May 14, 2018
By spin-polarized STM, a magnetically sensitive microscopy technique with atomic resolution capability, we could observe a novel theoretically predicted magnetic ground state, a so-called up-up-down-down (↑↑↓↓) spin structure. As shown in the STM image above, this exotic magnetic structure exists in three orientational domains in a mono-layer Fe on Rh(111). Calculations performed at the Forschungszentrum Jülich reveal that this magnetic structure is caused by a beyond-Heisenberg interaction. The result has been published in Phys. Rev. Lett.
Feb 27, 2018
The electrical resistance of materials or devices is often measured by the 4-point probe method to eliminate lead and contact resistance issues. In the recent decade, miniaturized versions, so-called nanoprobes, have been developed where four sharp tips are individually positioned by piezo-actuators and simultaneously imaged with a scanning electron microscope (see here for an example). However, the finite tip sharpness usually limits the minimal distance to about 100 nm.
In a new publication, which was also highlighted in Nature Nanotechnology, we describe the development of a novel method which enables to detect how charged quasiparticles propagate on length scales down to a few nm by remotely triggering the tautomerization of a single molecule with a scanning tunneling microscope (STM). In analogy to the 4-point nanoprobe we coined it “molecular nanoprobe” (MONA). In combination with atom-by-atom-engineered interferometers, MONA allows to unravel the quantum-mechanical wave nature of hot electrons. Two interferometers can even be combined to build an energy-dependent selector, which allows it to selectively switch one out of two molecules without changing the position of the STM tip. The MONA technique may, in the future, serve as a method to map the charge density distribution around an arbitrary quasiparticle injection point. more
Feb 13, 2018
In a recent highly collaborative publication in Phys. Rev. B with colleagues from Sweden, Italy, Russia, France, and Spain, we report on a systematic investigation of the transition metal-doped topological insulator Sb2Te3. By combining density functional theory with complementary experimental techniques, i.e., STM, resonant photoemission, and x-ray magnetic circular dichroism, we achieved a detailed characterization of the electronic and magnetic properties. Our results provide general guidelines how to realize a robust QAHE by doping Sb2Te3 towards a ferromagnetic state.