2015

August 16th

Lately intensive research has been carried out to investigate the elec­tronic and magnetic properties of phthalo­cya­nines. These or­gan­ic molecules have a planar organic frame with a transition metal ion at the center and are traditionally used to dye tex­tiles. More recently it has been discovered that they may also be po­ten­tial candidates for future molecular electronic or spintronic de­vices. Especially the so-called Kondo ef­fect, i.e., the collective screening of uncom­pen­sated spins by conduction electrons of the sub­strate, has been intensively investi­gated. Earlier studies showed a second satel­lite fea­ture whose origin could not be conclusively clarified. We have studied intact and chemi­cally modi­fied molecules by scanning tun­nel­ing spec­troscopy, density func­tional theory, and Monte-Carlo calcu­lations. Our results reveal that the satellite feature is caused by the central tran­si­tion metal ion's dz2 orbital which gradually shifts towards the Fermi level as hydrogen atoms are removed from the molecule. The result has been published in Phys. Rev. B.

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June 16th

Iron (Fe) is the prototypical ferro­magnet. Its latin name, ferrum, is even used as a prefix to describe ordered magnetic materials. How­ever, Fe is also a good example for the con­se­quences of allotropy, i.e., the ability to exist in different crystal struc­tures. For example, face-­centered cubic (fcc) Fe is known to be antiferromagnetic, while Fe in its usual body-centered cubic (bcc) crystal structure is ferro­magnetic. In this publication we verify the anti­ferro­magnetic ground state of an fcc Fe monolayer on Rhodium by imaging the spin orientation with atomic resolution (see image). Our results show that thicker Fe films are ferro­magnetic and exhibit stripe domains with the magnetization alternatingly pointing up and down. The result has been published in Phys. Rev. B.

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May 21th

The success of topological insulators (TI) in creating devices with unique functionalities is directly connected to the ability of coupling their helical spin states to well-defined perturbations. With collaborators from the Russian Academy of Sciences in Novosibirsk, we demonstrated that molecular self-assembly processes offer the opportunity to create well-defined networks at TI surfaces. The symmetry of the overlayer can be finely controlled by appropriate chemical modifications. This approach offers a precise and fast way to produce tailor-made nanoscale surface landscapes. The result has been published in Nano Letters.

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April 15th

Topological materials with their unusual spin structure offer an ideal platform to explore novel magnetoelectric effects.  In cooperation with scientists from the Russian Academy of Sciences in Novosibirsk, we have investigated the influence of single magnetic atoms deposited on the topological insulator Bi2Te3. We obtain signatures of Dirac fermion-mediated magnetic order for extremely dilute adatom concentrations.

The result has been published in Nature Communications.

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