Seminars Archive

Electronic structure, magnetic domain structure, and competing ordering phenomena of metal surfaces detected by quasiparticle interference and spin-polarized STM

Abstract
In the past various STM-based techniques have been developed to unravel the electronic structure and magnetic properties of surface with high spatial resolution. For example, the observation of interference patterns created by coherent electronic states, so-called quasi-particle interference (QPI), can be used to obtain the dispersion relation of electronic bands in k-space. Complementary to spatially averaging techniques, such as angular-resolved photoemission spectroscopy, the QPI technique is allows the detection of electronic states with very high energy resolution, but gives access to both, electronic states below and above the Fermi level. In my presentation I will show how this technique can be used to clarify the surface electronic structure of exchange-split surface state and surface resonance bands of Ni(111) [1]. In the second part of the talk I will present data obtained on ultrathin Fe films epitaxially grown on face-centered cubic (fcc) Rh(001). Our results spin-polarized scanning tunneling microscopy (SP-STM) results obtained at T = 5.5 K indicate that the cleaning procedure applied to the Rh(001) substrate plays an important role for the formation of a clean and well-ordered Fe film. While the Fe monolayer is found to exhibit an out-of-plane antiferromagnetic c(2 × 2) spin structure, islands of the second Fe layer are found to be out-of-plane ferromagnetic. Coalescence of the double-layer islands results in the formation of larger domains, which extend over several hundred nanometers for a closed two-layer film. Interestingly, this magnetic order is found to coexist with a charge-ordered state. Temperature-dependent measurements reveal a pronounced cross-talk between charge- and spin-order at the ferromagnetic ordering temperature TC ≈ 70 K, which can successfully be modeled within an effective Ginzburg-Landau ansatz including sixth-order terms.