstract

The project aimed at the application of spin-polarized scanning tunneling microscopy on correlated electron systems. This method was successfully applied to a prototypical correlated electron system, namely Fe1+yTe, by directly imaging its double stripe magnetic structure in real space. Additionally the direct interplay of superconductivity and magnetism was investigated on thin FeTe films grown on the topological insulator Bi2Te3. Experiments on thin Fe1+ySe1-xTex grown on Bi2Se1+xTe2-x showed a two-fold anisotropic gap structure probably due to the emergent nature of superconductivity. First experiments addressing the spin- and charge ordering of magnetic vortices in the cuprate superconductor Bi2Sr2CaCu2O8 revealed a strong suppression of the superconducting gap upon deposition of small amounts of Fe. Furthermore the iron-based superconductor LiFeAs was investigated by quasi-particle interference, which lead to the identification of bosonic modes at Ω ≈ 8 meV with a small wave vector q and a connected resonance-like enhancement of the QPI signal in the superconducting state. Experiments on the Bi intercalation of graphene grown on Ir lead to the observation of an additional hexagonal √3 × √3 R30° surface structure and a strong n-type doping of the graphene. Furthermore spin-polarized STM experiments on the GdAu2 surface alloy revealed a local spin polarization of both Gd and Au atomic sites within the alloy.

Publications

• ”Band-gap engineering by Bi intercalation of graphene on Ir(111)”, Phys. Rev. B 93 165437 (2016)
  J. Warmuth, A. Bruix, M. Michiardi, T. Hänke, M. Bianchi, J. Wiebe, R. Wiesendanger, B. Hammer, P. Hofmann, and A. A. Khajetoorians
  
• ”Interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator”, Nature Comm. 8, 14074 (2017)
  S. Manna, A. Kamlapure, L. Cornils, T. Hänke, E.M.J. Hedegaard, M. Bremholm, B.B. Iversen, Ph. Hofmann, J. Wiebe, and R. Wiesendanger
  
• ”Reorientation of the diagonal double-stripe spin structure at Fe1+yTe bulk and thin-film surfaces”, Nature Comm. 8, 13939 (2017)
  T. Hänke, U.R. Singh, L. Cornils, S. Manna, A. Kamlapure, M. Bremholm, E. M. J. Hedegaard, B. Brummerstedt Iversen, P. Hofmann, J. Hu, Z. Mao, J. Wiebe and R. Wiesendanger
  
• ”Spatial variation of the two-fold anisotropic superconducting gap in a monolayer of FeSe0.5Te0.5 on a topological insulator”, Phys. Rev. B 95 104509 (2017)
  Kamlapure, S. Manna, L. Cornils, T. Hänke, M. Bremholm, Ph. Hofmann, J. Wiebe, and R. Wiesendanger
  
• ”Atomically resolved magnetic structure a Gd-Au surface alloy”, Phys. Rev. B 99 174419 (2019)
  M. Bazarnik, M. Abadia, J. Brede, M. Hermanowicz, E. Sierda, M. Elsebach, T. Hänke and R. Wiesendanger
  
• ”Spectroscopic evidence of nematic fluctuations in LiFeAs”, Phys. Rev. B 100, 024506 (2019)
  Z. Sun, P. K. Nag, S. Sykora, J. M. Guevara, S. Hoffmann, C. Salazar, T. Hänke, R. Kappenberger, S. Wurmehl, B. Büchner, C. Hess