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    Experimentelle Physik II

    Image & Results Gallery (2018 archive)

    Novel magnetic structure discovered

    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.

    MONA - a new technique to measure nanoscale transport

    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

    How to dope topological insulators towards ferromagnetism

    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.

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